Continental Tectonics (1980) / Chapter Skim
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I. Summary
I. Summary
Pages 13-30
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From page 15... ...
PLATE BOUNDARIES The study of modern plate boundaries allows us the opportunity to examine the geological and geophysical activity at the boundary and contemporaneous action ity adjacent to the boundary. Studies should be directed toward establishing relationships between plate-bounda~y activity and the wide range of geological and geophysical events, so that plate boundaries can be treated as dynamic systems.
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From page 16... ...
has outlined many of the features associated with continental rifts and has emphasized that to evaluate these divergent systems properly we must establish contemporaneity of events within the system, the evolution of riR systems, and the temporal stn~ctum1 relations of riRs to adjacent oceanic crust. A modern example of a rift system that has led to the development of continental separation, connation of oceanic crust, and a divergent plate boundary is the East African Red Sea, Gulf of Aden rift system.
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From page 17... ...
Some middle Precambrian deformed belts show no sedimentary record of a former passive margin, and the question of whether one was ever present may have to rely on studies of the geological and geophysical characteristics of the crust beneath passive-margin sedimentary sequences. Archean passive margins are unknown, which, along with much evidence, has suggested to many scientists that during most of Archean time continental lithosphere was thin and ductile (see Chapter 15~.
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From page 18... ...
An answer cannot be given wit}, our present state of knowledge of transfonn systems within continental lithosphere. CONVERGENT BOUNDARY SYSTEMS Convergent plate boundaries, where one lithosphenc plate passes beneath another, are Me sites of subduction or recycling back into the mantle of the lithosphere created at spreading ridges.
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From page 19... ...
has reviewed briefly some of the elements of convergent systems. The outermost elements of the system are the trench and outer nonvolcanic ridge fanned from deformed packages of sedimentary rocks containing occasional slivers of oceanic lithosphere, an outer or forearc basin of undeformed sedimentary rocks, and volcanic arc consisting of a characteristic sprite of volcanic rocks.
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From page 20... ...
Dunug much of Mesozoic time it appears that the convergent boundary system generated compression within the overriding plate and produced structural and magmatic effects more than 1000 km eastward from the surface trace of the plate boundary (see Chapters 3 and 6~. The sequence of terranes from west to east across the western United States consists of a western terrane composed of accreted oce~nic sedimentary and volcanic rocks, `~ central terr`~ne composed open Andean-type magmatic arc, an stem terrace composed of belts of folds and east-directed thrusts where older continental basement was reactivated, find locally ~ foreland belt of faulted Precambrian cry.stalline rocks fonned by older plate-boundary systems.
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From page 21... ...
If the geometry of the new convergent system subducts oceanic lithosphere beneath the collided arc, rocks of the collided system are overprinted by a noncollisional continentalmargin arc system and become deformed and metamorphosed to form the polyphase terranes common within continental crust. The transitions from arc collisions are not easy to interpret, and some of the volcanic rock associations developed following collision in New Guinea are difficult to relate to plate-tectonic processes Johnson et al., 1978~.
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From page 22... ...
Within the Cordilleran belt of Canada and Alaska, both collisional and noncollisional convergence during late Mesozoic time was associated with major strike-slip filults that were fanned within the continent several hundred kilometers from the plate boundary (Davis et al., 1978~. The evolution of the Pyrenees has been interpreted as a combination of transfo.~ and both extensional and convergent systems at different times (Mattauer and Seguret, 1971~.
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From page 23... ...
What these changes are and how they affect the continental crust and lithosphere are essentially unknown. INTRAPLATE DE FORMATION Even though continental lithosphere away from active plate-bounda~y systems is considered rigid.
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From page 24... ...
Yolcanic roclc associations at convergent plate boundaries: re-appraisal of the concept using case histories from Papua. New Guinea, Ceol.
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From page 25... ...
. The Colorado lineament: ~ middle Precambrian wrench fault system Geol.
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From page 26... ...
Since early Mesozoic time, modem continental margins have developed with distinctive physical and chemical characteristics that can serve as bases for comparative studies of older margins, which have been incorporated within the continents in the past. The recent progress of geological studies in North America ant!
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From page 27... ...
of earth history, various radiogenic isotope systems in rocks and minerals, increasingly supplemented by biological, chemical, and remanent magnetic information, will be the principal tools for both general time assignments and precise time resolution. The characterization of long-term evolutionary additions of radiogenic 87Sr, 206Pb, 207Pb, Mob, and '43Nd to the major crust and mantle reservoirs provides important genetic and temporal information on the nature and history of the source regions of continental rocks.
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From page 28... ...
the details of their local structure and stratigraphy, petrology, and mineralogy hare received considerable attention. However, their broad spatial distributions, their isolation in "seas" of ancient granitic gneisses, their spatial and temporal relations to granite crust development are still incompletely understood.
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From page 29... ...
of Proterozoic time essentially be represented by two great erogenic intervals, each approximately 300 400 m.y. long and separated from each other and We preceding Archean and succeeding Phanerozoic erogenic culminations by a quiet interval of comparative durations.
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