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Whether there is a relationship between widespread Cenozoic igneous rocks and the activated Ailao Shan–Red River shear zone (ASRR) in western Yunnan, SE Tibet, remains highly controversial. New geochronological, and geochemical data derived from Cenozoic igneous rocks both within and far from the ASRR offers answers. Although these coeval felsic rocks (36.9–33.5 Ma) are enriched in large‐ion lithophile elements relative to high field strength elements, they also display some special geochemical features, such as high Y and Yb values of syenitic porphyries, which contrast with the high Sr and low Y contents of monzoporphyries and granitic porphyries. The syenitic porphyries exhibit geochemical characteristics similar to those of coeval mafic magmas, e.g., high K2O, Y, and Yb contents, indicating that the former were probably generated by fractional crystallization of the latter. However, the high Sr/Y (56.1–109) monzoporphyries and granitic porphyries, combined with their low MgO, and Cr (or Ni) contents, suggest that they were mainly derived from partial melting of a thickened mafic lower crust. Given that these Cenozoic magmatic events exhibiting planar distributions occurred outside of the activation of the ASRR (31–20 Ma), then they were not controlled by the latter. Instead, they were tied to convective removal of a thickened lower lithospheric mantle in western Yunnan during the Paleogene. [ABSTRACT FROM AUTHOR]

A new species of the genus Suwallia Ricker, 1943 (Plecoptera, Chloroperlidae), Suwallia dengba sp. nov., is described from Tibet and Yunnan, southwestern China. A diagnosis and description of the adult habitus and aedeagal structure are illustrated with color images. Similarities in the terminalia with closely related species are discussed. In addition, an updated key to adult males of the Suwallia species of China is provided. [ABSTRACT FROM AUTHOR]

SKS wave splitting measurements revealed strong and complex seismic anisotropy in the upper mantle beneath the southeastern Tibetan Plateau. To better understand lithospheric deformation and upper mantle anisotropy observed in this region, we performed studies on microstructures, seismic anisotropy and chemical compositions of the mantle peridotite xenoliths collected from Maguan, Yunnan Province, in the SE Tibetan Plateau. The mantle xenoliths show two types of olivine crystal preferred orientation (CPO), AG–type and A–type. AG–type fabric is characterized by a concentration of [010]-axis normal to the foliation and a large circle girdle of the [100] and [001] axes in foliation. A–type fabric shows point concentrations of [100] and [010] axes subparallel to lineation and subnormal to foliation, respectively. Orthopyroxene and clinopyroxene align their [001]-axis sub-parallel to the [100]-axis of olivine. Seismic anisotropy calculated from the fabric of xenoliths displays moderate to strong polarization anisotropy (AV s) ranging from 3.1% to 7.0%, with 4.6% on average. Based on the seismic properties of xenoliths, we propose that, in SE Tibetan Plateau (south of 26°N), the SKS wave splitting is attributed to melt-enhanced anisotropy with a vertical structural frame lithosphere. Under this structural configuration, the large delay time could be expected with the fast wave polarization direction (FPD) in E–W direction. Our study also supports the model of double anisotropic layers in this area. The fast orientation of lower layer caused by lithospheric mantle anisotropy is in E–W direction, while the upper one with the NNW–SSE FPD is related to the frozen anisotropy in the middle-lower crust. • We first report the fabrics of mantle xenoliths from the SE Tibetan Plateau. • The dominant fabrics of olivine in the xenoliths are AG–type and A–type. • The large delay time in SE Tibet is attributed to a strong anisotropy enhanced by oriented melt. • SE Tibetan lithospheric mantle is characterized by vertical foliation with a horizontal shear motion in E-W direction. [ABSTRACT FROM AUTHOR]

Most previous studies advocate that crustal weakening in the Yunnan area is predominantly the result of eastward growth of the Tibetan Plateau. Here we observe regional variations in the Yunnan crustal structure from the waveform characteristic variations of receiver functions at 342 seismic stations. Furthermore, receiver function imaging along three seismic sections reveals the response of crustal structure to different tectonic evolution. Our results show that northwestern Yunnan is characterized by 49–64 km-thick crust with multi-layer low-velocity materials and local lower crustal "doublet". These low-velocity structures may reflect partial melting caused by crustal thickening associated with the eastward growth of the plateau. However, in southern and eastern parts of Yunnan, the topography of the Moho varies relatively gently with crustal thicknesses of 26–42 km, and widespread low-velocity zones are located above the crust-mantle boundary. We speculate that these features might favor the action of partial melting of crust triggered by asthenospheric upwelling related to the subduction of the India plate. • Receiver function analysis reveals regional variations in Yunnan crustal structures. • The effect of the eastward growth of the Tibet plateau is confined in NW Yunnan. • The tectonism of upwelling related to subduction is recorded in the South. [ABSTRACT FROM AUTHOR]