19 Tectonic Evolution and Competing Models for the Opening of the Gulf of California: From Subduction to Oblique Rifting
This symposium will explore major controversies in the tectonic evolution of the Gulf of California, highlighting the timing, kinematics, and driving mechanisms behind its transition from subduction to oblique continental rifting and transform faulting.
Thursday, 23 April 2026
8:00 AM - 12:00 PM
LMH, Fiesta Terrace Salon
Fault architecture and strain localization at the Alarcón Rise, Gulf of California: insights into oblique ridge-transform systems
Paper number: 19-12
Program: Technical Sessions
Time: 10:53 AM – 11:08 AM
Authors
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KatherineMonterey Bay Aquarium Research Institute, Moss Landing, California
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Jennifer PaduanMonterey Bay Aquarium Research Institute, Moss Landing, California
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Ryan PortnerSan José State University, San José, California
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David ClagueMonterey Bay Aquarium Research Institute, Moss Landing, California
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Luis Vega-RamírezUniversidad Autónoma de Baja California, Ensenada, Baja California
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David CaressMonterey Bay Aquarium Research Institute, Moss Landing, California
Abstract
The Alarcón Rise represents the northernmost segment of the East Pacific Rise and the first fully developed oceanic spreading center within the Gulf of California, marking a key stage in the transition from subduction-related tectonics to oblique rifting along the Pacific–North America plate boundary. Following the capture of the Baja California microplate and the establishment of ridge–transform geometry, the Alarcón Rise provides a natural laboratory to evaluate how strain is partitioned and localized in an oblique oceanic rift system.
Here we present new observations on fault and fissure architecture along the neovolcanic zone of the Alarcón Rise derived from high-resolution (1 m) autonomous underwater vehicle (AUV) bathymetry collected by MBARI, complemented by remotely operated vehicle observations. Detailed mapping and quantitative analysis of tectonic structures reveal that extensional strain is primarily accommodated by normal faults rather than open fissures, with estimated tectonic extension ranging from ~2.8–5% along most of the ridge axis and increasing to ~8.8% near the Pescadero Transform Fault. Fault density, throw, and orientation vary systematically along-axis, reflecting the influence of ridge–transform interactions and differential lithospheric flexure.
The spatial distribution of faults indicates progressive strain localization toward the ridge axis, with fissures representing an early stage of brittle deformation that evolves into through-going faults as the lithosphere cools and thickens. Near-transform segments exhibit fault populations and strain magnitudes comparable to those observed at slow-spreading ridges, suggesting enhanced mechanical coupling and localized bending stresses associated with transform fault geometry. These patterns imply that lithospheric flexure, rather than far-field extension alone, exerts a first-order control on fault development at the Alarcón Rise.
Our results provide direct observational constraints on how extensional strain is partitioned in an oblique ridge-transform setting. The fault architecture of the Alarcón Rise highlights the role of ridge–transform interactions in shaping the structural evolution of the southern Gulf of California and offers important insights into deformation processes operating in oblique oceanic spreading systems.
Geological Society of America Abstracts with Programs. Vol. 58, No. 3
doi: 10.1130/abs/2026CD-411035
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