KISSEYNEW METASEDIMENTARY GNEISS BELT, TRANS-HUDSON OROGEN (CANADA) -BACK-ARC ORIGIN AND COLLISIONAL INVERSION

The Kisseynew metasedimentary gneiss belt (Kisseynew domain), which re presents one of the most extensive tectonic segments of the Paleoprote rozoic Trans-Hudson orogen in north-central Canada, initially develope d in a back-are setting. It comprises turbidites and continental sands tones, both of which are interlayered with rare volcanic rocks and int ruded by plutons. The ages of detrital zircons and crosscutting pluton s constrain turbidite sedimentation to 1.855-1.841 Ga, postdating earl y deformation and metamorphism associated with are-are and are-contine nt collisions affecting much of the Trans-Hudson orogen. These turbidi tes are interpreted to have been deposited in a back-arc basin behind a retreating subduction boundary. The Kisseynew domain and its souther n flank are marked by 1.84-1.83 Ga magmatic rocks that may be related to subduction of back-are basin oceanic crust. Collapse of the Kisseyn ew ''basin'' by ductile fold-and-thrust deformation began during 1.84- 1.83 Ga magmatism and continued through peak metamorphism at ca. 1.820 -1.805 Ga. The result was that the high-grade core of the Kisseynew do main was structurally emplaced over adjacent low-grade terranes. The r egionally extensive high-temperature and low-pressure metamorphism tha t characterizes the Kisseynew domain is best explained by thickening a nd thermal relaxation of basin-fill rocks marked by a geotherm elevate d by 1.84-1.83 Ga magmatism.