Emplacement of the Santa Rita Flat pluton as a pluton-scale saddle reef

Regional mapping indicates that the Middle Jurassic Santa Rita Flat pluton, exposed in the Inyo Range of eastern California, is situated within the co re of a south-plunging synform defined by bedding in the surrounding metase dimentary wall rocks, which dip beneath the pluton. However, bedding in roc ks preserved above the pluton defines a south-plunging antiform. Anisotropy of magnetic susceptibility analysis revealed that magnetic foliation withi n the pluton also defines a south-plunging antiform, and the accompanying m agnetic lineation plunges subparallel to the axis of this antiform. Our dat a indicate that the pluton was initially intruded as a sill in the hinge zo ne of the enveloping synform. Subsequent vertical inflation of the sill res ulted in upward doming of the overlying roof and formation of the antiform now observed at the current erosion level in the pluton and preserved roof rocks. Emplacement of the pluton at 164 +/- 1.5 Ma (U-Pb zircon age) overla ps in time with regional thrust faulting and folding ca. 185-148 Ma recogni zed in the southern Inyo Range. We speculate that space for initial emplace ment of the pluton was produced during folding by layer-parallel slip and h inge-zone dilation, producing a saddle reef-like structure.