Emplacement of the Nain anorthosite : diapiric versus conduit ascent
Royse, Katherine; Park, R G. 2000 Emplacement of the Nain anorthosite : diapiric versus conduit ascent. Canadian Journal of Earth Sciences, 37 (8). 1195-1207. 10.1139/cjes-37-8-1195Before downloading, please read NORA policies.
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.
|Programmes:||BGS Programmes > Geology and Landscape Southern|
|NORA Subject Terms:||Earth Sciences|
|Date made live:||26 Nov 2008 12:52|
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