T167 Magmatism and Accreted Terranes from the North American Cordillera to the Norwegian Caledonides I: a Session in Honor of the Scientific Contributions of Calvin G. Barnes

Tuesday, 24 September 2024
8:00 AM - 12:00 PM
207B

PETROGENESIS OF A MIDDLE JURASSIC “HIGH SIERRA”-TYPE INTRUSION: THE SACATAR INTRUSIVE COMPLEX, KERN PLATEAU, SOUTHEASTERN SIERRA NEVADA, CA

Paper number: T167-8
Program: Technical Sessions
Time: 9:45 AM – 10:00 AM

Authors

Abstract

Unlike the Klamath Mountains of Cal Barnes’ fame, the record of Jurassic Sierra Nevada arc magmatism is largely obscured by Late Cretaceous plutons. However, a relatively complete record of Jurassic arc magmatism is exposed on the Kern Plateau (~36°N latitude) where zircon U-Pb data indicate that Jurassic magmas intruded as two suites: a large, intermediate to felsic intrusion mapped as the Middle Jurassic Sacatar granodiorite (ca. 185 - 162 Ma; N=13); and small pods and ring dikes of latest Jurassic Summit Igneous Complex (ca. 151 - 146 Ma; N=15), similar in age and orientation to the Independence dike swarm. The Tübatulabal hypabyssal-volcanic unit (N=6) spans emplacement of both suites: Tübatulabal A corresponds in age and εHfi with the Sacatar, Tübatulabal B with the Summit, and together indicate upper crustal emplacement of Jurassic magmas in the Kern Plateau. The Sacatar unit varies from quartz diorite to granite; the Summit is a bimodal gabbro-granite suite. Whole-rock compositions within the high-K calc-alkaline Sacatar vary from 51 to 73 wt. % SiO2, overlapping compositional trends of the latest Jurassic Independence dike swarm and the neighboring Late Cretaceous Mt. Whitney intrusive complex. We propose including coeval, adjacent NW-elongate plutons, bracketed by the Middle Jurassic Redrock Meadows and Grasshopper Flats granitoids, in a compositionally zoned, ~1500 km2 Sacatar Intrusive Complex, comparable to Cretaceous complexes such as the Fine Gold (>3100 km2 intruded over ca. 19 m.y.) and Mt. Whitney (~1200 km2 over ca. 5 m.y.).

Enriched mantle derivation of eastern Sierra magmas was initially proposed to explain whole-rock Sri-εNdi values in Late Cretaceous High Sierra intrusive complexes. Although initial Sr-Nd ratios are generally enriched in the Summit-Sacatar systems, zircon εHfi values require sourcing in a depleted mantle reservoir beneath the southeastern Sierra. Coupled Sri-εNdi-εHfi indicate that differentiation within the deep Laurentian crust produced enriched mafic magmas, and additional mid-crustal differentiation produced voluminous intermediate-felsic magmas. Upper crustal Triassic-Early Jurassic extension migrated deeper in the Middle Jurassic to evacuate Sacatar magmas from a mid-crustal mush column. Latest Jurassic rifting along the Kern Plateau shear zone liberated bimodal Summit magmas from the lower crustal MASH zone.

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

doi: 10.1130/abs/2024AM-402294

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