Elevated magma fluxes deliver high-Cu magmas to the upper crust

Research output: Contribution to journalArticlepeer-review

Authors

  • Daniel Cox
  • Frances E. Jenner
  • Samantha J. Hammond
  • Barbara E. Kunz

Colleges, School and Institutes

Abstract

Porphyry Cu-Au ore deposits are globally associated with convergent margins. However, controls on the distribution of the chalcophile elements (e.g., Cu) during convergent margin magmatism remain disputed. Here, we show that magmas feeding many Chilean stratovolcanoes fractionate high Cu/Ag sulfides early in their crustal evolution. These magmas show evidence of lower crustal garnet and amphibole crystallisation, and their degree of sulfide fractionation and Cu depletion increase with both crustal thickness and the extent of garnet fractionation. However, samples from a small proportion of volcanoes with elevated eruptive fluxes depart from this Cu-depleting trend, instead erupting Cu-rich magmas. This implies that at these atypical sites, elevated magma productivity and crustal throughput, potentially facilitated by pathways exploiting major crustal fault systems, enables rapid magma transit, avoiding lower-crustal Cu-depleting sulfide fractionation and potentially playing an important role in porphyry ore genesis.

Details

Original languageEnglish
Number of pages4
JournalGeology
Early online date10 Jun 2020
Publication statusE-pub ahead of print - 10 Jun 2020