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

¹ Ottawa-Carleton Geoscience Centre, Carleton University, Ottawa, Ontario K1S 5B6, Canada
² 23 Newton Street, Ottawa, Ontario K1S 2S6, Canada
³ Department of Geology, State University of New York at Potsdam, Potsdam, New York 13976, USA
⁴ Ottawa-Carleton Geoscience Centre, Carleton University, Ottawa, Ontario K1S 5B6, Canada
⁵ Canada-Nunavut Geoscience Office, P.O. Box 2319, Iqaluit, Nunavut X0A 0H0, Canada
⁶ Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada

Ultrapotassic rocks of the Christopher Island Formation (Baker Lake basin) were emplaced across an enormous area (240 000 km² 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 _{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 _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.

Key Words: lamprophyres • Hearne domain • Snowbird zone • Paleoproterozoic • mantle metasomatism • Archean subduction

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