Late Paleozoic tectonism in the northern Snake Mountains, Elko County, Nevada.

摘要

Evaluation of the Paleozoic stratigraphy and structure of the northern Snake Mountains, Elko County, Nevada, reveals a tectonic history that includes periods of Paleozoic extension and contraction across the continental margin of western North America. Early to Middle Paleozoic stratigraphy is interpreted to represent a long-lived, backarc basin extensional setting (with the Japan Sea as a modern analog) behind eastward-directed subduction. The backarc basin contracted with eastward thrusting during the Late Paleozoic, creating the tectonic effects now expressed in the Antler orogenic belt.; Ordovician through Devonian ocean basin strata of the Roberts Mountains allochthon (RMA) reflect backarc extension of the outer continental margin. Backarc extension during the Famennian (Late Devonian) was particularly intense, as reflected in alkalic volcanism, bedded barite sedimentation, and coarse clastic sedimentation within a rift basin setting. Intense Late Devonian to Early Mississippian extension caused subsidence across the entire continental margin, forming a pre-Antler-aged taphrogen on the former shelf. Taphrogenic subsidence is reflected in formations such as the Woodruff, Pilot, and Webb. Late Paleozoic contraction of the continental margin (the “Antler” orogeny) began AFTER the deposition of these formations.; After Early Mississippian (Kinderhookian) subsidence, contractional deformation complexly imbricated and duplexed strata of both the RMA and the former shelf. In post-Kinderhookian time, the RMA was emplaced in the Snake Mountains region on the Roberts Mountains thrust, above the footwall of highly deformed Early to Middle Paleozoic shelf strata. In the middle to late Missourian (Late Pennsylvanian), the Strathearn Formation deposited upon an angular unconformity on the RMA, and post-dates all intense contractional deformation in the Snake Mountains.; The Late Paleozoic contractional tectonism now reflected in the northern Snake Mountains is here interpreted to be the result of the eastward collapse of a backarc basin behind a fringing arc. The arc had been present outboard of the continental margin throughout much of the earlier Paleozoic, and is now represented in the eastern Klamath and northern Sierra terranes. The backarc basin model presented in this study provides coherence with observations along the entire western continental margin of North America.