Document Type
Thesis
Abstract
Located ~50 km north of Tucson, the Suizo Mountains form a small, isolated part of the larger Santa Catalina metamorphic core complex to the south. Our research seeks to quantify the kinematics and strain associated with the ductile deformation produced during low-angle normal faulting as related to major crustal extension in the mid-Tertiary. The Suizos are underlain by the Proterozoic Pinal Schist and a younger, two-mica, garnetbearing leucogranite thought to be part of the early Eocene Wilderness Suite. Rocks are variably mylonitized in an east dipping high-strain zone at least 400 m thick, the base of which is exposed on the western flank of the range. Mylonitic foliation strikes N-S and dips ~20°-40° east, while a well-developed elongation lineation trends ~040° to 090° and plunges 10° to 20°. Stepped porphyroclasts, S-C fabrics, and asymmetric quartz c-axis fabrics indicate to a top-to-the west shear sense. Additional displacement is accommodated by discrete, narrow (~cm thick) high-strain zones with a top-to-the west shear sense, as evidenced by deflected quartz veins and leucogranite pegmatite. The present-day east-dipping foliation, combined with the top-to-the west shear, would normally indicate reverse (thrust) faulting. We suggest, however, that rocks were deformed and mylonitized during extension with the foliation originally dipping west, and that a subsequent deformation allowed for tilting or warping of the mylonites into the current, east-dipping orientation. Sectional strain values were determined through quartz grain shape analysis, R/@ analysis, and NIH image analysis, with average Rxz values ranging from 10-15:1. K-values vary from ~0.3-3, but overall 3D strain ellipsoids are consistent with plane strain. Best values for W,,, mean vorticity, range from 0.3 to 0.98, and indicate general shear. Based on the finite strain geometry and vorticity, we estimate the displacement accommodated by ductile deformation to be 2+1 km.
Date Awarded
2006
Department
Geology
Advisor 1
Christopher M. Bailey
Recommended Citation
Buchanan, Laura Jane, "Kinematic and Strain Analysis of Myonites from the Suizo Mountains, Santa Catalina Metamorphic Core Complex, Arizona, U.S.A." (2006). Geology Senior Theses. William & Mary. Paper 156.
https://scholarworks.wm.edu/geologyseniors/156
