Continental Tectonics (1980) / Chapter Skim
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III. Intraplate Tectonics
III. Intraplate Tectonics
Pages 63-114
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From page 65... ...
Oblique subduction can produce strike-slip faulting. Horizontal compression in the overriding plate can lead to the development of complex erogenic belts.
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From page 66... ...
The Mesozoic Cordilleran orogen~c belt of the western United States is an older and more deeply eroded Andean-type mountain belt (Hamilton, 1969; Burchfiel and Davis, 1972, 1975~. South of the latitude of central Oregon, the geological history of the Cordilleran erogenic belt suggests that the eastward subcluction of an oceanic plate beneath the North American plate occurrecl contemporaneously with defonnation and magmatic activity that at times extender!
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From page 67... ...
Even if an arc collision did occur in the Late Jurassic, eastward under~rusting of oceanic lithosphere dominated Triassic and Jurassic plateboundary activity. Cretaceous and early Tertiary rocks fonn the western part of the western terrane and were accreted to the North American plate during east-directed subduction of Cretaceous and early Tertiary time (figure 6.4~.
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From page 68... ...
In early Mesozoic time in western Nevada thrust faults developed within Paleozoic "eugeosynclinal" rocks and early Mesozoic back arc sedimentary and volcanic rocks (Figure 6.3~. The age of these thrust faults is Early and Middle Jurassic, and post-Middle Jurassic and preMiddle Cretaceous.
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From page 69... ...
Late Mesozoic plutonism occulted farther eastward in Nevada and to the north than in early Mesozoic time, but in southeastern California and to the south early and late Mesozoic igneous activity is superposed. Associated with the Mesozoic plutonic and volcanic rocks, but characteristically lying east of their major areas of development, thus transitional between the central and eastern terraces, are numerous isolated areas of metamorphic rocks that probably represent exposed culminations of ~ metamorphic belt that may be continuous at depth.
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From page 70... ...
Low-angle thrust faults developed during Laramide deformation have a structural style similar to Hose developed in He earlier Cretaceous events but generally lie somewhat farther east. COLORADO—WYOMING ROCKY MOUNTAIN TE RBANE Lee fourd1 te'Tane is only locally developed both spatially ant]
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From page 71... ...
These data suggest that the development of the Amide structures in the Colorado Wyoming Rocky Mountains is related to events Mat took place throughout the erogenic belt and are ultimately related to plate-boundary interaction. PROBLE M S The geological data from the four terranes within that part ofthe North American plate considered here demonstrate an approximate contemporaneity for Mesozoic events.
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From page 72... ...
Evidence suggests that thrust faults of the eastern terrane may be related to crustal shortening within the leading edge of an ovemding continental plate, but more precise geological and time relations are necessary to establish the correct threedimensional models. The attack must be an integrated study of the metamorphic, structural, and geochronological history of the entire thrusted and folded tenant.
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From page 73... ...
Geological evidence has led to He assumption that this area has undergone only minor tectonism during the past several hundred million years and that this tectonism has largely taken the fonn of broad, slow, vertical movements. However' during the past decade there has been accumulating geological evidence and increasing awareness that the midcontinent region has been and is at present tectonically active.
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From page 74... ...
EARLY ~ MIDDLE PA L E OZ O I C K E Y C CONTINENTAL CRUST a OCEANIC CRUST i' FAULTS a, RlfTS SUBDUCTION ZONE ~ CONTINENT AND/OR ISLAND ARC COLLISION REACTIVATION, LOCALLY INCLUDING FAULTING, IGNEOUS ACTIVITY, AND COMPRESSION C BASINS ANOROGENIC IGNEOUS ROCKS ~ CENOZOIC
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From page 75... ...
These events were followed by uplift and stabilization of the Grenville Front, whose extension into the southeastern United States has not been defined. By latest Precambrian to Eocambnan time, the ancient continental land mass of eastern North America began to split (Figure 7.1B)
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From page 76... ...
The regional stress distribution in the eastern United States as measured by several methods (Sbar and Sykes, 197.~3; Haimson, 1976) shows that the maximum compressive stress is nearly horizontal and trends east to
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From page 77... ...
(1974) suggests that the stress distribution in the eastern United States can be locally complex.
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From page 78... ...
An analysis of vertical crustal movements in He eastern United States determined from leveling data (Brown and Oliver, 1976) shows, in general, that modern vertical movements appear to be related to earlier Phanerozoic tectonic trends.
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From page 79... ...
Models for Midcontinent Tectonism FIGURE 7.5 Schematic diagrams of proposed tectonic mechanisms.
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From page 80... ...
Lawrence Valley system as a rift zone that was probably initiated in Mesozoic time but is skill active today. They suggested that this rife zone may extend into the micicontinent and connect with Me New Maciricl seismic zone.
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From page 81... ...
As the mantle is cooled by conduction, He basin subsides under the load of eclogite. CONCLUSIONS A summary of data and interpretations that pertain to the tectonic framework of the midcontinent region of the United States has been presented, which should help to delineate critical information that is needed to obtain an understanding of the contemporary tectonism of this area.
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From page 82... ...
Although the mechanisms of contemporary deformation in the midcontinent are unclear, we expect that intraplate tectonism ultimately relater] to the motion of the Now American plate is the cause.
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From page 83... ...
. Hypothesis: many ear~qualces in the central and southeastern United States are casually related to mafic intrusive bodies,J.
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From page 84... ...
The Cordillera of the western United States offers many examples of structures that do not appear to fall in the categories cited above. These form the basis for this summary of the problems of continental, intraplate extensional tectonics.
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From page 85... ...
Does such extension represent the response of the North American plate to transform motion along its western edge, to back-arc "spreading," to the inception of subplate asthenospheric plumes, to rifting of Atlantic type, or to undetermined factors? In what ways are stress fields in upper plates along convergent plate boundaries determined by the geometry of subduction and the rate of plate convergence?
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From page 86... ...
Zoback and Thompson (1978) have proposed continuity of Miocene rifling along a 700- long linear zone that includes the Nevada dike swarms described above, the graben of the western Snake River Plain, and the feeder dikes of the Columbia River basalts.
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From page 87... ...
Relations Between Extension and St~ke-Sl~p Faulting Not all portions of the western United States have expenenced the same amounts of Cenozoic extension. The boundaries between areas of differential extension are geometrically interesting and of considerable importance in defining the kinematics of intraplate deformation.
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From page 88... ...
Hi! \ — ~ KQ \ \ ~ SAN \ GARLoCX FAuLt \ ~ ANDREA S \ \\ FA V ~ r — ~ .~ 140JAVE DESERT E| FIGURE 8.4 Northward diagrammatic view of Garlock Fault, sounder California, as a boundary between a northern, distended crustal block (Basin and Range province)
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From page 89... ...
terrane of low-angle faults that begins near Hoover Dam in the Las Vegas area, follows the Colorado River trough as far south as Parker, then swings southeastward and extends across southern Arizona into areas near Tucson (Figure 8.3~. On the flanks of several ranges that characteristically owe their elevation to doming or arching rather than block faulting, basal detachment faults are found that separate allochthonous upperplate units from crystalline rocks in the cores of the ranges.
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From page 90... ...
An earlier suggestion (Davis et al., 1977) that low-angle faults in the Colorado River trough may everywhere have developed
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From page 91... ...
reached a similar conclusion in their western Arizona investigations. The origin of the Colorado River area structures and their relationship, if any, to conventional basin-range faulting in the western United States is unclear.
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From page 92... ...
PLATE-TECTONIC SPECULATIONS ON THE CAUSE(S) OF LATE CENOZOIC EXTENSION IN THE WESTERN UN ITE D STATE S Throughout essentially its entire length, from southeastern Washington to southern Nevada, the interior portions of the western United States experienced variable amounts and styles of E-W to ENE-WSW extension GREGORY A
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From page 93... ...
Accelerated global rates of plate convergence in mid-.Miocene time may be indicated, and it is perhaps in this general plate context that the Columbia River dike swarms and basalt outpouring should be viewed. An additional or alternative explanation for Miocene back-arc extension in the western United States is provided by the fact that this extension followed a probable steepening of the Farallon-juan de Fuca plate approximately 20 m.y.
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From page 94... ...
. Cenozoic tectonics ofthe western United States, Rev.
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From page 95... ...
. Tectonic implications of space-time paKems of Cenozoic volcanism in the western United States, Earth Planet.
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From page 96... ...
EATON U.S. Geological Survey INTRODUCTI ON Selected geophysical and geological characteristics of the Basin and Range province of Me western United States are examined here.
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From page 97... ...
PRESENT AND PAST CRUSTAL EXTE NS ION Nonnal faults, the surface evidence of crustal extension, are widespread in the western United States. Their distribution in the Basin and Range province is broad and pervasive, but in the Rio Grande riPc [see Figures 9.5(a)
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From page 98... ...
It distinguishes the Great Basin section ofthe Basin and Range province from the Sonoran Desert section. It also clearly defines the Rio Grande nR.
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From page 99... ...
If the topography is a reflection of block faulting, this difference, in conjunction with die data of Figures 9.1 and 9.2, suggests that extensional stresses had a markedly different orientation in the Sonoran Desert region dian Hey do in the Great Basin today. They were generally southwest to westsouthwest, in contrast to later east-west to west-nor~west extension in the rest of the western United States.
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From page 100... ...
Figure 9.6 shows the spatial distribution of known Cenozoic plutons and ash flow-related calderas. The calderas represent large magma chambers at crustal levels shallow enough to permit catastrophic eruptions of great volumes of pyroclastic material Such magma chambers are in the upper 5 to 10 km of the crust and give up large amounts of heatthere.
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From page 101... ...
High temperature probably influenced extensional deformation from its outset; at the very least it thennally weakened the cmst and thereby helped to determine where extension and thinning would ultimately take place. THE DISTRIBUTION OF EARTHQUAKES The spatial distribution of earthquakes in the western United States is shown in Figure 9.8.
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From page 102... ...
FIGURE 9.5 Post-P eozolc magmatisrr.t in the western United States (data from Kin and Beikm g an. 19 ~ 47 Snyder et al., 19 / 6)
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From page 103... ...
Atwater (1970) considered Me San Andreas to be the key element in the transform boundary between the Pacific and Norm American plates.
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From page 104... ...
104 (w31..N . \J i `~-N .~~N -~Q FIGURE 9.7 Active and fossil hydrothermal systems in the western United States Dato ~~ we (1967)
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From page 105... ...
Heavy line, based on seismic data, marks inboard limit of highest earthquake event frequency and areal density in California, high cumulative seismicstrain energy release, and major strikeslip faulting related to dextral shear of the western plate boundary in Holocene time. Major faults within 150 km east of this line show oblique slip, with active stnke-slip components, but farther east, the dominant mechanism is simple extension.
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From page 106... ...
for 14 areas within the region of active extension in the western United States. Data Mom Gumper and Scholz (1971)
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From page 107... ...
( 1974) suggested that surface extension by normal faulting at the surface is absorbed in a soft, plastically extending region of lowered seismic velocity.
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From page 108... ...
. An electrically conductive layer by itself does not require abnormally high pore pressures and, hence, does not require the presence of an impermeable cap to keep the system closed.
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From page 109... ...
These observations and speculations lend themselves to the interpretation that prolonged thermal conditioning of die crust plus horizontal shearing simply may have continued earlier initiated dynamotherrnal metamorphism of rocks Mat now serge as a boundary layer between parts of Me lithosphere extending by fundamentally different mechanisms. As young nominal faults developed near the surface in the regime of crustal extension, they became Iistric to (they came to sole on)
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From page 110... ...
ages, all exposed at the surface somewhere in the region; diagram composed near its top of igneous and metamorphic basement shows Cenozoic continental sedimentary and volcanic rocks at rocks like those of layer ~l but grading downward into increas the surface (patterns of dense stippling and solid black, ing proportions of old granites, migmatites, gneisses, amphi respectively) overlyingoldersedimentaryrocks(openstippling)
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From page 111... ...
. Cenozoic tectonics of die western United States, Ret;.
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From page 112... ...
. Relation of some metal mining districts in the western United States to regional tectonic environments and igneous activity, Nevada Burl Mines Bull.
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From page 113... ...
. A compilation of fault plane solutions of He western United States, in Cenozoic Tectonics and Regional Geophysics of the Westem Cordillera, R
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