Polyphase Deformation, Thrust-Induced Strain and Metamorphism, and Mesozoic Stratigraphy of the Granite Wash Mountains, West-Central Arizona (Tectonics, Mylonite, Geophysics, Mineralization, Terranes)
Laubach, Stephen Ernest
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https://hdl.handle.net/2142/71143
Description
Title
Polyphase Deformation, Thrust-Induced Strain and Metamorphism, and Mesozoic Stratigraphy of the Granite Wash Mountains, West-Central Arizona (Tectonics, Mylonite, Geophysics, Mineralization, Terranes)
Author(s)
Laubach, Stephen Ernest
Issue Date
1986
Department of Study
Geology
Discipline
Geology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Geology
Abstract
The Granite Wash Mountains of west-central Arizona are composed of variably metamorphosed and deformed sedimentary and volcanic rocks, here called the 'Granite Wash' (GW) and 'Salome Peak' (SP) sequences. The GW sequence is at least 1500 meters thick, and can be divided into seven map units, the lowest of which is depositional on 'cratonic' Paleozoic rocks. The sequence is cut by a major fault (the Hercules thrust zone) which places Precambrian rocks over Mesozoic and Paleozoic rocks. Both the metasedimentary rocks and the thrust zone are cross cut by undeformed Late Cretaceous plutons. The GW sequence is tentatively correlated with basal units of the McCoy Mountains Formation. This correlation extends the range of the McCoy depositional basin further to the northeast than previously recognized. The Salome Peak sequence occurs within the Hercules thrust zone, where it unconformably overlies Precambrian gneiss. It may be Early Mesozoic. Three non-coaxial phases of deformation affect the Mesozoic rocks of the GWM. The first event (D1) resulted in a megascopic ENE-trending, SSE-facing tight recumbant syncline, which is associated with slaty cleavage. D2 folds refold D1 structures and are associated with NE-dipping spaced cleavage. D2 cleavage becomes especially well developed near the Hercules thrust zone. S-C fabrics and other kinetic indicators in mylonites in the thrust zone indicate SW-directed tectonic transport. Slip lines calculated from F2 folds are parallel to the transport direction derived from the mylonites, suggesting thrusting was part of the D2 event. Strain magnitude associated with the D2 event is variable. D3 only produced locally-developed SW-dipping spaced cleavage. Two episodes of greenschist-facies metamorphism, corresponding to D1 and D2 deformation events, affected the Mesozoic strata. An inverted metamorphic zone of D2 age was produced by thrusting.
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