Insights into the Laramide: Cretaceous deformation in the Little Piute Mountains, eastern Mojave Desert

Session: Evolution of Orogenic Belts Through Time: Insights from Sedimentation, Deformation, Magmatism, and Metamorphism, Part I

Presenting Author:

Authors:

Abstract:

The Little Piute Mountains of the eastern Mojave Desert host the NE terminus of two undated ductile structures which extend for >45 km to the SW, comprising the largest continuous deformation zone in the Mojave. These structures–the Meteor extensional fault, Scanlon thrust, and associated nappes–lie between the Sevier fold and thrust belt to the north, and the Maria fold and thrust belt to the south. The undeformed sheet-like ~73 Ma Old Woman granodiorite provides a minimum age constraint on deformation and displays a roof contact parallel to the structurally higher foliated basement. The Mississippian Redwall Formation is juxtaposed above the basement mylonitic orthogneisses via the Meteor fault. Between the Meteor fault and the overlying Scanlon thrust to the NW are ~600 meters of deformed and attenuated (≤90%) Paleozoic strata forming a reclined, SE-verging syncline. The youngest unit coring this syncline has been interpreted as Triassic Moenkopi Formation overlying Permian Kaibab marble [1,2]. However, a regional provenance study yielded a robust U-Pb zircon maximum depositional age (MDA) of ~119 Ma near the base [3].

We corroborate this basal MDA with strategic sampling from the base, middle, and top of section. The top of the section yields an extremely robust MDA of ~112 Ma from >80 zircons, demonstrating: (1) Cretaceous deformation is required, rather than proposed Jurassic, (2) the existence of an unrecognized Cretaceous basin and stratigraphic formation, and (3) that new detritus was entering the basin from ~119–112 Ma. We also present new LA-SS-MC-ICPMS U-Th-Pb monazite petrochronology from basement mylonitic orthogneisses in the Meteor and Scanlon shear zones that yield indistinguishable ~73 Ma ages, which are interpreted as recording a fluid-flow event. Current efforts are focused on obtaining peak temperature data from Raman spectroscopy on carbonaceous material (RSCM), and quartz c-axis preferred orientation data.

The lack of Laramide contraction in the region has led to the dismissal of end-loading as a shortening mechanism in the Rocky Mountain foreland province. However, this new ~112 Ma MDA, coupled with recent ⁴⁰Ar/³⁹Ar muscovite ages from the Winters Pass thrust [4], suggest Laramide-aged shortening in the eastern Mojave.

            [1] Stone et al. GSA Bulletin (1983); [2] Howard et al. USGS (1995); [3] Kwiatkowski, C.J. Northern Arizona University (2021); [4] Wells et al. GSA Connects Meeting (2024).