内蒙古腮林忽洞群含铁燧石团块和微晶丘的成因及构造环境指示意义  

Genesis of Iron-bearing Chert and Carbonate Mud Mound in the Sailinhudong Group,Inner Mongolia,China and its Environmental Implication

作　　者：孙剑[1] 朱祥坤[1] 

机构地区：[1]中国地质科学院地质研究所大陆构造与动力学国家重点实验室,国土资源部同位素地质重点实验室,北京100037

出　　处：《地质学报》2015年第10期1873-1883,共11页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号41403009;40973037;41273065;2012CB416806)资助的成果

摘　　要：内蒙古腮林忽洞群地层中发育含铁燧石团块和微晶丘。本文报道了它们的地质特征及铁同位素、稀土元素地球化学特征,并探讨了它们的成因及构造环境指示意义。燧石一般呈团块状、脉状发育于腮林忽洞群碳酸盐地层中。燧石中发育铁质丝状体,由非晶质的铁(氢)氧化物(赤铁矿和针铁矿)组成,具有丝状、网状形态特征,类似于现代海底热液Fe-Si产物。燧石的铁同位素组成δ56 Fe为-0.71‰^-0.25‰,与海底热液铁同位素组成(δ56Fe为-0.7‰^-0.1‰)一致。燧石的页岩(PAAS)标准化的稀土配分模式具有Eu正异常,La、Y正异常,显示海水和热液混合的稀土配分特点。这些特征表明含铁燧石为海底热液活动产物。腮林忽洞微晶丘成分主要为白云岩,铁同位素组成比该区域正常沉积碳酸盐岩要轻,与含铁燧石及海底热液的铁同位素组成相似;稀土配分模式与燧石一致,显示海水和热液混合的稀土配分特点。表明该微晶丘的形成可能与海底热液活动有关。腮林忽洞群含铁燧石团块、微晶丘的发育以及前人报道的震积岩、滑塌岩的发育表明腮林忽洞群沉积过程中可能处于拉张的构造背景,海底热液活动活跃。由于腮林忽洞群的沉积时代很可能为中元古代,腮林忽洞群的海底热液活动有可能是整个华北地区中元古代(1.3~14Ga)拉张构造背景的一个响应。Here we present the geological characters,iron isotope and rare earth element geochemistry of ironbearing chert and carbonate mud mound in the Sailinhudong Group in Inner Mongolia,China.The ironbearing chert contains elongate highly ramified Fe oxides aggregates,which is similar to submarine hydrothermal Fe-Si deposits.δ56Fe values for iron-rich chert are-0.71‰^-0.25‰,similar to those for submarine hydrothermal fluids.The PAAS-normalized REE pattern shows positive Eu,La and Y anomalies,the characters of the mixture of seawater and high-temperature hydrothermal fluids.These indicate that the iron-bearing chert deposited from submarine hydrothermal activity.The carbonate mud mound（the micrite mound）in the Sailinhudong Group has Fe isotope compositions that isotopically lighter than the normal sedimentary carbonates in the same Group,but similar to those for submarine hydrothermal fluids.It has PAAS-normalized REE pattern that similar to that for chert mentioned above and the submarine hydrothermal fluids.These indicate that the carbonate mud mound also formed related to submarine hydrothermal activity.The existence of iron-bearing chert and carbonate mud mound is accordant with the existence of seismite and earthquake slump-fold blocks reported previously,implying that the Sailinhudong Group deposited in an extending basin when the submarine hydrothermal activities were active.These submarine hydrothermal activities recorded in the Sailinhudong Group may correlate with the extending tectonic setting during 1.3~1.4Ga in the North China Craton.

关 键 词：腮林忽洞 含铁燧石 微晶丘 铁同位素 稀土 海底热液 

分 类 号：P587[天文地球—岩石学]