Origin and evolution of mid- to late-Archean crust in the Hanikahimajuk Lake area, Slave Province, Canada; evidence from U–Pb geochronological, geochemical and Nd–Pb isotopic data

Abstract

A geochronological, major/trace element geochemical and Nd–Pb isotopic study of early- to mid-Archean basement granitoids/gneisses, ∼2.68 Ga greenstone belt and 2.58–2.62 Ga late-Archean granitoids from the Hanikahimajuk Lake area of the northern Slave province was undertaken to constrain the tectonomagmatic evolution of the north-central area of Slave province, Northwest Territories, Canada. The basement tonalites are precisely dated at 3378±1 Ma by U–Pb zircon methods and are characterized by steeply fractionated REE patterns with no negative Eu anomalies. They were likely produced through partial melting of mafic crust at >0.8 GPa. The εNd T of these rocks range from −0.3 to +2.1, implying involvement of even older crustal material in their genesis.Two different types of ∼2.68 Ga mafic to intermediate volcanic rock are recognized in the Hanikahimajuk Lake area: tholeiitic rocks with no Ta–Nb depletions and calc-alkaline rocks with slight negative Ta–Nb depletions. All of these rocks show clear evidence for contamination by the ∼3.4 Ga basement tonalite, thus precluding the possibility that some of these tholeiitic mafic rocks were produced in a mid-oceanic ridge setting. From the data presented here, we conclude that the tholeiitic rocks were produced in a back-arc setting, likely similar to that of the Japanese arc. The calc-alkaline rocks may either be a remnant of the volcanic arc or part of the same back-arc system. However, the close proximity with the tholeiitic rocks in the field favours the latter possibility. Mafic to intermediate rocks with similar geochemical and isotopic characteristics are also found from the Yellowknife area of the southwestern Slave province, and from the Indin Lake area of the westernmost Slave province (south of Grenville Lake area). This observation may indicate that the mafic-dominated volcanic belts of the western Slave province may be a remnant of a single, now collapsed and shortened back-arc basin. The existence of syn-volcanic calc-alkaline plutonic rocks with similar geochemical and isotopic features as the calc-alkaline volcanic rocks supports this possibility.The geochemistry of late-Archean granitoids suggests that they are produced mainly through partial melting of mafic igneous protoliths and clastic sedimentary rocks (and possibly tonalitic rocks). Similarity in the εNd(2.6) values between these granitoids and the supracrustal rocks in the area is in accord with this model. Such protoliths are also consistent with the tectonic setting at which the ∼2.68 Ga volcanic rocks were generated, because mafic igneous rocks and clastic sedimentary rocks (with lesser felsic igneous rocks) are the major constituents of a back-arc basin.