11 Future Voices in Geoscience- Undergraduate Research Posters

This session is for two-year college and four-year college and university students presenting research posters in any subdiscipline of geosciences. Posters and presentations will be judged for awards.

Monday, 18 May 2026
8:00 AM - 5:30 PM
Alvarado D/E

Age and Metamorphic Conditions of Fluid Interaction in Metasomatized Rocks at Cemetery Ridge, AZ

Paper number: 11-16
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

Orocopia Schist comprises metamorphosed trench sediments that were transported within the subduction channel during Laramide flat-slab subduction and is exposed at Cemetery Ridge in southwestern Arizona. The exposure is surrounded by intrusive igneous rocks dated 20-22 Ma. Here we report on data collected from samples of spotted gneiss, a lithology within the quartzofeldspathic gneiss interpreted to have developed by mechanical mixing with actinolite, and samples of potassic gneiss. We analyzed titanite and monazite by simultaneously collecting isotopes for U-Pb dating and trace element abundances using the laser ablation split-stream (LASS) laboratory at the University of California, Santa Barbara. Monazite 207Pb-corrected ages from three samples of spotted gneiss (THCR24-3, THCR24-3A, CRSA24-4A) range from 22 to 25 Ma, and titanite lower intercept Tera–Wasserburg ages from two samples of spotted gneiss (CRSA24-3, CRSA24-2) range from 21 to 22 Ma. Trace element abundances in the analyzed grains do not display temporally correlated enrichments or depletions. However, there is scatter spanning orders of magnitude variation in both monazite and titanite trace element abundances. A negative Eu anomaly is displayed by the monazite rare earth element (REE) data, while both negative and positive Eu anomalies occur in titanite. Isochemical plots of mineral assemblage stability were produced for two dated samples of potassic gneiss (THCR24-3, THCR24-3A). Overlapping mineral assemblage fields indicate peak pressure and temperature conditions of 4.5-5 kbar and 700-725 °C. The plot for one sample predicts the presence of a small amount (~2% vol.) of partial melt, which is visible along feldspar grain boundaries. The conditions of metamorphism and concurrence of Miocene metamorphic ages with the age of the surrounding intrusions provide evidence of contact metamorphism.  We interpret that evolving and Eu-depleted fluids were expelled from the crystallizing granite and infiltrated rocks at Cemetery Ridge. The fluid imparted its trace element signature to the actively crystallizing monazite and titanite. The production of Miocene granite and related metasomatic alteration at Cemetery Ridge may have been caused by foundering of the lithospheric mantle at that time.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410669

© Copyright 2026 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.