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Newly identified hydromagmatic volcaniclastics of Isla Guadalupe, Mexico

James K. Muller1, Rebecca Ruwe2, Nick Varley3, Marco Rodriguez Delgado3, Alejandra Reyes Torres4, Jamie R. Worthington1, Emily J. Chin1

  • Affiliations: 1Scripps Institution of Oceanography, UC San Diego, La Jolla, USA; 2Institut für Geowissenschaften, Johannes Gutenburg-Universität Mainz, Mainz, Germany; 3Facultad de Ciencias, Universidad de Colima, Colima, Mexico; 4Facultad de Ciencias, Universidad Autónoma de Baja California, Ensenada, Mexico

  • Presentation type: Poster

  • Presentation time: Monday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 200

  • Programme No: 3.3.27

  • Theme 3 > Session 3

Abstract

The geology of Isla Guadalupe -- located astride an abandoned spreading center west of Baja California -- was reconnoitered in the 1960s--1970s. Mapping showed the island to comprise two overlapping shield volcanoes overlain by a younger flank/fissural series; both stages span basalt to trachyte compositions. However, while that mapping also identified pyroclastic deposits, the nature of such rocks and the eruption(s) that formed them have thus far been unexplored. This work reports on a 2024 field campaign that studied these rocks in greater detail to ascertain the dynamics of their emplacement. The volcaniclastics are diverse in character, including, e.g., (a) white, massive matrix-supported ash tuffs; (b) yellowish, grain-supported, coarse pumice deposits with diffuse grading and occasional m-scale thicknesses; and (c) finely bedded, gray-black, occasionally cross-stratified, grain-supported ash and lapilli. The latter often host lenses of coarser pumice lapilli. Lithics and crystals are common accidentals in all deposits. Multiple deposit types can be found within a single stratigraphic sequence, e.g., one section grades upwards from gray-black ash and fine lapilli to a ~0.5 m thick pumice lapilli unit, overlain by a capping series of gray-black ash beds. We infer that many are hydromagmatic deposits, previously unreported at Isla Guadalupe. Differences in grain size and componentry likely reflect different eruption styles associated with magma-water ratios that varied from "wetter" (tuffs, bedded ash surge deposits) to "dryer" (i.e., more magmatic; pumice lapilli airfall(?)), even as discrete phases within a single eruption.