242-3 Internal Strain Localization in the Papoose Flat Pluton: Evidence from Structure, Petrography, and Geochemistry

Abstract:

Continental arc plutons preserve records of magma assembly and deformation, yet the processes responsible for internal strain localization during emplacement remain debated. The relatively isolated Papoose Flat Pluton (PFP), located in the northern Inyo Mountains of eastern California, provides an opportunity for emplacement-related deformation to be examined with limited overprinting from adjacent plutons. The PFP has traditionally been interpreted as a forcefully emplaced body with deformation concentrated along its margins.

This study addresses whether the PFP was assembled through multiple intrusive pulses and whether repeated magma emplacement contributed to the formation or reactivation of a broad internal high-strain zone. Gradational transitions from protomylonite to orthomylonite and ultramylonite were identified through field mapping. Structural measurements, oriented samples, petrography, paleomagnetism, and a newly generated whole-rock XRF dataset were used to evaluate variations in strain, mineralogy, and composition. This XRF dataset provides new geochemical constraints on the internal architecture of a pluton for which bulk geochemical characterization has previously been limited.

Spatially organized compositional variation and discrete Fe–Mg groups were identified within the pluton interior and across the mylonitic zone. These preliminary results could suggest that the high-strain zone developed during incremental pluton assembly. The observed geochemical differences may represent distinct magma pulses, deformation-related mineral redistribution, or both. Overall, emplacement-related strain is favored over movement along a regionally continuous fault.

Geological Society of America Abstracts with Programs. Vol. 58, No. 5, 2026

doi: 10.1130/abs/2026AM-21878

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