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南岭地区新元古代变质沉积岩的地球化学特征及构造意义

ISSN号：0379-1726
期刊名称：《地球化学》
时间：0
分类：P595[天文地球—地球化学;天文地球—地质学] P588.2[天文地球—岩石学;天文地球—地质学]
作者机构：[1]内生金属矿床成矿机制研究国家重点实验室,南京大学地球科学系,江苏南京210093
相关基金：国家自然科学基金（40634022,40672125,40221301）感谢韶关核工业290研究所谭正中高级工程师在野外工作中给予的帮助;感谢研究生谢磊和赵蕾在野外和样品处理上的帮助.

关键词：地球化学, 新元古代, 变质沉积岩, 南岭地区, geochemistry, Neoproterozoic, metasedimentary rocks, Nanling Range area

中文摘要：

对华夏地块南岭地区38个新元古代基底变质岩的岩相学和地球化学分析表明，它们的原岩都是沉积岩。不同地区变质沉积岩的化学成分存在一定的变化，但是它们大都具有明显的轻重稀土元素分异和Eu负异常（Eu／Eu^＋=0．35～0．76），高K2O／Na2O、La／Co、Th／Sc比值和低Cr／Zr比值，显示了高成熟度和沉积再循环地壳的特点，表明沉积岩的物质主要来源于古老的再循环的地壳，它们沉积于被动大陆边缘。与其他地区元古宙沉积岩的地球化学对比显示，南岭地区这些新元古代沉积岩不同于赣中和扬子地块南缘的元古宙沉积岩，而与印度东北部ksser Himalaya地区的元古宙沉积岩较为相似。所以，南岭地区新元古代沉积岩的物质不可能来自与赣中和扬子地块南缘沉积物相同的扬子南部的源区，而应该来自南方，这一推论与岩相古地理分析以及沉积物中碎屑锆石形貌特征和年龄谱变化的结论是一致的，指示华夏南部新元古代时曾与一个大陆源区相邻。根据地球化学对比研究，结合已有的年代学对比，推断华夏地块南岭地区（特别是中部）新元古代沉积物很可能来源于与Lesser Himalaya地区元古宙沉积岩相同的源区，即东Gondwana大陆的北缘。这样，华夏地块在Rodinia超大陆裂解时期很可能是位于西澳大利亚-东印度-东南极之间。

英文摘要：

Petrographical and geochemical analyses of 38 Neoprotemzoic basement metamorphic rocks of Nanling Range in Cathaysia block have shown that their protoliths are mainly sedimentary rocks. The chemical compositions of the metasedimentary rocks from different areas show some by significant fractionation of LREE and HREE, negative Eu variations among them, but they are all characterized anomaly （Eu/Eu^＊ =0.35 - 0. 76）, high K2O/Na2O, La/Co and Th/Sc ratios and low Cr/Zr ratio, which suggest the high degree of maturity and the recycling features of sediments, implying that the sedimentary rocks were disposed sediments mainly derived from the recycled old crust. The Nanling Neoproterozoic in the passive continental margin. In geochemical comparison with the Proterozoic sedimentary rocks in other areas, it is shown that Nanling Neoproterozoic sedimentary rocks are different from those in the central Jiangxi Province and southern Yangtze Block, but are similar to those from the Lesser Himalaya in northeastern India. Thus, the Nanling Neoproterozoic sediments unlikely came from northern source region same as those sediments in the central Jiangxi Province and southern Yangtze block, and on the contrary, it must came from the south. The inference is consistent with paleogeographical analysis of sediment lithofacies and the conclusion deduced from the morphological features and age spectra of detritus zircons from the sediments, suggesting that in Neoproterozoic, southern Cathaysia was the present paper, and combined with adjacent to a continental source. Based the previous geochronological study, on the geochemical comparison in it can be concluded that the late Neoproterozoic sediments in the Nanling Range of Cathaysia block （especially the central part） may have the same source region as the Proterozoic sedimentary rocks in Lesser Himalaya, i.e. the northern margin of East Gondwanaland. Consequently, Cathaysia block was probably between West Australia, East India and East Antarctica during the breakdown of Rod