海南文昌二辉橄榄岩中辉石出溶结构的结晶学取向分析
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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.
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.
引文
Boland JN.1974.Lamellar structures in low-calcium orthopyroxenes.Contributions to Mineralogy and Petrology,47(3):215-222
Bollmann W.1970.Crystal Defects and Crystalline Interfaces.Berlin,Heidelberg:Springer-Verlag,1-254
Boyd FR and Brown GM.1969.Electron-probe study of pyroxene exsolution.Mineral.Sco.Am.Spec.Pap.,2:211-216
Bozhilov KN,Green II HW and Dobrzhinetskaya L.1999.Clinoenstatite in Alpe Arami peridotite:Additional evidence of very high pressure.Science,284(5411):128-132
Champness PE and Lorimer GW.1973.Precipitation(exsolution)in an orthopyroxene.Journal of Materials Science,8(4):467-474
Coe RS and Muller WF.1973.Crystallographic orientation of clinoenstatite produced by deformation of orthoenstatite.Science,180(4081):64-66
Coe RS and Kirby SH.1975.The orthoenstatite to clinoenstatite transformation by shearing and reversion by annealing:Mechanism and potential applications.Contributions to Mineralogy and Petrology,52(1):29-55
Domeneghetti MC,Tazzoli V,Boffa BT et al.1996.Orthopyroxene from the Serra de Mage meteorite:A structure-refinement procedure for a Pbca phase coexisting with a C2/c exsolved phase.American Mineralogist,81:842-846
Feinberg JM,Wenk HR,Renne PR and Scott GR.2004.Epitaxial relationships of clinopyroxene-hosted magnetite determined using electron backscatter diffraction(EBSD)technique.American Mineralogist,89(2-3):462-466
Fleet ME,Bilcox GA and Barnett RL.1980.Oriented magnetite inclusions in pyroxenes from the Grenville Province.Canadian Mineralogist,18(1):89-99
Kirby SH and Etheridge MA.1981.Exsolution of Ca-clinopyroxene from orthopyroxene aided by deformation.Physics and Chemistry of Minerals,7(3):105-109
Liu L,Yang JX,Zhang JF et al.2009.Exsolution microstructures in ultrahigh-pressure rocks:Progress,controversies and challenges.Chinese Science Bulletin,54(12):1983-1995
Liu XW,Jin ZM and Green II HW.2007.Clinopyroxene exsolution in diopsidic augite of Dabieshan:Garnet peridotite from depth of300km.American Mineralogist,92(4):546-552
Mikouchi T and Miyamoto M.2008.Mineralogy and pyroxene cooling rate of unique achondritic meteorite GRA 06129.In:Proceedings of the39thLunar and Planetary Science Conference.League City,Texas,2297
Peacor DR.1967.Refinement of the crystal structure of a pyroxene of formula M1M2(Si1.5Al0.5)O6.American Mineralogist,52:31-41
Robinson P,Ross M,Nord GL Jr,Smyth JR and Jaffe HW.1977.Exsolution lamellae in augite and pigeonite:Fossil indicators of lattice parameters at high temperature and pressure.American Mineralogist,62(9-10):857-873
Zhang RY and Liou JG.1999.Exsolution lamellae in minerals from ultrahigh-pressure rocks.International Geology Review,41(11):981-993
Zhao SR.2011.Crystallography and Mineralogy.2thEdition.Beijing:Higher Education Press(in Chinese)
Zhu YF and Xu X.2007.Exsolution texture of two-pyroxenes in lherzolite from Baijiangtan ophiolitic mélange,western Junggar,China.Acta Petrologica Sinica,23(5):1075-1086(in Chinese with English abstract)
刘良,杨家喜,章军锋等.2009.超高压岩石中矿物显微出溶结构研究进展、面临问题与挑战.科学通报,54(10):1378-1400
赵珊茸.2011.结晶学及矿物学.第2版.北京:高等教育出版社
朱永峰,徐新.2007.西准噶尔白碱滩二辉橄榄岩中两种辉石的出溶结构及其地质意义.岩石学报,23(5):1075-1086
Bollmann W.1970.Crystal Defects and Crystalline Interfaces.Berlin,Heidelberg:Springer-Verlag,1-254
Boyd FR and Brown GM.1969.Electron-probe study of pyroxene exsolution.Mineral.Sco.Am.Spec.Pap.,2:211-216
Bozhilov KN,Green II HW and Dobrzhinetskaya L.1999.Clinoenstatite in Alpe Arami peridotite:Additional evidence of very high pressure.Science,284(5411):128-132
Champness PE and Lorimer GW.1973.Precipitation(exsolution)in an orthopyroxene.Journal of Materials Science,8(4):467-474
Coe RS and Muller WF.1973.Crystallographic orientation of clinoenstatite produced by deformation of orthoenstatite.Science,180(4081):64-66
Coe RS and Kirby SH.1975.The orthoenstatite to clinoenstatite transformation by shearing and reversion by annealing:Mechanism and potential applications.Contributions to Mineralogy and Petrology,52(1):29-55
Domeneghetti MC,Tazzoli V,Boffa BT et al.1996.Orthopyroxene from the Serra de Mage meteorite:A structure-refinement procedure for a Pbca phase coexisting with a C2/c exsolved phase.American Mineralogist,81:842-846
Feinberg JM,Wenk HR,Renne PR and Scott GR.2004.Epitaxial relationships of clinopyroxene-hosted magnetite determined using electron backscatter diffraction(EBSD)technique.American Mineralogist,89(2-3):462-466
Fleet ME,Bilcox GA and Barnett RL.1980.Oriented magnetite inclusions in pyroxenes from the Grenville Province.Canadian Mineralogist,18(1):89-99
Kirby SH and Etheridge MA.1981.Exsolution of Ca-clinopyroxene from orthopyroxene aided by deformation.Physics and Chemistry of Minerals,7(3):105-109
Liu L,Yang JX,Zhang JF et al.2009.Exsolution microstructures in ultrahigh-pressure rocks:Progress,controversies and challenges.Chinese Science Bulletin,54(12):1983-1995
Liu XW,Jin ZM and Green II HW.2007.Clinopyroxene exsolution in diopsidic augite of Dabieshan:Garnet peridotite from depth of300km.American Mineralogist,92(4):546-552
Mikouchi T and Miyamoto M.2008.Mineralogy and pyroxene cooling rate of unique achondritic meteorite GRA 06129.In:Proceedings of the39thLunar and Planetary Science Conference.League City,Texas,2297
Peacor DR.1967.Refinement of the crystal structure of a pyroxene of formula M1M2(Si1.5Al0.5)O6.American Mineralogist,52:31-41
Robinson P,Ross M,Nord GL Jr,Smyth JR and Jaffe HW.1977.Exsolution lamellae in augite and pigeonite:Fossil indicators of lattice parameters at high temperature and pressure.American Mineralogist,62(9-10):857-873
Zhang RY and Liou JG.1999.Exsolution lamellae in minerals from ultrahigh-pressure rocks.International Geology Review,41(11):981-993
Zhao SR.2011.Crystallography and Mineralogy.2thEdition.Beijing:Higher Education Press(in Chinese)
Zhu YF and Xu X.2007.Exsolution texture of two-pyroxenes in lherzolite from Baijiangtan ophiolitic mélange,western Junggar,China.Acta Petrologica Sinica,23(5):1075-1086(in Chinese with English abstract)
刘良,杨家喜,章军锋等.2009.超高压岩石中矿物显微出溶结构研究进展、面临问题与挑战.科学通报,54(10):1378-1400
赵珊茸.2011.结晶学及矿物学.第2版.北京:高等教育出版社
朱永峰,徐新.2007.西准噶尔白碱滩二辉橄榄岩中两种辉石的出溶结构及其地质意义.岩石学报,23(5):1075-1086