一种含自生独居石富钾、富稀土的多硅白云母泥岩  

A K and REE Rich and Authigenic Moazite-bearing Phengite Mudstone

作　　者：宋天锐[1] 张巧大[1] 万渝生[1] 

机构地区：[1]中国地质科学院地质研究所,北京100037

出　　处：《沉积学报》2003年第3期428-433,共6页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目 (批准号 :40 1 72 0 4 4 )资助

摘　　要：1999年在《沉积学报》发表了“大连地区前寒武纪沉积岩中发现自生独居石及其意义”一文 ,此后又获得了国家自然科学基金的资助加以继续研究。含自生独居石的泥岩研究的新成果介绍如下 :①泥岩的特征化学成分 :K2 O11.94 % ,Al2 O3 16 .4 7% ,SiO2 6 1.91% ;ΣREE 330 .6 9μg/ g ,Ce 130 .80 μg/g ;La(N) /Yb(N) 12 .4 4 ,δEu 0 .75 ,δCe1.17;②泥岩造岩矿物经电子探针能波和波谱分析和X—射线衍射曲线对比 ,认为是由伊利石转变成的多硅白云母 ,长期的成岩作用和中生代滑脱构造的压力促进了伊利石的转化 ;③自生独居石也经受了成岩作用及其后的影响 ,表现为矿物晶形包括 :散点状、单针状、晶簇状和连晶状等 ,大小由 1～ 6 0 μm ;其晶形与产生自岩浆岩、变质岩和碎屑物中的短柱状单斜晶系独居石外形截然不同 ;由此得出结论认为该泥岩是一种罕见的特殊泥岩 ,富钾、富稀土元素和内部—外部环境创造了独居石的形成和生长条件。同时 ,本文强调在华北地台元古宙富稀土元素层位 ,有可能找到自生独居石并进而开展U、Th -Pb同位素地质测年研究 ;A paper entitled discovery of authigenic monazite in Precambrian sedimentary roc k of Dalian area and its significance has been issued in the《Acta Sedimentologi ca Sinica》 (1999). After that we have got financial support for continuing stud y by the Chinese National Natural Scientific Foundation (No.40172044) .This pape r introduces the new achievements of the mudstone study as follows: (1) characte ristic chemical composition: K 2O 11.94%, Al 2O 3 16.47%, SiO 2 61.91%; REE 330.69,μg/g, LREE 266.15μg/g, Ce 130.80μg/g; La(N)/Yb(N) 12.44,δEu 0.75,δCe 1.17;(2)the main rock-frming mineral composition is phengite,which is determin ed by electron probe analysis of enery spectrum and wave spectrum methods and co mpared with X-ray diffraction curve. The phengite was altered from illite by in fluence of deep diagenesis and Mesozoic thrust tectonic movement; (3) the authig enic monazite was also suffered by the diagenetic and tectonic influences showin g in the crystal form types such as scattered mini-grains, single needle-like crystal, aggregate of crystals and connected crystals, etc. The size of authigen ic monazite crystals is from 1 to 60 μm, which are quiet different from the sh ort monoclinic prism taken from metamorphic, magmatic rocks or clastic placers. According to above, this paper concludes that the mudstone is a K and REE rich one, which created favorable inner-outside environment for authigenic monazite formation. Meanwhile this paper emphasized on that the wide spread Proterozoic strata in North China might contain many REE-rich beds with authigenic monazite to be used for U, Th-Pb isotopic timing study. It is proposed that the REE-ri ch beds might be the mineral source of the huge rare earth mineral deposits of t he Baiyun Obo along the margin of North China platform.

关 键 词：自生独居石 多硅白云母泥岩 成岩作用 前寒武纪震旦系 大连 同位素地质测年 变质岩 

分 类 号：P571[天文地球—矿物学] P588.245[天文地球—地质学]