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detrital zircons
    SHRIMP U-Pb Geochronological Research on Detrital Zircons from the Beidahe Complex-Group in the Western Segment of the North Qilian Mountains, Northwest China
    北祁连山西段北大河岩群碎屑锆石SHRIMP U-Pb年代学研究
    Metamorphosed detrital zircons from them yield two discordia with upper intercepts of 2.80±0.11 Ga and 2.03±0.05 Ga, respectively.
    变泥砂质岩石给出 2 .80± 0 .11Ga和 2 .0 3± 0 .0 5 Ga两组 (变质 )碎屑锆石年龄数据。
    Some zircons from paragneiss retain inherited cores with inherited ages of 345~743 Ma, indicating the complexity of the detrital zircons in protoliths.
    其中副片麻岩锆石核部记录了345~743 Ma的继承性锆石年龄,标志着原岩碎屑锆石来源的复杂性;
    All the analyzed zircons retain inherited detrital cores with inherited ages (206Pb/238U age) of 313 -659 Ma, indicating that the detrital zircons of the protolith have a variety of sources, and partial loss of Pb from some zircons in the protolith.
    Most detrital zircons show heavy Pb loss. Five data points near the upper intercepts yield a weighted mean 207Pb/206Pb age of 3399±8 Ma, representing the age of the sedimentary source.
    U-Pb ages of detrital zircons from the para-metamorphic rocks of the Qinling Group and their geological significance
    The detrital zircons from the sedimentary rocks were dated through SHRIMP and LA-ICP-MS. The result shows that the detrital zircon U-Pb ages concentrate in 1400 to 600Ma, especially 900-700 Ma,which was the most intensive crustal growth stage in western margin of the Yangtze block. But, tectonic and magmatic events of 1000-700Ma have not been identified yet in North China block.
    Paragneisses from Ximashan contain evidence of detrital zircons that were not recrystallised during the granulite facies metamorphism. These show a spectrum of concordant to weakly discordant 207Pb/206Pb ages from~ 550 Ma to 1 900 Ma, indicating source rocks of Neoproterozoic, Mesoproterozoic and Palaeoproterozoic age.
    西麻山副片麻岩中含有在后期麻粒岩相变质过程中未重结晶的碎屑锆石,由此形成从协和一致的 550 Ma到弱不一致 1 900 Ma的较大 207Pb/206Pb年龄变化范围,表明其原岩具有从新元古代到中元古代-古元古代的年龄。
    The early Cretaceous (130 Ma ± ) magmatism probably resulted in a major Pb loss in some inherited and detrital zircons and might have been an important period of the lithospheric thinning in the eastern part of the North China Block.
    早白垩世(130 Ma左右)的岩浆作用是引起继承锆石和碎屑锆石Pb丢失的重要原因,同时也是华北地块东部岩石圈减薄的最重要时期。
    Zircon SHRIMP dating suggests that detrital zircons of khondalites were derived from old metamorphic basement older than 644 Ma. The khondalites formed in the Caledonian (428~445 Ma) and underwent strong shear deformation in the Indosinian (250~210 Ma).
    锆石 SHRIMP同位素年代测试表明 ,孔兹岩的碎屑锆石来源于 6 4 4~ 873Ma或更老的周缘古老变质基底剥蚀区 ,孔兹岩形成于加里东期(42 8~ 4 4 5 Ma) ,并遭受印支期 (2 5 0~ 2 10 Ma)强烈的剪切应变。
    In combination with the analysis of zircon internal structure revealed by CL images and SHRIMP dating results, the provenance of detrital zircons was discussed.
    The discovery of HP-UHP mineral inclusions in detrital zircons of Triassic age further proved that the HP-UHP rocks of the Dabie Orogen had been already exposed to the earth's surface in the early Jurassic time, and provided an important source for the Hefei Basin.
    HP UHP矿物包裹体在具有三叠纪年龄的变质碎屑锆石中的发现,进一步证明大别造山带高压-超高压岩石在早侏罗世时期已经出露地表并为合肥盆地提供了重要物源;
    The diversity of internal structure and genesis of detrital zircons indicated that the source rocks in the Dabie orogen are complicated at that time.
    (3) Some of the crystal zircons contain rounded or unregular cores in shape, and it is thought that the rounded zircons were captured from the wall rocks during the upwelling of the granitic magma or detrital zircons from partial melting of the lower crust.
    The present of Proterozoic detrital zircons indicate that the Songpan-Ganzi terrane is presumably floored with Precambrian basement rocks.
    Age structure for the detrital zircons from these rocks is characteristic of the Qinling and Erlangping groups with ages of 400~480 Ma. Evidently,the Carboniferous sediments in the northern margin of the Dabie Shan were mainly derived from same rocks as the Qinling and Erlangping groups in the southern margin of the North China Block,and the source area experienced similar tectonic evolution of island arc setting as the Qinling Orogen.
    SHIRIMP U-Pb dating of detrital zircons from the low-grade metamorphic rocks suggests that the obtained minimum age of 524 Ma represents the lower limit of the ages of deposition of this suite of rocks. Based on this age, coupled with the fact that unmetamorphosed Devonian strata are exposed in the area, the age of this suite of low-grade metamorphic series is assigned to Early Paleozoic.
    The detrital zircons yield a wide range of ages,whichare focused on Proterozoic with minor contribution from late Archean material.
    Combined with a regional stratigraphic comparison, ages of the detrital zircons can place a constraint of Neoproerozoic age, later than about 740 Ma, for the deposition time of the Yuntai Formation.


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