The Late Cretaceous batholithic massifs of Sierra La Laguna and Sierra La Trinidad, southern Baja California, Mexico: constraints on extensional structures from geology, geochronology, and thermobarometry

The Los Cabos Block, at the southern end of Baja California, exposes part Late Cretaceous Peninsular Ranges Batholith over 2700 km2. In block, Batholitic Complex is exposed in two massifs, Sierra La Laguna to west and Trinidad east. sierras are separated by ~75 km long, N-S striking, San José del Cabo extensional fault system, homonymous basin. Here, we present field observations, new U–Pb Ar–Ar ages, thermobarometric determinations constrain magmatic history this composite batholith structural relations between Trinidad. Field observations show that comprises several granodiorite bodies, felsic sills, dikes with complex magma mingling mixing features typical an upper-middle crustal system within a mush zone intermediate silicic composition. zircon crystallization ages for massif define main period plutonism ~89.9 73.9 Ma, progressively younger from Zircon chemistry published whole-rock isotopic data point mantle contributions arc magmatism significant thickening time. Hornblende thermobarometry suggests wide range interval (depth: 12–18 km; temperature: 670–740°C). has more narrow compositional range, like those eastern, lower depth, indicating it represents shallower portion system. integration our study previous research indicates hanging wall block which implies low angle geometry (<30°) older age activation than previously considered (>18 Ma).