Petrogenesis and metallogenic implications for the Machang, Huangdaoshan, and Tuncang plutons in eastern Anhui: an integrated age, petrologic, and geochemical study

摘要

The Tuncang-Chuzhou-Machang area (eastern Anhui province) is geologically located in the intersection between the Yangtze block and the Qinling-Dabie orogenic belt. Many Mesozoic plutons outcrop in this district that are Cu-Au prospective but inadequately studied. We report new LA-ICP-MS zircon U-Pb ages, petrologic, and whole rock geochemical data for three representative plutons at Machang, Huangdaoshan, and Tuncang. New dating results suggest that all the Machang (129.3 +/- 1.6Ma), Huangdaoshan (129 +/- 1.7Ma), and Tuncang (130.8 +/- 1.9Ma) plutons were emplaced in the Early Cretaceous, slightly older than other plutons in neighbourhood of the Zhangbaling uplift. The three plutons contain typical low-Mg adakitic affinities, in which the rocks contain SiO2 56%, Al2O3 15%, Mg# 53, elevated Sr, Ba, Cr, Ni, Sr/Y, and La/Yb, low Y and Yb and no discernible Eu anomaly. Their petrogenesis may have been related to the delamination and partial melting of the lower crust, which is different from the Chuzhou pluton, which was interpreted to have formed by partial melting of the subducted slabs. We suggest that this petrogenetic difference may explain why the pluton at Chuzhou is Cu-Au fertile, whereas those at Machang, Huangdaoshan, and Tuncang are largely barren. It is proposed that adakitic plutons formed by partial melting of the subducted slabs have high metallogenetic potentiality in the area.