Variations in the convergent margin metallogenic cycle as a key to secular tectonic processes

Abstract:

Convergent margin processes are an inherent feature of modern style plate tectonics and supercontinent amalgamation. One expression of these processes is metallogenesis, which therefore may yield important insights into secular changes in styles of convergence. A global comparison of metallogenesis along convergent margins indicates a consistent progression of mineral deposit types, which we term the convergent margin metallogenic cycle. This cycle mirrors the different stages of convergent margin evolution.

Each metallogenic cycle begins with the formation of porphyry copper deposits and/or volcanic-hosted massive sulphide deposits associated with arc construction and back arc basin formation, respectively. When the convergent margin transitions into contraction due to processes such as accretion of terranes or oceanic plateaus, flattening of subduction, or continent-continent collision, mineral deposits that form include orogenic gold, structurally hosted base metal, and pegmatites. The formation of intrusion related rare metal (tin, tungsten, molybdenum) and gold deposits, and alkaline porphyry copper deposits accompanies post-contractional extension, closing the convergent margin metallogenic cycle.

Our analysis suggests that the duration and recurrence of convergent margin metallogenic cycles changes with age, with younger convergent margins showing longer and recurring metallogenic cycles. This reflects secular changes in tectonic processes, in particular the style of subduction from shallow to deep slab breakoff. Supercontinents including Nuna and Rodinia were characterised by mostly non-recurring convergent margin metallogenic cycles, whereas Gondwana-Euramerica-Pangaea had longer-lived and recurring cycles. Recurring cycles increase the chance to form similar deposit types during different times within the same metallogenic province.