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Title: Structural and stratigraphic evolution of Aleutian convergent-margin basins - Ridge crest to trench floor

Abstract

The Aleutian Ridge lies along nearly 2,000 km of the north Pacific's obliquely converging plate boundary with North America. Since middle Eocene time, convergent-margin basins have repeatedly formed here, typically as summit basins along the ridge crest, and as forecarc basins on the landward trench slope. Thick (1-4 km) sequences of terrigenous, hemipelagic, and biogenic debris have accumulated in these depressions, which are mostly intra-arc structures floored by arc-basement rocks. Summit and forearc basins formed as a consequence of plate-boundary coupling and the application of compressional and right-lateral shear stresses to the arc massif. Basins typically evolved along shear zones in response to transtensional processes, and as trailing-edge grabens behind rotating blocks of arc massif. In the late Cenozoic, high rates of trench sedimentation led to the growth of an accretionary complex that underthrust forearc basement. Wedging and improved plate coupling elevated and laterally shifted blocks of outer forearc rocks, creating much of the structural framework of the regionally extensive Aleutian Terrace forearc basin. Changes in plate-boundary conditions that affected the ridge's volcanic activity and regional elevation importantly influenced basinal sedimentation. Changes of greatest significant were a major shift in convergence direction and rate about 42 Ma (reduced volcanism), ridgemore » underthrusting by increasingly younger ocean crust in Oligocena and Miocene time (arc elevation), and the combination of more orthogonal underthrusting and the subduction of a dead spreading center 5-120 Ma (arc subsidence).« less

Authors:
; ; ;
Publication Date:
OSTI Identifier:
6083665
Report Number(s):
CONF-880301-
Resource Type:
Conference
Resource Relation:
Conference: Annual meeting of the American Association of Petroleum Geologists, Houston, TX, USA, 20 Mar 1988
Country of Publication:
United States
Language:
English
Subject:
02 PETROLEUM; 03 NATURAL GAS; ALEUTIAN ISLANDS; PETROLEUM GEOLOGY; NATURAL GAS DEPOSITS; GEOLOGIC HISTORY; PETROLEUM DEPOSITS; SEDIMENTARY BASINS; PLATE TECTONICS; BASEMENT ROCK; CONTINENTAL MARGIN; EXPLORATION; SEDIMENTATION; STRATIGRAPHY; TERTIARY PERIOD; CENOZOIC ERA; GEOLOGIC AGES; GEOLOGIC DEPOSITS; GEOLOGIC STRUCTURES; GEOLOGY; ISLANDS; MINERAL RESOURCES; RESOURCES; TECTONICS 020200* -- Petroleum-- Reserves, Geology, & Exploration; 030200 -- Natural Gas-- Reserves, Geology, & Exploration

Citation Formats

Scholl, D.W., Ryan, H.F., Geist, E.L., and Vallier, T.L. Structural and stratigraphic evolution of Aleutian convergent-margin basins - Ridge crest to trench floor. United States: N. p., 1988. Web.
Scholl, D.W., Ryan, H.F., Geist, E.L., & Vallier, T.L. Structural and stratigraphic evolution of Aleutian convergent-margin basins - Ridge crest to trench floor. United States.
Scholl, D.W., Ryan, H.F., Geist, E.L., and Vallier, T.L. 1988. "Structural and stratigraphic evolution of Aleutian convergent-margin basins - Ridge crest to trench floor". United States. doi:.
@article{osti_6083665,
title = {Structural and stratigraphic evolution of Aleutian convergent-margin basins - Ridge crest to trench floor},
author = {Scholl, D.W. and Ryan, H.F. and Geist, E.L. and Vallier, T.L.},
abstractNote = {The Aleutian Ridge lies along nearly 2,000 km of the north Pacific's obliquely converging plate boundary with North America. Since middle Eocene time, convergent-margin basins have repeatedly formed here, typically as summit basins along the ridge crest, and as forecarc basins on the landward trench slope. Thick (1-4 km) sequences of terrigenous, hemipelagic, and biogenic debris have accumulated in these depressions, which are mostly intra-arc structures floored by arc-basement rocks. Summit and forearc basins formed as a consequence of plate-boundary coupling and the application of compressional and right-lateral shear stresses to the arc massif. Basins typically evolved along shear zones in response to transtensional processes, and as trailing-edge grabens behind rotating blocks of arc massif. In the late Cenozoic, high rates of trench sedimentation led to the growth of an accretionary complex that underthrust forearc basement. Wedging and improved plate coupling elevated and laterally shifted blocks of outer forearc rocks, creating much of the structural framework of the regionally extensive Aleutian Terrace forearc basin. Changes in plate-boundary conditions that affected the ridge's volcanic activity and regional elevation importantly influenced basinal sedimentation. Changes of greatest significant were a major shift in convergence direction and rate about 42 Ma (reduced volcanism), ridge underthrusting by increasingly younger ocean crust in Oligocena and Miocene time (arc elevation), and the combination of more orthogonal underthrusting and the subduction of a dead spreading center 5-120 Ma (arc subsidence).},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1988,
month = 1
}

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  • The Aleutian Ridge lies along nearly 2000 km of the north Pacific's obliquely converging plate boundary with North America. Since middle Eocene time, convergent-margin basins have repeatedly formed here, typically as summit basins along the ridge crest, and as forearc basins on the landward trench slope. Summit and forearc basins formed as a consequence of plate-boundary coupling and the application of compressional and right-lateral shear stresses to the arc massif. Basins typically evolved along shear zones in response to transtensional processes, and as trailing-edge grabens behind rotating blocks of arc massif. In the late Cenozoic, high rates of trench sedimentationmore » led to the growth of an accretionary complex that underthrust forearc basement. Wedging and improved plate coupling elevated and laterally shifted blocks of outer forearc rocks, creating much of the structural framework of the regionally extensive Aleutian Terrace forearc basin. Changes in plate-boundary conditions that affected the ridge's volcanic activity and regional elevation importantly influenced basinal sedimentation. Changes of greatest significance were a major shift in convergence direction and rate about 42 Ma (reduced volcanism), ridge underthrusting by increasingly younger ocean crust in Oligocene and Miocene time (arc elevation), and the combination of more orthogonal underthrusting and the subduction of a dead spreading center 5-10 Ma (arc subsidence).« less
  • Sediment being subducted in the eastern part of the convergent margin of the Aleutian Trench has a potential to generate large volumes of natural gas, perhaps as much as 2.8 x 10/sup 6/ m/sup 3/ of methane per km/sup 3/ of sediment, even though the content of organic carbon in the sediment is very low, averaging about 0.4%. This high potential for gas generation results primarily from the enormous volume of sediment undergoing subduction. Along the eastern Aleutian Arc-Trench system a 3-km thick sheet of sediment is being subducted at a rate of about 60 km per million years. Wemore » estimate, based on considerations of the stability requirements for gas hydrates observed as anomalous reflectors in some of our seismic records, and on one measurement in a deep well, that the geothermal gradient in this region is about 30/sup 0/C/km. Such a gradient suggests a temperature regime in which the maximum gas generation in the subducting sediment occurs beneath the upper slope. Thus the sediment of the upper slope, as opposed to that of the shelf and lower slope, could be the most prospective for gas accumulation if suitable reservoirs are present. 40 refs., 11 figs., 3 tabs.« less
  • The most prominent and well-preserved remnants of the convergent margins are present in southern Alaska and California. The southern Alaska convergent margin appears to have developed in response to northward-directed subduction of the Kula plate and the California margin in response to eastward-directed subduction of the Farallon plate. The chief elements of the southern Alaska convergent margin, on the basis of paleomagnetic data, appear to have subsequently migrated northward and rotated in the post-Cretaceous. The chief elements of the California margin have been disrupted by Neogene strike-slip displacements on the San Andreas fault system and accretion of younger terranes tomore » the west. In both southern Alaska and California, the forearc-basin deposits are well preserved and produce major amounts of gas. The principal reservoirs in Alaska are Tertiary nonmarine deposits and in California are Late Cretaceous and Tertiary deep marine and deltaic deposits. The accretionary wedge in southern Alaska forms a remarkably well-preserved assemblage of trench and trench-slope deposits that extend for about 2000 km along the Gulf of Alaska, flanked oceanward by younger accreted terranes. The accretionary wedge in California consists of a great variety of older and younger terranes, including some fragments of ocean crust that originated in southern latitudes. Comparative structural and stratigraphic analyses of the two Late Cretaceous margins reveals the complexity of tectonic, depositional, and stratigraphic patterns associated with subduction of very large oceanic plates at the margins of very large continental plates.« less
  • Large portions of the Late Cretaceous continental margin of western North America were dominated by a convergent tectonic framework characterized by the development of trenches, accretionary wedges, forearc basins, magmatic arcs, and back arc basins. The most prominent and well-preserved remnants of the convergent margins are present in southern Alaska and California. The southern Alaska convergent margin appears to have developed in response to northward-directed subduction of the Kula plate and the California margin in response to eastward-directed subduction of the Farallon plate. The chief elements of the southern Alaska convergent margin, on the basis of paleomagnetic data, appear tomore » have subsequently migrated northward and rotated in the post-Cretaceous. The chief elements of the California margin have been disrupted by Neogene strike-slip displacements on the San Andreas fault system and accretion of younger terranes to the west. In both southern Alaska and California, the forearc-basin deposits are well preserved and produce major amounts of gas. The principle reservoirs in Alaska are Tertiary nonmarine deposits and in California are Late Cretaceous and Tertiary deep marine and deltaic deposits.« less
  • An examination of the depositional history of two middle Cenozoic active margin basins in central California provides insights into the relative importance of tectonics and eustasy for controlling large-scale stratigraphic relationships. Both the Cuyama and southernmost San Joaquin basins were analyzed with respect to benthic foraminiferal biofacies, biostratigraphic and lithostratigraphic events, and the nature and extent of regionally important unconformities. The Cuyama basin exhibits two distinct cycles of basin subsidence and filling - one (late Oligocene to early Miocene) associated with the Vaqueros formation and the other (early to late Miocene) associated with the Monterey formation. The San Emigdio areamore » of the southernmost San Joaquin basin exhibits only one major basin cycle (late Oligocene to late Miocene) associated with the Temblor and Monterey Formations. An analysis of the distribution of major unconformities, rapid bathymetric deepenings, periods of peak transgression, major shallow-marine progradational events, episodes of submarine fan development, and fluctuations in foraminiferal biofacies is used to compare basin history in the two areas. The timing of events is not always very well constrained but indicates that both eustasy and tectonics were important in shaping basin history. Several relationships suggest that tectonics is the relatively more important factor in these basins. Depositional history also is a key to understanding benthic foraminiferal biofacies distribution (particularly with respect to three-dimensional distribution of key marker species), which in turn provides insights into benthic foraminiferal biostratigraphy.« less