KINEMATICS OF THE ROCKLAND BROOK FAULT, NOVA-SCOTIA - IMPLICATIONS FOR THE INTERACTION OF THE MEGUMA AND AVALON TERRANES

The Cobequid-Chedabucto fault system of northern mainland Nova Scotia represents the surface expression of the Avalon-Meguma terrane boundar y, but because it is exposed at high crustal levels in the Cobequid Hi ghlands, the fault system provides little information as to the kinema tic relationships of the two terranes in this area. In the eastern Cob equid Highlands, the Rockland Brook Fault (RBF) is exposed within the more deeply eroded highlands massif and juxtaposes units of widely var ying ages and lithologies. Therefore, this fault is better suited to d efine the nature and timing of fault movement associated with Avalon-M eguma terrane interaction. In several large Carboniferous plutons alon g the length of the RBF, and in previously deformed Precambrian rocks, mylonitic foliation orientations are predominantly east-west trending and mineral lineations plunge southeast. Kinematic indicators such as minor fold vergence, prophyroclast systems, asymmetric boundins, shea r-band fabrics, and preferred recrystallization orientations indicate dextral shear. These data are taken to infer that the central section of the RBF is dominated by dextral strike-slip motion. Transpression o ccurs locally where the RBF curves into restraining bends. Kinematic d ata in these bends indicate top to the northwest thrusting. At the eas ternmost extent of the RBF, high-level brittle normal faults predomina te in the locally extensional environment. The timing of RBF movement is constrained only by the ca 360 Ma granite bodies which it deforms a nd by the Westphalian sedimentary rocks which are affected by only the latest stages of movement. These kinematic data are consistent with p reviously published kinematic models for the interaction of the southe rn margin of the Avalon Composite Terrane with the Meguma Terrane in m ainland Nova Scotia. These models suggest that regional dextral shear was accompanied by localized components of transpressional thrusting, wrench tectonism, and small-scale sedimentary basin development during Devonian to Carboniferous terrane interaction.