Emplacement history of the Pearly Gates anorthosite pluton and spatially related Tessiarsuyungoakh intrusion, and metamorphic petrology of the adjacent Tasiuyak paragneiss, northern Labrador

• Main Author: Tettelaar, Tanya Anne
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2004
• Subjects: Nain
• Online Access: https://research.library.mun.ca/6657/; https://research.library.mun.ca/6657/1/TanyaAnneTettelaar.pdf; https://research.library.mun.ca/6657/3/TanyaAnneTettelaar.pdf

The Mesoproterozoic Nain Plutonic Suite consists of anorthositic and granitic intrusions, which were emplaced along an older suture zone marked by the Torngat Orogen in northern Labrador. This study concerns the western margin of the Nain Plutonic Suite where the Pearly Gates Anorthosite pluton and spatially related Tessiarsuyungoakh intrusion, and the Makhavinekh Lake pluton, were intruded into the Paleoproterozoic Tasiuyak paragneiss of the Southeastern Churchill Province. Detailed geological mapping, petrography and U-Pb Thermal Ionization Mass Spectrometry dating of zircon and baddeleyite of the Pearly Gates Anorthosite pluton and Tessiarsuyungoakh intrusion were used to ascertain the mode of emplacement and crystallization ages of the major intrusive units. In addition, studies of the Paleoproterozoic regional metamorphism and Mesoproterozoic contact metamorphism of the Tasiuyak paragneiss were performed using the NaKFMASH petrogenetic grid to determine P-T conditions. The results of this thesis project indicate the following geological history of the study area. -- The Tasiuyak paragneiss contains evidence of the Paleoproterozoic regional metamorphic mineral sub-assemblage garnet + biotite + sillimanite. Detailed petrography of this sub-assemblage indicated that the prograde and retrograde history of this unit occurred within the sillimanite stability field and peak P-T conditions were constrained in the range of 7.2 to 10.2 kbar and 800° to 830°C. Prior to ca. 1363 Ma, reactivation of structures in the paragneiss provided fractures into which monzonitic and monzodioritic magmas intruded as sheets. The 1363 ± 3 Ma monzonite and 1360 ± 4 Ma monzodiorite formed the composite Tessiarsuyungoakh intrusion. This intrusion produced a small (< 20 m) contact aureole in the Tasiuyak paragneiss. Incipient development of the contact metamorphic sub-assemblage cordierite + orthopyroxene + spinel replaced the regional sub-assemblage of garnet + biotite + sillimanite. This suggests that the Tessiarsuyungoakh intrusion ...