44-18 Petrologic and Geochemical Constraints on the Volcanic Evolution of the Cerralvo Basin, Southern Gulf of California

Abstract:

The Cerralvo Basin, located in the southern Gulf of California, represents a key geological setting for investigating tectonomagmatic processes associated with the transition from subduction to lithospheric extension. This study presents a petrographic, geochemical, and geochronological characterization of volcanic, volcaniclastic, and sedimentary rocks recovered from submarine escarpments within the basin, with the goal of reconstructing its magmatic and tectonic evolution.

Samples were collected during the FK210922 cruise of the Schmidt Ocean Institute using the ROV SuBastian (dives S0-461 and S0-469) at water depths ranging from 245 to 996 m. The analyzed lithologies include andesitic lava flows, volcanic breccias, tuffs, and fossil-bearing sedimentary deposits, recording a complex depositional and volcanic history. Petrographic observations and whole-rock geochemical data indicate predominantly calc-alkaline affinities consistent with arc-related magmatism, along with evidence for post-emplacement hydrothermal alteration.

Four main evolutionary stages are recognized: (1) explosive volcanism, (2) transgressive terrigenous sedimentation with fossiliferous deposits, (3) renewed explosive volcanic activity, and (4) a final phase of effusive andesitic volcanism. K–Ar geochronology of the volcanic groundmass constrains the effusive andesitic stage to ca. 20–16 Ma, These results provide new petrographic and geochemical constraints on the evolution of the western Gulf of California margin and establish a comparative framework for understanding magmatic and sedimentary processes in similar tectonically active basins.

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