75-23 A Geologic Map of Isla Tortuga: A Contribution to the Volcanic History of the Guaymas Basin, Gulf of California (México)

Session: Mineralogy, Geochemistry, Petrology, and Volcanology Student Session (Posters)

Poster Booth No.: 316

Presenting Author:

Emilia Pelegano-Titmuss

Authors:

Pelegano-Titmuss, Emilia¹, Piña, Adriana², Stock, Joann³, Hausback, Brian⁴, Höfig, Tobias⁵, Martín-Barajas, Arturo⁶, Batiza, Rodey⁷

(1) Caltech, Pasadena, CA, USA; CUNY Hunter College, New York, NY, USA, (2) Caltech, Pasadena, CA, USA, (3) Caltech, Pasadena, CA, USA, (4) California State University - Sacramento, Sacramento, CA, USA, (5) International Ocean Discovery Program, Texas A&M University, College Station, TX, USA; Jülich Research Center, Jülich, Germany, (6) CICESE, Ensenada, BC, Mexico, (7) University of Minnesota, Minneapolis, MN, USA,

Abstract:

Isla Tortuga (IT) is a young, basaltic volcanic island located in the Guaymas Basin (GB), which is a pull-apart basin in the Gulf of California (GOC) oblique rift system of México. The GOC is located at the boundary of the Pacific and North America plates and occupies part of a 1750 km-long oblique divergent plate boundary. There is no detailed map for the geologic units cropping out on IT, besides a general geologic map provided by Batiza (1978). In 2023, an expedition to IT was conducted to collect more samples for petrographic, geochemical, and geochronological analyses. In addition, sonar data around the island was collected using a Lowrance Fish Finder. Previously, in 2019, the International Ocean Discovery Program Expedition 385 drilled several kilometers of sediments at different sites in the GB and found several sills that have intruded the Quaternary sediments. Petrographic comparison showed that the offshore sills and samples collected from IT have similar mineral textures and composition. Additionally, the geochemical compositions of these units and the GB sills suggest that the early eruptions at IT may correspond to the sill compositions. Subsequent eruptions indicate magmatic evolution away from the early composition. The latest IT eruptions suggest a return to more primitive composition, possibly reflecting a magma recharge event that has been proposed to have occurred before the last eruption. It has been hypothesized that IT and the sills may be part of the same magmatic plumbing system in the GB. Therefore, IT is a key component of the volcanic and tectonic history of the GB. In this study, we are presenting a new, detailed geologic map of IT that has been produced using QGIS. We mapped a total of twenty-one units on IT from Holocene to Pleistocene ages. This study represents the first detailed geologic map of Isla Tortuga, as well as helps to constrain the chronological history of the magmatic events in the GB that led to the formation of IT and the sill emplacement.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.