Petrogenesis of the Xihuashan granites in southeastern China: Constraints from geochemistry and in-situ analyses of zircon U[sbnd]Pb[sbnd]Hf[sbnd]O isotopes

Abstract

The Xihuashan tungsten deposit, located in the Nanling tungstentin province, is renowned for being one of the largest and the earliest exploited deposits of tungsten worldwide. It is a vein‐type deposit genetically associated with the Xihuashan granite pluton. The granite was emplaced in four phases, and representative samples from each phase were analyzed using SIMS zircon UPb techniques, and the results indicate ages ranging from 161±3Ma to 158±2Ma (2σ). Whole rock analyses show the Xihuashan granitic rocks have high contents of SiO2 (74.5wt.%–78.1wt.%) and total alkali (7.68wt.%–8.86wt.%), and their aluminum saturation index (ASI) values have a narrow range of 1.01–1.16. The second and third phases of the Xihuashan granite are enriched in heavy rare earth elements and are depleted in Eu, Ba, Sr, P and Ti. P2O5 vs SiO2, zirconium saturation temperatures and zircon δ18O values indicate that the Xihuashan granites are highly evolved I–S transformation-type. Whole rock εNd(t), zircon εHf(t) and δ18O values fall into the ranges −11.3 to −10.4, –14.0 to −4.8, and 6.93‰–11.23‰ respectively, and the Nd and Hf two-stage model ages (TDM2) are 1.63–1.88Ga and 1.51–2.09Ga, respectively. The data indicate a primary reworking of Late Paleoproterozoic to Early Mesoproterozoic lower crust without any obvious participation of mantle material. The Xihuashan intrusion was emplaced at the same time as the widespread 165–150Ma I-type and A-type granites and syenites of the Nanling region, following the initiation in adjacent areas of intraplate basaltic activity, gabbros, bimodal volcanic rocks, and A-type granites from 190 to 165Ma. It can be inferred that the Nanling Range and neighboring regions were subjected to lithospheric extension during the Early Jurassic.