内蒙古大青山地区孔兹岩系中大理岩岩组的地球化学特征及原岩建造  

Geochemical characteristics and protoliths of the marble rock group of the khondalite series in the Daqing Mountains, Inner Mongolia

作　　者：毕明丽[1] 路来君[1] 赵庆英[1] 刘正宏[1] 

机构地区：[1]吉林大学地球科学学院,吉林长春130000

出　　处：《中国地质》2008年第4期639-647,共9页Geology in China

基　　金：国家自然科学基金项目(40572117);中国地质调查局地质大调查项目(200113000021)资助

摘　　要：大理岩岩组是内蒙古大青山地区孔兹岩系3个岩组中最上部的一个岩组,该岩组是一套富镁质的大理岩系,以巨厚的、大面积分布的白云质大理岩的发育为特征,底部有少量碎屑岩沉积,矿物组成除白云石外,普遍含蛇纹石化橄榄石、透辉石、金云母等一种或多种富镁硅酸盐矿物。岩石地球化学以富CaO、MgO和LOI为特征,反映了碳酸盐岩的地球化学特征,CaO+MgO含量达44.96%以上,且CaO/MgO比值较小(1.37～10.94),其原岩应为一套碎屑含量极低的白云岩,以化学沉积为主。原岩建造的沉积环境:由初期的陆海过渡的三角洲相,过渡到滨海-浅海相,最后到干燥气候条件下有障蔽岛相隔的封闭海盆相。构造环境也从亚稳定状态过渡到稳定构造环境,表明该套变质沉积地层的原岩可能形成于被动大陆边缘,但更类似于中元古界长城系、蓟县系这样的克拉通内裂陷槽或裂谷沉积。The marble rock group is the top one of three rock groups of the khondalite series in the Daqing Mountains area, Inner Mongolia. It, as a suite of Mg-rich marble, is characterized by development of very thick and extensive dolomitic marble, with small amount of clastic rocks at the bottom. Besides dolomite, the mineral composition also commonly includes one or several Mg-rich silicate minerals such as serpentinized olivine, diopside and phlogopite. The rocks are rich in CaO, MgO and LOI, reflecting the geochemical characteristics of carbonate rocks. The CaO＋MgO content is more than 44.96% and the CaO/MgO ratio is relatively low, being 1.37-10.94; so the protolith should be dolostone that has a very low content of fragments and mainly formed by chemical deposition. The sedimentary environment of the protoliths graded from the paralic deltaic facies at the initial stage through the littoral-neritic faces to the enclosed sea basin facies which was separated by barrier islands under dry climatic conditions. The tectonic environment also passed from the metastable to stable one. This suggests that the protoliths of the suite of metamorphosed sedimentary strata may have formed on the passive continental margins, but were more likely to be similar to intracratonic aulacogen or rift deposits such as the Mesoproterozoic Changchengian System and Jixianian System.

关 键 词：内蒙古 大青山地区 孔兹岩系 大理岩岩组 岩石地球化学特征 原岩建造 沉积环境 

分 类 号：P588.313[天文地球—岩石学]