Ž .Lithos 57 2001 143–161www.elsevier.nlrlocaterlithos

High-pressure aluminous mafic rocks from the Ronda peridotitemassif, southern Spain: significance of sapphirine- and

corundum-bearing mineral assemblages

Tomoaki Morishita a,b,), Shoji Arai a, Fernando Gervilla c

a Department of Earth Sciences, Kanazawa UniÕersity, Kanazawa, 920-1192, Japanb Research School of Earth Sciences, The Australian National UniÕersity, Canberra ACT 0200, Australia

c Instituto Andaluz de Ciencias de la Tierra, UniÕersidad de Granada-CSIC, 18002 Granada, Spain

Received 19 June 2000; accepted 26 February 2001

Abstract

We firstly present detailed microtextural relationships in sapphirine- and corundum-bearing aluminous mafic rocksalternating with peridotites from the Ronda massif, southern Spain. Garnet and clinopyroxene are the main phases in the

Ž .aluminous mafic rocks. Garnet is partially to completely kelyphitized. Clinopyroxene CPX I has high Al O content in the2 3Ž .core up to 16 wt.% and is partially converted to spherical symplectitic aggregates consisting of lower-Al O clinopyroxene2 3

Ž . Ž .CPX II -5 wt.% and plagioclase. Corundum is associated with spinel and plagioclase. Sapphirine occurs in two differentmineralogical associations, i.e., as elongated lamellae within CPX I and as very fine-grained crystals in plagioclase-richdomain. The sapphirineqplagioclase aggregate suggests the former presence of kyanite as one of reactants. Sapphirine ispartially converted to symplectitic aggregate of spinel and plagioclase. The earliest metamorphic mineral assemblagerecorded in the aluminous mafic rock was garnetqclinopyroxene"kyanite"corundum, i.e., eclogitic mineral assem-blages, at PG1.5 GPa and TG9008C. Many reaction textures were developed during decompression possibly coupled withcooling. The latest P–T conditions recorded in the aluminous mafic rock were at Ps1 GPa and Ts800–9008C. Thisdecompression had possibly followed the compression of plagioclase-rich, low-pressure cumulate or residue. q 2001Published by Elsevier Science B.V.

Keywords: Ronda peridotite massif; Mafic rock; Sapphirine; Corundum; Kyanite; High pressure

1. Introduction

Aluminous mafic rocks including pyroxenite andeclogite—referred to as Amafic rockB hereafter—oc-

Žcur as thin layers within peridotite massifs e.g.,

) Corresponding author. Department of Earth Sciences, Facultyof Science, Kanazawa University, Kakuma-machi, Kanazawa,920-1192, Japan. Tel.: q81-76-264-5723; fax: q81-76-264-5746.

E-mail address: moripta@kenroku.kanazawa-u.ac.jpŽ .T. Morishita .

Kornprobst et al., 1982, 1990b, Takazawa et al.,.1999; Morishita and Arai, 2001 . Aluminous eclog-

ites, e.g., grospydite, kyanite eclogite and corundumŽeclogite, are also captured in kimberlite e.g., Sobolev

et al., 1968; Ater et al., 1984; Smyth et al., 1984;.Taylor and Neal, 1989; Qi et al., 1997 . Although

their origin is still controversial, some aluminousmafic rocks are thought to be recycled crustal mate-

Žrials e.g., Kornprobst et al., 1990b; Qi et al., 1997;.Takazawa et al., 1999; Morishita and Arai, 2001 .

Investigation of the P–T history of mafic rocks in

0024-4937r01r$ - see front matter q 2001 Published by Elsevier Science B.V.Ž .PII: S0024-4937 01 00036-6

( )T. Morishita et al.rLithos 57 2001 143–161144

peridotites is a significant step in understanding thenature of heterogeneity in recycled mantle, whichmay be reflected in later magmatism. Metamor-phosed aluminous mafic rocks are a good indicatorfor P–T history because they display various reac-tion microtextures recording well the metamorphicevolution from higher-pressure, e.g., eclogite-facies

Žmetamorphic rocks e.g., Carswell et al., 1989; Grant1989; Johansson and Moller, 1986; Tenthorey et al.,¨1996; Liati and Seidel, 1996; Gregoire et al., 1998;´

.Straume and Austrheim, 1999 .The Ronda peridotite massif in south Spain is one

of the most famous peridotite massifs in the world,and has been known to have various kinds of mafic

Žrocks Dickey, 1970; Obata, 1980; Suen and Frey,.1987; Garrido and Bodinier, 1999 . Origins of these

mafic rocks have been discussed mainly on the basisŽof geochemistry Suen and Frey, 1987; Garrido and

.Bodinier, 1999 . Textures of some mafic rocks, how-Žever, show their metamorphic evolution Dickey,

.1970; Obata, 1980 . We have sampled sapphirine-andror corundum-bearing aluminous mafic rocks al-ternating with peridotite from the Ronda massif.Evolution history of the corundum-bearing garnetpyroxenite was suggested from the Beni Bousera

Ž .peridotite massif northern Morocco , which hasclosely similar geological setting to the Ronda mas-

Ž .sif Kornprobst et al., 1990b . Kornprobst et al.Ž .1990b interpreted corundum-bearing garnet pyrox-enites as recycled oceanic gabbros. These authorssuggested that corundum-bearing garnet pyroxenitesin the Beni Bousera massifs were equilibrated atPs22–25 kbar and Ts1300–13508C but notedthat calculated temperature using garnet–clinopyro-xene thermometer showed an apparent wide tempera-ture range )3008C within a single corundum-

Ž .bearing mafic layer. Recently, Alaoui et al. 1997investigated the apparent temperature variation withinthe corundum-bearing mafic layer from the BeniBousera massif and suggested that the garnet–clinopyroxene thermometer is inaccurate for CaO-

Žrich, low-SiO system i.e., corundum-bearing lay-2.ers . They suggested that all garnet-clinopyroxenites

in the Beni Bousera massif probably equilibrated at850"508C, as deduced from clinopyroxene–ortho-pyroxene thermometry in surrounding peridotites, andgarnet–clinopyroxene thermometry in the CaO-poormargins of the mafic layer. In the case of the Ronda

massif, petrographical characteristics of sapphirine-and corundum-bearing aluminous mafic rocks havenever been detailed, although a SHRIMP zircon ageŽ .131"5 Ma was reported from a Acorundum-bearing garnet pyroxeniteB by Sanchez-Rodrıguez´ ´

Ž .and Gebauer 2000 . It is clear that additional geo-chemical and petrographical data are needed forfurther understanding of evolution history of alumi-nous mafic rocks in both massifs in the context of apossible recycled crustal material now observed inmantle-derived peridotite massifs.

In this paper, we firstly show detailed microtextu-ral relationships in sapphirine- and corundum-bearingmafic rocks in the Ronda peridotite and discuss theirP–T conditions, focusing on origin of sapphirine asa reaction product from one of high-pressure mineralassemblages.

2. Geological background and sample description

The Ronda and Beni Bousera massifs are largealpine-type peridotite massifs occurring in theBetic–Rifean orogen around the western end of the

Ž .Alboran Sea. Van der Wal and Vissers 1993, 1996have divided the Ronda massif into three structuralzones with different metamorphic characteristics cor-

Ž . Žrelated with petrological zones of Obata 1980 Fig..1 . We collected aluminous mafic rocks from the

garnet–spinel mylonite zone of Van der Wal andŽ .Vissers 1993 within a few hundred meters from the

Ž . Ž .north upper contact of the Ronda massif Fig. 1 .This part of the massif has not been affected bypetrological and geochemical modification attributedto partial melting and the infiltration of astheno-

Žspheric melt defining a recrystallization front Vander Wal and Bodinier, 1996; Garrido and Bodinier,

.1999; Lenoir et al., 2001 .Aluminous mafic rocks, light gray in color in

outcrop, occur as thin layers alternating with myloni-tized peridotite with intervals of a few millimeters to

Ž .a few tens of centimeters Fig. 2a . Contacts betweenperidotite and mafic rock are usually very sharp. Thelayers are parallel to the foliation of the peridotiteand are frequently boudinaged. One aluminous maficrock sample in this study is more than 8 cm in

Ž .thickness and is divided into six sublayers a to f onthe basis of color differences corresponding to the

Ž .modal mineral variations Fig. 2b,c and Table 1 .

( )T. Morishita et al.rLithos 57 2001 143–161 145

Fig. 1. Sample locality on a structural facies map of the westernpart of the Ronda massif simplified from Van der Wal and VissersŽ . Ž .1996 . Thick lines partly broken represent lithologically bound-

Ž .aries by Obata 1980 . Abbreviations: GrtrAr, garnetperidotiterariegite facies; ArrSe, ariegite faciesrseiland facies;SerPl, seiland faciesrplagioclase peridotite.

Ž .Sublayer a contains sapphirine, whereas sublayersŽ . Ž .b and d contain both sapphirine and corundum.One side of the sample is in contact with serpen-

Ž .tinized peridotite layer -2 mm in width .The layered structure is crosscut by fractures,

which are sub-perpendicular to the layered structureŽ .Fig. 2b,c . Ca-clay and zeolite minerals, e.g.,apophyllite and chabazite, are centered in the frac-

Ž .ture and amphibole pargasite occurs within -1mm each side of the fracture associated withclinopyroxene, orthopyroxene, green spinel andopaque minerals. Microfractures appear to providethe locus for fluid and mass transfer necessary for

Žmetasomatism and metamorphism e.g., Austrheim,1986; Erambert and Austrheim, 1993; Straume and

.Austrheim, 1999; Jamtveit et al., 2000 . Amphiboliti-zation is restricted to occurrence along fractures, andthe other portions mainly consist of anhydrous min-erals. The degree of recrystallization of the earliestmetamorphic minerals to new metamorphic mineralsdiffers from layer to layer, probably corresponding tobulk composition as suggested below. In this paper,we focus on anhydrous mineral assemblages and donot consider any further the ‘fracture-related’ parga-site or lower temperature minerals, involving latepressure of a fluid phase.

Mafic rocks from the Ronda and Beni BouseraŽmassifs have been divided into several types Dickey,

1970; Obata, 1980; Suen and Frey, 1987; Garridoand Bodinier, 1999; Kornprobst, 1969; Kornprobst et

. Ž .al., 1990b . Suen and Frey 1987 and Garrido andŽ .Bodinier 1999 demonstrated geochemical diversity

of the mafic rocks in the Ronda massif. The presenceof sapphirine in mafic rocks has not been docu-mented from the Ronda massif. The aluminous mafic

Ž .Fig. 2. Photographs of aluminous mafic layers. a Outcrop of thealuminous mafic layers. Dark-colored bands are peridotite, andlight-colored bands are mafic layers. The mafic layers are fre-

Ž .quently boudinaged. The scale is 20 cm. b Sawed surface of theŽ . Ž .aluminous mafic layer. c Sketch of b , which is separated into

six sublayers on the basis of color differences corresponding toŽ .different mineral assemblages Table 1 . Fractures are shown by

Ž .broken lines see text .

( )T. Morishita et al.rLithos 57 2001 143–161146

Table 1Mineral assemblages of six sublayers

Garnet Clinopyroxene Plagioclase Spinel Corundum Sapphirine

a completely partly replaced kely. and symp. kely. and symp. with cpxkelyphitized by symp. reaction products reaction products partly replaced by

symplectitic assemblageŽ .b partly partly replaced rich rich with crn present rare with plagioclase

kelyphitized by symp. and kely. and symp. partly replaced byreaction products symplectitic assemblage

c completely partly replaced kely. and symp. kely. and symp.kelyphitized and by symp. reaction products reaction productskelyphite network

d partly partly replaced rich rich with crn present with plagioclasekelyphitized by symp. and kely. and symp. partly replaced by

reaction products symplectitic assemblagee weekly partly replaced rich kely. and symp.

kelyphitized by symp. reaction productsf completely partly replaced kely. and symp. kely. and symp.

kelyphitized and by symp. reaction products reaction productskelyphite network

Abbreviations: symp., symplectite; kely., kelyphite.

rock in this study contains garnet as a main phaseand in one of range of garnet-bearing mafic rocks.

Ž .The sample R705A of Suen and Frey 1987 has thesame geochemical and textural characteristics as thestudied rocks and appears to have been collected inthe same area. Group A and some of Group B of

Ž .Garrido and Bodinier 1999 contain garnet, and theformer occurs exclusively in the spinel tectonic do-

Ž .main of Van der Wal and Vissers 1993 . GarridoŽ .and Bodinier 1999 interpreted their Group A as the

oldest mafic rock and inferred that Group B wasformed at the expense of Group A by melt-rockreactions, which were coeval with the formation ofthe recrystallization front. In the Beni Bousera mas-

Ž .sif, Kornprobst et al. 1990b divided garnet-bearingŽpyroxenites into two types, I and II we call them

.Types I and II layers hereafter . The Type I layer ischaracterized by high FeOrMgO ratio and TiO2

content. Type II layer is characterized by lowFeOrMgO ratios and high Al O content. Some of2 3

the Type II layers in the Beni Bousera massif havesapphirine- and corundum-bearing mineral assem-

Ž .blages Kornprobst et al., 1982, 1990b . Graphitized-diamond-bearing garnet pyroxenites were reported

Žfrom both massifs Slodkevich, 1983; Pearson et al.,.1989; Davies et al., 1993 . Sanchez-Rodrıguez and´ ´

Ž .Gebaur 2000 suggested 131"5, 178"6 and 143"16 Ma SHRIMP zircon ages as protolith age for

corundum-bearing garnet pyroxenite, garnet pyroxen-ite and graphite-bearing garnet pyroxenite from theRonda massif, respectively.

3. Bulk chemistry

Bulk rocks were analyzed for major elements onfused disks using an X-ray fluorescence spectrometer

Ž .of Rigaku System 3270 at Kanazawa University.

Table 2Bulk chemical compositions of six sublayers

a b c d e fŽ . Ž . Ž .spr spr and crn spr and crn

SiO 44.08 44.38 45.04 45.24 47.71 47.532Ž . Ž . Ž . Ž .TiO 0.05 0.04 0.06 0.03 0.2 0.112

Al O 20.72 25.11 21.4 24.29 17.86 15.592 3

FeO 4.83 3.56 4.47 3.58 5.88 4.97MnO 0.07 0.05 0.07 0.06 0.11 0.11MgO 16.58 12.84 15.81 11.73 13.59 18.36CaO 12.53 13.58 12.35 13.43 13.33 12.64Na O 0.91 1.53 1.22 1.91 1.76 0.992

Ž . Ž . Ž . Ž . Ž . Ž .K O 0.00 0.01 0.00 0.01 0.01 0.002Ž . Ž . Ž . Ž . Ž . Ž .P O 0.01 0.00 0.01 0.01 0.00 0.012 5

Total 99.66 101.00 100.29 100.19 100.04 100.28Mga 85.9 86.5 86.3 85.4 80.5 86.8

Ž .FeO is total iron. Mgas100Mgr MgqFe atomic ratio. Num-bers in parenthesis means lower than the detection limit.

( )T. Morishita et al.rLithos 57 2001 143–161 147

The XRF analyses were performed under an acceler-ating voltage of 50 kV and a beam current of 20 mA.

The sample was sliced into six sublayers with adiamond saw. Fractures were eliminated by cuttingon the fracture using a diamond saw and by grindingthe cut surface. This procedure was, however, imper-fect to completely eliminate all fractures becausesmall fractures are invisible to the naked eye, whereasinvisible fractures are rare. The six sublayers have

Ž .different bulk chemical compositions Table 2 . Sub-Ž . Ž total.layer e is lower in 100Mgr MgqFe atomicŽ . Ž . Ž .ratio 81 than the others 85–87 . Sublayers b and

Ž .d , which contain both sapphirine and corundum,Ž . Ž .are rich in Al O up to 25 wt.% Figs. 3 and 4 .2 3

Ž .Sublayer a , which contains sapphirine, is relatively

Ž . Ž .poor in SiO 44 wt.% Fig. 4 . The aluminous2

mafic rocks of this study from the Ronda massif areroughly equivalent to the Type II layer from the Beni

Ž .Bousera massif Fig. 3a . The corundum-bearingsublayers are richer in Al O and poorer in MgO2 3

than the corundum-free sublayers both from theŽ .Ronda and Beni Bousera massifs Fig. 4 .

4. Petrography and interpretation of mineral re-actions

4.1. Aluminous mafic rocks

The rock shows a granoblastic metamorphic tex-ture consisting of partially to completely kelyphi-

Ž . Ž .Fig. 3. Relationships between FerMg atomic ratio and Al O contents mol% in the bulk rock from the garnet-bearing mafic layers from2 3Ž . Ž . Ž .the Ronda and Beni Bousera massifs. Fields of Types I and II layers are after Kornprobst et al. 1990b . a This study, b Groups A, B and

Ž . Ž .C from the Ronda massif of Suen and Frey 1987 , Groups A and B from the Ronda massif of Garrido and Bodinier 1999 and graphitizedŽ . Ž .diamond-bearing and -free garnet pyroxenites from the Beni Bousera massif of Pearson et al. 1993 . R705A of Suen and Frey 1987 and

Ž . Ž .A2 RO175 of Garrido and Bodinier 1999 show positive Eu anomaly. Abbreviations: crn-free, corundum-free layer; spr and crn-bear,sapphirine- and corundum-bearing layer; crn-bear, corundum-bearing layer; GGP, graphitized diamond-bearing garnet pyroxenite; GP,garnet pyroxenite.

( )T. Morishita et al.rLithos 57 2001 143–161148

Fig. 4. Variations of CaO and Al O against SiO and MgO for bulk chemistry from both the aluminous mafic layers from the Ronda2 3 2Ž . Ž .massif this study and the Type II layers from the Beni Bousera massif Kornprobst et al., 1990a .

tized garnet and colorless clinopyroxene with minoramounts of plagioclase, green-spinel, corundum, sap-

Ž .phirine and opaque minerals Figs. 5 and 6 . Plagio-clase commonly occurs along the grain boundaries ofclinopyroxene. These features suggest that the pre-sent plagioclase has been formed mostly from thebreakdown of former minerals, such as aluminousclinopyroxene, garnet, corundum and sapphirine.Lenticular mineral aggregates rich in plagioclase oc-

Ž .cur parallel to the foliation plane in sublayers b andŽ .d . Thus, garnet and clinopyroxene are the main

Ž .phases in all sublayers Table 1 . Back-scatter elec-Ž .tron images BSE give us detailed information of

Ž .textural relationships of minerals Fig. 6 .

4.1.1. Garnet and clinopyroxeneGarnet is partially to completely replaced by an

extremely fine-grained, symplectitic aggregateŽ .kelyphite probably consisting of orthopyroxene,

Ž .plagioclase and spinel Figs. 5 and 6 . Kelyphitiza-tion of garnets occurs at their grain boundaries.Garnet is, therefore, never in contact with clinopy-roxene in the studied rock. Garnets do not show

Ž .detectable zoning on BSE images Fig. 6a . Almost

all garnet relics in kelyphite are less than 2 mmacross. In some sublayers, kelyphite develops as a

Ž .network around clinopyroxene Fig. 5a . The ke-lyphite network around clinopyroxene may be formedby complete breakdown of secondary garnet ex-solved from clinopyroxene, which was found in the

ŽBeni Bousera and Ronda massifs Kornprobst et al.,.1990b; Garrido, 1995 .

Kelyphitization of garnet may be due to the fol-lowing simplified reactions:

GarnetqClinopyroxene

sOrthopyroxeneqSpinelqPlagioclase 1Ž .Ž .e.g., Kushiro and Yoder, 1966; Thompson, 1979 ,or

GarnetsOrthopyroxeneqSpinelqPlagioclase2Ž .

Ž .Zang et al., 1993 .Ž .Clinopyroxene CPX I in the sublayers is fine-

grained, less than 1 mm across. Spherical symplec-Ž .titic aggregates consisting of clinopyroxene CPX II

Ž .and plagioclase occur in CPX I Fig. 4b . The forma-tion of CPX IIqplagioclase from more omphacitic

( )T. Morishita et al.rLithos 57 2001 143–161 149

Ž . Ž . Ž . Ž .Fig. 5. Photomicrographs of the aluminous mafic layer. a Kelyphite kely as a network around clinopyroxene sublayer c . b CorundumŽ . Ž . Ž .grains crn: arrows frequently show prismatic shapes parallel to the foliation horizontal sublayer b . Spherical symplectitic aggregates

Ž . Ž . Ž . Ž . Ž .symp can be sporadically observed. c Sapphirine spr coexisting with clinopyroxene cpx sublayer a . Note that the sapphirine occursŽ . Ž . Ž . Ž .as a very fine elongated grain in and around kelyphite arrow . d sapphirineqplagioclase aggregate arrows sublayer d .

CPX I, with higher Tschermak solid solution, re-quires additional SiO or formation of phases such2

as spinel, sapphirine or corundum. A general reac-tion is implied as:

CPXI high in Ca-Tschermak CaTsŽ .Ž

and Jadeite Jd componentsomphacitic pyroxene qSiOŽ . . 2

sCPX II low in CaTs- and Jd-componentsŽ .qPlagioclase. 3Ž .

Chemical compositions of clinopyroxenes are shownin Table 3.

The kelyphite network around clinopyroxene aswell as the relatively smaller grain size of CPX Isuggests that the studied aluminous mafic rocks mightbe affected by the mylonitization, which is also

recorded in peridotite of the garnet–spinel myloniteŽ .zone e.g., Van der Wal and Vissers, 1993, 1996 . It

is not clear, however, whether or not mylonitizationpreceded kelyphitization of garnet. The kelyphite rimis sometimes weakly flattened to the direction of thefoliation plane but the texture is not definitive. Van

Ž .der Wal and Vissers 1993, 1996 assigned the for-mation of the garnet–spinel mylonite zone prior tocrustal emplacement of the Ronda massif but timingof the deformation in the garnet–spinel mylonite

Žzone is still controversial e.g., Van der Wal and.Vissers, 1997; Zeck, 1997 .

4.1.2. CorundumŽCorundum is commonly less than 0.5 mm up to 4

.mm across and shows prismatic crystal shapes par-

( )T. Morishita et al.rLithos 57 2001 143–161150

Ž .Fig. 6. Back-scattered electron micrographs showing microtextural relationships between minerals in the aluminous mafic layer. a GarnetŽ . Ž . Ž . Ž .grain Grt surrounded by kelyphite sublayer d . b CPX I partially replaced by symplectitic intergrowth consisting of CPX II brighter

Ž . Ž .and plagioclase Pl: darker, vermicular sublayer b . Note that the CPX II is brighter than the CPX I due to a difference in Al and NaŽ . Ž . Ž . Ž . Ž . Ž . Ž .contents. c Corundum Crn associated with spinel Spl and plagioclase Pl sublayer b . d Sapphirine Spr coexisting with

Ž .clinopyroxene CPX I . Note that sapphirine is almost mantled by plagioclase and is partially replaced by symplectite consisting of spinelŽ . Ž . Ž . Ž .and plagioclase arrows sublayer a . e Sapphirine in plagioclase-rich domain sublayer d . Note that sapphirine is partially replaced by

Ž . Ž .spinel and plagioclase. f Symplectitic aggregate of spinel in a plagioclase-rich domain R705A of Suen and Frey, 1987 .

( )T. Morishita et al.rLithos 57 2001 143–161 151

Table 3Representative chemical compositions of minerals with corundum and sapphirine

Corundum-related minerals Sapphirine–clinopyroxene Sapphirine–plagioclase

crn spl plag spr cpx plag spr pl An-rich pl An-rich

SiO 0.01 0.03 56.32 13.46 48.78 54.96 13.64 48.91 54.972

TiO 0.01 0 0.03 0.11 0.17 0.06 0.05 0.14 0.082

Al O 99.33 67.83 27.94 64.01 14.52 28.66 63.24 32.91 28.712 3

Cr O 0.12 0.12 0.05 0.16 0.11 0.01 0.19 0.08 0.002 3wFeO 0.19 11.24 0.18 2.4 1.96 0.11 2.97 0.00 0.1

MnO 0.01 0.07 0.03 0.01 0.02 0.03 0.02 0.00 0.00MgO 0.02 20.39 0.13 19.89 11.72 0.25 19.65 0.12 0.00CaO 0.01 0.04 9.29 0.09 20.55 10.89 0.06 15.18 10.58Na O 0.00 0.00 6.32 0.09 2.23 5.34 0.07 2.67 5.562

K O 0.02 0.02 0.04 0.00 0.01 0.02 0.03 0.00 0.032

total 99.71 99.74 100.33 100.21 100.07 100.31 99.91 100.01 100.04Os 3 6 8 20 6 8 20 8 8Si 0.000 0.001 2.523 1.563 1.754 2.47 1.592 2.232 2.476Ti 0.000 0.000 0.001 0.010 0.005 0.002 0.004 0.005 0.003Al 1.996 2.998 1.475 8.759 0.615 1.518 8.702 1.770 1.524Cr 0.002 0.004 0.002 0.014 0.003 0.000 0.017 0.003 0.000

wFe 0.002 0.352 0.007 0.233 0.059 0.004 0.290 0.000 0.004Mn 0.000 0.002 0.001 0.001 0.001 0.001 0.002 0.000 0.000Mg 0.000 1.139 0.009 3.441 0.627 0.016 3.418 0.008 0.000Ca 0.000 0.002 0.446 0.011 0.791 0.524 0.007 0.742 0.510Na 0.000 0.000 0.548 0.020 0.155 0.465 0.016 0.236 0.486K 0.000 0.001 0.002 0.000 0.001 0.001 0.004 0.000 0.002Total 2.001 4.499 5.013 14.051 4.010 5.002 14.054 4.995 5.003

Ž .Mga An 76.4 44.8 93.7 91.4 53.0 92.2 75.8 51.3

Ž . 3qFeO and Fe are total iron except for corundum numbers with star . FeO and Fe for corundum are Fe O and Fe , respectively.2 3Ž total. Ž .Mgas100Mgr MgqFe atomic ratio. Ans100Car CaqNa atomic ratio. Abbreviations: crn, corundum; spl, spinel, plag,

plagioclase; spr, sapphirine.

Žallel to the layered structure of the mafic rock Fig..5b . Corundum is always associated with spinel and

Ž .plagioclase Fig. 6c , suggesting that it was notstable during the later P–T conditions of the Rondacomplex. A possible corundum-out reaction is:

CorundumqClinopyroxenesSpinelqPlagioclase4Ž .

Ž .e.g., Nozaka, 1997; Morishita and Arai, 2001 .

4.1.3. SapphirineŽ .Sapphirine occurs in two mineral associations: i

Žas elongated lamella-like shapes less than 0.2 mm. Ž . Žacross within clinopyroxene CPX I Figs. 5c and

.6d . A very thin plagioclase film almost surroundsŽ .sapphirine of this type Fig. 6d . This occurrence can

Ž .be only observed in sublayer a of the rock. Sap-Žphirine coexisting with clinopyroxene andror sym-

plectitic mineral aggregate after sapphirine as sug-.gested below is found along the outer edge of

kelyphitized garnet and within kelyphitized garnetŽ .Figs. 5c and 6d , indicating that garnet was one ofthe reactants to form sapphirineqclinopyroxene asfollows:

GarnetqSpinelqPlagioclase

sSapphirineqClinopyroxene, 5Ž .

andror

GarnetsClinopyroxeneqSapphirine

qOrthopyroxeneqPlagioclase 6Ž .

Ž . Ž .Christy, 1989 . ii As aggregates of very fine platesŽ .less than 0.05 mm across in plagioclase-rich do-

Ž .main Figs. 5d and 6e . This occurrence is observed

( )T. Morishita et al.rLithos 57 2001 143–161152

Ž . Ž .in two sublayers b and d , which also containcorundum. Reactants to form sapphirineqplagio-clase have never been observed in the studied alumi-nous mafic rocks. Several reactions to form thesapphirineqplagioclase assemblage suggested inprevious studies have inferred kyanite to be one of

Žthe reactants Johansson and Moller, 1986; Carswell¨et al., 1989; Grant, 1989; Liati and Seidel, 1996;Moller, 1999; Straume and Austrheim, 1999; Naka-¨

.mura and Hirajima, 2000 . Possible reactions arewritten as follows:

GarnetqClinopyroxeneqKyanite

sSapphirineqPlagioclase 7Ž .Ž .Carswell et al., 1989; Moller, 1999 , or¨ClinopyroxeneqKyaniteqCorundum

sSapphirineqPlagioclase 8Ž .Ž .Liati and Seidel, 1996; Moller, 1999 .¨

An additional reaction, involving corundum ratherthan kyanite is:

ClinopyroxeneqOrthopyroxeneqCorundum

sSapphirineqPlagioclase 9Ž .Ž .Moller, 1999 .¨

Corundum is never in contact with the sapphirineqplagioclase aggregate in the aluminous mafic rock

Ž .and is surrounded by spinel due to the reaction 4described above. The sapphirineqplagioclase aggre-gate was found in other corundum-free aluminousmafic rock, taken from the same locality as thestudied samples. Thus, corundum is not consideredto be an important reactant to form the sapphirineqplagioclase aggregate in the studied aluminous maficrock. Textural analogy to other sapphirine qplagioclase aggregates described in the literaturesuggests the former presence of kyanite as one ofreactants to form sapphirineqplagioclase in thestudied aluminous mafic rock from the Ronda mas-

Ž .sif. Moller 1999 suggested that reactions to form¨sapphirineqplagioclase are a common feature inkyanite eclogites that have undergone decompressionat high temperatures.

Sapphirine is partially to completely converted toform a fine-grained symplectitic mineral aggregatesconsisting of spinel and possibly plagioclase irre-

Ž .spective of occurrences Fig. 6d,e . Sapphirine waspossibly converted to spinelqplagioclase symplec-tite by the reaction:

SapphirineqClinopyroxenesSpinelqPlagioclase.10Ž .

Although we have never confirmed sapphirine coex-Ž . Ž .isting with clinopyroxene in sublayers b and d ,

Fig. 7. Variations of core compositions of clinopyroxene and garnet across the layered structure. Al, Ca and Na are cation numbers inclinopyroxene based on Os6. Abbreviations: crnqspr, corundum and sapphirine-bearing sublayer; spr, sapphirine-bearing sublayer; grs,grossularite; alm, almandine; pyp, pyrope.

( )T. Morishita et al.rLithos 57 2001 143–161 153

symplectitic spinel, which is similar to that replacingsapphirine, is rarely observed within andror alongkelyphite.

4.2. Peridotite layer

The peridotite layer in contact with the studiedaluminous mafic rock is serpentinized in the centerbut a small amount of unaltered peridotite minerals,such as olivine, orthopyroxene, clinopyroxene andspinel, still remains at the contact between the alumi-nous mafic rock and the peridotite layer. Symplec-titic mineral assemblages consisting of orthopyrox-ene, clinopyroxene and spinel are rarely found withinserpentine matrix and are probably a complete re-

Žplacement after garnet e.g., Obata, 1980; Van der.Wal and Vissers, 1996 :

GarnetqOlivinesOrthopyroxeneqClinopyroxene

qSpinel 11Ž .Ž .e.g., Kushiro and Yoder, 1966 .

5. Mineral chemistry

Almost all garnet and clinopyroxene compositionsin the mafic rocks were analyzed using a JEOLJXA-8800R Superprobe at Kanazawa University. Theanalyses were performed under an accelerating volt-age of 15 kV and a beam current of 12 nA. Sap-phirine with associated minerals and minerals in theperidotite layer were analyzed using a JEOL 6400SEM fitted with Link Energy Dispersive Detector atElectron Microscopy Unit, The Australian NationalUniversity. The analyses were performed under anaccelerating voltage of 15 kV and a beam current of1 nA.

5.1. Aluminous mafic rock

Garnet core compositions vary in pyrope contentsfrom 60 to 74 mol% corresponding to the variation

Ž .registered in bulk chemistry Fig. 7 , and are similarin chemistry to that of the Type II layer from the

Ž .Beni Bousera massif Fig. 8 . Garnet in the sublayerŽ .e has selectively survived from kelyphitization be-cause it is rich in almandine component according to

Žits low-Mga and high-SiO bulk composition Fig.2.7 . Grossular contents of garnet are slightly higher in

Ž . Ž . Ž .Fig. 8. Pyrope pyr –almandine alm –grossularite grs moleŽ . Ž .ratios for garnet in the aluminous mafic layer; a cores and b

rims. Garnet of the graphitized-diamond bearing garnet pyroxeniteŽ . Ž .GGC in the Ronda massifs is after Nixon et al. 1991 . Fields ofthe Types I and II layers from the Beni Bousera massif are after

Ž .Kornprobst et al. 1995 . Field of the GGC in the Beni BouseraŽ .massif is after Pearson et al. 1989 .

the sapphirine- and corundum-bearing sublayers thanŽ .in the other sublayers Fig. 7 . Grossular and alman-

dine contents of the garnet increase slightly fromŽ .core to rim Fig. 8 .

Al O and Na O contents of CPX I cores show2 3 2

wide ranges from 6 to 16 wt.% and from 1.5 to 3.3wt.%, respectively, corresponding to the bulk chemi-

Ž .cal compositions Fig. 7 . In addition, these contentsusually decrease from core to rim, and are signifi-

Ž .cantly lower less than 5 and 1 wt.%, respectively inŽ . Ž .the symplectite clinopyroxene CPX II Fig. 9 . In

Žthe case of CPX I in the kelyphite network sublayer.c , systematic compositional differences between the

core and rim are not observed. The Al O contents2 3

( )T. Morishita et al.rLithos 57 2001 143–161154

Fig. 9. Al–Na relations for clinopyroxenes. The Al and Nacontents slightly decrease from core to rim in the primary clinopy-roxene and are significantly lower in the symplectite than in theprimary clinopyroxene.

of Aprimary clinopyroxeneB in the Type II layer ofthe Beni Bousera massif reach up to 20 wt.% in core

Ž .and 14–16 wt.% in rim Kornprobst et al., 1990b .Clinopyroxene coexisting with sapphirine is high in

Ž . Ž .Al O content 14.5 wt.% Table 3 , suggesting that2 3

the clinopyroxene belongs to CPX I.Ž ŽAnorthite contents of plagioclase 100 Car Caq

. .Na atomic ratio are heterogeneous ranging from 41to 76 corresponding to the differences of occurrenceŽ .Table 3 . The geochemical heterogeneity of plagio-

Ž .clase is also recognized on BSE images Fig. 6e .The outermost margins of plagioclase associated withsapphirineqplagioclase aggregate are higher in

Ž .anorthite content Table 3 .Corundum is almost pure Al O containing only2 3

traces of Cr O and Fe O , which are less than 0.22 3 2 3Ž .wt.% in total Table 3 . Spinel is very poor in Cr and

Ž 2q.the Mgr MgqFe atomic ratio ranges from 0.74Ž .to 0.79 Table 3 . The calculated compositions of

sapphirine are close to the 7:9:3 aluminous end-Ž . Žmember in the SiO – FeO q MgO – Al O q2 2 3

.Cr O qFe O diagram following Higgins et al.2 3 2 3Ž .1979 .

5.2. Peridotite layer

Fo content in olivine of the peridotite layer is 91.Cra of spinel core is 0.02. It is difficult to determinechemical composition of the symplectite spinel be-cause of its small grain sizes. The Al O contents of2 3

Žpyroxenes slightly decreases from the core 2.8–3.9wt.% in orthopyroxene, 4.4–5.6 wt.% in clinopyrox-

. Žene to rim 1.9–2.8 wt.% in orthopyroxene, 3.3–4.7.wt.% in clinopyroxene . The Na O content of2

clinopyroxene also slightly decreases from the coreŽ . Ž .1.2–1.7 wt.% to rim 0.7–1.5 wt.% . The Al O2 3

contents of symplectite orthopyroxene and clinopy-roxene are 3.6 and 4.4 wt.%, respectively. The Na O2

content of symplectite clinopyroxene is 0.8 wt.%.

6. Discussion

6.1. A protolith of the aluminous mafic rock

Ž .R705A of Suen and Frey 1987 belongs to theType II layer on the discrimination diagram of Korn-

Ž . Ž .probst et al. 1990b Fig. 3b , and has high MgrFeand SrrNd ratios, low REE concentration and posi-tive Eu anomaly. Some samples of Groups A and B

Ž .of Garrido and Bodinier 1999 also show low REEconcentrations and slight positive Eu anomalies. Suen

Ž .and Frey 1987 suggested that R705A was formedas a plagioclase-rich accumulate or residue. Theysuggested another possibility for the genesis ofR705A, modification from an igneous rock by meta-somatic fluids from the country rock. R705A has thesame petrographical characteristics as the studiedaluminous mafic rock except for the absence of

Ž .corundum and sapphirine Suen and Frey, 1987 .Ž .Kornprobst et al. 1990b considered that a protolith

Žof the corundum-bearing garnet pyroxenites the Type.II layer from the Beni Bousera massif was a plagio-

clase-rich, lower-pressure cumulative product be-cause of its significant positive Eu anomaly.

Similarly, a plagioclase-rich protolith for the alu-minous mafic rock of the Ronda massif can beinferred, especially for sapphirine- and corundum-bearing sublayers because of the high Al O and2 3

CaO in their bulk composition. Our mineral andpetrographical data in this study, however, cannotshow any constraints for the condition under whichthe protolith of the aluminous mafic rocks wasformed. Further study of the aluminous mafic rocksin terms of geochemistry may be needed to provideevidence of the formation of its protolith at lowpressures, i.e., as plagioclase-rich cumulates.

( )T. Morishita et al.rLithos 57 2001 143–161 155

6.2. The latest P–T conditions recorded in the alumi-nous mafic rocks and the peridotite layer

In the peridotite layer associated with the alumi-nous mafic rock, aluminous spinel is coexisting withtwo pyroxenes both in constitute minerals and insymplectite, suggesting that the peridotite layer wasequilibrated within the spinel-lherzolite stability fieldŽ .0.8–1.5 GPa in the CMAS system; Gasparik, 1987 .Temperatures of 850–9308C for rim of pyroxenesand symplectite pyroxenes were estimated usingclinopyroxene–orthopyroxene geothermometerŽ .Wells, 1977 .

Sapphirine coexisting with clinopyroxene has beenŽrarely reported from xenoliths in volcanics Meyer

and Brookins, 1976; Griffin and O’Reilly, 1986;.Gregoire et al., 1998 as well as from mafic gran-´

ulites along the boundary with the Finero peridotite,Ž .Italy Lensch, 1971; Sills et al., 1983 . Sapphirine

typically occurs in Mg- and Al-rich metamorphicrocks of granulite and uppermost amphibolite faciesŽ .e.g., Ackermand et al., 1975; Higgins et al., 1979 ,

Ž .although Liu and Presnall 1990, 2000 experimen-tally investigated a possible igneous origin of sap-phirine from Mg-, Al-rich magmas at high pressuresŽ . Ž .2 GPa . Christy 1989 proposed a semiquantitativepetrogenetic grid for the CMAS system to define thestability field of sapphirineqclinopyroxene at about

Ž .1 GPa and lower than 9008C Fig. 10 . ChristyŽ .1989 suggested that addition of Fe in the systemwill shift the reactions involving garnet and spinel tolower pressures and temperatures. Mineral composi-tions in the studied aluminous mafic rock are alsodifferent from end-member compositions used in the

Ž .thermodynamic calculations of Christy 1989 . De-Žspite these problems, this P–T condition Ps1

.GPa and TF9008C for formation of sapphirineqŽ .CPX I by the reaction 5 is concordant with that

estimated from the peridotite layer.Sapphirine is partially replaced by symplectitic

aggregate of spinel and plagioclase. As suggested byŽ .Christy 1989 , sapphirine is converted by a reaction:

SapphirineqClinopyroxene

sOrthopyroxeneqSpinelqPlagioclase. 12Ž .This reaction will be caused by further decompres-sion after formation of sapphirineqclinopyroxene.It is, however, difficult to constrain the P–T condi-

tions for the disappearance of sapphirine in the stud-ied rocks because of the lack of orthopyroxene.

We concluded that the latest P–T conditionrecorded in the aluminous mafic rock was at Ps1

Ž .GPa and Ts800–9008C. Alaoui et al. 1997 sug-gested that a corundum-bearing Type II layer in theBeni Bousera massif was also equilibrated at 850"508C, which was deduced from clinopyroxene–or-thopyroxene thermometer in websteritic margin ofcorundum-bearing Type II layer.

6.3. P–T path for the reactions in the aluminousmafic rocks

As noted above, kelyphitization of garnet occursat grain boundaries. CPX IIqplagioclase symplec-tite in CPX I sometimes occurs as spherical shapeincluded in CPX I without fractures. Chemical zon-ing along fractures has not been observed in eithergarnet or CPX I. Thus, kelyphitization of garnet andformation of CPX IIqplagioclase symplectite from

Ž .CPX I omphacitic pyroxene observed in the studiedrocks are generally interpreted to be caused by de-compression. Jd and CaTs components in clinopy-roxene varies corresponding to P–T conditions and

Žcoexisting minerals e.g., White, 1964; Gasparik,.1984b, 1987 . Geochemical variation of clinopyrox-

ene shows that the Jd component decreases with aŽ .slight decreasing of the CaTs component Fig. 9 ,

suggesting that temperature might decrease duringdecompression. This interpretation is consistent withthe reaction for the formation of sapphirine, whichmay have formed as a result of temperature decreasecoupled with decompression from the earliest meta-morphic mineral assemblages.

In the CMAS system, a possible reaction forŽ Ž ..corundum disappearance Eq. 4 is written by end-

members of minerals:

2 corundumqdiopsidesspinelqanorthite. 4XŽ .Ž X.Reaction 4 was calculated with THERMOCALCŽ .software Powell and Holland, 1988 and the thermo-

Ž . Ždynamic data of Holland and Powell 1990 Fig..10 . It is noted that the presence of Fe in the system

will stabilitze the spinel to lower pressure and tem-perature. However, the presence of Na in the systemwill stabilize the plagioclase at higher pressure. Re-

Ž X.action 4 will not occur at P)2 GPa because ofthe disappearance of plagioclase.

( )T. Morishita et al.rLithos 57 2001 143–161156

Fig. 10. A possible decompression P–T path of the aluminous mafic layer. See text for more explanation. Dotted area represents P–TŽ .regime for sapphirine stability field coexisting with clinopyroxene after Christy 1989 . Reaction for the crnqdissplqan was calculated

Ž . Ž .with THERMOCALC software Powell and Holland, 1988 and the thermodynamic data of Holland and Powell 1990 . Broken lines areŽ . Ž . Ž . Žphase boundaries between eclogite, high-pressure granulite HPG , intermediate pressure granulite IPG and gabbro GB Green and

. Ž .Ringwood, 1972 . Phase boundary between kyanite and sillimanite is from Holdway 1971 . Reaction for the anorthitesgrossularqkyaniteŽ . Ž .qquarz is from Koziol and Newton 1988 . Phase boundary of plagioclase-out and kyanite-in R and G, 1974 is from Raheim and Green˚

Ž . Ž .1974 . End-member compositions for thermodynamic calculations of sapphirine-related reactions in the CMAS system of Christy 1989 isŽ . Ž . Žas follows; garnet grt, Ca Mg Al Si O , clinopyroxene cpx: Ca Mg Al Si O , orthopyroxene opx:0.45 2.55 2 3 12 0.93 0.93 0.28 1.86 6

. Ž . Ž . Ž .Ca Mg Al Si O , sapphirine spr: Ca Mg Al Si O , spinel spl: MgAl O and anorthite an: CaAl Si O .0.01 1.91 0.16 1.92 6 0.02 3.85 8.26 1.87 20 2 4 2 2 8

Abbreviations: ky, kyanite; qz, quartz; sil, sillimanite; di, diopside; crn, corundum; an, anorthite; cats, Ca-tschermak; grs, grossular; pyp,pyrope; gh, gehlenite; chr, chrolite; an, anorthite; grt, garnet; spl, spinel; cpx; clinopyroxene; opx, orthopyroxene; chr, chrolite; spr,sapphirine; plag, plagioclase; spl, spinel; grt, garnet.

Ž .A rapid cooling 200–3408CrMa and exhuma-Ž .tion rate )31 mmryear was reported for the

country rock around the Ronda peridotite and fromŽthe Westen Alpujarrides Zeck et al., 1992; Monie et´ ´

al., 1994; Garcıa-Casco and Torres-Roldan, 1996;´ ´Zeck, 1996; Sosson et al., 1998; Sanchez-Rodrıguez´ ´

.and Gebauer, 2000 . The reaction textures describedabove could also be quenched by relatively fastexhumation and cooling of the peridotite massif to-gether with its country rocks.

6.4. The earliest metamorphic mineral assemblages

Microtextural and reaction relationships suggestthat the mineral assemblage at the earliest metamor-

phic conditions in the aluminous mafic rock wasgarnetqclinopyroxene"kyanite"corundum, indi-cating eclogitic mineral assemblage.

Temperature at which the earliest metamorphicmineral assemblages were equilibrated is difficult toestimate from mineral compositions using geother-mometers because minerals now observed in thealuminous mafic rocks were significantly affected bychemical re-equilibration reflecting the later P–T

Ž .conditions sapphirine–granulite to more later . Re-action textures in the aluminous mafic rocks mayhave proceeded as a result of decompression possi-bly coupled with cooling from the earliest metamor-phic conditions, indicating that temperature in the

Žearliest metamorphic mineral assemblage eclogitic

( )T. Morishita et al.rLithos 57 2001 143–161 157

.mineral assemblage was probably higher than thatŽ .of the latest P–T conditions )9008C .

Pressure in the earliest metamorphic conditionsrecorded in the aluminous mafic rocks is character-ized by the presence of kyanite. Raheim and Green˚Ž .1974 experimentally determined the solidus and

Žliquidus relations for the Lunar Highland basalt gab-.broic anorthosite , which is similar in chemistry to

the aluminous rocks with sapphrine and corundumŽ . Žexcept for the lower Mga 72.5 of the former Fig.

.6 . Their experimental results demonstrated thatkyaniteqquartz appears first in the anorthositic gab-bro composition on the final breakdown of plagio-

Ž . Žclase at high pressures ca. 1.5 GPa at 9008C Fig..10 .The presence of pyroxene–spinel symplectite in

the peridotite layer suggests the former presence ofgarnet in the peridotite layer. However, origin ofgarnet in peridotites from the spinel–garnet mylonitezone reamins debatable, i.e., all garnet grains weremechanically derived from thinned and disrupted

Žlayers of garnet pyroxenite e.g., Schubert, 1982;.Zeck, 1997 or some garnet grains were grown in

garnet-lherzolite stability field as a constitute phaseŽof the peridotite Obata, 1980, 1982; Van der Wal

.and Vissers, 1996, 1997 . The earliest metamorphicpressure conditions estimated from the aluminousmafic rocks are located at transition P–T spacebetween garnet-lherzolite to spinel-lherzolite stablityfields, which depends on bulk compositions of peri-

Ždotite e.g., O’Neill, 1981; Nickel, 1986; Gasparik,1987; Walter and Presnall, 1994; Green and Falloon,

.1998 .Corundum-bearing garnet pyroxenites alternating

with peridotites were reported from several peridotitecomplexes of high-pressure origin, e.g., the Beni

ŽBousera in Northern Morocco Kornprobst et al.,.1990b , Cabo Ortegal massif in Northwestern Spain

Ž .Girardeau and Gil Ibarguchi, 1991 and the ValŽMalenco in Italian Alps Muntener and Hermann,¨

. Ž .1996 . Corundum-bearing AeclogitesB grospyditeswere also reported as xenoliths in kimberlite pipesŽe.g., Sobolev et al., 1968; Ater et al., 1984; Qi et

.al., 1997 . Corundum coexisting with both garnetand clinopyroxene also occurs as inclusions in dia-

Ž .mond Sobolev et al., 1998 . It is difficult to estimateprecise P–T conditions at which corundum is stablein equilibrium with garnet and clinopyroxene possi-

bly because of a wide pressure range of their coexis-Ž .tence e.g., Gasparik, 1984a, 2000 .

Thus, the maximum P–T condition reached bythe aluminous mafic rock still remains open. Thepresence of graphitized diamond-bearing garnet py-

Ž .roxenite GGP both in the Ronda and Beni Bouseramassifs, which has distinct difference in chemical

Žcomposition from the aluminous mafic rocks Fig..3b , indicates that peridotites were also probably

Ž .derived from the diamond stability field )5 GPaŽ .e.g., Davies et al., 1993 . There is, therefore, a highprobability that the earliest metamorphic assem-blages of the aluminous mafic rocks were also de-rived from the ultrahigh-pressure conditions associ-ated with peridotite. This conclusion must follow ifthe primary layering is attributed to low-pressureprocesses or events in the olivineqplagioclase sta-bility field, followed by subduction of the layeredcomplex.

We concluded that the earliest metamorphic con-dition in the aluminous mafic rocks was at PG1.5

ŽGPa and TG9008C high-pressure granulite to.eclogite facies of Green and Ringwood, 1972 and

the reaction textures in the aluminous mafic rockwere caused by decompression coupled with coolingfrom the earliest metamorphic conditions. Decom-pression P–T path for the aluminous mafic rocks isconsistent with that of peridotite in the garnet–spinel

Ž .mylonite zone Van der Wal and Vissers, 1993 ,which was not been affected by heating event thatprompted partial melting in the granular domain and

Žgenerated the recrystallization front Van der Waland Vissers, 1996; Van der Wal and Bodinier, 1996,

.Lenoir et al., 2001 . The results in this study indicatethat the aluminous mafic rocks were exhumed fromupper mantle conditions with surrounding peridotite.

We confirmed the presence of symplectitic spinelboth in a kelyphite and plagioclase-rich domain in

Ž .the same sample of R705A of Suen and Frey 1987Ž .Fig. 6f . The symplectitic spinel is possibly a prod-uct of complete disappearance of sapphirineqplagioclase after kyanite, suggesting that R705Amight have experienced high P–T conditions afterits formation as low-pressure cumulate or residue as

Ž .suggested by Suen and Frey 1987 . Kornprobst etŽ .al. 1990b suggested that the assemblage of clinopy-

roxeneqgarnetqcorundum was accomplished deepin the mantle after subduction andror dragging down

( )T. Morishita et al.rLithos 57 2001 143–161158

of the plagioclase-rich protolith of crustal originŽ .during convection of the mantle. Qi et al. 1997

examined corundum-bearing eclogite xenolith fromthe Obnazhennaya kimberlite, Yakutia, and showedhigh Al O and CaO contents for bulk rock compo-2 3

sitions and positive anomaly of Eu for garnets. Theseauthors suggested that the protolith of the eclogitewas a noritic anorthosite, possibly a part of theancient oceanic crust. We envisage that the alumi-nous mafic rocks studied also experienced high-pres-sure metamorphism after they were formed as pla-gioclase-rich low-pressure rocks. We need furthergeochemical study of the aluminous mafic rocks todetermine not only their origin but also their geo-chemical evolution reflecting their P–T history inthe context of a possible recycling crustal materialsassociated with peridotite.

7. Conclusion

Ž .1 Garnet and clinopyroxene are the main phasesin the aluminous mafic rocks from the Ronda massif.The sapphirineqplagioclase aggregate suggests theformer presence of kyanite as one of reactants, indi-cating that the aluminous mafic rocks were onceequilibrated at high-pressure conditions.

Ž .2 The earliest metamorphic mineral assemblageswere characterized by garnetq clinopyroxene"kyanite"corundum at PG1.5 GPa and TG9008C.The maximum P–T condition reached by the alumi-nous mafic rock still remains open. Reactiontextures, such as kelyphitization of garnet, clinopy-roxene–plagioclase symplectite, corundum disap-pearance and sapphirine formation followed by dis-appearance of sapphirine, were caused duringdecompression possibly coupled with cooling. Thelatest P–T condition recorded in the aluminous maficrocks was Ps1 GPa and Ts800–9008C and isconsistent with that of corundum-bearing garnet py-roxenite from the Beni Bousera massif as suggested

Ž .by Alaoui et al. 1997 .Ž .3 The aluminous mafic rocks studied might

experience high-pressure metamorphism after theywere formed as plagioclase-rich low-pressure rocksalthough further geochemical study of the aluminousmafic rocks is needed to make clear their protolith.

Acknowledgements

We are indebted to David H. Green for his com-ments on this manuscript, and to Frederick A. Freyfor giving us the sample R705 described by Suen

Ž .and Frey 1987 . We thank Hiroshi Shukuno, TatsukiTujimori, Akira Ishiwatari, Yoshihiko Tamura andAtsushi Toramaru for their technical helps on micro-probe and XRF analyses at Kanazawa University,and Frank Brink for technical guidance and assis-tance in microprobe analyses at Electron MicroscopyUnit, ANU. Takashi Sawaguchi helped us to collectsamples. Constructive reviews by Hakon Austreheim˚and Charlotte Moller improved the manuscript. This¨research was partly supported by the Spanish DGESproject PB97-1211 to F.G. and the JSPS Fellowshipsfor Japanese Junior Scientists to T.M.

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