川中地区中二叠统茅口组白云岩特征及成因机理
发布时间：2018-11-12 14:48
【摘要】：川中地区茅口组白云岩主要位于茅口组二段中、上部和茅口组三段下部,根据岩石学特征可分为含灰质细—中晶白云岩、细—中晶白云岩、角砾白云岩,且以后两者为主。对比泥晶灰岩与不同类型白云岩样品地球化学特征后发现,白云岩相对于同层灰岩具有较低的Fe含量、较高的Mn含量和较低的Sr含量;泥晶灰岩与不同类型白云岩具有相似的稀土配分特征,均表现为LREE亏损、轻微正La异常和负Ce异常,且白云岩样品具有微弱的Eu正异常;细—中晶白云岩与角砾白云岩δ~(18)O值均明显低于原始灰岩,而~(87)Sr/~(86)Sr比值则明显高于原始泥晶灰岩。不同类型白云岩与灰岩相似的稀土配分特征表明茅口组白云岩形成过程中保留了原始灰岩的部分地球化学特征,而白云岩微弱Eu正异常及其与灰岩同位素差异性可能是由于白云岩化过程中高温地质热流体的参与而引发的。茅口组白云岩化作用受多种因素控制:地层残余海水和岩浆活动伴生的热液流体为白云岩化作用中Mg的主要来源;峨眉山大火成岩省热效应为白云岩化提供异常高的古地温背景;断裂系统为异常地温对流和白云岩化流体提供了快速运移通道;颗粒滩相灰岩较好的孔、渗性使之比泥晶灰岩更易发生白云岩化。峨眉山大火成岩省伴生的异常地温和充足Mg供给是茅口组发生白云岩化的关键,不同类型白云岩形成于白云岩化过程的不同阶段。
[Abstract]:The dolomite of Maokou formation in central Sichuan is mainly located in the middle of the second member of Maokou formation, the upper part and the lower part of the third member of Maokou formation. According to the petrological characteristics, it can be divided into fine gray-mesocrystalline dolomite, breccia dolomite and the latter two. Comparing the geochemical characteristics of mudstone and different types of dolomite, it is found that dolomite has lower Fe content, higher Mn content and lower Sr content compared with the same layer limestone. The mudstone and dolomite have similar REE distribution characteristics, all of them show LREE deficiency, slight positive La anomaly and negative Ce anomaly, and the dolomite samples have weak Eu positive anomaly. The 未 ~ (18) O value of fine-mesocrystalline dolomite and breccia dolomite is obviously lower than that of the original limestone, while the ratio of ~ (87) Sr/~ _ (86) Sr is obviously higher than that of the primitive marl limestone. The REE partitioning characteristics of different types of dolomite and limestone indicate that some geochemical characteristics of the original limestone were preserved during the formation of the Maokou formation dolomite. The weak Eu positive anomaly of dolomite and its isotopic difference with limestone may be caused by the participation of high temperature geological thermal fluid in dolomitization. The dolomitization of Maokou formation is controlled by many factors: the hydrothermal fluid associated with residual sea water and magmatic activity is the main source of Mg in dolomitization; The thermal effect of Emeishan igneous rocks provides a high paleogeothermal background for dolomitization, and the fault system provides a rapid migration channel for anomalous geothermal convection and dolomized fluids. The porosities of granular beach limestone are more likely to occur dolomitization than that of mudstone. The abnormally moderate and sufficient Mg supply associated with the great igneous rocks in Emeishan province is the key to the dolomitization of the Maokou formation. Different types of dolomite are formed in different stages of dolomitization.
【作者单位】： 北京大学地球与空间科学学院;北京大学石油与天然气研究中心;
【基金】：国家自然科学基金项目(No.41672123,No.41272137)资助
【分类号】：P618.13
[Abstract]:The dolomite of Maokou formation in central Sichuan is mainly located in the middle of the second member of Maokou formation, the upper part and the lower part of the third member of Maokou formation. According to the petrological characteristics, it can be divided into fine gray-mesocrystalline dolomite, breccia dolomite and the latter two. Comparing the geochemical characteristics of mudstone and different types of dolomite, it is found that dolomite has lower Fe content, higher Mn content and lower Sr content compared with the same layer limestone. The mudstone and dolomite have similar REE distribution characteristics, all of them show LREE deficiency, slight positive La anomaly and negative Ce anomaly, and the dolomite samples have weak Eu positive anomaly. The 未 ~ (18) O value of fine-mesocrystalline dolomite and breccia dolomite is obviously lower than that of the original limestone, while the ratio of ~ (87) Sr/~ _ (86) Sr is obviously higher than that of the primitive marl limestone. The REE partitioning characteristics of different types of dolomite and limestone indicate that some geochemical characteristics of the original limestone were preserved during the formation of the Maokou formation dolomite. The weak Eu positive anomaly of dolomite and its isotopic difference with limestone may be caused by the participation of high temperature geological thermal fluid in dolomitization. The dolomitization of Maokou formation is controlled by many factors: the hydrothermal fluid associated with residual sea water and magmatic activity is the main source of Mg in dolomitization; The thermal effect of Emeishan igneous rocks provides a high paleogeothermal background for dolomitization, and the fault system provides a rapid migration channel for anomalous geothermal convection and dolomized fluids. The porosities of granular beach limestone are more likely to occur dolomitization than that of mudstone. The abnormally moderate and sufficient Mg supply associated with the great igneous rocks in Emeishan province is the key to the dolomitization of the Maokou formation. Different types of dolomite are formed in different stages of dolomitization.
【作者单位】： 北京大学地球与空间科学学院;北京大学石油与天然气研究中心;
【基金】：国家自然科学基金项目(No.41672123,No.41272137)资助
【分类号】：P618.13
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