Abstract

The Early to Middle Devonian Acadian and Late Carboniferous Hercynian faulting history, together with the distribution and composition of Upper Devonian to Lower Carboniferous igneous rocks, suggest a passive subsidence rather than a strike-slip pull-apart mechanism for the genesis of the Martimes Basin during Late Devonian time.

Specifically, there are two major, pre-Carboniferous, offsets in the northeast-trending Belleisle Fault that indicate its Acadian heritage, and preclude significant post-Acadian strike-slip motion along it. One is in western Bay of Fundy where 50 km of left-lateral displacement has occurred on the northwest-trending Oak Bay Fault. The other is beneath the Gulf of St. Lawrence where up to 200 km of right-lateral displacement has occurred on the northwest-trending Canso Fault (new name). The Canso Fault also appears to cut off other major northeast-trending faults from New Brunswick, including the Fredericton-Norumbega Fault. These northeast- and northwest-trending faults are considered to be the product of Acadian overthrusting, and thus predate the Maritimes Basin. In contrast, the east-trending Cobequid-Chedabucto Fault is an Upper Carboniferous structure that largely postdates the Maritimes Basin.

Upper Devonian to Lower Carboniferous granites and bimodal volcanic rocks are common around the Maritimes Basin and can be interpreted as being the result of the culminating phase of magmatism, which was precipitated by Acadian continental collision. The crustal thinning process following this collision and the corresponding isostatic adjustments were probably largely responsible for the two stage subsidence of the Maritimes Basin.