DEVONIAN-CARBONIFEROUS IGNEOUS INTRUSIONS AND THEIR DEFORMATION, COBEQUID HIGHLANDS, NOVA-SCOTIA

Field relationships and regional distribution patterns of igneous rock s in the Cobequid Highlands provide information on sequential styles o f deformation during the later Devonian and Carboniferous formation of the Magdalen Basin. New mapping and aeromagnetic data show that large diorite plutons have orthogonal outlines, suggesting that they occupy pull-apart space. Diorites both cut and are cut by granite plutons, w ith magma intermingling relationships suggesting co-existing magmas. L imited dating suggests that most plutonism occurred at about the Devon ian-Carboniferous boundary and was preceded by mid to late Devonian vo lcanism in the eastern Cobequids, younger ages reflect alteration and/ or deformation events. Granite veins in diorite plutons show strike-sl ip syn-magmatic deformation. Ductile thrust deformation of the western granite plutons and Fountain Lake Group was followed by brittle fault ing and emplacement of dykes along zones of weakness showing east-west pull-apart. Magnetic data reveal that rocks similar to the major dior ite plutons underlie much of the central and western Cobequid Highland s and the northeastern part of the Minas sub-basin. The diorite pluton s may be an exposed representative of mafic magma that underplated muc h of the extensional Magdalen Basin. The structure of the Cobequid Hig hlands is dominated by east-west faults parallel to the Cobequid-Cheda bucto Fault that at times acted as transfer faults for major extension al structures in the Magdalen Basin.