Dissertation/Thesis Abstract

Petrographic Constraints on the Exhumation of the Sierra Blanca Metamorphic Core Complex, AZ
by Koppens, Kohl M., M.S., University of Louisiana at Lafayette, 2018, 79; 10816907
Abstract (Summary)

The Sierra Blanca metamorphic core complex (SBMCC), located 90 miles west of Tucson, is part of the southern belt of metamorphic core complexes that stretches across southern Arizona. The SBMCC exposes Jurassic age sedimentary rocks that have been metamorphosed by intruding Late Cretaceous peraluminous granites and pegmatites. Evidence of this magmatic episode includes polysythetic twinning in plagioclase, albite exsolution of alkali feldspar resulting in myrmekitic texture, and garnet, mica and feldspar assemblages. The magmatic fabric is overprinted by a Tertiary (Miocene?) tectonic fabric, associated with the exhumation of the Sierra Blanca metamorphic core along a low-angle detachment fault, forming the SBMCC. The NW-SE elongated dome of metamorphic rocks forms the footwall of the detachment shear zone, and is separated from the hanging wall, composed of Paleozoic and Mesozoic metasedimentary rocks, by a low-angle detachment shear zone. Foliation is defined by gneissic layering and aligned muscovite, and is generally sub-horizontal, defining the dome. The NNW-SSE mineral stretching lineation is expressed by plagioclase and K-feldspar porphyroclasts, and various shear sense indicators consistent with a top-to the-NNW shear sense. Lineation trends in a NNW-SSE orientation; however, plunge changes across the domiform shape of the MCC. Much of the deformation is preserved in the blastomylonitic gneiss derived from the peraluminous granite, including epidote porphyroclasts, grain boundary migration in quartz, lozenged amphiboles, mica fish, and retrograde mineral alterations. Detailed petrologic observation and microstructural analysis indicate deformation temperatures of 450–575 ± °C presented here provide thermomechanical constraints on the evolution of the SBMCC.

Indexing (document details)
Advisor: Gottardi, Raphaël
Commitee: Duex, Timothy, Schubert, Brian
School: University of Louisiana at Lafayette
Department: Geology
School Location: United States -- Louisiana
Source: MAI 58/05M(E), Masters Abstracts International
Subjects: Geology, Mineralogy, Petrology
Keywords: Brittle ductile, Calc-silicates, Deformation, Metamorphic core complex, Microstructure, Shear zone
Publication Number: 10816907
ISBN: 978-1-392-04155-0
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