24 Tectonics, Volcanism, and Sediment Dispersal Within and Proximal to the Rio Grande Rift and Southern Rocky Mountains (Posters)

This session integrates research on coupled tectonics, volcanism, and sediment dispersal in the Rio Grande Rift and southern Rockies. We examine how extensional faulting controls volcanic processes and reshapes sediment routing from Colorado through Texas.

Tuesday, 19 May 2026
8:00 AM - 5:30 PM
Alvarado D/E

Trace and major element metasomatism of platform facies Paleozoic strata and Jurassic metagranites in the Big Maria Mountains, southeastern California

Paper number: 24-0
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Big Maria Mountains in southeastern California expose mid-crustal metamorphic rocks that comprisePaleozoic strata of the Grand Canyon, Proterozoic basement, and Jurassic metagranitic rocks. The rocks underwent metasomatism during the Late Cretaceous, temporally linked to flat-slab subduction of the conjugate of the Shatsky Rise. The timing of metasomatism is documented by titanite ages from Paleozoic strata at 70.32 ± 0.23 Ma and Jurassic metagranites at 70.1 ± 1.4 Ma. This study investigates the trace-element abundances in major (not accessory) minerals in metasedimentary units (Supai and Hermit Formations) to characterize thesolute chemistry of infiltrating fluids. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to identify mineral phases, and laser ablation mass spectrometry (LA-Quad) was used to analyze trace elements, focusing on fluid-mobile elements (e.g., Rb, Sr, Ba, Pb) and rare earth elements (REEs).Veins of K-feldspar in a sample from the Supai containelevated concentrations of Sr in epidote and hornblende. K-feldspar in two Hermit Formation samples possesselevated concentrations of Ba, Rb, and Sr, while tremolite and diopside possess moderately elevated concentrations of Cr. Variations in REE patterns between diopside grains in different formations (Supai vs. Hermit) suggest a control by bulk rock composition. However, the high abundancesof large ion lithophile elements (LILEs) in K-feldspar grainsappear to reflect introduction from an external source via fluid infiltration. We also compared the bulk rock chemistryof metamorphic upper Paleozoic strata in the Big Maria Mountains (Hermit, Supai, Coconino and Kaibab Formations) with pristine sedimentary equivalent lithologies collected in the southern Plomosa Mountainsnear Black Mesa. Ba abundance is elevated in metamorphic samples of the Coconino and SupaiFormations, Sr and Zn are elevated in the Kaibab Formation, and Rb and Zn are elevated in the Hermit Formation. These formation-dependent patterns likelyreflect a mineral-specific acceptance of different fluid-mobile elements and not necessarily differing chemistry of the infiltrating fluid. These data contribute to our understanding of metasomatic processes and thegeochemical constraints on fluid-rock, fluid-mineralinteractions, and helps us better understand how fluids interacted with rocks in the middle crust above the Laramide flat slab.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410653

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