12 Guaymas Basin and Gulf of California Subsurface Systems and Energy Applications

This session will present subsurface research in the Gulf of California, especially IODP Expedition 385 to Guaymas Basin that explored the linkages between tectonics, magmatism, sedimentation, hydrothermalism, carbon cycling, and microbial life. Merged sessions: Subsurface Research  in Guaymas Basin and the Gulf of California and Energy Resources and Economic Development in Baja California: Fossil, Renewable, and Transition Minerals.

Wednesday, 22 April 2026
1:30 PM - 5:30 PM
LMH, Isla Carmen

A Mechanical Model for Sill Emplacement in Sedimented Rift Basins: Insights from the Guaymas Basin

Paper number: 12-2
Program: Technical Sessions
Time: 1:50 PM – 2:05 PM

Authors

Abstract

Understanding sill emplacement is key to interpreting magmatic plumbing systems and their thermal impact on sedimentary basins. Conventional models emphasize mechanical contrasts, diagenetic barriers, or buoyancy forces as the primary controls, yet their role in shallow unconsolidated, water-rich sediments remains debated.

We investigate sill emplacement in an active rift setting, in the Guaymas Basin, focusing on the Ringvent intrusion by comparing sill-affected and unaffected sites drilled during IODP Expedition 385. We integrate wireline logs, laboratory measurements, and core descriptions to characterize density, porosity, P-wave velocity, AVS shear strength, and opal transitions in surrounding sediments.

Through a model of lithospheric strength as a function of depth, we found compaction-driven trends that reveal progressive increases in density and strength, and decreasing porosity with depth. However, Ringvent intrudes a distinct siliceous claystone interval that deviates from these trends: a porous, water-saturated, ductile layer with unusually low yield strength, bounded by a brittle, indurated claystone and a stiff elastic-plastic layer.

Contrary to conventional assumptions, sill emplacement is not guided by sharp lithological interfaces or diagenetic barriers. Instead, our results indicate that lateral propagation was promoted by the host sediments' finite strain rheology. The combination of low shear strength and high porosity enhanced hydrostatic pressure equilibration, suppressed vertical dike propagation, and favored sustained lateral sill growth, bending the overlying strata.

These findings highlight the critical role of rheological heterogeneity in controlling sill emplacement and provide a testable framework for young rift basins worldwide, where weak, ductile horizons may localize magma intrusion and shape crustal architecture.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-410842

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