ORIGIN AND TECTONIC DEVELOPMENT OF THE RATTLESNAKE CREEK TERRANE, KLAMATH MOUNTAINS, NORTHERN CALIFORNIA

The Klamath Mountains are located in Southern Oregon and Northern California. They contain four major rock belts: the Eastern Paleozoic, Central Metamorphic, Western Paleozoic and Triassic, and Western Jurassic belts. The Western Paleozoic and Triassic belt contains the Rattlesnake Creek Terrane, an ophiolite basement mélange that is overlaid by a volcanic sequence.

The basement serpentinite-matrix mélange formed by Late Triassic and is interpreted to have developed in a fracture zone near a mid ocean ridge. By the Late Jurassic, the overlying cover sequence formed deep ocean sedimentary rocks and basaltic lava in an intra oceanic arc setting, or potentially near the continental margin. The Western Hayfork terrane later intruded and thrust over the Rattlesnake Creek terrane. Based on detrital zircon geochronology, there is clear evidence of terrigenous input in the cover sequence. However, in the basement mélange the terrigenous input seen is inferred to come from eolian dust. There are no published detrital zircon ages for blocks in the basement mélange.

Whether the basement mélange of the Rattlesnake Creek Terrane contains terrigenous sediment or if it is composed entirely of oceanic mélange is unclear and needs to be further studied. To determine this, sandstone blocks from the basement mélange were collected and prepared for microscopic analysis of mineral composition. Zircons from these sandstones were also dated using uranium and lead isotopes to determine if the sample came from the North American continent or if the continent was too far for terrigenous input.