海南文昌二辉橄榄岩中辉石出溶结构的结晶学取向分析  

Crystallographic orientation of the exsolution microstructure in pyroxene,occurring in lherzolite from Wenchang area,Hainan,China

作　　者：赵珊茸[1] 徐畅[1] 徐海军[1,2] 张保民[1] 刘惠芳[2] 

机构地区：[1]中国地质大学地球科学学院,武汉430074 [2]中国地质大学地质过程与矿产资源国家重点实验室,武汉430074

出　　处：《岩石学报》2016年第6期1644-1652,共9页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41372058)资助

摘　　要：本文用电子背散射衍射技术(electron backscatter diffraction,EBSD)测试了海南文昌玄武岩中二辉橄榄岩包体中的辉石主晶与其出溶片晶的结晶学取向关系。结合电子探针成分测试,得出:单斜辉石(透辉石)主晶中出溶了两组不同方向的片晶,一组为斜方辉石(顽火辉石-易变辉石)片晶,另一组为单斜辉石(普通辉石)片晶。由于出溶片晶在EBSD测试切面上体现为以线状体,因此需要找到一种方法将线状体所代表的片晶的晶面符号推算出来。本文介绍了一种利用吴氏网进行坐标系旋转的"晶带相交法",该方法可以作图推算出溶片晶的晶面符号。根据"晶带相交法"得出,斜方辉石(顽火辉石-易变辉石)出溶片晶为(100),单斜辉石(普通辉石)出溶片晶为^(401)。根据前人的研究资料,出溶片晶^(401)可能指示最小出溶压力为9.5~12.5GPa。出溶片晶的结晶学取向涉及到主晶与出溶体的晶体结构匹配关系,并且与出溶温度-压力有关,因此出溶片晶的结晶学取向分析具有晶体化学理论意义和反映地质温压过程的实际意义。这种"晶带相交法"可以推广应用于其他矿物出溶结构的结晶学取向研究中。Exsolution lamellae in pyroxene,occurring in lherzolite xenoliths in basalts from Wenchang area,Hainan,China,had been investigated by electron backscatter diffraction（ EBSD） to determine the eptaxial relationship. Combining with the electron microprobe analysis（ EMPA）,it is shown that clinopyroxene（ diopside） host exsoluded a set of orthopyroxene（ enstatite-pigeonite）lamellae and a set of clinopyroxene（ augite） lamellae,with different orientations. The lamellae appear as liner traces on the thin sections tested by EBSD,so it is necessary to find a method to determine the crystallographic plane indices of the lamellae. We introduced a ＂zone cross＂method,by coordination rotation on Wuff net,to determine the plane indices for the lamellae. Based on this method,we get that the orthopyroxene（ enstatite-pigeonite） lamella is（ 100） and clinopyroxene（ augite） lamella is -（ 401）.According to the studies reported before,the lamella -（ 401） possibly indicates the minimum exsolution pressure is 9. 5 - 12. 5GPa.Crystallographic orientations of the exsolution microstructures are related to crystal structure coincidence between host and lamellae,and also related to the exsolution temperature and pressure,so it is of theoretic significance in crystallochemistry and can be used to estimate the exsolution temperature and pressure. The ＂zone cross＂method can be widely used to determine the crystallographic orientation of the exsolution structures in other minerals.

关 键 词：出溶 辉石 EBSD 吴氏网 晶带 

分 类 号：P575.1[天文地球—矿物学] P585.2[天文地球—地质学]