Geology and geochronology of the Barth Concentric Plutonic Suite and the central western margin of the Hosenbein pluton, Nain Plutonic Supersuite, Labrador : a fundamentally descriptive study detailing previous and new data, including new observations on the petrographic context of baddeleyite and zircon in olivine-gabbroic rocks of the Barth Concentric Plutonic Suite

• Main Author: Hinchey, Stephen
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2010
• Subjects: Nain; Barth Island
• Online Access: https://research.library.mun.ca/9614/; https://research.library.mun.ca/9614/1/Hinchey_Stephen.pdf

The Barth Concentric Plutonic Suite of the Mesoproterozoic Nain Plutonic Supersuite, northern Labrador, is an oblong, sinistrally offset body underlying 35 km² of land occupying western and central Barth Island and the shores of Nain Bay to the northwest and southeast. The Barth Concentric Plutonic Suite is bounded by intrusive contacts and is subdivided into concentrically disposed units bounded by intrusive contacts. With some minor exceptions, each unit is characterised by one of four categories of rock type: 1) mineralogically Fe-rich diorite and gabbroic; 2) Ol-gabbroic (includes troctolite); 3) charnockitic; or 4) Ol-free anorthosite and gabbroic. The sum of all rock volumes, documented and undocumented, belonging to each category of rock type are here called rock-type clans, and the sum of all units each rock-type clan characterises are here called rock-type predominancies. The intrusive contacts between the units of the Barth Concentric Plutonic Suite variously exhibit sharp and straight intrusion, chilling, magma mingling, magma mixing, hybridisation, and interleaving. Most such contacts occur between rock-type predominancies, and therefore generally between disparate rock types, the exception being that some physically opposing rock types are similar in composition due to mixing. Intrusive contacts have also been recognised within several units. Extreme differentiation is not evident in any of the major units. -- The overall structural pattern within the Barth Concentric Plutonic Suite is roughly concentric, assuming a north-south long axis before fault offset, with all three-dimensionally assessed structures dipping inward except for one dipping outward, an internal intrusive contact within the charnockitic rock-type predominancy south of Nain Bay. -- Olivine forsterite contents generally do not vary significantly within thin-sections of Ol-gabbroic rock. South of Nain Bay, where thin-sectioning is relatively dense and regular, a locally concentric pattern in the distribution of forsterite content in ...