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The roles of the mantle in generating granites and the extent of crust-mantle interaction are fundamental topics to our understanding of Sn mineralization. In this study, we report geochronological, geochemical, and Sr-Nd–Hf isotopic data for the granites, and muscovite 40Ar/39A isotopic data of the greisen type Sn ores, in the Dashunlong Sn deposit, Dayishan orefield, middle Qinzhou-Hangzhou metallogenic belt. LA–ICP–MS zircon U–Pb dating for the medium-fine grained- and coarse grained-biotite monzogranite of Dayishan pluton yields emplacement ages of 154.6 ± 1.2 Ma (MSWD = 0.73) and 154.7 ± 1.6 Ma (MSWD = 1.9), respectively, which are consistent with the muscovite 40Ar/39Ar plateau age of 151.1 ± 0.9 Ma (MSWD = 0.09) for the greisen-type Sn ores. It is indicated that the Sn mineralization in the Dashunlong deposit is related to the Late Jurassic Dayishan granite. The granite shows the geochemical features of highly fractionated A-type granite: 1) high 10,000 Ga/Al ratios of 2.95–3.88; 2) high Zr + Nb + Ce + Y contents of 292–637 ppm; 3) high TFeO/(TFeO* + MgO) ratios of 0.86–0.97; and 4) high Rb/Sr ratios of 2.80–18.8. Whole rocks isotopes show that this granite has variable initial 87Sr/86Sr ratios (0.71607–0.72437), negative eNd(t) values (−7.20 to −5.46), and two-stage Nd model ages of 1530–1388 Ma. LA–MC–ICP–MS zircon Lu-Hf isotopes show that the medium-fine-grained monzogranite has eHf(t) values of −0.94–2.20 and two-stage Hf model ages of 1298–1059 Ma, whereas the coarse-grained biotite monzogranite has relatively high eHf(t) values of −0.84–5.95 and two-stage Hf model ages of 1257–823 Ma. Different Hf and Nd isotopes indicate that the Nd-Hf isotopic decoupling occurs in the Dayishan granite, which was likely caused by the partial melting of the rocks containing abundant high Lu/Hf minerals. The magma of the Dayishan granite is reduced, highly fractionated, and enriched in Sn and F, resulting in large-scale Sn mineralization in the Dayishan orefield. It is proposed that these granites are originated from melts mixed by crustal- and mantle constituents and are formed in an extensional setting caused by the subduction of the Palaeo-pacific plate. A two end-member modeling indicates that ca. 10–20 percent of mantle-derived melts were likely involved in the formation of the Dayishan granites. |
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