Geochronological and geochemical constraints on the petrogenesis and geodynamic setting of the Qianlishan granitic pluton, Southeast China

The Qianlishan is a well-known granitic pluton directly related to the super large W-Sn-Mo-Bi polymetallic Shizhuyuan deposit in southeast China. The pluton is composed of three intrusive phases: the first phase of microfine-grained porphyritic biotite granite, the second phase of fine-grained porphyritic biotite granite, and the third phase of medium-grained equigranular zinnwaldite granite. SIMS zircon U-Pb dating yields precise ages for three phases; they are 154.5 and 152.3 Ma, 153.4 and 152.5 Ma, 152.4 and 151.6 Ma, respectively. Overall, all three granite phases contain high SiO2 (73.2–77.7 wt.%) and total alkalis (K2O+Na2O = 7.27–9.36 wt.%). Their aluminum saturation index values increase from 0.91–0.99 for Phase 1, through 0.92–1.01 for Phase 2, to 1.01–1.27 for Phase 3. Average (La/Yb)N ratios are 3.88, 4.12, and 1.06, respectively, in three phases. Compared with Phase 3 granite, the Phase 1 and 2 granites have less conspicuous negative Eu anomalies (Phases 1, 2 Eu/Eu* = 0.13–0.28; Phase 3 Eu/Eu* = 0.01–0.02); Phase 3 granite also shows stronger depletion in Sr, P, Zr, and Ti. Mica compositions change from Mg- and Fe- to Al, F, Li-rich, whereas plagioclase compositions evolve from andesine/oligoclase to albite from Phases 1 to 3 granites. Mineralogical features and whole-rock geochemistry indicate that Phase 3 granite experienced more intensive fractional crystallization than others. The Qianlishan granites have low εNd(t) values (−12.9 to −7.9). Zircon εHf(t) and δ18O values are −11.1‰ to −5.14‰ and 7.97‰ to 10.35‰, respectively. Two-stage model ages of whole-rock Nd isotopes (1.2–1.9 Ga) and zircon Hf isotopes (1.5–1.9 Ga) indicate that these granites were derived from partial melting of late Paleoproterozoic to early Mesoproterozoic crustal material. Phase 1 and 2 are fractionated I–type granites, and Phase 3 is high-degree fractionated S–type granite. High zirconium saturation temperature (~780 °C) and presence of diopside indicate that these granites originated from partial melting under the relatively high temperature environment. Combined with alkaline basalts, tholeiitic basalts, and intraplate shoshonitic intrusions in time and space, the Qianlishan pluton occurs right within an intercontinental rift along the Qin-Hang deep fault zone in the middle to late Jurassic.