杨庆坤,刘勇,张小亮,等. 浙江江山宁国组热水沉积事件的岩石地球化学及碳氧同位素证据[J]. 海洋地质前沿,2022,38(1):24-32. DOI: 10.16028/j.1009-2722.2021.197
    引用本文: 杨庆坤,刘勇,张小亮,等. 浙江江山宁国组热水沉积事件的岩石地球化学及碳氧同位素证据[J]. 海洋地质前沿,2022,38(1):24-32. DOI: 10.16028/j.1009-2722.2021.197
    YANG Qingkun, LIU Yong, ZHANG Xiaoliang, et al. Hydrothermal sedimentary origin of the Ningguo Formation in Jiangshan, Zhejiang Province: evidence of elemental geochemistry and C-O isotopes[J]. Marine Geology Frontiers, 2022, 38(1): 24-32. DOI: 10.16028/j.1009-2722.2021.197
    Citation: YANG Qingkun, LIU Yong, ZHANG Xiaoliang, et al. Hydrothermal sedimentary origin of the Ningguo Formation in Jiangshan, Zhejiang Province: evidence of elemental geochemistry and C-O isotopes[J]. Marine Geology Frontiers, 2022, 38(1): 24-32. DOI: 10.16028/j.1009-2722.2021.197

    浙江江山宁国组热水沉积事件的岩石地球化学及碳氧同位素证据

    Hydrothermal sedimentary origin of the Ningguo Formation in Jiangshan, Zhejiang Province: evidence of elemental geochemistry and C-O isotopes

    • 摘要: 近年,在江南地层区奥陶系宁国组下段陆续发现了多处透镜状灰岩及菱铁矿等碳酸盐岩夹层,前人对其岩相学特征的研究多限于定性描述,缺乏系统的成因分析。通过对其开展岩石地球化学和碳氧同位素研究,探讨了其形成与热水作用之间的关系,结果表明:样品Σ(CaO+MgO+LOI)为95.67%~89.89%,分布范围较窄,反映了相对稳定的沉积环境;SiO2和TFe2O3与Σ(CaO+MgO+LOI)呈负相关关系,Al2O3、MnO、P2O5、TiO2与Σ(CaO+MgO+LOI)不具有明显相关性;Co/Ni值为0.24~0.28(<1.0),Mn/Sr值为0.14~0.33(<10);ΣREE为(13.89~40.73)×10−6,远低于上地壳平均值,略高于球粒陨石;在Al-Fe-Mn、(Cu+Co+Ni)×10-Fe-Mn、Ni-Co-Zn三角图和lgU-lgTh关系图中,样品全部落入热水沉积碳酸盐岩区域;δ13CV-PDB为0.33‰~0.67‰,δ18OV-PDB为-9.76‰~-10.1‰,δ18OSMOW为12.56‰~12.9‰,与正常海相或湖相碳酸盐岩的灰岩碳氧同位素组成差异明显,碳氧同位素分布图指示其形成所需热水主要来自岩浆热液与加热海水的混合。丰富的断裂系统为海水下渗和热液混合提供了运移通道,海水与热液的对流活动为海盆持续输入热量并提供成岩所需物质。

       

      Abstract: In recent years, many carbonate interlayers, including lenticular limestones and siderites, have been discovered in the Lower Member of Ningguo Formation of Ordovician in the Jiangnan Area of East China. Controversies occur with regards to the origin of such carbonate rocks. In this paper, the carbonate rocks are studied by means of the petrogeochemistry and C-O isotopes. The Σ(CaO+MgO+LOI) values of these carbonate rocks vary in a relatively narrow range from 95.67% to 89.89%, and the SiO2 and TFe2O3 values are negatively correlated with the Σ(CaO+MgO+LOI) values. However, the values of Al2O3, MnO, P2O5 and TiO2, are not significantly correlated with the Σ(CaO+MgO+LOI) values. The Co/Ni values of these carbonate rocks vary within the range from 0.24 to 0.28, much lower than 1.0, and the Mn/Sr ratios change from 0.14 to 0.33, much lower than 10. In the ternary plots of Al-Fe-Mn, (Cu+Co+Ni)×10-Fe-Mn and Ni-Co-Zn as well as the crossplot of LgU-LgTh, all the studied samples fall in the domain of hydrothermal carbonates. The ΣREE values of these carbonate rocks vary between 13.89×10−6 and 40.73×10−6, much less than the average ΣREE value of the upper crust (146.37×10−6) and slightly higher than the ΣREE value of chondrite (about 2.56×10−6). The δ13CV-PDB, δ18OV-PDB and δ18OSMOW of these carbonate rocks are 0.33‰~0.67‰, −9.76‰~−10.1‰ and 12.56‰~12.9‰ respectively, which are obviously different from those of Marine and lacustrine limestones. Fault systems are well developed in the area, which may provide channels for the downward infiltration of seawater, of which the mixing effects the hydrothermal solution. As a result, the convective activities between seawater and hydrothermal continuously supply heat and diagenetic ions for the ocean basin. This marine hydrothermal deposition event represents a special genetic mode. It lasted for a long time and occurred in a wide range, depending on the provenance of hydrothermal materials and their properties.

       

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