Early Paleoproterozoic Post-Collisional Basaltic Magmatism in Quanji Massif: Implications for Precambrian Plate Tectonic Regime in NW China

Basaltic magmas can provide important information about mantle source nature, tectonic settings and tectonic evolution for a given terrain. This paper reports geology, petrography and geochemistry of whole-rock major and trace elements and Nd−Sr isotopes for a suite of garnet amphibolites from southeastern Wulan (Ulan), Quanji Massif, northwestern China. The garnet amphibolites were likely generated from basaltic lavas, associated with both paragneisses and orthogneisses of the lower Delingha Group. The basaltic protolith of these amphibolites can be broadly constrained to be formed at ∼2.33 Ga in an extensional setting post-collision. The geochemistry of amphibolites shows subalkaline and highly evolved characteristics. They display high-Fe low-Ti characteristics, with TFeO of 13.1 wt.%–17.9 wt.% and TiO 2 of 1.42 wt.%–3.09 wt.% (in most samples TiO 2 ⩽2.5 wt.%). The chondrite-normalized REE patterns show enrichment of LREE and LILE and the primitive-mantle-normalized incompatible element patterns display negative P, Ti, Nb−Ta and Zr−Hf anomalies. The ( 87 Sr/ 86 Sr), values of 0.697 8–0.712 3 and ε Nd ( t ) values of −2.81–5.08 respond to depleted mantle model ages ( T DM ) of 2.33–3.30 Ga. These suggest that the precursor magmas of the protolith of the garnet amphibolites were probably derived from the Early Paleoproterozoic depleted sub-continental lithospheric mantle that had been metasomatized by subduction-induced fluids and melts. The precursor basaltic magmas were contaminated by the older crustal components during magma ascending. This post-collisional basaltic magmatic event at ∼2.33 Ga in Quanji Massif thus enhanced the subduction shutdown or slowdown tectonic regime both in NW China and coevally with those plate tectonics in some important domains worldwide during the Early Paleoproterozoic.