THERMOBAROMETRY AND GEOCHRONOLOGY OF THE UVAUK COMPLEX, A POLYMETAMORPHIC NEOARCHEAN AND PALEOPROTEROZOIC SEGMENT OF THE SNOWBIRD TECTONIC ZONE, NUNAVUT, CANADA

Abstract

The Uvauk complex is an ultramylonite-bounded, granulite-facies suite of anorthosite-gabbro that forms part of the Chesterfield Inlet segment of the Snowbird tectonic zone. Following initial anorthosite-gabbro magmatism at ca. 2.71 Ga and a cryptic 2.62-2.60 Ga event marked by zircon and monazite growth, the Uvauk complex experienced two high-grade tectonometamorphic events at 2.56-2.50 and 1.91-1.90 Ga. Similar to the 2.56-2.50 Ga development of other shear zones in the region, the upper-amphibolite-facies to granulite-facies, moderately high-pressure (8.4-11.0 kbar and 705-760 degrees C) (1 kbar = 100 MPA) M1 event is interpreted to have involved the structural emplacement of ca. 2.71 Ga Uvauk complex rocks on ca. 2.68 Ga tonalitic rocks to the south. Granulite-facies, high-pressure (11.2-14.7 kbar and 695-865 degrees C) M2 metamorphism, gabbroic magmatism, and mylonite development within the complex at ca. 1.9 Ga culminated with similar to 3.5 kbar decompression at high temperature. Clockwise pressure-temperature-time (P-T-t) paths reflect crustal thickening, thought to be related to the early accretionary history of the Trans-Hudson Orogen. A thermal overprint at ca. 1.85-1.75 Ga resulted in retrograde metamorphism (5.8-6.0 kbar and 625-695 degrees C) associated with post-tectonic granitoid plutonism.