Fractionation characteristics of magnesium isotope in the ancient weathering crust  

作　　者：Jia-Qi Yang Jun-Tao Zhang Zhi-Liang He Ni-Na Luo Xiao-Hui Jjin Tao Zhang Ning Gu Kang-Jun Huang jian Gao 

机构地区：[1]School of Energy Resources,China University of Geosciences,Beijing,100083,China [2]SINOPEC Exploration and Production Research Institute,Beijing,100083,China [3]China Petrochemical Corporation Ltd.,Beijing,100728,China [4]Key Laboratory of Deep Geology and Resources,SINOPEC,Bejing,102206,China [5]Chongqing Gas Field of Petro China Southwest Oil and Gas Field Company,Chongqing,400021,China [6]Shaanxi Key Laboretory of Early Life and Environments,Department of Geology,Northwest University,Xi'an,Shaanxi,710069,China

出　　处：《Petroleum Science》2023年第3期1446-1457,共12页石油科学（英文版）

基　　金：supported by the National Natural Science Foundation of China(42072177);National Natural Science Foundation of China(U19B6003);Frontier Project of Chinese Academy of Sciences(XDA14010201).

摘　　要：Weathering has always been a concerned around the world,as the first and most important step in the global cycle of elements,which leads to the fractionation of isotopes on the scale of geological age.The Middle Ordovician Majiagou Formation in Daniudi area of the Ordos Basin had experienced weathering for>130 Myr.Through thin section observation,major and trace element analysis,carbon,oxygen,and magnesium isotopes composition analysis,the dolomitization modes and weathering of ancient dolo-mite in Daniudi area were analyzed in detail.The results showed that the Sabkha and brine-reflux dolomitization modes had developed,and the Mg isotopes in different layers of the karst crust were fractionated by various factors.The vertical vadose zone was affected by weathering,the Mg isotope of dolomite(δ^(26)Mgdol)showed a downward decreasing trend;the horizontal underflow zone was controlled by diagenesis and formation fluid,δ^(26)Mgdol showed a vertical invariance and negative;the main reason for Mg isotope fractionation in the deep slow-flow zone was the brine-reflux dolomitization mode during early burial period,which showed a vertical downward increase.Finally,the Mg isotope characteristic data of the ancient weathering crust were provided and the process of Mg isotope frac-tionationinthekarstcrust was explained.

关 键 词：Magnesium isotope Dolomitization mode Weathering Ancient weathering crust Ordos Basin 

分 类 号：P618.13[天文地球—矿床学]