云开地区变质沉积岩碎屑锆石U-Pb年龄、Lu-Hf同位素特征及其地质意义

发布时间：2018-06-15 14:53

本文选题：云开地区 + 碎屑锆石　；参考：《岩石学报》2017年09期

【摘要】：华夏陆块西南部云开地块变质杂岩主要由天堂山岩群和云开群以及古生代花岗质岩石组成。天堂山岩群主要由片麻岩、变粒岩、石英岩等岩石组成,变质程度较深;云开群主要由片岩、板岩、千枚岩、变质砂岩等岩石组成。应用LA-ICP-MS U-Pb微区定年和Lu-Hf同位素分析以及全岩地球化学分析方法,本文对天堂山岩群和云开群变质沉积岩进行了研究。在阴极发光图像中,变质沉积岩的锆石显示岩浆震荡环带,但普遍遭受重结晶改造及存在变质增生边。由于变质增生边普遍较窄,U-Pb定年和Hf同位素分析几乎都在具岩浆环带和重结晶结构的成分域上完成的。具岩浆环带和重结晶结构的成分域的Th/U比值普遍大于0.1。年龄变化从3000~500Ma,但主要集中在600~1200Ma之间,主峰值为960Ma左右。碎屑锆石的ε_(Hf)(t)值在-25.6~15.4之间,两阶段Hf模式年龄在972~4496Ma之间。全岩地球化学分析显示LREE富集,HREE亏损,具有较明显的负Eu异常(δEu=0.55~0.71),天堂山岩群与云开群REE配分模式一致,反映源区物质相似,主要来源于花岗质地壳物质。结合前人研究成果,可得出如下结论:天堂山岩群与云开群形成时代没有明显差别,虽然它们在变质变形方面存在较明显区别;天堂山岩群和云开群沉积时代为古生代早期-新元古代;格林威尔期岩浆岩为主要物源区,新元古代时期华夏陆块处于格林威尔造山带内与之相邻;华夏陆块存在太古宙古老陆壳。
[Abstract]:The metamorphic complex of Yunkai block in southwestern Huaxia block is mainly composed of Paradise rock group, Yunkai group and Paleozoic granitic rocks. The Paradise rock group is mainly composed of gneiss, granulite, quartzite and so on, and the Yunkai group is mainly composed of schist, slate, phyllite, metamorphic sandstone and other rocks. Using LA-ICP-MS U-Pb dating, Lu-Hf isotopic analysis and whole-rock geochemical analysis, metamorphic sedimentary rocks of the Paradise and Yunkai groups have been studied in this paper. In the catholuminescence images, zircon from metamorphic sedimentary rocks shows magmatic oscillatory ring, but it is generally subjected to recrystallization and metamorphic accretion. Due to the narrow U-Pb dating and HF isotopic analysis of metamorphic accretive edges, almost all isotopic analyses have been completed in the domain of composition with magmatic ring and recrystallization structure. The Th-U ratio in the composition domain with magmatic ring and recrystallization structure is generally greater than 0.1. The age varies from 3000 Ma to 500 Ma, but it is mainly concentrated between 600 Ma and 1200 Ma, and the main peak value is about 960Ma. The 蔚 ~ (-1) of zircon from clastic zircons ranges from -25.6N to 15.4, and the two-stage HF model age is between 9722 and 4496 Ma. The whole rock geochemical analysis shows that LREE is enriched with HREE deficiency and has obvious negative EU anomalies (未 EU ~ (0.55) ~ (0.71). The REE distribution pattern of the Paradise rock group is consistent with that of the Yunkai Group, which shows that the source area is similar to that of the source area and is mainly derived from granitic crust material. Combined with the previous research results, we can draw the following conclusions: there is no obvious difference between the formation age of the Paradise rock group and the Yunkai group, although they have obvious differences in metamorphic deformation; The sedimentary age of the Paradise and Yunkai groups is early Paleozoic to Neoproterozoic, the Granville magma is the main source area, and the Neoproterozoic Huaxia block is adjacent to it in the Greenwell orogenic belt. The ancient Archean continental crust exists in the Cathaysian continent block.
【作者单位】：中国地质科学院地质研究所;
【基金】：中国地质调查局项目(1212011120115、DD20160345) 科技基础性工作专项(2012FY120100)联合资助
【分类号】：P587;P597

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