HIGH-P PARTIAL MELTING OF DIORITIC GNEISS: LA-ICPMS ANALYSIS OF PEMBROKE GRANULITE MINERALOGY, FIORDLAND, NEW ZEALAND

Pods of granulite facies dioritic gneiss in the Pembroke Valley, Milford Sound, New Zealand, preserve peritectic garnet surrounded by trondhjemitic leucosome and vein networks, evidence of high-P partial melting. Garnet-bearing trondhjemitic veins extend into host gabbroic gneiss, where they are spatially linked with the recrystallisation of comparatively low-P two-pyroxene-hornblende granulite to fine-grained high-P garnet granulite assemblages in garnet reaction zones (GRZ). New data acquired using LA-ICPMS for minerals in various textural settings indicates differences in the partitioning of trace and REE elements in the transition of the two rock types to garnet granulite, mostly due to the presence or absence of clinozoisite. Garnet in the GRZs (gabbroic gneiss) has a distinct REE pattern, inherited from reactant hornblende. Peritectic garnet in the dioritic gneiss and most garnet in trondhjemitic veins throughout both dioritic and gabbroic gneiss have a trace and REE pattern inherited from hornblende and clinozoisite reactants to the melt-producing reaction in the dioritic gneiss. The distinct REE patterns of garnet geochemically links the trondhjemitic veins to sites of partial melting in the dioritic gneiss.