42 Celebrating the 50th Anniversary of the Department of Geoscience at University of Nevada, Las Vegas

Thursday, 17 March 2022
1:30 PM - 5:30 PM
CBC-A 106

DEVELOPING NEW TOOLS TO ASSESS REDOX DIVERSITY IN BASALTS AND THEIR MANTLE SOURCES: A CASE STUDY IN THE RIO GRANDE RIFT

Paper number: 42-6
Program: Symposia Sessions
Time: 3:00 PM – 3:20 PM

Authors

  • Aaron Bell Presenting Author
    University of Colorado Boulder, Boulder, CO
  • Laura Waters
    New Mexico Institute of Mining and Technology, Socorro, NM

Abstract

The redox record preserved in primitive basaltic magmas is an accessible, albeit indirect, archive of redox heterogeneity among various geochemical reservoirs within Earth’s mantle. Quantitative redox studies basalts can provide important new insights into the spatial and temporal changes in the oxidation state of various geochemical reservoirs in the mantle which are driven by the cycling of oxygen between surficial lithospheric material and the mantle. Primitive, olivine-phyric basalts from the Rio Grande Rift are well suited to addressing questions about the processes and intensive variables that are important for generating magmatic redox heterogeneity and how these variables relate to mantle processes, as they originate from a range of depths and mantle sources. To access the redox record in the non-glassy, RGR basalts, we have calibrated two thermodynamic oxybarometers (olivine-aSiO2-spinel and Cr Valence in Olivine) and applied them to a suite of Quaternary RGR basalts. Our new models yield oxygen fugacities that range from ∆QFM –0.5 to +1.2 for RGR basalts in the Albuequrque basin and Jemez Lineament. The southernmost basalt from the Potrillo volcanic field has the most reducing signature (∆QFM–0.5); basalts become nearly an order of magnitude more oxidizing northward through the rift (~∆QFM+0.5). Redox variation in basalts from at least one volcanic field (Cat Hills) span nearly an order of magnitude (∆QFM+0.6 to +1.3), despite close geographic proximity, suggesting a locally heterogeneous mantle source. Samples with elevated oxidation states are correlated with Nd isotopic signatures associated with the lithospheric mantle and lower crust; those samples with low fO2 values reflect an asthenospheric Nd isotopic signature. We postulate that the oxidized signatures of the RGR basalts are a product of melting a variably metasomatized mantle, residual from Farallon subduction, and that any metasomatized mantle in the southern part of the RGR has been exhausted.

Geological Society of America Abstracts with Programs. Vol. 54, No. 2

doi: 10.1130/abs/2022CD-373740

© Copyright 2022 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.