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In western Yunnan, potassic felsic suites with important Cu mineralization have been interpreted as being genetically associated with the Ailao Shan-Red River (ASRR) shear zone. In this paper, we show that the magmatism is unrelated to the shear zone, but shares many characteristics in common with potassic suites along the Jinsha suture to the north and northwest on the northern Tibetan Plateau, representing a magmatic response to the continued India-Asia convergence since the collision in the early Eocene. These felsic suites include syenite, monzogranite porphyries and granite porphyries. We dated 15 representative samples using zircon U-Pb method that gives a tight emplacement age of ~37–35 Ma. On 45 representative samples, we have done bulk-rock major element, trace element and Sr-Nd-Pb isotope analysis. We use these data, together with zircon Hf isotope data and the literature data on potassic mafic suites in the region to discuss the petrogenesis of these rocks. We conclude that the petrogenesis of the felsic potassic suites is most consistent with a scenario of deep (≥ 40 km) melting of thickened crust. The crustal melting is caused by intrusion and underplating of potassic mafic melts derived from melting of metasomatized mantle lithosphere. The mafic potassic suites in the region result from such mantle melts. Mixing of the mafic melts with the felsic melts explains the syenite and monzogranite porphyries and their extended fractional crystallization gives rise to the granite porphyries. The potassic suites along the Jinsha suture, including those from northern Tibet, western Yunnan and Vietnam, share the same tectonic setting during the Eocene-Oligocene. In response to the continued India-Asia convergence, removal of the lower continental lithospheric mantle triggered by Rayleigh-Taylor convective instability induces asthenosphere upwelling, partial melting of the metasomatized mantle lithosphere. We hypothesize that the eastward migration of the potassic magmatism along the Jinsha suture in the period of Eocene-Oligocene results from eastward thickening and removing of the continental lithospheric mantle along the suture, which, in time and space, correlates with the dischronal subduction of the torn Indian continental slab at ca. 52 Ma along the India-Asia collision zone. • The 35-37 Ma potassic suites in western Yunnan result from lower crust melting. • Their varied felsic compositions result from varying extent of fractional crystallization. • The removal of lithospheric mantle along the Jinsha suture was eastward-migrating. [ABSTRACT FROM AUTHOR]

Cenozoic mantle-derived magmas are widespread on the Tibetan Plateau, and provide evidence for the evolution of deep mantle and its influence on the Plateau development. Miocene basalts in the Maguan area on the southeastern Plateau have high MgO (9.13–13.10 wt%) and Mg# (0.60–0.70) with high Ce/Pb (10.6–32.5) and Nb/U (43.7–52.9) ratios, similar to those of oceanic basalts. Distinct from Eocene-Oligocene mantle-derived potassic magmas in Western Yunnan and Cenozoic basic volcanic rocks in Tengchong, these Maguan basalts are characterized by high large ion lithophile elements (LILEs) concentrations, positive anomaly in high field strength elements (HFSEs) and depleted Sr Nd isotopes, consistent with the melt of an asthenospheric mantle origin. The high Ce/Pb and Nb/Y (1.80–2.68) ratios together with low Ba/Y and Ba/Th ratios indicate a significant input of slab-derived melt into the asthenospheric source. Besides, Hf/Hf* and Ti/Ti* ratios are significantly lower than those of ocean island basalt (OIB), which are proportional to the lighter δ26Mg (-0.6‰ to -0.4‰) values. Based on the results of experimental petrology, the Sr Mg isotope mixing model suggests that the asthenospheric mantle beneath the Maguan area had undergone the significant metasomatism of recycled carbonates prior to the late Miocene. The above petrological and geochemical understanding, together with the geophysical data, allows us to propose that the mantle metasomatism is most probably associated with the Neo-Tethys seafloor subduction, which is further testified by the decoupling between depleted Sr Nd isotopes and elevated LILE concentrations. • Miocene basalt in Maguan area, SW China was evolved without crustal contamination • The Maguan basalt is derived from metasomatized asthenospheric mantle • The mantle metasomatism was predominantly caused by deep recycled carbonates. [ABSTRACT FROM AUTHOR]

Determining the origin and related mantle dynamics responsible for the generation of giant granitic batholiths in convergent margins is critical to unravel the formation mechanism of the silica–rich continental crust. This paper reports the whole–rock major element, trace element, Sr-Nd isotopic, and zircon U-Pb age and Hf isotope data of samples from the Menglian Batholith in the eastern Tengchong Terrane of southwest Yunnan. These samples consist of two groups, including the Group I rocks that are mostly granitic with zircon U-Pb ages of 132–122 Ma and the Group II rocks that display varying compositions from gabbroic to granitic with zircon U-Pb ages of 122–112 Ma. The Group I samples have zircon ε Hf (t) of −11.7 to −4.2 and whole–rock ε Nd (t) of −10.1 to −8.9, whereas the Group II samples show elevated zircon ε Hf (t) of −7.8 to +7.1 and whole–rock ε Nd (t) of −9.0 to −6.9 and ε Hf (t) of −3.1 to −1.0. The Nd-Hf isotopic compositions of the Group I rocks are coupled, likely resulting from the partial melting of an ancient lower crust. However, the Nd-Hf isotopic compositions of the Group II rocks are decoupled, likely inheriting from the mantle–derived material with decoupled Nd-Hf isotopic compositions. Regional geological correlation and compositional transition documented by the Group I and Group II samples collectively indicate that the slab rollback and subsequent breakoff of the subducting Bangong–Nujiang ocean lithosphere during the Tengchong–Baoshan collision can be invoked to explain the generation of the Menglian Batholith. The similarity of average compositions between the Group II samples and the bulk continental crust suggests that the addition of mantle–derived material to the ancient crust–derived melts seems to be an efficient process for crustal growth during continental collisions. • Menglian Batholith was emplaced at 132–122 Ma (Group I) and 122–112 Ma (Group II). • Group I and II samples are coupled and decoupled in Nd-Hf isotopes, respectively. • Decoupling Nd-Hf isotopic compositions are inherited from mantle–derived material. • Group I and II samples are associated with slab rollback and breakoff. • Addition of mantle–derived material contributes to crustal growth efficiently. [ABSTRACT FROM AUTHOR]