摘要
成岩作用与变质作用界线的划分是当前地质学界关注的焦点之一。传统的观点将沸石相作为最低级变质相,本文以鄂尔多斯盆地东部上三叠统延长组的浊沸石和吐鲁番-哈密盆地哈密凹陷三叠系的浊沸石为例,提出浊沸石的形成条件为高pH值、低Pco_2和Xco_2、高钙离子活度、高SiO_2活性和高盐度等,稳定在从80℃到200℃左右的广大温度范围内,常与油气生成带一致,属成岩矿物相。取消沸石相,用明确的综合划分标志来确定成岩作用与变质作用的界线已成为当前地质工作者研究的主要课题。
Laumontite in the Triassic of the Turpan-Hami and Ordos basins gives two typical examples of laumontite belonging to diagenetic facies. On the basis of the data of vitrinite reflectance, inclusion geothermometry, transformation of clay minerals, color and TAI of sporopollen and temperature logging as well as examination of sections, the author suggests that the sandstones of the Upper Triassic Yanchang Formation in the eastern sector of the Ordos basin were formed at the mature stage of mesodiagenesis at temperatures in the range of 80-120 ℃, while the temperatures of the oil-bearing beds Chang4+5- Chang7 where laumontite is present were about 89-101℃. The laumontite-bearing beds of the Middle Triassic in the Hami depression is presently at the supermature stage of organic matter, the corresponding diagenetic temperature being about 140℃.Laumontite must have formed by precipitation from pore liquids at conditions of high pH, lower PCO2 and XCO2, high concentration of NaCl ions and high ion activity of Ca and Si. It was mainly derived from hydration of volcanic matter and from albitization of feldspars.Because the assumption of laumontite as delimiting the lowest metamorphic facies has no practical significance, it is proposed that the zeolite facies be rejected and that the term an-chimetamorphic zone be used to designate the extensive transitional zone between diagenesis'and metamorphism. The features determining that rocks reach the metamorphic stage should be as follows: closely packed grains, absence of pores or cements, and characteristic mineral assmblages including paragonite, rectorite, pyrophyllite, chlorozeolite, dickite, epidote, illite(2M1), chlorite ( II b, β=97°) and sericite formed by recrystallization or metamorphic recrystallization at temperatures of 200 ℃ and R0 values of 2. 5% ; the stage is also characterized by schistosity and illite crystallinity of IC = 0. 42°/0. 25°△2θ(Kubler indices) as well as other quantitative parameters of orgenic matter.
出处
《地质论评》
CAS
CSCD
北大核心
1996年第3期215-222,T001,共9页
Geological Review
关键词
浊沸石
成岩作用
变质作用
鄂尔多斯盆地
laumontite, diagenesis, metamorphism, Ordos basin, Turpan-Hami basin