摘要
CH_(4)和CO_(2)是岩浆热液系统中的重要挥发组分,两者之间的转换机制是一个重要的科学问题,在碳循环和流体作用等诸多方面都具有重要意义。例如在成矿过程中,CH_(4)和CO_(2)的加入会改变成矿流体性质,CO_(2)还能缓冲流体pH,对成矿元素的迁移和沉淀富集有重要影响。前人通过研究瑞士阿尔卑斯山中部石炭纪、二叠纪、三叠纪地层裂隙石英中的流体包裹体发现,在较高温度条件下,黑云母的绿泥石化能将CH_(4)氧化生成CO_(2),然而缺少相关的实验地球化学证据。因此,本项研究选择黑云母作为氧化剂开展了CH_(4)的氧化实验研究。通过对黑云母-甲烷-水体系、黑云母-碳化铝-水体系以及甲烷-水体系的实验研究发现,证实了黑云母能够将CH_(4)氧化为CO_(2),起始反应温度约150℃,远低于地质研究结果。对于黑云母-甲烷-水体系和甲烷-水体系实验,采用熔融毛细硅管作为反应腔,而对于黑云母-碳化铝-水体系实验,则采用粗石英管作为反应腔。对反应后黑云母残片的能谱分析表明,变价元素Fe含量大量降低,表明黑云母中三价Fe作为氧化剂参与了反应。这一结果为地质系统中黑云母等铁锰暗色矿物在中低温条件下氧化CH_(4)形成CO_(2)提供了实验和理论支撑。而CH_(4)向CO_(2)的转变过程,将改变热液流体的性质,有利于富CO_(2)成矿流体的形成,对金属矿床形成具有重要意义。
The conversion mechanism between CH_(4) and CO_(2),two essential volatiles in earth system,is one of the most important scientific problems that is significantly related to many geological processes,such as carbon cycle and fluid-rock interaction.For example,CH_(4) and CO_(2) have a deep impact on the migration and enrichment of ore-forming elements,since CH_(4) and CO_(2) could change the properties of ore-forming fluids in the process of mineralization,especially CO_(2) could buffer the pH of fluids.Based on the fluid inclusions in fractured quartz from Carboniferous,Permian,and Triassic strata in central Swiss Alps,it has been shown that CH_(4) might be oxidized to CO_(2) along with the chloritization of biotite at high temperatures.However,there is no relevant experimental work to illustrate it.This study focused on the oxidation mechanism of methane through a series of laboratory experiments using biotite as the oxidant.Through three batches of experiments i.e.,(1)biotite,methane and water,(2)biotite,aluminum carbide and water,(3)methane and water,this study confirms that CH_(4) can be oxidized to CO_(2) by biotite at an initial reaction temperature of~150℃,which is much lower than the results of field geological studies.Fused Silica Capillary Capsule was used for batch one and three,and thick quartz tube was used for batch two.The energy spectrum analysis on residual biotite show that the content of Fe in biotite decreases greatly,indicating that the trivalent Fe in biotite was involved in the reaction as an oxidant.This result provides experimental and theoretical support for the oxidation of CH_(4) to CO_(2) by biotite and other Fe-Mn minerals in geological system at low temperature.The conversion of CH_(4) to CO_(2) will change the properties of hydrothermal fluids,which could benefit the formation of CO_(2)-rich ore-forming fluids,and is significant for the formation of metal deposits.
作者
陈惠娴
胡文瑄
王小林
CHEN Huixian;HU Wenxuan;WANG Xiaolin(Nanjing University School of Earth Sciences and Engineering,Nanjing,Jiangsu 210023,China)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2022年第6期2107-2115,共9页
Acta Geologica Sinica
基金
国家自然科学基金重点项目(编号41830425)资助成果。
关键词
甲烷氧化
黑云母
实验研究
富CO
流体
methane oxidation
biotite
experimental study
CO2-rich fluids
