A zircon case for super-wet arc magmas

Area of Science:

• Geochemistry
• Petrology
• Economic Geology

Background:

• Arc magmas typically contain 2-6 wt.% H2O.
• Evidence suggests some deep arc magmas are 'super-wet' (>6 wt.% H2O).
• Zircon's behavior during magmatic differentiation is sensitive to melt water content.

Purpose of the Study:

• To investigate the influence of melt water content on zirconium behavior during magmatic differentiation.
• To determine if zircon titanium concentrations can indicate the presence of super-wet magmas.
• To assess the role of super-wet magmas in porphyry copper deposit formation.

Main Methods:

• Thermodynamic modeling of magmatic systems.
• Analysis of zircon titanium concentrations.
• Geochemical investigation of magmatic systems associated with porphyry copper deposits.

Main Results:

• Super-wet magmas crystallize zircon with low, homogeneous titanium concentrations (<10 ppm).
• This occurs due to decreased zircon saturation temperatures with increasing melt H2O.
• Zircon titanium concentrations reveal a transition to super-wet magmatism preceding the Río Blanco-Los Bronces copper deposit formation.

Conclusions:

• Super-wet magmas are more prevalent than previously thought.
• Low, homogeneous zircon titanium concentrations are a key indicator of super-wet magmatism.
• Super-wet magmas play a fundamental role in the genesis of porphyry copper deposits.