The 2.00 GA purtuniq ophiolite, Cape Smith Belt, Canada: Morb-like crust intruded by OIB-like magmatism

The Quebec-Baffin segment of the Paleoproterozoic Trans-Hudson Orogen compr ises a collage of tectonostratigraphic elements that accumulated on, or wer e accreted to, the northern margin of the Archean Superior craton throughou t more than 200 million years of divergent and subsequent convergent tecton ic activity. The Cape Smith Belt, on the Ungava peninsula in northern Quebe c, preserves a series of thrust imbricates of >2.04-1.87 Ga sedimentary and mafic volcanic rocks that record the subsidence and rifting of the Superio r craton and subsequent development of an oceanic basin. The structurally h ighest component of the Cape Smith Belt, the Watts Group, consists of ultra mafic and mafic cumulate rocks, gabbros, sheeted mafic dykes, pillowed and massive basalts that are interpreted as the igneous crustal components of a 2.00 Ga ophiolite. Although the rocks have been deformed and metamorphosed , primary igneous features Such as cumulate textures, intrusive contacts, c hilled dyke margins and pillow selvedges are locally well preserved. The op hiolite is a composite of two physically, chemically and isotopically disti nct suites of tholeiitic rocks; the older consists of gabbroic cumulate roc ks, pillowed basalts and sheeted mafic dykes, and is similar to suites form ed at modem mid-ocean spreading ridges, whereas the younger suite consists of ultramafic and mafic cumulate rocks and mafic dykes, and is analogous to modern hotspot-related oceanic-island complexes such as Hawaii. Reconstruc tions of the pre-deformation crustal configuration suggest that the mid-oce an ridge suite was at least 5 km thick, and the younger, oceanic-island sui te was greater than 4 km thick, a total thickness of this composite oceanic crust of >9 km.