UNRAVELING MANTLE AND SUBDUCTION CONTRIBUTIONS IN A CONTINENTAL ARC VOLCANO: TATARA-SAN PEDRO COMPLEX, CHILE

The Chilean southern volcanic zone (SVZ) is a classic continental arc that has been fundamental for our knowledge of continental, mantle, and subduction contributions to arc magmatism. Among SVZ investigators, Fred Frey and students Leopoldo López-Escobar, Rosemary Hickey and David Gerlach applied modern geochemical approaches that have had profound impacts on our understanding of arc magma genesis, and has been the foundation of subsequent work in the region.

Our investigation of the Tatara-San Pedro complex (TSPC) follows from the Fred’s work and takes advantage of high-density lava sampling and characterization by Mike Dungan and colleagues. Our data show systematic chemical and isotopic variability, reflecting three mantle-derived end-members that have contributed to magmas throughout TSPC’s ~925 ka history. Two end-members are directly impacted by subduction. The most common magma source is ‘prevalent TSPC mantle’, representing the SVZ mantle wedge, modified over time by components from subducted Pacific basalt and sediments. A second end-member shows strong enrichments of hydrous fluid-mobile/fluid-immobile elements and very low HFSE abundances, and is derived from ‘prevalent TSPC mantle’ that experienced melt-loss, followed by remelting caused by fluxing of solute-rich fluids from subducted basalt. A third end-member has the highest incompatible element abundances, and ‘enriched’ radiogenic isotope ratios, and is derived from behind-the-arc mantle advected into the mantle wedge. No TSPC lavas are simple mixtures of the latter two end-members, indicating they are spatially separated in the wedge, rather both show mixing with ‘prevalent TSPC mantle’.

The TSPC suite shows greater isotopic and chemical diversity than any other southern SVZ volcano, and our study elucidates the magma sources and their spatial relationships. Nevertheless, we note that Fred and colleagues recognized all three end-members in volcanoes farther south, although interpretations differ.