Browsing by Author "Ao, S.J"
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Item The metasedimentary rocks from the eastern margin of the Tarim Craton: petrology, geochemistry, zircon U-Pb dating, Hf isotopes and tectonic implications.(Lithos, 179: 120-136 doi:10.1016/j.lithos.2013.08.010, 2013) Wang, Z. M; Han, C.M; Su, B.X; Sakyi, P.A; Malaviarachchi, P. K. S; Ao, S.J; Wang, L. J.The Dunhuang Block, located in the eastern Tarim Craton, widely exposes Precambrian TTG gneisses and metamorphosed supracrustal rocks. A suite of metasedimentary rocks of the Dunhuang Group in the Hongliuxia area on the easternmargin of the TarimCraton are characterized bymoderate contents of quartz, plagioclase, and biotite, with minor amounts of garnet or kyanite, most of which have experienced strong deformation, resulting in well-developed amphibolite-facies foliations. The examined samples are characterized by moderate Fe2O3+MgOand TiO2 contents, and Al2O3/SiO2 and K2O/Na2O ratios with low Chemical Index of Alteration (CIA) and high Index of Compositional Variability (ICV) values, suggesting that the protolith sediments originated from continental island arc environment. The U–Pb ages of magmatic-type detrital zircons from the Hongliuxia metasedimentary rocks range between 2476 Ma and 1950 Ma, with a peak at 2417 Ma. Detrital zircons of metamorphic origin yielded an age peak at 1832 Ma, which may represent a tectono-thermal event in the Paleoproterozoic. Considering that the main age populations of the analyzed samples are consistent with the tectono-thermal events in the Tarim Craton during the early Paleoproterozoic, we propose that the Tarim Craton was possibly the major source for the protolith sediments of the metasedimentary rocks in the Hongliuxia area. Zircon Hf isotopic compositions (εHf(t) =−5.8 to +2.9) suggest voluminous addition of juvenile materials to the crust and minor reworking of old materials in the eastern Tarim Craton during the Mesoarchean (TDM C = 2.8–2.9 Ga). The metasedimentary rocks of the Hongliuxia area provide clear constraints to the evolution of the Tarim Craton. A possible tectonic model is that multiple thermal events (~2.4 Ga, 2.2 Ga, 2.0 Ga and 1.8 Ga) occurred in the study area, and the time period of Mesoarchean was important for crustal growth in the eastern Tarim Craton, whereas the ~1.83 Ga metamorphism might represent a thermal event associated with the Tarim Craton within the supercontinent Columbia.Item SIMS U–Pb zircon dating and Re–Os isotopic analysis of the Hulu Cu–Ni deposit, eastern Tianshan, Central Asian Orogenic Belt, and its geological significance(Journal of Geosciences, 58: 255-274., 2013) Han, C.M; Xiao, W; Zhao, G; Su, B.X; Sakyi, P.A; Ao, S.J; Wan, B; Zhang, J; Zhang, ZExploration of the Hulu Cu–Ni–Co sulfide deposit in Eastern Tianshan, Central Asian Orogenic Belt, has detected horizons of sulfide mineralization in pyroxenite and peridotite units. SIMS U–Pb zircon ages of the gabbro-hosting Cu–Ni–Co sulfide deposit indicate that the Hulu intrusion was emplaced at 282.3 ± 1.2 Ma (95% confidence level, MSWD = 3.30, n = 13). Osmium isotopic data suggest that the Hulu intrusion and associated Cu–Ni mineralization were derived from crustally-contaminated mantle melts. The intrusions clearly show island-arc geochemical signatures, such as negative Nb, Ta, Zr and Ti anomalies and enrichment in LILE. These geochemical tracers indicate that the Hulu mafic–ultramafic intrusions, along with the Cu–Ni deposit, formed as a result of subduction of oceanic crust in the Early Permian. The arc-related geodynamic setting of the Hulu Cu–Ni deposit is unusual for magmatic sulfide deposits. This new type of ore deposit offers an alternative perspective for Cu and Ni exploration.