ZIRCON TRACE ELEMENT COMPOSITION SPACE IN PLUTONIC AND VOLCANIC ARCS: IMPLICATIONS FOR ZIRCON PROVENANCE AND MAGMATIC ARC EVOLUTION

Lithophile trace element enrichment in zircons reflects melt evolutionary paths and can discriminate among potential zircon source rocks. Compilations of internally consistent, global zircon data sets (Grimes et al., 2009, 2015) show that ratios of conservative trace elements and subduction-related, non-conservative to conservative elements are useful for (1) discriminating sources in depleted (MORG) to enriched (plume) oceanic rocks and (2) defining variably enriched ‘continental’ zircon sources. In this study we utilize Hf abundances and ratios of variably non-conservative elements in zircons from arc batholithic and volcanic source rocks to devise a classification scheme for arc-derived zircons. Hf abundances in cogenetic zircon suites define fractionation-induced arrays. Discrimination of arc zircon sources relies on U/Yb enrichment across these Hf arrays that records subduction-related lithophile element enrichment from primitive oceanic arcs to continental arcs. Correlated non-conservative element enrichments define low U/Yb to high U/Yb magmatic arc zircon sources roughly analogous to low to high K arcs defined by whole rock chemistry. U/Yb and light rare earth element ratios (Ce/Gd and Ce/Yb) may record both sympathetic enrichments during melt fractionation and lithophile element decoupling due to source variations in long-lived, thermally mature arcs. We demonstrate that this discrimination of arc zircon sources is useful for defining secular magmatic variation across magma pulses and for petrologic characterization of hydrothermally altered volcanic rocks in the long-lived Sierran volcano-plutonic arc. Arc provenance characterization of populations of forearc and rear-arc detrital zircons also illuminates arc evolution through time and enhances characterization of the arc volcanic carapace and the petrologic connection between arc volcanism and plutonism.