SLATE MOUNTAIN AND NORTHERN SAND SPRINGS RANGE, NEVADA GEOLOGIC MAPS CLARIFY KEY CROSS-CUTTING RELATIONS IN THE CORDILLERAN HINTERLAND

The Sand Springs Range (SSR) and Slate Mountain (SM) are located in the Cordilleran hinterland, within the Sierran magmatic arc, and in the western Great Basin. Recent 1:8000-scale geologic mapping for a 2015 undergraduate research project and for part of 2016 field camp documents two key timing relations: 1) amphibolite facies metamorphism and coeval deformation is a regional event (D1) that predated Cretaceous plutons, 2) a low-angle fault forming klippen that cross-cuts S1 in northern SSR is a Luning-Fencemaker belt (LFTB) thrust fault (D2), not a detachment fault. A tied grid of cross-sections accompanies geologic maps.

The northern SSR contains metamorphic tectonites (andalusite schist, foliated marble, garnet biotite quartz schist, and meta-rhyolite sills dated at 237 Ma; Satterfield, 2002), Cretaceous intrusive igneous, and Tertiary intrusive and extrusive igneous map units. The Sand Springs granitoid pluton, dated at 81-90 Ma (John, 1992; Satterfield, 2002), sharply cross-cuts S1, D1 folds, and a low-angle fault. However, abundant Tertiary and Cretaceous sills which intruded parallel to steep S1 typically terminate at the low-angle fault. Mapped relations demonstrate the fault is pre-Cretaceous: a) two sills thicken upward before terminating at the fault, b) sills in the upper plate of the thrust do not terminate at the fault, and c) a Tertiary sill cross-cuts the fault. NE- and NW-trending folds, the characteristic LFTB sequence, deform the thrust and tectonites.

SM contains map units similar to southern SSR units: hornblende schist containing stretched pebble conglomerate, foliated marble, a lineated granitoid, meta-rhyolite, and Tertiary igneous rocks. Granitoid mineral lineations parallel hornblende schist stretching and mineral lineations, indicating the granitoid lineation is metamorphic. The 81-82 Ma Slate Mountain granitoid pluton is porphyritic and not lineated (John, 1992). Overall NE-trending SM metamorphic foliation (S1) could be one limb of a large NE-trending D2 fold. Several map-scale NW-trending D3 folds warp this limb. Fairview Peak rupture (1954) fault scarps cross-cut the range front. Shutter ridges document older right-lateral slip.

D1 and coeval amphibolite facies metamorphism correlate with eastern Sierra Nevada structures and predate LFTB thrusting and folding.