Tectonic controls on porphyry copper formation in the western USA

Project Background The Basin and Range Province in the western USA is a hyperextended piece of the crust previously thickened by >100 Ma of orogenesis. The region is also notable for its porphyry copper deposits (Fig. 1), which mainly formed towards the end of crustal compression. However, due to the extreme dissection of the landscape by subsequent extension, spatial and temporal constraints on crustal shortening and its relationship to porphyry copper formation are limited. Across much of the province, compressional features are poorly preserved, but metamorphic core complexes offer a window into the pre-extensional history. This PhD project will use contractional structures and exhumed remnants of the middle to lower crust preserved within select core complexes to constrain patterns of pre-extensional crustal thickness and the timing and duration of compression to investigate potential links to porphyry copper formation. Project Aims and Methods This project aims to determine spatial and temporal patterns in the magnitude and longevity of pre-extensional compression within the Basin and Range Province to compare with patterns of porphyry copper formation. This will be achieved through structural and petrological investigation combined with geothermobarometry, U-Pb zircon, Lu-Hf garnet, and in-situ Rb-Sr mica dating [2]. There are three objectives: 1: Identify contractional structures and constrain the paleostress field The student will identify and characterize contractional structures preserved within a selection of metamorphic core complexes to constrain the pre-extensional paleostress field. 2: Estimate crustal thickness from the maximum burial depth of key metamorphic core complexes Geothermobarometry and Lu-Hf garnet geochronology will be used to determine the magnitude and timing of maximum burial in a selection of core complexes. Maximum burial depths will serve as a proxy for crustal thickness, elucidating temporal and spatial patterns of crustal thickening. 3: Place absolute constraints on the duration and cessation of contractional deformation In-situ Rb-Sr dating of syn-tectonic mica (e.g. Fig. 2) or U-Pb dating of zircons within contractional structures [2,3] will place absolute constraints on fault motions, allowing the student to build a spatial and temporal picture of compression across the region that can be compared with porphyry copper mineralisation.