Petrogenesis of Late Mesozoic granitoids and coeval mafic rocks from the Jiurui district in the Middle–Lower Yangtze metallogenic belt of Eastern China: Geochemical and Sr–Nd–Pb–Hf isotopic evidence

• Published in: Lithos 2014-03, Vol.190-191, p.467-484
• Main Authors: Xu, Yao-Ming, Jiang, Shao-Yong, Zhu, Zhi-Yong, Yang, Shui-Yuan, Zhou, Wei
• Format: Article
• Language: English
• Subjects: Granitoid; Jiurui district; Mafic rock; Mantle involvement; Middle–Lower Yangtze metallogenic belt
• ISSN: 0024-4937; 1872-6143
• DOI: 10.1016/j.lithos.2013.12.022

Large-scale Cu–Au mineralization is associated with the Late Mesozoic granitoids in the Jiurui district of the Middle–Lower Yangtze Mineralization Belt in Eastern China. To constrain the petrogenesis of these granitoids and coeval mafic rocks, a detailed geochemical and Sr–Nd–Pb–Hf isotopic study was performed. The Jiurui granitoids are made up primarily of granodiorite porphyry and quartz diorite porphyry. These granitoids are characterized by SiO2 and K2O contents of 58.8wt.% to 68.6wt.% and 1.9wt.% to 5.7wt.%, respectively. These granitoids show relatively high MgO contents (1.0wt.% to 3.1wt.%, average 2.1wt.%) and high Mg# values (39 to 70, average 54). The Jiurui granitoids are enriched in light rare earth elements (LREE), large ion lithophile elements (LILE), and compatible trace elements (Cr, Ni and V) but are relatively depleted in Nb, Ta, Y and Yb. These rocks show a negligible negative Eu anomaly (Eu/Eu⁎=0.76–1.13, average 0.91) and nearly no negative Sr anomaly. The whole-rock initial 87Sr/86Sr ratios range from 0.7060 to 0.7092, and the εNd(t) values vary from −5.4 to −2.0. The granitoids show radiogenic Pb isotopic ratios with values of 206Pb/204Pb (17.93–18.21), 207Pb/204Pb (15.55–15.58), and 208Pb/204Pb (38.16–38.56) for the plagioclases. The zircon Hf isotopic compositions show εHf(t) values from −11.8 to 2.4. The coeval mafic rocks consist of lamprophyre, diabase and fine-grained mafic dyke. These rocks are characterized by SiO2 contents ranging from 47.6wt.% to 54.8wt.%, with a negative Eu anomaly and a positive to negative Sr anomaly. The whole-rock initial 87Sr/86Sr ratios range from 0.7059 to 0.7071, and the εNd(t) values vary from −3.8 to −1.4. By comparing the geochemical and isotopic compositions of the Jiurui granitoids and the coeval mafic rocks, we conclude that the granitoids are similar to adakites that were likely related to the delamination processes, and the coeval mafic rocks may have originated directly from enriched lithospheric mantle. The thickened lower continental crust and underlying enriched lithospheric mantle may have been simultaneously delaminated into the asthenospheric mantle. This process led to the partial melting of the thickened lower crust and the enriched lithospheric mantle, and the melts experienced an interaction with the asthenospheric mantle during ascension. Mafic melts could be generated from the enriched lithospheric mantle, which was heated by the upwelling asthenospheric mantle. The geochemical