Tonian to Mississippian magmatic pulses recorded within the Pearya Succession I in the vicinity of Yelverton Inlet, Ellesmere Island, Canada

The Pearya Terrane of northern Ellesmere Island is composed of a Tonian crystalline arc, Neoproterozoic to Paleozoic sedimentary successions, an Ordovician island arc complex and related volcaniclastics, and middle Ordovician to Silurian sedimentary rocks. Igneous rocks of the Pearya Succession I, dominated by Tonian gneiss, were targeted for ion microprobe U-Pb zircon dating. Two felsic gneisses yielded Tonian c. 960 Ma and 940 Ma ages, respectively. Another two felsic gneisses gave ages of c. 870 Ma and c. 750 Ma. The latter exhibited common inherited zircon cores dominated by a c. 870 Ma signature. Out of three dated mafic samples, a gabbro yielded an age of c. 470 Ma, while basaltic dykes gave c. 415 Ma and c. 340 Ma. The c. 415 Ma dyke is cutting the c. 940 Ma gneiss, whereas the c. 360 Ma dyke is emplaced within the c. 870 Ma gneiss. While the obtained ages in the range of c. 960-940 Ma are typically reported from the Pearya Succession I, felsic gneisses of c. 870 Ma and 750 Ma, to our knowledge, have not been reported so far. Tentatively, we interpret these two ages as a potential expression of post-Grenville extension, associated with an attempted, repeated, but unsuccessful rifting. The c. 470 Ma gabbro is interpreted to have formed in an active margin environment as a part of the Thores Arc during the main phase of the Caledonian (M’Clintock) subduction and amalgamation. The age of c. 415 of the older mafic dyke somewhat corresponds to other Early Devonian magmatic rocks known from Pearya. Interestingly, it slightly precedes the timing of prograde metamorphism within an adjacent Barrovian sequence of the Petersen Bay Assemblage. Thus, it may represent the earliest expression of a hypothesized igneous heat source for the Barovian sequence (Kośmińska et al. 2022, JPet). Lastly, the c. 340 Ma mafic dyke is coeval with metamorphism and granitic magmatism known from Pearya (Trettin 1998 GSC Bulletin, Estrada et al. 2016 JGeodyn, Powell & Schneider 2022 Tectonics). It is also coeval with regional extension and deposition of the Emma Fiord and Borup formations of the Sverdup Basin. Notably, the latter contains the Audchild basaltic lavas and pyroclastic sediments (Thorsteinsson 1974, GSC Bulletin). Thus, we postulate that the mafic dyke of c. 340 Ma age is closely related with extension and rifting responsible for the formation of the Sverdrup Basin. This discovery calls for much more careful interpretation of numerous undated mafic dykes occurring within the Pearya Succession I.

This research is funded by the National Science Centre (Poland) project no. 2019/33/B/ST10/01728.