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| 1 | High-Temperature Metamorphism, Anataxis and Tectonic Evolution of a Mafic Granulite from the Eastern Himalayan Orogen显示文摘The Himalayan Orogen, resulting from the Tertiary collision of Indian and Asian continents, is a natural laboratory for studying metamorphism, partial melting and granite formation of collisional orogens. However, metamorphic and anatectic conditions and timescales of meta-mafic rocks in the Greater Himalayan Sequences(GHS) in the east-central Himalaya remain controversial. In this paper, we conduct a study of petrology and geochronology of mafic granulite from the Eastern Himalayan Syntaxis(EHS). The mafic granulite with abundant leucosome bands occurs as layers within felsic granulites and is well deformed. The granulite consists of garnet, plagioclase, amphibole and quartz with minor clinopyroxene, orthopyroxene, biotite, rutile, titanite and ilmenite. The garnet has growth compositional zoning and contains abundant mineral inclusions in its core. Peak metamorphic mineral assemblage of the granulite is garnet, amphibole, plagioclase, quartz, clinopyroxene and rutile, recording a high-pressure(HP) and high-temperature(HT) peak-metamorphism under conditions of 14–15.5 kbar and 780–790℃ in the presence of melt. The reconstructed clockwise P-T path is characterized by an early heating and burial prograde metamorphism, and late isothermal and cooling decompression retrogression. The granulite witnessed a long lasting HT metamorphism, partial melting and melt crystallization process which began at ca. 39 Ma and lasted to ca. 11 Ma. The present study shows that various high-grade rocks of the GHS in the EHS core experienced similar metamorphic conditions and P-T-t paths, indicating that they occurred as a coherent slab during the subduction and exhumation of Indian lithosphere. The significant melts generated during the prograde metamorphism of the GHS rocks not only contributed to the formation of the Himalayan leucogranite, but also resulted in the rheological weakening and ductile flow of the thickened lower crust of the Himalayan Orogen. | Zeming Zhang Huixia Ding Xin Dong Zuolin Tian Dongyan Kang Hongchen Mu Shengkai Qin Yuanyuan Jiang Mengmei Li | 2018 | Journal of Earth Science2018，29，5： | 7 |
| 2 | Petrogenesis and Tectonic Implications of the Latest Cretaceous Intrusive Rocks from the Eastern Gangdese Belt,Southeast Tibet显示文摘The latest Cretaceous magmatic activity in the eastern segment of the Lhasa terrane provides important insights for tracking the magma source and geodynamic setting of the eastern Gangdese batholith,eastward of eastern Himalayan Syntaxis.Detailed petrological,geochemical and geochronological studies of the intrusive rocks(monzodiorites and granodiorites)of the eastern Gangdese batholith are presented with monzodiorites and granodiorites giving zircon U-Pb crystallization dates of 70-66 Ma and 71-66 Ma withεHf(t)values of−4.8 to+6.2 and−1.9 to+5.3,respectively.These rocks are metaluminous to weakly peraluminous I-type granites showing geochemically arc-related features of enrichment in LREEs and some LILEs,e.g.,Rb,Th,and U,and depletion in HREEs and some HFSEs,e.g.,Nb,Ta,and Ti.The rocks are interpreted to be derived from partial melting of mantle material and juvenile crust,respectively,which are proposed to be triggered by Neo-Tethyan slab rollback during northward subduction,with both experiencing ancient crustal contamination.The studied intrusive rocks formed in a transitional geodynamic setting caused by Neo-Tethyan oceanic flat subduction to slab rollback beneath the eastern Gangdese belt during the latest Cretaceous. | CHEN Yanfei CHEN Xuanhua ZHANG Zeming SHAO Zhaogang TIAN Zuolin DONG Xin QIN Shengkai YUAN Yuelei | 2022 | Acta Geologica Sinica(English Edition)2022，96，3： | 1 |
| 3 | The Eocene corundum-bearing rocks in the Gangdese arc, south Tibet:Implications for tectonic evolution of the Himalayan orogen显示文摘The genesis of Liangguo corundum deposit in the southern Gangdese magmatic arc, east-central Himalaya, remains unknown. The present study shows that the corundum-bearing rocks occur as lenses with variable sizes in the Eocene gabbro that intruded into marble. These corundum-bearing rocks have highly variable mineral assemblage and mode. The corundum-rich rocks are characterized by containing abundant corundum, and minor spinel, ilmenite and magnetite, whereas the corundum-poor and corundum-free rocks have variable contents of spinel, plagioclase, sillimanite, cordierite, ilmenite and magnetite. The host gabbro shows variable degrees of hydration and carbonization. The corundum grains are mostly black, and rarely blue, and have minor Fe O and TiO_2. The spinel is hercynite, with high Fe O and low Mg O contents. The corundum-bearing rocks have variable but high Al_2O_3, FeO and TiO_2, and low SiO_2 contents. Inherited magmatic and altered zircons of the corundum-bearing rocks have similar U e Pb ages(~47 Ma) to the magmatic zircons of the host gabbro, indicating corundum-bearing rock formation immediately after the gabbro intrusion. We considered that emplacement of gabbro induced the contact metamorphism of the country-rock marble and the formation of silica-poor fluid. The channeled infiltration of generated fluid in turn resulted in the hydrothermal metasomatism of the gabbro, which characterized by considerable loss of Si from the gabbro and strong residual enrichment of Al. The metasomatic alteration probably formed under Pe T conditions of ~2.2 -2.8 kbar and ~650 -700℃. We speculate that SiO_2, CaO and Na_2O were mobile, and Al_2O_3, FeO, TiO_2 and high field strength elements remained immobile during the metasomatic process of the gabbro. The Liangguo corundum deposit, together with metamorphic corundum deposits in Central and Southeast Asia, were related to the Cenozoic Himalayan orogeny, and therefore are plate tectonic indicators. | Zeming Zhang Huixia Ding Xin Dong Zuolin Tian Hongchen Mu Mengmei Li Shengkai Qin Zhixiang Niu Ning Zhang | 2018 | Geoscience Frontiers2018，9，5： | 0 |
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