THERMOCHRONOLOGICAL AND GEOCHEMICAL INSIGHTS ON THE TRANSITION BETWEEN THE METAMORPHIC CORE COMPLEX AND THE NORTH AMERICAN CORDILLERA, SOUTHERN ARIZONA

Metamorphic Core Complexes represent remnants of metamorphic middle crust which have been exhumed by large extensional faults. In the North American Cordillera, Metamorphic Core Complexes have been interpreted as a response to the over-thickened crustal root produced by earlier crustal shortening and thickening and subsequently exposed through isostatic uplift during orogenic collapse. However, recent work has questioned this hypothesis due to the presence of late Cretaceous subduction-zone related material beneath some core complexes, which implies tectonic erosion of a potential crustal root prior to exhumation. This new view suggests that the core-complexes formed where a deep-crustal layer, coupled to low-angle subduction, flowing at tectonic rates and scales caused the middle-crust to rise to the shallow levels where zones of weakness were present or where the divergence between upper-crustal blocks was large. These contrasting hypotheses regarding emplacement underlines that it remains unclear how Metamorphic Core Complexes relate, both temporally and spatially, to the growth of the North American Cordillera.

Extensive local-scale structural studies have been carried out investigating the relationship between the Cordillera, orogenic collapse, and Metamorphic Core Complexes. However, there currently remains a unique opportunity to expand on our current understanding by applying modern, regional scale thermochronology and geochemistry. In order to interrogate the relationship between the growth of the North American Cordillera and development of the Metamorphic Core Complexes, we present a roughly east-west transect across the Pinaleno, Galiuro, and Santa-Catalina mountain ranges in Southern Arizona. Applying low- to mid-temperature thermochronology in combination with geochemistry to link the late Cretaceous crustal thickening generated during development of the North American Cordillera to the formation and subsequent Paleogene-Miocene exhumation of the Metamorphic Core Complexes.