Testing plate geodynamic forcing on Cu-porphyry deposits through kinematic restoration in Tibet and Southeast Asia

Abstract

Cu-porphyry deposits are an important mineral deposit as they are a primary source of the world’s supply of copper and are also a source of molybdenum and gold. Consequently, there have been extensive studies on the formation of these deposits, particularly on their geochemical traits. It has been shown that they are widely associated with the subduction of oceanic lithosphere, but the exact drivers and necessary requirements for porphyry formation have not been tested and applied to a kinematic reconstruction. This report intends to do that using the India-Asia Cenozoic collision. The temporal and spatial data of known Cu-porphyry deposits from Tibet to Sumatra were input into kinematic tectonic models of the Cenozoic collision and compared against each other. The models compared were the Greater India Basin model and the Continental Crust Subduction model as they both imply continental and oceanic subduction events, but differ in how much of continental and oceanic subduction there was. The results show that tectonic transitions generally favour Cu-porphyry generation. Three prominent porphyry belts in Tibet and Sumatra are shown to coincide with major geodynamic events and processes in the two models. However, the belt’s distribution and timing better fits the geodynamic timings and processes inferred in the Greater India Basin model. A list of requirements has been proposed to favour Cu-porphyry generation: (1) Enrichment of the lower crust in Cu-porphyry bearing magmas by metasomisation of the mantle wedge by oceanic slab subduction, or by the partial melting of the lower crust by heat from asthenospheric upwelling; (2) a kinematic or geodynamic event to weaken the crust and triggering initial Cu-porphyry magma ascent through the weakened crust; (3) a fault system to provide more weakened crust near the surface and the shortest vertical pathways for Cu-porphyry magmas to exploit to continue ascent to the surface; (4) exhumation of the region where the porphyry deposit is allowing for exposure.