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

Geochemical Characterization, Correlation, and Provenance of Tephra Intervals in Quaternary Strata Recovered During IODP Expedition 385 in the Guaymas Basin, Gulf of California

Paper number: 1-3
Program: Technical Sessions
Time: 8:35 AM – 8:50 AM

Authors

Abstract

The International Ocean Discovery Program (IODP) Expedition 385 recovered more than four kilometers of Quaternary sediments from eight drill sites in the Guaymas Basin (GB), Gulf of California, a young marginal rift basin characterized by rapid sediment deposition, sills, volcanic knolls, and one subaerial volcano (Isla Tortuga). Thin tephra layers interbedded with these sediments were analyzed to characterize their composition, constrain their provenance, and establish a tephrostratigraphy. Preliminary petrographic analyses (point counts; n=300) of 36 of the coarser tephra samples document the types and proportions of fragments by:  glass types and their degree of crystallinity, phenocryst mineralogy, particle morphologies, and particle shapes. Building on the petrographic observations, 48 pyroclastic samples were analyzed using an electron microprobe (1,677 single glass analyses) and LA-ICP-MS (480 single glass analyses) to determine major and trace element compositions. Geochemical data highlight five compositionally distinct intervals (age range of ~252 ka and 96ka), exhibiting tholeiitic, MORB-like signatures with fractional crystallization trends. Stratigraphically younger tephras are more primitive, suggesting reduced crustal residence times and possible recharge events in the magma chamber. Comparisons of geochemical signatures with regional volcanic centers indicate that at least the youngest of these intervals was sourced from Isla Tortuga, which is also supported by evidence of epiclastic debris reworked by coastal erosion of the volcanic edifice. This study provides the first systematic geochemical dataset for marine tephras in the GB and the Gulf of California oblique rift, revealing an episodic, compositionally evolving volcanic system influenced by mantle metasomatism, tectonics, and sedimentary processes. These results improve understanding of volcanism at sedimented-nascent oceanic spreading centers and establish a framework for future correlation of young tephra deposits in the Guaymas Basin and surrounding basins in the central-southern Gulf of California.

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

doi: 10.1130/abs/2026CD-411041

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