THE NATURE AND ORIGIN OF ENCLAVES IN 4 PERALUMINOUS GRANITOID INTRUSIONS FROM THE MEGUMA ZONE, NOVA-SCOTIA

Four mid- to late Devonian peraluminous granitoid intrusions in the Me guma Zone of southwestern Nova Scotia contain abundant enclaves typica l of orogenic granitoid bodies. The Barrington Passage and Shelburne p lutons contain an assemblage of granoblastic metasedimentary hornfelsi c enclaves (49%) that have aluminosilicate porphyroblasts, and surmica ceous enclaves (51%) that consist of > 70% decussate biotite with apat ite and zircon inclusions. Metasedimentary enclaves predominate in the Port Mouton Pluton and the South Mountain Batholith (52%), but these intrusions also contain abundant microgranular and coarse-grained gran itoid enclaves (25% and 23%, respectively) that have peraluminous mine ral assemblages and tonalitic to leucomonzogranitic compositions. High concentrations of metasedimentary enclaves at the country rock contac ts suggest that they probably formed as xenoliths stoped from the Megu ma Group. No xenoliths reflect palaeosomes of basement gneiss from the protolith of the granitoid melts, but the surmicaceous enclaves may b e 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 granit oid enclaves apparently represent stoped autoliths of both quenched an d slowly cooled granitic melt in the multiply-intrusive granitoid bodi es.