Late Devonian shear-zone reactivation in the Canadian Appalachian orogen

Abstract

Abstract Oblique accretion zones often display transpressive, strike-slip and transtensive structures of different orientations with respect to the convergence axis. The Late Devonian oblique collision of Meguma within the Canadian Appalachian orogen is often characterized as transpressive. However, the simultaneous opening of the Maritimes Basin indicates that the orogenesis also partitioned into an extensional component. In this context, few of the shear zones reactivated during this time period have been characterized while accounting for the possibility of strain partitioning. To do so, we characterize the kinematics and timing of deformation of the Eastern Highlands Shear Zone (EHSZ) and the Coinneach Brook Shear Zone (CBSZ) on Cape Breton Island, Nova Scotia, using a combination of U–Pb geochronology (zircon, monazite, xenotime and apatite) and 40 Ar/ 39 Ar geochronology in situ and step-heating experiments (amphibole, muscovite and biotite). Results show that the Silurian EHSZ was reactivated at c. 385–367 Ma and the CBSZ was formed at c. 395–369 Ma, both yielding oblique kinematics. Together, these structures accommodated the rapid exhumation of the Cape Breton Highlands during the docking of the Meguma terrane. This study thus highlights the heterogeneous distribution of transtensive and transpressive deformation during the Neoacadian Orogeny.