Cordilleran Section (104th Annual) and Rocky Mountain Section (60th Annual) Joint Meeting (19–21 March 2008)
Paper No. 7-4
Presentation Time: 2:40 PM-3:00 PM

A 2D KINEMATIC-THERMAL MODEL OF FLAT SUBDUCTION INITIATION AND ACCRETION OF THE PELONA AND RELATED SCHISTS OF SOUTHERN CALIFORNIA

KIDDER, Steven, Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Blvd, MC 100-23, Los Angeles, CA 91125, kidder@gps.caltech.edu, HERMAN, Frédéric, ETH, Geologisches Institut HAD G 4, Haldenbachstr. 44, Zurich, 8092, Switzerland, SALEEBY, Jason B., Geological & Planetary Sciences, California Institute of Technology, 1200 E. California Blvd., MC 100-23, Pasadena, CA 91125, AVOUAC, Jean-Philippe, Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, and DUCEA, Mihai N., Department of Geosciences, University of Arizona, Gould-Simpson Bldg, Tucson, AZ 85721-0077

The Pelona and related schists of Southern California represent continental detritus deposited, subducted to depths of ~30 km, and accreted during a major Late Cretaceous-Early Tertiary collisional event. Emplacement of the schists coincided with the termination of magmatism along a ~500 km segment of the California continental arc, the disappearance and probable subduction of the forearc and western portions of the arc, and the loss of the mafic lower crust and root of eastern portions of the arc. Conceptual models of schist emplacement differ in detail, but generally involve a dramatic flattening of subduction. In order to better understand the stresses, accretion rates, and emplacement histories of the schists, we constructed a two-dimensional, finite element, kinematic-thermal model of flat subduction initiation using the program Pecube (Braun, 2003). The model is able to satisfy geologic constraints available from the literature on cooling rates (15°/m.y.), peak temperatures (635°C), and steep inverted metamorphic gradient (240°/km) in the Pelona schist with an accretion rate of .5-1 mm/yr. It is likely that accretion rates varied significantly between schist bodies.

At a constant accretion rate of .5-1 mm/yr, the thickest exposures of schist were built over 4-8 m.y. as material was scraped off 400-800 km of lower plate. In two less widely accepted alternative tectonic models, the schists represent either transpressional basin or forearc Great Valley deposits. Both alternative basin types are too narrow (<100 km) to produce the observed inverted gradients.

Cordilleran Section (104th Annual) and Rocky Mountain Section (60th Annual) Joint Meeting (19–21 March 2008)
General Information for this Meeting
Session No. 7
Causes and Consequences of Laramide Tectonics in the Forearc, Arc, and Backarc of the Southwestern United States
University of Nevada-Las Vegas: Student Union 208C
1:30 PM-5:40 PM, Wednesday, 19 March 2008

Geological Society of America Abstracts with Programs, Vol. 40, No. 1, p. 48

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