Geological Society of America

T102 The Virtue of Fieldwork in Volcanology, Sedimentology, Structural Geology, and Tectonics (Posters): A Session to Honor Cathy Busby, MGPV Distinguished Geological Career Award Recipient of 2020

Monday, 10 October 2022
9:00 AM - 1:00 PM
Exhibit Hall F

DETRITAL TOURMALINE IN THE ARCHEAN JARDINE METASEDIMENTARY SEQUENCE OF THE WESTERN BEARTOOTH MOUNTAINS, MT-WY, USA: EVIDENCE FOR HIGHLY EVOLVED ROCKS EXPOSED AT THE EARTH’S SURFACE AT 2.9-3.6 GA

Paper number: T102-2
Program: Technical Sessions
Time: 9:00 AM – 1:00 PM

Authors

Darrell Henry Presenting Author
Louisiana State University, Baton Rouge, LA
David W. Mogk
Montana State Univ, Bozeman, MT
Paul Mueller
University of Florida, Gainesville, FL
Barbara Dutrow
Louisiana State University, Baton Rouge, LA
Matthew Loocke
Louisiana State University, Baton Rouge, LA
Larry Tuttle
Louisiana State University, Baton Rouge, LA

Abstract

The Jardine Metasedimentary Sequence (JMS) is a well-preserved, metamorphosed turbidite sequence deposited after 2.9 Ga (youngest detrital zircon) and before intrusion by granitoids at 2.8 Ga in the South Snowy Block of the western Beartooth Mountains in the northern Wyoming Province, USA. U-Pb ages of detrital zircons (2.9 to 3.6 Ga) and Sm-Nd depleted mantle model ages (3.2-4.0 Ga) suggest an ancient provenance for the protoliths, which included graywacke, quartzite, arkose, and shale. Sedimentary structures typically found in turbidite sequences are well preserved (e.g., graded beds, scour and fill, crossbedding) and suggest a mid-to-distal submarine fan on an active continental margin. Medium-grade, low-pressure metamorphism (550-600°C, 3-4 kbar) of metapelitic rocks commonly produces the diagnostic assemblage of staurolite-andalusite-biotite found in the JMS.

Within these rocks are well-developed metamorphic tourmalines, many with detrital cores. Based on tourmaline textures and compositions, metamorphic tourmaline began to crystallize in the JMS metaclastic rocks ~350°C and continued to grow along the prograde path to peak metamorphic conditions. More significantly, cores of pre-metamorphic detrital tourmaline are well preserved in the metamorphic tourmalines. These cores are distinguished from metamorphic overgrowths based on several features, including rounding, fracturing, distinctly different mineral inclusions, elemental zoning, and discrete discontinuities in chemical composition. Applying tourmaline provenance criteria of Henry and Guidotti (1985) and other distinctive elemental concentrations (e.g., Ca, Cr, Ti, and F), suggests the lithologic sources of these cores likely included peraluminous granitic rocks, weakly fractionated and oxidized granitic rocks, aluminous metapelites, Al-poor and Fe³⁺-rich metapsammites, magnesian metasediments, and calc-silicate rocks. Although it is uncertain whether the detrital tourmaline cores have experienced single or multiple sedimentary cycles, the compositions of these cores represent the erosional remnants of more evolved crust. Thus, the crust that formed during the 2.9-3.6 Ga interval contained a wider range of more evolved compositions than typically assumed for Mesoarchean and older crust.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-378123

© 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.