昌都地区晚侏罗世达孜剖面粘土矿物组合特征及其成岩环境意义

Characteristics of Clay Minerals and Their Diagenetic Environmental Significance in the Late Jurassic Dazi Section,Changdu

中文关键词:  昌都地区  粘土矿物  成岩环境  含膏盐地层

英文关键词:Changdu area  Clay mineral  Diagenetic environment  Gypsum-bearing strata

中文摘要:

      昌都地区位于西藏自治区东部,区内有蒸发岩大范围分布。通过对昌都地区晚侏罗世含膏盐达孜剖面粘土矿物类型及其组合特征的深入研究,对成岩环境进行了分析,主要得到如下4点认识:1)达孜剖面粘土矿物以伊利石为主,伊利石/蒙脱石混层次之,高岭石、绿泥石和绿泥石/蒙脱石混层含量均较低；2)IS Ⅱ型有序伊/蒙混层矿物中,每隔9~19个伊利石晶层才有蒙脱石晶层出现,表明蒙脱石伊利石化程度高,受成岩作用影响较大；3)达孜剖面呈晚成岩阶段的特征,其成岩温度大于190 ℃,沉积环境和成岩环境具有弱碱性的特点,同时这一时期物源区呈干燥、弱水解作用的特征；4)高含量的Na⁺、K⁺、Al³⁺和低含量的Fe²⁺、Mg²⁺碱性介质对蒙脱石—蒙脱石/伊利石—伊利石这一转化过程有一定的促进作用,但同时抑制了埋藏过程后期绿泥石的大量生成。以上晚侏罗世含膏盐达孜剖面的成岩环境特征可为进一步探讨蒸发岩对青藏高原演化的响应关系提供一定的线索和依据。

英文摘要:

      The Changdu area is located in the eastern part of Tibet Autonomous Region and evaporites are widely distributed here.In this paper,diagenetic environment is discussed through study of the assemblage characteristics of clay minerals in the late Jurassic gypsum-bearing Dazi section in the Changdu area and the main conelusions are gotten as follows:1) The clay mineral assemblage consists mainly of illite and illite/smectite(I/S) with minor kaolinite,chlorite and chlorite/smectite in Dazi section.2) Smectite crystal layer appears after 9-19 illite crystal layers in the ISII type ordered I/S mixed layer minerals,which indicates the high degree of illitization of smectite influenced by diagenesis.3) The Dazi section is characterized by late diagenesis,and its diagenetic temperature is more than 190℃.The sedimentary and diagenetic environment is characterized by weak alkalinity.At the same time,the source region was characterized by dry and weak hydrolysis.4) High contents of Na⁺,K⁺,Al³⁺ and low content of Fe²⁺,Mg²⁺ alkaline medium can promote the transformation process of S-I/S-I,but in the same time hinder the massive formation of chlorite in the later stage of the burial process.These diagenetic environment characteristics can provide some clues and basis for further investigation of the response relationship of evaporates to the evolution of the Qinhgai-Tibet Plateau.