41 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 III)

This session highlights recent research on the Gulf of California–Salton Trough plate boundary from ~12 Ma to today. We welcome terrestrial and marine studies involving tectonics, basin analysis, volcanology, sedimentology, and more. English or Spanish.

Friday, 24 April 2026
1:30 PM - 5:30 PM
LMH, Fiesta Terrace Salon

Age and structure of Pliocene volcanic and marine sedimentary strata, Southeastern Isla Ángel de la Guarda, Gulf of California, Mexico

Paper number: 41-11
Program: Technical Sessions
Time: 4:40 PM – 5:10 PM

Authors

Abstract

In the southeastern part of Isla Ángel de la Guarda (IAG), in the Gulf of California, Pliocene andesite to dacite lava flows and sedimentary units preserve an important history of the evolving Pacific North America plate boundary. Mapped volcanic and sedimentary rocks dip moderately to gently to the east. Geochemical data from X-ray fluorescence suggests that the units are more silicic toward the northwest and become less silicic towards the southeast.  40Ar/39Ar ages of the lava flows range from 3.9 to 2.7 Ma. These subaerial lava flows are separate in age and composition from the Pliocene volcanic sequences from the Puertecitos volcanic province to the west on the Baja California peninsula. The geochemistry follows a calcalkaline trend corresponding to bulk continental crust. A package of fossiliferous sediments including sandstone, gypsum, and limestone, with pectens, oysters, and microfossils is interbedded between the 3.9 and 2.75 Ma andesites. In the southern area these lava flows overlie Cretaceous tonalite. The northern area contains interbedded rhyolite lavas as well as some Miocene-Pliocene rhyolite beneath the dated part of the section. At the time of these Pliocene eruptions and intervening marine sedimentation, IAG was already separated from the Baja California peninsula and moving as an independent continental microplate within the Gulf of California oblique rift system before being mostly transferred to the North America plate after 3 Ma.

After the Pliocene eruptions and tilting, the southeast part of the island was overlain by at least three generations of extensive, non-marine terraces, distinguished by differences in elevation and surface roughness in satellite imagery, drone-based DEMs, and field geology. The terraces and lava flows are cut by several sub-parallel, NNE-striking normal faults. Fault motion is dominantly down-to-the-east with <100 m of total offset per fault. A few faults show evidence for minor dextral motion. Luminescence ages indicate that the terraces are Late Quaternary (Higa et al, Tectonics 2021).  The most recent onshore fault activity occurred in the last ∼50 kyr. This part of IAG is accommodating extensional strain adjacent to the Ballenas transform fault zone west of the island, without any accompanying volcanic activity.

 

 

 

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

doi: 10.1130/abs/2026CD-410788

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