应用国际标样对伊利石结晶度测定值的校正及其意义

伊利石的结晶度(IC),又称Kbler指数(K.I.),是指粘土矿物伊利石10×10-8cmXRD峰的半高宽。作为一个变质程度的指标,结晶度广泛用于研究高级成岩—极低级变质—低级变质作用的演变过程,随着变质程度的提高,伊利石结晶度逐渐增大。根据Kbler的建议,近变质带(极低级变质带)上、下边界的伊利石结晶度分别为0.42(°Δ2θ)和0.25(°Δ2θ)。然而,测定伊利石结晶度时,由于缺少国际标样,且各实验室间的样品制备、仪器条件、测试方法也不相同,因而导致获得的数据有较大差别,缺少可比性;因此,使用国际标样对数据进行校正,使各实验室获得的数据都能直接地进行对比,是非常必要的。利用X射线衍射方法测定了由L.N.Warr提供的5个伊利石结晶度的国际标样(其中,4个为岩石碎屑样品,采自英格兰西南部的极低级变质带;1个为单矿物样品,采自印度的花岗岩),获得了校正方程,ICCIS=0.977IC测定值+0.0336(°Δ2θ),R2=0.9835。在实验室内对213件采自国内的样品进行测定,测试条件与国际标样的测试条件相同,利用此方程对测得的伊利石结晶度数值进行校正,证实本实验室对伊利石结晶度的测定具有较高的可信度和国际可比性。

Calibration of Illite Crystallinity Measurements by Using International Standards and Its Significance

The illite crystallinity index(IC),i.e.,Kübler index(K.I.),is defined as the width of the(001)XRD peak(10×10-8 cm)at half of its height(FWHM)for illites.It is an indicator widely used to evaluate the degree of metamorphism in the range from late diagenesis to very low-grade metamorphism then to low-grade metamorphism as illite crystallinity increases with metamorphic grade.The lower and upper boundary limits of the anchizone(very low-grade metamorphic zone)were originally defined by illite crystallinity values IC(K.I.)=0.25(°Δ2θ)and IC(K.I.)=0.42(°Δ2θ),respectively.However,the lack of sufficient interlaboratory standardization causes difficulties in comparison of the data measured by different laboratories,among which the sample preparation,conditions of facilities,and the measurement methods were widely of variety.It is therefore necessary to use commonly accepted standards to calibrate the data produced by different laboratories for making interlaboratory data comparable.In this paper the XRD measurements in our laboratory of illite crystallinity of five international standards provided by L.N.Warr were reported.These international standards consist of four sets of rock chips from the very low-grade metamorphic belt of Southwestern England and one sample of single muscovite crystal from India.A linear regression equation of our data versus Warr & Rice(1994)'s data was obtained,i.e.,ICCIS=0.977 ICmeasured+0.033,6(°Δ2θ),R2=0.983,5.This equation was then used to calibrate 213 data of illite crystallinity,which were measured under the same condition as that for the measurement of the international standards in our laboratory.It turns out that the data for illite crystallinity measured by this laboratory are reliable and internationally comparable.