STRAIN AND VORTICITY ANALYSIS OF MYLONITIC ROCKS FROM SOUTHERN ARIZONA METAMORPHIC CORE COMPLEXES

Reconstructing the deformation path and exhumation history for mid-crustal rocks from lower plate settings in metamorphic core complexes is critical for understanding the tectonics of highly extended continental terranes. Mylonitic rocks derived from granitic protoliths in the Rincon, Santa Catalina, and Suizo core complexes in southern Arizona experienced deformation at greenschist to lower amphibolite facies conditions during the Tertiary. These rocks record modest to high strain ratios (R_XZ = 1.5 to >20) and formed under general shear conditions (W_m = 0.6 – 0.9). The three-dimensional strain geometry ranges from apparent plane strain to moderately constrictional (K = 1 – 3). Fabric asymmetries in protomylonites and mylonites are consistent with monoclinic flow. Possible deformation paths, based on the relationship between total strain, vorticity, and 3D deformation shape factors define linear trends. Narrow ultramylonite bands, which typically cut the main penetrative fabrics in these high-strain zones, record a pure shear dominated deformation with triclinic asymmetries. Ultramylonite zones experienced dramatic strain softening such that these zones follow significantly different deformation paths from the main mylonite zone. The bulk extension direction remains similar across the Rincon, Santa Catalina, and Suizo core complexes, but deformation is partitioned into dip-slip and oblique-slip domains related to the arched and corrugated structure of these core complexes.