2 Mysteries of the Sierra Nevada

Wednesday, 2 April 2025
8:00 AM - 12:00 PM
Fresno

MID-CRETACEOUS DEFORMATION AND ISOTOPIC DISTURBANCE OF THE NEOPROTEROZOIC-PALEOZOIC METASEDIMENTARY FRAMEWORK OF THE SOUTHWESTERN SIERRA NEVADA ARC

Paper number: 2-3
Program: Theme Sessions
Time: 8:40 AM – 9:00 AM

Authors

Abstract

Metasedimentary pendants straddling the Great Western Divide constrain the Neoproterozoic-Paleozoic depositional and accretionary history along the truncated Laurentian margin across which the southern Sierra Nevada arc was constructed. New zircon U-Pb data from the Cow Creek pendant clarify local deformational and hydrothermal history. The Kernville Series contains at least two detrital zircon assemblages that are in likely fault contact within the Cow Creek pendant (35.8°N): a western chronofacies interpreted as late NeoProterozoic detritus derived from lower crust Mojavia exposed along the rifted continental edge; and an eastern chronofacies interpreted as late Cambrian passive margin strata derived from a Laurentian source. Age constraints are provided by zircon of presumed rift origin, with youngest zircon of Ediacaran through Cambrian age (584-495 Ma) in the Laurentia-derived strata (N=10) and dominantly Cryogenic zircon (693-660 Ma) zircon in the Mojavia-derived strata (N=4).

An Early Cretaceous ash (126.5 Ma) caps the eastern portion of the Cow Creek pendant, similar in age to mylonitic granite (127.0-124.7 Ma; N=3) exposed along the mapped fault trace. These dates expand the plutonic footprint of the Early Cretaceous arc southeastward, crossing the accreted ophiolite belt and into the Laurentian continent. Age distributions are disturbed by Pb-loss culminating at ca. 104 Ma, locally manifest as undeformed veins of blue-green tourmaline. Volumetrically major magmatism in the southern Sierra immediately followed this Pb-loss climax: the Bear Valley Intrusive Series (103-100 Ma) to south and the Domelands Intrusive Complex (100-92 Ma) to east. Bordering the pendant is the undeformed granite of Portuguese Pass in which U-Pb systematics are undisturbed (102.6 Ma). Together these ages constrain local Early Cretaceous deformation to 124-103 Ma, a period overlapping a transpressional regime documented ~50 km north (Mineral King pendant, Greene et al., 2024).

Geological Society of America Abstracts with Programs. Vol. 57, No. 4

doi: 10.1130/abs/2025CD-410308

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