28-4 Fault and Fissure Scaling at the Alarcón Rise: Tectonic Extension, Lithospheric Flexure, and Magmatic Controls in the Gulf of California Rift

Session: Recent Advances in the Gulf of California Oblique Rift: Offshore and Onshore Studies // Avances Recientes en el Rift Oblicuo del Golfo de California: Estudios Marinos y Terrestres (Part I)

Presenting Author:

Luis Vega-Ramirez

Authors:

Vega-Ramirez, Luis Angel¹, Spelz-Madero, Ronald Michael², Contreras-Pérez, Juan³

(1) Departamento de Geología Costera, Facultad de Ciencias Marinas, Universidad Autónoma de Baja California, Ensenada, Baja California, Mexico, (2) Departamento de Geología Costera, Facultad de Ciencias Marinas, Universidad Autónoma de Baja California, Ensenada, Baja California, Mexico, (3) Departamento de Geología, Centro de Investigación Científica y de Educación Superior de Ensenada, Ensenada, Baja California, Mexico,

Abstract:

The Alarcón Rise is an active intermediate spreading center located at the mouth of the Gulf of California. High-resolution bathymetric data (1 m horizontal, 0.2 m vertical) acquired in 2012 and 2015 using an autonomous underwater vehicle reveal a dense network of normal faults and fissures cutting pillow mounds, sheet flows, and a rhyolitic lava dome. This study analyzes fault and fissure populations within a 6.9 × 1.5 km² area encompassing the neovolcanic axis and adjacent axial summit trough in the northeastern Alarcón Rise.

Fault and fissure populations exhibit distinct scaling behaviors. Normal faults follow a power-law length distribution, consistent with nucleation under tectonic extension and growth through segment interaction, overlap, and linkage. In contrast, fissures display an exponential length distribution, suggesting formation controlled by lithospheric flexure and alignment perpendicular to the maximum tensile stress within young lava flows (~0.6 ka, ¹⁴C). These contrasting distributions indicate fundamentally different growth mechanisms for faults and fissures at this spreading center.

Faults proximal to an off-axis rhyolitic dome show asymmetric displacement profiles with steep gradients oriented toward the dome. These profiles indicate that the dome acts as a mechanical barrier that restricts lateral fault propagation and promotes the accumulation of vertical displacement. Compressive stresses associated with dike intrusion appear to suppress fault nucleation and propagation locally, highlighting the role of magmatic and lithological heterogeneities in fault evolution.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3, 2026

doi: 10.1130/abs/2026CD-12581

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