75-32 Zircon U-Pb and Lu-Hf isotopic data from the Lesser Antilles Island Arc – evidence for incorporation of Orinoco River accretionary prism material into mantle derived arc volcanics
Session: Mineralogy, Geochemistry, Petrology, and Volcanology Student Session (Posters)
Poster Booth No.: 325
Presenting Author:
Marlin HumphreysAuthors:
Humphreys, Marlin S.M.1, Kimbrough, David L.2(1) Stanford Online High School, Redwood, California, USA, (2) Department of Earth and Environmental Sciences, San Diego State University, San Diego, California, USA,
Abstract:
The Lesser Antilles is an intra-oceanic arc with Atlantic seafloor slowly subducting westward beneath the Caribbean plate. The Orinoco River of South America discharges into the Lesser Antilles trench to produce a thick accretionary prism with material from the Precambrian Guyana Shield. The trench farther north has thinner, mainly pelagic sediments. This study is a test to see whether the N-S contrast in trench sediment exerts influence on arc volcanic rock composition. Rock samples and modern sand from beaches and drainages were collected from nine islands stretching 620 km along strike from Saba in the north to Bequia in the south. Zircon U-Pb and Lu-Hf isotope ratios were determined by LA-ICPMS at the University of Arizona. Of 129 grains analyzed, 79% were Pleistocene (0.17-2.48 Ma) with mostly positive eHf(i) values (14-8) reflecting derivation from juvenile mantle sources, but no clear N-S variation. Sand from two islands, Bequia (13.0°N) and Guadalupe (16.3°N), yielded 21 xenocrystic zircon (309-1959 Ma) with lower eHf(i) values (7 to -10). These grains match Orinoco River zircon indicating recycling of accretionary prism material into the mantle magma source region. Beach sand zircon from Martinique in the middle of the arc (14.5°N) is anomalous, with 15 Pleistocene zircon yielding a smoothly variable spread of eHf(i) values from +11 to +1.4, with two outlier grains with -5.8 and -20. This reflects heterogeneity in mantle sources due likely to incorporation of accretionary prism sediment via subduction. We conclude that sediment subduction influences arc volcanic rocks, but with no clear N-S variation.
Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025
© Copyright 2025 The Geological Society of America (GSA), all rights reserved.
Zircon U-Pb and Lu-Hf isotopic data from the Lesser Antilles Island Arc – evidence for incorporation of Orinoco River accretionary prism material into mantle derived arc volcanics
Category
Topical Sessions
Description
Session Format: Poster
Presentation Date: 10/19/2025
Presentation Room: Hall 1
Poster Booth No.: 325
Author Availability: 3:30–5:30 p.m.
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