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Emplacement of the Nain anorthosite; diapiric versus conduit ascent

K. R. Royse and R. G. Park
Emplacement of the Nain anorthosite; diapiric versus conduit ascent
Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre (August 2000) 37 (8): 1195-1207

Abstract

Estimation of settling velocities of large orthopyroxene megacrysts, found within anorthosite intrusions, are calculated and compared with ascent rates achieved by diapirism and conduit propagation. Calculations suggest that diapirism is far too slow to be an appropriate ascent mechanism for anorthositic crystal mush and favour conduit emplacement. The intrusions of the Nain Plutonic Suite (NPS) are located along the Abloviak shear zone, which marks the boundary between the Nain and Churchill provinces, and within the zone of juxtaposition of the Saglek and Hopedale blocks of the Nain Province. These crustal weaknesses have probably controlled the emplacement and distribution of the intrusions. Contact relations between intrusions of anorthosite and their gneissic host rock provide evidence for two emplacement styles within the NPS, the first typified by strongly deformed and recrystallized rocks, and the second by an outer border zone of mafic rocks. It is proposed that these differences in intrusive style are due to differences in ductility contrast between the magma and its surrounding host rocks, such that those intrusions emplaced into the thermally softened shear zone have deformed margins, whereas those intruded into the cooler Archaean crust have undeformed margins.


ISSN: 0008-4077
EISSN: 1480-3313
Coden: CJESAP
Serial Title: Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre
Serial Volume: 37
Serial Issue: 8
Title: Emplacement of the Nain anorthosite; diapiric versus conduit ascent
Affiliation: Keele University, Department of Earth Sciences, Keele, United Kingdom
Pages: 1195-1207
Published: 200008
Text Language: English
Summary Language: French
Publisher: National Research Council of Canada, Ottawa, ON, Canada
References: 115
Accession Number: 2000-070315
Categories: Structural geologyIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, geol. sketch map
N53°00'00" - N53°00'00", W63°00'00" - W62°00'00"
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200022
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