FIELD AND PETROGRAPHIC ANALYSIS OF MYLONITIC FABRICS: IMPLICATIONS FOR TECTONIC CORRGUATION DEVELOPMENT, TANQUE VERDE RIDGE, ARIZONA, USA

Tanque Verde Ridge (TVR) in Saguaro National Park, Arizona, USA, represents a large-scale lineation parallel ridge (tectonic corrugation) within the Santa Catalina-Rincon Core Complex. Field and petrographic features record a history of lineation parallel extension and boudinage occurring across a ductile to brittle deformational continuum during core complex exhumation. Lineation perpendicular ductile features suggest the importance of extension orthogonal to lineations during exhumation and may factor into the debate on tectonic corrugation evolution.

TVR is a foliation-defined antiformal flexure, concordantly bounded at the toe by a brittle detachment fault system. The footwall mylonite is strongly foliated (suggestive of flattening, rather than constriction) and lineated (WSW trending). Ductile, micro- to macro-scale features oriented both lineation parallel (S-C fabrics, asymmetric porphyroclasts, shear zones) and perpendicular (shear zones, asymmetric quartz fabrics) suggest WSW and NNW directed material transport, respectively. Foliation flexures exhibiting both lineation parallel and perpendicular fold axes, and micro- to meso-scale boudinage features, the distended necks of which are spatially correlated with NNW striking zones of intense brittle fracturing, brecciation and cataclasis, occur across the corrugation. The ductile, mylonitic foliation is passively affected across these boudin neck zones as foliation dip varies from sub-horizontal to >45°. This suggests a temporal link between mylonite formation, extension-related deformation and the development of the corrugated surface.

Oriented thin sections and field observations from across TVR and across outcrop-scale analogs of the corrugation constrain both the conditions during mylonite development (upper-greenschist to lower-amphibolite facies) and the spatial relationship of micro- to meso-structural features across the corrugation. Both lineation parallel and perpendicular extensional shear played a significant role during the evolution of the TVR-defined tectonic corrugation.