变形组构引起的超高压榴辉岩地震波速各向异性
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摘要
超高压榴辉岩通常显示了强塑性变形和地震各向异性特征.对实验和天然变形超高压榴辉岩中主要矿物的地震波速性质及其变形晶格优选方位(CPO)与榴辉岩地震波速和各向异性之间的成因关系研究结果表明:(1)除石榴石表现为近地震波速各向同性外,榴辉岩中其他矿物都具有强地震各向异性(AVp=23.0%～40.9%,Max.AVs=18.5%～47.1%),是造成榴辉岩地震各向异性的主要来源矿物,石榴石和金红石的平均地震波速相对较高,绿辉石和柯石英中等,石英最小;(2)变形榴辉岩最大纵波波速(8.33～8.75km/s)方向近平行变形线理或面理,最小纵波波速(8.25～8.62km/s)近垂直线理或面理,纵波波速各向异性1.0%～1.7%,平均横波波速4.93～4.97km/s,其各向异性在同时与线理和面理成近45°方位接近最大(0.73%～1.78%),在面理面上接近垂直线理方位达到最小,横波快波极化取向近平行面理.超高压峰值变质条件(3～5GPa,900～1100℃)下榴辉岩地震纵波和横波波速预计比常温常压下分别高出3.4%～7.2%和6.3%～12.1%;(3)绿辉石矿物组分主导了榴辉岩各向异性基本特征,而石榴石矿物组分则起到了降低榴辉岩各向异性程度和增加地震波速的作用,石英矿物组分对榴辉岩地震各向异性影响不大但可以一定程度上降低榴辉岩的地震波速,金红石矿物组分的作用基本可以忽略;(4)榴辉岩地震波速在纯石榴石岩中最大但各向异性接近于零,随绿辉石含量的增加,地震波速逐步降低,各向异性逐步升高,纯绿辉石岩比纯石榴石岩地震波速低6%～8%,而各向异性则达到3%～4%.根据榴辉岩组成矿物的单晶弹性性质和变形CPO计算的榴辉岩地震物性与前人实测结果基本相当.研究成果获得了超高压变形榴辉岩的三维地震物性资料和相关的矿物物理成因解释.
引文
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21Zhang J,Green H W.Experimental investigation of eclogite rheology and its fabrics at high temperature and pressure.J Meta-morph Geol,2007,25:97—115
22Mainprice D.A Fortran program to calculate seismic anisotropy from the lattice preferred orientation of minerals.Comp Geo-science,1990,16:385—393
23Mainprice D,Humbert M.Methods of calculating petrophysical properties from lattice preferred orientation data.Surv Geophys,1994,15:575—592
24Ji S,Wang Q,Xia B,et al.Mechanical properties of multiphase materials and rocks:a phenomenological approach using generali-zed means.J Struct Geol,2004,26:1377—1390
25Hill R.The elastic behavior of a crystalline aggregate.Proc Phys Soc,Sec A,1952,65:349—354
26Collins M D,Brown J M.Elasticity of an upper mantle clinopy-roxene.Phys Chem Mineral,1998,26:7—13
27Leitner B J,Weidner D J,Liebermann R C.Elasticity of single crystal pyrope and implications for garnet solid solution series.Phys Earth Planet Int,1980,22:111—121
28Soga N.Elastic constants of garnet under pressure and temperature.J Geophys Res,1967,72:4227—4234
29Bass J.Elasticity of grossular and spessartite garnets by Brillioun spectroscopy.J Geophys Res,1989,94:7621—7628
30Levien L,Weidner D J,Prewitt C T.Elasticity of diopside.Phys Chem Miner,1979,4:105—113
31Kandelin J,Weidner D J.The single-crystal elastic properties of jadeite.Phys Earth Planet Int,1988,50:251—260
32McSkimin H J,Andreacht P,Thurston R N.Elastic moduli of quartz versus hydrostatic pressure at25°and-195.8°.J Appl Phys,1965,36:1624—1632
33Weidner D J,Carleton H R.Elasticity of coesite.J Geophys Res,1977,82:1334—1346
34Isaak D G,Carnes J D,Anderson O L,et al.Elasticity of TiO2rutile to1800K.Phys Chem Miner,1998,26:31—43
35Christensen N I.Compressional wave velocities in possible mantle rocks to10kilobars.J Geophys Res,1974,79:407—412
36Tommasi A,Gibert B,Seipold U,et al.Anisotropy of thermal di-ffusivity in the upper mantle.Nature,2001,411:783—786
2Zhang J,Green H W,Bozhilov K,et al.Faulting induced by pre-cipitation of water at grain boundaries in hot subducting oceanic crust.Nature,2004,428:633—636
3Anderson D L.Speculations on the nature and cause of mantle heterogeneity.Tectonophysics,2006,416:7—22
4杨晓松,金振民.大陆科学钻探中岩石物理性质研究的意义.地学前缘,1998,5:338—346
5Xu Z,Wang Q,Ji S,et al.Petrofabrics and seismic properties of garnet peridotite from the UHP Sulu terrane(China):implications for olivine deformation mechanism in a cold and dry subducting continental slab.Tectonophysics,2006,421:111—127
6Fountain D M,Boundy T M,Austrheim H,et al.Eclogite-facies shear zones-deep crustal reflectors-Tectonophysics,1994,232:411—424
7高山,金振民,Kern H,等.大别山超高压榴辉岩高温高压下地震波速和密度的初步研究—对造山带地壳深部组成和莫霍性质的启示.科学通报,1997,42(8):862—865
8Kern H,Gao S,Jin Z,et al.Petrophysical studies on rocks from the Dabie ultrahigh-pressure(UHP)metamorphic belt,Central China:implications for the composition and delamination of the lower crust.Tectonophysics,1999,301:191—215
9Kern H,Jin Z,Gao S,et al.Physical properties of ultra-high-pressure metamorphic rocks from Sulu terrain,eastern China:implications for the seismic structure of the Donghai(CCSD)drilling site.Tectonophysics,2002,354:315—330
10赵志丹,谢鸿森,周文戈.大别山榴辉岩的密度和波速及其对壳幔循环的启示.矿物岩石地球化学通讯,2001,20:52―57
11金振民,欧新功,徐海军,等.中国大陆科学钻探主孔100~2000m岩石弹性波速度:对地震深反射的约束.岩石学报,2004,20:81.96
12Wang Q,Ji S,Salisbury M,et al.Shear wave properties and Pois-son’s ratios of ultrahigh-pressure metamorphic rocks from the Dabie-Sulu orogenic belt,China:implications for the crustal composition.J Geophys Res,2005,110,doi:10.1029/2004-JB003435
13Wang Q,Ji S,Salisbury M,et al.Pressure dependence and anisot-ropy of P-wave velocities in ultrahigh-pressure metamorphic rocks from the Dabie-Sulu orogenic belt(China):implications for seis-mic properties of subducted slabs and origin of mantle reflections.Tectonophysics,2005,398:67—99
14王勤,嵇少丞,许志琴,等.榴辉岩的地震波性质:对苏鲁超高压变质带地壳成分和折返机制的探讨.岩石学报,2005,21:451—464
15Mauler A,Burlini L,Kunze K,et al.P-wave anisotropy in ec-logites and relationship to the omphacite crystallographic fabric.Phys Chem Earth,2000,25:119—126
16Mauler A,Godard G,Kunze K.Crystallographic fabrics of ompha-cite,rutile and quartz in Vendee eclogite(Armorican Massif,France):consequences for deformation mechanisms and regimes.Tectonophysics,2001,342:81—112
17Bascou J,Barruol G,Vauchez A,et al.EBSD-measured lat-tice-preferred orientations and seismic properties of eclogites.Tectonophysics,2001,342:61—80
18Ji S,Saruwatari K,Mainprice D,et al.Microstructure,petrofabrics and seismic properties of ultrahigh-pressure eclogites from Sulu region,China:implications for rheology of subducted continental crust and origin of mantle reflections.Tectonophysics,2003,370:49—76
19章军锋,金振民,Green H W.结构水引起的榴辉岩变形组构和变形机制.科学通报,2005,50(6):559—564
20Zhang J,Green H W,Bozhilov K N.Rheology of omphacite at high temperature and pressure and significance of its lattice pre-ferred orientations.Earth Planet Sci Lett,2006,246:432—443
21Zhang J,Green H W.Experimental investigation of eclogite rheology and its fabrics at high temperature and pressure.J Meta-morph Geol,2007,25:97—115
22Mainprice D.A Fortran program to calculate seismic anisotropy from the lattice preferred orientation of minerals.Comp Geo-science,1990,16:385—393
23Mainprice D,Humbert M.Methods of calculating petrophysical properties from lattice preferred orientation data.Surv Geophys,1994,15:575—592
24Ji S,Wang Q,Xia B,et al.Mechanical properties of multiphase materials and rocks:a phenomenological approach using generali-zed means.J Struct Geol,2004,26:1377—1390
25Hill R.The elastic behavior of a crystalline aggregate.Proc Phys Soc,Sec A,1952,65:349—354
26Collins M D,Brown J M.Elasticity of an upper mantle clinopy-roxene.Phys Chem Mineral,1998,26:7—13
27Leitner B J,Weidner D J,Liebermann R C.Elasticity of single crystal pyrope and implications for garnet solid solution series.Phys Earth Planet Int,1980,22:111—121
28Soga N.Elastic constants of garnet under pressure and temperature.J Geophys Res,1967,72:4227—4234
29Bass J.Elasticity of grossular and spessartite garnets by Brillioun spectroscopy.J Geophys Res,1989,94:7621—7628
30Levien L,Weidner D J,Prewitt C T.Elasticity of diopside.Phys Chem Miner,1979,4:105—113
31Kandelin J,Weidner D J.The single-crystal elastic properties of jadeite.Phys Earth Planet Int,1988,50:251—260
32McSkimin H J,Andreacht P,Thurston R N.Elastic moduli of quartz versus hydrostatic pressure at25°and-195.8°.J Appl Phys,1965,36:1624—1632
33Weidner D J,Carleton H R.Elasticity of coesite.J Geophys Res,1977,82:1334—1346
34Isaak D G,Carnes J D,Anderson O L,et al.Elasticity of TiO2rutile to1800K.Phys Chem Miner,1998,26:31—43
35Christensen N I.Compressional wave velocities in possible mantle rocks to10kilobars.J Geophys Res,1974,79:407—412
36Tommasi A,Gibert B,Seipold U,et al.Anisotropy of thermal di-ffusivity in the upper mantle.Nature,2001,411:783—786
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