Native terranes of the Central Klamath Mountains, California

Abstract

The Klamath Mountains of northern California and southern Oregon contain several good examples of terranes which have developed in situ. The term "native" is proposed for five of these terranes and all terranes whose development can be tied to an adjacent cratonal area. The Klamath terranes discussed herein include disrupted, stratigraphic, and metamorphic types. Three disrupted terranes, the Rattlesnake Creek, eastern Hayfork, and North Fork, contain fossiliferous blocks derived from both North American and exotic sources. The unique mixed faunal assemblage, stratigraphic ties to North America in the source terranes of the blocks, and paleomagnetic evidence indicate that the tectonic and sedimentary processes responsible for mixing these blocks occurred in proximity to North America, not distant from the terranes' present positions. Coeval blueschist metamorphism in a fourth, inboard terrane, the Stuart Fork, suggests that all four terranes developed during a Late Triassic to Early Jurassic subduction event. A fifth, stratigraphic terrane, the western Hayfork, was constructed upon the assembled disrupted and metamorphic terranes in the Middle Jurassic. Disrupted terranes with similar mixtures of North American and exotic faunas occur throughout the Cordillera from central California possibly as far north as British Columbia. Late Triassic deformation has been documented in several of these terranes, suggesting that (1) subduction operated along at least this portion of North America during the Late Triassic‐Early Jurassic, and (2) many additional Cordilleran terranes should also be considered native.