Speculative reconstruction of the Mojave‐Snow Lake Fault: IMPLICATIONS FOR Paleozoic and Mesozoic orogenesis in the western United States

Abstract

Available evidence suggests that the Mojave‐Snow Lake fault, a major Early Cretaceous dextral fault with up to 400 km displacement, formerly existed in what is now the axial part of the Sierra Nevada batholith. Regional relations suggest that the fault formerly continued in western Nevada, the Mojave Desert, and in rocks now exposed in the Salinian block. Restoration of 400 km of Early Cretaceous dextral displacement on the Mojave‐Snow Lake fault leads to speculative but testable reconstructions of Mesozoic and Paleozoic tectonic features of California and Nevada. Insights derived from these reconstructions include the following: (1) Two regionally extensive Jurassic thrust belts of opposed vergence appear to have intersected in the northern Sierra Nevada. The eastern, east‐vergent thrust belt, which includes the Fencemaker and Liming thrusts in western Nevada and several east‐vergent thrusts in the northern Sierra, may be a contractional belt along which an Early Jurassic interarc or marginal basin was closed in Middle to Late Jurassic time. The western, west‐vergent thrust belt is part of the classic Nevadan orogen of the western Klamath Mountains and the western Sierra metamorphic belt, in which collisions and/or thrusting of various island arc terranes occurred during Middle and Late Jurassic time. (2) The early Mesozoic continental arc included paired belts of Triassic‐Jurassic blueschist and melange, and igneous rocks including Late Triassic and younger plutons and volcanic rocks. This conclusion is not new, but the reconstruction provides a slightly different geometry than previously thought. (3) Sonomia, the late Paleozoic island‐arc terrane of the western U. S., may have formed a relatively narrow belt extending from northwestern Nevada to the latitude of the western Mojave Desert. The geologic development of the Paleozoic basement complex of Sonomia was very different from that of the Cordilleran miogeocline in Death Valley and the Mojave Desert, requiring that a continuation of the Sonoma suture belt (or Golconda thrust) must have extended southward through the Sierra Nevada batholith to the Mojave region. (4) A heterogeneous belt of Permian to Triassic or Triassic deformation in the Mojave and eastern Sierra Nevada, together with the Golconda allochthon in Nevada, may represent the protracted response to the collision of Sonomia with the western margin of North America. The contractional deformation continued during the evolution of the early Mesozoic continental arc. (5) Several predictions can be made about the nature of concealed basement within the Sierra Nevada batholith and within western Nevada. The reconstruction suggests that elements of the Antler and Sonoma orogenic belts should underlie areas of the batholith and western Nevada, as a result of northward displacement along the Mojave‐Snow Lake fault from the western Mojave and southern Sierra Nevada.