云南个旧老厂细脉带型锡矿白云母40Ar-39Ar年龄及其地质意义

细脉带型锡矿是云南个旧矿田老厂矿区的主要矿床类型之一.文章利用40Ar-39Ar同位素测年方法对老厂细脉带型锡矿床白云母-电气石-石英脉中的白云母进行了年龄测试.结果显示,该白云母的40Ar-39Ar同位素坪年龄为(827±07)Ma,表明其形成时代为晚白垩世.进一步结合区域资料,指出包括个旧锡多金属矿床在内的右江褶皱带内与岩浆作用有关的矿床具有相同的成矿地质背景,为华南晚中生代岩石圈大规模伸展的产物.     

内蒙古武川县赵井沟铌钽多金属矿床白云母~(40)Ar-~(39)Ar同位素年龄及地质意义

内蒙古赵井沟铌钽多金属矿是近年来取得较大找矿进展的大型稀有金属矿床,初步探明铌钽氧化物储量超过8200吨,前人对其矿床地质特征已有初步研究,但其成矿时代尚未精确厘定。本文以赵井沟铌钽多金属矿区内天河石花岗伟晶岩脉中的白云母为研究对象,利用~(40)Ar-~(39)Ar同位素年代学方法,以确定其成矿时代。研究发现矿区内铌钽矿化主要赋存在碱长花岗岩、碱长花岗细晶岩、云英岩和天河石花岗伟晶岩中,且铌钽矿物与白云母同时形成,有重要的共生关系,故本次研究获得的白云母坪年龄123.57±0.66 Ma和等时线年龄124.0±2.0 Ma具有地质意义,可代表成矿年龄。这一成果表明赵井沟铌钽多金属矿床形成于燕山晚期(至少延续至早白垩世),与前人获得的锆石年龄有较大差异,这对分析其矿床成因有重要意义。同时,结合区域地质资料,本文认为华北地台北缘内蒙古地轴中部在燕山运动的晚期存在一次重要的稀有金属成矿事件。     

Reference Minerals for the Microanalysis of Light Elements

The quantitative determination of light element concentrations in geological specimens represents a major analytical challenge as the electron probe is generally not suited to this task. With the development of new in situ analytical techniques, and in particular the increasing use of secondary ion mass spectrometry, the routine determination of Li, Be and B contents has become a realistic goal. However, a major obstacle to the development of this research field is the critical dependence of SIMS on the availability of well characterized, homogeneous reference materials that are closely matched in matrix (composition and structure) to the sample being studied. Here we report the first results from a suite of large, gem crystals which cover a broad spectrum of minerals in which light elements are major constituents. We have characterized these materials using both in situ and wet chemical techniques. The samples described here are intended for distribution to geochemical laboratories active in the study of light elements. Further work is needed before reference values for these materials can be finalized, but the availability of this suite of materials represents a major step toward the routine analysis of the light element contents of geological specimens.     

华北陆块东南缘蚌埠地区侏罗纪花岗岩中多种类型白云母的识别及其地质意义

三叠纪华南俯冲陆壳已经延伸到华北克拉通东南缘的蚌埠地区, 而该地区的俯冲陆壳是否经历超高压变质仍存在诸多争议。对华北克拉通东南缘蚌埠地区的侏罗纪花岗岩——荆山岩体中的暗色残留体、主体花岗岩以及细晶岩脉中的白云母进行岩相学观察、电子探针和拉曼光谱分析,结果表明荆山残留体和主体花岗岩中白云母颗粒较大且相对于一般花岗岩中原生的、次生的白云母具有较高的Si、Fe+Mg原子数和较低的Al原子数。拉曼光谱分析结果显示残留体和主体花岗岩中大颗粒白云母也具有相似的铝原子桥氧键(Al,O(br))的拉曼位移(421 cm^-1),低于经历超高压的黄镇榴辉岩中多硅白云母的原子数和铝原子桥氧键的拉曼位移,而高于本研究中未经历超高压变质作用的奥地利Spail片岩中的白云母。残留体和花岗岩中大颗粒白云母的主量元素和拉曼位移特征指示其为变质成因的多硅白云母。因此,可以利用多硅白云母地质压力计来指示花岗岩形成的压力,并且确定荆山花岗岩发生部分熔融的压力为1.0~1.3 GPa。荆山花岗岩的源岩为华南深俯冲的陆壳碎片,华南板块俯冲到华北克拉通东南缘的深度为33~45 km,相当于华北克拉通中下地壳深度。     

滇西澜沧变质带中白云母b_0值特征及其多期变质作用意义

滇西澜沧变质带中199件白云母b_0值分析结果表明,b_0值均在0.9020nm以上。与澜沧变质带遭受蓝片岩相高压变质作用的事实相吻合。此外,白云母b_0值的统计规律显示,澜沧变质带经历了多期变质作用,一期为高压变质作用,另一期为中压变质作用,这也与已知的地质现象相符。由此可见,白云母b_0值可以很好地反映多期变质作用。     

Microstructural evidence of rotation and non-rotation of mica porphyroblasts

Abstract Mica porphyroblasts in schists from several regions show nearly planar inclusion trails that are parallel over areas much larger than the wavelengths of later folds. This indicates that the porphyroblasts have not rotated, with respect to geographical co-ordinates, during deformation. Instead, the matrix has rotated, as suggested by Ramsay (1962). Even in zones of marked shortening in the matrix adjacent to large rigid porphyroblasts (e.g. of cordierite or staurolite), small biotite porphyroblasts have not rotated, but have become thinned by solution, as indicated by parallelism of inclusion trails in separate biotite grains and by evidence of truncation of inclusion trails by the matrix foliation. Less common are biotite porphyroblasts that have single asymmetrical microfolds in the matrix adjacent to the porphyroblasts and so appear to have rotated; these porphyroblasts are characterized by kinking.     

针状白云母的发现及其成因探讨

针状白云母产于新疆科科托海附近辉长岩－闪长岩内含稀有元素的3号伟晶岩脉中，呈针状或纤维丝状产出，长短轴之比一般大于1：80，最大达1：500。它的晶体结构、化学组成、物理和光学性质与普通白云母相同或类似，属于普通白云母。依据针状白云母产出的地质构造环境和与剪切裂隙的关系，笔者认为针状白云母可能是结晶粗大的白云母在其形成过矿中和形成以后受到垂直于（001）晶面压应力作用，产生三组微裂隙，并沿其中一组发育完全的微裂隙裂开而成。     

新疆阿斯喀尔特伟晶—气成—热液型绿柱石及海蓝宝石的研究

本文根据阿斯喀尔特矿区地质特征,通过化学分析、包体测温、红外光谱、光学吸收光谱等测试方法的研究,总结出本区绿柱石及海蓝宝石的矿物特征。     

川西滇东地区前寒武系地层中白云母b0值的初步研究

在川西滇东地区的前寒武系变泥质岩地层中采了263个样品并测了其白云母b₀值,结果表明:渡口运动时发生低压高温的变质作用;川滇运动时在河口组及相应地层发育区发生中压变质作用,向两侧变质压力降低;晋宁运动挤压幕第Ⅰ期形变时发生低压变质作用,第Ⅱ期形变时发生中-高压变质作用,第Ⅲ期形变和澄江运动时发生中压变质作用。基于这一工作探讨了白云母b₀值研究在进行地层对比和构造分析中的积极作用。     

Very Low-grade Metamorphic Evolution of Pelitic Rocks under High-pressure/Low-temperature Conditions, NW New Caledonia (SW Pacific)

The P–T gradient in a Late Eocene low-T high-P metamorphicbelt in northern New Caledonia increases from SW to NE. Metapelitesin the pumpellyite–prehnite and blueschist zones containlawsonite, Mg-carpholite, Fe-stilpnomelane and Fe-glaucophane.Thermodynamic calculations indicate a progression of metamorphicconditions from less than 0·3 GPa and 250°C in akaolinite-bearing rock in the SW, up to 1·5 GPa and 410°Cin a lawsonite–glaucophane-bearing sample in the NE ofthe Diahot terrane. Through a multi-method investigation ofphyllosilicates, organic matter and fluid inclusions, we demonstratethat the evolution of organic matter and illite crystallinitydepends strongly on the evolution of the P–T path withtime. In addition, we show that the illite–muscovite bcell dimension provides a robust estimate of maximum pressurereached in low-temperature domains with polyphase metamorphichistories, despite subsequent high-temperature–low-pressureevents. Fluid inclusion study reveals an isothermal decompressionin the Diahot terrane. KEY WORDS: low-temperature/high-pressure metapelites; illite crystallinity; coal rank; illite–muscovite b cell dimension; New Caledonia