106 37th Annual Undergraduate Research Exhibition Sponsored by Sigma Gamma Epsilon (Posters)

All students are encouraged to submit research to this poster session. Investigations from ANY geological subdiscipline are welcome. Presenters who are SGE members are eligible to compete for monetary awards distributed at the meeting.

Monday, 20 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Petrology and Correlation of Newly Recognized Cenozoic Dacite and Tuff Units in NW Knoll Basin, NE Nevada

Paper number: 106-22
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

Geologic mapping in the NW part of Knoll Basin in northeastern Nevada revealed the presence of two newly recognized, distinct Cenozoic volcanic units below the 16–14 Ma Jarbidge Rhyolite. These new units include felsic lava, the Boies dacite and an underlying ash-flow tuff, Jakes tuff. Based on their stratigraphic position, we infer that the age of these rocks is between ca. 45–16 Ma. The goals of this project were to analyze three samples of each unit along the northwestern margin of the basin to assess possible lateral petrological and geochemical changes, and to compare them to known volcanic rocks in the region for possible correlation. Samples were analyzed for constituents using a petrographic microscope and for major and trace element chemistry using XRF. The Boies dacite contains phenocrysts of plagioclase, sanidine, biotite, hornblende, and minor quartz in a microcrystalline groundmass. Chemical analyses indicate that the two northernmost Boies dacite samples are dacite, and the southernmost is a rhyolite. The major and trace element composition of the Boies dacite was compared to rocks in the nearby 43–39 Ma NE Nevada volcanic field in the Pequop Mountains and East Humboldt Range area. Our data indicate that the two northernmost Boies dacite samples are most similar to hornblende-biotite dacite in the East Humboldt Range. Thin-section analysis of the southernmost Boies dacite reveals the presence of secondary quartz-filled voids, suggesting its rhyolitic chemistry is a product of this added silica. The Jakes tuff samples are dominantly composed of unsorted glass shards and pumice fragments up to 2 cm in diameter. Additionally, the tuff contains a minor amount of plagioclase, sanidine, quartz, biotite, and hornblende phenocrysts, as well as randomly-distributed lithic fragments of local Triassic shale up to 2 cm in diameter. These characteristics suggest a pyroclastic flow origin of the tuff. Our study suggests that the NE Nevada volcanic field may extend farther north than previously recognized. Future research will include radiometric dating of samples to assist in correlating these units.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412274

© Copyright 2025 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.