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

• The Jiurui granitoids exhibit geochemical characteristics similar to those of adakite.
• The petrogenesis involved delamination and partial melting of the thickened lower crust and the enriched lithospheric mantle.
• The Juirui granitoids show the highest proportion of mantle interaction.
• The Angui and Tongling granitoids show lesser amounts of mantle signatures.

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 58.8 wt.% to 68.6 wt.% and 1.9 wt.% to 5.7 wt.%, respectively. These granitoids show relatively high MgO contents (1.0 wt.% to 3.1 wt.%, average 2.1 wt.%) 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 47.6 wt.% to 54.8 wt.%, 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 and isotopic compositions of mafic rocks were most likely controlled by the AFC process. A geochemical and isotopic comparison of the granitoids in the Jiurui district with those of two other districts (e.g., Angui and Tongling) in the same mineralization belt indicates that a significant crust–mantle interaction played a crucial role in their petrogeneses and metallogeneses. From the southwest to northeast in this metallogenic belt, the proportion of mantle component that was involved in the granitic magma shows a decreasing trend from the Jiurui to the Angui and Tongling districts. It is suggested that the Juirui district has the highest potential for a significant amount of Cu–Au accumulation because the mantle is an important supply for these metals.