EMPLACEMENT OF THE MONO CREEK GRANITE BULGE, SIERRA NEVADA, CALIFORNIA: CONSTRAINTS ON TRANSLATIONAL, ROTATIONAL, AND STRETCHING COMPONENTS OF THE DISPLACEMENT FIELD

Forceful emplacement of granitic magmas requires that the rocks, which were initially located where the granitic magmas subsequently intruded, were deformed or moved out of the way. The Late Cretaceous Mono Creek granite in the Sierra Nevada batholith – a subduction-related magmatic arc complex - provides an ideal location to study this process. A ~8 km wide bulge occurs on the NE side of this pluton, which is otherwise oriented in the NW-SE orientation. A compositional gradient in the Mono Creek granite suggests that the bulge is distinct from the main body of magma. The bulge displaces, from W to E, the Late Cretaceous Round Valley granodiorite, Paleozoic rocks of the Mt Morrison pendant, and the Triassic Wheeler Crest granodiorite. Deformation in the Round Valley granodiorite occurred in the high-temperature solid-state or magmatic state, and is recorded by elongation of mafic enclaves. The stretching of these enclaves suggests flattening strain that is concentric around the bulge. Anisotropy of magnetic susceptibility data, which is controlled primarily by the shape and alignment of multidomain magnetite grains, is also consistent with a flattening strain concentric around the bulge. The marbles of the Mt Morrison pendant are locally deflected ~7 km outward, to the NE, from their original strike. Finally, the fractures of the Wheeler Crest granodiorite appear to wrap around the bulge. We present new paleomagnetic data to attempt to address the translational vs rotational components of deformation. Paleomagnetic data from the Wheeler Crest pluton is most consistent with translation of the central portion of the Wheeler Crest pluton to the NE based on analysis of samples of the Wheeler Crest pluton furthest away from the high temperature deformation of the Round Valley pluton. Using this data together, we attempt to address the translational, rotational, and stretching components of the displacement field, in order to constrain the emplacement geometry of the Mono Creek bulge.