Enhanced terrestrial input into Paleoproterozoic to Mesoproterozoic carbonates in the southwestern South China Block during the fragmentation of the Columbia supercontinent
Enhanced terrestrial input into Paleoproterozoic to Mesoproterozoic carbonates in the southwestern South China Block during the fragmentation of the Columbia supercontinent
复制标题
哥伦比亚超大陆破碎过程中华南地块西南部古元古代至中元古代碳酸盐岩的陆地输入增加
DOI：
10.1016/j.precamres.2018.05.001
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发表时间：
2018
影响因子：
3.8
通讯作者：
Zhao Xin-Fu
中科院分区：
文献类型：
--
作者：
Wang Wei;Bolhar Robert;Zhou Mei-Fu;Zhao Xin-Fu
通过对华南陆块西南缘古元古代-中元古代洛穴组和绿之江组碳酸盐岩的岩石元素、C、O和Sr同位素数据的研究，探讨了物源和沉积环境。元素示踪表明，上部洛雪和芦之江碳酸盐岩没有受到地壳混染和成岩/变质叠加的显著影响，从而保留了它们的原始化学特征，这也与原始沉积结构和结构的保存相一致。与此相反，下洛雪碳酸盐岩的C、O和Sr同位素则受到成矿流体的强烈蚀变。与现代海水和海相碳酸盐岩相比，洛雪碳酸盐岩均缺乏Y的富集，对应于25-31的碳酸盐岩Y/Ho比值。页岩标准化REE + Y配分模式显示，洛雪碳酸盐岩明显富集中稀土元素，但缺乏La、Gd、Y等元素的强烈异常。根据岩石学和沉积学特征，洛雪组可能形成于浅水陆表海盆地，与开阔洋的交换有限但可变，陆源输入占主导地位。另一方面，芦之江碳酸盐岩是纯化学沉积物，没有碎屑物质，页岩（PAAS）标准化REE + Y分布显示正La、Gd和Y（Y/Ho：39-47）异常，这是太古代和元古宙时期海相沃茨的典型特征。罗穴上段和芦之江上段碳酸盐岩的87 Sr/86 Sr值均显著高于同时代海水，表明风化大陆源的贡献增加。这种来自陆地来源的注入量增加很可能对应于假设的哥伦比亚/努纳超大陆的破裂，因为洛穴和绿之江碳酸盐沉积在与超大陆碎裂相关的裂谷相关盆地中。
Bulk rock elemental, C, O and Sr isotopic data for carbonates of the Palaeoproterozoic to Mesoproterozoic Luoxue and Luzhijiang formations from the southwestern margin of the South China Block are studied to infer aspects of the provenance and depositional environment. Elemental tracers demonstrate that the upper Luoxue and Luzhijiang carbonates were not significantly affected by crustal contamination and diagenetic/metamorphic overprinting, thus preserving their primary chemical signature, which is also consistent with the preservation of primary sedimentary structures and textures. In contrast, C, O and Sr isotopes of the lower Luoxue carbonates appear to have been variably altered by ore-forming fluids. All the Luoxue carbonates lack enrichment of Y, corresponding to chondritic Y/Ho ratios of 25–31, in contrast to modern seawater and marine carbonates. Shale-normalized REE + Y patterns for the Luoxue carbonates show pronounced enrichment in middle REE, but lack strong elemental anomalies (La, Gd, Y). Based on petrographic and sedimentological characteristics, the Luoxue Formation was probably formed in a shallow water, epicontinental basin with restricted but variable exchange to the open ocean, and dominant terrigenous input. The Luzhijiang carbonates, on the other hand, are pure chemical sediments devoid of detrital material, and shale (PAAS) normalized REE + Y distributions exhibit positive La, Gd, and Y (Y/Ho: 39–47) anomalies, which are typical features of marine waters throughout the Archean and Proterozoic periods.87Sr/86Sr values in both the upper Luoxue and Luzhijiang carbonates are significantly higher than coeval seawater, indicative of enhanced contribution from weathered continental sources. This increased influx from terrestrial sources very likely corresponds to the break-up of the hypothesized Columbia/Nuna supercontinent, as the Luoxue and Luzhijiang carbonates were deposited in a rift-related basin associated with supercontinental fragmentation.