滇东北地区下寒武统龙王庙组白云石化模式研究:来自钙同位素模拟结果  

Dolomitization in the Lower Cambrian Longwangmiao Formation in northeastern Yunnan:Insights from a simulation study

作　　者：李柯然 杨迪[1] 宋金民[1,2] 李智武[1] 金鑫[1,2] 刘芳 杨雄[3] 刘树根 叶玥豪 范建平[1,2] 任佳鑫 赵玲丽 夏舜 陈伟 LI Keran;YANG Di;SONG Jinmin;LI Zhiwu;JIN Xin;LIU Fang;YANG Xiong;LIU Shugen;YE Yuehao;FAN Jianping;REN Jiaxin;ZHAO Lingli;XIA Shun;CHEN Wei(State Key Laboratory of Oil and Gas Reservoir Geology,Chengdu University of Technology,Chengdu 610059,China;College of Energy,Chengdu University of Technology,Chengdu 610059,China;College of Earth and Planetary Sciences,Chengdu University of Technology,Chengdu 610059,China;Xihua University,Chengdu 610039,China)

机构地区：[1]成都理工大学油气藏地质及开发工程全国重点实验室,四川成都610059 [2]成都理工大学能源学院,四川成都610059 [3]成都理工大学地球与行星科学学院,四川成都610059 [4]西华大学,四川成都610039

出　　处：《地学前缘》2024年第2期313-326,共14页Earth Science Frontiers

基　　金：国家自然科学基金项目(41872150);国家自然科学基金重点项目(42230310)。

摘　　要：滇东北地区桧溪剖面位于四川盆地南缘外侧,剖面龙王庙组地层白云石化活动强烈,广泛发育泥晶灰岩、砂屑灰岩、泥晶白云岩、云质灰岩和灰质云岩等岩性。剖面3个灰岩过渡岩性白云岩旋回中具有混积特征,石英颗粒大量发育。阴极发光下,3个岩性旋回主要呈暗红色,可见石膏。地球化学测试显示:旋回1中灰岩白云岩碳同位素为-0.78‰~-0.49‰,氧同位素为-9.28‰~-8.96‰,锶同位素为0.70979554~0.71218318,钙同位素为0.54‰~1.12‰;旋回2中灰岩白云岩碳同位素为0.37‰~0.41‰,氧同位素为-9.76‰~-9.64‰,锶同位素为0.71008711~0.71374167,钙同位素为0.63‰~0.81‰;旋回3中灰岩白云岩碳同位素为-0.03‰~0.23‰,氧同位素为-9.90‰~-9.24‰,锶同位素为0.70990934~0.71237617,钙同位素为0.56‰~0.94‰;3个旋回中灰岩锶、钙同位素测试结果明显偏低,白云岩锶、钙结果明显偏高。钙同位素对流、缓冲模型模拟结果显示,旋回1白云石化流体Mg^(2+)浓度为2倍海水当量(105.64 mmol/kg,Mg^(2+)/Ca^(2+)=1.99),旋回2白云石化流体Mg^(2+)浓度为7倍海水当量(369.74 mmol/kg,Mg^(2+)/Ca^(2+)=6.79),旋回3白云石化流体Mg^(2+)浓度为2.3倍海水当量(121.48 mmol/kg,Mg^(2+)/Ca^(2+)=2.29)。温度模拟显示,白云石化流体温度主要为30℃。综合岩石学、常规地球化学及钙同位素模拟结果,滇东北地区龙王庙组白云岩为渗透回流模式成因。The Guixi outcrop is located at the southernmost margin of the Sichuan Basin,northeastern Yunnan.The Longwangmiao Formation in the outcrop experienced strong dolomitization activity and developed widespread micritic limestone,arenaceous limestone,micritic dolomite,dolomitic limestone and calcareous dolomite.The three limestone-transition-dolomite cycles in the outcrop were characterized by presence of large quartz grains,and appeared mostly dark red under cathodoluminescence,with observable gypsum.Geochemical tests showed that the isotopic compositions of limestone-dolomite in cycle 1 were:carbon,-0.78‰-0.49‰,oxygen,-9.28‰-8.96‰,strontium,0.709795540.71218318,calcium,0.54‰1.12‰;in cycle 2:carbon,0.37‰0.41‰,oxygen,-9.76‰-9.64‰,strontium,0.71008711-0.71374167,calcium,0.63‰0.81‰;and in cycle 3:carbon,-0.03‰-0.23‰,oxygen,-9.90‰-9.24‰,strontium,0.709909340.71237617,calcium,0.56‰0.94‰.The strontium and calcium isotope values were obvious low in limestone and high in dolomite.Calcium isotope simulation revealed the Mg^(2+)concentration in dolomitized fluid in cycle 1 was twice the seawater equivalent(105.64 mmol/kg,Mg^(2+)/Ca^(2+)=1.99),in cycle 2 seven times(369.74 mmol/kg,Mg^(2+)/Ca^(2+)=6.79),and in cycle 32.3 times(121.48 mmol/kg,Mg^(2+)/Ca^(2+)=2.29).Temperature simulation revealed the temperature of dolomitization fluid was around 30℃.The above results indicate dolomitization in the Longwangmiao Formation in northeastern Yunnan was mainly by seepage reflux.

关 键 词：滇东北地区 龙王庙组 白云石化 钙同位素 流体温度模拟 流体元素模拟 

分 类 号：P597.2[天文地球—地球化学] P588.245[天文地球—地质学]