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Latest Jurassic–earliest Cretaceous closure of the Mongol-Okhotsk Ocean: A paleomagnetic and seismological-tomographic analysis

By
Rob Van der Voo
Rob Van der Voo
Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA
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Douwe J.J. van Hinsbergen
Douwe J.J. van Hinsbergen
Department of Earth Sciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, the Netherlands
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Mathew Domeier
Mathew Domeier
Physics of Geological Processes (PGP), University of Oslo, Sem Sælands vei 24, NO-0316 Oslo, Norway, and Center for Earth Evolution and Dynamics (CEED), University of Oslo, Sem Sælands vei 24, NO-0316 Oslo, Norway
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Wim Spakman
Wim Spakman
Department of Earth Sciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, the Netherlands, and Center for Earth Evolution and Dynamics (CEED), University of Oslo, Sem Sælands vei 24, NO-0316 Oslo, Norway
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Trond H. Torsvik
Trond H. Torsvik
Physics of Geological Processes (PGP), University of Oslo, Sem Sælands vei 24, NO-0316 Oslo, Norway, and Center for Earth Evolution and Dynamics (CEED), University of Oslo, Sem Sælands vei 24, NO-0316 Oslo, Norway, and School of Geosciences, University of the Witwatersrand, Wits 2050, South Africa
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Published:
December 01, 2015

The Mongol-Okhotsk Ocean closed when the Amuria block, normally considered to have been part of the North China block since the early Mesozoic, and the southern margin of Siberia collided in Late Jurassic to Early Cretaceous times. The resulting suture runs WSW-ENE and is reasonably well defined to the east of longitude 100°E. Because no evidence exists for any westward prolongation of the Mongol-Okhotsk Ocean suture toward the Tarim block, the cryptic termination of the suture is an enigma, compounded by the fact that a tomographically identified slab in the lower 1000 km of the mantle, interpreted as a remnant of Mongol-Okhotsk oceanic lithosphere, has a clear N-S trend, at almost right angles to the surface suture. No sensible explanation can be constructed for a rotation of some 90° of this slab. There is a solution, however, to both these enigmas if we consider that the Triassic Mongol-Okhotsk Ocean existed east of an initially meridian-parallel, but later progressively more sinuous, late Paleozoic Pangea margin. This margin consisted of Siberia, Amuria, and the China continental elements. The Mongol-Okhotsk Ocean was subducting westward during the early Mesozoic and likely older times underneath this margin. This would readily explain the tomographic N-S slab orientation at depths of 2000 km and greater. Paleomagnetic inclination differences between the global apparent polar wander path in Siberian coordinates and results from the North China block show a gradually diminishing trend with time, as these cratons approached each other during the Jurassic. During this time, the paleomagnetic data of the North China block show that it underwent a slight northward motion, but with a considerable counterclockwise rotation of ∼90°. At the same time, the Mongol-Okhotsk Ocean–bordering margin of Eurasia (between Siberia and Tarim) moved southward by ∼30° and rotated 45° clockwise. These continental scissoring movements caused doubly vergent subduction of the Mongol-Okhotsk Ocean. Paleomagnetic data suggest final closure of the Mongol-Okhotsk Ocean in latest Jurassic–earliest Cretaceous time. Arc-related rocks above the subduction zone follow the outline around the core of the Tuva-Mongol belt in the eastern Altaids between Amuria and Siberia, and they form a tightening, westward-convex Tuva-Mongol orocline. This large-scale oroclinal bending of the crust above a disappearing ocean is reminiscent of similarly tightening oroclines in Kazakhstan and Variscan Europe, which closed earlier by subduction in the late Paleozoic.

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GSA Special Papers

Late Jurassic Margin of Laurasia–A Record of Faulting Accommodating Plate Rotation

Thomas H. Anderson
Thomas H. Anderson
Department of Geology and Environmental Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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Alexei N. Didenko
Alexei N. Didenko
Institute of Tectonics and Geophysics, Far Eastern Branch Russian Academy of Sciences, Khabarovsk 680000, Russia, and Geological Institute, Russian Academy of Science, Moscow 119017, Russia
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Cari L. Johnson
Cari L. Johnson
Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, USA
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Alexander I. Khanchuk
Alexander I. Khanchuk
Far East Geological Institute, Far Eastern Branch Russian Academy of Sciences, 159, Prospekt 100-letiya Vladivostoku, Vladivostok 690022, Russia
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James H. MacDonald, Jr.
James H. MacDonald, Jr.
Department of Marine and Ecological Sciences, Florida Gulf Coast University, Fort Myers, Florida 33965, USA
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Geological Society of America
Volume
513
ISBN print:
9780813725130
Publication date:
December 01, 2015

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