Paleoproterozoic Nb–enriched meta-gabbros in the Quanji Massif, NW China: Implications for assembly of the Columbia supercontinent

Abstract

Diverse models have been proposed for the role of the Tarim Craton within the Paleoproterozoic Columbia supercontinent assembly. Here we report a suite of ∼1.71 Ga Nb-enriched meta–gabbro lenses in the eastern Quanji Massif, within the Tarim Craton in NW China. The meta–gabbroic rocks have Nb contents of 11.5–16.4 ppm with Nb/La ratios varying from 0.84 to 1.02 ((Nb/La)N = 0.81–0.98) and Nb/U ratios from 38.0 to 47.2. They show low SiO2 (45.1–48.5 wt.%) and MgO (5.96–6.81 wt.%) and Mg# (Mg# = Mg/(Mg + Fe) = 43.5–47.7), high FeOt (13.0–15.7 wt.%) and moderate TiO2 (1.70–2.51 wt.%), with tholeiitic affinities. These rocks possess low fractionated REE patterns without obvious Eu anomalies (Eu/Eu* = 0.87–1.02). Their primitive mantle-normalized elements patterns display significant Zr–Hf troughs, positive Nb anomalies, weak negative Ti and P anomalies, and high contents of Rb and Ba, resembling Nb-enriched basalts generated in arc-related tectonic settings. Their arc–like geochemical signatures together with whole rock ɛNd(t) values of 0.4–2.1 and corresponding old TDM (2.22–2.37 Ga) as well as (143Nd/144Nd)t and (87Sr/86Sr)t (t = 1712 Ma) values of 0.5104–0.5105 and 0.7030–0.7058, respectively, suggest that their precursor magma originated from mantle wedge peridotite metasomatised by subduction-derived melts. The results from our study reveal subduction along the eastern periphery of the Tarim Craton and marginal outgrowth continuing to ∼1.7 Ga within the Columbia supercontinent.