CRUSTAL EVOLUTION AND TECTONIC ASSEMBLY OF THE TRANS-HUDSON OROGEN OF BAFFIN ISLAND: CONSTRAINTS FROM GRANITOID ROCKS

Voluminous post-accretion granitoid magmatism has obscured major tectonic boundaries in the Trans-Hudson Orogen (THO) of Baffin Island, making it difficult to fully understand the crustal evolution and tectonic assembly of key building blocks in NE Laurentia. Nonetheless, given their voluminous character and timing of emplacement, these granitoid rocks have been used as 'crustal probes' to map out, and constrain the timing of assembly of, different crustal domains. The petrogenesis and tectonic context of the ~221,000 km², ca. 1.865-1.845 Ga Cumberland batholith (CB) have been interpreted based on a 900 km geochemical - Nd isotopic transect across the THO. This batholith stitches tectonic boundaries between microcontinental block(s) within the internal THO and bounding Archean domains including the Archean Rae craton in central Baffin Island and the Archean Sugluk and Hall Peninsula blocks in southern Baffin Island. The mainly granulite grade, high-K to shoshonitic CB consists of infracrustal (I-type) granites which display a spectrum of tectonic affinities. Previously interpreted as a continental arc batholith like many other large volume Proterozoic granitoid batholiths (e.g. Wathaman batholith, central THO), the CB best represents a post-accretion batholith resulting from large-scale lithospheric mantle delamination. Isotopic signatures (e_Nd at 1.85 Ga) within the interior CB (-2 to -7) are more radiogenic than those within the Archean domains in central (-8 to -15) and southern (-5 to -19) Baffin Island. The isotopic transect is interpreted as ‘imaging’ an accreted microcontinental block (Meta Incognita) of Neoarchean-Paleoproterozoic age and bounding Archean basement domains in southern (Sugluk block) and central (Rae) Baffin Island. Combined with Nd data from pre-accretion plutonic rocks, post-CB (ca. 1.84–1.82 Ga) granitoid plutons, and supracrustal rocks sourced from Meta Incognita microcontinent, we interpret the isotopically more evolved domain in southern Baffin Island as imaging the Archean Sugluk block at depth beneath the Meta Incognita microcontinent. The results further imply that assembly of the Sugluk block and Meta Incognita microcontinent occurred prior to CB magmatism, sometime between 1.95 and 1.90 Ga.