Black Giants Anorthosite, New Zealand: A Paleozoic analogue of Archean stratiform anorthosites and implications for the formation of Archean high-grade gneiss terranes

The Black Giants Anorthosite, a mid-Paleozoic (349 ± 5 Ma U-Pb zircon age) layered anorthosite complex in Fiordland, New Zealand, bears striking compositional and lithologic similarities to Archean stratiform anorthosites and, like many of its Archean counterparts, occurs within a high-grade gneiss terrane, preserving a record of metamorphism at mid-crustal depths followed by higher-pressure metamorphism and burial to lower-crustal levels. These and other similarities point to formation of the Black Giants Anorthosite and its Archean equivalents in comparable tectonic environments, most likely a subduction-related magmatic arc which, in the case of Fiordland, resulted from plate convergence along the Pacific margin of Gondwana.