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.

Structure and evolution of the East Sierran thrust system, east central California

“…We concur with and expand upon the informal suggestions by Schweickert and Lahren [1990] and Taylor et al [1993] that the most likely northern correlative of the ESTS is the Luning-Fencemaker fold-thrust belt of western Nevada (Figure 1). Despite significant differences in the kinematic and geometric characteristics of these two belts, such a correlation of these two belts is warranted by similar locations along the eastern margin of the same magmatic arc (Figure 1) and by at least partly coeval multiphase Early (?)…”

“…[30] Confident identification of structures potentially dcorrelative with the ESTS located north of the Saddlebag Lake/northern White Mountains region is difficult because of the uncertain effects of a >110 km eastward deflection (Figure 1) of all prior to late Mesozoic rock units and structures [Stewart, 1985, and references therein], and because of the uncertain location and slip amount of the Mojave-Snow Lake fault [Schweickert and Lahren, 1990]. We concur with and expand upon the informal suggestions by Schweickert and Lahren [1990] and Taylor et al [1993] that the most likely northern correlative of the ESTS is the Luning-Fencemaker fold-thrust belt of western Nevada (Figure 1).…”

Jurassic Barrovian metamorphism in a western U.S. Cordilleran metamorphic core complex, Funeral Mountains, California

“…Reconstruction of Cretaceous dextral strike-slip displacement along the Mojave-Snow Lake fault places the Funeral Mountains east of the northern Sierra Nevada and Franciscan complex of the northern Coast Ranges ( Fig. 1; Schweickert and Lahren, 1990;Wyld and Wright, 2001;Dickinson, 2006). Although there is debate about when Franciscan subduction initiated, most agree that subduction was underway by 170-160 Ma, the time of metamorphism of high-grade metamorphic rocks within the Franciscan complex (e.g., Anczkiewicz et al, 2004;Wakabayashi and Dumitru, 2007).…”

Triassic and Jurassic stratigraphy and paleogeography of west-central Nevada and eastern California

“…These include one model which indicates no significant movement between terranes (fixist view) and three models with significant movement between terranes (mobilistic views). Major structures considered in these models include (1) the Jurassic or Cretaceous northwest-trending left-lateral Pine Nut fault (Oldow, 1983(Oldow, , 1984 in west-central Nevada with proposed displacement of several hundreds of kilometers, (2) the Early Cretaceous northwest-trending right-lateral Snow Lake fault (proposed displacement of approximately 400 km) in the axial part of the Sierra and possible offset parts coextensive with the the Pine Nut fault in western Nevada (Lahren and Schweickert, 1989;Lahren and others, 1990;Schweickert and Lahren, 1990), (3) major Jurassic or Cretaceous northwest-trending right-lateral faults in the eastern part of the Sierra (such as the Lake Tahoe fault) (Oldow, 1984;Robinson and Kistler, 1986;Saleeby and others, 1986;Kistler, 1990) that have apparently offset the Sri=0.706 isopleth about 300 km, (4) the east-west-trending rightlateral Jurassic or Cretaceous Excelsior fault (45 to 55 km of displacement) and Coaldale fault (60 to 80 km of displacement) in western Nevada near the southern border of the area described here (Stewart, 1985), (5) the Jurassic or Cretaceous Pamlico and Luning thrusts whose upper plates may have had hundreds of kilometers of contraction (Oldow, 1983(Oldow, , 1984, (6) northwest-trending right-lateral and left-lateral late Cenozoic faults in the Walker Lane belt (Stewart, 1988), and (7) major late Cenozoic extensional faults with amounts of extension greater than 100 percent in the area from the Pine Nut Mountains to the Wassuk Range (Proffett, 1977).…”

“…Model 2: Reconstruction made on basis that Sq isopleth was originally straight. Model 3: Reconstruction based on model of Lahren and Schweickert (1989) and Schweickert and Lahren (1990) showing about 400 km of right-lateral displacement on Mojave-Snow Lake fault. Model 4: Reconstruction based on model of Oldow (1984) showing early left-lateral movement on the Pine Nut fault and later right-lateral movement on the east side of the Sierra Nevada.…”