The nature and origin of enclaves in four peraluminous granitoid intrusions from the Meguma Zone, Nova Scotia

Authors

  • Marcus C. Tate Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia

DOI:

https://doi.org/10.4138/2130

Abstract

Four mid- to late Devonian peraluminous granitoid intrusions in the Meguma Zone of southwestern Nova Scotia contain abundant enclaves typical of orogenic granitoid bodies. The Barrington Passage and Shelbume plutons contain an assemblage of granoblastic metasedimentary homfelsic enclaves (49%) that have aluminosilicate porphyroblasts, and surmicaccous enclaves (51%) that consist of > 70% decussate biotitc with apatite and zircon inclusions. Metasedimentary enclaves pre dominate in the Port Mouton Pluton and the South Mountain Batholith (52%), but these intrusions also contain abundant microgranular and coarse-grained granitoid enclaves (25% and 23%, respectively) that have peraluminous mineral assemblages and tonalitic to leucomonzogranitic compositions. High concentrations of metasedimentary enclaves at the country rock contacts suggest that they probably formed as xenotiths stoped from the Meguma Group. No xenoliths reflect palaeosomes of basement gneiss from the protolith of the granitoid melts, but the surmicaccous enclaves may be restite in the Port Mouton Pluton and the South Mountain Batholith; in the Barrington Passage tonalite they probably represent melanosomes after incorporated xenoliths. Microgranular and coarse-grained granitoid enclaves apparently represent stoped autoliths of both quenched and slowly cooled granitic melt in the multiply-intrusive granitoid bodies. RÉSUMÉ Quatre intrusions granitiques du Dévonien supérieur dans la zone de Meguma, dans le sud-ouest de la Nouvelle-Écosse, renferment des enclaves abondantes typiques de masses granitiques orogéniques. Les intrusions ignées de Barrington Pas sage et de Shelbume renferment un assemblage d'enclaves cornéennes métasédimentaires granoblastiques (49 %) comprenant des enclaves surmicacles et porphyroblastes d'aluminosilicates (51 %) constituées de moins de 70 % de biotitc entrecroisée d'inclusions d'apatite et de zircon. Les enclaves métasédimentaircs prédominent dans le pluton de Port Mouton et le batholite de South Mountain (52 %), mais ces intrusions renferment en outre des enclaves granitiques microgrenues et a gros grains (25 % et 23 % respectivement) comportant des assemblages minéraux hyperalumineux et dotées de compositions tonalitiques à leucomonzogranitiques. Des concentrations élevées d'enclaves métasédimentaires aux surfaces de contact encaissantes laissent supposer qu'elles se sont probablement formées en tant que xinolites abattus du groupe de Meguma. Aucun xéiolite ne correspond aux paléosomes du gneiss du socle provenant du protolite des magmas granitiques, mais les enclaves surmicacees pourraient etre des melanosomes dans le pluton de Port Mouton et le batholite de South Mountain. Dans la tonalite de Barrington Passage, dies représented probablement des melanosomes apparus apres l'incorporation des xénolites. Les enclaves granitiques microgrenues et à gros grains represented apparemment des enclaves syngénétiques de magma granitique tant figéque douce men t refroidi dans les masses granitiques intrusives multipli. [Traduit par la rédaction]

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Published

1994-11-01

How to Cite

Tate, M. C. (1994). The nature and origin of enclaves in four peraluminous granitoid intrusions from the Meguma Zone, Nova Scotia. Atlantic Geoscience, 30(3). https://doi.org/10.4138/2130

Issue

Vol. 30 No. 3 (1994)

Section

Articles

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