26 Undergraduate Research (Posters)

Thursday, 16 May 2024
9:00 AM - 5:30 PM
Grand Ballroom

AGE AND GEOCHEMISTRY OF SILLIMANITE GNEISS FROM A POSSIBLE CORE COMPLEX NEAR CHENEY, WA

Paper number: 26-9
Program: Theme Sessions
Time: 9:00 AM – 5:30 PM

Authors

Abstract

Northeast of Cheney, Washington a series of hills display various rock types from garnet-bearing granitic rocks to sillimanite bearing gneiss. Surrounding these high-grade metamorphic rocks are fine to medium grained sandstone and quartzites mapped as the Ravalli Group of the Belt Supergroup. The lower-grade metamorphosed Belt rocks are cross cut by pegmatite dikes and multiple normal faults intruded by foliated granitic dikes, which are generally 49 Ma. The contact between the metamorphic grades seems to be gradational as faulted rocks, grade to folding and crenulation, and then to mylonitic textures and gneiss. U/Pb ages of separated zircon grains from the gneiss are older than 1.1 Ma, generally agree with expected detrital zircon ages from the Belt Supergroup and are comparable to samples from the proximal Priest River core complex. This area has been generally referred to as the Needham Hill core complex, but is it a stand-alone structure, part of a larger core complex that has been masked by younger basalt and megaflood deposits, or a remnant from the uplift of the Priest River core complex? New U/Pb ages, geochemistry, and structural analyses are presented to evaluate this unique geologic feature.

Geological Society of America Abstracts with Programs. Vol. 56, No. 4

doi: 10.1130/abs/2024CD-399904

© 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.