T23 Linking Continental Geologic Records to Geodynamic Models for the Cretaceous-Paleogene Development of the Mojave Region

Sunday, 22 September 2024
8:00 AM - 12:00 PM
304B

A GEO-THERMOCHRONOLOGIC AND PB ISOTOPIC PERSPECTIVE UPON THE LATE CRETACEOUS-PALOEGENE EVOLUTION OF THE SOUTHERNMOST SIERRA NEVADA AND WESTERN MOJAVE REGION

Paper number: T23-6
Program: Technical Sessions
Time: 9:10 AM – 9:30 AM

Authors

Abstract

Uncertainty regarding the timing of magmatism, shallow accretion of trench-derived sediment, and exhumation of arc crust in the southernmost Sierra Nevada and western Mojave region during the Late Cretaceous–Early Paleogene has clouded models proposed to explain the tectonic evolution of the region. These geodynamic issues include the spatial-temporal patterns of magmatism, proposed plateau subduction, erosion of lowermost continental crust and subcontinental mantle lithosphere (LCC-SCML), shallow subduction-related accretion of sediment, denudation of overlying arc crust, and breachment of the continental margin batholith to allow a dramatic influx of extraregional sediment. We present an up-to-date summary of geologic, geochemical, geochronologic, and thermochronologic data from plutonic rocks and underplated schist in the region. Generally, cessation of arc magmatism appears to have preceded schist accretion by ~5 m.y. at most locations examined. While the onset of shallow sediment subduction appears to have occurred between 75–70 Ma in the southern California Transverse ranges, southeastern California, and southwestern Arizona, these processes occurred earlier (ca. 90–75 Ma) and over a more protracted period in the southernmost Sierra Nevada and western Mojave region (i.e., northwestern domain of schist accretion). This is consistent with patterns of shifting magmatism and cooling in the northwest relative to the southeast domains of the Mojave region. We speculate that the delayed response to shallow subduction in the northwestby up to 5–10 m.y. reflects the time required for subduction erosion of LCC-SCML to occur. Subducted schist near the margin (i.e., the southernmost Sierra Nevada, northwestern Mojave, and Salinia) was exhumed to near-surface positions in the crust by the end of the Late Cretaceous. At more interior locations (e.g., Rand Mountains), deep arc crust and underplated schist remained at > 10 km depth until the Miocene. Combined detrital zircon U-Pb age distributions and detrital K-feldspar Pb isotopic compositions indicate that the breached segment of the southern California margin began to receive distinctive extraregional, craton-derived sediment by 75 Ma with the largest influx occurring after 55 Ma.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-402846

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