Redox state of subducted sediments controls porphyry copper mineralization along the Tethyan belt.

Abstract

The Tethyan orogenic belt hosts numerous world-class porphyry copper deposits, with most forming during the Cenozoic continental collision and fewer during earlier Mesozoic subduction. To understand this pattern, we integrate redox indicators from detrital zircon grains with constraints from sedimentary geology and granite geochemistry during these times. Our analysis reveals a major shift from reduced magmas forming during the Mesozoic to more oxidized intrusive systems in the Cenozoic. Here we show that subduction of organic-rich, reduced marine sediments in the Mesozoic suppressed the oxidation state of arc magmas, locking chalcophile elements in the lower crust and inhibiting the formation of porphyry Cu deposits. In contrast, the subduction of more oxidized continental sediments during Cenozoic collision elevated the mantle's oxidation state, releasing stored copper to melts that form porphyry deposits. These findings highlight the critical role of redox state of subducted sediments and tectonic history in shaping the distribution of porphyry mineralization along the Tethyan belt.