Does Neoproterozoic Nam Co Formation in Northwest Vietnam belong to South China or Indochina?
Does Neoproterozoic Nam Co Formation in Northwest Vietnam belong to South China or Indochina?
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越南西北部新元古代纳木错组属于华南还是印度支那？
DOI：
10.1016/j.precamres.2019.105556
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发表时间：
2020-02
影响因子：
3.8
通讯作者：
DinhLuyen Nguyen
中科院分区：
文献类型：
--
作者：
Xueyao Zhou;Jin-Hai Yu;Tao Sun;Xiaolei Wang;MyDung Tran;DinhLuyen Nguyen
纳木错构造带位于越南西北部的宋马断裂带东北部。关于该区前寒武纪基底岩石的性质及其构造属性一直存在争议。本文通过对纳木错带内纳木错组变质沉积岩锆石U-Pb-Hf同位素组成和全岩地球化学组成的综合研究，揭示了纳木错带基底岩石的组成及其形成的构造背景。锆石U-Pb测年结果表明，纳木错组的时代为新元古代中晚期。纳木错组下部可能形成于821 ~ 726 Ma之间，上部可能晚于726-721 Ma。纳木错组上部和下部的沉积岩具有新元古代（900-800 Ma）碎屑物质丰富的特点，但上部比下部含有更多的中-古元古代沉积物。纳木错组碎屑锆石年龄分布和Hf同位素组成与扬子地块南部新元古代沉积岩相似。锆石U-Pb-Hf同位素和全岩地球化学资料表明，新元古代纳木错组的物质来源以长英质岩为主，少量镁铁质物质，碎屑物质主要来自扬子地块南部的江南造山带，扬子地块西部的攀西造山带、哀牢山-宋洪造山带和盘寺盘造山带的贡献较小。纳木错组下部含有较多的来自攀西带的沉积物。新元古代中晚期纳木错组可能为大陆伸展盆地沉积，晚期（<726-721 Ma）沉积环境较稳定。综合研究表明，纳木错组属于扬子陆块基底，纳木错带原位于扬子陆块西南角。这进一步表明，宋马断裂可能是华南地块与印支地块的分界线。
The Nam Co belt is located to the northeast of Song Ma fault in Northwestern Vietnam. The nature of the Precambrian basement rocks in this area and its tectonic attribute have still been controversial. In this study, zircon U-Pb-Hf isotopic compositions and whole rock geochemical compositions of meta-sedimentary rocks from the Nam Co Formation in this belt have been integrated to reveal the components and tectonic setting of the formation of the basement rocks in the Nam Co belt. Zircon U-Pb dating results show that the Nam Co Formation is of middle-late Neoproterozoic age. The lower Nam Co Formation probably formed between 821 and 726 Ma, and the upper Formation was deposited later than 726–721 Ma. The sedimentary rocks from the lower and upper Nam Co formations are characterized by numerous Neoproterozoic (900–800 Ma) detrital materials, but the upper part contains more Meso- to Paleoproterozoic sediments than the lower part. Detrital zircon age distribution and Hf-isotope compositions of the Nam Co Formation are similar to those of Neoproterozoic sedimentary rocks in the southern Yangtze Block. Both zircon U-Pb-Hf isotopic and whole rock geochemical data suggest that the source materials of the Neoproterozoic Nam Co Formation were dominated by felsic rocks with minor mafic materials, and the detrital materials were mainly derived from the Jiangnan Orogenic Belt in the southern Yangtze Block, with minor contribution from the Panxi belt in the western Yangtze Block, Ailaoshan-Song Hong and Phan Si Pan belts. The lower Nam Co Formation contains more sediments derived from the Panxi belt than the upper part. The middle-late Neoproterozoic Nam Co Formation probably was deposited in a continental extensional basin, and the sedimentation environment in later period (<726–721 Ma) was more stable. Integration of our data with other lines of evidence suggests that the Nam Co Formation belongs to the basement of the Yangtze Block, and the Nam Co belt was originally located in the southwest corner of the Yangtze Block. This further suggests that the Song Ma fault probably is the boundary between the South China and Indochina blocks.
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