Minas Fault Zone: Late Paleozoic history of an intra-continental orogenic transform fault in the Canadian Appalachians

摘要

The Minas Fault Zone (MFZ) defines the boundary between the Avalon and Meguma terranes in the Canadian Appalachians and is exposed in mainland Nova Scotia and southern New Brunswick. These terranes originated along the Gondwanan margin, but had accreted to Laurentia by the middle Devonian. The surface trace of the MFZ is adjacent to the southern margin of the LateDevonian-Permian Maritimes Basin. The Late Devonian-Late Carboniferous evolution of the MFZ involves several episodes of oblique dextral shear that resulted in basin formation and inversion and at various times the zone was the focus of magmatism, regional fluid flow and mineralization. In the Late Devonian—Early Carboniferous, asymmetric rifting accompanied by dextral shear produced two coeval sequences: the Horton Group, which is dominated by continental clastic strata, and the Fountain Lake Group, which consists predominantly of bimodal volcanic rocks that overlie high-level plutons emplaced along active shear zones. The overall tectonic environment may have been dominated by dextral transtension along the southern margin of Laurentia, which corresponded with the northern flank of the Rheic Ocean. A major change in the evolution of the Minas Fault Zone occurred in the Late Mississippian-Early Pennsylvanian and produced the E-W Chedabucto Fault, clockwise rotation of pre-existing structures, local zones of transtension and transpression, as well as regional fluid flow and extensive mineralization. This major change may reflect the onset of Laurentia—Gondwana oblique collision, the effects of which continued into the latest Carboniferous with coeval development of flower structures and pull-apart basins in zones of local transpression and transtension.