Journal of Asian Earth Sciences 117 (2016) 1–12

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Journal of Asian Earth Sciences

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Titanite-bearing omphacitite from the Jade Tract, Myanmar:Interpretation from mineral and trace element compositions

http://dx.doi.org/10.1016/j.jseaes.2015.12.0111367-9120/� 2015 Elsevier Ltd. All rights reserved.

⇑ Corresponding author.E-mail addresses: shigunaghai@263.net.cn, shigh@cugb.edu.cn (G.-H. Shi).

Yi-Nok Ng a, Guang-Hai Shi a,⇑, M. Santosh a,b

a State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, ChinabCentre for Tectonics, Resources and Exploration, Department of Earth Sciences, University of Adelaide, Adelaide 5005, Australia

a r t i c l e i n f o a b s t r a c t

Article history:Received 6 July 2015Received in revised form 4 December 2015Accepted 9 December 2015Available online 9 December 2015

Keywords:Myanmar jadeititeOmphacititeTitaniteIlmeniteReplacement

Jadeitite is a rare rock composed predominantly of jadeite, which typically occurs in association with tec-tonic blocks of high-pressure/low-temperature metabasaltic rocks such as eclogite or blueschist, often asa matrix in exhumed serpentinite mélanges. Omphacitite are far less common occurring together withjadeitite, such as those in the ‘‘Jade Tract” of Hpakan area in Myanmar. The omphacitite in this localityis mostly composed of omphacite and jadeite, with minor titanite, ilmenite, epidote and zircon. Thejadeite formed after omphacite shows a lower Jd-content than that in the neighboring white jadeitite.The omphacite shows significant variation in Jd-content and is associated with aegirine augite. Both rocksshow relatively linear and upslope pattern from LREE to HREE, and a slight enrichment of Ba, Th, U, Zr andHf relative to chondrites, in the absence of Eu-anomaly. The titanite occurs in two groups: one as discreteislands replacing ilmenite, and the other as precipitation within jadeite veinlet. Titanite grains show con-vex patterns from LREE to HREE, and depletion of Sr, Zr and Hf with no Eu-anomaly. Chemical character-istics of the titanite and ilmenite alteration around titanite suggest that the omphacitite is of secondaryorigin, likely derived from pyroxenite through the replacement of pyroxene by jadeite. Based on the pre-vious findings of jadeitization of chromitite, serpentine, and rodingite, it is suggested that protoliths suchas plagiogranite or gabbro trapped within serpentinite mélange might have undergone jadeitization.

� 2015 Elsevier Ltd. All rights reserved.

1. Introduction

Jadeitite is a rare rock that is composed mainly of jadeite, withminor amounts of omphacite, diopside, kosmochlor, and otherclinopyroxene components. It is usually found in serpentinitemélange formed at high-pressure low-temperature (HP/LT) condi-tions and records fluid transport and water–rock reaction in thesubduction factory (e.g., Harlow and Olds, 1987; Shi et al., 2003,2005a; Harlow et al., 2014, 2015; Sorensen et al., 2006; Tsujimoriand Harlow, 2012). Jadeitites also record the transport of largeion lithophile elements, such as Li, Ba, Sr, and Pb, as well as ele-ments generally considered more refractory, such as U, Th, Zr,and Hf (e.g., Shi et al., 2008a,b, 2009, 2010; Simons et al., 2010;Yui et al., 2013). The rock finds utility as a popular gemstone andas carved materials, from antiquity in the form of tools, adorn-ments, and symbols of prestige to contemporary jewelry (e.g.,Harlow et al., 2015; Lucas et al., 2015).

The petrogenesis of jadeitite has been a subject of debate. Earlytheories proposed a metasomatic replacement process of tectonic

blocks within serpentinite (Coleman, 1961; Dobretsov, 1963) orthrough pressure solution and re-deposition in fractures (Harlow,1994). In later studies, jadeitites were interpreted as the result ofvein precipitation from fluid flowing through serpentinite (Shiet al., 2000, 2003, 2005b, 2012; Harlow and Sorensen, 2005;Sorensen et al., 2006; Harlow et al., 2007, 2012a, 2014, 2015;Cárdenas-Párraga et al., 2012). In a recent review by Tsujimoriand Harlow (2012), the global occurrence of jadeitite was catego-rized into two types: fluid precipitates from a Na–Al–Si-rich fluid(P-type), and metasomatic replacement of plagiogranite, metagab-bro, etc. (R-type) by a similar fluid. This classification establishes alinkage among jadeitite and its associated rocks, and their petroge-netic relationship is particularly important in evaluating the tecton-ics of the associated HP–LT rocks. Among nineteen or more jadeititelocalities reportedworldwide, themost important andwell-studiedones include those in Myanmar (e.g., Chhibber, 1934a,b; Harlowand Olds, 1987; Harlow and Sorensen, 2001, 2005; Shi et al.,2001, 2003, 2005a), Guatemala (e.g., Harlow et al., 2004, 2006;Tsujimori et al., 2005; Flores et al., 2013), Japan (e.g., Kobayashiet al., 1986; Tsujimori, 2002) and Cuba (e.g., García-Casco et al.,2009; Cárdenas-Párraga et al., 2012). The other localities aredescribed in recent reviews by Shi et al. (2012), Tsujimori and

2 Y.-N. Ng et al. / Journal of Asian Earth Sciences 117 (2016) 1–12

Harlow (2012) and Harlow et al. (2014, 2015). Among these occur-rences, attention has been focused on jadeitite, and associated rockssuch as kosmochlor aggregates, jadeitized rodingite, and albiterocks (Ouyang, 1984; Wang et al., 2013). Another rare and lessinvestigated association is omphacitite (Yi et al., 2006), which iscomposed of more complex mineral components.

Fig. 1. (a) Simplified tectonic map of northern Myanmar (modified after Morley, 2004), a1983), jadeitite outcrops have been listed previously by him.

Recently omphacitites bearing titanite were found in theHpakan Jade Mine Tract in Myanmar (Fig. 1). In this study wefocus on these omphacitites, and report the occurrence, textureand chemical composition of titanite and titanite-rimmed ilmenitein the omphacitites in an attempt to evaluate the origin ofthis rock.

nd (b) geological sketch map of the Myanmar jadeitite area (modified after Bender,

Y.-N. Ng et al. / Journal of Asian Earth Sciences 117 (2016) 1–12 3

2. Geological setting and petrography

The jadeite uplift (Fig. 1) containing the Myanmar jadeitedeposit and high-pressure rocks in Hpakan area of Kachin Statestraddles the northwestern parts of the Sagaing fault belt(Bertrand et al., 1999; Bertrand and Rangin, 2003). The regionforms part of the Indo-Burma Range (Mitchell et al., 2004), theeastern boundary of which is generally defined by a discontinuouszone of serpentinite mélange. The Sagaing Fault is a major right-lateral strike-slip fault that roughly runs north–south and contin-ues into the Andaman Sea. It is argued that the uplift, theTagaung-Myitkyina Belt and the Indo-Burma Range were once acontiguous belt, which has been separated by the Sagaing Fault,leaving the jadeite uplift straddling along the fault between theBelt and the Range (Shi et al., 2014). Previous studies proposed thatthis belt was once in an intra-oceanic subduction setting, associ-ated with the Woyla Intra-Oceanic Arc or the Incertus Arc duringthe Mesozoic (e.g., Shi et al., 2009, 2014). However, there is stillsome controversy over the timing of the jadeitization event(s).Shi et al. (2008a,b) reported three zircon U–Pb ages of circa 163,147 and 122 Ma, which represent three episodes (magmatic and/or hydrothermal). Yui et al. (2012) and Yui (2014), however, arguedthat the Jurassic age is inherited from a protolith, with younger ageof circa 77 Ma is recorded in their zircon rims. Either way, collisionbetween the Greater Indian Plate and Eurasia (circa 55–50 Ma)occurred after the jadeitite formation.

The Jade Tract is characterized by serpentinized peridotiteand dunite bodies sandwiched by phengite-bearing blueschist,garnet-bearing amphibolite, diopside-bearing marble, and quart-zite (Chhibber, 1934a,b; Shi et al., 2001). Within the serpentinitebodies, some massive jadeitite veins (termed ‘‘dikes” byChhibber, 1934b) or blocks of more than 10 m wide occur(Harlow et al., 2014). The jadeitites are often surrounded byamphibole-rich margins of up to 1 m thickness, based on whichsome workers termed these rocks as amphibolite, comprisingsix types of amphiboles: nyböite, eckermannite, katophorite,glaucophane, richterite, and winchite (Bleeck, 1907; Chhibber,1934b; Shi et al., 2003; Nyunt et al., 2009; Harlow et al.,2014). Other related rocks such as kosmochlor occur typicallyin the proximity of chromite (e.g., Harlow and Olds, 1987; Shiet al., 2005a). Cr-omphacitite with Ba-minerals (Shi et al.,2010) and jadeitized rodingites (e.g., Wang et al., 2012) alsooccur. Veins from later stage(s) contain albite (Wang et al.,2013), zeolite, and pectolite (e.g., Shi et al., 2012). Other rareminerals such as trinephline and fabriesite (Ferraris et al.,2014) have also been reported in the Jade Tract. Small blocksof omphacitite ranging in color from dark green to black typi-cally occur as boulders (Fig. 2c in Shi et al., 2012) distributedaround the Hpakan city (Fig. 1).

The omphacitite sample (locally called ‘‘black jade” – black inreflect light, but green in transmitted light) was collected nearHpakan in the Jade Tract. Four samples of omphacitite for thisinvestigation were purchased from a local miner who excavatedthese from the Uru boulder conglomerate west of Hpakan town(Fig. 1). These are roughly round in shape, compact, dark greenin color, and fine grained (similar to the sample in Fig. 2c in Shiet al., 2012). Thin sections were prepared for petrographic studyand for microprobe analysis.

The major minerals in the samples investigated are omphacite(>85 vol.% of the rock) and jadeite (�10 vol.%), with minor amountsof titanite, zircon, ilmenite, epidote and apatite. The jadeite veinshows sharp boundary with the omphacite matrix (Fig. 2a).Omphacite occurs as prismatic, subhedral or granular crystals upto 1 mm in size. In the jadeite domain, omphacite occurs asisolated grains with irregular shapes (Fig. 2b), and some with

indistinct prismatic shapes are cut by jadeite, suggesting replace-ment of omphacite by jadeite. Jadeite occurs as veins infiltratingand crosscutting omphacite matrix. In a wider vein (Fig. 2a), alongthe omphacite matrix is a thin layer of microcrystalline jadeite,whereas larger, needle-like jadeite crystals radiate in fan spraysperpendicular to the thin layer (Fig. 2c). Two-phase (liquid–gas)inclusions, similar to those described by Shi et al. (2005b), arefound in the larger jadeite grains. In smaller veins, only microcrys-talline jadeites occur.

The titanite can be categorized into two groups. Group-Atitanite, which ranges in size from �50 to 500 lm, is foundwithin omphacite as isolated grains or as local clusters (Fig. 2b).Occasionally titanite carries relict ilmenite (Fig. 2e), indicating thattitanite is a replacement at the expense of ilmenite. Group-Btitanite, which also ranges from �50 to 500 lm in size, is foundin the infiltrating jadeite veins (Fig. 2d). It lacks relict ilmeniteinclusion (Fig. 2f), which suggests local precipitation rather thanreplacement.

Among the accessory minerals, zircon is usually less than100 lm long and is found in omphacite matrix. Epidote occurs onlyin omphacite matrix, whereas apatite is found only in small jadeiteveins.

3. Analytical methods

Back-Scattered Electron (BSE) images and EPMA (Electron ProbeMicro-Analysis) data were obtained at the Geological Lab Center,China University of Geosciences, Beijing, using a JXA-8100 ElectronMicroprobe Analyzer operated at 15 kV accelerating voltage, 20 nAbeam current and <10 lm spot size. The EPMA standards includethe following minerals: andradite for Si and Ca, rutile for Ti, corun-dum for Al, hematite for Fe, eskolaite for Cr, rhodonite for Mn, bun-senite for Ni, periclase for Mg, albite for Na, K-feldspar for K, andbarite for Ba. Mineral formulae of titanite were recalculated byMINPET 2.02 software (Richard, 1988–1997) on basis of 3 cationsand 5 oxygens. Formulae of clinopyroxene were recalculated byPX-NOM, a spreadsheet program created by Sturm (2002), withFe2+/Fe3+ estimation using the equation of F = 12 (1 � 4/S) fromDroop (1987) (in F = 2X (1 � T/S), following the method ofOkamoto and Maruyama (2004), where T represents the idealnumber of cations per formula unit and S describes the observedcation total per X oxygens assuming all iron is Fe2+).

Trace element compositions were analyzed on polished thicksections (�50 lm thick) by in-situ LA-ICP-MS (Laser AblationInductively-Coupled Mass Spectrometry) at the Geological LabCenter, China University of Geosciences, Beijing. The laser ablationsystem is a New Wave UP193SS, which is equipped with a 193 nmArF excimer laser. An Agilent 7500A ICP-MS instrument was usedto acquire ion-signal intensities. Laser ablation spots were set tobe 35 lm in diameter, with the laser energy of 60 mJ, a frequencyof 5 Hz and e beam energy of 12 J/cm2.

Standard materials for off-line selection and integration ofbackground signals, and time-drift correction and quantitativecalibration were performed using workstation data-processingprogram included with the 7500A operating system. The NISTSRM 610 was used as a reference material for calibration, and NISTSRM 612 as a quality control material (QCM). The concentration ofvarious elements (V, Cr, Mn, Co, Ni, Rb, Sr, Y, Zr, Nb, Cs, Ba, La, Ce,Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, Th, U) wereacquired using Ca as internal standard. Analytical uncertaintiesfor most elements are less than 10%, except for Cr, Ta and Cd whichare less than 15%. To ensure highest reliability of data, the time-resolved spectrum of every element for each sample was carefullyexamined. Data for which fluctuations in the spectrum wereobserved were discarded.

Fig. 2. Photomicrograph and BSE images illustrating petrography of the studied samples: (a) A wide jadeite vein against the omphacite aggregate (crossed-polars). (b)Omphacite aggregate with titanite (Group-A) crosscut by jadeite veins. (c) Jadeite crystals, microcrystalline jadeite layer in a wider jadeite vein (crossed-polars). (d) Group-Btitanite in jadeite vein. (e) BSE image of a Group-A titanite containing relict ilmenite. (f) BSE images of the framed area of (d); Ttn(A) and Ttn(B) refer to Group-A and -Btitanite, respectively.

4 Y.-N. Ng et al. / Journal of Asian Earth Sciences 117 (2016) 1–12

4. Mineral chemistry

EPMA spot analyses of jadeite veins (‘‘Jd veins” in Table 1) showJd-content varying from 54.0 to 84.2 mol%, Ae-content from 11.6 to27.0 mol% and Quad-content from 2.2 to 19.9 mol%. Most of theanalyses confirm with the Jadeite Zone of Morimoto (1988)(Fig. 3) with the exception of spot no. 1 in sample YX-1 (a spotclose to jadeite vein border) which is compositionally omphacite.Omphacite (‘‘Omp matrix” in Table 1) shows Jd-content between21.3 and 55.6 mol%, Ae-content from 0 to 38.9 mol% and Quad-content from 20.3 to 46.1 mol.%. Some aegirine-augite (no. 11 ofYX-2, no. 16 and 23 of YN-1) is also observed within omphacite.Since the thin sections are made on jadeite infiltrated area, theabove values may suggest overlapped compositions and conflicting‘‘forbidden zones” for clinopyroxenes as suggested by Green et al.(2007).

The LA-ICP-MS spot measurements on a large jadeite crystal(from the center of a thick jadeite vein) and from the central partof an omphacite aggregate show similar REE and trace elements(Table 3). In trace element variation diagrams (Fig. 4a), both showlinear increase from LREE to HREE. In a spidergram plot of trace

elements (Fig. 4c), jadeite and omphacite display a general upslopepattern from left-hand-side (i.e. elements of lower compatibility)toward right-hand-side (i.e. elements of higher compatibility),with enrichment of U, Zr and Hf. Eu-anomaly is mild positive(Eu/Eu⁄ = 1.04 for jadeite, 1.16 for omphacite).

Despite the textural differences, the chemical composition oftitanite (CaO, TiO2, and SiO2) does not display any significant varia-tion between the two groups (Table 2). The Al2O3 content is low(max. XAl [=Al/(Ti + Al)] = 0.059), showing that Ti is only slightlyreplaced by Al. Althoughmeasurement of F is lacking due to analyt-ical limitation, the low Al-content suggests a low (F, OH)-contentsince their substitutions are paired by [Ti + O]M [Al + (F, OH)](e.g., Enami et al., 1993). The total content of trace elements intitanite is low (Table 3), with a convex pattern characterized bydepletion in LREE, a somewhat flat-top in the MREE, and a slightdrop in HREE (Fig. 4b). No pronounced Eu-anomaly is observed;however a negative Gd-anomaly occurs, the cause of which remainsunknown. Elements of lower compatibility are more depleted, andelements of higher compatibility are flat-topped; depletions of Th,La, Sr, Zr and Hf are observed, whereas enrichment of other ele-ments (e.g., Ba, Nb, and Nd) are not strong (Fig. 4d).

Table 1Chemical compositions of clinopyroxenes in omphacitite from the Jade Mine Tract, Myanmar, as determined by EPMA.

Sample YX-1 YX-2 YN-1 YN-3

Point Vein Mx Mx Vein Mx Mx Mx Mx Mx Mx Vein Mx Vein Mx Mx Vein Vein Mx Vein Vein Mx Mx Mx VeinNo. 1 2 3 4 5 6 7 8 9 10 11 21 22 1 2 3 4 11 12 13 14 16 23 13

SiO2 56.80 55.62 55.49 57.62 55.88 55.56 57.13 55.33 55.99 56.24 56.52 55.48 57.69 56.47 57.68 56.38 56.45 54.54 56.35 57.55 54.80 53.20 53.24 54.61TiO2 0.43 0.29 0.17 0.28 n.d. 0.26 0.33 0.26 0.22 0.04 0.14 0.11 0.61 0.10 n.d. 0.72 1.25 0.27 1.32 0.81 0.10 0.06 0.11 1.07Al2O3 13.64 10.35 10.67 18.23 9.36 9.56 10.11 10.60 9.60 7.40 13.10 8.52 20.85 11.43 11.91 15.66 15.41 5.97 15.90 20.54 8.37 7.59 7.52 15.91Fe2O3 7.75 5.21 5.64 7.05 11.82 10.95 9.23 10.80 4.67 9.30 8.92 9.21 3.73 2.45 0.00 7.27 6.00 9.17 6.28 4.78 7.53 13.46 12.90 6.78FeO 0.00 2.42 3.62 0.31 0.00 1.27 0.00 0.00 2.88 0.50 0.00 0.00 0.00 0.00 2.66 0.00 0.51 0.00 0.00 0.00 0.00 0.60 0.00 0.00MnO 0.10 n.d. n.d. 0.08 0.15 0.14 0.26 0.45 0.13 0.40 0.12 0.15 0.11 0.02 0.18 n.d. 0.11 0.30 0.19 0.10 0.24 0.34 0.36 0.12MgO 3.76 5.75 5.13 0.62 4.20 4.82 4.85 4.23 6.28 6.57 3.47 7.54 0.10 8.18 8.16 2.53 2.61 8.83 2.40 0.19 8.22 4.87 5.21 2.18CaO 5.93 10.30 9.37 2.55 7.50 6.91 7.38 7.01 9.79 9.40 5.19 9.51 1.11 11.74 11.33 5.19 4.71 13.68 3.05 1.38 11.69 12.35 11.63 4.11Na2O 11.81 8.82 9.00 13.81 11.00 10.29 11.14 10.67 8.70 9.19 11.86 9.79 15.47 8.53 7.99 12.66 12.36 7.17 14.28 15.55 8.08 8.24 8.74 14.22K2O n.d. n.d. n.d. 0.11 n.d. 0.03 n.d. n.d. 0.02 n.d. n.d. n.d. 0.01 n.d. n.d. 0.02 n.d. 0.03 n.d. n.d. 0.08 0.01 n.d. 0.08Cr2O3 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.02 n.d. 0.05 0.14 n.d. 0.15 n.d.Total 100.22 98.76 99.09 100.66 99.91 99.79 100.43 99.35 98.28 99.04 99.32 100.31 99.68 98.92 99.91 100.43 99.41 99.98 99.77 100.95 99.25 100.72 99.86 99.08

Si 1.98 2.00 2.00 1.99 1.99 1.99 2.01 1.98 2.02 2.02 1.99 1.95 1.97 1.99 2.02 1.96 1.98 1.96 1.94 1.94 1.96 1.92 1.93 1.90Ti 0.01 0.01 0.01 0.01 – 0.01 0.01 0.01 0.01 0.00 0.00 0.00 0.02 0.00 – 0.02 0.03 0.01 0.03 0.02 0.00 0.00 0.00 0.03Al (T) 0.02 – 0.00 0.01 0.01 0.01 – 0.02 – – 0.01 0.05 0.03 0.01 – 0.04 0.02 0.04 0.06 0.06 0.04 0.08 0.07 0.07Al (M1) 0.54 0.44 0.45 0.73 0.38 0.39 0.42 0.42 0.41 0.31 0.54 0.30 0.80 0.47 0.49 0.61 0.62 0.21 0.59 0.76 0.31 0.25 0.25 0.58Fe3+ (M1) 0.23 0.16 0.17 0.20 0.36 0.33 0.28 0.32 0.14 0.28 0.27 0.28 0.11 0.07 – 0.22 0.18 0.28 0.19 0.14 0.23 0.41 0.41 0.21Fe2+ – 0.07 0.11 0.01 0.00 0.04 – – 0.08 0.02 – – – – 0.08 – 0.02 – – – – 0.02 – –Mn 0.00 – – 0.00 0.01 0.00 0.01 0.01 0.00 0.01 0.00 0.00 0.00 0.00 0.01 – 0.00 0.01 0.01 0.00 0.01 0.01 0.01 0.00Mg 0.20 0.31 0.27 0.03 0.22 0.26 0.25 0.23 0.34 0.35 0.18 0.40 0.01 0.43 0.43 0.13 0.14 0.47 0.12 0.01 0.44 0.26 0.28 0.11Ca 0.22 0.40 0.36 0.09 0.29 0.26 0.28 0.27 0.38 0.36 0.20 0.36 0.04 0.45 0.43 0.19 0.18 0.53 0.11 0.05 0.45 0.48 0.44 0.14Na 0.80 0.61 0.63 0.92 0.76 0.71 0.76 0.74 0.61 0.64 0.81 0.67 1.02 0.58 0.54 0.85 0.84 0.50 0.96 1.02 0.56 0.57 0.61 0.96K – – – 0.0 0.00 0.00 – – 0.00 – – – – – – 0.00 – 0.00 – – 0.00 – – 0.00Cr – – – – 0.00 – – – – – – – – – – – – 0.00 0.00 0.00 – 0.00 –Total 4.00 4.00 4.00 4.00 4.00 4.00 4.01 4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00

Jd 55.63 45.14 45.60 72.82 38.20 38.97 44.47 42.45 44.78 33.70 54.07 33.16 86.22 49.45 53.87 61.68 65.12 21.27 67.58 82.25 32.09 22.69 23.71 63.87Ae 23.66 16.11 17.15 20.34 36.70 32.84 29.58 32.51 15.47 30.01 27.00 30.76 11.60 7.73 0.00 22.35 18.53 28.71 21.42 14.91 23.75 37.68 38.91 23.95Quad 20.71 38.75 37.25 6.84 25.10 28.18 25.95 25.03 39.75 36.29 18.92 36.08 2.18 42.82 46.13 15.97 16.35 50.02 11.00 2.84 44.16 39.63 37.38 12.19

Minerala Omp Omp Omp Jd Omp Omp Omp Omp Omp Omp Jd Omp Jd Omp Omp Jd Jd Ae-Aug Jd Jd Omp Ae-Aug Ae-Aug Jd

a Nomenclature follows Morimoto (1988). Note: n.d. = not detected, Mx: matrix. Formulae calculated on the basis of 6 Oxygen.

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Fig. 4. (a) Chondrite-normalized REE patterns of the omphacite and jadeite. (b) Chondriteand jadeite. (d) Spidergram of trace elements of titanite. Chondrite data refer to Sun an

Fig. 3. Compositional plot for pyroxenes after Morimoto (1988).

6 Y.-N. Ng et al. / Journal of Asian Earth Sciences 117 (2016) 1–12

Ilmenite occurs as patches in titanite (Fig. 2e). Due to the smallsize, only one EPMA spot measurement with reliable accuracy isacquired, and the results showMn-rich nature (6.23 wt.%; Table 4).

5. Discussion and conclusions

5.1. Characteristics of trace elements in titanite and omphacite

Titanite in our study shows Zr/Hf = 14 –37, Nb/Ta = 5 –14 andTh/U = 0.1 –1.6 (Fig. 5), which is different from the values inmagmatic titanite which has Zr/Hf (27 –66), Nb/Ta (8 –71) andTh/U (2–8) by Marks et al. (2008). Titanite from both plutonic rocks(Marks et al., 2008) and alkaline intrusions (Vuorinen andHålenius, 2005) have patterns of enriched LREE and depletedHREE (i.e. a downslope pattern), which are different from thefeatures of titanite in this study. Also, the Ta-, Nb-, Y- and/orZr-enriched titanites in pegmatite, carbonatitic rock, syenite andAe-enriching jadeitic pyroxene described by Cerny et al. (1995),Chakhmouradian et al. (2003), Liferovich and Mitchell (2005) andHarlow et al. (2012b) are in contrast to the features observed inthis study. The chemical features of titanite in our samples areremarkably similar to those of metamorphic titanites (in bothREE and incompatible elements) such as those reported by Gao

-normalized REE patterns of titanite. (c) Spidergram of trace elements of omphacited McDonough (1989).

Table 2Chemical compositions of titanite in omphacitite from the Jade Mine Tract, Myanmar as determined by EPMA.

YX-1 YX-2 YN-1 YN-3

No. 1 2 3 4 5 6 7 11 12 13 21 22 23 1 2 11 12 13 14 15 16 21 22 23 24 26 11 14 15 18 21 11

SiO2 30.07 30.59 30.11 30.50 30.60 30.62 30.50 31.54 31.78 32.17 30.24 30.29 30.23 30.27 30.00 31.07 31.81 31.38 31.65 30.98 32.27 30.06 30.14 30.53 30.56 30.68 30.60 30.89 30.29 30.63 30.96 30.78

TiO2 40.23 40.26 40.73 40.31 39.73 40.49 40.44 39.16 39.08 39.76 41.49 40.41 40.91 40.54 40.96 39.26 38.84 40.33 39.01 38.75 39.09 41.50 41.94 41.19 40.72 40.71 39.96 39.78 39.54 39.96 40.90 40.10

Al2O3 0.93 0.85 0.83 0.64 0.65 0.60 0.53 1.02 0.71 0.65 0.63 0.97 0.83 0.63 0.45 0.98 0.99 0.75 1.18 1.34 1.41 0.73 0.47 0.99 1.05 0.91 1.50 1.53 1.57 1.15 1.06 1.01

FeOT 0.57 n.d. 0.37 0.40 0.57 0.46 0.12 0.52 0.45 0.39 0.32 0.16 n.d. 0.30 n.d. 0.60 0.53 0.20 0.36 0.14 0.31 0.05 0.07 0.19 0.14 0.24 0.25 0.41 0.35 0.21 0.32 0.40

MnO n.d. 0.36 n.d. n.d. n.d. n.d. n.d. n.d. 0.28 0.16 0.05 n.d. 0.01 0.22 n.d. n.d. n.d. 0.22 n.d. n.d. n.d. n.d. n.d. 0.16 n.d. n.d. 0.28 0.04 0.04 0.04 0.10 n.d.

MgO n.d. n.d. n.d. 0.01 n.d. n.d. 0.19 n.d. n.d. n.d. n.d. 0.08 0.08 0.17 n.d. 0.09 n.d. 0.03 0.07 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.08 n.d. n.d. n.d.

CaO 26.78 27.13 26.93 26.59 26.70 26.87 26.57 27.08 26.49 26.90 26.74 27.01 27.07 27.46 26.81 27.25 26.71 26.66 27.36 28.15 27.28 26.52 27.03 27.16 27.01 27.07 27.11 26.94 26.92 27.12 27.48 26.89

Na2O n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.32 0.24 0.08 0.11 n.d. n.d. n.d. n.d. n.d. 0.09 0.09 0.09 0.17 0.17 0.19 0.12 0.18 0.13 0.07 0.19 0.21 0.16 0.16 0.26

Cr2O3 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.06 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.12 n.d. n.d. n.d. 0.22 n.d. n.d. n.d. 0.14 0.14 0.05

P2O5 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.05 n.d. 0.08 n.d. 0.07 0.07

V2O5 0.64 0.38 n.d. 0.44 0.84 n.d. 0.36 n.d. n.d. n.d. n.d. n.d. n.d. 0.83 0.62 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.

Total 99.22 99.57 98.97 98.90 99.09 99.04 98.71 99.32 99.10 100.28 99.56 99.05 99.18 100.41 98.85 99.24 98.88 99.64 99.71 99.44 100.53 99.16 99.87 100.33 99.66 99.96 99.82 99.78 99.08 99.41 101.19 99.56

Si 0.99 1.00 0.99 1.00 1.00 1.01 1.00 1.03 1.04 1.04 0.99 0.99 0.99 0.98 0.99 1.02 1.04 1.02 1.03 1.01 1.04 0.99 0.98 0.99 1.00 1.00 1.00 1.01 0.99 1.00 1.00 1.00

Al 0.04 0.03 0.03 0.03 0.03 0.02 0.02 0.04 0.03 0.03 0.02 0.04 0.03 0.02 0.02 0.04 0.04 0.03 0.05 0.05 0.05 0.03 0.02 0.04 0.04 0.04 0.06 0.06 0.06 0.04 0.04 0.04

Ti 0.99 0.99 1.01 1.00 0.98 1.00 1.00 0.96 0.96 0.97 1.02 1.00 1.01 0.99 1.01 0.97 0.96 0.99 0.95 0.95 0.95 1.02 1.03 1.00 1.00 1.00 0.98 0.97 0.98 0.98 0.99 0.98

Fe2+ 0.02 0.00 0.01 0.01 0.02 0.01 0.00 0.01 0.01 0.01 0.01 0.01 0.00 0.01 0.00 0.02 0.02 0.01 0.01 0.00 0.01 0.00 0.00 0.01 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.01

Mg – – – 0.00 – – 0.01 – – – – 0.00 0.00 0.01 – 0.01 – 0.00 0.00 – – – – – – – – – 0.00 – – –

Mn – 0.01 – – – – – – 0.01 0.01 0.00 – 0.00 0.01 – – – 0.01 – – – – – 0.01 – – 0.01 0.00 0.00 0.00 0.00 –

Na – – – – – – – – 0.02 0.02 0.01 0.01 – – – – – 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.02

Ca 0.94 0.95 0.95 0.94 0.94 0.95 0.94 0.95 0.93 0.93 0.94 0.95 0.95 0.96 0.95 0.96 0.94 0.93 0.95 0.99 0.94 0.93 0.94 0.94 0.94 0.94 0.95 0.94 0.95 0.95 0.95 0.94

Cr – – – – – – – – – – – – 0.00 – – – – – – – – 0.00 – – – 0.01 – – – 0.00 0.00 0.00

Rcats 2.98 2.98 2.99 2.97 2.97 2.98 2.97 2.99 3.00 2.99 2.98 2.99 2.99 2.97 2.97 3.00 2.99 2.98 3.00 3.01 3.00 2.98 2.99 2.99 2.99 2.99 3.00 3.00 3.00 3.00 3.00 3.00

XAl 0.04 0.03 0.03 0.02 0.02 0.02 0.02 0.04 0.03 0.03 0.02 0.04 0.03 0.02 0.02 0.04 0.04 0.03 0.05 0.05 0.05 0.03 0.02 0.04 0.04 0.03 0.06 0.06 0.06 0.04 0.04 0.04

Note: n.d. = not detected. Calculated on basis of 5 Oxygen.

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Table 3Trace element compositions of titanite, jadeite and omphacite in omphacitite from the Jade Mine Tract, Myanmar as determined by LA-ICP-MS.

Sample YX-1(Titanite) YX-2(Titanite) YX-1 YX-1

No.a 3(1) 3(2) 4(1) 4(2) 6 7 22 2(1) 2(2) 12(1) 12(2) 15 21 5 (Omp) 11 (Jd)

V 842.7 479.4 226.6 232.7 219.8 966.1 94.8 25.1 102.3 150.4 33.9 312.8 294.9 99.13 43.41Cr 9.2 2.6 1.5 1.1 4.6 11.9 6.4 10.6 10.7 0.7 4.2 0.7 0.7 2.63 60.20Mn 1689.0 414.5 264.0 251.8 224.9 1379.2 380.0 130.2 178.9 179.8 112.2 204.8 201.6 902.87 371.36Co 2.1 0.3 0.5 0.3 0.4 5.1 3.2 0.5 0.5 0.1 0.1 0.1 0.1 5.82 10.78Ni 25.0 3.4 3.9 4.1 0.9 97.0 28.4 7.8 9.3 1.5 1.6 1.3 1.3 60.93 40.03Rb 3.5 0.5 0.6 0.7 0.3 4.7 1.4 0.6 0.5 0.5 1.1 0.3 0.3 0.19 0.23Sr 890.2 424.2 319.8 139.9 169.7 2074.3 397.0 351.4 344.5 130.2 268.2 277.4 312.7 14.72 5.45Y 7226.3 1012.6 1017.2 1042.9 494.2 9242.8 2945.5 1523.6 1085.6 1091.9 2536.7 629.9 657.7 10.96 9.55Zr 167.7 112.3 97.2 44.9 722.8 516.2 52.5 70.6 103.2 1856.8 26.4 42.0 466.7 57.23 64.35Nb 428.9 108.8 72.7 64.2 64.3 476.4 110.9 81.6 54.1 55.0 138.0 50.2 60.8 0.45 0.41Cs 0.1 0.0 0.1 0.1 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.2 0.0 0.02 0.02Ba 40.1 11.6 14.3 11.5 7.6 95.0 13.5 34.0 28.8 6.6 24.6 42.5 48.5 5.46 4.16La 126.0 9.0 14.9 13.2 14.7 120.5 46.7 57.2 17.4 22.1 95.2 15.3 13.5 0.20 0.13Ce 817.8 71.3 111.1 94.3 105.8 888.5 352.4 449.3 143.5 178.5 737.4 128.6 106.8 0.89 0.46Pr 236.2 20.7 28.7 22.3 24.0 266.0 106.2 112.1 38.4 45.2 174.6 31.8 26.7 0.18 0.10Nd 1767.0 160.6 203.2 143.8 145.5 1937.0 754.8 677.0 250.3 295.0 1072.5 210.8 175.8 1.04 0.55Sm 951.4 101.8 114.9 71.6 64.2 1099.3 423.8 301.3 129.2 138.1 489.9 98.2 83.8 0.50 0.40Eu 384.9 47.0 51.2 29.4 26.0 516.7 184.0 113.6 57.4 55.0 191.3 39.2 35.3 0.23 0.14Gd 1610.8 164.3 169.1 90.1 70.6 1512.2 508.2 242.4 126.1 129.3 445.0 90.0 86.0 0.74 0.42Tb 249.4 33.1 35.0 24.9 16.8 363.2 128.6 65.3 40.3 38.3 112.6 23.1 22.4 0.20 0.16Dy 1668.4 232.1 227.7 191.3 104.9 2230.2 750.5 379.0 261.3 249.6 666.5 146.7 152.1 1.63 1.50Ho 334.3 47.5 45.3 44.0 20.8 459.0 145.5 69.0 52.1 50.3 119.6 28.6 31.1 0.42 0.41Er 868.4 126.3 118.7 121.3 54.0 1126.5 332.3 151.8 124.2 128.8 269.4 72.2 80.8 1.20 1.20Tm 120.6 18.4 17.5 18.1 8.1 153.0 43.1 18.2 16.9 18.2 33.9 10.2 11.9 0.22 0.21Yb 862.5 134.8 120.0 115.1 52.3 1012.1 260.5 94.7 94.2 108.3 185.2 65.0 81.1 1.78 1.74Lu 59.1 11.2 9.9 10.7 5.4 76.1 18.2 6.5 7.5 9.1 12.4 5.8 7.8 0.35 0.24Hf 9.9 7.4 5.2 2.4 19.4 31.5 3.7 3.4 4.5 50.9 1.6 1.4 13.6 1.73 1.90Ta 37.6 10.0 6.7 5.2 4.5 51.1 21.7 6.5 6.3 7.1 17.6 5.5 5.9 0.04 0.04Th 1.0 0.1 0.2 0.1 0.1 1.0 0.4 0.4 0.2 0.2 1.0 0.1 0.2 0.09 0.09U 1.8 0.7 1.0 0.6 0.3 9.1 1.4 0.9 1.3 0.3 0.6 0.6 0.6 0.10 0.06

Zr/Hf 16.9364 15.1334 18.6130 18.8529 37.3540 16.3760 14.0831 20.5320 23.1798 36.5017 16.5912 29.5845 34.2170 33.0809 33.8684Nb/Ta 11.4041 10.8671 10.8921 12.3385 14.2031 9.3213 5.1083 12.6347 8.6252 7.7181 7.8298 9.0906 10.3754 10.7143 9.2325Th/U 0.5519 0.1459 0.1699 0.2460 0.4636 0.1084 0.2867 0.4237 0.1695 0.5452 1.6295 0.2065 0.3419 0.8500 1.5464Lu/Hf 5.9707 1.5054 1.9042 4.4748 0.2801 2.4150 4.8794 1.8983 1.6944 0.1787 7.8239 4.1056 0.5682 0.2023 0.1242Eu/Eu⁄ 0.9506 1.1097 1.1224 1.1188 1.1807 1.2252 1.2123 1.2848 1.3759 1.2576 1.2526 1.2743 1.2725 1.1560 1.0381(Gd/Lu)N 3.3682 1.8183 2.1031 1.0457 1.6098 2.4555 3.4513 4.5878 2.0665 1.7576 4.4212 1.9089 1.3714 0.2613 0.2200

a Sample and No. are same as these in Tables 1 and 3. Eu/Eu⁄ = EuN/p(SmN ⁄ GdN), where N denotes normalization to chondrite values after Sun and McDonough (1989). Unit in ppm.

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Fig. 6. Discrimination plot for the titanites (after Kowallis et al., 1997; Mohammadand Maekawa, 2008). Diamonds are from this investigation, and ‘‘K” stands forKowallis.

Fig. 5. Comparison of ratios of Zr/Hf, Nb/Ta and Th/U of the titanites (Marks fromMarks et al. (2008); Gao (Mag): magmatic titanite from Gao et al. (2012); Gao(Meta): metamorphic titanite from Gao et al. (2012)).

Table 4Chemical compositions of other accessory minerals in omphacitite from the Jade Mine Tract, Myanmar as determined by EPMA.

Sample YX-1 YX-2

No. 12 14 15 18 5 6 7

SiO2 0.95 67.28 n.d. 38.75 n.d. 37.81 37.68Al2O3 0.09 19.32 n.d. 17.93 n.d. 17.10 18.30TiO2 59.40 0.08 0.15 3.18 0.19 6.24 2.16Na2O 0.16 12.24 n.d. 1.55 n.d. 1.10 1.17CaO 1.91 0.08 53.39 32.00 53.85 28.80 31.75FeOT 31.84 0.10 n.d. 4.64 n.d. 4.47 4.51MgO n.d. n.d. n.d. n.d. n.d. 0.38 0.44MnO 6.23 0.11 0.06 n.d. n.d. n.d. 0.26P2O5 n.d. n.d. 43.57 n.d. 43.18 n.d. n.d.Total 100.56 99.23 97.17 98.05 97.22 95.91 96.28

Mineral Ilmenite Albite Apatite Epidote Apatite Epidote Epidote

a n.d. = not detected.

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et al. (2012) (Fig. 4b and d). Furthermore, comparison with theresults in Kowallis et al. (1997) (who distinguished igneous andmetamorphic titanite from Fe- vs. Al-content) and Mohammadand Maekawa (2008) (who utilized the methodology), confirms ametamorphic origin for the titanites of the present study (Fig. 6).

Omphacite and jadeite in this study have depleted LREE andenriched HREE, and the M/HREE concentrations are ten times morethan that of the white/colorless neighbor jadeitite (which is highlyhomogeneous, Jd > 98 vol.%; Shi et al., 2008a,b). When compared tothe Ba-minerals-bearing Cr-omphacitic rock of Shi et al. (2010), theomphacite in this study is not enriched in Ba and Cr. However,

enrichment of Zr and Hf is observed, which is similar to theadjacent jadeitite (Shi et al., 2008a,b), but without a positiveEu-anomaly. In most cases, the Eu-anomalies are related to feld-spar fractionation. In this case, the lack of negative Eu-anomalywould imply that omphacitite (or its protolith) did not experiencefeldspar fractionation. The lack of positive Eu-anomaly would sug-gest that omphacitite was not a replacement product from afeldspar-rich protolith.

5.2. Origin of omphacitite

Studies over the past �20 years have interpreted jadeitite eitheras the direct precipitate from hydrous fluids released in subductionchannel through dewatering into the overlying mantle wedge, oras the fluid-induced metasomatic replacement of oceanic pla-giogranite, graywacke, or metabasite along the channel margin(e.g., Harlow et al., 2015). However, the petrogenesis of jadeitite-related omphacitites are poorly understood (Yi et al., 2006;Shigeno et al., 2012). The possibilities can be considered for theomphacitite occurrence: (1) fluid precipitation (i.e., no protolith);(2) jadeitite as a protolith was metasomatically transformed intoomphacitite; and (3) another precursor rock (other than jadeitite)was transformed into omphacitite. The occurrence of titanite andits mineral chemistry suggest derivation from another precursorrock (other than jadeitite) that was transformed into omphacitite.

Petrological observations preclude the formation of omphacititethrough direct precipitation from fluids. Formation of titanite canoccur during metamorphism (closed system), metasomatism(open system), or by direct precipitation, whereas the occurrence

10 Y.-N. Ng et al. / Journal of Asian Earth Sciences 117 (2016) 1–12

of ilmenite is commonly related to upper mantle conditions. It ispossible that the assemblage ilmenite ± titanite is produced byfluid precipitation and/or metasomatism (e.g., Ionov et al., 1999;Putnis and Austrheim, 2010 and references therein). The occur-rence of titanite-rimmed ilmenite represents at least one stage ofphase alteration, which in turn implies at least one stage ofreplacement for omphacitite formation, excluding direct fluidprecipitation.

It is also unlikely that the jadeitite served as protolith of theomphacitite. The occurrence of jadeite as a later product relativeto omphacite clearly excludes the possibility of a jadeitite protolith.In addition, no major occurrence of titanite has been reported inhomogeneous jadeitites from Myanmar. The Ti-content is low inserpentinite, and Ti-mobility is suggested to be low in metasomaticfluid because of its extremely low solubility in H2O (Tropper andManning, 2005). If nucleation of titanite (Group-B) occurred, itwould be a local phenomenon compared to thewide-spread jadeiti-zation. In addition, albitization is a significant post-jadeitizationevent in Myanmar (Wang et al., 2013). As both jadeitization andalbitization require a Na–Al–Si fluid, if extensive jadeitite-to-omphacitite transformation occurred, an additional Ca–Mg/Fe-rich fluid would be required, which is in conflict with the fluidsassociated with these two processes.

Several lines of evidence lead to the suggestion of another pre-cursor rock (other than jadeitite) for the omphacitite, and the pre-cursor rock is more likely a mafic, pyroxene-bearing rock. Someomphacites with residual diopside core from the Myanmar Tract(e.g., Shi et al., 2012; Wang et al., 2013) clearly show that theomphacite was replaced at the expense of pre-existing diopside.As omphacite is the intermediate member in jadeite–omphacite–diopside or jadeite–aegirine–diopside systems, and petrographicobservations show that jadeite formed earlier than its neighboromphacite in omphacite-bearing rocks such as jadeitized rodingite(Wang et al., 2012), the potential precursor rock for the omphaci-tite in the present case is inferred to be diopside-bearing rocks.

It is known that diopside is a common mineral constituent inmafic rocks within serpentinite mélange (e.g., Tsujimori, 1997;Miyazoe et al., 2009; Marchesi et al., 2013). Among the mafic rocksin the mélange – such as gabbro, blueschist, eclogite, or pyroxenite,ilmenite occurs either in (meta-) gabbro (e.g., amphibolite faciesmetagabbro; Liou et al., 2009; Ding et al., 2013), (meta-) basalt,(meta-) rodingite (e.g., Mohammad and Maekawa, 2008), pyroxen-ite (Zhang et al., 2009) or other rocks. However, the known P–Tconditions for formation of the jadeitite (e.g., Shi et al., 2012)exclude metabasites in eclogite facies, and the absence of garnetin this study does not support garnet-bearing rodingite (Wanget al., 2012) as protolith. Thus, the potential candidates for the pro-toliths of the omphacitite are pyroxenite and gabbro.

In titanite, the lack of Eu-anomaly suggests a pyroxene-dominated protolith which has nil or very minor plagioclase. Inthe REE patterns of titanite, those in pyroxenite (Marks et al.,2008) do not show any Eu-anomaly, whereas those associated withintermediate to acidic (meta-) volcanic, feldspar-rich rocks (Storeyet al., 2007) andmetagranite (Gao et al., 2012) showprominent neg-ative Eu-anomaly. These features suggest a fractionation mecha-nism of Eu between titanite and surrounding minerals. It has alsobeen shown (Gao et al., 2012) that metamorphism would weakenthe negative Eu-anomaly. Titanite reported here resembles that ofmetamorphic titanite (Gao et al., 2012), but has no Eu-anomaly.As most Fe in omphacite is Fe3+ (Table 1), the lack of Eu-anomalyin our samples is not caused by low oxygen fugacity(e.g., Sverjensky, 1984). This in turn implies that the protolith ofomphacitite has no or very minor feldspar. In addition, the jadeiteand omphacite in this study contain higher content of Ti (max.TiO2 = 1.25 wt.%) than those in other jadeite and omphacite (mostly<0.3 wt.%) in jadeitite, or even in the jadeitized rodingite from

Myanmar (Shi et al., 2012;Wang et al., 2012), leading to the sugges-tion of a Ti-rich basic protolith. For some basic rocks, their bulk TiO2

can reach up to more than 2.8 wt.% (e.g., Shi et al., 2009). Therefore,pyroxenite would be themost possible candidate as the protolith ofthe omphacitite, excluding the possibility of feldspar-bearing gab-bro. The process of omphacitization is then interpreted as thereplacement of pyroxene in pyroxenite by jadeitic material, intoan omphacite–jadeite system. Eventually, the omphacitite withjadeite vein and minor titanite were formed.

5.3. Undiscovered rock types replaced by jadeitic fluids?

Recent studies have revealed extensive jadeitization in theMyanmar Jade Tract. More than thirty mineral species have beenidentified so far in jadeitite and related rocks, including jadeite,chromite, kosmochlor, Cr-jadeite (Ouyang, 1984; Harlow andOlds, 1987; Shi et al., 2008a,b); nyböite, eckermannite, katophorite,glaucophane, richterite, winchite, kaolinite, magnesio-arfvedsonite(Shi et al., 2003; Oberti et al., 2014a,b, 2015); vesuvianite(e.g., Nyunt et al., 2009); Cr-free omphacite, titanite (Yi et al.,2006); celsian, hyalophane, cymrite, Ba-zeolite (Shi et al., 2010);grossular, Mg-omphacite (Wang et al., 2012); albite (e.g., Wanget al., 2013); banalsite, analcime, natrolite, Ca-thomsonite, pecto-lite, uvarovite, allanite, phlogopite, zircon, graphite, quartz, dias-pore, pyrite, and galena (Bleeck, 1908; Mével and Kiénast, 1986;Shi et al., 2012; Tsujimori and Harlow, 2012 and referencestherein). Among these, kosmochlor and Cr-jadeite were reportedas replacement minerals after chromite by jadeitic fluids (Ouyang,1984; Harlow and Olds, 1987; Shi et al., 2005a). Amphiboles likenyböite, eckermannite, katophorite, glaucophane, richterite, win-chite, kaolinite, magnesio-arfvedsonite were found as replacementof serpentinized peridotite by jadeitic fluids (Shi et al., 2003; Obertiet al., 2014a,b, 2015). The same situation occurs in the omphacite,which was formed by jadeitization (e.g., Yi et al., 2006; Shi et al.,2010, 2012; Wang et al., 2012)

Kosmochlor rock, amphibole rock, jadeitized rodingite andomphacitite are the best examples for jadeitization in the Myan-mar Jade Tract, and their protoliths (chromite rock, serpentinite,rodingite, pyroxenite) form part of the serpentine mélange(e.g., Shi et al., 2003, 2005a; Yi et al., 2006; Wang et al., 2012).All these rocks are R-type ones as classified by Tsujimori andHarlow (2012). Since all the rock types of the protoliths are notrepresented by the mélange, it is possible that some of the rocktypes generated by the extensive jadeitization in the Myanmarjadeitite area have not been identified.

Among the typical lithologies found in serpentinite mélanges,basalts and pillow lavas, plagiogranites, gabbros, pyroxenite, andmantle peridotites, together with metamorphic rocks such asmetagabbro, metabasite, rodingite, and listvenite also occur(e.g., Shirdashtzadeh et al., 2010 and references therein). Whenthese igneous and metamorphic rocks are infiltrated by sodic fluidswith high chemical activity under high-P and low-T conditions insubduction zone, several new rock types would form in relation tojadeitite. Among these, jadeitized metabasite (such as metagabbroormetabasalt) or jadeitized plagiogranitewould be highly probable.Therefore, we speculate that these rocks are likely to be identified asthe new jadeitized rock types in the Myanmar jadeitite area infuture studies.

Acknowledgements

We are indebted to W.Y. Cui and R.X. Zhu for their kind supportduring the field work and subsequent research. We thanks J.W. Yinand Q. Mao for their help with EMPA, and L. Su with LA-ICP-MS.The first author would like to thank G.E. Harlow for the warmhospitality and in-depth discussions during a trip to American

Y.-N. Ng et al. / Journal of Asian Earth Sciences 117 (2016) 1–12 11

Museum of Natural History (AMNH). Thoughtful and constructivecomments by G.E. Harlow, K. Okamoto and A. Garcia-Casco dogreat helps for improving this manuscript and are gratefullyappreciated. This research was supported by the NationalNatural Science Foundation of China (No. 41373055), SpecializedResearch Fund for the Doctoral Program of Higher Education (No.20120022110004).

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