Tectonophysics 475 (2009) 251–266

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Geochemistry, petrofabrics and seismic properties of eclogites from the ChineseContinental Scientific Drilling boreholes in the Sulu UHP terrane, eastern China

Qin Wang a,⁎, Luigi Burlini b, David Mainprice c, Zhiqin Xu d

a Department of Earth Sciences, Nanjing University, Nanjing 210093, Chinab Geologisches Institut, ETH-Zürich, Leonhardstrasse, 19, CH-8092 Zürich, Switzerlandc Géosciences Montpellier UMR 5243, CNRS and Université Montpellier II, Montpellier, Franced Key Laboratory of Continental Dynamics, Ministry of Land and Resources, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China

⁎ Corresponding author. Tel.: +86 25 8359 6887; faxE-mail address: qwang@nju.edu.cn (Q. Wang).

0040-1951/$ – see front matter © 2008 Elsevier B.V. Aldoi:10.1016/j.tecto.2008.09.027

a b s t r a c t

a r t i c l e i n f o

Article history:

We present an integrated Received 21 December 2007Received in revised form 18 June 2008Accepted 11 September 2008Available online 27 September 2008

Keywords:EclogiteCrystal preferred orientationP-wave velocity and anisotropyTemperature derivativesMantle reflectionsSulu terrane

study of geochemistry, petrofabrics and seismic properties of strongly shearedeclogites from the Chinese Continental Scientific Drilling (CCSD) project in the Sulu ultrahigh-pressure(UHP) metamorphic terrane, eastern China. First, geochemical data characterize diverse protoliths of thestudied eclogites. The positive Eu- and Sr-anomalies, negative Nb anomaly and flat portion of heavy rareearth elements in coarse-grained rutile eclogites (samples B270 and B295) suggest a cumulate origin in thecontinental crust, whereas the negative Nb anomaly and enrichment of light rare earth elements inretrograde eclogites (samples B504, B15 and B19) imply an origin of continental basalts or island arc basalts.Second, P-wave velocities (Vp) of three typical eclogite samples were measured under confining pressuresup to 500 MPa and temperatures to 700 °C. At 500 MPa and room temperature, the mean Vp reaches8.50–8.53 km/s in samples B270 and B295 but drops to 7.86 km/s in sample B504, and the P-wave anisotropychanges from 1.7–2.7% to 5.5%, respectively. The pressure and temperature derivatives of Vp are larger in theretrograde eclogite than in fresh ones. Third, the electron backscatter diffraction (EBSD) measurements of theeclogites reveal random crystal preferred orientation (CPO) of garnet and pronounced CPO of omphacite,which is characterized by a strong concentration of [001]-axes sub-parallel to the lineation and of (010)-polesperpendicular to the foliation. The asymmetric CPO of omphacite in sample B270 recorded a top-to-the-southshear event during subduction of the Yangtze plate. The calculated fastest Vp is generally sub-parallel to thelineation, but a different deformation environment during exhumation could form second-order variationsin omphacite CPO and affect the Vp distribution in eclogites (e.g., the fastest Vp is at ~35° from the foliation insample B295). Comparison between measured and calculated seismic properties indicates that the CPO ofomphacite controls the seismic anisotropy of eclogites at high pressure, and compositional layering andretrograde minerals will increase the anisotropy. Calculated P-wave velocities agree well with velocitiesmeasured at 500 MPa and room temperature for fresh eclogites, but much higher than those of retrogradeeclogite. As a case study, the laboratory-derived Vp–P and Vp–T relationships were used to estimate P-wavevelocities of eclogites and peridotites beneath the Western Superior Province, Canada. The results indicatethat besides the fabric-induced anisotropy, the direction dependence of pressure and temperaturederivatives of Vp can significantly increase seismic anisotropy of eclogites with depth, which results ineclogites being an important candidate for the seismic anisotropy in the upper mantle. Due to their very highdensity and velocity, garnet-rich eclogites within peridotite could be detected in seismic reflections insubduction zones.

© 2008 Elsevier B.V. All rights reserved.

1. Introduction

Eclogites play a key role in the recycling of material between thecrust and upper mantle, e.g., subduction and exhumation of ultrahigh-pressure (UHP) metamorphic rocks (e.g., Ringwood, 1990; Chemendaet al., 1996; Chopin, 2003; Jolivet et al., 2005), lower crustal delami-nation and detachment (e.g., Kay and Kay, 1991; Philippot and van

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Roermund, 1992; Lustrino, 2005), a mass imbalance for Nb, Ta and Tibetween the continental crust and depleted mantle (Rudnick et al.,2000). Knowledge about seismic properties of eclogites is critical to theinterpretation of seismic data beneathmodern and ancient subductionzones. Although eclogites are generally characterized by high density,high seismic velocities and weak anisotropy, the complex eclogitiza-tion of basaltic material during subduction and the retrogression ofeclogites during exhumationwill modify their chemical compositions,microstructure, and seismic properties (Gao et al., 2001; Hacker et al.,2003; Ji et al., 2003a; Wang et al., 2005a, b). The great variations of

252 Q. Wang et al. / Tectonophysics 475 (2009) 251–266

chemical compositions in the Dabie–Sulu eclogites imply multiplesources of protoliths and possiblemodification before, during and afterthe UHP metamorphism (Jahn, 1998; Liou et al., 2000). Recently, theChinese Continental Scientific Drilling (CCSD) project in the Sulu UHPterrane revealed more than 1000 m of eclogites with distinctpetrological and geochemical characteristics (Zhang et al., 2004,2006; Liu et al., 2005; Zhao et al., 2005), which provide an idealopportunity to investigate the relationships between chemicalcomposition, microstructure and seismic properties of eclogites.

Laboratory measurements of seismic velocities of eclogites havebeen undertaken since Birch's pioneering work (1960), but mostly athigh pressure and room temperature (see Ji et al., 2002 for a review).Using a cubic anvil pressure apparatus, temperature derivatives of P-and S-wave velocities in eclogites have been investigated at 600 MPa(Kern and Richter, 1981; Kern and Tubia, 1993; Kern et al., 1999, 2002).However, the state of near-hydrostatic stress in the cubic anvil

Fig. 1. Simplified geological map of the Sulu terrane, eastern China. The tectonic units from stemperature and high-pressure kyanite zone; III, UHP supracrustal zone; IV, UHP granitic z

pressure apparatus may potentially cause an overestimation of bothpressure derivatives and seismic anisotropy, and occasionally producepositive temperature derivatives at high pressure (e.g., Kern et al.,2002). Burlini et al. (2005) set up an internally heated gas mediumapparatus (Paterson rig) to measure rock seismic velocities atpressures up to 500 MPa and temperatures up to 950 °C. The Patersonseismic apparatus allows us to measure the effect of temperature onseismic properties of eclogites under purely hydrostatic pressures,which is very important in extrapolating laboratory measurements tothe depths of interest.

The electron backscatter diffraction (EBSD) technique can rapidlydetermine crystal orientations of any symmetry, including cubicgarnet, which has stimulated recent studies of crystallographic fabricsand deformationmechanism of eclogites. Based on theory of elasticity,calculation of rock seismic properties opens a way to decipher therelationships between the crystal preferred orientations (CPO) of

outh to north are: I, low-temperature and high-pressure glaucophane zone; II, medium-one (modified after Xu et al., 2003).

Table 1Lithology and major oxides (wt.%) of the eclogites from the Sulu UHP terrane.

Lithology Rutile eclogite Retrograde eclogite Garnetite

Sample no. B270 B295 B504 B15 B19 MBF3

Boreholedepth (m)

CCSD-MH547.20

CCSD-MH586.10

CCSD-MH925.70

CCSD-PP445.84

CCSD-PP451.72

Outcropat Maobei

SiO2 44.71 41.43 50.18 49.00 46.74 42.05Na2O 2.73 1.40 3.21 3.85 3.50 0.23MgO 4.77 6.74 5.19 4.70 5.33 13.46Al2O3 18.97 13.49 14.64 14.61 14.08 21.26P2O5 0.41 0.02 0.50 0.46 0.31 0.02K2O 0.05 b0.01 0.20 0.08 0.02 b0.01CaO 11.48 11.90 8.49 8.80 9.63 13.00TiO2 2.73 3.27 1.77 2.23 2.41 0.09MnO 0.20 0.23 0.22 0.26 0.26 0.13Fe2O3 1.44 5.60 3.11 3.18 3.71 1.33FeO 11.01 14.57 11.51 11.08 12.66 7.06H2O+ 0.42 0.52 0.78 0.40 0.66 0.38CO2 0.40 0.31 0.31 0.83 0.31 0.31LOI 0.23 −0.32 0.22 −0.03 0.01 0.13Total 99.55 99.16 100.33 99.45 99.63 99.45

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constituent minerals and the seismic anisotropy of eclogites (e.g.,Mauler et al., 2000, 2001; Bascou et al., 2001, 2002; Ji et al., 2003a;Mainprice et al., 2004). Because the single crystal elastic constants aregenerally determined at room conditions on small crystals of gemquality, free of cracks or inclusions, the calculated properties provideresults representative the effective elastic properties of crack-free andalteration-free aggregates, which may not be comparable with the insitu velocities of rocks in the upper crust or experimental measure-ments on rock cores.

In this paper, we present an integrated study of geochemistry,petrofabrics and seismic properties of eclogites from the CCSD bore-

Fig. 2. Microphotographs of eclogites from the CCSD drill holes, showing flattened and elong(a) B270, (b) B295, (c) B504, (d) B15. Mineral symbols: Grt=garnet, Omp=omphacite, Rt=r

holes. First, themajor, trace elements and rare earth elements of the bulksamples were analyzed to investigate the geochemical characteristicsand protoliths of eclogites. Second, P-wave velocities of three typicaleclogite samples were measured under confining pressures up to500 MPa and temperatures up to 700 °C using the Paterson seismicapparatus. Third, the CPOs of garnet and omphacite were measuredusing the EBSD technique. The P- and S-wave velocities and anisotropyof the eclogites were calculated using the CPO data and the Hill average.Comparison between laboratorymeasurements and theoretical calcula-tions will improve our understanding on the fabric development andseismic properties of eclogites under various tectonic environments.

2. Geological setting

The Dabie–Sulu orogenic belt in east central China was formed bycontinental collision between the Sino-Korean and Yangtze plates inthe early Triassic. Coesite, micro-diamond and other UHP mineralassemblages were widely found in eclogite, garnet peridotite,quartzofeldspathic and pelitic gneisses, marble and quartzite, sug-gesting that the Yangtze plate have been subducted to depths greaterthan 120 km (see Liou et al., 1998 for a review). Despite differentialexhumation rate of the UHP rocks, the peak UHP metamorphism andrapid syn-collisional exhumation took place at ~220–240 Ma, fol-lowed by slow uplift under amphibolite facies conditions during 180–210 Ma (e.g., Chavagnac and Jahn, 1996; Hacker et al., 2000; Li et al.,2004; Liu et al., 2004). In the Late Jurassic to Early Cretaceous, crustalextension and granite intrusion reconstructed the Dabie–Sulu orogenand resulted in the final exposure of the UHP rocks (Ratschbacheret al., 2000). The extremely low δ18O in the Dabie–Sulu UHP rocksindicate restricted crust–mantle interaction and a lack of fluidmobility during subduction and exhumation of cold, dry and oldsupracrustal rocks (Zheng et al., 1998).

ated garnet and omphacite grains with various deformation and retrogression degrees.utile, Hbl=hornblende, Qtz=quartz, Bt=biotite, Mag=magnetite, Sym=symplectites.

Table 2Minor element compositions of the eclogite samples.

Sample B270 B295 B504 B15 B19 MBF3

Rare earth elements in ppmLa 7.97 0.86 14.4 23.0 9.20 0.34Ce 17.8 2.15 34.7 58.9 23.6 0.63Pr 2.42 0.39 4.72 8.31 3.46 0.14Nd 12.0 2.62 22.6 39.2 17.5 1.09Sm 2.91 1.44 5.29 9.12 5.05 0.54Eu 1.52 0.80 2.03 2.97 1.87 0.35Gd 2.91 1.79 5.42 8.65 6.28 0.45Tb 0.45 0.33 0.92 1.44 1.21 0.07Dy 2.49 2.12 5.62 8.81 8.00 0.37Ho 0.46 0.41 1.11 1.78 1.66 0.07Er 1.25 1.13 3.28 5.47 5.11 0.20Tm 0.16 0.15 0.45 0.75 0.73 b0.05Yb 0.92 0.93 2.76 4.93 4.65 0.16Lu 0.14 0.14 0.42 0.73 0.70 b0.05ΣREE 53.4 15.26 103.72 174.06 89.02 4.41

Trace elements in ppmY 12.8 11.1 31.4 50.9 47.2 1.97Zr 31.6 25.6 92.6 229 207 21.9Hf 0.82 0.68 2.54 5.61 4.99 0.35Be 0.15 0.15 0.50 0.96 0.82 0.09Sc 13.9 74.4 47.2 43.2 55.8 11.5Cr 133 4.48 45.0 14.3 17.8 167Co 32.4 63.9 49.8 39.3 42.7 68.3Ni 45.0 13.7 23.4 60.4 29.3 137Cu 24.7 34.0 46.4 37.2 44.5 82.9Zn 101 123 143 157 143 58.5Ga 17.1 19.7 19.0 22.5 20.8 11.1Rb 0.45 0.65 3.30 0.84 1.16 0.26Nb 0.95 0.33 2.15 4.59 2.65 0.32Mo 3.21 2.72 4.49 2.77 2.23 1.97Cd 0.13 b0.05 0.17 0.23 0.18 0.08In 0.05 0.07 0.09 0.14 0.12 b0.05Cs b0.05 b0.05 0.22 0.16 0.05 b0.05Ta 0.10 0.06 0.17 0.34 0.23 0.05W 0.37 0.19 0.71 0.41 0.40 0.50Tl b0.05 b0.05 b0.05 b0.05 b0.05 b0.05Pb 5.14 3.83 4.77 9.16 8.01 3.83Bi 0.06 0.06 0.06 0.05 0.05 0.05Th 0.22 0.19 1.04 1.63 1.00 0.24U 0.05 0.07 0.20 0.31 0.21 0.06Ba 14.6 4.88 47.5 470 225 7.04Sr 398 51.9 99.7 132 104 20.3V 266 535 314 403 517 28.3

254 Q. Wang et al. / Tectonophysics 475 (2009) 251–266

The Sulu terrane is bounded by the Jiashan–Xiangshui fault in thesouth, the Qingdao–Wulian fault in the north, and the Tan–Lu fault in thewest (Fig. 1). From south to north, the Sulu terrane consists of a series ofNE-trending tectonic slices with increasing metamorphic P–T conditionsfrom greenschist facies to eclogite facies (Xu et al., 2003). The Maobeiultramafic–mafic complex is about 2000-m-long and260-m-wide, foldedwithin quartzofeldspathic gneisses in the southern Sulu terrane. A 5158-m-deepborehole (CCSD-MH)penetrates theMaobei complexat 735.76mand reveals interlayered eclogites, serpentinized garnet peridotite andpyroxenite, granitic gneiss and paragneiss. The petrostructural profile ofthe CCSD-MH recognizes three ductile shear zones DFa (835–1280 m),DFb (2010–2280 m) and DFc (2920–3225 m), which are composed ofmylonitic gneisses and strongly deformed retrograde eclogite (Xu et al.,2009-this issue).Next to theCCSD-MH, a113.7-m-deeppre-pilot boreholeCCSD-PP4 also penetrates interlayered eclogites and felsic gneisses.

3. Rock samples and geochemical analysis

3.1. Sample description

We collected three eclogite samples from the CCSD-MH and twofrom the CCSD-PP4 (Table 1). Samples B270 andB295 are fresh, coarse-grained rutile eclogites from the Maobei complex. Sample B504 isretrograde quartz eclogite from a top-to-NW ductile shear zone DFabeneath the Maobei complex, which is similar with samples B15 andB19 from the CCSD-PP4 in composition and microstructure. Theeclogite samples develop the SE-dipping foliation and SE-plunginglineation as host gneisses, with the exception of sample B270 thatdisplays steeply eastward-dipping foliation and SN-trending lineation.For comparison, amassive garnetiteMBF3was collected froma garnet-rich layer in the CCSDdrilling site.MBF3has a remarkable red color dueto the presence of ~90 vol.% coarse-grained garnet.

As shown in Fig. 2, the CCSD eclogites contain garnet, omphaciteand rutile as essential phases with minor quartz, and/or quartzpseudomorphs after coesite, green hornblende and symplectites. Thefoliation is defined by compositional banding of alternating garnet-and omphacite-rich layers, and the stretching lineation is defined byelongated garnet, omphacite and rutile. Garnet and omphacite havethe grain size of ~0.5–1.5 mm, and are characterized by transgranularcracks that are preferentially aligned at high angles to the foliation andlineation. Occasionally, radial extensional fractures around quartzpseudomorphs of coesite are observed in samples B270 and B295.Brownish rutile appears as small inclusions in garnet and omphacite,or as intergranular grains in size up to 0.3 mm. The symplectitesconsist of plagioclase, hornblende, quartz, epidote and/or biotite anddistribute along grain boundaries and cracks, especially in retrogradeeclogites B504, B15 and B19. So we have typical samples to representthe strongly deformed eclogites at peak UHP metamorphism condi-tions (B270 and B295) and overprinted by amphibolite facies retro-grade metamorphism during exhumation (B504, B15 and B19).

3.2. Chemical compositions and protoliths

The whole-rock major elements of the five CCSD eclogites and onegarnetite MBF3 were analyzed by X-ray fluorescence (XRF) withuncertainties of less than 0.5% (Table 1). Table 2 lists their traceelements and rare earth elements (REE) determined by inductivelycoupled plasma mass spectrometry (ICP-MS), except that Sr, Ba and Vwere analyzed using inductively coupled plasma-atomic emissionspectrometry (ICP-AES). The cation-exchange technique was appliedto separate REE. Analytical uncertainties are 10% for elements withabundances b10 ppm, and ~5% for those N10 ppm. All chemicalanalyses were carried out in the National Research Center forGeoanalysis, Chinese Academy of Geological Sciences (Beijing).

The SiO2 contents of the six samples vary from 41–42% in rutileeclogite B295 and garnetite MBF3, to ~50% in retrograde eclogite B504

(Table 1). Compared with the eclogite samples, the garnetite MBF3is extremely rich in MgO and Al2O3, but poor in Na2O and TiO2.Combined with previous chemical analysis on eclogites from the CCSDboreholes (Zhang et al., 2004, 2006; Liu et al., 2005; Zhao et al., 2005;Qiu et al., 2006; Ji et al., 2007) and outcrops in the Sulu UHP terrane(Zhang et al., 1994, 2003; Jahn et al., 1996; Jahn, 1998; Ji et al., 2003a;Wang et al., 2005a), the SiO2 content of the Sulu eclogites has positivecorrelation with total alkali content (Na2O+K2O), but negativecorrelation with CaO content (Fig. 3a–b). However, the correlationbetween SiO2 and alkali do not exist for the retrograded coesite-bearing eclogites from the Weihai area, which have andesiticcompositions and ultrahigh εNd values due to severe metasomatism(water–rock interaction) in the middle Proterozoic (Jahn et al., 1996).The abundance of total FeO decreases almost linearly with increasingSiO2 content, but increases with TiO2 content (Fig. 3c–d). Althoughthe high-Ti (TiO2N2%) eclogites generally contain b45% SiO2, the cor-relation between TiO2 and SiO2 is not so evident, especially in low-Ti(TiO2 b2%) eclogites and garnetites (Fig. 3e). In Fig. 3f, eclogites fromthe Dabie Mountains (Zhang et al., 1995; Chavagnac and Jahn, 1996;Kern et al., 1999; Wang et al., 2005a) are also plotted. It is worthy toindicate that the negative correlations between Al2O3 or MgO contentwith SiO2 or Na2O, which were observed by Wang et al. (2005a) using25 eclogite samples from the Dabie–Sulu orogen, become ambiguouswhen the new data are included.

Fig. 3. Relationships betweenmajor oxides (wt.%) of the Sulu eclogites. (a) Na2O+K2O vs. SiO2, (b) CaO vs. SiO2, (c) Total FeO vs. SiO2, (d) Total FeO vs. TiO2, (e) TiO2 vs. SiO2, (f) Na2O vs.MgO. N is the sample number, total iron is presented as FeOT, the solid line is the least-squares fit to the core samples from the CCSD boreholes.

255Q. Wang et al. / Tectonophysics 475 (2009) 251–266

The great variations of major elements in the Sulu eclogites suggestmultiple sources of protoliths and later modification, which can bedemonstrated by distribution patterns of trace and rare earthelements. In primitive-mantle normalized spider grams of theeclogites (Fig. 4a), all the samples display the negative Nb anomaly,which has been observed in the Dabie–Sulu eclogites and attributed toa continental affinity or island arc basalts (Jahn, 1998). Therefore oursamples did not derive from the subducted paleo-Tethyan oceaniccrust. In chondrite-normalized REE patterns (Fig. 4b), the enrichmentof light rare earth elements (LREE) in samples B270, B504, B15 andB19 has been widely observed in Precambrian continental basalts andamphibolites (Hall and Hughes, 1990), as well as in the Dabie–Sulueclogites within gneisses (Jahn, 1998; Zhang et al., 2004).

By contrast, samples B295 and MBF3 display a LREE-depletedpattern, which was only reported in the high-Ti-Fe rutile eclogitesfrom 548–596 m in the CCSD-MH for the Dabie–Sulu eclogites (Zhang

et al., 2004; Liu et al., 2005). The relatively flat portion of heavy rareearth elements (HREE) in samples B270, B295 and MBF3 indicatesthat garnet, which strongly favors the HREE, was not in equilibriumwith the melts during segregation. Except the different LREE patterns,samples B270 and B295 are similar in HREE distribution, low ΣREE,positive Ti anomaly and high CaO content. The flat HREE and positiveEu- and Sr-anomalies in samples B270, B295 and MBF3 are charac-teristic of plagioclase enrichment, suggesting that they originatedfrom gabbroic cumulates within continental crust.

4. Velocity measurements at high pressure and high temperature

4.1. Experimental technique

The ultrasonic P-wave velocities (Vp) were measured using thepulse transmission technique (Birch, 1960) at confining pressures up

Fig. 4. (a) Primitive-mantle normalized trace element, and (b) chondrite-normalizedREE distribution patterns of the Sulu eclogites. Values of primitivemantle and chondriteare from McDonough and Sun (1995).

Fig. 5. P–T path of a temperature cycle for velocity measurements. Filled and opensymbols are measurements during heating and cooling processes, respectively.

256 Q. Wang et al. / Tectonophysics 475 (2009) 251–266

to 500 MPa and temperatures to 700 °C in the Rock DeformationLaboratory at ETH Zurich. For each sample, three cylindrical mini-cores, 22 mm in diameter and ~30 mm in length, were cut inorthogonal directions X, Y and Z (X — parallel to the stretchinglineation, Y — normal to lineation and parallel to foliation, Z — normalto foliation) to study the seismic anisotropy. The top and bottomsurfaces of the cores were carefully polished to assure they wereparallel within±10 µm. Then the cores were dried at 120 °C for morethan 24 h before measurements. The entire sample/buffer-rod/transducer assemblage was enclosed in a stainless steel jacket. Theset up of the internally heated gas medium apparatus (Paterson rig)and experimental details were reported by Burlini et al. (2005) andFerri et al. (2007).

The confining pressure was determined using a manganin coilpressure transducer with a precision of about 1 MPa at 500 MPa. In apressure cycle, the elastic wave velocities were measured at roomtemperature with increasing pressure by approximately 50 MPaincrements until ~500 MPa, and then with decreasing pressure by50 MPa decrements to room pressure. For velocity measurements athigh temperature, a small pressure increment (1 MPa/°C) is requiredto avoid thermal cracking of core samples, but in quartz-rich rocks thepressure increment should be higher due to the very large thermalexpansion of quartz (Kern, 1982). Here we adopted a specific P–T pathto avoid thermal cracking of eclogites in the temperature cycle (Fig. 5).First, pressure and temperature were raised to 500 MPa and 700 °C atsteps of 100 MPa and 100 °C, respectively, then the temperature wascooled down to 50 °C by 100 °C decrements, and finally the pressurewas released to room pressure by 50 MPa decrements. Temperature

was controlled using two K-type thermocouple (within ±1 K) placeddirectly on the top and bottom surfaces of the specimen. The dif-ference between the two thermocouples at the highest temperatureand highest pressure was less than 10 K. At each step, the time of flightwas recorded until the temperature equilibrium was achieved.

Before and after the velocity measurements, the grain volume ofthe cores was determinedwith a helium gas pycnometer, and then thebulk volume from the dimension of the cores. Accordingly, grain andbulk densities were calculated from the weight and the volume. Thevery low porosity (b0.7%) of the core samples makes the graindensity only a little bit larger than the correspondent bulk density(Table 3). After experiments, the increase of grain density is less than0.005 g/cm3, which is within the accuracy of density measurement.The changes of core diameter and length are between −0.082 to0.038 mm, and −0.018 to 0.052 mm, respectively. Both are withinstandard error of the mean values. Comparison of thin sections beforeand after experiments indicates that omphacite, garnet, rutile,amphibole and symplectites remain intact during velocity measure-ments, suggesting that no plastic deformation, mineral reactions,dehydration or phase transition occurred during experiments. Thelength changes of the cores with pressure and temperature areignored because the greatest correction on the velocity is within theexperimental error. The accuracy is estimated to be ±1% for Vp mea-surements at 1 MHz (Burlini et al., 2005; Ferri et al., 2007).

4.2. Pressure dependence of Vp

Retrograde eclogites B504, B15 and B19 exhibit similar micro-structure and modal composition, so we only performed velocitymeasurements on samples B270, B295 and B504 from the CCSD-MH.Because some microcracks closed with increasing pressures do notreopen during depressurization, the velocities measured at lowpressures during initial pressurization are lower than those measuredduring depressurization (e.g., Birch, 1960; Ji et al., 2007). For instance,sample B295 shows remarkable velocity hysteresis below 300 MPa(Fig. 6). The velocity hysteresis along the X direction is morepronounced than along the Yand Z directions, which can be attributedto the fast closure of aligned transgranular cracks with increasingpressure. Table 3 gives P-wave velocities and anisotropy measured atvarious pressure and room temperature during decompression.

As shown in Figs. 6–7, at low pressures the P-wave velocities ofeclogite samples increase rapidly with increasing pressures, and thengradually increase at high pressure. At 500 MPa all the three eclogitesdisplay the fast Vp along the X direction. The P-wave anisotropy isdefined as A=(Vmax−Vmin) /Vm⁎100%, where Vm is the arithmetic

Table 3P-wave velocities (km/s), anisotropy (%) and densities of the eclogites from the CCSD main hole.

Sample Bulk density(g/cm3)

Grain density(g/cm3)

Pressure (MPa)

50 75 100 150 200 250 300 400 500 1000

B270 X 3.513 3.514 7.89 8.08 8.20 8.30 8.37 8.43 8.49 8.53 8.55 8.67Y 3.558 3.560 8.05 8.21 8.29 8.39 8.45 8.47 8.49 8.52 8.53 8.59Z 3.513 3.519 7.90 8.02 8.08 8.17 8.24 8.31 8.36 8.41 8.43 8.52M 3.528 3.531 7.95 8.11 8.19 8.29 8.35 8.40 8.44 8.48 8.50 8.59A 2.06 2.38 2.56 2.68 2.51 2.00 1.55 1.40 1.46 1.68

B295 X 3.707 3.725 8.29 8.41 8.48 8.54 8.58 8.60 8.62 8.63 8.64 8.67Y 3.702 3.728 7.91 8.05 8.16 8.26 8.30 8.35 8.39 8.41 8.42 8.47Z 3.729 3.756 7.89 8.07 8.20 8.34 8.41 8.45 8.48 8.51 8.55 8.70M 3.713 3.736 8.03 8.17 8.28 8.38 8.43 8.47 8.50 8.52 8.53 8.61A 5.00 4.38 3.93 3.42 3.24 3.00 2.74 2.57 2.53 2.68

B504 X 3.355 3.360 7.50 7.64 7.70 7.79 7.86 7.93 7.98 8.02 8.06 8.24Y 3.260 3.280 7.18 7.29 7.37 7.46 7.52 7.54 7.56 7.61 7.63 7.70Z 3.334 3.353 7.27 7.41 7.51 7.63 7.71 7.79 7.83 7.88 7.89 8.12M 3.316 3.331 7.32 7.45 7.52 7.63 7.70 7.76 7.79 7.84 7.86 8.02A 4.43 4.69 4.43 4.37 4.35 5.03 5.38 5.27 5.53 6.80

Abbreviations: X, Y, Z: propagation direction; M, mean; A, P-wave anisotropy. Values at 1000 MPa are extrapolated.

257Q. Wang et al. / Tectonophysics 475 (2009) 251–266

mean of the velocities measured from the X, Y and Z directions (Birch,1960). Samples B270 and B295 have high density, high P-wavevelocities and lowanisotropy. In contrast, the occurrence of quartz andfibrous symplectites in sample B504 significantly decreases densityand P-wave velocities but increases the P-wave anisotropy. The effectsof retrograde metamorphism on seismic properties of eclogites areclearer at high pressure. For example, at 500 MPa Vm decreases from8.50 km/s in sample B270 to 7.86 km/s in sample B504, while the P-wave anisotropy increases from 1.46% to 5.53%, respectively (Table 3).

According to Wang et al. (2005a), the laboratory-derived Vp–Pcurves of rocks can be described by a rapid, nonlinear increase below acritical pressure (Pc) and a linear increase above Pc, which correspondsto the velocity variations in the poroelastic regime at low pressuresand in the pure elastic regime at high pressures, respectively. Using aMatlab program VPPLOT (Wang et al., 2005a), we can obtain the Vp–Prelationships for the nonlinear and linear regimes:

Vp ¼ a lnPð Þ2þblnP þ c PVPcð ÞV0 þ DP PzPcð Þ

�ð1Þ

where P is the confining pressure, a and b are parameters describingthe closure of microcracks below Pc, c is the velocity when P is equalto 1 MPa, V0 is the projected velocity of a crack-free sample at roomconditions, and D is the intrinsic pressure derivative above Pc. Table 4

Fig. 6. P-wave velocity hysteresis along the X, Y, and Z directions of eclogite B295 atroom temperature. Open symbols are measured during pressurization and filledsymbols measured during depressurization.

gives the parameters of Vp–P relationships with R2N0.97 in a sense ofleast squared errors.

Ji et al. (2007) proposed a four-parameter exponential equation todescribe the Vp–P relationship in the full range of pressure:

Vp ¼ V0 þ DP−B0exp −kPð Þ ð2Þ

where B0 is the initial velocity difference between the nonporousmaterial and its porous counterpart at zero pressure, k is the decayconstant of the velocity drop. The values of B0 and k depend on theporosity and geometric shape of pores. When the velocity drop ratioB0 exp(−kP) /B0≤0.2%, the effects of microcracks on the velocity canbe ignored and the critical pressure Pc can be approximately definedas 6.215/k. Table 5 lists the least square solutions of Vp–P curves usingEq. (2), with R2N0.89 in a sense of least squared errors.

The critical pressure Pc of the three eclogite samples variesbetween 299 and 425 MPa in Table 4, and 377–690 MPa in Table 5.Because microcracks in eclogites are not fully closed until PN500 MPa(Wang et al., 2005a), the lower Pc will result in lower V0 and higher Din regression results. It is interesting to notice that although the Pcvalues in Table 5 are higher than those in Table 4, such correlation doesnot exist for the values of V0 and D fit by Eq. (1) and Eq. (2). In fact, themodel of Ji et al. (2007) tends to moderate the difference of elasticityalong different propagation directions, e.g., giving higher V0 andsmaller D values for core samples B295Z, B504X and B504Z, but lower

Fig. 7. P-wave velocities versus confining pressure along the X, Y, and Z directions forrutile eclogite B270 and retrograde eclogite B504 at room temperature.

Table 4Pressure and temperature dependence of Vp for the eclogites from the CCSD main hole.

Sample Pc (MPa) P0 (MPa) Vp=a(lnP)2+blnP+c (P≤Pc) Vp=V0+DP (P≥Pc) dVp/dT

a (km s−1 MPa−2) b (km s−1 MPa−1) c (km/s) V0 (km/s) D (10−4 km s−1 MPa−1) (500 MPa) (600 MPa)

(−10−4 km s−1 °C−1)

B270 X 365 248 −0.0547 0.8409 5.463 8.436 2.297 2.86 2.86Y 386 233 −0.0820 1.0259 5.309 8.465 1.272 3.61 3.58Z 398 283 −0.0172 0.4217 6.499 8.333 1.889 7.06 7.06M 365 241 −0.0538 0.7951 5.658 8.400 2.068 4.51 4.50

B295 X 339 243 −0.0590 0.7413 6.307 8.600 0.722 4.17 4.17Y 382 285 −0.0714 0.9500 5.283 8.373 0.937 2.99 2.94Z 316 178 −0.1287 1.5799 3.654 8.386 3.122 4.69 4.69M 299 201 −0.0841 1.0769 5.090 8.436 1.988 3.95 3.93

B504 X 351 203 −0.0213 0.4719 5.971 7.878 3.637 6.52 6.52Y 425 272 −0.0381 0.5774 5.516 7.557 1.399 4.46 4.42Z 307 197 −0.0168 0.4673 5.709 7.711 4.058 6.56 6.55M 355 229 −0.0340 0.5976 5.487 7.730 2.629 5.85 5.83

Table 5Vp–P relationships for the eclogites from the CCSD-MH using model of Ji et al. (2007).

Sample V0

(km/s)D(10−4 km s−1 MPa−1)

B0(km/s)

k(10−2 MPa−1)

R2 Pc(MPa)

Vp at1000 MPa(km/s)

B270 X 8.460 2.190 0.781 0.901 0.933 690 8.68Y 8.466 1.678 0.575 0.976 0.888 637 8.63Z 8.342 1.882 0.781 0.953 0.981 652 8.53M 8.400 2.109 0.833 1.217 0.995 511 8.61

B295 X 8.583 1.190 0.666 1.647 0.990 377 8.70Y 8.354 1.440 0.880 1.346 0.986 462 8.50Z 8.474 1.164 1.071 1.287 0.993 483 8.59M 8.452 1.645 0.880 1.469 0.998 423 8.62

B504 X 7.960 1.895 0.862 1.087 0.978 572 8.15Y 7.522 2.142 0.673 1.318 0.995 471 7.74Z 7.798 2.263 0.911 1.031 0.994 603 8.02M 7.770 2.277 0.817 1.065 0.991 584 8.00

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V0 and larger D for B295X, B295Y and B504Y. For sample B270, thevalues of V0 and D calculated from Eqs. (1) and (2) are close despitethe much higher Pc in Table 5. Clearly, the extrapolation of Vp–Prelationships in Table 5 will give lower seismic anisotropy of samplesB295 and B504 at great depths. The P-wave velocities of the eclogitesare calculated by using parameters in Tables 4 and 5, which yield themaximum relative error of 1.2% at 1000 MPa and room temperature(Tables 4–5). For the Vp–P curves below 300 MPa, Eq. (1) fits betterthan Eq. (2) with R2N0.99, especially for data points below 80 MPa.Further work is required to investigate which model is better todescribe the laboratory-derived Vp–P curves of rocks.

4.3. Temperature dependence of Vp

Using the Vp–P relationship obtained in a pressure cycle (Table 4),P-wave velocities measured in a temperature cycle can be corrected to500 MPa, and then to obtain dVp/dT at 500 MPa by linear regression.Fig. 8 illustrates the regression results of dVp/dT at 500MPa for sampleB270. To assure data quality in the linear regression, only the Vp

measurements above 300 MPa in both pressure and temperaturecycles are selected to calculate the temperature derivatives. Thegoodness-of-fit of the least-squares solution to dVp/dT at 500 MPa isN0.92, considerably larger than the critical R2 for a positive F test. Thedifference between Vp0 in the linear function Vp(500MPa)=Vp0+dVp/dT and Vp measured at 500 MPa and room temperature is within theexperimental error (±1%). To check if the effects of microcracks havebeen eliminated in the regression, we also calculate dVp/dT at 600 MPafor the eclogites, which are nearly equal to the dVp/dT values at500 MPa (Table 4). Moreover, although Vp measured at low pres-sure and low temperature are not included in regression, the correctedP-wave velocities agree fairly well with the linear trend. Therefore ourmethod provides reliable dVp/dT values for estimating the tempera-ture dependence of rocks under the stable regimes of constituentminerals.

The temperature derivatives of Vm in samples B270 and B295 are−4.51 and−3.95×10−4 km s−1 °C−1, respectively, which are smallerthan thatof the retrogradeeclogiteB504with−5.85×10−4 kms−1 °C−1.Interestingly, the P-wave velocities exhibit a direction dependence oftemperature derivative, i.e., the velocity decrease with increasingtemperature is anisotropic (Table 4). For instance, dVp/dT along the Zdirection is about twice of that along the X direction in sample B270(Fig. 8). The rapid velocity decrease with increasing temperature alongthe Z direction could be explained by the anisotropic properties ofclinopyroxene (omphacite), the volumetrically most important aniso-tropic phase (volume fraction 23% in sample B270). It is probably notdue to the elastic anisotropy as the dCij/dT in GPa K−1 is −0.0291,−0.0248 and −0.0179 along the (100)-pole, [010]-axis and [001]-axis

respectively for diopside (Isaak et al., 2006) and the Z sample directioncorresponds to a high concentration of [010]-axes (Fig. 9). A largethermal expansion normal to the foliation (Z) is a more likelyexplanation of the Vp decrease because the thermal expansion ofclinopyroxene structure is very high at 20.5×10−6 K−1 in [010]direction compared to 7.8 and 6.5×10−6 K−1 in the (100)-pole and[001] directions, respectively (Cameron et al., 1973).

5. EBSD measurements

The crystal preferred orientations of omphacite, garnet, rutile andquartz from the six eclogite samples were measured on a scanningelectron microscope JEOL JSM 5600 equipped with EBSD system, atGéosciences Montpellier, Université Montpellier II, France. The finelypolished XZ section was tiled at 70° from the horizontal within themicroscope chamber. At working distance of 41 mm and acceleratingvoltage of 17–18 kV, a vertical incident electron beam interacted withcrystal interfaces and produced the electron backscattering patternson a phosphor screen. The photonic image was captured by a low-light, high-resolution camera and then processed and indexed usingthe CHANNEL+software. To avoid duplicate measurements in biggrains, we manually scanned the whole section and indexed themineral phases according to the pattern quality and the agreementbetween detected and simulated Kikuchi bands. The relative precisionof crystal orientations is better than 1° (Krieger Lassen,1996). Becausethe grain amounts of rutile and quartz are very limited, here we focuson the CPOs of omphacite and garnet.

In Fig. 9, the CPO of omphacite is characterized by a strongconcentration of [001]-axes sub-parallel to the lineation and a

Fig. 8. P-wave velocities versus temperature along the X, Y, and Z directions for eclogiteB270. Solid line represents the least square fit to data measured above ~300 MPa andcorrected to 500 MPa.

259Q. Wang et al. / Tectonophysics 475 (2009) 251–266

relatively poor orientation of [100]-axes. The concentration of (010)-poles is weaker than that of [001]-axes. (010)-poles form a girdleperpendicular to the lineation with a maximum density close to the Zdirection in sample B270, but with a maximum density close to the Ydirection and a sub-maximum parallel to the Z direction in sampleB295. In samples B504, B15 and B19, (010)-poles display a pointmaximum normal to the foliation. Moreover, in sample B270 thatdevelops steeply eastward-dipping foliation and SN-trending linea-tion, [001]-axes and (010)-poles show an asymmetric CPO withrespect to the foliation and lineation. The pfJ index, which describesthe sharpness of a pole figure and increases with the fabric strength,reaches 4.76 for [001]-axes in sample B270. Sample MBF3 wasrandomly cut due to its massive texture, and then the section wasrotated to fit the typical CPO pattern of omphacite in the structural

reference frame. The relatively weak fabric strength of omphacite insample MBF3 can be attributed to the small number of measuredgrains, because generally at least 100–150 grains are required torepresent the fabric strength (Ben Ismaïl and Mainprice, 1998).

The omphacite (110)-poles present similar orientationwith (010)-poles, but yield a smaller pfJ index than [001]-axes and (010)-poles. Insamples B270 and B295, (110)-poles form a girdle perpendicular to thelineationwith amaximum at ~45° to the foliation.While in retrogradeeclogites B504, B15 and B19, (110)-poles concentrate around the Zdirection. The axes [104] and [

–102] respectively correspond to the

fastest and slowest Vp propagation directions in an omphacite crystaldescribed by Bhagat et al. (1992) (Fig.10). Althoughnot involved in theslip systems of omphacite, the axes [104] and [

–102] tend to concen-

trate sub-parallel to the lineation, but have a much weaker pfJ indexthan [001]-axes.

In contrast to the pronounced CPO of omphacite, garnet from theeclogites has very weak and complex crystallographic fabrics (Fig. 11).Garnet displays elongated grain shape and well-developed subgrainsin SEM, especially in samples B270 and B295, implying that garnet hasexperienced ductile deformation. Previous TEM observations havefound dislocation microstructures in naturally deformed garnets fromultradeep xenoliths (Doukhan et al., 1994), high-temperature mylo-nites (Ji andMartignole,1994), and eclogites (Ando et al., 1993; Ji et al.,2003a). Recent numerical modeling on garnet fabrics indicate that theb111N{110} system contributes over 86% to the total strain in garnet,but due to its cubic symmetry and 66 available slip systems, polefigure densities of garnet are very weak (Mainprice et al., 2004).Although the volume fraction of garnet reaches 60–87% in oursamples, only garnetite MBF3 develops the garnet CPO that is com-parable with the simulation results using the interaction parameterα=100 and equivalent stain of 1.0 for simple shear (Mainprice et al.,2004). Therefore even volumetrically dominant and strongly elon-gated, garnet will not produce strong CPO during ductile deformation.Compared with the simulated garnet CPO (Mainprice et al., 2004), it isvery difficult, if not impossible, to distinguish deformation regimefrom the fabrics of naturally deformed garnet.

6. Calculation of seismic properties

Ignoring minor minerals, the studied eclogites can be regarded astwo-phase aggregates of garnet and omphacite. Based on the EBSD-derived CPOs of garnet and omphacite, we calculated seismicproperties of the studied samples using the Hill average and therevised modal compositions (Table 6). The density and single crystalelastic constants are frommeasurements on pyrope (Chai et al., 1997)and omphacite (30 mol% diopside, 58 mol% jadeite) (Bhagat et al.,1992). The computations were performed using the program ofMainprice (1990).

The calculated P- and S-wave velocities are very high for eclogites,ranging from 8.59 to 8.80 km/s and 4.90 to 4.99 km/s, respectively(Table 6). The calculated P-wave anisotropy is less than 2%, and yieldsonly 0.6% in garnetite MBF3. Except sample B295, the eclogites arecharacterized by themaximum Vp sub-parallel to the lineation and theminimum Vp sub-normal to the foliation (Fig. 12). As illustrated inFig. 10, the fastest Vp propagates along the [104]-axis (9.37 km/s), theslowest Vp along [

–102]-axis (7.64 km/s), relatively fast Vp along the

[001]-axis (9.0 km/s) and slow Vp along the [010]-axis in an omphacitesingle crystal. Because the similar orientation trend and fabric strengthof axes [104] and [

–102] counteract the contribution to the anisotropy,

the fastest and slowest P-wave velocities of eclogites will follow thepreferred orientation of the [001]-axes and (010)-poles of omphacite,respectively. The fast S-wave polarization plane is generally parallelto the foliation, which is consistent with the S-wave anisotropycharacteristics of omphacite.

However, in sample B295 the fastest Vp lies in the YZ plane and at~35° from the foliation, which is different from the characteristic Vp

Fig. 9. EBSD-measured omphacite CPO of the Sulu eclogites. Equal area projection, lower hemisphere, contouring at multiples of a uniform distribution and an inverse log grey scale.Normal to foliation (Z direction) is vertical and lineation (X direction) is horizontal. N: number of data points; pfJ: texture index. The dashed line in B270 represents the inferred shearplane from the omphacite fabrics.

260 Q. Wang et al. / Tectonophysics 475 (2009) 251–266

distribution in eclogites observed so far. In order to investigate if it iscaused by the CPO of garnet, we computed the seismic properties ofsample B295 assuming 100% omphacite (B295⁎ in Fig. 12). The similarvelocity distribution between B295 and B295⁎ indicates that thisunusual seismic anisotropy is totally controlled by the CPO ofomphacite. In fact, the omphacite fabric in sample B295 is different

from the other samples. As shown in Fig. 9, instead of being a pointmaximum normal to the foliation, (010)-poles of sample B295 form agirdle perpendicular to the lineation with the maximum densityclose to the Y direction and a sub-maximum close to the Z direction.Therefore although omphacite [001]-axes still display a strong con-centration parallel to the lineation, the fastest Vp changes the

Fig. 10. Upper hemisphere equal area projection of P-wave velocity distribution in anomphacite single crystal.

261Q. Wang et al. / Tectonophysics 475 (2009) 251–266

propagation direction to the YZ plane in sample B295. In addition, thefastest Vp of sample B270 rotates about 30° from the maximumconcentration of omphacite [001]-axes, which can be attributed to theobliquity between the fastest Vp direction [104] and the slowest Vp

direction [–102]. Clearly, although a concentration of omphacite [001]-

axes results in the fast Vp sub-parallel to the lineation, the orientationof [104] and [

–102] can modify the seismic anisotropy pattern of

eclogites.

7. Comparison between measured and calculated velocities

Although the elastic constants of pyrope (Chai et al., 1997) andomphacite (Bhagat et al., 1992) were obtained at room conditions, thecalculated P-wave velocities of the three eclogites in Table 6 are muchhigher than the projected V0 values in Tables 4 and 5, implying anincomplete closure of microcracks in specimen at 500 MPa. In fact, thereliable calculations of rock seismic velocities depend on not onlyaccurate elastic properties and volume fractions of constituentminerals, but also the mixture rule used. Ji et al. (2003b) found thatstatistically, the P-wave velocities of eclogites calculated using the Hillaverage and the room pressure elastic constants agree well with Vp

measured at 500 MPa. In this study, the calculated P-wave velocitiesare a little bit higher than Vp measured at 500 MPa in samples B270and B295, but significantly higher than that in sample B504. Thecalculated P-wave anisotropy is larger than the measured anisotropy,especially in sample B504. However, the Vp distribution is consistentin samples B270 and B504: the fast P-wave velocities are sub-parallelto the X direction, and the slow P-wave velocities are sub-parallel tothe Z direction in sample B270 and to the Y direction in sample B504.In sample B295, the calculated P-wave velocities have similar valuesalong the X, Y, and Z directions and produce very weak anisotropy. Themeasured P-wave velocities appear as Vp(X)NVp(Z)NVp(Y) at 500MPa,but become Vp(Z)NVp(X)NVp(Y) when extrapolated to 1000 MPa insample B295.

Several factors may contribute to the discrepancy betweenlaboratory measurements and theoretical calculations: (1) Asdiscussed above, a small amount of microcracks remain open at500 MPa, which will reduce seismic velocities of eclogites and resultin higher dVp/dP and lower V0 values; (2) The minor minerals (e.g.,quartz, plagioclase, epidote, hornblende, mica) that have lowvelocities and high anisotropy will significantly decrease seismicvelocities, but may decrease or increase the seismic anisotropydepending on the alignment degree of their anisotropic elasticcontribution with that of omphacite in retrograde eclogites; (3) TheEBSD-derived volume fractions of constituent minerals are notrepresentative of the bulk sample because of the different grainsizes, ignored alteration minerals and compositional heterogeneity;(4) Garnet and omphacite in our eclogite samples have different

chemical compositions and elastic constants as the single crystalsused in calculation, although this contribution is probably minor. Theaverage chemical composition of garnet from the Sulu coarse-grained eclogites is Alm24.0±0.5Prp41.7±1.1Grs33.7±1.1Spe0.5±0.1 (Ji et al.,2003a), which has lower P-wave velocities than pyrope studied byChai et al. (1997).

8. Discussion

8.1. Omphacite CPO significance

Despite the different protoliths of eclogites, the CPO of omphacitegenerally exhibits strong concentration of [001]-axes sub-parallel tothe lineation and (010)-poles normal to the foliation (Fig. 9), whichbelongs to the constriction or L-type fabrics described by Helmstaedtet al. (1972). Therefore the fabric development of omphacite is totallycontrolled by the deformation regime of eclogites during the UHPmetamorphism. TEM investigations (e.g., van Roermund and Boland,1981; Godard and van Roermund, 1995) and numerical simulations(Bascou et al., 2002) indicate that instead of an “easy slip” on the [001](010), multiple dislocation glide on 1/2b110N{1

–10}, [001]{110} and

[001](100) slip systems controls the CPO of omphacite. Moreover,sample B295 contains two [010] maxima, one on the foliation planenormal to the lineation (Y) and the other perpendicular to thefoliation (Z). Such “composite fabrics” have been found in the CaboOrtegal eclogite (NW Spain) and were attributed the combination ofthe deformation conditions that produce the flattening, constrictionand annealed fabrics (Ábalos, 1997). The [010] maximum along the Ydirection is probably related to increased activity of [001](100) slip,which is an easy slip system in clinopyroxene at 800–900 °C (Ingrinet al., 1992).

Our omphacite CPO is characterized by a stronger concentration of[001]-axes than (010)-poles and a weak orientation of [100]-axes,which is consistent with the omphacite fabrics predicted by simpleshearmodels with relaxed strain compatibility (Bascou et al., 2002). Inaddition, (010)-poles form a girdle normal to the lineation in samplesB270 and B295, but display a point maximum normal to the foliationin samples B504, B15 and B19, which are correspondent with themodels using critical resolved shear stresses inferred from experi-mental deformation of diopside (CRSS 1) and from TEM analyses ofnaturally deformed omphacite (CRSS 2), respectively. It is noteworthythat samples B270 and B295 associated with ultramafic rocks, whilesamples B504, B15 and B19 were deformed with paragneiss in a top-to-NW thrust shear zone. Field observations have revealed a regionaltop-to-NW thrusting during exhumation of the Sulu UHP rocks (Xuet al., 2003). Therefore the second-order variations in omphacite CPOmay be caused by the different deformation environment during syn-collisional exhumation of eclogites in the upper mantle.

Omphacite in naturally deformed eclogites often generates sym-metric CPO (e.g., Boundy et al.,1992; Godard and van Roermund,1995;Bascou et al., 2001; Mauler et al., 2001; Ji et al., 2003a). Taking accountof the errors in determining the reference frame in samples from drillcores, a slight obliquity of omphacite CPO is not reliable to deduce theshear sense. Using a five-axis U-stage, Ábalos (1997) observed a 6–8°obliquity of the omphacite CPO and attributed it to the top-to-NNEtectonic displacement of Cabo Ortegal eclogite (NW Spain). Bascou etal. (2002) observed an asymmetric omphacite CPO in eclogites fromthe Sulu, Western Gneiss Region, and Alpe Armi and indicated that the[001]-axes are intermediate between the shear direction and thelineation. In our strongly deformed eclogite B270, a significantobliquity of 10° between the [001]-axes concentration and thelineation suggests a dextral shear with respect to the structuralframe (Fig. 9). The inferred top-to-the-south shear event is consistentwith the shear sense recorded in the subduction-induced olivine CPOin the Zhimafang garnet peridotite (Xu et al., 2006), but contrary tothe top-to-NW thrusting in exhumation-induced quartz CPO in

Fig. 11. EBSD-measured garnet CPO of the Sulu eclogites. Equal area projection, lower hemisphere, contouring as multiples of a uniform distribution and an inverse log grey scale.Normal to foliation (Z direction) is vertical and lineation (X direction) is horizontal. N: number of data points; pfJ: texture index.

262 Q. Wang et al. / Tectonophysics 475 (2009) 251–266

paragneiss and granitic gneiss (Xu et al., 2003), suggesting that theasymmetric omphacite CPO in sample B270 was formed during thenorthward subduction of the Yangtze plate. Hence the opposite shear

Table 6Calculated density and seismic properties of the eclogites using revised modal composition

Sample Omp/Grt (vol.%) Density (g/cm3) Vpmax (km/s) Vpmin (km/s) A (Vp) (%) Vs1max

B270 23/77 3.699 8.78 8.68 1.20 4.99B295 22/78 3.704 8.76 8.70 0.70 4.97B504 17/83 3.728 8.79 8.72 0.80 4.98B15 40/60 3.617 8.69 8.59 1.20 4.96B19 33/67 3.651 8.74 8.59 1.70 4.98MBF3 13/87 3.746 8.80 8.74 0.60 4.98B295⁎ 100/0 3.327 8.56 8.31 3.00 4.95

⁎ For sample B295, seismic properties of the omphacite aggregate (100% Omp) are also c

senses inferred from CPOs of omphacite and quartz reflect the tectonicdisplacement of the Sulu UHP rocks during subduction in the uppermantle and exhumation in the crust, respectively.

s.

(km/s) Vs1min (km/s) Vs2max (km/s) Vs2min (km/s) A (Vs) (%) (Vs1−Vs2)max (km/s)

4.94 4.96 4.92 1.17 0.064.95 4.96 4.94 0.56 0.034.96 4.97 4.94 0.56 0.034.93 4.95 4.90 1.28 0.064.93 4.95 4.91 1.17 0.064.96 4.97 4.96 0.36 0.024.85 4.90 4.82 2.39 0.12

alculated.

Fig. 12. Calculated seismic properties of the eclogites. Equal area projection, lower hemisphere. Normal to foliation (Z direction) is vertical and lineation (X direction) is horizontal.

263Q. Wang et al. / Tectonophysics 475 (2009) 251–266

8.2. Seismic properties of eclogites

Samples B270 and B295 are fresh coarse-grained eclogites withvery high density, high P-wave velocities and low anisotropy at500 MPa. By contrast, sample B504 is retrogressed with relatively lowdensity, low P-wave velocity and high anisotropy (Table 3). Comparedwith the three types of eclogites described byWang et al. (2005a), theformer belongs to the Type-1 eclogites subjected to the UHP meta-morphism in the diamond stability field, while the latter is Type-3

eclogite overprinted by amphibolite facies metamorphism duringexhumation in the crust. The intrinsic pressure derivatives of Vm are2.0×10−4 kms−1MPa−1 for samplesB270andB295, and2.6×10−4 kms−1 MPa−1 for sample B504 (Table 4), which are slightly higher thanthe values for Type-1 eclogites (1.41×10−4 km s−1 MPa−1) and Type-3eclogites (2.04×10−4 km s−1 MPa−1), respectively (see compilation ofWang et al., 2005a). Because the microcracks in eclogites are notfully closed at the given Pc, the extrapolation of Vp–P relationships inTable 4 may slightly overestimate the in situ eclogite velocities at great

Fig. 13. Laboratory-derived pressure and temperature derivatives of Vp in eclogites.

264 Q. Wang et al. / Tectonophysics 475 (2009) 251–266

depths, but is still appropriate if taking accuracy of experimentalmeasurements into account.

So far experimental work on temperature derivatives of Vp are verylimited for eclogites. The dVp/dT values of our three eclogites rangefrom−3.95 to−5.85×10−4 kms−1 °C−1,whichare similar to the resultsfrom Christensen (1979), Kern and Tubia (1993) and Kern et al. (1999),but larger than those from Kern and Richter (1981) and Kern et al.(2002) (Fig. 13). Christensen (1979) measured P-wave velocities of agranular eclogite at confining pressure of 200 MPa and found that P-wave velocities decrease linearly with increasing temperature until300 °C. In experiments of Kern and his colleagues, the temperaturederivatives of eclogites were measured in a cubic anvil apparatus up to700 °C at 600 MPa. The almost linear decrease of velocity between 25and 500 °C was used to estimate dVp/dT at 600 MPa. The relativelysmall dVp/dT values result from weak velocity decrease or evenvelocity increase with increasing temperature below 500 °C, whichwas attributed to a higher exhumation rate and/or greater sourcedepth of eclogites (Kern et al., 2002). However, such “unusual”

Fig. 14. Calculated in situ (a) P-wave velocities of samples B270 and B295, (b) reflection coeffiand B295.

temperature dependence was not observed in our samples. Further-more, in Fig. 13 the dVp/dP values of our samples are significantlylower than those determined from the linear regression of Vp between200 and 600 MPa and room temperature (Kern and Richter, 1981; Kernand Tubia, 1993; Kern et al., 1999, 2002). As indicated by the authors,200 MPa is not high enough to completely close microcracks and theirregression results give an upper bound of dVp/dP in eclogites.

Combined with P–T conditions of study area, Table 4 allowsextrapolation of the laboratory-derived seismic velocities of eclogitesto depths of interest, which will be helpful in tracing subducted slabsin the upper mantle, e.g., the western Pacific (Widiyantoro et al.,1999), the Dabie–Sulu orogenic belt (Xu et al., 2001), Canada'sSuperior Province (Calvert et al., 1995) and the Northwest Territories(Bostock, 1998; Cook et al., 1999). As a case study, we calculated P-wave velocities and anisotropy with depth for samples B270 and B295beneath the Western Superior Province, Canada (Fig. 14). Thelithostatic pressure P=ρgz, where z is the depth and the averagedensities of rocks (ρ) are assumed to be 2.85 g/cm3 and 3.3 g/cm3 forthe crust and upper mantle, respectively. Assuming a stableconductive thermal regime, the geothermal profile was calculatedusing heat flow data (~45 mW/m2, Jaupart et al., 1998), the thermalconductivities of rocks (Clauser and Huenges, 1995) and a three-layered crustal structure (Musacchio et al., 2004). The very lowgeothermal gradient (b7 °C/km) in the Western Superior Province iscomparable with that in subduction zones (Liou et al., 1998). Forcomparison, the mean P-wave velocities of peridotite and serpenti-nized peridotite with depth were also calculated using the parametersfrom Wang et al. (2005b).

In Fig. 14a, the rapid increase of Vp with depth in the upper crust(b14 km) reflects the closure of microcracks with increasing pressurewhile the effects of temperature are minor. Above the critical pressure(N18–20 km), positive pressure derivatives and negative temperaturederivatives of Vp essentially counteract each other and Vp increasesslowly with depth. In the upper mantle (N42 km), the fast velocitydirection is still parallel to the X direction in sample B270, butpropagates along the Z direction in sample B295 due to a much largerpressure derivative normal to the foliation. Peridotite exhibits similarVp with samples B270 and B295, whereas serpentinized peridotite

cients at the interfaces of eclogite–peridotite, and (c) P-wave anisotropy of samples B270

265Q. Wang et al. / Tectonophysics 475 (2009) 251–266

has much lower velocity. The reflection coefficients (Rc) betweenperidotite and our eclogite samples also change with depth (Fig. 14b).Although the difference between the mean P-wave velocities ofperidotite and eclogites are very small, the high density and velocity ofsample B295 produce a relatively high Rc (N0.5) in contact withperidotite, implying that garnet-rich eclogites within peridotite couldbe detected in seismic reflections and the serpentinization ofperidotite will increase their reflectivity. In Fig. 14c, despite the greatvariations in the upper crust, the P-wave anisotropy of samples B270and B295 tends to increases with depth in the upper mantle andreaches 6% at 120 km. Clearly, although both high-pressure velocitymeasurements and theoretical calculations present weak anisotropyin fresh eclogites, direction-dependent pressure and temperaturederivatives will increase in situ seismic anisotropy of eclogites in theupper mantle.

The remarkable direction dependence of dVp/dT has been found inmylonite (Burlini et al., 2005) and metapelitic xenolith (Ferri et al.,2007). Due to limited data, the anisotropic temperature dependenceof seismic velocities in other lithologies is not clear, which reflectsanisotropic elastic response to temperature in rocks and related withmicrostructure (e.g., foliation and lineation, compositional layering,distribution and shape of microcracks, etc.). It is urgent to performmore experimental and theoretical work on this topic that yieldsimportant constraints on the interpretation of seismic data.

9. Conclusions

We investigated geochemical characteristics, petrophysics andseismic properties of eclogites from the CCSD boreholes in the SuluUHP terrane, eastern China. The main results are summarized below:

(1) Great variations inmajor, trace and rare earth elements indicatedifferent protoliths of the studied eclogites. The negative Nbanomaly in all the samples implies a continental affinity orisland arc basalts. The positive Eu- and Sr-anomalies, flat HREEand high CaO content in the coarse-grained rutile eclogitessuggest that they originated from gabbroic cumulates in thecontinental crust, whereas the LREE enrichment in retrogradeeclogites indicates an origin of continental or island arc basalts.

(2) P-wave velocities of three typical eclogite samples weremeasured at confining pressures up to 500 MPa and tempera-tures to 700 °C using the Paterson seismic apparatus. At500 MPa and room temperature, the coarse-grained rutileeclogites B270 and B295 show high Vp (~8.50 km/s) and weakanisotropy (b2.5%), but retrograde eclogite B504 yield low Vp

(7.86 km/s) and high anisotropy (5.5%). The pressure andtemperature derivatives of Vp are larger in the retrogradeeclogite than in fresh ones. The direction-dependent pressureand temperature derivatives of Vp can significantly affect theseismic anisotropy of eclogites with depth and increasereflectivity of eclogite–peridotite contact in subducted slabs.

(3) The CPOs of garnet and omphacite were determined usingEBSD technique. Garnet appears randomly orientated, whileomphacite is characterized by a strong concentration of [001]-axes sub-parallel to the lineation and (010)-poles normal to thefoliation. Different deformation environment during exhuma-tion could form second-order variations in omphacite CPO andaffect the fastest Vp direction in eclogites. The asymmetric CPOof omphacite in sample B270 recorded a top-to-the-south shearevent during subduction of the Yangtze plate.

(4) The calculated P-wave velocities agree well with the measuredVp of fresh eclogites at 500 MPa and room temperature, butsignificantly larger than those of retrograde eclogite. Thecalculated maximum Vp is sub-parallel to the lineation in allthe samples but is at ~35° from the foliation in sample B295 dueto the variations in omphacite fabrics. Although the omphacite

CPO controls the seismic anisotropy of eclogites at highpressure, compositional layering and retrograde minerals willincrease the anisotropy.

Acknowledgements

We are grateful to R. Hofmann for his technical assistance in thevelocity measurements, to A. Tommasi for help with EBSD measure-ments, and to J.H. Yu and L.H. Chen for discussion on protoliths ofeclogites. Q. Wang thanks Prof. D. Marcotte for providing the MATLABprogram to compute the velocity–pressure relationships using modelof Ji et al. (2007). The constructive reviews by S.C. Ji and T. Watanabeare appreciated. This research is funded by the NSFC (40502022) andthe Chinese Ministry of Science and Technology (2003CB716504).Laboratory equipment and analyses of seismic properties weresupported by the R'equip NF grant 2160-053289.98 and the ETHgrant # 02150/41-2704.5.

References

Ábalos, B., 1997. Omphacite fabric variation in the Cabo Ortegal eclogite (NW Spain):relationships with strain symmetry during high-pressure deformation. J. Struct.Geol. 19, 621–637.

Ando, J., Fujino, K., Takeshita, T., 1993. Dislocation microstructures in naturallydeformed silicate garnets. Phys. Earth Planet. Inter. 80, 105–116.

Bascou, J., Barruol, G., Vauchez, A., Mainprice, D., Egydio-Silva, M., 2001. EBSD-measuredlattice-preferred orientations and seismic properties of eclogites. Tectonophysics342, 61–80.

Bascou, J., Tommasi, A., Mainprice, D., 2002. Plastic deformation and development ofclinopyroxene lattice preferred orientations in eclogites. J. Struct. Geol. 24,1357–1368.

Ben Ismaïl, W., Mainprice, D., 1998. An olivine fabric database: an overview of uppermantle fabrics and seismic anisotropy. Tectonophysics 269, 145–157.

Bhagat, S., Bass, J.D., Smyth, J., 1992. Single-crystal elastic properties of omphacite-C2/cby Brillouin spectroscopy. J. Geophys. Res. 97, 6843–6848.

Birch, F., 1960. The velocity of compressional waves in rocks to 10 kilobar, Part 1.J. Geophys. Res. 65, 1083–1102.

Bostock, M.G., 1998. Mantle stratigraphy and evolution of the Slave province. J. Geophys.Res. 103, 21183–21200.

Boundy, T.M., Fountain, D.M., Austrheim, H., 1992. Structural development andpetrofabrics of eclogite facies shear zones, Bergen Arcs, western Norway:implications for deep crustal deformation processes. J. Metamorph. Geol. 10,127–146.

Burlini, L., Arbaret, L., Zeilinger, G., Burg, J.P., 2005. High-temperature and pressureseismic properties of a lower crustal prograde shear zone from the Kohistan ArcPakistan. In: Bruhn, D., Burlini, L (Eds.), High-Strain Zones: Structure and PhysicalProperties, vol. 245. Geological Society Special Publication, pp. 187–202.

Calvert, A.J., Sawyer, E.W., Davis, W.J., Ludden, J.N., 1995. Archaean subduction inferredfrom seismic images of a mantle suture in the Superior Province. Nature 375,670–674.

Cameron, M., Sueno, S., Prewitt, C.T., Papike, J.J., 1973. High-temperature crystalchemistry of acmite, diopside, hedenbergite, jadeite, spodumene, and ureyite. Am.Mineral. 58, 594–618.

Chai, M., Brown, J.M., Slutsky, L.J., 1997. The elastic constants of pyrope-grossuar-almandine garnet to 20 GPa. Geophys. Res. Lett. 24, 523–526.

Chavagnac, V., Jahn, B.-M., 1996. Coesite-bearing eclogites from the Bixiling Complex,Dabie Mountains, China: Sm–Nd ages, geochemical characteristics and tectonicimplications. Chem. Geol. 133, 29–51.

Chemenda, A.I., Mattauer, M., Bokun, A.N., 1996. Continental subduction and amechanism for exhumation of high-pressure metamorphic rocks: new modellingand field data from Oman. Earth Planet. Sci. Lett. 143, 73–182.

Chopin, C., 2003. Ultrahigh-pressure metamorphism: tracing continental crust into themantle. Earth Planet. Sci. Lett. 212, 1–14.

Christensen, N.I., 1979. Compressional wave velocities in rocks at high temperatures andpressures, critical thermal gradients, and crustal low-velocity zones. J. Geophys.Res. 84, 6849–6857.

Clauser, C., Huenges, E., 1995. Thermal conductivity of rocks and minerals. In: Ahrens,T.J. (Ed.), Rock Physics and Phase Relations: A Handbook of Physical Constants.American Geophysical Union, Washington, pp. 105–126.

Cook, F.A., van der Velden, A.J., Hall, K.W., 1999. Frozen subduction in Canada'sNorthwest Territories: Lithoprobe deep lithospheric reflection profiling of thewestern Canadian Shield. Tectonics 18, 1–24.

Doukhan, N., Sautter, V., Doukhan, J.C., 1994. Ultradeep, ultramafic mantle xenoliths —transmission electron microscopy preliminary results. Phys. Earth Planet. Inter. 82,195–207.

Ferri, F., Burlini, L., Cesare, B., Sassi, R., 2007. Seismic properties of lower crustalxenoliths from El Hoyazo (SE Spain): experimental evidence up to partial melting.Earth Planet. Sci. Lett. 253, 239–253.

Gao, S., Kern, H., Jin, Z.M., Popp, T., Jin, S.Y., Zhang, H.-F., Zhang, B.-R., 2001. Poisson'sratio of eclogite: the role of retrogression. Earth Planet. Sci. Lett. 192, 523–531.

266 Q. Wang et al. / Tectonophysics 475 (2009) 251–266

Godard, G., van Roermund, H.L.M., 1995. Deformation-induced clinopyroxene fabricsfrom eclogite. J. Struct. Geol. 17, 1425–1443.

Hacker, B.R., Abers, G.A., Peacock, S.M., 2003. Subduction factory 1. Theoreticalmineralogy, densities, seismic wave speeds, and H2O contents. J. Geophys. Res.108. doi:10.1029/2001JB001127.

Hacker, B.R., Ratschbacher, L., Webb, L.E., McWilliams, M.O., Ireland, T., Calvert, A., Dong,S., Wenk, H.-R., Chateigner, D., 2000. Exhumation of ultrahigh-pressure continentalcrust in east central China: Late Triassic-early Jurassic tectonic unroofing.J. Geophys. Res. 105, 13339–13364.

Hall, R.P., Hughes, D.J., 1990. Early Precambrian Basic Magmatism. Blackie, Glasgow andLondon.

Helmstaedt, H., Anderson, O.L., Gavasci, A.T., 1972. Petrofabric studies of eclogite, spinel-websterite and spinel-lherzolite xenoliths from kimberlite-bearing breccia pipes insoutheastern Utah and northeastern Arizona. J. Geophys. Res. 77, 4350–4365.

Ingrin, J., Doukhan, N., Doukhan, J.C., 1992. Dislocation glide systems in diopside singlecrystals deformed at 800–900 °C. Eur. J. Mineral. 4, 1291–1302.

Isaak, D.G., Ohno, I., Lee, P.C., 2006. The elastic constants of monoclinic single-crystalchrome-diopside to 1,300 K. Phys. Chem. Miner 32, 691–699.

Jahn, B.-M., 1998. Geochemical and isotope characteristics of UHP eclogites of the Dabieorogen: implications for continental subduction and collision tectonics. In: Hacker,B., Liou, J.G. (Eds.), When Continents Collide: Geodynamics and Geochemistry ofUltrahigh-pressure Rocks. Kluwer Academic Publisher, Dordrechi, pp. 203–240.

Jahn, B.-M., Cornichet, J., Cong, B., Yui, T.F., 1996. Ultrahigh-Nd eclogites from anultrahigh-pressure metamorphic terrane of China. Chem. Geol. 127, 61–79.

Jaupart, C., Mareschal, J.C., Guillou-Frottier, L., Daville, A., 1998. Heat flow and thicknessof the lithosphere in the Canadian Shield. J. Geophys. Res. 103, 15269–15286.

Ji, S.C., Martignole, J., 1994. Ductility of garnet as an indicator of extremely hightemperature deformation. J. Struct. Geol. 16, 985–996.

Ji, S.C., Saruwatari, K., Mainprice, D., Wirth, R., Xu, Z.Q., Xia, B., 2003a. Microstructures,petrofabrics and seismic properties of ultrahigh-pressure eclogites from Suluregion, China: implications for rheology of subducted continental crust and originof mantle reflections. Tectonophysics 370, 49–76.

Ji, S.C., Wang, Q., Marcotte, D., Salisbury, M.H., Xu, Z.Q., 2007. P-wave velocities,anisotropy and hysteresis in ultrahigh-pressure metamorphic rocks as a function ofconfining pressure. J. Geophys. Res. 112. doi:10.1029/ 2006JB004867 B09204.

Ji, S.C., Wang, Q., Xia, B., 2002. Handbook of Seismic Properties of Minerals, Rocks andOres. Polytechnic International Press, Montreal. 630p.

Ji, S.C., Wang, Q., Xia, B., 2003b. P-wave velocities of polymineralic rocks: comparison oftheory and experiment and test of elastic mixture rules. Tectonophysics 366,165–185.

Jolivet, L., Raimbourg, H., Labrousse, L., Avigad, D., Leroy, Y., Austrheim, H., Andersen, T.B.,2005. Softening triggered by eclogitization, the first step toward exhumation duringcontinental subduction. Earth Planet. Sci. Lett. 237, 532–547.

Kay, R.W., Kay, S.M., 1991. Creation and destruction of lower continental crust. Geol.Rundsch. 80, 259–278.

Kern, H., 1982. Elastic-wave velocity in crustal and mantle rocks at high pressure andtemperature: the role of the high-low quartz transition and of dehydrationreactions. Phys. Earth Planet. Inter. 29, 12–23.

Kern, H., Richter, A., 1981. Temperature derivatives of compressional and shear wavevelocities in crustal and mantle rocks at 6 kbar confining pressure. J. Geophys. 49,47–56.

Kern, H., Tubia, J.M., 1993. Pressure and temperature dependence of P- and S-wavevelocities, seismic anisotropy and density of sheared rocks from Sierra Alpujatamassif (Ronda peridotites, southern Spain). Earth Planet. Sci. Lett. 119, 191–205.

Kern, H., Gao, S., Jin, Z., Popp, T., Jin, S., 1999. Petrophysical studies on rocks from theDabie ultrahigh-pressure (UHP) metamorphic belt, central China: implications forthe composition and delamination of the lower crust. Tectonophysics 301, 191–215.

Kern, H., Jin, Z., Gao, S., Popp, T., Xu, Z.Q., 2002. Physical properties of ultrahigh-pressuremetamorphic rocks from the Sulu terrain, eastern central China: implications forthe seismic structure at the Donghai (CCSD) drilling site. Tectonophysics 354,315–330.

Krieger Lassen, N.C., 1996. The relative precision of crystal orientations measured fromelectron backscattering patterns. J. Microsc. 181, 72–81.

Li, X.-P., Zheng, Y.-F., Wu, Y.-B., Chen, F.-K., Gong, B., Li, Y.-L., 2004. Low-T eclogite in theDabie terrane of China: petrological and isotopic constraints on fluid activity andradiometric dating. Contrib. Mineral. Petrol. 148, 443–470.

Liou, J.G., Zhang, R.Y., Ernst, W.G., 1998. High-pressure minerals from deeply subductedmetamorphic rocks. In: Hemley, R.J. (Ed.), Ultrahigh-pressure Mineralogy: Physicsand Chemistry of the Earth's Deep Interior. Mineralogical Society of America,Washington, D.C., pp. 33–50.

Liou, J.G., Zhang, R.Y., Jahn, B.-M., 2000. Petrological and geochemical characteristics ofultrahigh-pressure metamorphic rocks from the Dabie–Sulu terrane, East-CentralChina. Int. Geol. Rev. 42, 328–352.

Liu, Y.S., Zhan, Z.M., Lee, C.T., Gao, S., Zong, K.Q., 2005. Decoupled high-Ti from Low-Nb(Zr) of eclogites from the CCSD: implications formagnetite fractional crystallizationin basalt chamber. Acta Petrol. Sin. 21, 339–346.

Liu, F.L., Xu, Z.Q., Xue, H.M., 2004. Tracing the protolith, UHP metamorphism, andexhumation ages of orthogneiss from the SW Sulu terrane (eastern China): SHRIMPU–Pb dating of mineral inclusion-bearing zircons. Lithos 78, 411–429.

Lustrino, M., 2005. How the delamination and detachment of lower crust can influencebasaltic magmatism. Earth Sci. Rev. 72, 21–38.

Mainprice, D., 1990. A Fortran program to calculate seismic anisotropy from the latticepreferred orientation of minerals. Comp. Geosci. 16, 385–393.

Mainprice, D., Bascou, J., Cordier, P., Tommasi, A., 2004. Crystal preferred orientations ofgarnet: comparison between numerical simulations and electron back-scattereddiffraction (EBSD)measurements in naturally deformed eclogites. J. Struct. Geol. 26,2089–2102.

Mauler, A., Burlini, L., Kunze, K., Philippot, P., Burg, J.P., 2000. P-wave anisotropy ineclogites and relationship to the omphacite crystallographic fabric. Phys. Chem.Earth A. 25, 119–126.

Mauler, A., Godard, G., Kunze, K., 2001. Crystallographic fabrics of omphacite, rutile andquartz in Vendée eclogites (Armorican Massif, France): consequences fordeformation mechanism and regimes. Tectonophysics 342, 81–112.

McDonough, W.F., Sun, S.S., 1995. The composition of the Earth. Chem. Geol. 120,223–253.

Musacchio, G., White, D.J., Asudeh, I., Thomson, C.J., 2004. Lithospheric structure andcomposition of the Archean western Superior Province from seismic refraction/wide-angle reflection and gravity modeling. J. Geophys. Res. 109, B03304.

Philippot, P., van Roermund, H.L.M., 1992. Deformation processes in eclogitic rocks:evidence for the rheological delamination of the oceanic crust in deeper levels ofsubduction zones. J. Struct. Geol. 14, 1059–1077.

Qiu, J.S., Wang, R.C., Jiang, S.Y., Hu, J., Zhang, X.L., Ni, P., 2006. Geochemical comparisonbetween high-Ti and low-Ti eclogites from themain hole of the Chinese ContinentalScientific Drilling Project and its implications for rutile mineralization. Acta Petrol.Sin 22, 1875–1882.

Ratschbacher, L., Hacker, B.R., Webb, L.E., Williams, M.M., Ireland, T., Dong, S., Calvert, A.,Chateigner, D., Wenk, H.-R., 2000. Exhumation of the ultrahigh-pressure con-tinental crust in east central china: Cretaceous and Cenozoic unroofing and the Tan-Lu fault. J. Geophys. Res. 105, 13303–13338.

Ringwood, A.E., 1990. Slab–mantle interactions: 3. Petrogenesis of intraplate magmasand structure of the upper mantle. Chem. Geol. 82, 187–207.

Rudnick, R.L., Barth, M., Horn, I., McDonough, W.F., 2000. Rutile-bearing refractoryeclogites: missing link between continents and depleted mantle. Science 287,278–281.

van Roermund, H.L.M., Boland, J.N., 1981. The dislocation substructures of naturallydeformed omphacites. Tectonophysics 78, 403–418.

Wang, Q., Ji, S.C., Salisbury, M., Pan, M., Xia, B., Xu, Z.Q., 2005a. Pressure dependence andanisotropy of P-wave velocities in ultrahigh-pressure metamorphic rocks from theDabie–Sulu orogenic belt (China): implications for seismic properties of subductedslabs and origin of mantle reflections. Tectonophysics 398, 67–99.

Wang, Q., Ji, S.C., Salisbury, M., Xia, B., Pan, M., Xu, Z.Q., 2005b. Shear wave propertiesand Poisson's ratios of ultrahigh-pressure metamorphic rocks from the Dabie–Suluorogenic belt, China: implications for the crustal composition. J. Geophys. Res. 110.doi:10.1029/2004JB003435.

Widiyantoro, S., Kennett, B.L.N., van des Hilst, R.D., 1999. Seismic tomography with Pand S data reveals lateral variations in the rigidity of deep slabs. Earth Planet. Sci.Lett. 173, 91–100.

Xu, P.F., Liu, F.T., Wang, Q.C., Cong, B.L., Chen, H., 2001. Slab-like high velocity anomaly inthe upper most mantle beneath the Dabie–Sulu orogen. Geophys. Res. Lett. 28,1847–1850.

Xu, Z.Q., Zhang, Z.M., Liu, F.L., Yang, J.S., Li, H.B., Yang, T.N., Qiu, H.J., Li, T.F., Meng, F.C.,Cheng, S.Z., Tang, Z.M., Chen, F.Y., 2003. Exhumation structure and mechanism ofthe Sulu ultrahigh-pressure metamorphic belt, central China. Acta Geol. Sin. 77,433–450.

Xu, Z.Q., Wang, Q., Ji, S.C., Chen, J., Zeng, L.S., Yang, J.S., Chen, F.Y., Liang, F.H., Wenk, H.R.,2006. Petrofabrics and seismic properties of garnet peridotite from the UHP Suluterrane (China): implications for olivine deformation mechanism in a cold and drysubducting continental slab. Tectonophysics 421, 111–127.

Xu, Z.Q., Wang, Q., Tang, Z.M., Chen, F.Y., 2009. Fabric kinematics of ultrahigh-pressuremetamorphic rocks fromthemainborehole of theChineseContinental ScientificDrillingProject: implications for continental subduction and exhumation. Tectonophysics 475,233–248 (this issue).

Zhang, Z.M., Xu, Z.Q., Liu, F.L., You, Z.D., Meng, F.C., Li, T.F., 2003. Petrology andpetrochemistry of UHP metamorphic rocks from the Sulu orogenic belt, easterncentral China. Acta Geol. Sin. 77, 478–491.

Zhang, B.H., Liu, Y.S., Zong, K.Q., Gao, S., 2006. Geochemical behavior of trace elementsduring retrograde metamorphism of eclogites: study on the retrograde eclogitesfrom the CCSD main hole. Acta Petrol. Sin. 22, 1833–1844.

Zhang, R.Y., Liou, J.G., Cong, B.L., 1994. Petrogenesis of garnet-bearing ultramafic rocksand associated eclogites in the Su-Lu ultrahigh-P metamorphic terrane, easternChina. J. Metamorph. Geol. 12, 169–186.

Zhang, R.Y., Liou, J.G., Cong, B.L., 1995. Talc-, magnesite-, and Ti-clinohumite bearingultrahigh-pressure meta-mafic and ultramafic complex in the Dabie Mountains,China. J. Petrol. 36, 1011–1037.

Zhang, Z.M., Xu, Z.Q., Liu, F.L., You, Z.D., Shen, K., Yang, J.S., Li, T.F., Chen, S.Z., 2004.Geochemistry of eclogites from the main hole (100~2050 m) of the ChineseContinental Scientific Drilling Project. Acta Petrol. Sin. 20, 27–42.

Zhao, Z.F., Zheng, Y.F., Chen, B., Wu, Y.B., 2005. A geochemical study of element and Sr–Nd isotopes for eclogite and gneiss form CCSD core 734 to 933 m. Acta Petrol. Sin.21, 325–338.

Zheng, Y.F., Fu, B., Li, Y.L., Xiao, Y.L., Li, S.G., 1998. Oxygen and hydrogen isotopegeochemistry of ultrahigh-pressure eclogites from the Dabie Mountains and theSulu terrane. Earth Planet. Sci. Lett. 155, 113–129.