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
KEYNOTE: Competing Models for the Opening of the Gulf of California: Constraints from the Northern and Central Gulf
Paper number: 19-2
Program: Technical Sessions
Time: 8:07 AM – 8:37 AM
Authors
Abstract
In early studies of plate tectonics, the Gulf of California was identified as the modern plate boundary between the Pacific and North America plates. It was not known how the Baja California peninsula (BC), which started on the North America plate, was transferred onto the Pacific plate. Because BC south of the Agua Blanca Fault has been a rigid block since Miocene time, initial models proposed a uniform distance of opening along the entire length of the Gulf of California. This allowed the style of extension to vary along the length of the Gulf while the net displacement was the same. True sea floor spreading started in the southern Gulf basins while the northern Gulf basins (Upper Delfin, Lower Delfin, and Tiburon) experienced distributed extension.
Gastil et al (1973) suggested a net slip of 300 km between conglomerate outcrops near San Felipe and in coastal Sonora. Subsequent findings including detailed geological mapping of both margins, volcanic stratigraphy, improved geochronology, and paleomagnetic studies revealed 6.3 Ma and 12.5 Ma units that could be correlated across the plate boundary in this sector. An updated model of displacement between the Pacific and North America plates (Demets and Merkouriev 2016) suggests that the displacement across the N Gulf transform faults and surrounding continental blocks, including rotational deformation and detachment faulting, matches well to the expected plate motion since 6.3 Ma. The transform faults are not parallel to the proposed direction of Pacific North America plate motion, so some post-6.3 Ma orthogonal motion is required. There was relatively steady motion since 10 Ma, and no change in azimuth of the plate motion. The plate circuit requires more displacement since 12.5 Ma than can be found in the Gulf. Fault-bounded basins started developing from 9 to 7 Ma based on ages of the volcanic rocks and sedimentary rocks on Tiburon Island and in coastal Sonora, with marine flooding by 6.3 Ma (Umhoefer et al., 2018; Darin et al. 2025). In the northern Gulf transect, widespread deposits from a supervolcano eruption at 12.5 Ma indicate that no basin was present then. This requires a more complicated history prior to 6.3 Ma with additional slip either west of BC or on unrecognized faults in Sonora.
Geological Society of America Abstracts with Programs. Vol. 58, No. 3
doi: 10.1130/abs/2026CD-410829
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