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Geology of the Point Sur-Lopez Point region, Coast Ranges, California: A part of the Southern California allochthon

By
Clarence A. Hall, Jr.
Clarence A. Hall, Jr.
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Published:
January 01, 1991

This volume delineates the Southern California allochthon (SCA) and proposes reconstruction of the pre-Eocene geology of western California. The reconstruction is based on: (1) the structural relations between the pre-Cretaceous igneous and metamorphic complexes and unconformably overlying Upper Cretaceous rocks of late Campanian–early Maastrichtian age and the structurally lower Franciscan Complex and associated slabs of Late Cretaceous age (possibly Cenomanian to Campanian in age) in the Point Sur–Lopez Point region of coastal western central California; (2) the restoration of offset stratigraphic assemblages of rocks along faults within the San Andreas fault system; and (3) the counterclockwise back-rotation of the Transverse Ranges.

In Late Cretaceous time the SCA was in eastern California and Arizona, with the generally north-south-oriented Coast Range fault and Cretaceous-early Tertiary subduction zone lying to the west. It is proposed that the Sur thrust forms the sole of the SCA, which includes Salinia. The allochthon was thrust westward or northwestward a minimum of 180 km (110 mi) from the Mojave and eastern Peninsular Ranges provinces of southwestern North America during early Paleocene time (Danian, ~65 to 62 Ma; and possibly early Ynezian, ∼6 0 Ma) and perhaps during a second pulse in late Paleocene time (Bulitian, ~57 to 55 Ma). The allochthon was thrust over the Pelona Schist, Great Valley sequence, and Franciscan Complex. Thrusting occurred prior to the allochthon being slivered and translated northwestward along the San Andreas fault system, and possibly being flexed in the Santa Cruz orocline during Neogene time. Today, the dismembered allochthon extends in the north from Point Arena, in northwestern California, southward to the Chocolate Mountains in southeastern California.

The driving force for moving the SCA northwestward or westward relative to the Sierra Nevada-Peninsular Ranges trend is hypothesized to have been provided by the conveyor beltlike action of oblique subduction that was accompanied by tectonic erosion of the underside of the allochthon.

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GSA Special Papers

Geology of the Point Sur-Lopez Point region, Coast Ranges, California: A part of the Southern California allochthon

Clarence A. Hall, Jr.
Clarence A. Hall, Jr.
Search for other works by this author on:
Geological Society of America
Volume
266
ISBN print:
9780813722665
Publication date:
January 01, 1991

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