| Exposures of mid-to lower-crust in Fiordland contain evidence of high temperature and pressure processes occurring beneath magmatic arcs. This thesis presents new U-Pb zircon ages that constrain emplacement of the Malaspina Pluton, Western Fiordland Orthogneiss (WFO) to 116-114 Ma and new Sm-Nd garnet ages of 115-110 Ma for partial melting of the Malaspina near the Doubtful Sound Shear Zone (DSSZ), central Fiordland. U-Pb igneous zircon ages, from west to east across Doubtful Sound (DS), are 114.2 +/- 2.2, 115.4 +/- 2.2, and 116.1 +/- 2.4 Ma. This compares to a contact metamorphic zircon rim age of 114.8 +/- 2.4 Ma for the 119.8 +/- 2.9 Ma Misty Pluton. From west to east across DS, Sm-Nd garnet ages are 113.6 +/- 2.5, 113.2 +/- 2.8, 115.6 +/- 2.6, 111.6 +/- 3.1, 110.6 +/- 1.9, 113.3 +/- 2.6, and 111.9 +/- 3.0 Ma. Hence partial melting and garnet granulite-facies metamorphism lasted ≥ 5 m.y. in DS and occurred within 5.5 m.y. of pluton emplacement. These ages compare to Sm-Nd garnet ages for garnet granulite of 126-109 Ma in northern Fiordland (Pembroke) and ca. 110 Ma in southern Fiordland (Resolution Island). Mineral assemblages in DS migmatite include Amp + Cpx + Grt + Qtz + Pl +/- Bt + Rt + Ilm +/- relict OPx +/- relict Czo. Euhedral, peritectic garnet occurring in leucocratic veins and reaction zones, has little zoning in composition and ranges from Alm53Prp27Sps3Grs17 in the west to Alm44Prp36Sps1.5Grs18.5 in the east. Ilmenite with exsolved rutile and oriented exsolution needles of rutile in garnet indicate re-equilibration after high T and P. Phase diagram sections for melted WFO and thermobarometry using garnet, clinopyroxene, and plagioclase compositions indicate 700-840°C and 10.6-14.2 kbar for metamorphism on DS. Similar methods for Pembroke Granulite of >750°C at 12-16 kbar indicate diachronous widespread high P metamorphism and partial melting for this ca. 4,375 km2 section of mid-to lower-crust with these processes occurring early in the north and later in the south (126-105) Ma. |
