THE RATTLESNAKE CREEK TERRANE: AN ENIGMATIC TECTONOSTRATIGRAPHIC TERRANE OF THE KLAMATH MOUNTAINS, CALIFORNIA AND OREGON

The Rattlesnake Creek terrane is the westernmost tectonostratigraphic terrane of the western Paleozoic and Triassic belt, which is part of the Klamath Mountains province in northern California. This tectonostratigraphic terrane is divided into a structurally lower basement assemblage and higher cover sequence, both cut by various intrusions. The basement assemblage is composed of a serpentinite-matrix mélange or block-on-block mélange, with peridotite massifs - and blocks of peridotite, greenstone, amphibolite, pillow basalt, chert, argillite, limestone and plutonic rocks. The Late Triassic cover sequence is divided into the lower Salt Creek assemblage (basalt, chert, argillite and clastic rocks) and the higher Dubakella Mountain assemblage (volcanogenic mafic and felsic successions). Paleozoic to Triassic fossils and blocks of the cover sequence in the mélange indicate mélange deformation was active through the Late Triassic. Previous studies have interpreted that the basement mélange formed in an oceanic transform and that the cover sequence represents a Late Triassic intra-oceanic arc. The Early Jurassic is a notable gap in the complex geologic history of the Rattlesnake Creek terrane. By the Middle Jurassic, it was part of the western margin of North America, where it was metamorphosed in an arc setting and deformed by east-west compression. How and when did the Rattlesnake Creek terrane accrete to North America? We present new compositional and structural data from geologic mapping and thin section petrography to better understand the formation and deformation of the Rattlesnake Creek terrane and Triassic-Jurassic tectonics of western North America.