2 Future Directions in Mineralogy and Petrology: A Session for Undergraduate and Graduate Researchers

Sunday, 21 April 2024
1:30 PM - 5:30 PM
Fiji Ballroom, Oasis CC

INSIGHTS INTO ISLAND-ARC MAGMATISM: A PETROGRAPHIC STUDY OF MAFIC ENCLAVES IN THE UTUADO PLUTON, PUERTO RICO

Paper number: 2-4
Program: Theme Sessions
Time: 2:15 PM – 2:35 PM

Authors

Abstract

Puerto Rico comprises over 17 intrusive bodies associated with the Greater Antilles island arc system, two of which are quite large: the San Lorenzo Batholith (~500 km2) and the Utuado Pluton (~220 km2). The Greater Antilles system ceased magmatic activity in the Oligocene and subsequent uplift and erosion exposed granodiorite, quartz-monzonite, diorite and tonalite, and gabbro. This study focuses on mafic enclaves that are hosted in granodiorite within the Utuado Pluton, north-central Puerto Rico. Understanding these island arc remnants is crucial for revealing the processes associated with crust generation and the evolution of island arc systems.

The host-rock is a phaneritic, equigranular granodiorite consisting of quartz, feldspar, hornblende, and minor biotite with some alteration to chlorite. Crystalline mafic enclaves are present within the granodiorite, and range in size from ~5 cm - 45 cm. At the outcrop scale, variations in textures are present, with some enclaves containing large (~5 mm) plagioclase feldspar and amphibole phenocrysts that are subhedral to euhedral in shape, with minor quartz. Phenocrysts are present within a finer grained matrix, and some appear to be oriented.

Ten enclave samples were collected and will be made into thin sections for light microscopy. Mineralogy and textures thereof will be extensively characterized at the micrometer scale with a specific focus on mineral phases such as amphibole and plagioclase. Bulk-rock major and trace elements will be analyzed via XRF and ICP-MS. Previously, few studies have investigated the origin of the Utuado Pluton. Particularly, the enclaves have been described as xenoliths with similar composition to the granodiorite host-rock. However, field investigations suggest that textural and mineralogical differences between the host-rock and enclaves exist. This will be further explored through a comprehensive mineralogical and geochemical characterization of the mafic enclaves.

Geological Society of America Abstracts with Programs. Vol. 56, No. 3

doi: 10.1130/abs/2024NC-398847

© Copyright 2024 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.