GEOCHEMISTRY OF MAFIC MAGMAS FROM THE UNGAVA OROGEN, QUEBEC, CANADA, AND IMPLICATIONS FOR MANTLE RESERVOIR COMPOSITIONS AT 2.0 GA

The Ungava orogen of northern Quebec is one of the best preserved Prot erozoic mobile belts of the world, recording > 200 Ma of plate diverge nce and convergence. Voluminous magmatism associated with rifting of t he Superior Province basement similar to 2.04 Ga resulted in the devel opment of a volcanic rift margin sequence and an ocean basin. Four dis tinct mafic magma suites were erupted: (1) continental basalts (Eskimo Formation, western and central Povungnituk Group) with moderate to hi gh Zr/Nb and negative Nb anomalies which have interacted with the cont inental crust (epsilon(Nd(2.0 Ga) from - 7.4); (2) mafic lavas from th e Flaherty Formation, eastern Povungnituk Group and some Watts Group l avas associated with passive margin rifting, having slightly enriched isotopic signatures (epsilon((Nd)(2.0 Ga)) = +2.7 to +4.4) compared to the contemporaneous depleted mantle, high (Nb/Y)(n) and low Zr/Nb rat ios (similar to 4.4 and similar to 8.9, respectively); (3) a highly al kaline GIB-like suite (epsilon((Nd)(2.0 Ga)) = + 2.3 to + 3.2, (Nb/Y)( n) > 12) within the Povungnituk Group composed of nephelinites, basani tes and phonolites; and (4) depleted Mg-rich basalts and komatiitic ba salts (epsilon((Nd)(2.0 Ga)) approximate to + 4.5 to + 5.5) with trace -element characteristics of N-MORB, but with higher Fe and lower Al th an primitive MORE (Chukotat Group, Ottawa Islands and some Watts Group samples), The ocean basin into which these lavas were erupted was sub sequently destroyed during subduction between similar to 1.90 and simi lar to 1.83 Ga, resulting in the development a magmatic are (Narsajuaq terrane and Parent Group). The Ungava magmas provide a unique window into the mantle at 2.0 Ga. The chemical and isotopic similarity of the se Proterozoic magmas to modern-day magmas provides strong evidence th at the interplay between depleted mantle, OIB mantle and sub-continent al mantle during the Proterozoic was comparable to that of the modern Earth.