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

• Published in: International geology review 2023-12, Vol.ahead-of-print (ahead-of-print), p.1-26
• Main Authors: Gutiérrez-Navarro, Rodrigo, Ferrari, Luca, Orozco-Esquivel, Teresa, Hernández-Quevedo, Gabriela, Maldonado, Roberto
• Format: Article
• Language: English
• Subjects: Age; Batholiths; Cretaceous; Crystallization; Data points; Dikes; Earth mantle; Embankments; Geochronology; Geochronometry; Geology; Gulf of California; Hanging walls; Lava; Los Cabos Block; low-angle fault system; Magma; Massifs; Peninsular Ranges Batholith; Sills; thermobarometry; U-Pb and Ar-Ar dating; Zircon
• ISSN: 0020-6814; 1938-2839
• DOI: 10.1080/00206814.2023.2196553

The Los Cabos Block, at the southern end of Baja California, exposes part of the Late Cretaceous Peninsular Ranges Batholith over 2700 km 2 . In the Los Cabos block, the Los Cabos Batholitic Complex is exposed in two massifs, Sierra La Laguna to the west and Sierra La Trinidad to the east. The two sierras are separated by the ~75 km long, N-S striking, San José del Cabo extensional fault system, and the homonymous basin. Here, we present field observations, new U-Pb and Ar-Ar ages, and thermobarometric determinations to constrain the magmatic history of this composite batholith and the structural relations between Sierra La Laguna and Sierra La Trinidad. Field observations show that the batholith at Sierra La Laguna comprises several granodiorite bodies, felsic sills, and dikes with complex magma mingling and mixing features typical of an upper-middle crustal system within a mush zone of intermediate to silicic composition. U-Pb zircon crystallization ages for La Laguna massif define the main period of plutonism between ~89.9 and 73.9 Ma, with progressively younger ages from west to east. Zircon chemistry and published whole-rock isotopic data point to mantle contributions to arc magmatism with significant crustal thickening with time. Hornblende thermobarometry suggests a wide range interval of crystallization (depth: 12-18 km; temperature: 670-740°C). Sierra La Trinidad has a more felsic and narrow compositional range, with crystallization ages like those from the eastern, younger part of Sierra La Laguna and lower crystallization depth, indicating that it represents the shallower portion of the Los Cabos Batholitic Complex magmatic system. The integration of our study with previous research indicates that Sierra La Trinidad is the hanging wall block of the San José del Cabo fault system, which implies a low angle geometry (18 Ma).