Age of granulite from Huangtuling, Dabie Mountain:Pb-Pb dating of garnet by a stepwise dissolution technique

A new stepwise dissolution scheme, involving acids with different properties, enables the selective recovery of radiogenic and common Pb from a mineral, and makes single-mineral Pb-Pb dating possible. Garnet from a granulite sample from Huangtuling, northern Dabie Mountain yields a Pb-Pb isochron age of (1098 ± 35) Ma, which is interpreted as the timing of peak metamorphism of granulite facies.

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)t values of 0.6978-0.7123 andε_(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.