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    SHRIMP U-Pb zircon geochronology of Yangfang aefiriteaugite syenite in Wuyi Mountains of South China and its tectonic implications [查看] WANGQiang、ZHAOZhenhua、JIANPing、BAOZhiwei、XIONGXiaolin、MAJinlong
    Abstract In addition to the wide spread peraluminous granites, some alkaline or alkali-rich intrusive rocks were recently observed in the Wuyi Mountains. The Yangfang aegiriteaugite syenites in the Wuyi Mountains are strongly enriched in light rare earth elements (LREE), K, Ba, Ga, Zr and Y. What is more, differentiations of REE are obvious. In addition, the Yangfang aegiriteaugite syenites have also some characteristics similar to A-type granite. Zircons are selected from the Yangfang aegiriteaugite syenites for Sensitive High-Resolution Ion Microprobe (SHRIMP- Ⅱ ) U-Pb geochronology study. 15 analyses give concordant 206Pb/238U ages in a narrow range of 233—249 Ma, which correspond to a single age population with a weighted mean 206Pb/238U age of 242 ± 4 Ma, which records the crystallization time of the aegiriteaugite syenites. It is suggested that: (1) there were early Triassic peralkaline intrusive rocks in South China; (2) the early Indosinian extension event was probably active in local area, South China. This discovery provides a new insight for farther understanding of “Indosinian orogeny” in South China.
    SHRIMP U-Pb zircon geochronology and its implications on the Xilin Gol Complex，Inner Mongolia,China [查看] SHIGuanghai、LIUDunyi、ZHANGFuqin、JIANPing、MIAOLaicheng、SHIYuruo、
    Abstract The Xilin Gol Complex, consisting of deformed and metamorphosed rocks, was exposed as a large geological unit within the Central Asian Orogenic Belt, but its forming and subsequent deformed and metamorphic time has been an issue of little consensus. Petrographic analyses and SHRIMP dating on biotite-plagioclase gneiss, one of the major rocks within the Xilin Gol Complex, in southeast Xilinhot City, Inner Mongolia, China, where the Xilin Gol Complex was identified and named, yield its lower limit age of 437 ± 3 Ma (2s ) by its magmatic zircon SHRIMP U-Pb dating, and an upper limit age of 316 ± 3Ma (2s ), which was constrained by SHRIMP dating of magmatic zircons from adjacent undeformed garnet-bearing granite which intruded the Complex.The Complex was thus determined to be formed and subsequently deformed/metamorphosed from the late Ordovician-early Silurian to the mid-Carboniferous. Consequently, it is not the Precambrian terrane as previously considered by most geologists. More or less, the major rock —— biotiteplagioclase gneiss within the Complex is more likely to be Paleozoic fore-arc turbidite formation before metamorphism and intensive deformation, in which the detrital zircons gave sporadic Precambrian ages as old as up to 3.1 Ga. The source of the turbidite formation is multiple, which may be derived either from the North China Craton, or from the South-Mongolia Micro-continent, or probably came from a potential and undiscovered in situ terranes aged 600—800 Ma or even up to ca 3.1 Ga near the Complex.
    SHRIMP dating of volcanic rocks from Ningwu area and its geological implications [查看] ZHANGQI、JIANPING、LIUDunyi、WANGYanglong、QIANQing、WANGYan、XUEHuaimin
    Abstract The SHRIMP U-Pb ages are reported for the volacnic rocks from the Longwangshan and the Dawangshan formations respectively,Ningwu area,Jiangsu Province,The Dawagnshan formation(NB-01) is dated at(127±3）Ma，and the Longwangshan formation(NL-01),(131±4）Ma，besides,a few Archean zircons are also found in the Longwangshan formation,which suggests a possible Archean basement in the region.
    Paleoproterozoic lower crust beneath Nushan in Anhui Province Evidence from zircon SHRIMP U-Pb dating on granulite xenoliths in Cenozoic alkali basalt [查看] HUANGXiaolong、XUYigang、LIUDunyi、JIANPing
    Abstract Zircon SHRIMP U-Pb dating was carried out for an intermediate granulite xenolith in Cenozoic alkali basalt from Nushan. The results suggest that the lower crust beneath Nushan may have formed at about 2400—2200 Ma,and have been subjected to granulite-facies metamorphism at 1915±27 Ma. The old age of the Nushan lower crust is consistent with the geochemical similarities between Nushan granulite xenoliths and Archean-Paleoproterozoic granulite terrains in the North China craton, but it is not distinguishable from high-grade metamorphic rocks in the Yangtze craton where such old ages were also reported.Significant Pb-loss occurs in the Nushan zircons, implying important influence of widespread Mesozoic to Cenozoic underplating in East China on the lower crust beneath Nushan.
    Determination of U-Pb age and rare earth element concentrations of zircons from Cenozoic intrusions in northeastern China by laser ablation ICP-MS [查看] YUANHonglin、WUFuyuan、GAOShan、LIUXiaoming、XUPing、SUNDeyou
    Abstract Using the in situ zircon U-Pb dating method of LA-ICPMS, we analyzed the 31 Ma old SHRIMP U-Pb age of the Yongsheng nepheline syenite from southern Jilin Province under different spot sizes. The obtained ages are comparable with that of SHRIMP in both accuracy and precision. The age is also identical to that of the Yinmawanshan gabbro from the Liaodong Peninsula within error. Both the Yongsheng nepheline syenite and the Yinmawanshan gabbro represent the youngest known exposed intrusions in northeastern and even eastern China.The results indicate the Eocene mantle-derived magmatic underplating, and the rapid crustal uplifting of this region since 30 Ma. The analyses also document extremely high LREE concentrations and relatively flat REE patterns for the zircons from the Yongsheng nepheline syenite, which represent a new type of zircon REE pattern.
    Zircon U-Pb SHRIMP ages of high-pressure granulite in Yushugou ophiolitic terrane in southern Tianshan and their tectonic implications [查看] ZHOUDingwu、SULi、JIANPing、WANGRunsan、LIUXiaoming、LUGuanxiang、WANGJuli
    Abstract Zircons from two high-pressure granulite samples from the Yushugou ophiolitic terrane, southern Tianshan have been investigated by cathodoluminescence, LAICPMS and ion microprobe (SHRIMP) for their internal textures, trace elemental compositions and in situ dating. The weighted mean ages of these two samples are 392±7 and 390±11 Ma, respectively, representing the granulite-facies metamorphic age of the ophiolitic terrane, and indicating that the southern Tianshan ocean initiated its northward subduction since the early Devonian.
    Zircon U-Pb SHRIMP dating of the Yematan batholith in Dulan,North Qaidam,NW China [查看] WUCailai、YANGJingsui、JosephL.Wooden、SHIRendeng、CHENSongyong、AndersMeibom、ChrisMattinson
    Abstract The Yematan batholith crops out over 120 km2 in the North Qaidam ultrahigh pressure (UHP) metamorphic belt. It consists of granodiorite, monzogranite and biotite granite and forms an irregular intrusion into Neoproterozoic gneiss that has undergone Caledonian UHP metamorphism. Zircons from the Yematan granodiorite yield a SHRIMP U-Pb age of 397±3 Ma. These granitic rocks have geochemical characteristics intermediate between I- and S-type granites，and are post-collisional. We suggest that the Yematan granitic rocks were formed during the last exhumation event of the North Qaidam UHP belt.
    Zircon SHRIMP U-Pb age ofgarnet olivine pyroxenite at Hujialin in the Sulu terrane and its geological significance [查看] GAOTianshan、CHENJiangfeng、XIEZhi、YANGShenghong、YUGang
    Abstract Garnet olivine pyroxenite at Hujialin is situated in the Sulu ultrahigh pressure (UHP) metamorphic belt,Shandong Province. Most of the zircon separated from the rock is well crystallized, prismatic and granular with a length to width ratio of 1︰1.3—1︰2.5. CL and BSE images show the magmatic oscillatory zoning in the zircon. Th/U ratio ranges from 0.99 to 2.81. These suggest a magmatic origin for the zircon studied. SHRIMP dating yields 206Pb/238U ages of 207—223 Ma, with a weighted average of 216±3 Ma. This age corresponds to zircon growth during exhumation of UHP slab and thus the timing of amphibolite-facies retrogression. The garnet olivine pyroxenite was wrapped and brought to the crust by the UHP slab during exhumation, and then suffered from metasomatism by fluid from the UHP slab itself. The zircon U-Pb age records the timing of the crystallization of metasomatic melt. Therefore,fluid that was released during exhumation of deeply subducted continental slab may be the important source for zircon growth.
    Zircon SHRIMP dating of sodium alkaline rocks from Maomaogou area of Huili country in Panxi,SW China and its geological implications [查看] LIUHongying、XIABin、ZHANGYuquan
    Abstract Alkali-feldspar syenites from the Maomaogou area of Huili County in Panxi of Sichuan Province, SW China are sodium alkaline rocks, the minerals of which are mainly composed of calcic ferroaugite, ferroamphibole and biotite. Most of the zircons (>80%) selected for SHRIMP U-Pb dating are magmatic compound zircons and they have relict inner cores and growing outer shells. The age of zircon SHRIMP U-Pb dating is 224±8 Ma, suggesting that the Maomaogou alkali-feldspar syenite was formed in the late Triassic period. At the same time, two old age periods of relict cores of zircon are determined, they are the Archean age(2692—2818 Ma) and Neoproterozoic age (622—691 Ma),respectively. These periods indicate that the cores derived from the crystal basement. Furthermore, the Archean age of zircon provides the first reliable SHRIMP U-Pb zircon dating evidence of >2.8 Ga basement in the Xikang-Yunnan Axis of southwest China.
    Sm-Nd and SHRIMP U-Pb zircon geochronology of high-pressure granulites in the Sanggan area,North China Cratontiming of Paleoproterozoic continental collision [查看] J.H.Guo、M.Sun、F.K.Chen、M.G.Zhai
    Abstract High-pressure(HP)mafic granulites are widely distributed as sheet-like and lenticular bodies within highly deformed tonalitic gneisses in the Sanggan area.North China Craton.THey have clockwise isothermal decompression and isobaric cooling P-T paths implying continental collision tectonics,Whole-rock analyses of 15 samples define a Sm-Nd isochron yielding an age of 2547±87Ma withεNd(t)=2.7.Corresponding Nd depleted mantle model ages show a similar range and are interpreted as the age of the magmatic protolith to the high pressure granulites.A combined Sm-Nd mineral+whole-rock isochron from one of these samples yields an age of 1813±23Ma，taken to represent the metamorphic age at an early stage on the cooling path.SHRIMP U-Pb zircon analyses of three HP mafic granulite samles give uniform weighted mean 207Pb/206Pb ages of 1817±12,1817±12 and 1819±16Ma，these ages are interpreted to date metamorphism of the HP granulites and,with the Sm-Nd mineral＋whole-rock result,strongly suggest that the time of continental collision was at ca.1.82Ga.An additional sample records two age populations;one at 1803±9Ma and an older one at 1872±16Ma。The latter may indicate the timing of either an earlier metamorphic event or possibly the earliest stage of a single prolonged metamorphic episode that peaked at ~1.82Ga.These results confirm the Paleproterozoic age of assembly of the North China Craton
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