Chalcophile element processing and distribution beneath a continental volcanic arc

Cox, Daniel ORCID: 0000-0001-7280-4145 (2020). Chalcophile element processing and distribution beneath a continental volcanic arc. University of Birmingham. Ph.D.

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Abstract

Published datasets of the concentrations of the chalcophile elements in volcanic rocks are rare, and most of our knowledge of their behaviour is based on oceanic arc-like settings, rather than continental arcs, where economically viable deposits of the chalcophiles are generally associated. This thesis, therefore, investigates the processing and distribution of the chalcophile elements within a continental volcanic arc, by presenting novel whole rock analyses of the near complete suite of chalcophile elements in volcanic rock samples collected from several edifices along the Chilean Andes. The data presented demonstrates that continental arc magmas typically achieve saturation in a crystalline sulfide phase early during magmatic evolution, likely at or near the base of the overriding continental crust, prior to ascent and low-pressure fractional crystallisation, and before magnetite fractionation, in contrast to oceanic arc-like settings. Observations are replicated at stratovolcanoes and small eruptive centres. The degree of crystalline sulfide fractionated is modelled to be minimal (≤0.6 wt.%). The thickness of the overriding crust at convergent margins is argued to be the dominant control on the distribution of the chalcophile elements. The implication of these findings is that either secondary processes are required to transport chalcophile elements to the sites of ore deposit formation, or such ore deposits are generated in atypical scenarios (e.g., high magma throughput).

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):