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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 68 (1984)

Issue: 4. (April)

First Page: 474

Last Page: 474

Title: California Blueschists and the Tectonostratigraphic Terrane Concept: ABSTRACT

Author(s): W. G. Ernst


Glaucophane and related schists are present as tectonic fragments in ophiolite-decorated suture zones and as discrete lithotectonic belts along the accreted Mesozoic/Tertiary California margin. Occurrences include parts of the Klamath Mountains, the western Sierran foothills, the Coast Ranges, faulted margins of the Mojave Desert, the Transverse Ranges, and the southern California borderland. Blueschist assemblages formed under high-pressure, low-temperature metamorphic conditions, reflecting the thermal regime of subduction zone environments. Considerable underflow accompanied rifting, drifting, and assembly of far-traveled tectonostratigraphic terranes, as documented by sea-floor magnetic anomaly patterns and age relationships of the oceanic crust-capped lithosphere; th eastern limbs of paleo-Pacific plates (Farallon-Cocos, Kula, etc), have been extensively or completely overridden by the westward encroaching North American plate--7,000 km (4,300 mi) since the Early Cretaceous, and nearly 10,000 km (6,200 mi) since the Jurassic. Thus, although substantial northward drift brought exotic oceanic and continental materials to the growing California crust and caused extensive dislocation in the late Mesozoic and Cenozoic, much plate motion evidently involved a large component of convergence and eastward underflow, as indicated by preserved remnants of high-pressure mineral assemblages scattered throughout California, as well as by the construction of roughly contemporaneous calc-alkaline volcanic-plutonic belts. Subduction appears to have been the dominant rocess attending accretion of the California continental margin.

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