1 Tectonic Controls on Cenozoic Volcanism in the Gulf of California-Salton Trough Region and the Adjacent Southwestern North American Plate Boundary

Tectonic reconstructions of the southwestern North American plate boundary provide an excellent framework for understanding Cenozoic volcanism (arc, rift, slab window, seafloor) in this largely extensional and transtensional setting. Geologic, geochemical and geophysical submissions encouraged.

Wednesday, 22 April 2026
8:00 AM - 10:00 AM
LMH, Deli

Possible Comundú Group equivalent in Bahia de los Angeles, Baja California

Paper number: 1-6
Program: Technical Sessions
Time: 9:20 AM – 9:35 AM

Authors

Abstract

We identify three sedimentary sections in the Angostura Canyon of Sierra Libertad, the Salorio Range and the northern tip of the Cerros de Agua de Higuera in Agua Amarga.  ranges west of Bahia de Los Angeles that underlie rhyolitic ignimbrites likely equivalent to the widespread 12.5 Ma San Felipe Tuff (Stock et al, 1999). Two of these sections have ~100 m of continuous section exposed, while the third has ~60 m of section with covered intervals. The sections are in basal contact with underlying crystalline basement and in angular unconformity with the overlying San Felipe Tuff.  They are characterized by a coarse basal section of variable thickness characterized by clasts that transition from mostly metamorphic at the base to mostly plutonic towards the top.  Imbricated clasts indicate an east to west paleocurrent. After an abrupt infusion of felsic tuff, the section transitions to planar bedded sandstone with reworked abundant lapilli. Finally, two of the three sections end with large-scale channelized cross-bedded sandstones with cross-sets of 4-5 m with little-to-no ash in them. This suggests the development of a large integrated drainage network.   We sampled sandstone and ash beds for zircon U-Pb analysis from each section to assess whether these sections correspond to a single basin with lateral facies changes that has been dismembered by subsequent faulting or whether the facies variations correspond to different sub-basins with intervening basement highs. The San Felipe Tuff lies directly on crystalline basement in many locations around the stratigraphic section exposures, suggesting that the faulting that leads to either of those scenarios predates it. The mid-Miocene of the overlying San Felipe Tuff (Stock et al., 1999) implies that these rocks are equivalent to the Comondú Group, which is widely exposed further south and also records westward paleocurrents (Umhoeffer et al., 2001).

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

doi: 10.1130/abs/2026CD-411076

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