内蒙古二连盆地白音查干凹陷下白垩统湖相白云岩成因*

早白垩世，白音查干凹陷处于强裂陷伸展环境，并具有高地热异常。在此背景下，该凹陷发育一套仅限于深湖—半深湖相的、富含铁白云石、钠沸石和泥级长石（钠长石、钾长石）等特殊矿物成分的白云岩。该套湖相白云岩受北东向同沉积断裂控制，主要分布于凹陷北部陡坡带和湖盆中央断裂带的下降盘处，沿断裂呈线性展布。白云岩中的白云石多以铁白云石为主，并与钠沸石、长石、重晶石、水镁铁石等低温热液矿物共生，其结构可分为泥晶结构、微晶结构和中—细晶斑块状结构（多元矿物组合）3种。此外，白云岩的岩石组构还具有明显热水沉积特征，包括纹层状构造、热水碎屑结构、星散状构造、同生塑性变形、网脉状构造。综合以上初步分析，认为研究区湖相白云岩为深部热液参与并发生沉积作用形成的，即热水沉积白云岩。

Origin of the Lower Cretaceous lacustrine dolostones in Baiyinchagan Sag of Erlian Basin, Inner Mongolia

In the Early Cretaceous,there was a set of lacustrine dolostones in the Baiyinchagan Sag with the strong rift extension and high geothermal anomaly.The dolostones were rich in special minerals including ankerite,natrolite,clay sized feldspar (albite,potash feldspar) etc.,and were only developed in semi-deep-deep lacustrine facies.The dolostone is controlled by NE-trending synsedimentary faults and distributed mainly in downthrown side of fault zone in northern steep slope zone and southern ramp zone adjacent to the central part in this sag.The lacustrine dolostone is mainly composed of ankerite and paragenetic minerals(natrolite,feldspar,barite,sjogrenite,etc.). Its texture can be divided into three types: micrite,microcrystalline and fine-medium grained porphyritic texture(multivariate mineral assemblage).The dolostone also has obvious rock fabric characteristics of hydrothermal sedimentation,including lamellar structure,hydrothermal clastic texture,starrily structure,contemporaneous plastic deformation and net vein structure.Based on the above preliminary analyses, we think that the formation of the lacustrine dolostone is the sedimentation with deep hydrothermal fluids participation,namely hydrothermal sedimentary dolostone.