SW Pacific Tectonics and the E. Pacific Cordillera

The SW Pacific contains a complex series of island arc-continent, and island arc-island arc collisions, and resultant plate polarity changes, large within-arc strike-slip movement, and rapid change in plate configuration in a geologically short time (few million years; e.g. R. Hall, 1996). A similar series of complex interactions probably characterized the E. Pacific margins for the past 400 million years. A 4-decade old proposal for evolution of the US Pacific margin by collision of ophiolite and associated island arc complexes with the the continental margin followed by subduction polarity flip has achieved partial acceptance. A refinement and extension of this hypothesis suggests approximately six or so collisional events involving ophiolite or related terrane emplacement along the N. American Western margin or since the early Paleozoic. Some terranes may have been derived from western Gondwana (Wright and Wyld, 2006), implying earlier Caribbean-like tectonics and extensive intra-oceanic along-strike movement, reminiscent of Tertiary W. Pacific movements. Incorporation of the 3-dimensional structural geometry of rock sequences, that are more difficult to analyze than miogeoclinal sequences, and recognition that ophiolite emplacement is a tectonic event of primary importance are key components to realistic tectonic reconstruction of any orogen. The relative neglect of structural features in favor of petrology/geochemistry in many syntheses of the ophiolite-bearing Eastern Pacific margins has perpetuated a single-subduction zone model that began as a "premature theory" in the late 1960's, and subsequently has attained "ruling theory" status in the sense of Chamberlin (1890).