Implications of paleomagnetism for the tectonic history of the Eastern Klamath and related terranes in California and Oregon

Abstract

Paleomagnetic study of Permian to Jurassic volcanic and sedimentary strata of the Eastern Klamath terrane has shown the remanent magnetism of these rocks to be prefolding and primary. The Permian and Triassic rocks are both indicated to have rotated 100° clockwise, while the Jurassic strata have rotated 60° clockwise. The respective amounts of rotation for Permian and Jurassic strata are similar along two widely-spaced transects of the arcuate Eastern Klamath terrane, which indicates rigid-block rotation rather than oroclinal bending. These results suggest that the Permian and Triassic strata began to rotate during Late Triassic or Early Jurassic time, possibly in response to the beginning of accretion of the Eastern Klamath terrane to the continental margin. Measurements on superjacent Cretaceous strata indicate that the rotation of the Eastern Klamath terrane as well as other parts of the Klamath Mountains province was virtually compete by Early Cretaceous time. The virtual cessation of rotation probably marked the completion of the accretion of the Eastern Klamath terrane to North America. Neither these nor other data currently available show evidence for any significant latitudinal displacement of the Klamath Mountains terranes.