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Mid-Jurassic to early Miocene clastic deposition along the northern California margin: Provenance and plate-tectonic speculations

By
W.G. Ernst
W.G. Ernst
Department of Geological & Environmental Sciences, Stanford University, Stanford, California 94305-2115, USA
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Published:
December 01, 2015

Based on relationships among volcanic-plutonic arc rocks, high-pressure–low-temperature (HP-LT) metamafic rocks, westward relative migration of the Klamath Mountains salient, and locations of the Mariposa-Galice, Great Valley Group, and Franciscan depositional basins, the following geologic evolution is inferred for the northern California continental edge: (1) By ca. 175 Ma, onset of transpressive plate underflow generated an Andean-type Klamath-Sierran arc along the margin. At ca. 165 Ma and continuing to ca. 150–140 Ma, erosion supplied volcanogenic debris to proximal Mariposa-Galice ± Myrtle overlap strata. (2) Oceanic crustal rocks were metamorphosed under HP-LT conditions in an inboard, east-inclined subduction zone from ca. 165 to 150 Ma. Most such mafic rocks remained stored at depth, and HP-LT tectonic blocks only returned surfaceward during the Late Cretaceous, chiefly entrained in circulating, buoyant Franciscan mud-matrix mélange. (3) At end-of-Jurassic time, before onset of paired Franciscan and Great Valley Group + Hornbrook deposition, the Klamath salient was deformed and displaced ∼100–200 km westward relative to the Sierran arc. (4) After this ca. 140 Ma seaward step-out of the Farallon–North American convergent plate junction—stranding preexisting oceanic crust on the south as the Coast Range ophiolite—terrigenous debris began to arrive at the Franciscan trench and intervening Great Valley forearc. Voluminous sedimentation and accretion of Franciscan Eastern + Central belt and Great Valley Group coeval detritus took place during paroxysmal igneous activity and rapid, nearly orthogonal plate convergence at ca. 125–80 Ma. (5) Sierran arc volcanism-plutonism ceased by ca. 80 Ma in northern California, signaling a transition to shallow, nearly subhorizontal eastward plate underflow attending Laramide orogeny far to the east. (6) Paleogene–Lower Miocene Franciscan Coastal belt sedimentary strata were deposited in a tectonic realm nearly unaffected by HP-LT subduction. (7) Grenville-age detrital zircons apparently are absent from the post–120 Ma Franciscan section. Detritus from the Pacific Northwest is not present in the Central belt sandstones, whereas zircons from the Idaho Batholith, the Challis volcanics, and the Cascade Range appear in progressively younger Paleogene–Lower Miocene Coastal belt sediments. This trend suggests the possible gradual NW dextral offset of Franciscan trench deposits of up to ∼1600 km relative to the autochthonous Great Valley Group forearc and basement terranes of the American Southwest.

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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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