Strain partitioning in the mid-crust of a transpressional shear zone system: Insights from the Homestake and Slide Lake shear zones,central Colorado |
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| Institution: | 1. Department of Earth & Atmospheric Sciences, University of Houston, Houston, TX 77204, USA;2. School of Geography and Earth Sciences (SGES), McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4 L8, Canada;3. Department of Civil and Environmental Engineering, University of Houston, Houston, TX 77204, USA;1. Geology Department, University of Otago, Dunedin, New Zealand;2. SESES, Northern Arizona University, Flagstaff, AZ, USA;1. Simon Fraser University, Department of Earth Sciences, 8888 University Drive, Burnaby, BC V5A 1S6, Canada;2. British Columbia Geological Survey, 1810 Blanshard St., Victoria, BC V8T 4J1, Canada;3. Boise State University, Department of Geosciences, 1910 University Drive, Boise, ID 83725, USA;4. University of Florida, Department of Geological Sciences, PO Box 2120, Gainvesville, FL 32611-2120, USA;1. Sorbonne Universités, UPMC Univ Paris 06, CNRS, Institut des Sciences de la Terre de Paris (iSTeP), 4 place Jussieu, 75005 Paris, France;2. IFP Energies nouvelles, 1-4 avenue du bois Préau, 92500 Rueil-Malmaison, France |
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| Abstract: | Kinematic analysis and field mapping of the Homestake shear zone (HSZ) and Slide Lake shear zone (SLSZ) in central Colorado may provide insight into the interaction between subvertical and low-angle shear zones in the middle crust. The northeast-striking, steeply dipping HSZ comprises a ～10-km-wide set of anastomosing ductile shear zones and pseudotachylyte-bearing faults. Approximately 4 km south of the HSZ, north–northeast-striking, shallowly dipping mylonites of the SLSZ form three 1–10-m-thick splays. Oblique stretching lineations and shear sense in both shear zones record components of dip-slip (top-up-to-the-northwest and top-down-to-the-southeast) and dextral strike-slip movement during mylonite development. Quartz and feldspar deformation mechanisms and quartz c] axis lattice preferred orientation (LPO) patterns suggest deformation temperatures ranging from ～280–500 °C in the HSZ to ～280–600 °C in the SLSZ. Quartz c] axis LPOs suggest plane strain general shear across the shear system. Based on the relative timing of fabric development, compatible kinematics and similar deformation temperatures in the SLSZ and the HSZ, we propose that both shear zones formed during strain localization and partitioning within a transpressional shear zone system that involved subvertical shuffling in the mid-crust at 1.4 Ga. |
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