ORIGIN OF HIGH FIELD STRENGTH ELEMENT ENRICHMENT IN VOLCANIC ARCS: GEOCHEMICAL EVIDENCE FROM THE SULU ARC, SOUTHERN PHILIPPINES

Abstract

Lavas from the Sulu Arc, southern Philippines, exhibit an enrichment in high field strength elements (HFSE) that represents a departure from the typical volcanic arc geochemical signature. It has been postulated that this relative enrichment arises from metasomatism of mantle wedge peridotites by melts derived from the subducting oceanic lithosphere, through formation of amphibole which subsequently breaks down and enriches the mantle source of parental arc magmas in HFSE. Divergent chemical and isotopic characteristics between Sulu Arc HFSE-enriched lavas and the Sulu Sea crust being subducted—the presumed source of slab-derived melts—render it unlikely, however, that HFSE enrichment arises from the influence of such melts. New geochemical data suggest that the varying degrees of HFSE enrichment in Sulu Arc lavas are instead the result of variable amounts of mixing between enriched and depleted mantle end-components—the sources of South China Sea intraplate lavas and Sulu seafloor basalts, respectively—within a compositionally heterogeneous mantle wedge.