Abstract: Hydrothermal sedimentary rock is deposited from the mixture fluid of hydrothermal water and the lake/ocean water from sedimentary basins. It belongs to a transitional type between magmatic rocks and sedimentary rocks,with some similarities and differences in mineral composition,rock texture and structure between these two types. The hydrothermal sedimentary rock contains much alminosilicate formed from the magma hydrothermal fluid,such as zeolite and feldspar,and also much carbonate minerals formed at normal lake/ocean water temperature,such as dolomite,magnesite,siderite,etc. A set of more than 300 m thick hydrothermal sedimentary rocks has been found in the Lower Cretaceous Tenggeer Formation of the Baiyinchagan sag,Erlian Basin. Base on the microscopy,electronic probe and Qemscan,several mineral precipitation sequences are established: (1)In lamellar rock,there is a sequence of precipitation from aluminosilicate to carbonate. In the association of aluminosilicate minerals,the analcime deposits first,then followed by natrolite,and the last by albite. In the association of carbonate minerals,magnesite first appears,the followed by siderite,and the last by ankerite. Calcite can appear after dolomite precipitation. (2)In flocculent nodule,pyrite appears at the center,and analcime,natrolite,magnesite,siderite,ankerite appear outward gradually. Sometimes the reverse of the above sequence appears. (3)In the fractures,the filling sequence is from aluminosilicate such as zeolite,chlorite to carbonate such as ankerite,from the edge of the fracture to the center. The most complete and ideal sequence of precipitation in the study area is pyrite-analcime-natrolite-albite-orthoclase-magnesite-siderite-dolomite-calcite. This complete sequence is often not fully observed. However, it is common to observe combinations of some of these minerals in the same order. The type of precipitation sequence is controlled by the jet and overflow stage,occurring time, temperature and hydrothermal chemical properties. Under the high temperature and salinity conditions at the early stage,the aluminosilicate sequences often occurred,or the carbonate mineral sequences mainly formed at the later stage.

Key words: hydrothermal mineral, precipitation sequence, process of sedimentation, controlling factors, Baiyinchagan sag

摘要： 基于岩心、岩石薄片及元素分析等资料,通过偏光显微镜、定量矿物扫描(QemScan)、电子探针、能谱和流体包裹体分析等技术手段,探讨了二连盆地白音查干凹陷下白垩统腾格尔组热水沉积岩中热水沉积矿物的沉淀顺序。研究区热水沉积矿物主要为铝硅酸盐和碳酸盐,含少量黄铁矿、重晶石、萤石等矿物。这些矿物在空间上具有特定的先后关系或位置关系: (1)在纹层状岩层中,由下到上从铝硅酸盐过渡为碳酸盐。在铝硅酸盐矿物组合中,首先出现的是方沸石,其次是钠沸石,再次为钠长石;在碳酸盐矿物中,首先出现的是菱镁矿,其次是菱铁矿,再次为铁白云石,有时还可见到方解石,但其含量很低。(2)在凝絮状团块中,团块中心为黄铁矿,从中心向外依次过渡为方沸石、钠沸石、菱镁矿、菱铁矿,最外层为铁白云石。在纹层状岩层和凝絮状团块中,有时还能见到上述顺序的逆顺序。(3)在后期充填的裂缝中,边部为沸石或绿泥石等铝硅酸盐矿物,向中心逐渐过渡为铁白云石碳酸盐。综合研究区所有的矿物序列来看,最完整的序列应为黄铁矿—钾长石—方沸石—钠沸石—钠长石—菱镁矿—菱铁矿—白云石—方解石,但是这种完整的序列是不常见的,通常仅为其中某几种矿物的组合,然而不管是哪些矿物进行组合,其出现的顺序都不变。推测该矿物序列的类型受热液喷流和溢流阶段、时间、温度和热水化学性质控制,早期高温、高盐度条件下出现的铝硅酸盐矿物序列较多,而晚期主要形成碳酸盐矿物序列。

关键词: 热水沉积矿物, 沉淀顺序, 沉积过程, 控制因素, 白音查干凹陷

CLC Number: 

• P588.2