Geochemical and zircon U–Pb–Hf–O isotopic evidence for a coherent Paleoproterozoic basement beneath the Yangtze Block, South China
Geochemical and zircon U–Pb–Hf–O isotopic evidence for a coherent Paleoproterozoic basement beneath the Yangtze Block, South China
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DOI：
10.1016/j.precamres.2016.04.002
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发表时间：
2016-07
影响因子：
3.8
通讯作者：
Zhihong Chen;Guangfu Xing
中科院分区：
文献类型：
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作者：
Zhihong Chen;Guangfu Xing
由于太古代至古元古代岩石露头稀少，扬子地块的早期历史没有得到很好的制约。本文报道了扬子地块东部东岭杂岩正片麻岩锆石U-Pb、Hf-O同位素、全岩常量元素、微量元素和Nd同位素的综合研究。LA-ICP-MS锆石U-Pb定年获得207 Pb/206 Pb年龄。1.85 Ga为正片麻岩的原岩年龄，揭示扬子地块东部存在可靠的古元古代基底。正片麻岩中锆石的εHf（t）值为-13.4 ~-9.0，对应于3.03- 2.80Ga的THfDM 2模式年龄。锆石δ 18 O值变化在6.5‰ ~ 8.8‰之间，平均值为7.8‰。全岩εNd（t）值介于-9.3 ~-8.0之间，TNdDM 2模式年龄介于2.98 ~ 3.05 Ga之间。正片麻岩中SiO2、K2 O + Na 2 O、Rb、Ga、Zr、Nb、Y和Ce含量较高，而CaO、Eu、Ba和Sr含量较低。它们的10，000 *Ga/Al比率在3.0和3.5之间。所有这些地球化学和Nd-Hf-O同位素特征表明东岭杂岩中的正片麻岩为A型花岗岩原岩。它们是由太古代地壳物质在后碰撞构造环境中部分熔融而成。当我们的数据与现有的地质年代学数据在扬子地块的其他部分相结合，它表明一个连贯的古元古代基底下扬子地块，代表了哥伦比亚超大陆的重要组成部分。CA。1.85 Ga A型岩浆活动可能导致整个扬子地块的克拉通稳定。此外，扬子地块东部可能存在一个潜在的前寒武纪双重基底结构，它受古元古代变质基底支撑，上覆新元古代沉积盖层。
The early history of the Yangtze Block is not well constrained owing to the scarce outcrops of the Archean to Paleoproterozoic rocks. Here, we report an integrated study of zircon U–Pb and Hf–O isotopes, as well as whole rock major and trace elements and Nd isotopes for the orthogneisses of the Dongling Complex in the eastern Yangtze Block. LA-ICP-MS zircon U–Pb dating yields a207Pb/206Pb age of ca. 1.85 Ga for the protolith age of the orthogneiss, revealing a reliable Paleoproterozoic basement in the eastern Yangtze Block. Zircons from the orthogneiss haveεHf(t) values ranging from −13.4 to −9.0, corresponding toTHfDM2model ages of 3.03–2.80 Ga. The zircon δ18O values range between 6.5‰ and 8.8‰ with an average of 7.8‰. In addition, the whole rockεNd(t) values of the orthogneisses range from −9.3 to −8.0 andTNdDM2model ages from 2.98 Ga to 3.05 Ga. The orthogneisses have relatively high SiO2, K2O + Na2O, Rb, Ga, Zr, Nb, Y and Ce contents and show low CaO, Eu, Ba and Sr concentrations. Their 10,000*Ga/Al ratios range between 3.0 and 3.5. All these geochemical and Nd–Hf–O isotopic signatures suggest A-type granite protolith for orthogneisses in the Dongling Complex. They were generated by partial melting of Archean crustal materials in a post-collisional tectonic setting. When our data is combined with the existing geochronological data in other parts of the Yangtze Block, it demonstrates a coherent Paleoproterozoic basement beneath the Yangtze Block, representing an important part of the Columbia supercontinent. The ca. 1.85 Ga A-type magmatism may have led to craton stabilization over all of the Yangtze Block. In addition, a potential Precambrian dual basement structure may exist in the eastern Yangtze Block, which is supported by Paleoproterozoic metamorphic basement and overlaying Neoproterozoic sedimentary cover.