San Emigdio intrusive suite
San Emigdio intrusive suite
Late to Middle Jurassic, ~155-161 Ma
Forms a small, faulted body in the western San Emigdio Mountains. Includes the White Ridge tonalite (hornblende tonalite, zircon U-Pb age ~155 Ma [Chapman and others, 2012]), gabbro of Eagle Rest Peak (cumulate and static gabbro, zircon U-Pb age ~161 Ma [James, 1986]), and unnamed mafic and ultramafic plutonic rocks and serpentinite. Intrudes the Paleozoic Eagle Rest Peak terrane (unit ERP). Equivalent to the Jurassic part of the Western San Emigdio mafic complex of Chapman and Saleeby (2012). Base defined by the north-dipping Maricopa (detachment) normal fault which is everywhere concealed by overlying Tertiary strata. Both dense and magnetically susceptible, this unit forms a distinctive gravity and especially aeromagnetic high, superimposed on broader and lower highs related to the rocks below the Maricopa normal fault to the south, which emphasize its limited extent, reaching less than 15 km eastward from the San Andreas fault. Gravity and magnetic modelling of this unit (Fuis and others, 2012; Appendix A) show this unit as a 3 km thick slab extending to about 7 km depth. This unit has been correlated with the Logan gabbro roughly 300 km to the northwest, constraining offset on the San Andreas fault (Ross, 1970).