PLUTON-HOST ROCK SYSTEMATICS OF THE JURASSIC SANTA RITA FLAT PLUTON AND ITS AUREOLE; MULTIPLE HOST ROCK TRANSFER MECHANISMS AT MULTIPLE SCALES DURING PLUTON EMPLACEMENT

The Jurassic Santa Rita Flat pluton (SRFP) intruded into Paleozoic metasediments in the Inyo Mountains of eastern California. We synthesize new and existing data to evaluate magma and host rock transfer processes and existing pluton emplacement models. The observations favor multiple material transfer processes operating at multiple scales during pluton emplacement.

The SRFP is ~80 km² and has an aspect ratio of 3:1 with the long axis of the pluton aligned NNW. Symmetrical compositional zoning indicates that the current exposure preserves most of the original pluton shape (Metz, 1978). Lithology grades inward from granodiorite to granite with sheets at the tips of the pluton spanning these compositions. Two new zircon U-Pb ages within error at ~159 Ma suggest relatively short timescales of pluton growth. Transitions between pluton wall and connected roof flaps of host rock indicate exposure represents the top of the pluton. Two distinct host lithologies form the aureole. The Rest Springs shale contains two to three well-developed cleavages, slicken surfaces on bedding surfaces, large-scale folds, and bedding discordant to contacts between the pluton and host rock roof flaps. The Keeler limestone is folded and faulted along both east and west margins, with a pronounced rim syncline along the western pluton margin. Epidote skarn halos are present at pluton-limestone contacts and as rinds of stoped limestone blocks. Magmatic fabrics are inconsistent in the pluton’s interior and moderately developed near the margins. Previous workers described magnetic fabrics as forming a fold-like pattern within the pluton (Vines and Law, 2000).

Vines and Law (2000) proposed the SRFP was emplaced in a syncline hinge during regional contraction based on the fold-like magnetic fabrics they observed. The pattern may alternatively record the pluton’s domed roof shape. Connected roof flaps and no regional syn-emplacement faults suggest limited brittle upward host rock displacement at the exposed level. Stoping and folding of host rocks, magma wedging during sheeting, and vertical transfer during folding show that multiple host rock transfer processes operated during magma emplacement. These data highlight the value of drawing on structures and petrology spanning the pluton-host rock system when evaluating emplacement histories.