TIMING AND KINEMATICS OF THE QUITOBAQUITO SHEAR ZONE, SOUTHWESTERN ARIZONA

The North American Cordillera is an archetypal example of an ocean-continent subduction zone and contains classic contractional deformational features including the thin-skinned Sevier retroarc thrust belt and the thick-skinned, Laramide basement-uplift province. Sevier and Laramide contractional deformation extends southward from northwestern Canada to southeastern California and equivalent structures exist in Mexico (the Mexican fold and thrust belt but these features are not so well understood in southern Arizona and northern Sonora. We examine the Quitobaquito shear to help better understand contractional deformation and to determine if Sevier or Laramide contractional features were continuous in this region. The Quitobaquito shear zone is located in Organ Pipe National Monument, southwestern Arizona and places Proterozoic gneiss structurally above Jurassic meta-sedimentary and meta-igneous rocks. Geologic mapping, cross-section construction, and microstructural analysis is used to determine the sense of motion of the shear zone. The shear zone is strongly mylonitized and dips gently to the south. Kinematic indicators and structural relationships suggest that the shear zone displays reverse fault kinematics with top-to-the-north motion. Preliminary zircon (U-Th)/He and Ar thermochronology suggests that exhumation of the shear zone may be related to Laramide and/or Sevier deformation. Resolving the timing and kinematics of this fault will lead to a better understanding of mid-crustal Cordilleran style deformation.