Nd isotopic and geochemical signature of the paleoproterozoic Trans-HudsonOrogen, southern Baffin Island, Canada: implications for the evolution of eastern Laurentia

The southern Baffin Island segment of the Trans-Hudson Orogen comprises a t hree-part crustal architecture. The lowest structural level (level 1) inclu des ca. 2.88 Ga tonalite-diorite-granite orthogneisses of the parautochthon ous Superior Province. Level 2 comprises monzogranite-tonalite-diorite orth ogneisses of the 1.86-1.82 Ga Narsajuaq are. At the highest structural leve l (level 3), ca. 1.95 Ga tonalite-monzogranite orthogneiss, ca. 1.93 Ga she lf metasediments of the Lake Harbour Group, and dominantly psammitic metase diments of the Blandford Bay assemblage are tectonically imbricated and cro ss-cut by 1.86-1.85 Ga monzogranitic to tonalitic rocks of the Cumberland b atholith. Level 2 Narsajuaq are felsic orthogneisses display strongly fract ionated rare earth elements, with La-n/Yb-n > 100, epsilon (Nd) (1.85 Ga) v alues ranging from - 12 to - 19, and T-DM ages from 2.7 to 3.6 Ga, consiste nt with derivation by underplating and melting of strongly fractionated cru st bearing components as old as Paleoarchean, such as parts of the Nain Pro vince or the northernmost Superior Province. The Narsajuaq are rocks on sou thern Baffin Island show more evolved Nd isotopic compositions and strongly fractionated REE profiles relative to correlated rocks on the Ungava Penin sula in northern Quebec. The north-south change in Nd isotopic and REE geoc hemical signatures is consistent with northward subduction beneath an Arche an cratonic nucleus. At structural level 3, the peraluminous Cumberland bat holith shows La-n/Yb-n mostly < 50, negative Eu anomalies, weakly fractiona ted HREE, <epsilon>(Nd) (1.85 Ga) values from - 2.7 to - 7.4, and T-DM ages from 2.35 to 3.08 Ga. The data are consistent with pervasive assimilation of Lake Harbour Group metasediments (epsilon (Nd) (1.85 Ga) = -4.5 to -7.3) and lesser amounts of Ramsay River orthogneiss (epsilon (Nd) (1.85 Ga)= -5 .2 to -16.5). Lake Harbour Group Nd isotopic and REE compositions are simil ar to the Tasiuyak metasedimentary gneiss of Labrador, and support correlat ion of the two units. The Blandford Bay metasediments show Nd isotopic evid ence for contribution of Mesoarchean detritus (epsilon (Nd) (1.85 Ga) = -10 .9 to -13.4), and may be derived from Archean Nain Province. The distinctiv e lithologies, Nd isotopic signatures, REE chemistry and crystallization ag es of structural levels 2 and 3 metaplutonic rocks suggest that they repres ent two separate Paleoproterozoic terranes showing distinctive crustal evol ution histories involving separate and distinctive Archean crustal nuclei. Tectonic models for the eastern Trans-Hudson Orogen require two spatially-d istinct 1.86-1.82 Ga subduction systems reworking distinct Archean cratonic margins in order to account for the differences between Paleoproterozoic o rthogneisses on southern Baffin Island. One subduction system would have pr oduced the Narsajuaq are of level 2, by pervasive assimilation of crustal r ocks with epsilon (Nd) (1.85 Ga) lower than -11.6 and La-n/Yb-n > 100. The differences between the less evolved Nd isotopic compositions of the Narsaj uaq are of Ungava Peninsula and the highly evolved Nd isotopic compositions of the Narsajuaq are rocks on Baffin Island may explained by: (i) subducti on beneath a northward-thickening Archean cratonic block: or (ii) by a reli ct north-south age boundary in the Archean cratonic margin. A second subduc tion zone would have produced the Cumberland batholith by melting and assim ilation of a cratonic margin less fractionated REE and more elevated E,, va lues. Data from structural levels 2 and 3 are consistent with correlation of thes e rocks across the eastern segments of the Trans-Hudson Orogen. (C) Publish ed by Elsevier Science B.V.