Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 97
c Workshop White Papers SCIENTIFIC OCEAN DRILLING: The most important difference in how this “cutting PAST, PRESENT AND FUTURE edge” (for 1968) technology was used by DSDP scientists as opposed to how it was being used by the oil industry lay in the overall purpose of the drilling. The purpose of drilling Ted Moore for oil is to create a hole through which to extract hydro- University of Michigan carbons. The purpose of the scientiﬁc drilling is to recover the sedimentary and rock section in the deep sea and avoid U.S. oceanographic institutions banded together in encountering oil and gas at all costs. From the start, a safety 1968 to take the ﬁrst steps toward exploring the sedimentary advisory panel of oil company experts was set up to review record and the crustal rocks of the deep ocean basins. It was required surveys and seismic data from every site drilled to auspicious timing. The new paradigms of seaﬂoor spreading assure there was no likelihood that reservoirs of oil and gas and plate tectonics had only recently been accepted by the would be encountered in the drilling. broad scientiﬁc community. Based on the early results and The desire by scientists to recover a complete, undis- technological developments of the Moho Project and on turbed section of the uppermost crustal material has required a careful consideration of all the potential scientiﬁc ques- some technological development by the scientiﬁc commu- tions that might be addressed by drilling in the deep sea, nity. The greatest advance in this regard for the recovery of a new effort was proposed that led to the development of sediments was the development of a hydraulic piston core the Deep Sea Drilling Project (DSDP). Unlike the Moho that can be triggered to shoot out ahead of the drill bit and Project, DSDP would not involve large-scale technological recover a virtually undisturbed 9 m section of sediment. development. Rather it would use “off the shelf” technology When the sediment becomes too stiff to core in this way, an developed by the offshore oil drilling industry and placed on extended core barrel with a thin cutting face can be pushed a single deep-water, dynamically positioned drillship. This ahead of the massive roller-cone drill bit and recover rela- did, of course, limit the scope of the problems addressed by tively undisturbed sections, until ﬁnally when the section the project. There would be no deep drilling down to the becomes totally lithiﬁed, the standard roller-cone drill bit Mohorovičić discontinuity; drilling in ice-covered regions with an open center can core and recover the section. could not be undertaken; and drilling in very shallow water In addition to the technical enhancements that were was not appropriate for the deep-water drill ship. But this achieved during DSDP and the subsequent Ocean Drilling still left a vast, unexplored region of the deep oceans open Program (ODP), there was a continued improvement in how to investigation. In addition to limits on the range of opera- these devices were used to achieve the recovery of a complete tions, the technology of that day did not allow drilling with section and how the recovered section was described and a riser in deep water. Seawater rather than drilling “mud” documented. Initially in DSDP on-board core description was usually used as the drilling ﬂuid to clear debris from the was rather rudimentary: physical core/rock description, bio- hole and expel it onto the seaﬂoor. This approach to deep-sea stratigraphic age, smear slide description, core photographs, drilling has effectively limited the depth of section drilled physical properties, and carbonate content. This could all be and recovered to about 2 km. done on board with about 10 scientists and 6 technicians. By 97
OCR for page 98
98 SCIENTIFIC OCEAN DRILLING the end of the ODP program the greatly improved quality of New Jersey and the reefs of Tahiti to delve into the history the cores permitted the useful employment of core scanning of sea level changes and its impact on the sedimentary archi- devices that measure density, magnetic susceptibility, P-wave tecture of shallow water environments. And we are beginning velocity, natural gamma radiation, color, and magnetic polar- an ambitious program of exploring the tectonic, depositional, ity. These digital measurements are in addition to pore water and hydrologic environment of convergent margins. We no chemistry, physical properties, microbiological samples, longer have to drill lacking the well control provided by a biostratigraphy, and other measurements that were standard riser and will hopefully extend the water depth in which we in the days of DSDP. In ODP the shipboard scientiﬁc party can operate in the riser (or “well control”) mode beyond the grew to as many as 30 scientists who operated the machines, present 2,500 m. did the descriptions, made the measurements, and carried The envisioned scope of the great exploration that await- out the scientiﬁc studies. Their efforts over 12-hour shifts, 7 ed us in the beginning days of scientiﬁc ocean drilling has days/week, on a 56-day expedition constitute an aggregate been exceeded. Not only have we applied crucial tests to the 9 to 10 man-years of work achieved during the at-sea time. plate tectonic theory but also we have created a whole new These expeditions are very productive efforts. scientiﬁc ﬁeld—paleoceanography. Through the exploration The substantial improvements made in the recovery and of the deep-sea environment we have also expanded the sci- documentation of the recovered section came in parallel to ence we address far beyond that envisioned in the early days improvements in how we used the holes that were drilled. of DSDP. The chemistry and hydrology of water in the sedi- Logging of the holes has come very close to keeping pace ments and the crust are now thought to play a key role in the with developments in the industry. Other measurements such chemistry of the oceans and the weathering of the basalt both as heat ﬂow and vertical velocity proﬁles have also been near the ridge axes and far off the axes into the older crust. commonly made. Perhaps one of the most elegant innova- The structure of the oceanic crust itself is gradually being tions in down-hole instrumentation has been the circulation revealed as we penetrate deeper into the basaltic sections. obviation retroﬁt kit (CORK), a device that seals off one or And we are just beginning to realize the great importance more sections of the drill hole and allows measurements of of microbes in the ocean environment. These are just some the chemical and physical nature of the waters in that sec- of the aspects of scientiﬁc ocean drilling that continue to tion to be made over time. Thus, the holes themselves can intrigue the scientiﬁc mind and expand both the science and become deep-sea observatories or laboratories for chemistry, the scientiﬁc community that use scientiﬁc ocean drilling to microbiology, and seismology. increase the scope of our knowledge. As our knowledge of the deep-sea environment and the scientiﬁc questions we address expands, our technical Supporting References capabilities continue to improve. Now with the Integrated Cofﬁn, M.F. and J.A. McKenzie. 2001. Earth, Oceans and Life: Scientiﬁc Ocean Drilling Program (IODP) we have also been able Investigation of the Earth System Using Multiple Drilling Platforms and to go beyond the limitations ﬁrst accepted as necessary in New Technologies, Initial Science Plan, 2003-2013. Integrated Ocean the early days of DSDP. We have drilled in the ice-covered Drilling Program, Texas A&M University, College Station, Texas. region of the high Arctic and brought back a startling record Gornitz, V. 2009. Encyclopedia of Paleoclimatology and Ancient Environ- of climate change associated with the CO2 rich atmosphere ments. Springer, The Netherlands. of the Eocene. We have drilled on the very shallow shelf off
OCR for page 99
99 APPENDIX C THE RECORD OF HYDROTHERMAL The felsic-hosted PACMANUS hydrothermal system PROCESSES IN THE OCEANIC CRUST (~3°S, Manus Basin) provided the opportunity to investigate the characteristics of hydrothermalism in a back-arc basin. Drilling beneath active hydrothermal systems revealed a cap Susan E. Humphris of unaltered dacites and rhyolites, below which the volcanics Woods Hole Oceanographic Institution are pervasively and intensely altered rather than alteration being conﬁned to a narrow upﬂow zone, with clay miner- Hydrothermal chemical exchange between the crust and als dominating the alteration assemblage. In addition, ﬂuid oceans is a fundamental component of global geochemical inclusion data provided clear evidence for a magmatic com- cycles, affecting the composition of the lithosphere, the ponent to the hydrothermal ﬂuid that played a fundamental oceans and, through subduction, the mantle and arc magmas. role in the nature of alteration—a clear distinction from the In addition, this process provides the energy and nutrients TAG and Middle Valley hydrothermal sites. for chemosynthetic organisms. Understanding the processes Although drilling seaﬂoor sulﬁde deposits has been that control chemical ﬂuxes resulting from water-rock reac- technologically challenging, often with poor recovery, it tions requires direct sampling of in situ crust, and has been has nevertheless revealed previously unrecognized shallow an overarching goal of the lithosphere community for more subseaﬂoor processes—entrainment of seawater, mixing of than 40 years. Scientiﬁc ocean drilling has played a critical hydrothermal ﬂuids with seawater and magmatic compo- role in (i) advancing our understanding of subsurface water- nents, deposition of secondary phases that play key roles in rock reactions and the mechanisms of formation of seaﬂoor deposit construction but are not preserved in ancient depos- massive sulﬁde deposits in active hydrothermal systems at its—that are now demonstrated to be critical in the formation mid-ocean ridges, and (ii) the development of a conceptual of massive sulﬁde deposits. model for the alteration reactions that occur in off-axis con- vection systems driven by lithospheric cooling. THE RECORD OF OFF-AXIS CONVECTION SYSTEMS ACTIVE HYDROTHERMAL SYSTEMS AT OCEANIC SPREADING CENTERS As the crust spreads, hydrothermal alteration continues in off-axis convection systems driven by lithospheric cool- Scientiﬁc drilling at three active hydrothermal sites in ing. This process is believed to continue to an age of ~65 different geotectonic settings has revolutionized our under- myr when the crust effectively becomes “sealed.” Hence, the standing of the formation and subsurface structure of seaﬂoor ocean crust provides a time-integrated record of water-rock massive sulﬁde deposits. Drilling at the basalt-hosted active reactions that occurred both on- and off-axis. TAG hydrothermal mound (~26°N, Mid-Atlantic Ridge) Scientiﬁc ocean drilling has provided many sections revealed abundant anhydrite (CaSO4)—a mineral that is of the uppermost few hundred meters of ocean crust. These very uncommon in ancient deposits due to its retrograde have predominantly been focused in young (< 20 Ma) and solubility—attesting to considerable entrainment and heat- ancient (> 110 Ma) crust. Of particular note are two long ing of seawater into the subsurface. Although its formation sections of upper ocean crust formed at intermediate (Hole provides a framework for construction of the deposit, the ulti- 504B on 6 Ma crust) and superfast spreading rates (Hole mate dissolution of anhydrite was recognized as an important 1256D on 15 Ma crust) in the eastern Paciﬁc. No holes pen- mechanism for the formation of sulﬁde breccia—a lithology etrate greater than 50 m in 45-80 Ma basement, the interval that had been previously interpreted in ancient ophiolite in which the crust becomes sealed. Although details vary, massive sulﬁde deposits to result from post-depositional the mineralogical and geochemical characteristics of all the weathering. upper crustal sections support a model whereby greenschist Drilling at the sediment-hosted Middle Valley hydro- alteration of dikes at low water/rock ratios is overprinted thermal sites (~48°N, Juan de Fuca Ridge) resulted in the ﬁrst by fracture-controlled alteration and mineralization by successful recovery of feeder zone mineralization underlying upwelling hydrothermal ﬂuids, a conductive boundary layer a seaﬂoor massive sulﬁde deposit. Feeder zones in ancient above gabbroic intrusions, leaching of metals from dikes deposits commonly account for a signiﬁcant portion of and gabbros in the deep “root zone,” and stepped thermal the economic reserves of a deposit. An unexpected ﬁnding and alteration gradients in the basement. The prediction that was the presence of a stratiﬁed zone of high-grade Cu-rich conductive boundary layers separate hydrothermal systems replacement mineralization (~16 wt.% Cu) at the base of the from the heat source that drives them has been conﬁrmed feeder zone formed by lateral ﬂow of hydrothermal ﬂuids by the identiﬁcation of recrystallized sheeted dikes at the beneath an impermeable siliciﬁed mudstone horizon. This dike–gabbro transition at all locations. Incipient alteration type of mineralization had not been previously recognized of the uppermost gabbros occurs at high temperatures, with below seaﬂoor mineral deposits, and hence has implications ﬂuid ﬂow along fracture networks occurring over very short for land-based mineral exploration. timescales.
OCR for page 100
100 SCIENTIFIC OCEAN DRILLING Drilling at oceanic core complexes on the more litho- magma chamber. Investigations of this interplay, and of the logically heterogeneous slow spreading ridges (e.g., the hydrological-geochemical-microbiological feedbacks in Atlantis Massif [30°N, Mid-Atlantic Ridge] and Atlantis aging oceanic lithosphere—the largest fractured aquifer on Bank [Southwest Indian Ridge]) has provided access to Earth—require access to in situ oceanic crust and subsurface lower ocean crust that has been tectonically exhumed at the experimentation that can be provided only by drilling. seaﬂoor. The combination of regional-scale geophysical and geological surveys with deep drill holes at these locations Supporting References indicate that detachment zones act to focus ﬂuids at high Alt, J. 2004. Alteration of the upper oceanic crust: Mineralogy, chemistry, and low temperatures. Gabbroic rocks are variably altered and processes. In Hydrogeology of the Oceanic Lithosphere, Elderﬁeld, at these two sites, and preserve complex, but different, H. and E. Davis (Eds.). Cambridge University Press, New York. records of metamorphism, brittle failure, and hydrothermal Humphris, S.E., P.M. Herzig, D.J. Miller, J.C. Alt, K. Becker, D. Brown, alteration. At the Atlantis Massif, greenschist facies altera- G. Brügmann, H Chiba, Y. Fouquet, J.B. Gemmell, G. Guerin, M.D. tion occurred at depths at least 1 km below seaﬂoor, with Hannington, N.G. Holm, J.J. Honnorez, G.J. Iturrino, R. Knott, R. Ludwig, K. Nakamura, S. Petersen, A.L. Reysenbach, P.A. Rona, S. variable degrees of interaction with seawater at temperatures Smith, A.A. Sturz, M.K. Tivey, and X. Zhao. 1995. The internal structure generally >250 °C. In contrast, at Atlantis Bank, patchy high of an active sea-ﬂoor massive sulphide deposit. Nature 377:713-716. temperature alteration (up to 600 °C) by hydrothermal ﬂuids Zierenberg, R.A., Y. Fouquet, D.J. Miller, J.M. Bahr, P.A. Baker, T. over a wide range of temperatures likely occurred at or very Bjerkgard, C.A. Brunner, R.C. Duckworth, R. Gable, J. Gieskes, W.D. near the spreading axis, while later, low temperature altera- Goodfellow, H.M. Groschel-Becker, G. Guerin, J. Ishibashi, G.J. Iturrino, R.H. James, K.S. Lackschewitz, L.L. Marquez, P. Nehlig, J.M. tion is likely related to cooling during uplift. Peter, C.A. Rigsby, P.J. Schultheiss, W.C. Shanks, B.R.T. Simoneit, M. In summary, drilling to date has highlighted the critical, Summit, D.A.H. Teagle, M. Urbat, and G.G. Zuffa. 1998. The deep but highly variable, interplay between ﬂuid ﬂow, lithol- structure of a sea-ﬂoor hydrothermal deposit. Nature 392:485-488. ogy, and magmatism from the seaﬂoor down to the axial
OCR for page 101
101 APPENDIX C HEAT AND FLUID FLOW ﬂowing down the cased section into upper basement, and it was shown that these data could be interpreted to estimate both downhole ﬂow rate and permeability of the formation Keir Becker into which the ﬂow was directed (Becker et al., 1983). This University of Miami method has been applied to numerous holes since then, including some less common examples that were drilled in From the time of Project Mohole, researchers have rec- sediment-covered basement highs and actually produced ognized the opportunities that scientiﬁc ocean drilling pres- formation ﬂuids up the hole (e.g., Fisher et al., 1997). Since ents to investigate heat and ﬂuid ﬂow processes in oceanic 1979, drillstring packer experiments have been conducted sediments and crust (e.g., Von Herzen and Maxwell, 1964). deeper in Hole 504B and in the upper basement sections The early Deep Dea Drilling Project (DSDP) measurements of several crustal holes. The combined datasets have docu- were made primarily in sediments (see review by Erickson et mented a reduction over several orders of magnitude of per- al., 1975), before the discovery of hydrothermal circulation meability with depth in young oceanic crust and a reduction in the mid-1970s and the subsequent realization that ﬂuid of permeability of uppermost crust with crustal age (e.g., ﬂow in subseaﬂoor formations is a key process in nearly all Fisher, 1998; Fisher and Becker, 2000; Becker and Fisher, subsea geological type settings from spreading centers to 2000, 2008) that are often used in current numerical models continental margins. Hence, the COSOD I (Conference on of hydrothermal circulation in oceanic crust. It is probably Scientiﬁc Ocean Drilling) report recognized the importance an oversimpliﬁcation, but there seems to be a rough identity of subseaﬂoor ﬂuid ﬂow, and understanding it fully became among the most permeable and porous upper few hundred m a focal point/major theme of DSDP/ODP (Ocean Drill- of young oceanic basement, seismic Layer 2A, and the zone ing Program)/IODP (Integrated Ocean Drilling Program) of oxidative alteration. scientiﬁc drilling starting with the 1987 COSOD II report. While the down- or uphole ﬂow in many crustal reentry Since subseaﬂoor ﬂuid circulation occurs in most seaﬂoor holes can be interpreted to estimate permeability, it also geological type settings, this summary overlaps several oth- represents a signiﬁcant perturbation to the in situ subsea- ers from the workshop (e.g., S. Humphris on hydrothermal ﬂoor hydrological systems that we are trying to understand circulation, K. Edwards on deep biosphere, C. Ruppel on gas with scientiﬁc ocean drilling. This led to the development hydrates, and J.C. Moore on convergent margins). The table in 1989-1990 of a new experimental approach to seal these below summarizes in a historical context the main technical reentry holes, simultaneously emplacing long-term instru- and scientiﬁc contributions of scientiﬁc ocean drilling in mentation to record in situ temperatures and pressures and understanding subseaﬂoor heat and ﬂuid ﬂow. This written to sample formation ﬂuids. This concept was named the summary touches on some of the themes covered by other CORK (Circulation Obviation Retroﬁt Kit) hydrogeological speakers, but mainly features the off-axis, low-temperature, observatory (Davis et al., 1992). CORKs have allowed for ridge-ﬂank setting that for technical reasons has been the determination of in situ temperature and pore pressure state main setting to date for scientiﬁc ocean drilling into oceanic after the perturbation due to drilling has decayed (e.g., Davis crust. and Becker, 2002). The subseaﬂoor pressure data show an The early- to mid-1970s deduction of the likelihood of attenuated and phase-lagged seaﬂoor tidal loading signal hydrothermal circulation in young oceanic crust was roughly that can be interpreted to constrain hydraulic diffusivity and coincident with the internationalization of DSDP (the IPOD derived permeability at formation scales (Davis et al., 2000). or International Phase of Ocean Drilling) and a special IPOD In addition, once the tidal signals are ﬁltered out, the sub- focus on penetrating signiﬁcantly into ocean basement. The seaﬂoor pressures also show formation responses to tectonic last started with several important young Atlantic crustal events, acting essentially as crustal strain meters (e.g., Davis holes, and borehole temperature measurements in some et al., 2001). The combination of CORK and packer observa- of them revealed a new phenomenon: that ocean bottom tions in ridge-ﬂank sites indicates high lateral ﬂuids ﬂuxes water was being drawn down the holes into the upper levels and short residence times in very permeable upper basement of basement beneath the sediment cover required to spud under relatively small pressure differentials (e.g., Davis and the holes (e.g., Hyndman et al., 1976). It was deduced that Becker, 2002). This conclusion is supported by geochemi- the upper oceanic basement in young crust is much more cal analyses of pore waters and long-term “OsmoSamplers” permeable than the overlying sediments. The ﬁrst direct recovered from the CORKs (e.g., Elderﬁeld et al., 1999; measurements of the upper basement permeability—the key Wheat et al., 2000, 2003). parameter that controls ﬂuid ﬂow through the formation— During the late 1990s, newer CORK concepts were were made in 1979 with a drillstring packer experiment in developed to separately seal multiple zones in a single hole; the famous crustal reference Hole 504B, located in thickly these models include the “Advanced CORK,” “CORK-II,” sedimented young crust on the south ﬂank of the Costa Rica and a “wireline CORK” that can be installed from oceano- Rift (Anderson and Zoback, 1982). Thermal measurements graphic vessels. More than 20 CORKs of various models in Hole 504B also indicated that ocean bottom water was have been installed to date, primarily in ridge-ﬂank settings
OCR for page 102
102 SCIENTIFIC OCEAN DRILLING Selected Program Timeline/Program Historical Context Highlights Technical Contributions Scientiﬁc Contributions Mohole Pre-plate tectonics Deep sediment First sediment temperature 1961-1966 Pre-hydrothermal temperatures measured at probe Reconnaissance deep heat ﬂow Mohole pilot site measurements and pore ﬂuid sampling Early DSDP Pre-hydrothermal Exploration scientiﬁc Deep heat ﬂow measurements 1968-1974 drilling around the world, validated shallow oceanographic primarily in sedimentary heat ﬂow probe technique sections Later DSDP Hydrothermal circulation Deep Atlantic crustal holes Uyeda probe Interpretation of downhole ﬂow 1974-1983 deduced/veriﬁed in crustal holes Guaymas Basin Barnes probe JOIDES Hydrogeology First recorded uphole ﬂow Working Group Galapagos Mounds Water Sampler Temperature Probe (WSTP) Vertical ﬂow through sediments Costa Rica Rift – 504B veriﬁed Hydraulic Piston Corer (HPC) T-tool Deep sedimentary pore ﬂuids as proxy for basement ﬂuids First packer experiments First crustal permeability values First pore pressure probe Permeable, oxidative upper basement ~ Layer 2A First studies of ﬂuids in prisms Early ODP Reentries of deep ODP/IODP straddle packer Crustal permeability-depth 1985-1990 crustal holes (418A, proﬁle through sheeted dikes 395A, 504B) Borehole ﬂuid samplers Direct evidence for ﬂuid ﬂow in Barbados + Nankai prism subduction plate boundary faults studies Late ODP Boreholes as long-term First- and second- Original CORK Expansion of crustal 1991-2003 observatories generation CORK in-situ long-term permeability-depth proﬁle hydrogeological OsmoSamplers Initiative in In-situ observatories deployed medium-T (up to 200 °C) Documentation of age variation Monitoring of Geological in sedimented ocean sediment T and pore ﬂuid of upper crustal k Processes ridges, ridge ﬂanks, and probes Pilot Project in Deep subduction settings In ridge ﬂanks: huge lateral Biosphere Hi-T borehole T-tool (up to ﬂuid ﬂuxes with small Targeted drilling of 360 °C) pressure differentials and high Hydrogeology Program hi-T (270-365 °C) permeabilities Planning Group (2001) hydrothermnal systems Multi-zone Advanced CORK, CORK-II, and First direct measurement of ﬂuid First targeted gas hydrates wireline CORK pressure at subduction plate drilling in context of ﬂuid boundary fault ﬂow First in situ video in oceanic crust, showing microbiota IODP Initiatives in Deep Juan de Fuca 3-d CORK Addition of microbiological First crustal-scale cross-hole 2004-2011 Biosphere and Hydrates array capabilities to CORKs + hydrogeological experiments shipboard labs NanTroSEIZE seismic + First in situ microbiological ﬂuid observatories Improvement of downhole incubation experiments tools Gulf of Mexico margin First network cable-ready overpressured zone borehole observatories Three major biosphere/ﬂuid Excess ﬂuid pressures measured programs to come in Gulf of Mexico margin
OCR for page 103
103 APPENDIX C and in subduction zones. In the latter setting, a prime goal Becker, K., E.E. Davis, F.N. Spiess, and C.P. deMoustier. 2004. Temperature and video logs from the upper oceanic curst, Holes 504B and 896A, has been to document ﬂuid pressures in plate boundary faults Costa Rica Rift ﬂank: Implications for the permeability of upper oceanic and the relationship between ﬂuid processes and subduction crust. Earth and Planetary Science Letters 222(3-4):881-896. earthquakes. To date, overpressures as high as 1 MPa have Davis, E.E. and K. Becker. 2002. Observations of natural-state ﬂuid pres- been documented in the monitored plate boundary faults, but sures and temperatures in young oceanic crust and inferences regard- this is signiﬁcantly less than lithostatic pressure and thus not ing hydrothermal circulation. Earth and Planetary Science Letters 204(1-2):231-248. enough to enable slip along the faults. In the Hydrate Ridge Davis, E.E., K. Becker, T. Pettigrew, B. Carson, and R. MacDonald. 1992. subduction setting offshore Oregon, a CORK through a thrust CORK: A hydrologic seal and downhole observatory for deep-ocean fault apparently recorded the transient thermal signal of an boreholes. In Proceedings of the Ocean Drilling Program, Initial up-fault ﬂuid ﬂow event. Even more ambitious observatories Reports, Volume 139, Davis E.E., M.J. Mottl, A.T. Fisher, et al. (Eds.). are planned for the IODP NanTroSEIZE program, combining Ocean Drilling Program, Texas A&M University, College Station, Texas. Davis, E.E., K. Wang, K. Becker, and R.E. Thomson. 2000. Formation-scale seismic and strain instruments with the CORK hydrological hydraulic and mechanical properties of oceanic crust inferred from pore concept. pressure response to periodic seaﬂoor loading. Journal of Geophysical In the process of installing wireline CORKs in Hole Research 105(B6):13423-13435. 504B and a companion Hole 896A ~1km away in 2001, it Davis, E.E., K. Wang, R.E. Thomson, K. Becker, and J. Cassidy. 2001. An was determined that Hole 896A was producing crustal ﬂuids episode of seaﬂoor spreading and associated plate deformation inferred from crustal ﬂuid pressure transients. Journal of Geophysical Research and the ﬁrst (only?) true video from within oceanic basement 106(B10):21953-21963. was collected (Becker et al., 2004). That video seems to show Elderﬁeld, H., C.G. Wheat, M.J. Mottl, C. Monnin, and B. Spiro. 1999. Fluid copious microbiota within the hole and images individual and geochemical transport through oceanic crust: A transect across the formations that are producing ﬂuids into the hole and prob- eastern ﬂank of the Juan de Fuca Ridge. Earth and Planetary Science ably represent most of the bulk permeability of the formation. Letters 172(1-2):151-165. Erickson, A.J., R.P. Von Herzen, J.G. Sclater, R.W. Girdler, B.V. Marshall, That serves to emphasize the fact that the permeability of and R. Hyndman. 1975. Geothermal measurements in deep-sea drill oceanic crust—and probably most other subseaﬂoor forma- holes. Journal of Geophysical Research 80(17):2515-2528. tions—is fracture-dominated and multi-scalar, so it cannot Fisher, A.T. 1998. Permeability within basaltic oceanic crust. Reviews of be accurately represented as a single-valued parameter (e.g., Geophysics 36(2):143-182. Fisher, 1998; Becker and Davis, 2003; Fisher et al., 2008). Fisher, A.T. and K. Becker. 2000. Channelized ﬂuid ﬂow in oceanic crust reconciles heat-ﬂow and permeability data. Nature 403:71-74. In summer 2010, IODP Expedition 327 to the Juan de Fuca Fisher, A.T., K. Becker, and E.E. Davis. 1997. The permeability of young Ridge ﬂank featured the ﬁrst attempt to resolve directional oceanic crust east of Juan de Fuca Ridge determined using borehole ther- variation of crustal permeability and natural ﬂuid ﬂow via mal measurements. Geophysical Research Letters 24(11):1311-1314. the ﬁrst planned hole-to-hole pumping tests in an array of Fisher, A.T., E.E. Davis, and K. Becker. 2008. Borehole-to-borehole CORKs penetrating upper basement. (An unplanned hole-to- hydrologic response across 2.4 km in the upper oceanic crust: Impli- cation for crustal-scale properties. Journal of Geophysical Research hole experiment in the same array is described by Fisher et 113(B7):B07106. al., 2008.) That array of CORKs has also involved the ﬁrst Hyndman, R.D., R.P. Von Herzen, A.J. Erickson, and J. Jolivet. 1976. Heat in situ microbiological cultivation experiments in oceanic ﬂow measurements in deep crustal holes on the Mid-Atlantic Ridge. basement, and so represents an important new future direc- Journal of Geophysical Research 81(23):4053-4060. tion for CORKs and scientiﬁc ocean drilling discussed in Von Herzen, R.P. and A.E. Maxwell. 1964. Measurements of heat ﬂow at the preliminary Mohole site off Mexico. Journal of Geophysical Research more detail by K. Edwards. 69(4):741-748. Wheat, C.G., H. Elderﬁeld, M.J. Mottl, and C. Monnin. 2000. Chemical composition of basement ﬂuids within an oceanic ridge ﬂank: Impli- Supporting References cations for along-strike and across-strike hydrothermal circulation. Anderson, R.N. and M.D. Zoback. 1982. Permeability, underpressures, Journal of Geophysical Research 105(B6):13437-13447. and convection in the oceanic crust near the Costa Rica Rift, eastern Wheat, C.G., H.W. Jannasch, M. Kastner, J.N. Plant, and E.H. DeCarlo. equatorial Paciﬁc. Journal of Geophysical Research 87(B4):2860-2868. 2003. Seawater transport and reaction in upper oceanic basaltic base- Becker, K. and E.E. Davis. 2003. New evidence for age variation and scale ment: Chemical data from continuous monitoring of sealed borehole effects of permeabilities of young oceanic crust from borehole thermal in a ridge ﬂank environment. Earth and Planetary Science Letters and pressure measurements. Earth and Planetary Science Letters 216(4):549-564. 210(3-4):499-508. Becker, K. and A.T. Fisher. 2000. Permeability of upper oceanic base- ment on the eastern ﬂank of the Juan de Fuca Ridge determined with drill-string packer experiments. Journal of Geophysical Research 105(B1):897-912. Becker, K. and A.T. Fisher. 2008. Borehole packer tests at multiple depths resolve distinct hydrologic intervals in 3.5-Ma upper oceanic crust on the eastern ﬂank of the Juan de Fuca Ridge. Journal of Geophysical Letters 113(B07105):1-12. Becker, K., M.G. Langseth, R.P. Von Herzen, and R.N. Anderson. 1983. Deep crustal geothermal measurements, Hole 504B, Costa Rica Rift. Journal of Geophysical Research 88(B4):3447-3457.
OCR for page 104
104 SCIENTIFIC OCEAN DRILLING SUBSURFACE MICROBIAL OBSERVATORIES the lateral dimension of the experimental environment (i.e., TO INVESTIGATE THE DEEP OCEAN CRUST all instruments must ﬁt within the innermost borehole casing, BIOSPHERE: DEVELOPMENT, TESTING, AND which is typically on the order of 9 cm diameter). Downhole FUTURE instruments also must provide necessary power for the dura- tion of the deployment (4-5 years). The continuing adaptation of technologies from other Katrina J. Edwards disciplines will advance capabilities to observe and sample University of Southern California the subseaﬂoor crustal biosphere. Technologies that are suitable for long-term deployment, with ultra-low power Scientiﬁc ocean drilling has historically yielded some consumptions and minimal impact by biofouling, are ideal of the most transformative advances in the Earth sciences, for crustal biosphere observatories. Instrumentation for mak- cross-cutting many of its disciplines, and providing funda- ing remote measurements of downhole conditions is also mental advances to our knowledge of how the Earth works. required. This includes designing downhole electrochemical Today, ocean drilling is poised to offer these same transfor- and mass spectrometer analyzers, for measuring changes in mative advances to disciplines within the life sciences, and ﬂuid and gas compositions, and also developing new ways provide insight into how life operates and interacts with Earth to measure rates of chemical reactions in situ. For example, processes at and below the seaﬂoor. To date, many exciting a protoype downhole sampler for manipulative experiments discoveries have been made about the nature of the deep is nearly ready for ﬁeld trials. Another promising adaptation microbial biosphere in marine sediments. In comparison, would be instrumentation for measuring deep ultraviolet there is relatively little information about the nature, extent, ﬂuorescence downhole, permitting the detection of the native and activity of microorganisms living in the volcanic oce- ﬂuorescence of microbial cells without the use of stains or anic crust. Because of the size and hydrodynamics of this dyes or interference from auto-ﬂuorescent mineral particles. potential biome, crustal life may have profound inﬂuence on Future observatory experiments will also beneﬁt from global chemical cycles and, as a consequence, the physical the utilization of components that are compatible with objec- and chemical evolution of the crust and ocean. Hence, it is tives in multiple disciplines (microbiology, hydrogeology, imperative that the scientiﬁc community develops a more chemistry, etc.). complete understanding of life in ocean crust. To do this, researchers must develop the appropriate tools for studying Supporting References this unique habitat, and recent engineering and methodologi- cal advancements make now a particularly opportunistic Becker, K. and E.E. Davis. 2005. A review of CORK designs and operations time to do so. Subseaﬂoor borehole observatories (Circula- during the Ocean Drilling Program. In Proceedings of the Integrated tion Obviation Retroﬁt Kits or CORKs) can help to provide Ocean Drilling Program, Volume 301, Fisher, A.T., T. Urabe, A. Klaus, and the Expedition 301 Scientists (Eds.). Integrated Ocean Drilling representative samples of crustal ﬂuids and microbiological Program, Texas A&M University, College Station, Texas. samples, reducing the extent of contamination associated Bhartia, R., W.F. Hug, E.C. Salas, R.D. Reid, K. Sijapat, A. Tsapin, K.H. with drilling, coring, and other operations. Nealson, A.L. Lane, and P.G. Conrad. 2008. Native ﬂuorescence spec- troscopy: Classiﬁcation of organics with deep UV to UV excitation. Applied Spectroscopy 62(10):1070-1077. SUBSURFACE MICROBIAL OBSERVATORY Cowen, J.P., S.J. Giovannoni, F. Kenig, H.P. Johnson, D. Butterﬁeld, M.S. TECHNOLOGY Rappé, M. Hutnak, and P. Lam. 2003. Fluids from aging ocean crust that support microbial life. Science 299(5603):120-123. Tools available for CORK-associated microbial observa- D’Hondt, S., B.B. Jørgensen, D.J. Miller, A. Batzke, R. Blake, B.A. Cragg, tory experiments can be broken down into two categories: H. Cypionka, G.R. Dickens, T. Ferdelman, K.U. Hinrichs, N.G. Holm, those that are deployed down hole (“subsurface”) within the R. Mitterer, A. Spivack, G. Wang, B. Bekins, B. Engelen, K. Ford, G. Gettemy, S.D. Rutherford, H. Sass, C.G. Skillbeck, I.W. Aiello, G. CORK casing, and those that are deployed at the seaﬂoor Guèrin, C.H. House, F. Inagaki, P. Meister, T. Naehr, S. Niitsuma, R.J. and connected to the horizon of interest via pumping of Parkes, A. Schippers, D.C. Smith, A. Teske, J. Wiegel, C.N. Padilla, ﬂuids through umbilicals. Redundancy between seaﬂoor and J.L.S. Acosta. 2004. Distributions of microbial activities in deep and subsurface sampling and experimental units allows for subseaﬂoor sediments. Science 306(5705):2216-2221. a higher conﬁdence of capturing representative samples for Davis, E.E., K. Becker, T. Pettigrew, B. Carson, and R. MacDonald. 1992. CORK: A hydrological seal and downhole observatory for deep-ocean targeted questions. boreholes. In Proceedings of the Ocean Drilling Program, Initial Re- First-generation downhole observatory technology con- ports, Volume 139, Davis, E.E., M.J. Mottl, A.T. Fisher, and the ODP Leg sisted of subsurface temperature and pressure loggers and 130 Scientists (Eds.). Ocean Drilling Program, Texas A&M University, osmotically driven ﬂuid samplers (“OsmoSamplers”), which College Station, Texas. collect a continuous record of temperature, pressure, and composition of the ﬂuid within CORKed boreholes. Second- generation downhole devices couple these to microbial colo- nization experiments. All downhole technology is limited by
OCR for page 105
105 APPENDIX C Fisher, A.T., C.G. Wheat, K. Becker, E.E. Davis, H. Jannasch, D. Schroeder, Orcutt, B., C.G. Wheat, and K.J. Edwards. 2010. Subseaﬂoor ocean crust R. Dixon, T.L. Pettigrew, R. Meldrum, R. MacDonald, M. Nielsen, M. microbial observatories: Development of FLOCS (Flow-through Osmo Fisk, J. Cowen, W. Bach, and K.J. Edwards. 2005. Scientiﬁc and techni- Colonization System) and evaluation of borehole construction materials. cal design and deployment of long-term subseaﬂoor observatories for Geomicrobiology Journal 27(2):143-157. hydrogeologic and related experiments, IDOP Expedition 301, eastern Parkes, R.J., B.A. Cragg, S.J. Bale, J.M. Getliff, K. Goodman, P.A. Rochelle, ﬂank of Juan de Fuca Ridge. In Proceedings of the Integrated Ocean J.C. Fry, A.J. Weightman, and S.M. Harvey. 1994. Deep bacterial bio- Drilling Program, Volume 301, Fisher, A.T., T. Urabe, A. Klaus, and the sphere in Paciﬁc Ocean sediments. Nature 371:410-413. Expedition 301 Scientists (Eds.). Integrated Ocean Drilling Program, Preston, C., R. Marin, III, S. Jenson, J. Feldman, E. Massion, E. DeLong, Texas A&M University, College Station, Texas. M. Suzuki, K. Wheeler, D. Cline, N. Alvarado, and C. Scholin. 2009. Girguis, P.R., J. Robidart, and G. Wheat. 2008. The BOSS: A novel approach Near real-time, autonomous detection of marine bacterioplankton on a to coupling temporal changes in geochemistry and microbiology in the coastal mooring in Monterey Bay, California, using rRNA-targeted DNA deep subsurface biosphere. Eos, Transcripts American Geophysical probes. Environmental Microbiology 11(5):1168-1180. Union 89(53):B51F-03. Storrie-Lombardi, M.C., W.F. Hug, G.D. McDonald, A.I. Tsapin, and K.H. Inagaki, F., T. Nunoura, S. Nakagawa, A. Teske, M. Lever, A. Lauer, Nealson. 2001. Hollow cathode ion laser for deep ultraviolent Raman M. Suzuki, K. Takai, M. Delwiche, F.S. Colwell, K.H. Nealson, K. spectroscopy and ﬂuorescence imaging. Review of Scientiﬁc Instruments Horikoshi, S. D’Hondt, and B.B. Jørgensen. 2006. Biogeographical dis- 72(12):4452-4459. tribution and diversity of microbes in methane hydrate-bearing deep ma- Wankel, S.D., S.B. Joye, V.A. Samarkin, S.R. Shah, G. Friederich, J. Melas- rine sediments on the Paciﬁc Ocean Margin. Proceedings of the National Kyriazi, P.R. Girguis. 2010. New constraints on methane ﬂuxes and rates Academy of Sciences of the United States of America 103(8):2815-2820. of anaerobic methane oxidation in a Gulf of Mexico brine pool via in Jannasch, H.W., E.E. Davis, M. Kastner, J.D. Morris, T.L. Pettigrew, J.N. situ mass spectrometry. Deep-Sea Research II 57:2022-2029. Plant, E.A. Solomon, H.W. Villinger, and C.G. Wheat. 2003. CORK-II: Wheat, C.G., H.W. Jannasch, M. Kastner, J.N. Plant, and E.H. DeCarlo. Long-term monitoring of ﬂuid chemistry, ﬂuxes, and hydrology in in- 2003. Seawater transport and reaction in upper ocean basaltic basement: strumented boreholes at the Costa Rica subduction zone. In Proceedings Chemical data from continuous monitoring of sealed boreholes in a of the Ocean Drilling Program, Initial Reports, Volume 205, Morris, J.D. mid-ocean ridge ﬂank environment. Earth Planetary Science Letters and the ODP Leg 205 Scientists (Eds.). Ocean Drilling Program, Texas 216(4):549-564. A&M University, College Station, Texas. Wheat, C.G., H.W. Jannasch, M. Kastner, J.N. Plant, E.H. DeCarlo, and Luther, G.W., B.T. Glazer, S.F. Ma, R.E. Trouwborst, T.S. Moore, E. G. Lebon. 2004. Venting formation ﬂuids from deep sea boreholes in a Metzger, C. Kraiya, T.J. Waite, G. Druschel, B. Sundby, M. Taillefert, ridge ﬂank setting: ODP sites 1025 and 1026. Geochemistry, Geophys- D.B. Nuzzio, T.M. Shank, B.L. Lewis, and P.J. Brendel. 2008. Use of ics, Geosystems 5(8):Q08007. voltammetric solid-state (micro)electrodes for studying biogeochemi- cal processes: Laboratory measurements to real time measurement with an in situ electrochemical analyzer (ISEA). Marine Chemistry 108(3-4):221-235.
OCR for page 106
106 SCIENTIFIC OCEAN DRILLING SCIENTIFIC OCEAN DRILLING AND GAS tives, focusing on the extensive gas hydrates province in HYDRATES STUDIES the ﬁne-grained sediments of the Blake Ridge. For the ﬁrst time, ODP purposely cored and logged the entire hydrates stability zone and the underlying free gas zone, countering Carolyn Ruppel critics concerned about the safety of such activities. Many U.S. Geological Survey accomplishments of ODP Leg 164 have stood the test of time, with similar phenomena being rediscovered in other Gas hydrates and the huge quantities of methane that marine hydrates provinces even today. ODP Leg 164 proved they sequester in marine sediments are typically linked to that gas hydrates occurred even in the absence of the bottom three broad scientiﬁc themes: carbon cycling and global simulating reﬂector (BSR) that sometimes marks the base climate change (e.g., Dickens et al., 1995, 1997a; Dickens, of gas hydrates stability (Dillon et al., 1996) and provided 2003; Kennett et al., 2003), submarine slope stability (e.g., strong evidence that small-scale permeability variations Kvenvolden, 1999; Grozic, 2010; Maslin et al., 2010), and (e.g., slightly coarser-grained sediments or dual-porosity/ energy resources (e.g., Collett, 2002). The last element— diatomaceous layers) locally control preferential accumula- the energy resource potential of gas hydrates—renders gas tion of gas hydrates in seemingly homogeneous sediments hydrates unique within the scientiﬁc ocean drilling (SOD) (Ginsburg et al., 2000; Kraemer et al., 2000). The expedition community: There has always been the expectation that rou- yielded a rich dataset for calibration of logging, vertical seis- tine gas hydrates drilling for resource issues would someday mic proﬁles (VSP), and geochemical constraints on in situ reach such maturity that SOD would no longer be appropri- hydrates concentrations (e.g., Holbrook et al., 1996; Collett ate. We are largely operating in this era now, with no gas and Ladd, 2000; Lorenson et al., 2000); demonstrated that hydrates drilling having been conducted by the Integrated gas hydrates ﬁlled only a small percentage of available pore Ocean Drilling Program (IODP) since 2005 (Expedition space despite the widespread occurrence of a BSR; and 311; Riedel et al., 2006). Over the past decade, government/ marked a ﬁrst attempt at shipboard microbiology within SOD private-sector operators in Japan, the United States, South (Wellsbury et al., 2000). Korea, India, China, and Malaysia (e.g., Collett et al., 2008a, By the late 1990s, it was clear that ODP Leg 164, b, 2009; Hadley et al., 2008; Jones et al., 2008; Park et al., despite far exceeding initial expectations, had yielded a 2008; Ruppel et al., 2008; Wu et al., 2008; Yang et al., 2008; largely static picture of gas hydrates systems that are more Tsuji et al., 2009; National Energy Technology Laboratory, properly considered dynamic and hydrologically driven. 2010) completed and/or have begun planning deepwater With the publication of studies that linked the evolution of drilling operations to investigate the resource potential of gas gas hydrates provinces to ﬂuxes of ﬂuids, gas, and energy hydrates and, in some cases, to assess geohazards related to (Rempel and Buffett, 1998; Xu and Ruppel, 1999; Ruppel drilling and eventual production. None of this government/ and Kinoshita, 2000) and with the increasing emphasis on private-sector activity would have been possible without the gas hydrates “plumbing systems,” the Gas Hydrates PPG, the fundamental knowledge and technological developments Hydrogeology PPG (Ge et al., 2002), and subsequently the provided by SOD activities during the Ocean Drilling Pro- IODP science plan all alluded to a strategy of drilling in gas gram (ODP) and IODP. In this brief, I review the contribu- hydrates provinces characterized by different ﬂux regimes. tions of ODP/IODP to gas hydrates science, highlight special ODP Leg 204 (Tréhu et al., 2003) was the second SOD expe- technology developed by SOD for studying hydrates-bearing dition fully committed to the exploration of gas hydrates, sediments (known as HBS), and make recommendations this time in the highly dynamic setting of Hydrate Ridge, an about the appropriate niche for SOD in future gas hydrates accretionary ridge offshore Oregon. Leg 204 yielded impor- investigations. tant constraints on processes and gas hydrates distributions Gas hydrates research has had a long history in the SOD in three dimensions (Tréhu et al., 2004a), sometimes with the community, even before its elevation to a focus area within additional fourth dimension of time. Leg 204 had unusually the theme of “Subseaﬂoor Ocean and Deep Biosphere” dur- rich ancillary data-sets (e.g., 3D seismic [Tréhu et al., 2002] ing IODP’s formulation. Before the early 1990s, most of the and CSEM [Weitemeyer et al., 2006]), included sophisticated direct knowledge about subseaﬂoor gas hydrates had been microbiology (e.g., Colwell et al., 2008; Nunoura et al., acquired when gas hydrates were encountered, sometimes 2008), and provided detailed insights into the nature of ﬂux accidentally, during DSDP and ODP expeditions focused regimes and gas/hydrates dynamics at hydrates-bearing seeps on other scientiﬁc goals. Leg 146 in 1992 (Westbrook et al., (e.g., Torres et al., 2004; Tréhu et al., 2004b; Liu and Flem- 1994) was an exception, having been designed to conduct ings, 2006). A few years later, Expedition 311 (Riedel et al., limited gas hydrates investigations within the context of 2006) became the only IODP activity exclusively focused on broader-scale ﬂuids research on the Oregon and Vancouver gas hydrates, completing a drilling transect from the subduct- parts of the Cascadian margin. ing plate onto the overriding plate on the northern Cascadia In 1995, ODP Leg 164 (Dillon et al., 1996) was the ﬁrst margin. The project highlighted lateral heterogeneity in gas expedition committed exclusively to gas hydrates objec- hydrates distributions and discovered concentrations of gas
OCR for page 107
107 APPENDIX C hydrates in coarse-grained sediments well above the base Villinger Temperature Tool (DVTP) and DVTP-P; Graber et of the gas hydrates stability zone, a ﬁnding that challenges al., 2002), SOD’s model of rapid, post-drilling publication simple models (e.g., Hyndman and Davis, 1992; Rempel of archival initial reports, and the shipboard deployment of and Buffett, 1998; Xu and Ruppel, 1999) for gas hydrates imaging equipment capable of determining the distribution system dynamics (e.g., Malinverno, 2010). In September and character of gas hydrates in recovered cores (e.g., Abegg 2010, Site 889, which was drilled on Leg 146 and which et al., 2006). lies close to IODP Expedition 311 Sites U1327/U1328, will The international focus on developing deepwater be re-instrumented and prepared for eventual linkage of the hydrates as an energy resource means that SOD will not play borehole instrumentation to Canada’s NEPTUNE cabled a leading role in most future gas hydrates drilling. SOD’s observatory (Davis et al., 2010). While the primary focus drilling platforms may on occasion be suitable for use for of this effort is not gas hydrates, it is noteworthy that SOD non-SOD projects that involve straightforward gas hydrates boreholes drilled originally for gas hydrates objectives will investigations, little advanced mud handling, and few special be the ﬁrst on the North American Margin to be part of a logging requirements. cabled observatory. SOD does have an important role to play in non-resource Gas hydrates are unique among geologic materials stud- aspects of gas hydrates in a future program. First, marine ied by SOD: They are highly accessible to the drill (within gas hydrates at the upper feather edge of stability on the the uppermost 10s to 100s of meters subseaﬂoor), are stable continental slopes (e.g., Westbrook et al., 2009) and those over a speciﬁc pressure and temperature range, and rapidly associated with subsea permafrost in shallow circum-Arctic dissociate to water and large volumes of gas. The dissocia- areas (e.g., Rachold et al., 2007; Ruppel, 2009; Shakhova et tion process is strongly endothermic, which has led to reli- al., 2010) are probably actively deteriorating now in response ance on routine thermal infrared imaging (e.g., Ford et al., to climate change on relatively short timescales (contempo- 2003; Weinberger et al., 2005) to locate gas hydrates nodules rary to 20 ka). The dynamics of these gas hydrates systems in recovered conventional cores. Because the removal of represents a compelling, multidisciplinary problem that is hydrates-bearing cores from the gas hydrates stability ﬁeld well-suited for the future of SOD under the auspices of the leads to rapid degassing, the destruction of sediment textures, “Earth in Motion” theme. Second, despite decades’ worth of and irreversible changes in bulk sediment properties (e.g., anecdotal studies exploring possible links between subma- Francisca et al., 2005), pressure coring—coring that main- rine slope stability and gas hydrates (e.g., Carpenter, 1981; tains in situ hydrostatic pressure—has long been viewed as Kayen and Lee, 1991; Paull et al., 1991), there remains no a necessity for gas hydrates studies. Even in the mid-1980s, proof that gas hydrates and/or free gas play a causal role in SOD was experimenting with pressure coring, but true suc- triggering failures or exacerbate major failures once they are cess with the Pressure Core Sampler (PCS; Pettigrew, 1992) initiated (e.g., Bryn et al., 2005; Tappin, 2010). In light of was not attained until ODP Leg 164 (Dickens et al., 1997b, (a) the tsunamogenic potential of major slope failures that 2000). The success of the PCS set the stage for larger, more occur in or near gas hydrates areas (e.g., Long et al., 1990; sophisticated pressure corers (e.g., Hydrate Autoclave Cor- Hornbach et al., 2007), (b) advances in understanding the ing Equipment (HYACE)/deployment of HYACE tools in geomechanics of hydrate-bearing and gas-charged slope new tests on hydrates (HYACINTH); Fugro corer) that are sediments (e.g., Sultan et al., 2004; Nixon and Grozic, 2007; now routinely deployed to obtain high-quality, hydrates- Kwon et al., 2008; Liu and Flemings, 2009); and (c) inferred bearing samples, particularly in relatively ﬁne-grained sedi- climate-induced dissociation of marine gas hydrates (e.g., ments. Subsequent technical innovations made for sampling Westbrook et al., 2009) under way now in areas near previ- and testing of HBS at in situ hydrostatic pressure (e.g., Park ously documented slope failures, the time is ripe for a fresh et al., 2009) also owe a great deal to the initial work done focus on the links between gas hydrates and slope stability within SOD. These outside-SOD developments include: (a) issues within SOD. the pressure-temperature core sampler (PTCS), a chilled 3-m-long pressure corer developed for Nankai Trough Supporting References drilling (Takahashi and Tsuji, 2005); (b) a chilled vessel to Abegg, F., G. Bohrmann, and W. Kuhs. 2006. Data report: Shapes and transfer pressure cores into imaging/measurement devices structures of gas hydrates imaged by computed tomographic analyses, (PCATS) and an instrument to provide pressure core sub- ODP Leg 204, Hydrate Ridge. In Proceedings of Ocean Drilling Pro- samples for microbiological and other studies (Schultheiss gram, Scientiﬁc Results, Volume 204, Tréhu, A.M., G. Bohrmann, M.E. et al., 2006, 2010; Parkes et al., 2009); and (c) devices to Torres, and F.S. Colwell (Eds.). Ocean Drilling Program, Texas A&M measure the physical properties of pressure cores both at University, College Station, Texas. Bryn, P., K. Berg, C.F. Forsberg, A. Solheim, and T. Kvalstad. 2005. Explain- hydrostatic pressure (IPTC; Yun et al., 2006) and with effec- ing the Storegga slide. Marine and Petroleum Geology 22(1-2):11-19. tive stress restored (Ruppel et al., 2008). Other key technical Carpenter, G. 1981. Coincident sediment slump/clathrate compexes on the contributions of SOD to the numerous international non- U.S. Atlantic continental slope. Geo-Marine Letters 1(1):29-32. SOD gas hydrates drilling projects are the development of Collett, T.S. 2002. Energy resource potential of natural gas hydrates. AAPG reliable borehole pressure-temperature tools (e.g., the Davis- Bulletin 86(11):1971-1992.
OCR for page 134
134 SCIENTIFIC OCEAN DRILLING WHAT MAJOR TECHNOLOGICAL ADVANCES Innovations and improvement of drilling and coring AND INNOVATIONS HAVE DEVELOPED systems on JR over time include: unique bare-rock, spud-in FROM THE DRILLING PROGRAM? guide-base allowing use of rotary coring bit (RCB); extended core barrel (XCB) for improved recovery in formations too hard for piston coring; motor-driven core barrel for environ- Hans Christian Larsen ments of highly alternating formation strength; and advanced IODP Management International, Inc. piston coring (APC) system (developed from the previous hydraulic piston coring [HPC]) for ultra-high recovery This white paper summarizes some major technological (~100 percent) within soft sediments. Recent “drill over” advances and innovations made over the 40+ years since the technology has pushed the limit of APC to 458 m below inception of scientiﬁc ocean drilling by the Deep Sea Drill- seaﬂoor (HPC: ~100 m). True orientation of cores can also ing Project (DSDP) in 1966. The focus is on the more recent be achieved. Information systems for in-situ monitoring of developments from the later part of the Ocean Drilling Pro- drill bit conditions are being developed to further enhance gram (ODP) and from the Integrated Ocean Drilling Program recovery. (IODP). Limits on report length only allow highlights to be In addition, IODP saw two major new inventions: the included. Funding of many of the technical developments is deepwater, riser drilling vessel D/V Chikyu, purpose-built from outside the program, which traditionally deploy most for SOD by Japan; and application of the mission-speciﬁc of its funds for operations. According to AGI (American platform (MSP) approach to coring within uniquely chal- Geosciences Institute), scientiﬁc publications underpinned lenging environments. by these technologies now exceed 26,000 (>1,500 in Science Chikyu is one of the most capable drillships worldwide. or Nature). Her current riser capability is 2,500 m water depth, amongst Scientiﬁc ocean drilling (SOD) deployed the ﬁrst ever the deepest at time of ship design. A 4,000+ m deepwater, deepwater drill-ship, the CUSS 1 for project Mohole in benchmark-setting riser is currently being explored through 1961 in a water depth of 3,500 m. The thruster-supported optimization of conventional riser technology (material positioning system laid the groundwork for modern dynamic standards, downsizing of blowout preventors [BOPs]) and positioning (DP) systems. The offshore hydrocarbon indus- a riserless (or dual gravity) mud recovery system (RMR). try that subsequently developed is now a top global industry Chikyu’s double rig design is uniquely well suited for RMR, with development budgets many orders of magnitude higher but RMR could also be applied on JR and may be considered than within SOD. SOD therefore piggy-backs on industry for a new SOD vessel planned by China. Another ongoing developments, such as coring, sampling from boreholes, core riser innovation is a monitoring and vibration mitigation sys- description, core-log integration, borehole observatories, tem for operation under strong currents (a condition offshore and development of new research tools and environmental Japan), pushing the envelope of current industry standards. proxies. SOD set the benchmark in these ﬁelds using a truly The innovative application of the MSP concept to the unique set of tools and expertise, and is at the forefront of high Arctic (2004) resulted in a transformative technical coring within extreme environments. Four key topics of achievement of the ﬁrst ever deep coring within the central technology developments and spin-offs are reviewed. Arctic Ocean. This was achieved through sophisticated ice management in conjunction with two powerful ice breakers PLATFORMS, DRILLING, AND CORING and a purpose ﬁtted, ice-breaking drilling vessel (a concept TECHNOLOGY now adapted by industry). Application of a piggy-back, narrow kerf coring system to a DP positioned vessel for The DSDP R/V Glomar Challenger was a purpose-built, high-recovery drilling of carbonate reef material is another ﬁrst-generation deepwater drillship, globally breaking new noteworthy innovation that increased core recovery with one ground drilling in water as deep as 7,044 m (open hole, order (+) of magnitude. non-riser). ODP was served by the R/V JOIDES Resolution Developments by SOD partners (e.g., BGS and (JR), an oil exploration platform converted to a non-riser MARUM) are pushing the shallow (0-100 m) coring from scientiﬁc drilling vessel. Superior to Glomar Challenger in seabed frames (e.g., MeBo of MARUM), which can provide all aspects (e.g., tonnage, drill string capabilities, DP perfor- high-recovery cores from young oceanic crust, otherwise mance, heave compensation), JR drilled deeper, in shallower proven impossible to effectively core. SOD is also develop- waters, in higher latitudes, and with improved core recovery. ing high-temperature core barrels for such environments. JR underwent major refurbishment during IODP years 2006- Because of these many incremental innovations in 2008, extending vessel lifetime, improving accommodations drilling technology, SOD can effectively core in almost any and laboratory space, further improving heave compensation, environment, and maintains leadership in deepwater coring, and adding newly developed, state-of-the-art coring analyti- despite being the David compared to the Goliath in the global cal facilities. drilling industry.
OCR for page 135
135 APPENDIX C SHIPBOARD AND LAB-BASED academic-industry collaboration, IODP supported a logging- TECHNOLOGIES AND MEASUREMENTS while-coring system that measures an electrical image of the borehole while taking a core sample, thereby enhancing core Core splitting and processing tools and protocols still in log integration. SOD also developed formation temperatures use by IODP were developed by DSDP and laid the founda- tools and is the global source of deep temperature data for tion for an unparalleled collection of legacy data from below the sub-seaﬂoor. Large-diameter drill pipe (6-5/8”) will in the the oceans. Of course, major advances in both discrete and future allow for development of better pore ﬂuid sampling continuous core measurements have been made over time. In and formation testing, geochemical logging, nuclear mag- this ﬁeld, SOD can claim credit per se for innovations within netic resonance for pore size distribution, and high-coverage continuous core descriptions and measurements, laying the electrical imaging. groundwork for development of different physical/chemical Gas hydrates and associated logging and sampling tools proxies for environmental change and temporal constraints: is an area where SOD has led the initial research and develop- (1) A core cryogenic magnetometer, which contributed to ment. Hydrates are unstable at surface conditions. Through the commercial product now in use, provides onboard rapid core-log integration an estimate of gas hydrate content that paleomagnetic stratigraphy; (2) Multi-Sensor Track (MST), is continuous at depth can be made. An SOD-developed which is applied pre-core splitting to provide density, mag- pressure core sampler (PCS) paved the way for recovery netic susceptibility, p-wave velocity, and resistivity; (3) rapid of gas hydrate to the surface without sublimation of the measurement color spectrophotometry; (4) spectral natural hydrate. SOD partners (including Geotek Ltd) then devel- gamma ray analysis rapidly measuring cores at comparable oped the PCS into the HYACINTH for in situ pressure and resolution to downhole logging tools (unique for core-log temperature-preserving sampling tool for gas hydrates. This integration); (5) rapid, high-resolution, high dynamic range tool is pivotal in the many governmental and commercial linescan split core imager; (6) continuous XRF high-reso- investigations of gas hydrates as a possible new hydrocarbon lution core scanning (split core); (7) ultra-clean sample and energy source. curation protocols for microbiological sampling; (8) infrared In 2009 SOD took borehole-hosted vertical seismic cameras to identify gas hydrate horizons in core before sub- proﬁling (VSP) to a new level by conducting a wide-angle, limation; and (9) non-destructive rhizon porewater sampler. semi-3D walk-away experiment over the drill site location Ocean drilling has adapted a number of other advanced offshore Japan that is targeted for ultra-deep (7 km) riser facilities for use. Of these, the continuous core computed drilling and instrumentation of a seismic plate boundary. In tomography (CT) scanning stands out and has opened a new this location SOD activities eventually will enable surface world of 3D imaging before core splitting. 3D seismic data, advanced VSP data, borehole logging, The opportunities offered by these advanced core scan- sampling, and long-term borehole observatory data to be ning and analytical tools are vastly supplemented by a large integrated in a unique collage of plate-boundary data. number of (non-program) state-of-the-art analytical facili- ties for mainly discrete samples (e.g., isotopes, magnetic DEEP EARTH OBSERVATORY SCIENCE properties including paleo-intensity, microbiology, and DNA sequencing). More than 13,000 scientists are using SOD Following successful advances in downhole sampling samples. Approximately 2.2 million ODP samples have and logging, the concept of actually installing downhole been taken; this number is increasing, with a recent record observatories that could sample time series (e.g., ﬂuids, pres- of 53,000 samples provided by a SOD core repository. sure, and temperature) was introduced during the ODP by the CORK (Circulation Obviation Retroﬁt Kit) concept. IODP DOWNHOLE MEASUREMENTS/LOGGING is making big strides toward establishing a permanent pres- AND ADVANCED SAMPLING ence of subseaﬂoor observatories within critical ocean ﬂoor locations, and with a vastly expanded set of observations. Because of its unique expertise in core-log integration, These include time-series of pore water geochemistry from SOD is a respected partner of world-leading geophysical osmosamplers (resolution of ~a few days) and geochemical logging companies. Downhole logging has grown in SOD tracer ﬂow-meter allowing estimates of lateral ﬂuid ﬂow drilling, with logged drill sites increasing from 14 percent rates; microbiological observatory elements into hydro- during DSDP to 64 percent during IODP. Most technology logical observatories via use of substrates; vastly improved used in scientiﬁc drilling originates from the hydrocarbon pressure resolution (order of 1 ppb full scale) as a sensitive industry, from wireline logs to logging-while-drilling mea- proxy for strain, and with sampling frequency <1Hz linking surements. However, SOD likely has the globally best core- deformation to seismological data; and tilt meter and seismic log integration data, and specialty tools developed by SOD broadband sensors. Implementation protocols to co-locate include magnetic properties, high-resolution natural gamma multiple sensors for hydrological-geodetic-seismological ray radioactivity, borehole temperature, pressure-measuring purposes or hydrological-thermal-microbiological purposes penetrometers, and laser imaging for microbiology. Through are being developed and planned for upcoming experiments.
OCR for page 136
136 SCIENTIFIC OCEAN DRILLING Supporting References Extending these subseaﬂoor observatories to the high-pres- sure and -temperature regimes at 6-7 km depth (seismogenic Fisher, A. and K. Becker. 1993. A Guide to ODP Tools for Downhole Mea- zones) is currently under development, and links to land by surements: Technical Note 10. [Online]. Available: http://www-odp. ﬁberoptical networks for real-time monitoring are being tamu.edu/publications/tnotes/tn10/10toc.html [2010, November 29]. Goldberg, D. 1997. The role of downhole measurements in marine geology implemented offshore Japan and Northwest America in two and geophysics. Reviews of Geophysical 35(3):315-342. seismically active zones. This SOD development is in coop- Goldberg, D., G. Myers, G. Iturrino, K. Grigar, T. Pettigrew, and S. eration with and co-funded by other entities and programs. Mrozewski. 2006. Logging-while-coring: New technology for the si- These novel technologies, combined with the experience multaneous recovery of downhole cores and geophysical measurements. gained to implement them via drillships, submersibles, and Geological Society, London, Special Publications 267:219-228. Graber, K.K., E. Pollard, B. Jonasson, and E. Schulte. (Eds.). 2002. Over- remotely operated vehicles (ROVs), underpins a new sci- view of Ocean Drilling Program engineering tools and hardware. In entiﬁc paradigm of observing processes as they happen (as Ocean Drilling Program Technical Note 31. Ocean Drilling Program, opposed to simply studying the lasting imprint of processes Texas A&M University, College Station, Texas. in the geological record). Naturally, the new science plan (in Huey, D.P. and M.A. Storms. 1995. New downhole tools improve recovery. preparation) for SOD beyond 2013 makes this emerging ﬁeld Oil and Gas Journal 23:42-48. Huey, D.P. and M.A. Storms. 1995. Modiﬁed wire line tools improve open of “Earth in Motion” science one of its four grand challenges. hole logging operations. Oil and Gas Journal 30:94-96. Malinverno, A., M. Kastner, M.E. Torres, and U.G. Wortmann. 2008. Gas SOD STUDY OF ACTIVE LIFE BELOW THE hydrate occurrence from pore water chlorinity and downhole logs in a transect across the northern Cascadia margin (Integrated Ocean SEAFLOOR Drilling Program Expedition 311). Journal of Geophysical Research 113(B13):1-18. Rapid and ongoing technology development underpins Miller, J.E. and D.P. Huey. 1992. Development of a mud-motor-powered another emerging ﬁeld of science: the study of active micro- coring tool. In Offshore Technology Conference, Houston, Texas. bial life, below, in part deeply below (~1,600 m), the seaﬂoor Miyazaki, E., M. Ozaki, S. Nishioka, and J. Minamiura. 2008. Application (a second grand challenge of the new science plan). Technol- of riser fairings to the D/V “CHIKYU” during drilling in high current ogy development in this ﬁeld takes place globally, and with area. In Proceedings of Oceans ’08 Mts/Ieee Kobe-Techno-Ocean ’08, Kobe, Japan. many different entities and constituencies involved. Special Peter, S., M. Holland, and G. Humphrey. 2009. Wireline coring and analysis contributions by SOD, apart from making sampling pos- under pressure: Recent use and future developments of the HYACINTH sible, are laboratories (on platforms and at core repositories), system. Scientiﬁc Drilling 7:44-50. protocols for clean sampling, curation processes and storage Pettigrew, T.L. 1993. Design and operation of a Drill-In-Casing system (long-term and legacy), computer-automated cell counts (DIC). In Ocean Drilling Program Technical Note 21. Ocean Drilling Program, Texas A&M University, College Station, Texas. (living cells), and DNA replication from limited amount of Saffer, D., L. McNeill, E. Araki, T. Byrne, N. Eguchi, S. Toczko, K. Taka- material. Initial ﬁndings and technology developments by hashi, and the Expedition 319 Scientists. 2009. NanTroSEIZE Stage 2: SOD have generated very signiﬁcant spin-off activities by NanTroSEIZE riser/riserless observatory. In Proceedings of the Inte- other groups. grated Ocean Drilling Program, Volume 319. Integrated Ocean Drilling Program, Texas A&M University, College Station, Texas. Stahl, M.J. 1994. Automated stress analysis and design of drill strings for riserless offshore coring operations. Oil and Gas Journal 4:43-48.
OCR for page 137
137 APPENDIX C DRILLING THE OCEAN CRUST magma bodies, an absence of large magma chambers, melt- rock reaction, mass transfer by upward percolation of melts through the lower crust, and vertical rafting of intrusions and Henry J. B. Dick altered mantle peridotite all having been recognized as major Woods Hole Oceanographic Institution accretionary processes. Ocean crust drilling began in earnest in 1974 with Leg Formation of the ocean lithosphere is the principle mag- 37 of DSDP (Deep Sea Drilling Project), which drilled a four matic process on the planet, generating some three-ﬁfths of hole transect at 37°N on the Mid-Atlantic Ridge (MAR) in the Earth’s crust by surface area and representing the major shallow ocean crust from 3.5 to 13 myr. The sites included a transfer of heat, mass, and volatiles between the Earth’s planned deep hole at Site 332 that penetrated 583 m before interior, crust oceans, and atmospheres. At the present time abandoned. At Site 334, a tectonically emplaced layer of ser- we do not have direct knowledge of the composition of the pentinized peridotite and gabbro was recovered beneath 50 m ocean crust or a full understanding of how it forms. What we of pillow basalts. Ironically, this ﬁrst in situ section of lower do know is largely the result of ocean drilling both in intact crustal rocks proved to be atypical of what was later drilled sections of the ocean crust and in tectonic windows where on seven legs in the Paciﬁc, Atlantic, and Indian Oceans. the lower ocean crust and mantle have been unroofed to In all, about 50 holes were drilled into “intact” sections of the seaﬂoor. The initial stimulus for drilling was to test two oceanic crust up to the start of the Integrated Ocean Drilling competing models for the ocean crust, which at the time was Program (IODP) in 2004, when it was believed that layered assumed to be a relatively simple layered sequence some 6-7 crust, such as described in the Penrose model, existed in the km thick. Harry Hess, in his landmark paper, History of the Atlantic and Paciﬁc Oceans. At Hole 504B south of the Costa Ocean Basins (Hess, 1962), proposed that the ocean crust Rica Rift, and possibly at Hole 418A in the 108-million-year- largely consisted of mantle peridotite hydrothermally altered old MAR crust, seismic layer 2B was penetrated, with only to serpentine with the Mohorovičić discontinuity (Moho) Hole 504B possibly reaching the very top of seismic layer representing the upper temperature limit for the stability of 3 (Dick et al., 1992; Alt et al., 1993; Detrick et al., 1994). this mineral. The opposing model, which had gained general Drilling in young Paciﬁc crust was particularly difﬁcult, with acceptance from the Earth sciences community, was a layer 10 holes in crust less than 30 million years old reaching a cake consisting of pillow lavas overlying sheeted dikes and maximum penetration of only 178 m—a result attributed to gabbro, with the Moho representing the igneous crust-mantle the difﬁculty of drilling abundant glassy sheet ﬂows. Suc- boundary. In the latter, known as the Penrose ophiolite model cess was better at slower-spreading ridges, with 11 holes (Conference Participants, 1972) the lower ocean crust rep- penetrating greater than 200 m, and 7 reaching greater than resented the remains of a large magma chamber in which 500 m. This drilling showed that seismic layer 2A was com- mantle melts pooled and underwent fractional crystalliza- posed of basalt lavas and rubble, and that at an intermediate tion, while the dikes represented the conduits through which spreading ridge, seismic layer 2B at Hole 504B was sheeted differentiated magmas erupted to the seaﬂoor to form a layer dikes as in the Penrose model. Unexpectedly, however, the of pillow lavas. Obvious differences in the morphology of layer 2B-layer 3 seismic boundary there corresponded to an the seaﬂoor between relatively low relief smooth seaﬂoor alteration front in dikes, rather than the dike-gabbro transi- formed at the fast spreading East Paciﬁc Rise (EPR) and tion. Surprisingly, short sections of often brecciated serpen- slower spreading ridges were largely ignored in this model. tinized peridotite and gabbro, exhibiting high-temperature The ultimate goal of ocean drilling initially was to alteration and crystal-plastic deformation, were found in six achieve a full penetration of the crust from pillow lavas to Atlantic holes drilled in supposedly “intact” crust. Drilling mantle. Given the presumed simplicity of the ocean crust, a at slow spreading ridges demonstrated unexpected tectonic single core would answer all questions. A total penetration of complexity that did not ﬁt the Penrose model and proved a “intact” crust has not been achieved, although we now know harbinger of things to come. that it is technically feasible given the will. Thirty-ﬁve years The early failure to drill deeply into intact oceanic crust of ocean drilling, in combination with seaﬂoor mapping, was a huge disappointment. Recoveries were low, averag- however, has radically transformed our view of the ocean ing ~20 percent. Other than sporadic drilling at Hole 504B, crust, which is now viewed as highly varied in composition no serious attempt to drill ocean crust was made for many and architecture, with radically different models for fast and years after DSDP Leg 53 in 1977. Drilling difﬁculties were slow spread crust. Ironically, both the Hess and the Penrose attributed to highly fractured basalt and diabase and possibly models have proved to describe the ocean crust as it forms thermal problems deep in Hole 504B, although these were under different tectonic conditions. The mechanisms of likely due as much to not properly designing holes for deep accretion of the lower crust now believed to exist are also penetration. Thus, a new strategy was adopted during the radically different from the simple closed-system magma Ocean Drilling Program (ODP), using “tectonic windows” chamber that was the widely accepted paradigm at the start to drill lower crust and mantle (Dick, 1989; Dick and Mével, of ocean drilling, with direct intrusion of numerous small 1996). This drilling strategy targeted peridotite and gabbro
OCR for page 138
138 SCIENTIFIC OCEAN DRILLING exposed at topographic highs at oceanic core complexes: stratigraphy produced by upward compaction of interstitial Atlantis Bank on the Southwest Indian Ridge; the MARK melt to produced numerous high-level Fe-Ti rich oxide gab- area at 23°N; the MAR Atlantis Massif and tectonic blocks bro layers. In addition, olivine-rich troctolites occur in the in the rift mountains near the 15°20′ fracture zone; and Hess mid-section at Hole 1309D. These rocks form by reaction Deep in the Paciﬁc, where the amagmatic tip of the Cocos- between basalt melt and mantle peridotite at the base of the Nazca rift propagates into young (1.5–2 million-year-old) crust, and are subsequently mechanically rafted up through EPR crust. the section (Drouin et al., 2007a, b, 2009; Suhr et al., 2008). Drilling at Hess Deep recovered important sections of Overall, the large majority of gabbros drilled at these sites tectonically disturbed lower crust and mantle that was con- and by Leg 153 at MARK are far too evolved to crystallize sistent with the Penrose model. These sections included the directly from MORB. Thus, to date, we have not recovered important Hole 894G 154-m section of ﬁne-grained gabbros anything like the full lower crustal suite at either slow or fast with a few diabase dikes, which are believed to represent a spreading ridges, which is critical, because until we do we section of lower crust formed in the melt lens beneath the will have only indirect knowledge of the processes that shape EPR and resembled part of the Oman Ophiolite section. They MORB—the most abundant magma on earth. are believed to be the precursor to a similar thick underly- Leg 209 examined what was once thought to be atypical ocean crust. It is drilled 19 holes at eight sites from 14°43 ′N ing gabbro section. The gabbros are too evolved, however, to represent crystallization products of the relatively primi- to 15°39’N on the MAR where dredging found extensive tive pillow basalts that characterize the East Paciﬁc Rise, mantle outcrops intruded by small gabbro bodies. This ﬁnd- in conﬂict with the generally accepted hypothesis that the ing led to the hypothesis that the crust was largely serpen- melt lens is their primary source. A second result was a tinized peridotite with local small magmatic centers cut by series of holes at Site 895 that represent a transect across a small dike swarms and local eruptive sequences (Cannat et melt transport conduit through a mantle section. The host al., 1997, 2006). This was what Leg 209 drilled, conﬁrming peridotites were highly depleted residues of partial melting, the existence of crustal sections that form by direct intrusion consistent with a fractional melting model, while the dunite and hydrothermal alteration of mantle rock along a signiﬁ- conduits contained gabbroic segregations that demonstrated cant portion of slower spreading ridges. Moreover, the crust for the ﬁrst time that the mid-ocean ridge basalt (MORB) consisted of one tectonic block cutting another with alternate is formed within the mantle itself, rather than represent- fault capture, leading to spreading of blocks in opposite ing mixing of diverse magmas in a lower crustal magma directions from the rift valley (Schroeder et al., 2007)—a chamber. The segregations also showed that basaltic melts new form of seaﬂoor spreading, which morphological analy- can crystallize at near constant temperature by reaction with sis of the seaﬂoor suggests makes up a substantial portion the host mantle—a result whose importance was not fully (~40 percent) of the crust at slower spreading ridges (e.g., appreciated until analysis of the Hole 1309D gabbro section Escartin et al., 2008). in the Atlantic. One of the great successes of IODP has been Drilling in lower crust at slower spreading ridges shows the penetration of an intact section of EPR crust down to the that its accretion occurs by mechanisms previously not dike-gabbro transition at Hole 1256 penetrating 1257.1 m of considered: direct intrusion of small batches of melts at all the upper crust, including a 345.7 m sheeted dike complex levels, upward compaction of interstitial melts by permeable and 100.5 m into gabbro near the depth predicted by seis- ﬂow, and rafting of deeper intrusions and material formed by mologists for the layer 12-3 boundary. Besides afﬁrming the reaction between melts and mantle at the base of the crust. results from Hess Deep, Hole 1256D proved the hypothesis Moreover, it has also shown that both Penrose- and Hess-type that the shallow ocean crust (dikes and lavas) thins at the sections exist along slow and ultraslow spreading ridges. fastest spreading rates, conﬁrming the utility of seismology in shallow Paciﬁc crust. Supporting References Drilling lower crustal rocks in tectonic windows at slow Alt, J.C., H. Kinoshita, and L.B. Stokking, S. Allerton, W. Bach, K. Becker, and ultraslow spreading ridges is one of the dramatic suc- V.K. Boehm, T.S. Brewer, Y. Dilek, F. Filice, M.R. Fisk, H. Fujisawa, H. cesses of ODP and IODP. Hole 735B penetrated 1,508 m of Furnes, G. Guerin, G.D. Harper, J. Honnorez, H. Hoskins, H. Ishizuka, gabbro at the Atlantis Bank core complex on the southwest C. Laverene, A.W. McNeil, A.J. Magenheim, S. Miyashita, P.A. Pezard, Indian Ridge, while Hole 1309D penetrated 1,415 m at the M.H. Salisbury, P. Taratotti, D.A. Teagle, D.A. Vanko, R.H. Wilkens, and Atlantis Massif on the MAR. Recovery was ~87 percent of H.U. Worm. 1993. Costa Rica Rift. In Proceedings of the Ocean Drilling Program, Initial Reports, Volume 148. Ocean Drilling Program, Texas both sites. These successes show unequivocally for the ﬁrst A&M University, College Station, Texas. time that thick gabbro sequences do exist at slower spread- Cannat, M., Y. Lagabrielle, H. Bougault, J. Casey, N. de Coutures, L. ing ridges, but that they are the remains of numerous small Dmitriev, and Y. Fouquet. 1997. Ultramaﬁc and gabbroic exposures at intrusive swarms, not of large magma chambers. Moreover, the Mid-Atlantic Ridge: Geologic mapping in the 15°N region. Tecto- the sections are riddled with microgabbro dikes and solution nophysics 279(1-4):193-213. channels representing melt transport from depth through pre- existing gabbro. Equally startling is a superimposed igneous
OCR for page 139
139 APPENDIX C Cannat, M., D. Sauter, V. Mendel, E. Ruellan, K. Okino, J. Escartin, V. Drouin, M., M. Godard, and B. Ildefonse. 2007b. Origin of olivine-rich Combier, and M. Baala. 2006. Modes of seaﬂoor generation at a melt- troctolites from IODP Hole U1209D in the Atlantis Massif (Mid-At- poor ultraslow-spreading ridge. Geology 34(7):605-608. lantic Ridge): Petrostructural and geochemical study. Eos, Transactions, Conference Participants. 1972. Penrose ﬁeld conference on ophiolites. American Geophysical Union 88:52. Geotimes 17:24-26. Drouin, M., M. Godard, B. Ildefonse, O. Bruguier, and C.J. Garrido. 2009. Detrick, R., J. Collins, R. Stephen, and S. Swift. 1994. In situ evidence for Geochemical and petrographic evidence for magmatic impregnation in the nature of the seismic layer 2/3 boundary in oceanic crust. Nature the oceanic lithosphere at Atlantis Massif, Mid-Atlantic Ridge (IODP 370:288-290. Hole U1309D, 30°N). Chemical Geology 264(1-4):71-88. Dick, H.J.B. (Ed.). 1989. JOI/USSAC Workshop Report: Drilling the Oce- Escartin, J., D.K. Smith, J.R. Cann, H. Schouten, C.H. Langmuir, and S. anic Lower Crust and Mantle. Woods Hole Oceanographic Institution, Escrig. 2008. Central role of detachment faults in accretion of slow- Woods Hole, Massachusetts. spreading oceanic lithosphere. Nature 455:790-794. Dick, H.J.B. and C. Mével. (Eds.). 1996. The Ocean Lithosphere and Scien- Hess, H.H. 1962. The history of the ocean basins. In Petrologic Studies: A tiﬁc Drilling into the 21st Century. JOI/U.S. Science Support Program Volume in Honor of A.F. Buddington, Engel, A.E.J., H.L. James, and and the InterRidge Ofﬁce, Washington, DC. B.F. Leonard (Eds.). Geological Society of America, Boudler, Colorado. Dick, H.J.B., J.A. Eringer, L.B. Stokking, P. Agrinier, S. Allerton, J.C. Alt, Suhr, G., E. Hellebrand, K. Johnson, and D. Brunelli. 2008. Stacked L.O. Boldreel, M.R. Fisk, P.K.H. Harvey, G.J. Iturrino, K.T.M. Johnson, gabbro units and intervening mantle: A detailed look at a section of D.S. Kelley, P.K. Kepezhinskas, C. Laverne, F.C. Marton, A.W. McNeill, IODP Leg 305, Hole U1309D. Geochemistry, Geophysics, Geosystems H.R. Naslund, J.E. Pariso, N.N. Pertsev, P. Pezard, E.S. Schandi, J.W. 9(Q10007):1-31. Sparks, P. Tartarotti, S. Umino. D.A. Vanko, and E. Zuleger. 1992. 2. Schroeder, T., M.J. Cheadle, H.J.B. Dick, U. Faul, J.F. Casey, and P.B. Site 504. In Proceedings of the Ocean Drilling Program, Initial Reports, Kelemen. 2007. Nonvolcanic seaﬂoor spreading and corner-ﬂow rota- Volume 140, Dick, H.J.B., J.A. Erzinger, and L.B. Stokking (Eds.). tion accommodated by extensional faulting at 15N on the Mid-Atlantic Ocean Drilling Program, Texas A&M Univeristy, College Station, Texas. Ridge: A structural synthesis of ODP Leg 209. Geochemistry, Geophys- Drouin, M., M. Godard, and B. Ildefonse. 2007a. Origin of olivine-rich ics, Geosystems 8:Q06015. gabbroic rocks from the Atlantis Massif (MAR 30°N, IODP Hole U1309D): Petrostructural and geochemical study. Geophysical Research Abstracts 9(06550).
OCR for page 140
140 SCIENTIFIC OCEAN DRILLING LARGE IGNEOUS PROVINCES Focused investigations of oceanic plateaus have tar- geted the two largest features globally, the ~120 Ma Ontong Java Plateau (Paciﬁc Ocean) and ~120-95 Ma Kerguelen Millard F. Cofﬁn Plateau/Broken Ridge (Indian Ocean), each encompassing University of Tasmania, Australia an area approximately one-fourth the size of the contigu- ous United States. Several expeditions have drilled multiple Large igneous provinces (LIPs)—oceanic plateaus, volca- holes penetrating the igneous basement of each. In late 2009, nic rifted margins, and continental ﬂood basalts—result from igneous basement of a third oceanic plateau, the ~145-130 fundamental processes in Earth’s interior and have been impli- Ma Shatsky Rise (Paciﬁc Ocean), was drilled in various cated as a cause of major worldwide environmental changes. locations. These three features constitute the only oceanic Although the plate tectonics paradigm successfully explains plateaus where igneous basement has been drilled at more volcanic activity on Earth’s surface associated with seaﬂoor than one site. spreading and plate subduction, it does not elucidate the mas- Drilling results from Ontong Java Plateau basement sive “hotspot” volcanism that produces LIPs, which dominates rocks are complemented by studies of obducted plateau the record of volcanism on all other terrestrial planets and rocks exposed in the Solomon Islands. All basement rocks satellites in our solar system and the cause of which is debated recovered to date are remarkably homogeneous—submarine vigorously. Temporal correlations between LIP emplacements tholeiitic basalts with minor variations in elemental and iso- and environmental phenomena such as mass extinctions and topic composition. Partial batch melting (≥30 percent) gener- oceanic anoxic events (OAEs) are well documented, yet the ated the basalts, with melting and fractional crystallization underlying mechanisms causing these global catastrophes are at depths of <6 km. The lavas and their overlying sediment only beginning to be grasped. Scientiﬁc ocean drilling has indicate relatively minor uplift accompanying emplacement played a central and critical role in illuminating solid Earth and relatively minor subsidence since emplacement. Primar- processes causing LIPs and in comprehending the effects of ily on the basis of drilling results, multiple models—plume, LIP formation on Earth’s environment. bolide impact, and upwelling eclogite—have been proposed Reconnaissance drilling of oceanic plateaus and volca- for the feature’s origin. The Ontong Java Plateau correlates nic rifted margins began soon after scientiﬁc ocean drilling temporally with oceanic anoxic event (OAE-1a), and inter- started in 1968, but the ﬁrst targeted LIP investigations pretation of strontium, osmium, and lead isotopic systems involving drilling, focusing on the ~55 Ma North Atlantic during the time of OAE-1a points to a close linkage between volcanic rifted margins, commenced in the 1980s. Drilling the two, with CO2, Fe, and trace metal emissions from the on the UK margin conﬁrmed a hypothesis that submarine massive magmatism potentially triggering the event. “seaward-dipping reﬂectors” (SDRs) observed on seismic Uppermost igneous basement of the Kerguelen Plateau/ reﬂection data were stacks of originally subaerial lava ﬂows Broken Ridge is dominantly subaerial tholeiitic basalt, and it that subsequently cooled and subsided beneath sea level, shows two apparent peaks in magmatism at 119-110 Ma and where they were buried by sediment—a nearly ubiquitous 105-95 Ma. Geochemical differences among these basalts characteristic of submarine LIPs that precludes their volcanic are attributable to varying proportions of components from and plutonic rocks from being sampled by any means other the primary mantle source (plume?), depleted mid-ocean than drilling. Further focused drilling of the North Atlantic ridge basalt (MORB)-related asthenosphere, and continental LIP, on the Norwegian Margin in the 1980s and the conjugate lithosphere. Proterozoic-age zircon and monazite in clasts East Greenland Margin in the 1990s, documented extreme of garnet-biotite gneiss in a conglomerate intercalated with magmatic productivity over a distance of at least 2,000 km basalt at one drill site demonstrate the presence of fragments during continental rifting and breakup, provided the ﬁrst of continental crust in the Kerguelen Plateau, inferred previ- age data from an oceanic LIP showing that construction of ously from geophysical and geochemical data. For the ﬁrst these margins was geologically “instantaneous” (ca. 1 mil- time from an intra-oceanic LIP, alkalic lavas, rhyolite, and lion years), and yielded geochemical evidence that landward pyroclastic deposits were sampled. Flora and fauna preserved SDRs were contaminated during ascent through continental in sediment overlying igneous basement record long-term crust and that oceanward SDRs formed at a seaﬂoor spreading plateau subsidence, beginning with terrestrial and shallow center resembling Iceland. A proposed mechanism for these marine deposition and continuing to deep water deposition. ~55 Ma magmas triggering the Paleocene-Eocene Thermal The ﬁrst results of 2009 basement drilling on the Shatsky Maximum is intrusion of voluminous mantle-derived melts Rise include evidence for initial shallow water or subaerial into carbon-rich sedimentary strata in the northeast Atlantic eruption of predominantly massive lava ﬂows, subsequent that caused explosive release of methane into the ocean and deeper water eruption of mainly pillow lava ﬂows, and post- atmosphere via hydrothermal vent complexes. More than emplacement subsidence resembling that of normal oceanic 50 percent of passive margins globally are “volcanic,” but crust. to date scientiﬁc ocean drilling has only sampled the North Future LIP drilling has the potential to transform our Atlantic LIP at one site. understanding of the Earth system through investigating:
OCR for page 141
141 APPENDIX C Supporting References (1) magma (and hence mantle source) variability through time, through drilling deep sections in multiple LIPs; (2) the Burke, K. and T. Torsvik. 2004. Derivation of large igneous provinces of nature of melting anomalies, i.e., compositional vs. thermal, the past 200 million years from long-term heterogeneities in the deep that produce LIPs; (3) the precise durations of oceanic LIP mantle. Earth and Planetary Science Letters 227(3-4):531-538. Cofﬁn, M.F. and O. Eldholm. 1994. Large igneous provinces: Crustal events; (4) modes of eruption, i.e., constant effusion over structure, dimensions, and external consequences. Reviews of Geophys- one to several million years, or several discrete pulses over ics 32(1):1-36. the same time interval; and (5) relationships among oceanic Courtillot, V.E., A. Davaille, J. Besse, and J. Stock. 2003. Three distinct LIPs, OAEs, extinction events, and other major environ- types of hotspots in the Earth’s mantle. Earth and Planetary Science mental changes (e.g., ocean acidiﬁcation and fertilization). Letters 205(3-4):295-308. Eldholm, O. and M.F. Cofﬁn. 2000. Large igneous provinces and plate tec- The 2010 Eyjafjallajökull eruption underscores the nascent tonics. In The History and Dynamics of Global Plate Motions, Richards, state of and need for knowledge of the ﬁrst four pathways of M.A., R.G. Gordon, and R.D. van der Hilst (Eds.). Geophysical Mono- investigation above, and results from the last will contribute graph, American Geophysical Union, Washington, DC. to understanding and forecasting regional and global envi- Ernst, R.E., K.L. Buchan, and I.H. Campbell. 2005. Frontiers in large igne- ronmental changes during the Anthropocene. ous province research. Lithos 79:271-297. Kerr, A.C. 2005. Oceanic LIPs: The kiss of death. Elements 1:289-292. Advancing knowledge of LIPs and the Earth system Korenaga, J., P.B. Kelemen, and W.S. Holbrook. 2002. Methods for re- requires integrated multidisciplinary and cross-disciplinary solving the origin of large igneous provinces from crustal seismology. approaches involving mantle geodynamics, plume model- Journal of Geophysical Research 107(2178):1-27. ing, petrology, geochemistry, environmental impacts, pale- Mahoney, J.J. and M.F. Cofﬁn (Eds.). 1997. Large Igneous Provinces: oceanography, micropaleontology, physical volcanology, Continental, Oceanic, and Planetary Flood Volcanism. Geophysical Monograph, American Geophysical Union, Washington, DC. geophysics, and tectonics. Drilling and logging are critical Montelli, R., G. Nolet, F.A. Dahlen, and G. Masters. 2006. A catalogue of tools for most of these disciplines. Oceanic LIPs must be deep mantle plumes: New results from ﬁnite-frequency tomography. studied in concert with continental counterparts to better Geochemistry, Geophysics, and Geosystems 7(Q11007):1-69. understand emplacement mechanisms and environmental Neal, C.R., M.F. Cofﬁn, N. Arndt, R.A. Duncan, O. Eldholm, E. Erba, C. effects of their formation. Needed technology developments Farnetani, G. Fitton, S. Ingle, N. Ohkouchi, M. Rampino, M.K. Reichow, S. Self, and Y. Tatsumi. 2008. Investigating large igneous province include better recovery of syn-sedimentary sections, sidewall formation and associated paleoenvironmental events: A white paper for coring, oriented cores, and controlled circulation drilling in scientiﬁc drilling. Scientiﬁc Drilling 6:4-18. water depths >2,500 m. The oceanic and continental drilling Ridley, V.A. and M.A. Richards. 2010. Deep crustal structure beneath large communities should merge efforts for seamless thematic and igneous provinces and the petrologic evolution of ﬂood basalts. Geo- onshore/offshore investigations, and LIP-focused IODP- chemistry, Geophysics, and Geosystems 11(Q09006):1-21. Saunders, A.D. 2005. Large igneous provinces: Origin and environmental industry collaborations should be enhanced. consequences. Elements 1(5):259-263. Sleep, N.H. 2006. Mantle plumes from top to bottom. Earth Science Reviews 77(4):231-271. Svensen, H., S. Planke, A. Malthe-Sorenssen, B. Jamtveit, R. Myklebust, T.R. Eidem, and S.S. Rey. 2004. Release of methane from a volca- nic basin as a mechanism for initial Eocene global warming. Nature 429:542-545. White, R.S. and D. McKenzie. 1995. Mantle plumes and ﬂood basalts. Journal of Geophysical Research 100(17):543-17,585. Wignall, P. 2005. The link between large igneous province eruptions and mass extinctions. Elements 1(5):293-297.
OCR for page 142
142 SCIENTIFIC OCEAN DRILLING CONTINENTAL BREAKUP AND km to the east of the peridotite ridge, indicating that there is SEDIMENTARY BASIN FORMATION a wide zone of upper mantle rocks exhumed to the seaﬂoor and presumably separating extended continental crust from oceanic crust. Some of the sampled peridotite contained Dale S. Sawyer strong remnant magnetization, explaining the presence of Rice University apparent seaﬂoor spreading anomalies over crust that is not oceanic. ODP Leg 173 (Whitmarsh and Wallace, 2001) In the study of continental breakup (and other large-scale showed that the continental crust was thinned to nearly tectonic systems), scientiﬁc ocean drilling is not a capstone zero thickness by low-angle detachment faulting, which in activity, but rather is part of an iterative process comprising some places brought upper mantle peridotite to within a few drilling, improved geophysical (primarily controlled source hundred meters of the seaﬂoor at the time of breakup. The seismology) and geological (including onshore exposures peridotites are most likely to be subcontinental mantle. Maﬁc where available) characterization, ongoing geodynamic cores were shown to have been emplaced in or just below the modeling, and drilling again. Continental breakup and ensu- thinned lower continental crust. Surprisingly no samples of ing seaﬂoor spreading inherently separate the “ﬁeld area” upper continental crust or synrift melt were obtained, which for a study into a pair of conjugate rifted margins. Typically is attributed to gradual breakup and transition to seaﬂoor both margins must be studied comprehensively to learn about spreading. During Leg 173 shipboard scientists noted strong the whole. Every rifted margin is a blend of end-member similarities between cores obtained from the Iberia Abyssal types: (1) magma-dominated or magma-poor, (2) actively Plain and the character and history of rifted margins and rifting or no longer rifting, (3) normal spreading, obliquely transition zones exposed in the modern Alps (Manatschal and spreading, and transform, and (4) sediment-dominated or Bernoulli, 1998). This line of research has been very fruitful sediment starved. Examination of any single rifting system in expanding our understanding of both systems. ODP Leg cannot reveal details of all the important breakup processes. 210 (Tucholke and Sibuet, 2007) drilled off Newfoundland Successful drilling studies will include geodynamic model- in a position conjugate to the Legs 149/173 transect. The ing efforts before, during, and after each coordinated drilling primary site bottomed in a pair of diabase sills dated at 98 and activity 105 Ma. The upper sill is intruded at the level of the promi- In 1991, the Ocean Drilling Program (ODP) Planning nent and widespread “U” reﬂection, suggesting that sills Committee formed a North Atlantic Rifted Margins Detailed may be pervasive at this stratigraphic level. No equivalent Planning Group (NARM-DPG) with a charge to explore to these sills was observed on the Iberia Margin. A second options and make recommendations for conducting drilling site off Newfoundland sampled exhumed peridotite in a shal- on volcanic and non-volcanic conjugate rifted margins. The low basement high that is similar to peridotites sampled off NARM-DPG recommended that ODP efforts focus on the Iberia. As in Iberia, these peridotites showed little evidence Newfoundland-Iberia conjugate pair for studies of magma- of melting even though they were coincident with apparently poor rifting and the southeast Greenland–northeast Atlantic normal lineated magnetic anomalies. for studies of magma-dominated rifting. Extensive reinterpretation of seismic proﬁles after Legs Drilling on the magma-poor Newfoundland and Iberia 173 and 210, synthesis of Alps analogs (Peron-Pinvidic et rifted margins comprises DSDP (Deep Sea Drilling Project) al., 2007), comparison to drilling results, comparison to slow Leg 47 and ODP Legs 103, 149, 173, and 210. DSDP Leg spreading midocean ridge analogs (Cannat et al., 2009), and 47B (Sibuet and Ryan, 1979) drilled a deep sedimentary hole geodynamic modeling (Lavier and Manatschal, 2006) has led that provided stratigraphic information about the breakup to a new understanding of the Newfoundland–Iberia breakup of Newfoundland and Iberia. ODP Leg 103 (Boillot and (Peron-Pinvidic and Manatschal, 2009). This understanding Winterer, 1988) drilled a transect across the Deep Galicia moves past thinking of continental breakup as mono-phase Basin and demonstrated that (1) a prominent seismic reﬂec- and laterally uniform rifting followed by an abrupt breakup tor “S,” later to be characterized as a detachment fault, and formation of a sharp continent-ocean boundary. The is within or overlain by rotated, fault-bounded blocks of new model describes rifting as a process of progressive continental crust, (2) peridotite, which ascended from 30 strain localization, stacking different modes of extension km depth and shows a history of partial melting, stretching, in temporally and spatially varying domains. It deﬁnes the serpentinization, and fracturing, is exposed in a margin par- end of rifting and onset of seaﬂoor spreading neither as a allel ridge at the foot of the margin, and (3) obtained dates moment in time, nor a mappable boundary, but as a transi- for the syn- and post-rift sediments reﬂect the last stage tion zone in which a series of processes interact and overlap of breakup. ODP Leg 149 (Whitmarsh and Sawyer, 1996) in complex ways. Features that we could not explain are drilled a transect across the Iberia Abyssal Plain margin now comprehensible. Furthermore, this new understanding segment. Peridotite was again sampled at the top of a ridge, is revolutionizing the way academic and petroleum industry providing additional information about its exhumation his- scientists interpret other magma-poor rifted margins around tory. However, serpentinized peridotite was also sampled 20 the world (Reston, 2009).
OCR for page 143
143 APPENDIX C Drilling on the magma-dominated southeast Greenland Larsen, H.C. and R.A. Duncan. 1996. Introduction: Leg 163 background and objectives. In Proceedings of the Ocean Drilling Program, Initial Re- and northeast Atlantic volcanic margins comprises DSDP ports, Volume 163, Duncan, R.A., H.C. Larsen, J.F. Allan, Y. Aita, N.T. Legs 38 and 81 and ODP Legs 104, 152, and 163. DSDP Leg Arndt, C.J. Bücker, H. Cambray, K.V. Cashman, B.P. Cemey, P.D. Clift, 38 (Talwani and Udintsev, 1976) found that acoustic base- J.G. Fitton, B. Le Gall, P.R. Hooper, Y. Nakasa, Y. Niu, H. Philipp, S. ment of Vøring Plateau was composed of basaltic volcanics. Planke, J. Rehacek, A.D. Saunders, D.A.H. Teagle, and C. Tenger (Eds.). DSDP Leg 81 (Roberts et al., 1984) drilled Rockall Margin, Ocean Drilling Program, Texas A&M University, College Station, Texas. Larsen, H.C. and A.D. Saunders. 1998. Tectonism and volcanism at the suggesting that seaward dipping reﬂectors (SDRs) were Southeast Greenland Rifted Margine: A record of plume impact and subaerial volcanic constructions. ODP Leg 104 (Eldholm later continental rupture. In Proceedings of the Ocean Drilling Program, et al., 1989) drilled 900 m of subaerial ﬂows of the SDR Scientiﬁc Results, Volume 152, Saunders, A.D., H.C. Larsen, and S.W. at the Vøring Margin and was able to characterize events Wise, Jr. (Eds.). Ocean Drilling Program, Texas A&M University, Col- during the initial opening of a volcanic margin. ODP Leg lege Station, Texas. Lavier, L.L. and G.A. Manatschal. 2006. A mechanism to thin the continen- 152 (Larsen and Saunders, 1998) drilled a transect of holes tal lithosphere at magma-poor margins. Nature 440:324-328. across the southeast Greenland SDR from the middle shelf Manatschal, G. and D. Bernoulli. 1998. Rifting and early evolution of to deep water. They distinguished continental and oceanic ancient ocean basins: The record of the Mesozoic Tethys and of ﬂow sequences and located the seaward extent of rifted the Galicia-Newfoundland Margins. Marine Geophysical Research continental crust. They showed that the SDR overlies fully 20(4):371-381. Peron-Pinvidic, G. and G. Manatschal. 2009. The ﬁnal rifting evolution at oceanic crust and that it formed in the manner of the present- deep magma-poor passive margins from Iberia-Newfoundland: A new day Iceland rift zone. They were able to infer features of the point of view. International Journal of Earth Sciences 98(7):1581-1597. plume associated with the formation of the margin. ODP Leg Peron-Pinvidic, G., G. Manatschal, T.A. Minshull, and D.S. Sawyer. 163 (Larsen and Duncan, 1996) was not able to achieve its 2007. Tectonosedimentary evolution of the deep Iberia-Newfound- primary tectonic objectives because of “a drilling accident land margins: Evidence for a complex breakup history. Tectonics 26(TC2011):1-19. and damage to the ship sustained during extreme storm con- Reston, T.J. 2009. The extension discrepancy and syn-rift subsidence deﬁcit ditions” (Initial reports 163). During this period of drilling, at rifted margins. Petroleum Geoscience 15(3):217-237. 1976 to 1995, and complementary seismic, geological, and Roberts, D.G., J. Backman, A.C. Morton, J.W. Murray, and J.B. Keene. modeling studies, the understanding of magma-dominated 1984. Evolution of volcanic rifted margins: Synthesis of Leg 81 results continental breakup moved forward, as did our conception on the West Margin of Rockall Plateau. In Initial Reports of the Deep Sea Drilling Project, Volume 81, Roberts D.G., D. Schnitker, et al. about the global extent and importance of these margins (Eds.). Deep Sea Drilling Project, U.S. Government Printing Ofﬁce, and large igneous provinces, their counterpart in the oceans. Washington, DC. Future opportunities in the study of continental breakup Sibuet, J.C. and W.B.F. Ryan. 1979. Site 398: Evolution of the West Iberian will depend not just on access to ocean drilling, but also Passive Continental Margin in the framework of the early evolution of on coordinated high-quality, two- and three-dimensional the North Atlantic Ocean. In Initial Reports of the Deep Sea Drilling Project, Volume 47, Part II, Sibuet, J.C., W.B.F. Ryan, et al. (Eds.). Deep multichannel seismic reﬂection proﬁling and companion Sea Drilling Project, U.S. Government Printing Ofﬁce, Washington, DC. long-offset seismic surveys. The INVEST report mentions Talwani, M. and G. Udintsev. 1976. Tectonic synthesis. In Initial Reports several times the need for increased collaboration with of the Deep Sea Drilling Project, Volume 38. Deep Sea Drilling Project, industry. The study of continental breakup is one of the most U.S. Government Printing Ofﬁce, Washington, DC. obvious and important touch points between academic and Tucholke, B.E. and J.C. Sibuet. 2007. Leg 210 synthesis: Tectonic, mag- matic, and sedimentary evolution of the Newfoundland-Iberia rift. In industry science. Proceedings of the Ocean Drilling Program, Scientiﬁc Results, Volume 210, Tucholke, B.E., J.C. Sibuet, and A. Klaus (Eds.). Ocean Drilling Program, Texas A&M University, College Station, Texas. Supporting References Whitmarsh, R.B. and D.S. Sawyer. 1996. The ocean/continent transition Boillot, G. and E.L. Winterer. 1988. Drilling across the Galicia Margin: beneath the Iberia Abyssal Plain and continental-rifting to seaﬂoor- Retrospect and prospect. In Proceedings of the Ocean Drilling Program, spreading processes. In Proceedings of the Ocean Drilling Program, Scientiﬁc Results, Volume 103. Ocean Drilling Program, University of Scientiﬁc Results, Volume 149, Whitmarsh, R.B., D.S. Sawyer, A. Texas A&M, College Station, Texas. Klaus, and D.G. Masson (Eds.). Ocean Drilling Program, Texas A&M Cannat, M., G. Manatschal, D. Sauter, and G. Peron-Pinvidic. 2009. Assess- University, College Station, Texas. ing the conditions of continental breakup at magma-poor rifted margins: Whitmarsh, R.B. and P.J. Wallace. 2001. The rift-to-drift development of What can we learn from slow spreading mid-ocean ridges? Comptes the west Iberia nonvolcanic continental margin: A summary and review Rendus Geoscience 341(5):406-427. of the contribution of Ocean Drilling Program Leg 173. In Proceedings Eldholm, O., J. Thiede, and E. Taylor 1989. Evolution of the Vøring volca- of the Ocean Drilling Program, Scientiﬁc Results, Volume 173, Beslier, nic margin. In Proceedings of the Ocean Drilling Program, Scientiﬁc M.O., R.B. Whitmarsh, P.J. Wallace, and J. Girardeau (Eds.). Ocean Results, Volume 104, Eldholm, O., J. Thiede, E. Taylor, C. Barton, Drilling Program, Texas A&M University, College Station, Texas. K. Bjørklund, W. Bleil, P. Ciesielski, A. Desprairies, D. Donnally, C. Froget, R. Goll, R. Henrich, E. Jansen, L. Krissek, K. Kvenvolden, A. LeHuray, D. Love, P. Lynse, T. McDonald, P. Mudie, L. Osterman, L. Parson, J.D. Phillips, A. Pittenger, G. Qvale, G. Schönharting, and L. Viereck. (Eds.). Ocean Drilling Program, Texas A&M University, Col- lege Station, Texas.
OCR for page 144