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It is debated whether Cretaceous magmatism and mineralization in southeastern Yunnan (China) resulted from the subduction of Neo-Tethys or Paleo-Pacific lithosphere. To address this problem, we report whole-rock geochemical and Sr–Nd isotopic compositions and zircon U–Pb ages and Lu–Hf isotopic compositions from the Changlinggang syenites in the southeastern Yunnan Sn mineralization belt, western South China Block. LA–ICP–MS zircon U–Pb dating suggests that syenites were emplaced during the Late Cretaceous (79.2 ± 0.5 Ma). They contain nepheline and aegirine, and have high (K2O + Na2O) contents (16.0–18.6 wt %), K2O/Na2O ratios (0.7–1.7), FeOT/(FeOT + MgO) ratios (0.83–0.97), 104 × Ga/Al ratios (2.3–3.7), and (Zr + Nb + Ce + Y) contents (505–2138 ppm), which are typical of A-type granitoids. The samples have slightly more enriched initial Sr–Nd isotopic compositions than the coeval Jiasha gabbros, with (87Sr/86Sr)i ratios of 0.7088–0.7101 and εNd(Т) values of –7.5 to –6.6. The geochemical data suggest that the Changlinggang syenites were derived by partial melting of enriched lithospheric mantle that had been metasomatized by subducted-sediment-derived melts, followed by crustal assimilation and fractional crystallization of the partial melt during ascent. These results, along with those of previous studies, indicate that Cretaceous magmatism and mineralization in southeastern Yunnan were emplaced in an extensional setting related to subduction of Neo-Tethys lithosphere. Therefore, we propose that the Neo-Tethyan slab was subducted under the western South China Block during the Late Cretaceous. [ABSTRACT FROM AUTHOR]

This paper investigates the Jigede gabbros from the Shalazhashan tectonic belt, Alxa Block. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U-Pb dating reveals that they were emplaced in the Middle Permian (ca. 262 Ma). All the gabbro samples collected from the intrusion exhibit low contents of TiO2 (0.24–0.37 wt %) and (4.87–5.41 wt %), but high levels of MgO (11.15–12.15 wt %), CaO (11.45–12.75 wt %), Al2O3 (14.18–17.08 wt %) and high Mg# (0.81–0.83). Relative to HREEs and LILEs, the gabbros are enriched in LREEs and depleted in Th, Nb, Ce, Zr, Hf, and Ti, with positive Eu, Sr and U anomalies. In contrast to MORB, the Jigede intrusion has higher initial 87Sr/86Sr values of 0.7046 to 0.7054 and lower εNd(T) of + 1.8 to + 4.8. Elemental and isotopic data suggest that the intrusion was likely to have been produced by partial melting of a shallow lithospheric mantle source modified by slab-derived fluids, with subsequent cumulation of plagioclase. Thus, the Jigede intrusion was emplaced in a back-arc setting, in response to the Paleo-Asian oceanic subduction. In addition, the final closure of the Paleo-Asian Ocean did not occur prior to the Middle Permian. [ABSTRACT FROM AUTHOR]