Age and evolution of deep continental roots beneath northern Canada

Abstract:

The age, composition and extent of Archean lithosphere is well documented beneath the Slave Craton, however, little is known about the deep continental roots beneath the rest of Canada’s vast north, despite the discovery of many new diamond-bearing kimberlites. Here we present age and composition information for kimberlite-borne peridotite xenoliths from the western Rae Craton (two localities: Repulse Bay and Pelly Bay) and central Victoria Island (CVI - a possible northern extension of the Slave Craton), as well as the Parry Peninsula (a possible new micro-craton).

The peridotites from the western Rae Craton, CVI and Parry Peninsula are generally characterized by high forsterite contents (Fo 92-93) and low whole-rock Al₂O₃ contents (< 2 wt.%, many < 1wt.%), similar to typical cratonic peridotites worldwide. However, these peridotites show a large span in Re-depletion model ages (T_RD). For the western Rae Craton, both localities preserve evidence of Archean parentage, with more of the Repulse Bay samples yielding Archean T_RD ages (>2.5 Ga) than for Pelly Bay. The samples from these two localities with post-Archean T_RD ages indicate significant lithospheric disturbance likely related to the Arrowsmith Orogeny (ca. 2.3 to 2.5 Ga), contrasting with the little disturbed central Slave lithosphere by other studies. For both CVI and Parry Peninsula peridotites, despite whole-rock and mineralogical compositions analogous to previously studied portions of cratonic mantle, there is no evidence of any Archean T_RD ages. Given that the CVI peridotites have major modes in T_RD ages of 1.7 to 2.1 Ga, the local lithosphere is more likely to represent an extension of the Wopmay Orogen (ca. 1.9 Ga) to the southwest or the Thelon tectonic-magmatic zone to the east, instead of the northern extension of the Slave Craton. Similarly, T_RD ages of 1.8 to 2.3 Ga indicate that the highly depleted Parry Peninsula peridotites are also synchronous with formation of the Wopmay Orogen with a northern extension. Hence, deep, refractory, diamond-bearing lithosphere can form in post-Archean times, perhaps in subduction zone settings.