4 Constraints on the Formation, Assembly, and Evolution of Precambrian Rocks in the Rockies

Wednesday, 18 May 2016
8:00 AM - 12:00 PM
Crest Room

NEOARCHEAN(?) TO PALEOPROTEROZOIC METAMORPHIC AND STRUCTURAL EVOLUTION OF THE HARTVILLE UPLIFT, SOUTHEASTERN WYOMING

Paper number: 4-1
Program: Theme Sessions
Time: 8:00 AM – 8:20 AM

Authors

Abstract

The Hartville Uplift (HU) of southeastern Wyoming lies near the intersection of two major Paleoproterozoic crustal boundaries, the Cheyenne Belt (CB) and the Dakotan Orogen. Previous structural and geochronologic studies in the HU, Laramie Mountains, and the Black Hills show that temporal and kinematic relationships are complex and suggest an earlier episode of east-west compression and metamorphism prior to accretion along the CB and a younger (ca. 1715 Ma) suturing of the Wyoming and Superior Province (Chamberlain et al., 2003, Can. J. Earth Sci. ; Krugh, 1997, MS. thesis, U. of Wyoming). This study aims to unravel the polydeformational and polymetamorphic tectonic history of the HU by analyzing geologic structures and the metamorphic history of metapelites and other rocks during the Paleoproterozoic orogenies.

The HU is bisected by the Hartville Fault (HF) that separates high-pressure, low-temperature assemblages on its western side from the high-temperature assemblages on its eastern side. The first documented deformational event on the western side is a nappe-forming event, D1, that is associated with high-pressure metamorphism that is inferred from 12-25% of grs component in garnet. Although there are no clear noses of nappes exposed, north-trending hinges of parasitic folds suggest an east-west vergence. D2 structures refold D1 nappes about vertical W-SW fold axes, developing axial-planar foliation only in fold hinges.

On the eastern side of the HF, the dominant structural grain is defined by 1715 Ma D3 faults and folds, which have subvertical N-NE trending foliation and shear zones exhibiting east side up movement (Krugh, 1997). These faults juxtapose sillimanite-grade rocks on the eastern side against lower greenschist-facies rocks on the western side. Late D4 open folds refold D3 foliation with hinges defined by fibrolite lineations.

D1, west-verging nappes may be correlative with 1780 Ma nappes in the central Laramie Range and suggest a pre-CB, east-west compression (Bauer et al., 1998, Basement Tectoncis, 12.). North-south D2 compression is consistent with accretion of the Green Mountain Terrane along the CB. The large amount of vertical uplift and high-temperature metamorphism associated with D3 and D4 are attributed to the terminal collision of the Wyoming and Superior provinces.

Geological Society of America Abstracts with Programs. Vol. 48, No. 6

doi: 10.1130/abs/2016RM-276120

© Copyright 2016 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.