Structural evidence for northeastward movement on the Chocolate Mountains thrust, southeasternmost Calfornia

Journal Article · Sat Nov 10 00:00:00 EST 1990 · Journal of Geophysical Research; (United States)

OSTI ID:5226596

Dillon, J T ^[1]; Haxel, G B ^[2]; Tosdal, R M ^[3]

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1. Alaska Div. of Geological and Geophysical Surveys, Fairbanks (USA)
2. Geological Survey, Flagstaff, AZ (USA)
3. Geological Survey, Menlo Park, CA (USA)

The Late Cretaceous Chocolate Mountains thrust of southeastern California and southwestern Arizona places a block of Proterozoic and Mesozoic continental crust over the late Mesozoic continental margin oceanic sedimentary and volcanic rocks of the regionally distinctive Orocopia Schist. The Chocolate Mountains thrust is interpreted as a thrust (burial, subduction) fault rather than a low-angle normal (exhumation, unroofing, uplift) fault. The Chocolate Mountains thrust zone contains sparse to locally abundant mesoscopic asymmetric folds. Fabric relations indicate that these folds are an integral part of and coeval with the thrust zone. On a lower hemisphere equal-area plot representing the orientation and sense of asymmetry of 80 thrust zone folds from 36 localities, spread over an area 60 by 10 km, Z folds plot northwest of and S folds plot southeast of a northeast-southwest striking vertical plane of overall monoclinic symmetry. The only sense of movement consistent with the collective asymmetry of the thrust zone folds is top to the northeast. Paleomagnetic data suggest that the original sense of thrusting, prior to Neogene vertical axis tectonic rotation related to the San Andreas fault system, was northward. The essential point is that movement of the upper plate of the Chocolate Mountains thrust evidently was continentward. Continentward thrusting suggests a tectonic scenario in which an insular or peninsular microcontinental fragment collided with mainland southern California. Alternative tectonic models involving subduction of the Orocopia Schist eastward beneath continental southern California circumvent the suture problem but are presently not supported by any direct structural evidence.

• OSTI ID: 5226596
• Journal Information: Journal of Geophysical Research; (United States), Vol. 95:B12; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ARIZONA
GEOLOGIC FAULTS
CALIFORNIA
TECTONICS
CONTINENTAL MARGIN
CRETACEOUS PERIOD
DEFORMATION
GEOLOGIC MODELS
GEOLOGIC STRUCTURES
MESOZOIC ERA
MOUNTAINS
OCEANIC CRUST
PALEOMAGNETISM
PRECAMBRIAN ERA
SEDIMENTARY ROCKS
SUBDUCTION ZONES
VOLCANIC ROCKS
DEVELOPED COUNTRIES
EARTH CRUST
FEDERAL REGION IX
GEOLOGIC AGES
GEOLOGIC FRACTURES
IGNEOUS ROCKS
MAGNETISM
NORTH AMERICA
ROCKS
USA
580000* - Geosciences