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;SiO_(2)和TFe_(2)O_(3)与Σ(CaO+MgO+LOI)呈负相关关系,Al_(2)O_(3)、MnO、P_(2)O_(5)、TiO_(2)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;δ^(13)C_(V-PDB)为0.33‰~0.67‰,δ^(18)O_(V-PDB)为-9.76‰~-10.1‰,δ^(18)O_(SMOW)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。
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.TheΣ(CaO+MgO+LOI)values of these carbonate rocks vary in a relatively narrow range from 95.67%to 89.89%,and the SiO_(2) and TFe_(2)O_(3) values are negatively correlated with theΣ(CaO+MgO+LOI)values.However,the values of Al_(2)O_(3),MnO,P_(2)O_(5) and TiO_(2),are not significantly correlated with theΣ(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.TheΣREE values of these carbonate rocks vary between 13.89×10^(−6) and 40.73×10^(−6),much less than the averageΣREE value of the upper crust(146.37×10^(−6))and slightly higher than theΣREE value of chondrite(about 2.56×10^(−6)).Theδ^(13)C_(V-PDB),δ^(18)O_(V-PDB) andδ^(18)O_(SMOW) 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.
作者
杨庆坤
刘勇
张小亮
李海龙
YANG Qingkun;LIU Yong;ZHANG Xiaoliang;LI Hailong(Center of Geological Resource Economics and Management,East China University of Technology,Nanchang 330013,China;School of Earth Sciences,East China University of Technology,Nanchang 330013,China;China Nonferrous Metals Industry Kunming Survey Design and Research Institute Co.,Ltd.,Kunming 650051,China)
出处
《海洋地质前沿》
CSCD
北大核心
2022年第1期24-32,共9页
Marine Geology Frontiers
基金
江西省软科学研究培育基地东华理工大学资源与环境战略研究中心开放基金“精准扶贫视域下地质文化村的建设思路研究——以江西黄石镇大洲塘村为例”(20RJC02)
东华理工大学专业学位研究生实践基地建设项目“资源与环境硕士专业学位研究生实践基地”(yjsjd2202004)
中国地质调查局项目“全国地质遗迹立典调查与评价”(DD20190074)。
关键词
宁国组
碳酸盐岩
热水沉积
岩石地球化学
碳氧同位素
Ningguo Formation
carbonate rock
hydrothermal deposition
petrogeochemistry
carbon and oxygen isotopes
