Incipient metamorphism in the Lower Palaeozoic marginal basin of Wales

Abstract A diagenctic through anchizone to epizone transition is demonstrated in pelitic rocks of the Lower Palaeozoic marginal basin of Wales by examination of variations in phyllo-silicate mineralogy, illite crystallinity and b_o parameter of white micas. This transition represents a temperature range from ∼ 150°C to ∼ 400°C and the metamorphism is of a low-pressure facies series type, with a geothermal gradient of ∼ 40°Ckm^-1. Variations in grade can be correlated largely with the original basin and shelf form, suggesting a depth-related metamorphism. However, in areas closer to the site of Caledonian plate collision an increasingly syn-tectonic metamorphic event is apparent.
Correlation of pelite data with metabasite assemblages is variable, the most consistent relationship being between epizone crystallinity values andepidote-actinolite (greenschist facies) assemblages. Diagenetic clay mineral assemblages are found associated with prehnite-pumpellyite assemblages in metabasites and it is suggested that the latter represent non-buffered, and therefore non-diagnostic, assemblages.     

成岩带、近变质带与一维纳米级层状硅酸盐

运用X射线衍射分析技术，计算了成岩带、近变质带粘土矿物C^*方向的粒度。根据阿尔卑斯造山带前陆碎屑岩粘土矿物粒度与伊利石结晶指数的关系，推导出了伊利石、绿泥石、蒙脱石、伊蒙混层、高岭石和叶蜡石的c^*方向粒度变化趋势曲线。结果表明，大多数产于成岩带和近变质带的粘矿物其c6*方向粒工为几至几十纳米。成岩带和近为质带是一维天然纳为级土帮物的产地。     

A New Method for Clay Mineral Analysis and Its Application in Geology

X-ray diffraction (XRD) peaks in a low-angle diffraction section of clay minerals, especially those of authigenic origin, have broadening and tailing features in shape. Using the five basic parameters, peak position, peak height, width, shape coefficient and asymmetry, to describe an XRD peak is more accurate, comprehensive and integrated than using only 3 of them, position, height and width. Following the concept of the five basic parameters of an XRD peak, the program Decoform proposed in this study provides more information in mineralogical analyses by fitting actual XRD profiles. In combination with the HW-IR plot, Decoform can be systematically and accurately used in the comprehensive analyses of crystallinity, domain size, lattice strain and quantitative phase. It is also of value for the geological investigations of diagenesis, metamorphism, basin maturity, structural stress field and so on.     

伊利石测年在焉耆盆地油气成藏时期研究中的应用

油气藏成藏时期的确定是进行油气藏勘探与评价的重要工作内容之一。也是揭示成藏过程的有效途径，利用伊利石测年确定油气成藏期，能够得出其绝对年龄，因而受到人们重视，运用自生伊利石同位素年龄测定的原理和方法及自生伊利石同位素年龄资料对焉耆盆地博湖坳陷油气藏成藏时期及油气运移时期进行了分析，最后对自生伊利石同位素测年存在的问题和措施进行了有益的探讨并克服了以往只能根据地质综合研究定性确定油气藏成藏时期及油气运移时期问题，为定量确定油气藏成藏时期以及油气运移时期提供了科学的方法。     

伊利石多型——斑岩铜矿化的指示剂

德兴矿区内普遍存在伊利石 ,其多型特征表明 ,矿化围岩与区域围岩 (>2km)中伊利石的矿物结构与矿化流体有关。经长期埋藏变质作用 ,区域围岩中形成了结晶程度完好的 2M1伊利石 ,K櫣ｂｌｅｒ指数为 0 .1 6°,Ir=1 ,无膨胀层 ,是浅变质作用的产物。与发育热液成因 1M伊利石的花岗闪长斑岩一样 ,矿化围岩发育了具有较高K櫣ｂｌｅｒ指数 (平均值为 0 .5 5°)、含少量的膨胀层 (1 %～ 5 % )、1M型伊利石 ,它是热液流体作用下伊 /蒙矿物逆向退化的结果 ,且受热液流体量及水 /岩比制约。在此 ,斑岩铜矿中伊利石多型可能成为有效的矿化晕指示剂。     

北极圈海域表层沉积物的黏土矿物特征及其环境意义

应用X射线衍射(XRD)分析技术对北极圈海域15个表层沉积物的黏土矿物进行了研究。结合伊利石的结晶度指数综合分析了研究区黏土矿物的组成和分布特征及其物质来源、沉积环境和水动力条件。结果表明,北极圈海域研究区的黏土矿物以伊利石为主(33%),其次为伊/蒙间层矿物(25%)、绿泥石(23%)、高岭石(15%)以及蒙皂石(4%)。伊利石的开形指数(Ns)都比较小,大多在1~2之间,Ns的分布对物源有一定的指示意义。楚科奇海区具较弱的水动力条件,沉积环境较稳定;白令海具强烈的水动力条件,属于冲刷环境。认为北极圈海域研究区的黏土沉积物均有三方面来源,即河流输入、海洋自生和冰筏搬运物。     

伊利石:一种前景广阔的新型粘土矿物材料

伊利石是一种富钾、高铝的层状含水硅酸盐矿物,是近几年来才逐渐受到重视的新型粘土矿物材料。不同品种的伊利石可分别用作陶瓷制品的原材料,造纸用涂布粒等。经改性后的活性伊利石粉可作为橡塑制品的填充料。以优质伊利石为原料制取钾肥,同时还可获得４Ａ沸石、净水剂等多种副产品。伊利石的深层次开发具有广阔的市场前景。     

New findings on the tectono-metamorphic history of the western Rhenish Massif (Germany) by K–Ar dating of metasedimentary illite

Metapelites, clay-rich sandstones and volcanics from Cambrian, Ordovician and Lower Devonian strata of the western Rhenish Massif underwent a complex regional Variscan tectono-thermal evolution, as shown by mineralogical and K–Ar isotopic analyses of the illite to mica components from three NW-SE transects. The metamorphic degree extended from an anchimetamorphic to an epimetamorphic intensity during two major episodes of illite crystallization at 328 ± 6 and 282 ± 12 Ma. A further late orogenic or post-orogenic extensional activity could also be detected, but not precisely, around 270 Ma, probably recorded by the precipitation of illite in new or reactivated extensional faults with upward moving heat flows.     

Porosity preservation due to grain coating illite/smectite: Evidence from Buchan Formation (Upper Devonian) of the Ardmore Field,UK North Sea

The Buchan Formation sandstone reservoirs from the Ardmore Field in the UK Central North Sea are fluvial-aeolian deposits and provide examples of porosity preservation in deeply-buried reservoirs (2.7–3.2?km) caused by grain-coating illite/smectite (I/S). Here, high reservoir quality commonly correlates with the occurrence of grain-coating I/S and consequent inhibition of quartz cementation in the aeolian dune and interdune sandstones. Porosity is lower in fluvial sandstones lacking grain coating I/S but with intense quartz overgrowths. We propose that the presence of I/S reflects concentration of the smectitic-rich clay bearing water which would have been the deposits of the interdune and/or distal sector of fluvial distributary system, and were introduced into aeolian deposits by mechanical infiltration. Petrographic relationships indicate that these coatings grew mainly before the mechanical compaction as the clays occur at grain contacts. The use of empirical model suggested that about 6–7% porosity have been preserved. The burial-thermal history of the Ardmore area contributed to the high quality reservoir because throughout much of the time since deposition, the Devonian sandstones have been little buried. Only from the Palaeogene the reservoir temperatures exceeded about 70?°C and rapidly buried to today’s maximum depth, which have minimized the negative effect generally ascribed to smectitic clays on reservoir quality. The circumstances of porosity preservation shown in this study may be unusual, but nonetheless have profound consequences for exploration. It is possible to identify new Buchan Formation prospects in areas hitherto dismissed because they were generally assumed to be poor reservoir.     

伊利石结晶度Kübler指数的校正与近变质带的确定

就像用"砝码"标定"称"来测量物质质量一样,伊利石结晶度的测量也需要这样的"砝码"标定它的测量工具——衍射仪,从而能够进行伊利石结晶度的测量和对比。这个砝码就是伊利石结晶度标样或称伊利石结晶度国际标样。第2届Kübler-Frey国际研讨会伊利石结晶度圆桌会议就伊利石结晶度标样和近变质带的确定的问题进行了深入的讨论。会议一致认为,用伊利石结晶度标样校正X射线衍射仪是极为重要和必要的,没有进行标样校正的伊利石结晶度数据将被拒绝发表,经过伊利石结晶度国际标样校正后的伊利石结晶度数据才可用于近变质带的划分和国际对比。本文就伊利石结晶度测量的有关衍射仪类型与差别,衍射仪系统,测量条件,样品的影响和国际标样对仪器的校正等问题进行了分析研究。结果表明不同型号仪器,同型号仪器不同测量条件与状态,样品的不同制备方法都将影响伊利石结晶度Kübler指数的测量。指出只有使用国际标样才可校正测量的伊利石结晶度Kübler指数,从而达到消除偏差准确划分近变质带的标准和进行国际对比的目的。