古盐度对塔北隆起泥岩中粘土矿物组合和绿泥石成分的影响  

Effects of Paleosalinity on Clay Mineral Assemblages and Chlorite Composition in Mudstone of Tabei Uplift, Xinjiang, China

作　　者：赵明[1] 季峻峰[1] 陈小明[1] 蔡元峰[1] 吴昌志[1] 陈永权[2] 武兵[1] 

机构地区：[1]南京大学地球科学与工程学院,南京210023 [2]新疆塔里木油田公司勘探开发研究院,库尔勒841000

出　　处：《高校地质学报》2015年第3期365-375,共11页Geological Journal of China Universities

基　　金：国家自然科学基金课题(41172040;40772027)资助

摘　　要：粘土矿物组合和绿泥石成分常被用来讨论盆地沉积物的成岩作用和埋藏古温度.许多沉积盆地的研究结果显示,泥岩和页岩中的粘土矿物组合和绿泥石的成分与埋藏深度/温度有关.但也见有例外的现象存在.文中主要探讨了新疆塔北隆起泥岩中的粘土矿物组合和绿泥石成分的特征,以及与盆地古盐度的关系.研究结果表明：（1） 在塔北隆起泥岩中,埋藏深度2777.37-4604.41 m,地层单位为J1-N2的粘土矿物组合为I＋Chl和I＋Chl＋Ka; 埋藏深度5071.52-5299.37 m,地层单位为T1的粘土矿物组合为R0I/S＋ I ＋ Chl和R0I/S ＋Chl.（2） 研究区的成岩绿泥石为Ⅱb型铁镁绿泥石,其成分特征主要表现为：①配位八面体中阳离子的占位数为11.532 （总平均值）;②ⅥAl含量明显大于ⅣAl含量;③（Fe＋Mg） 为4.016（总平均值）;④Si/Al比值〉1.（3） 根据研究区盐类矿物的分布范围以及古盐度的数据,讨论了古盐度对该区粘土矿物组合和绿泥石成分的影响,指出古盐度是影响本区粘土矿物组合和绿泥石成分变化的主要因素.用古盐度解释了〈5000 m深度的粘土矿物组合中不含无序伊/蒙混层（R0I/S） 矿物,而〉5000 m深度粘土矿物组合中含有无序伊/蒙混层（R0I/S） 矿物的异常现象.揭示了在一定的深度范围（2777.37-4405.27 m）,-定的古盐度条件下（Sr/Ba比值≥0.4,并有盐类矿物出现）,绿泥石成分受到古盐度的制约,并且随着古盐度的增高,绿泥石成分中的Al 、ⅣAl、Na、Na2O、Al/Si随之增高,而Si/Al则随之降低.由绿泥石成分温度计获得的温度值也伴随着古盐度的增高而增高.因此,由绿泥石成分温度计所计算的温度不能代表本区实际埋藏的古温度.（4） 研究区内绿泥石成分中的SiO2和FeO与母岩的对应成分之间有一定的相关性,其SiO2绿泥石与SiO2岩石、FeO绿泥石与FeO岩石呈负相关的线性关系,并且这种关系在古盐度�Clay mineral assemblages and chlorite composition are often analyzed to study diagenesis of sediments and burial paleotemperature in basins. A number of previous studies show that clay mineral assemblages and chemical compositions of chlorites are related to the progressive burial depth/temperature in many sedimentary basins. However, some phenomena show that this opinion could not explain features in mudstones from some particular regions on the Earth. In order to investigate the main factors that influence diagenesis in basins, this paper focuses on the characteristics of clay mineral assemblages, and composition of chlorites in the mudstone in Xinjiang Tabei Uplift, China, as well as the relationship between the characteristics and the paleosalinity of the basin. The results show the following four points. (1) The assemblages of the clay minerals in the depth range of 2777.37 m to 4604.41 m, which were generated during Jurassic Period and Eogene Period (J1-N2), are I+Chl and I+Chl+Ka; while the assemblages in the depth range of 5071.52 m to 5299.37 m, which were generated during Triassic period (T1), are R0I/S+Chl+I and R0I/S+Chl. (2) The diagenetic chlorite in this area is brunsvlgite in TypeⅡb polymorphism;its composition features show that (a) the average value of octahedral occupancy is 11.532;(b) the octahedral Al amount is obviously greater than the tetrahedral Al amount;(c) the average value of (Fe+Mg) is 4.016;(d) the ratio of Si/Al is higher than 1. (3) According to the distribution of the mineral salts and the data of ancient salinity in the area, it is proposed that paleosalinity was the main factor that affects the clay mineral assemblages and the compositional changes of chlorites in the area. In this paper, paleosalinity is utilized to explain an abnormal phenomenon in the clay mineral assemblages. There is not a disorderly mixed layer of illite/smectite (R0I/S) in the samples from the depths less than 5000 m, while there is a disorderly mixed layer of illite/smectite(R0I/S) in the samples

关 键 词：新疆塔北隆起 粘土矿物组合 绿泥石成分 古盐度 岩石化学成分 

分 类 号：P578[天文地球—矿物学]