Hearne Domain Research Articles

Paleoproterozoic intracratonic basin processes, from breakup of Kenorland to assembly of Laurentia: Hurwitz Basin, Nunavut, Canada

Abstract The evolution of Hurwitz Basin records discontinuous tectonic processes in the Hearne domain (northern Canada) resulting from changing distant boundary conditions. Magmatic, eustatic and paleoclimatic influences, although significant, are considered to have been of secondary importance. In agreement with recent models, lower Hurwitz Group units record intracratonic basin formation during initial breakup stages of a speculative Neoarchean supercontinent (Kenorland). In contrast to recent models, new Sm–Nd and Pb–Pb data and recent detrital zircon geochronology document a hitherto unsuspected time break (at least 200 My) within the Hurwitz Group (ca. 2.11–1.91 Ga). These data indicate that the deposition of upper Hurwitz Group units overlapped with ca. 2.0–1.7 Ga amalgamation of the Slave, Superior, Sask, Wyoming and Nain cratons during assembly of Laurentia. Initiation of Hurwitz Basin and deposition of predominantly continental siliciclastic rocks in sequence 1 (Noomut, Padlei and Kinga Formations) were due to regional sagging in response to early lithospheric stretching. Immature deep-water pelites of sequence 2 (Ameto Formation) reflect basin-margin arching and basin-centered deepening related to a second episode of stretching. Gabbro sills and dykes (2.11 Ga), emplaced after lithification of the Ameto Formation represent continued stretching that ultimately led to dispersion of Kenorland's daughter fragments. The gap in the sedimentary record signifies a time when processes required to generate permanent subsidence were lacking. Mixed siliciclastic–carbonate ramp and fluvial deposits of sequences 3 and 4 (Watterson, Ducker and Tavani Formations) were deposited after ca. 1.91 Ga, during shortening from the west (related to Taltson–Thelon and Wopmay orogens), but boundary conditions to the south are less certain. These may have involved either extension related to late fragmentation and dispersion of the southern Hearne margin, or shortening due to early (ca. 1.87 Ga) collisional processes in western Trans-Hudson orogen. Similar to the classic Phanerozoic intracratonic basins of North America, we infer that tectonic subsidence in Hurwitz Basin is a reflection of plate tectonics, reinforcing similarities in basin-forming processes between the early Paleoproterozoic and the Phanerozoic.

Enriched Archean lithospheric mantle beneath western Churchill Province tapped during Paleoproterozoic orogenesis

Ultrapotassic rocks of the Christopher Island Formation (Baker Lake basin) were emplaced across an enormous area (240 000 km 2 minimum) of the western Churchill Province ca. 1.83 Ga. These rocks extend across the Snowbird zone, a geophysical feature postulated by others to represent a Paleoproterozoic suture that welded the Rae and Hearne domains. Minette dikes and flows of the Rae and Hearne domains display identical ϵ Nd, 1830 values and incompatible element patterns, and thus appear to have originated from a common lithospheric-mantle source. Christopher Island Nd model ages cluster at 2.8 Ga, and ϵ Nd data from one Archean lamprophyre and three 2.45 to ca. 2.2 Ga mafic suites suggest that enriched lithospheric-mantle sources beneath both the Rae and Hearne domains existed well before ca. 1.83 Ga, inconsistent with Paleoproterozoic suturing along the Snowbird zone. In contrast to commonly invoked models that envisage melting of local enriched domains, Christopher Island ultrapotassic rocks appear to have originated from an extensive reservoir. We suggest that such a reservoir was created during an Archean metasomatic event, perhaps owing to flat subduction, and that it remained in nearly complete isolation until tapped during Paleoproterozoic extension related to squeezing of western Churchill crust between flanking Wopmay and Trans-Hudson orogens.