Detrital zircon geochronology of Neoproterozoic-Lower Cambrian passive-margin strata of the White-Inyo Range, east-central California: Implications for the Mojave-Snow Lake fault hypothesis

摘要

Correlation of lithotectonic packages across major transcurrent structures is critical to understanding the tectonic evolution of the North American continental margin. Detrital zircon geochronology of uppermost Proterozoic to Lower Paleozoic miogeoclinal strata from the White-Inyo Mountains permits evaluation of: (1) the age and provenance of these metasediments and (2) a model for truncation of the passive margin along a postulated large-magnitude Cretaceous dextral shear zone, i.e., the Mojave-Snow Lake fault. U-Pb ages of detrital zircons from the Neoproterozoic Wyman Formation, the upper-most Proterozoic Reed Dolomite (Hines Tongue Member), and clastic strata of the Lower Cambrian Deep Springs, Campito (Montenegro Member), Poleta, and Harkless formations reflect ultimate derivation from the adjacent 1.7-pre-1.8 Ga Mojavia terrane and/or 1.7-1.8 Ga Yavapai continental basement, with subsidiary sources in both the ca. 1.4 Ga Yavapai-Mazatzal anorogenic granitoids and the >2.5 Ga North American craton, and a small proportion of 1.0-1.3 Ga grains, most likely reworked from Grenville clastic wedge deposits. Detrital zircon age spectra from the Lower Cambrian Andrews Mountain Member of the Campito Formation are unique in comparison with the remainder of the studied section, containing a major age peak centered at ca. 1.1 Ga and a subsidiary Lower Cambrian age peak, permitting calculation of a ca. 527 +/- 12 (2 sigma) Ma maximum depositional age. These features, in addition to abundant detrital magnetite-ilmenite grains, reflect a distal source for these rocks, most likely from the ca. 1.1 Ga Pikes Peak batholith and/or the Midcontinent rift and ca. 0.53 Ga bimodal intrusions of the Oklahoma-Colorado aulacogen. In terms of zircon age distribution, allochthonous metamorphic pendants in the Snow Lake terrane of the central Sierra Nevada batholith are most similar to those of stratigraphically equivalent units in the Death Valley region and, to lesser degrees, the White-Inyo section, and the Mojave Desert region. Given the similarity and relative proximity of Death Valley facies-assemblages to the Snow Lake terrane, we suggest that the latter was not transported northward from the Mojave Desert region and instead represents footwall assemblages of a late Early to early Middle Jurassic low-angle normal fault system, probably along the outer transform-truncated margin of the Last Chance thrust stack. This model implies a few tens of kilometers of offset, in contrast to the hundreds of kilometers required by the Mojave-Snow Lake fault hypothesis.