High to ultra-high temperature contact metamorphism and dry partial melting of the Tasiuyak Paragneiss, Northern Labrador: a petrographic, thermobarometic and phase equilibria modeling study

• Main Author: Mitchell, Rhea Katherine
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2011
• Subjects: Nain
• Online Access: https://research.library.mun.ca/11059/; https://research.library.mun.ca/11059/1/Mitchell_RheaKatherine.pdf

Contact aureoles of the anorthositic to granitic plutons of the Mesoproterozoic Nain Plutonic Suite, Labrador, are particularly well developed in the Paleoproterozoic, regionally metamorphosed, granulite-facies, migmatitic Tasiuyak paragneiss. Regional metamorphism formed the assemblage Qtz-Kfs-PI-Grt-Sil±Bt±Liquid. Phase equilibria modeling yields a minimum peak of 8.3 kbars and 852°C for this event, consistent with the conditions necessary for biotite dehydration melting. These rocks underwent a significant melt loss event(s), removing much of the hydrous material, leaving behind relatively dry compositions. Rocks within the contact aureoles were statically overprinted by lower P, but higher T mineral assemblages and by textures related to a second partial melting event. Samples collected within multiple contact aureoles, near Anaktalik Brook, west of Nain, Labrador are categorized into five main sample types based on textures and mineralogy: A: Spl-Crd domains (Sil pseudomorphs) and Opx-Crd (Grt pseudomorphs) within a quartzofeldspathic domain, B: interwoven PI-rich and Crd-rich domains with Spl-Crd and Opx-Crd regions, similar to type A samples, C: complex arrangements of Spl-Crd domains, rounded Pl-Crd domains, interstitial PI-Opx domains, very fine grained intergrowths of Ksp-Qtz-Crd-Opx (Osm pseudomorphs) and coarse-grained domains of Ksp-Qtz-Crd-Opx (neosome), D: Sil-rich and Fa-rich (Grt pseudomorphs) domains within quartzofeldspathic matrix, and E: garnetiferous domains (Opx or Grt pseudomorphs), amoeboid Spl-Pl domains (Sil pseudomorphs) and coarse-grained Ksp-Qtz-Opx domains enclosed in a quartzofeldspathic matrix. Type A and C samples contain a very fine- to medium-grained geometric intergrowth of Crd-Qtz interpreted to have formed during melt-production during the dissolution of Bt and feldspars in the presence of melt. Evidence for partial melting includes: (i) lobate Ksp and Qtz pseudomorphs after former melt films and pockets (locally enclosing euhedral, idiomorphic cordierite) within and around ...