摘要
绿泥石广泛存在于各种岩石和地质环境中 ,其化学成分的变化 ,可反映其形成时的物理化学条件。本文采集了塔里木沉积盆地钻孔中样品 ,利用电子探针微区技术 ,探讨埋藏成岩过程中绿泥石化学成分的变化特征。研究发现 ,在埋藏成岩过程中 ,绿泥石的种类、结构式中的主要元素和埋藏深度之间有较好的相关性。本文研究的绿泥石类型主要为铁斜绿泥石 (辉绿泥石 )和铁镁绿泥石两类 ,随深度的增加 ,其在分类图上逐渐向Fe含量增多和Si含量减少的方向分布。绿泥石结构式中Si含量随埋藏深度的增加而降低 ;AlⅣ 、Fe2 + 和Fe/(Fe+Mg)随埋藏深度的增加而增加。计算结果显示 ,绿泥石的形成温度为 1 4 0～ 1 87℃ ,本研究地区的古地温梯度为 :3 1 .2℃ /km。
Chlorite minerals, found in a great variety of rocks and geological environments, display a wide range of chemical compositions, which can reflect the physicochemical conditions under which they were formed. The compositional geothermometry has received much more attention, and several methods of estimating the temperature of chlorite formation from its composition have been proposed. However, previous studies were focused on chlorites from hydrothermal, geothermal systems, but little work on those from the diagenetic processes. In this paper, chlorites from different depths were investigated by electron microprobe in order to determine their chemical evolution during their burial process. \; The Si\+\{4+\} content and (Fe\+\{2+\}+Fe\+\{3+\}) ratio have been used for chlorite classification. The samples investigated belong to two kinds of chlorites: Brunsvigite (\{2772.10\}～\{4046.93\} m) and Diabantite (\{4358.70\} m). With increasing depth, the chlorite classification follows a trend from Brunsvigite to Diabantite. Si\+\{4+\} content decreases, and (Fe\+\{2+\}+Fe\+\{3+\}) increases.\; The contents of Si\+\{4+\} and Mg\+\{2+\} decrease with burial depth, while Al\+Ⅳ, Fe\+\{2+\}, Fe/(Fe+Mg) increase with depth. Particularly, the Si\+\{4+\} and Al\+Ⅳ contents have very good linear relations with depth. Thus we conclude that the composition of chlorite does have some relations with burial depth and temperature in diagenetic processes. \; In an attempt to study the relationship of chlorite chemical composition and its forming temperature, we apply the composition data to the geothermometry functions drawn from the literature to estimate the forming temperature. The temperatures calculated (from 140 to 187℃) have a good relation with burial depth. Thus it is estimated that the temperature gradient of the area is \{3.12℃\}/100 m.
出处
《矿物学报》
CAS
CSCD
北大核心
2001年第2期174-178,共5页
Acta Mineralogica Sinica
基金
国家自然科学基金 (批准号 :49873 0 2 6)
国家重点科技攻关项目 (96 111)
南京大学现代分析中心测试基金
