Browsing by Author "Qin, K.Z."
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Item Compositionally stratified lithosphere and carbonatite metasomatism recorded in mantle xenoliths from the Western Qinling (Central China)(Lithos, 2010-02) Su, B.X.; Zhang, H.F.; Sakyi, P.A.; Ying, J.F.; Tang, Y.J.; Yang, Y.H.; Qin, K.Z.; Xiao, Y.; Zhao, X.M.In Central China, long-distance effects from collision between the North China and Yangtze cratons, uplift of the Tibetan Plateau and subduction of the Pacific Ocean are believed to converge in the Western Qinling. Mantle xenoliths from Baiguan and Haoti kamafugites in the Western Qinling were investigated to understand the lithospheric structure and mantle metasomatism beneath the orogenic belt. The Western Qinling lithosphere with depths of at least 120 km is geothermally hot and compositionally stratified, companied by a step-wise decrease in fertility with depth. The shallower portion of the lithospheric mantle is represented by type 2 xenoliths which lack alteration and deformation, and have fertile characteristics in compositions. The dominant rock type in the mantle section is the type 1 peridotites, which have had undergone relatively higher melt extraction and subsequent metasomatism. In-situ trace element data for minerals in the Baiguan and Haoti xenoliths are presented in this study. Baiguan clinopyroxenes have high LREE and show Ba, Th, U, Pb, Sr enrichment and negative Hf and Y anomalies, but the Haoti clinopyroxenes have large variations in trace elements and complicated distributions in LILE, and show negative Ti, Zr and Hf anomalies. Clinopyroxenes from both xenolith types have Ti/Eu and (La/Yb)N ratios in large ranges of 902-15,813 and 0-20, respectively. The petrological and geochemical characteristics suggest that the Western Qinling peridotites had been subjected to silicate and subsequent carbonatite metasomatism, and that carbonatite metasomatism was predominant in Baiguan but lesser in Haoti. Comparisons with the Western Qinling carbonatites and world-wide carbonatites indicate that carbonatite melts involved in the metasomatism originated from deep mantle and most likely related to carbonatite magma, with contributions from subducted oceanic crust. The type 2 peridotites, comprising clinopyroxene megacrysts and clinopyroxenite display similar trace element abundances and patterns, suggesting a close affinity in petrogenesis. Crown Copyright © 2010.Item Geochemistry and geochronology of acidic rocks in the Beishan region, NW China: Petrogenesis and tectonic implications(Journal of Asian Earth Sciences, 2011-04) Su, B.X.; Qin, K.Z.; Sakyi, P.A.; Liu, P.P.; Tang, D.M.; Malaviarachchi, S.P.K.; Xiao, Q.H.; Sun, H.; Dai, Y.C.; Yan, H.The dacites and granites from the Beishan region are characterized by highly-fractionated REE, enrichments in LILE, and depletion in Nb, Ta and Sr. The dacites contain zircons with ages ranging from 265 to 748Ma. These features suggest that they were probably derived from the older lower continental crust and were later on subjected to significant crustal assimilation. The rhyolites, diorites and diabases, all of which share similar geochemical features such as trace element patterns, zircon U-Pb ages of ~280Ma, positive εHf(t) and εNd(t), high initial (87Sr/86Sr)i and δ18O‰ values, were most likely derived from the juvenile crustal sources and subsequently experienced fractional crystallization and crustal contamination. These acidic igneous rocks (except dacites and granites) and coeval mafic-ultramafic intrusions form a bimodal igneous series. This implies that the Beishan region was a Late Paleozoic rift probably developed in association with the early Permian mantle plume activity in the Tarim Basin. © 2010 Elsevier Ltd.Item The origin of spongy texture in minerals of mantle xenoliths from the Western Qinling, central China(Contributions to Mineralogy and Petrology, 2011-03) Su, B.X.; Zhang, H.F.; Sakyi, P.A.; Yang, Y.H.; Ying, J.F.; Tang, Y.J.; Qin, K.Z.; Xiao, Y.; Zhao, X.M.; Mao, Q.; Ma, Y.G.Spongy textures are observed in mantle peridotite xenoliths hosted in Cenozoic kamafugites from the Western Qinling, central China. These textures are mainly developed in clinopyroxenes and spinels, and occur as spongy rims consisting of low-Na clinopyroxene, ilmenite, and bubbles, enclosing nonspongy cores. The ilmenites and bubbles exhibit shapes and sizes that vary with the width of the spongy rims. The spongy-textured minerals preserve primary shapes and well-defined grain boundaries and do not show apparent interaction with contact minerals or observed melts except the subsequent melts forming melt pockets. The xenocrysts display reactive zoning textures with host magmas rather than spongy textures. Compositionally, the spongy rims are enriched in Ca, Ti, and most trace elements, have high Cr#, and are depleted in Na, Al, Fe, AlVI, and AlIV/AlVI compared with the cores. These observations suggest that melts/host magmas did not play any significant role in the formation of the spongy textures. We therefore propose that spongy-textured clinopyroxenes and spinels in Western Qinling peridotite xenoliths developed from a decompression-induced partial melting event prior to formation of melt pockets and xenolith entrainment in host magmas. © 2010 Springer-Verlag.Item Platinum-Group Mineral Occurrences and Platinum-Group Elemental Geochemistry of the Xiadong Alaskan-Type Complex in the Southern Central Asian Orogenic Belt(Minerals, 2018-11) Yang, S.H.; Su, B.X.; Huang, X.W.; Tang, D.M.; Qin, K.Z.; Bai, Y.; Sakyi, P.A.; Alemayehu, M.Alaskan-type complexes commonly contain primary platinum-group element (PGE) alloys and lack base-metal sulfides in their dunite and chromite-bearing rocks. They could therefore host PGE deposits with rare sulfide mineralization. A detailed scanning electron microscope investigation on dunites from the Xiadong Alaskan-type complex in the southern Central Asian Orogenic Belt revealed: various occurrences of platinum-group minerals (PGMs) that are dominated by inclusions in chromite grains containing abundant Ru, Os, S and a small amount of Pd and Te, indicating that they mainly formed prior to or simultaneously with the crystallization of the host minerals; A few Os–Ir–Rurich phases with iridium/platinum-group element (IPGE) alloy, anduoite (Ru,Ir,Ni)(As,S)2−x and irarsite (IrAsS) were observed in chromite fractures, and as laurite (RuS2) in clinopyroxene, which was likely related to late-stage hydrothermal alteration. The rocks in the Xiadong complex display large PGE variations with ∑PGE of 0.38–112 ppb. The dunite has the highest PGE concentrations (8.69–112 ppb), which is consistent with the presence of PGMs. Hornblende clinopyroxenite, hornblendite and hornblende gabbro were all depleted in PGEs, indicating that PGMs were likely already present at an early phase of magma and were mostly collected afterward in dunites during magma differentiation. Compared with the regional mafic–ultramafic intrusions in Eastern Tianshan, the Xiadong complex show overall higher average PGE concentration. This is consistent with the positive PGE anomalies revealed by regional geochemical surveys. The Xiadong complex, therefore, has potential for PGE exploration.Item Sims zircon U-Pb geochronology and Sr-Nd isotopes of Ni-Cu-bearing mafic-ultramafic intrusions in Eastern Tianshan and beishan in correlation with flood basalts in Tarim Basin (NW China): Constraints on a CA. 280 MA mantle plume(American Journal of Science, 2011-06) Qin, K.Z.; Su, B.X.; Sakyi, P.A.; Tang, D.M.; Li, X.H.; Sun, H.; Xiao, Q.H.; Liu, P.P.Zircon SIMS U-Pb dating of the Poshi, Hongshishan, Bijiashan, and Huangshan Ni-Cu-bearing and Xiangshan Ni-Cu-Ti-Fe-bearing mafic-ultramafic intrusions in the Eastern Tianshan and Beishan Rift yields a relatively restricted range of 278.6 Ma to 284.0 Ma. The histogram of compiled age data of basalts in the Tarim Basin and mafic-ultramafic intrusions in the Eastern Tianshan and Beishan Rift has a peak of 280 Ma, which probably represents the time of mantle plume activity. The basalts have lower εNd(t) values in the range of -9.2 ~ -1.7 and Mg# of <50, and higher TiO2 contents (>2 wt.%), indicating that they were generated directly from a peripheral zone of the mantle plume by low degree of melting. The mafic-ultramafic intrusions have higher εNd(t) of -1.3~11.2 and Mg# of 33~90, and lower TiO 2 < 1.8 weight percent, suggesting that their parental magmas were produced from lithospheric mantle source by high degree of melting due to higher temperature of the mantle plume head. A possible mantle plume model beneath lithospheric mantle of the Tarim Basin, Tianshan and Beishan and its spatial framework is suggested.Item U-pb ages and hf-o isotopes of zircons from late paleozoic mafic-ultramafic units in the southern central asian orogenic belt: Tectonic implications and evidence for an early-permian mantle plume(Gondwana Research, 2011-09) Su, B.X.; Qin, K.Z.; Sakyi, P.A.; Li, X.H.; Yang, Y.H.; Sun, H.; Tang, D.M.; Liu, P.P.; Xiao, Q.H.; Malaviarachchi, S.P.K.U-Pb age and Hf-O isotope data of zircons from the mafic-ultramafic complexes and their related rhyolites and granites in the Eastern Tianshan and Beishan regions were obtained by SIMS and LA-ICPMS. The Hf-O isotopic composition and Hf model age of the zircons are closely related to their tectonic setting and formation age. The zircons from the mafic-ultramafic complexes in the Bogeda-Haerlike and Jueluotage belts have higher εHf(t) (+8-+17) and lower δ18O (+4‰-+6‰), whereas most of the zircons in the gabbros, granites and rhyolite from the Middle Tianshan Massif and Beishan Rift display lower εHf(t) (0-+8) and higher ε18O (+5‰-+8‰). The positive εHf(t) and relatively lower δ18O values suggest that these mafic-ultramafic complexes were derived from depleted mantle which was subjected to subduction-related modification processes. The Hf isotopic composition of zircons in the granites has revealed that the growth of juvenile crust was also very significant in the southern margin of the Central Asian Orogenic Belt during the Paleozoic. The Hf model ages of the analyzed zircons, together with the regional geology suggest that the Beishan area had a northward subduction, possibly from ca. 900Ma to ca. 400Ma, whereas the Eastern Tianshan had a south-directed subduction most likely from ca. 600Ma to ca. 310Ma. Additionally, zircons with ca. 280Ma U-Pb ages display wider and more scattered εHf(t) and δ18O variations than the relatively older and younger ones, which further support the Early Permian mantle plume model. © 2010 International Association for Gondwana Research.