T98 Volcanism and Tectonics along Rifts and Volcanic Arcs: Understanding the Relationships between Timing, Volumes, and Distributions II

Tuesday, 27 October 2020
5:30 PM - 8:00 PM
Meeting Rooms

MAGMATISM IN THE EOCENE EMIGRANT PASS VOLCANIC FIELD, NORTHERN NEVADA: TRACE ELEMENT AND ISOTOPIC INDICATORS OF MAGMA SOURCES AND CRUSTAL INFLUENCES

Paper number: T98-13
Program: Technical Sessions
Time: 7:30 PM – 7:40 PM

Authors

Abstract

The Emigrant Pass Volcanic Field is a part of the Eocene igneous activity associated with continental arc volcanism in northern Nevada, western United States. The aim of this project is to use whole-rock major element, trace element, and the isotopic compositions of lead, hafnium, strontium and neodymium to determine the magma source(s) of this volcanic suite and establish if crustal contamination is important in petrogenesis. The Emigrant Pass suite is also important in that it falls within the transition zone between Phanerozoic accreted terrane basement to the west and Precambrian basement to the west, and isotopic compositions will indicate which of the two basement terranes influences magma chemistry. The volcanic rocks sampled for this study are from four units: Primeaux Lava Sequence (38.3–38.1 Ma), Mack Creek Lava Sequence (38.4-37.1), the Bob Creek lava dome (37.7 Ma), and late porphyritic dykes (36.7-36.4 Ma). The Emigrant Pass igneous rocks range from basaltic andesite to rhyolite in composition. Major mineral phases include plagioclase, hornblende, quartz, biotite, and pyroxene. All of the lavas and intrusive rocks have normalized incompatible element patterns typical of subduction-related magmas, like other Eocene lava sequences in the northern Great Basin (e.g., Fish Creek Mountains). Initial isotope ratios are: 87Sr/86Sr = 0.705143 to 0.707914, 143Nd/144Nd = 0.512122 to 0.512420 (εNd = -3.3 to -9.2), 176Hf/177Hf = 0.282393 to 0.282610 (εHf = -5.4 to -13.1), and 208Pb/204Pb = 38.9401 to 39.2212. The basaltic andesites have the lowest Sr and Pb, and highest Nd and Hf isotope ratios, and the primary magma source appears to be Phanerozoic lithospheric mantle (87Sr/86Sr < 0.706). The evolved magmas show strong correlations between trace element (e.g., Th/La) and isotopic ratios with increasing SiO2 content, and crustal contamination is a major process in magma evolution. The crustal component in the felsic lavas has highly negative εNd and εHf that may indicate a Precambrian crustal source. Based on this study and work at nearby Eocene volcanic centres, the Phanerozoic-Precambrian transition zone appears to include mantle and crustal components of varying age that are structurally interleaved.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-357297

© Copyright 2020 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.