GEOCHEMICAL CHARACTERIZATION AND CORRELATION OF TEPHRA INTERVALS IN QUATERNARY STRATA RECOVERED DURING IODP EXPEDITION 385 IN THE GUAYMAS BASIN, GULF OF CALIFORNIA

The International Ocean Discovery Program (IODP) Expedition 385 recovered more than four kilometers of Quaternary sediments at eight different drill sites in the Guaymas Basin, Gulf of California. The Guaymas Basin is a young marginal rift basin characterized by seafloor spreading, and has rapid biogenic and terrigenous sediment deposition, seamounts, and one subaerial volcano (Isla Tortuga). IODP Expedition 385 scientists found thin tephra layers sparsely interbedded within the Quaternary sediments cored at several sites. Preliminary inter-site tephra correlations based on petrographic analyses are now being evaluated using geochemical techniques. We analyzed a total of 48 tephra samples to determine their major and trace element compositions. We performed 1,677 single glass analyses on basaltic glass using an electron microprobe for major elements and 480 single glass analyses using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) for trace element compositions. Results are integrated with petrographic analyses of tephra layers and compared to subaerial volcanic units from Isla Tortuga to: 1) elucidate the source(s) of the tephra layers, 2) determine the timing of volcanic ash deposition, and 3) produce a regional model of volcanic and tephra stratigraphy for the Guaymas Basin. Determining the age and source of tephra intervals provides crucial insights into the eruptive history and magma rheology of local volcanoes, enabling the formation of multi-scale interpretations of volcanic activity in the Gulf of California.