A lithospheric-scale Arrowsmith (2.4 Ga) detachment system with major Trans-Hudson (1.8 Ga) reactivation documented in the Howard Lake shear zone, Rae craton, Canada

Abstract

This study characterizes the polyphase tectonometamorphic history of a major shear system in the Rae craton, the Howard Lake shear zone (HLsz), which exhumed high-grade rocks in the distant hinterland of the Paleoproterozoic Trans-Hudson Orogen. Prior work established a Mesoarchean mantle model-age discrepancy in basement rocks across the HLsz, which we interpret to have contributed a fundamental lithospheric rheology contrast that allowed for HLsz localization. Our work shows that the HLsz has a long-lived history starting in the early Paleoproterozoic as it abruptly separates 2.36 Ga granulite-facies metamorphic units to the east from 2.4 Ga greenschist-facies metamorphic basement rocks to the west. Subsequent reactivation during Trans-Hudson Orogen time between 1.86 and 1.82 Ga accommodated re-burial and re-exhumation of high-grade rocks in its footwall coeval with Sask craton collision. Strong penetrative overprinting deformation in metaigneous rocks and a newly discovered < 2.04 Ga schist preserve evidence for right-lateral transpression within the HLsz at ca. 1.82 Ga, which is coincident with the terminal collision of the Superior craton. Our work demonstrates that the HLsz is one of several major crustal-scale anisotropies in the south Rae craton and it is broadly analogous to major detachment fault systems documented in numerous Phanerozoic orogenic systems. Furthermore, the polycyclic deformation history of the HLsz, along which regional burial and exhumation was strongly localized, demonstrates the considerable influence crustal scale anisotropies can have on the evolution of craton architecture such as that presently found in the south Rae craton of the Canadian Shield.