Deformation history in part of the Lubec–Belleisle zone of southern New Brunswick

Abstract

Rocks of the Proterozoic Coldbrook Group on the north shore of the Bay of Fundy, New Brunswick, are bounded to the north by a major northeast trending fault (Lubec–Belleisle). North of the fault Paleozoic rocks of the Mascarene Group are overlain unconformably by Upper Devonian and Lower Carboniferous strata.Both the Coldbrook and Mascarene Groups have been deformed by three phases of deformation. Deformation of the two Groups was coeval; penetrative fabrics first developed during the Acadian (Middle Devonian) orogeny.Pre-Acadian Paleozoic movements were limited to local or regional uplift with possible attendant warping and/or gentle tilting.Mylonitic fabrics formed in Coldbrook rocks during the first two phases of the Acadian polyphase deformation. These northeast trending s- surfaces lie normal to the direction of maximum finite shortening. Also from the orientation of synmylonization quartz deformation lamellae of the second phase, it is apparent that the local trajectory of the maximum principal stress was normal to the s-surfaces of the mylonites.No evidence for major northeast–southwest strike slip faulting has been found. Fracture analyses in Upper Devonian and Lower Carboniferous rocks in the northeast trending fault zone, point to a northwest trending principal compressive stress.It is contended that the bulk of the ductile strain (first two phases) occurred In response to northwest principal compressive stress during the Middle Devonian, and these stresses were re-established in post-Devonian times, resulting in the development of high angle oblique to dip slip movements on the northeast trending faults.