37 Cordilleran Margin Evolution and Supercontinent Tectonics: From Pangea Assembly to North American Orogenesis (Posters)

This session integrates tectonics, petrology, geochronology, stratigraphy, and paleontology to illuminate how Paleo-Pacific plates drove subduction dynamics, crustal evolution, and paleogeographic reconstructions across the complex geological architecture of the American Cordilleras.

Friday, 24 April 2026
8:00 AM - 5:30 PM
LMH, 5th Floor Chapel

Microstructure and age of high-temperature mylonites across the footwall corrugation of the Miocene Whipple Mountain metamorphic core complex (southeastern California, U.S.A.)

Paper number: 37-7
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

In the eastern Mojave Region, Miocene-aged metamorphic core complexes and normal faults have exhumed rocks that preserve a complex geologic history that includes Jurassic, Cretaceous, and Cretaceous-Eocene events associated with Central and Southern Cordilleran tectonics. In southeastern California, the Whipple Mountains metamorphic core complex and Whipple Detachment Fault (WDF) are spectacularly exposed and well-known examples of extensional detachment fault systems and exhumation processes. Despite focused rheological studies, the absolute age of high-temperature mylonitic fabrics exposed in the footwall of the WDF remains debated. In this study, we present microstructural observations of quartz and feldspar across the footwall corrugation and at 20-50-100 m depth intervals below the WDF, as well as preliminary zircon U-Pb crystallization ages and apatite U-Pb high-temperature thermochronology. Dynamically recrystallized quartz within mylonitic gneisses on the northwestern and southeastern flanks of the footwall corrugation present bulging to sub-grain rotation texture. In the hinge zone of the footwall corrugation, quartz dynamically recrystallized via sub-grain rotation to grain boundary migration, indicative of possible higher-temperature deformation conditions. Zircon U-Pb crystallization ages from the mylonitic footwall range from Neoproterozoic (ca. 1450 Ma) to Cretaceous (ca. 70 Ma), while preliminary apatite U-Pb cooling ages range from Eocene to Oligocene (ca. 50-35 Ma). Preliminary EBSD analyses coupled with microstructural analyses and apatite U-Pb chronology suggest that higher-temperature slip systems may have been active in the Eocene-Oligocene, prior to Miocene motion of the WDF.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-410859

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