Gwhimics d Cosmrchimi@ Actoyol. 51, W, 219-290@ Pcrgmon Joumals Ltd. 1987. Priuted in U.S.A.

0016-7037/87i$3.00 + .00

Petrogenesis of layered pyroxenites from the Lherz, Freychindde andPrades ultramafic bodies (Ariige, Frenbh Pyr6n6es)

J. L. BoDn[Enr, M. GuneuDr, J. FatRrts2, J. Dosrel3 and C. DupuyrI Centre G6ologique et Gdophysique, U.S.T.L., Place E. Bataillon, 34060 Montpellier Cedex, France

2 Lab. Miner. Museum Histoire Naturelle, Rue Bufon, 75005 parii, France3 Department of Geology, Saint Mary's Univenity, Hdifax, Nova Scotia, B3H 3C3, Canada

(Received February 25, 1986; accepted in revised form November 17, 1986)

Abstract-The pyroxenite bands in spinel lherzolites from three high-temperature peridotite massifs (Lherz,Freychindde and Prades) in Aridge (French $nen6es) have geochemical features including distributions ofMg, Ca, K, Ti, Zr and REE typical of cumulates derived by high P-7 crystal segregation. However, thesefeatures of the whole-rocks are not reflected in the element distribution among the minerals which waspartially modified during subsequent recrystallization. In addition, samples from the margins of the pyroxenitebands were affected by secondary processos such as metasomatism or subsolidus re-equilibration. Unlikepyroxenite xenoliths from basalts which are usually assumed to be derived from alkalic basaltic magmas,the pyroxenite layers are related to tholeiitic magmas similar to the parental liquids of the Triassic doleritesencountered throughout the Brren6es. The data show that high P-T fractionation significantly affected theascending tholeiitic magma and suggest that the continental tholeiites could have been derived from anupper mantle source with a chondrite shaped REE pattern.

INTRODUCTION Jecrsox and THawn, 1972) represent pieces ofupper mantle

pRocpssEs wHrcH AFFECT the distribution or trace lffil'iyJtlTilTff:iX#:fiJJtrJ#;,:iilfff;elements in the upper mantle such as high-pressure- occur within the Cretaceous metamorphic zone along thetemperature crystallization and partial melting are of North Py:enean- Faylt. All three ultramafic bodies consist

prime importance in the study of basalt petrogenesis. n*{]lP::SspinellherzolitesintercalatedwithbandsofMost inrormation on these processes ,esurr ao- ii-" [fftffil.i, lyrrT.8il $#tri.HiT].:l$rffii,",,'ji:studies of ultramafic and mafic xenoliths scavenged by ering is especially marked by parallel bands olspinel websteriGalkalic basaltic magma(e.g. MENzes, 1983) and high- (3-20 cm thick) and rare g:rnet pyroxenite (0.3-l m thick).

temperature peridotites (e.g. WIIsHrne and Prre, 1975; llcal]I11he ?Yr9xenites predominate volumetricallv over the

oserA, a at., te80; SHEnvxs, teTea,b; porv6 and l[fisl]*:]"?t;i"Tgft:i"$:ii:1if#titffiAtticnn, 1980). The latter are particularly usefrrl in seqo.n". is cross-cut by dykes ofamprriUofe-iictr pyio*eniteithe interpretation of mantle processes, since these (upto30cmthick)andoccasionallyalsobyphlogopitehorn-

bodies crop out for distances of several meters up to blendites (lhezite of LacnoIx, 1917). The whole ultramafic

several kilometers thus allowing investigations on the i:t"Tjt]:llTlcomplex pre-emplacement history of plastic

relationship among the various rock types and t r"o'- *'jiTi!!l,U.lttf;?::ltr;;:"stallization (AvE LALLE-

ing many limitations on sampling.In the Pyr6n6es, the ultramafic bodies consist mainly

of peridotites and pyroxenites with subordinate horn- PETROGRAPHY AND MINERALOGY OF THEblendites. Since these rocks have been frequently men- LAYERED PYROXENITES

tioned in the literature (e.9. WIrsntns and Ptrn, 1975),a detailed geochemical study is needed to define their The samples were selected from the suite studied by CoN-characteristics and to provide clues to their origin. The qu6rE ( I 977' 1 978) who provided a detailed description ofpurpose of this paper is to examine the trace element 1*-T11"11*v,:^1d-mineralogv

of the pvroxenites and thus

disrribution in the pyroxenites rrom three high+e-J: il']jllil?'gffH:"ffi.'J#.ff1J#"|!tlttJ",i$; t'

perature peridotite bodies (Lherz, Freychindde and ThepyroxenitesdisplaylargevariationsinmineralogyandPrades) ofAridge (French $nen6es) and to discuss their can be subdivided into three rock ty'pes:

petrogenesis. The petrogenetic relationship of the pv-roxenites with the surrounding peridotites wlr ue coi- ,""'i l*t'l;:!:'H"%i|tit"lioll"fi,Bil,fj,tiil*1sidered in a forthcoming study on the lherzolites. 6-l5E..). The amount of gaiet, present;nly in the thickHowever, isotope data (PoLV6 and Arricnr, 1980; layers,increaseswithboththedecreaseoftheorthopyroxene-

HauruN et at., 1985) suggest that these two rock types clinoplroxene ratio. and the content of spinel.

are not closely genetically related. ' 2. Orthopyroxenite containspredominantly orthopyroxene

(usually as large crystals, up to 5 mm in size) and subordinate

.EOLOGICAL SETTING am^oults ofspinel and clinopyroxene.3. Garnet clinopyroxenite is characterized by abundant

The three high-temperature alpine peridotite bodies ex- gmet (up to 50Vo). Garnet ariegite (LAcRorx, l90l) has aamined in this study (orogenic lherzolite-type massifs of similar mineralogy but also contains spinel (-5-19q,;.

279

280 J. L. Bodinier et al.

Each petrographic type forms distinct individual layers oroccurs as a part ofa composite layer where one type grades

to another. The thick layers exhibit a symmetrical zoning dueto the concurrent decrease ofthe modal ratio oforthopyrox-ene/blinopyroxene and spinevgarnet from the edges to thecentre. The zoning is represented by the succession of spinelorthopyroxenit€, spinel websterite, and gamet pyroxenite. Theprimary magmatic assemblages of the pyroxenites do not in-clude olivine. This mineral phase occurs only in very thinlayers (- 1 mm thick) ofwebsterite and orthopyroxenite (e.g.72-427 and,72-364) whrch display fuzzy contacts with thesurrounding peridotite. These thin and discontinuous layersoccur only in zones affected by intense deformation and appearto represent stretched pyroxenitic veinlets which incorporatedsome olivine from the peridotite matrix.

The texture ofpyroxenites is generally porphyroclastic withporphyroclasts (2-5 mm in size) olpyroxenes and rarely alsospinel (e.9. sample 7l-262) or gunel(70-291,70-379), enclosedin a fine-grained matrix made up of pyroxenes, spinel andgarnet. In some thick layers (e.g. 70-385), relict porphyroclastsoforthopyroxene and clinopyroxene (1-4 cm in size) werenot affected by deformation and recrystallization and containan exsolution ofpyroxene, spinel and garnet. These texturalfeatures in conjunction with the mineralogical data (CoN-QUER6, 1977, 1978) indicate that the present mineral assem-blage of pyroxenite resulted from subsolidus recrystallizationof primary magmatic ass€mblages composed olvariable pro-portions of Al-rich orthopyroxene (bronzite) and clinopyrox-ene (augite) and a minor amount of spinel. Relicts of primarygarnet are present only in the centre ofthe most differentiatedlayen (e.9. sample 70-379b, Appendix l).

The systematic zoning observed in the thick pyroxenitebands led CoNeufn6 (1977) to postulate that the primarymagmatic mineral assemblages were produced by the segre-gation of phases from basaltic melts in the following order:the main liquidus phase, orthopyroxene, probably separatedafter the extraction of spinel and was followed successivelyby the appearance of clinopyroxene and gamet. The sym-metrical mineralogical zoning of the layers may be the resultof a flow crystallization process (SHnnv.r,rs, 1979b; IRvrNG,1980; Fnrv, 1980) where liquidus crystals of a flowing basalticmagma were successively plated on the conduit walls. Thisprocess contrasts with the classical flow differentiation model(BHATTAcHARJII and SMITH, 1964) whereby crystals are con-centrated in the core ofa flowing fluid.

The subsolidus recrystallization of the primary phases wasconnected with the plastic deformation. The available dataon the mineral composition of these recrystallized assemblages(CoNqufR6, 1977; CoNeu6n6 and FABRris, 1984), appliedto various geothermobarometers, suggest that this event oc-curred at about 910 + 45oC and ll.5 + 2.5kb. During asubsequent metamorphic episode, the subsolidus recrystalli-zation continued down to temperatures ofabout 650-700'Cand pressures not higher than 8 kb. This event was probablyrelated to the shearing of the upper mantle followed by atectonic introduction of the ultramafic slices into the lowercrust.

ANALYTICAL METHODS

Mineral separates were obtained by standard magnetic andheavy liquid techniques combined with handpicking under abinocular microscope. They were then ultrasonically washedin distilled water. Optically, the purity ofthe mineral concen-trates was estimated to be better than 999o.The major elementsin the whole rocks were determined by wet methods, whileRb, Sr, Ba, Y, Zr, and Nb were analyzed by X-ray fluorescence.In the whole-rocks and mineral sepzuates, transition ele-ments-V, Cr, Co, Ni, Cu and Zn-were analyzed by atomicabsorption, Sc and Hf by instrumenkl neutron activation andREE by a radiochemical neutron activation technique de-

scribed by Sevov,r,ilr et al. (1984).The precision and accuracyof the trace element determinations have been reported byDosrAL et al. (1983) and Sevoyexr et al. (1984). The pre-cision is generally better than 107o. The data on two pyroxenitesamples from Lherz reported by LoUBET and AuEcnr (1982)and reanalyzed during this study provide a comparison withthe isotope dilution technique (Fig. 1). Major element analysesofmineral phases, taken from CoNeuEnf (1977) were doneby the wet method. The locations of the analyzed samples aregiven in CoNauER€ (1977).

RESULTS

Mineral phases

The major and trace element concentrations of theminerals are given in Tables I and 2. Each mineralphase exhibits distinct abundances of trace elements.Regarding the transition elements, the Ni content de-creases in the order orthopyroxene-clinopyroxene-gar-net, while Sc increases in this direction; V decreasesfrom clinopyroxene through orthopyroxene to garnet.Compared to equivalent phases from peridotite xeno-liths (Surrrrrzu and AlrEcnn,1978; SroscH, 1981),the analyzed minerals have similar Sc and Co abun-dances but are lower in Cr and Ni. The partition coef-ficients ofthe coexisting clinopyroxene-garnet and cli-nopyroxene-orthopyroxene for transition elements(Table 3) are closely comparable to those from spinelperidotite xenoliths reported by SroscH (1981) indi-cating similar conditions of re-equilibration.

Clinopyroxene and orthopyroxene display two typesof REE patterns (Fig. 2) which correlate with the oc-currence ofsecondary garnet in the host rock. The py-roxenes with the first type of pattern are from rockswith little or no secondary garnet. Their patterns (e.g.

sample 70-379d) resemble those ofpyroxenes from type1-A spinel lherzolites (MENzrES, 1983) which are un-metasomatized and free of amphibole and mica. The

La Ce Nd Sm Eu Tb Dy Er Yb Lu

FIc. l. A comparison of REE analyses of two p1'roxenitesamples obtained by two different methods: empty circles-isotope dilution data ofLoussr and At-lEcnr (1982); solidcircles-this study.

UFEo2oIo

\1IDYooaE .5

r6

qoo

o

6

o

aox

A

F

ooo

E

oc

6

Aeo

aoaoo

oc

I

jF

ts

Aridge layered pyroxenites

+idr k o c dd d64Hotu-=ozH

patterns oftype I clinopyroxene are depleted in lightREE (LREE) with an unfractionated distribution ofheavy REE (HREE), while the patterns of type I or-thopyroxene are marked by a positive slope from Smto Lu. The second type (e.g. sample 70-357) whichbelongs to pyroxenes from the samples containing highproportions of garnet of subsolidus origin (CoNquER6,1977) displays a distinct depletion (with respect tochondritic proportions) of HREE for both clinopyrox-ene and orthopyroxene. The pattern ofclinopyroxeneis convex with the apex at Sm and Eu. In addition,type II pyroxenes are lower in Sc. The strong depletionof HREE and Sc in type II pyroxenes may be relatedto their subsolidus equilibrium with secondary garnetin a closed system. The chondrite-normalized REEpattern ofgarnet (Fig. 2) exhibits a positive slope withdistinct HREE enrichment and aYb/La ratio of 27 to54. In absolute terms, HREE (Lu) concentrations varyfrom 9 to 19 times chondritic abundances.

Like the transition elements, the REE partition coef-ficients (Kp) for coexisting mineral pairs including cli-nopyroxene-orthopyroxene and clinopyroxene-garnetshow consistent patterns suggesting the equilibriumdistribution. The K2 of clinopyroxene-orthopyroxene(Fig. 3) has a convex pattern with the apex at Nd toTb. This shape differs from those ofspinel peridotiteinclusions (OrroNELr,o, 1980; SroscH, 1982) and alsofrom those of coexisting phenocrysts in alkalic lavas(Ott-nrae et al., 1968), which usually display maximumvalues for LREE. On the other hand, the patternsshown in Fig. 3 resemble those of peridotites in al-pine bodies (Fnrv, 1969, 1970). The diference in theKocex/oox for REE between peridotite inclusions orphenocrysts in alkalic lavas and the pyroxenites ortherzolites of the alpine bodies is mainly related to theLREE depletion of the clinopyroxene in the latter,while orthopyroxenes have nearly identical composi-tions in both types (e.g. OrroNrr-lo, 1980).

The Ka of REE between clinopyroxene and garnet(Fig. 3) displays a negative slope with the lowest valuefor Lu. However, the K2 between type II clinopyroxeneand secondary garnet (70-357 and 70-291) differmarkedly from those involving type I clinopyroxeneand primary garnet (70-385C) particularly for Yb andLu which are 10 to 25 times lower than the values ofthe former pain (Fig. 3). The K2 for medium to heavyREE of the assemblages including secondary garnetare very similar to the range of values reported byPnnporrs et al. (1972) for garnet-bearing xenolithswith metamorphic paragenesis. This suggests that theKo for REE between clinopyroxene and garnet maybe used to distinguish the high-lnmagmatic assemblagesfrom the subsolidus recrystallized ones.

Vlrhole rocks

Major elements. Compared to basalts, the pyrox-enites are strongly depleted in Ti, P and K, enrichedin Ca (Table 4) and have higher [Mg] values (Mg[v1g

28r

F-6NOi@6QOO

06 eddd IoN4do€ F i6 600969NOd< € O@ OOON Oo10<o6 6 0< oooo ooda6

noo:oo o- 33 RX88 Ido<oa6 i6 00 0No6 0onaoo* o@ oi oooo 6oiN6

I iONO Oo 6 6000 0o N adoN o6 i OOOO O

6006 €66 N€N d66€ SNO 6O0 NO6ts Oao 600 ro60 6

Oa

N+N 6660o< 60d ts4@6 6N6 66Q 6006 0Oo 6oO dooo o6d

s6N@NS€N O646ts@66 00 60dNNO@€ IsNd:NrN NO 6000NO@6 0doooo60 00 6600ao60 asN o *

9€A€*OOOO6Nd6tsOOOOO6 NTiONOFNNN6Bd6dO6NAg O600iONFdO6@OOO<6iO6 <OaOOOOOO$+ i< 6

o600€ @€€o9OO6 OOts6a NOrOo a:6N600< Ndo60 @oooo @€oooooN 6i:oo :ooao aoo<6 :N O

no$$@Nr6<Fdos9Fooioo $Ndotsoodioosi6oda€o6 €ooooo€€<ooNQNO6riO@ aOOOOOOOO96 rN 6

tsood: 60€tsoN@9 OQ66S NOdOd hdO9ts606 96666 @OOOa @€OO

6OQO 6OiO6 EiOOOO OQO9+ :d 6 0

dqo N9$99NOtsNO6a$F€AOOO@ !6tsaO6ONiN6F+rOQa6ts6€ 06dOOOO66iO!"'

o9QOO@OiO6 6iOOOOOOOOSn rd 6 tz

€ts+€6NQ6@Od60€ts6040N €Fro:oNr€€ts€NNOTON6: €NOQ:O@OOOQOOOO€riO-Q iOOOOOOOOS6 *d e

@< <<o+60th 600F6 N €F oorio€€i €a66O ts 6d dQtsOOONS OONOO € aO OO:OOS606

<h66€4O6$doroirF6€o€ 4000€odoossoooajNo-ts €NooNQFoooN90@ONOOA@ aOOOOO<OOS600

od6N@:@o60$roo@o9{os6NOOTOtsOOOroooooioo9

a6N66Ndd66F600006€os6:OO6O€OOO

roooooroos

so N0sod+ :sooa6 !O€6SN

o6 9600ao o90sdO <O@69N

IoN

Io

€tsIo

N

l-

a

INN

A

Ia

t

Io

od606Noooo€*ooe{6rN@d6e€o6ooQ@666

$oNhFoo$6FO@-oOSrONiOoOOOiaOOO6a60

do o ts o No N NO O O O NOdd!ocd66ra<oE=>uzkh

282 J.L.Bodinier et al.

t BLE 2 - Trace eldent coDpoaltlon of Dlnerels froe pyroxenited

0rthopyroxene Cllnopyroxene Garnet

10-379d 7D-379b 72-226 70-351 70-319d 70-379b 72-226 70-357 10-358 70-29t 70-385c 70-29t 70-385C 70-357

sc(vCrCoN1CuZnLaCeNdSoEuTbYbI{Ef

ppr) 13.3145693

5l450

6r3

'14.15

.046

.019

.028

.35

.056

'08

20.3r3.5

605 8lr46 s7

.35 .043

.30 . l0

.068 ,012,031 .008.o32 .012.35 .31,068 .06I.05 .07

9.3 54.6i42 414315 107365 22

525 269188ir 20

.05I .21

.07 l.0l3.8

.010 r.66

.007 .5s

.01 .51

.03 1.21

.004 .20

.05 1.3

1.52 .t2 .512.a .45 2.262.3 t.26 3. rr.63 t. ll r.03.17 .51 .37.63 .2t .1 5

2.70 .13 . 19.56 .01 7 .026

r.2 .5 ,5

67.t

t73l6

77.t 31.4 30.I 14.9 48.5 8r.3 90.0 94.3338 65

1840 1353 rO77 4823 66 53 25

363 4214315 2l

. l0 .48 .062 .060

.51 2.03 .17 .303.2

.27 1.53 . 13 .29 .34.62 . 13 .24 .36

,043 .50 .20 .37 .38.043 t.42 1.65 3.68 3.26.004 .2t .3r .62 ,55.07 .7 .18 .45

23t4 560 t235 140619 24 28 33

1.504.84.92.02

,75.80

2.t7.34

t.2

+ Fe2 with Fe3+/Fe2+ assumed to be 0.15) ranging from0.83 to 0.91. Several other major elements such as Al,Ca, Mg and Fe display significant variations, some ofwhirch are related to the modal composition. The majorelement trends observed among the various pyroxenitelayers are very similar to those found within differentzones of the same layer, as shown, for example, by a

comparison of the variations among the different layenof the Freychindde massif to those observed betweensamples 70-379a and 70-379b, which were collectedrespectively in the external and central zone of thesame layer (Table 4).

The chemical variations are accompanied by inter-element correlations including Ca-Mg (Fig. 4) and Ca-Na. These two pain of elements exhibit a regular evo-lutionary trend suggesting, in agreement with CoN-qufn6 (1977), that the variations are dominated bythe fractionation of orthopyroxene and clinopyroxene.However, the fractionation or accumulation of thevaiiable proportions of clinopyroxene and orthopy-roxene cannot explain all the observed chemical trends.For example, the variable abundance3 of AlzO: andSiOz (Fig. 4) particularly the hieh Al contents of somesamples and the negative correlation between thosetwo oxides is consistent with the mineralogy and para-genesis of the samples which contain primary Al-richand Si-poor phases such as spinel or garnet.

Trace elemenls. In comparison to basalts, the py-

roxenites are significantly hrgher in Cr, Ni and Co buthave similar contents of Sc, V and Zn. Relative topyrolite (SuN er al., t979\thepyroxenites are enriched

TABLS 3 - Cllnopjrroiene/orthopyroxene partltl.on coefflcl-ents for transltl.on eleEenta

70-379d 70-379b 72-226 10-357

in Sc, V andZn and depleted in Cr, Ni and Co. Theirabundances of transition elements display a large rangebut are similar to those reported by FRnv and PRrNz(1978) and Fnrv (1980) from pyroxenite xenoliths inbasaltic rocks and by Lousrr and ArI-icne ( I 982) onpyroxenites from orogenic lherzolite bodies. Like majorelements, the trace element geochemistry appears tobe controlled by the modal abundances of the primaryphases and a few minor phases such as sulfides whichare abundant in some pyroxenite samples from thesemassifs (CoNqufn6, 1977; LoRAND, 1983). The cli-nopyroxene-rich rocks (e.g. 70-379b,72-18) are gen-erally higher in Sc and V and lower in Co, Cr andZnthan the orthopyroxene-rich samples (e.g. 7 0-319a, 72-364,72-427a).

Chondrite-normalized R.EE patterns of the pyrox-enites are depleted in LREE with La and Yb abun-dances ranging respectively from 0.6 to 3 and from 3

to 17 times chondrites (Fig. 5). They are comparableto the data compiled by FnEv (1984) on pyroxenitelayers from various alpine peridotite bodies and to thedata of Louser and AllEcnp (1982) on the pyrox-enites from the same massifs (Fig. 5). According totheir shape, the REE patterns can be subdivided into3 types:

-The first type which isthe most abundant, resem-bles the patterns ofthe clinopyroxene (Fig. 2) or theN-type MORB (SuN er a1.,1979\ with [Sm/Yb]N - I(N-chondrite-normalized) (e.g. sample 72-18, Fig. 5).

-The second type differs from the first by HREEfractionation accompanied by [Sm/Ybh < l. Amongthese samples, the pyroxeniteS (70-379b and70-291)with the lowest [Sm/Yb]p ratio (<0.2; 70-379b and70-291) also have the highest Al2O3 concentrations(>12.7V', and contain relicts of primary garnet (CoN-qu6n6, 1977\. The pattern resembles that of garnetand issimilarto gamet pyroxenites from Beni Bouchera(LouBEr and Alricnp, 1979).

-The third type of pattern (e.g. sample 70-379a,Fig. 5) displays a relatively flat shape without distinclLREE depletion and HREE fractionation. These pat-

ScvCrCo

Nt

4. I 5.0 3.82.9r.6 1.3 2.9.43 .35 .33.50

3.4 2.0 - 8.0

1.8 r.4 - 3.0,37 .36 - ,49

.39 - .62

(l): range of partltlon coefflcl.ent values flon aploelperldotlte xenollths (sto8ch, 1981).

Aridge layered pyroxenites 283

HlEo2.5oI

8.1zi.os

o1La Ce sm Eu Tb Yb Lu La Ce Nd SmEu Tb Yb Lu La Ce Sm Eu Tb Yb Lu

FIc. 2. Chondrite-normalized REE abundances in separated minerals from the pyroxenites. A: ortho-pyroxene; B: ctnopyroxene; C: garnet. In B, the dashed lines correspond to the clinopl,roxene from thegarnet clinopyroxenites which contain abundant proportions of secondary garnet (-40-507o). The othersamples are either devoid ofgarnet(72-226; spinel orthopyroxenite) or contain variable amounts ofprimarygarnet (70-379b and d, 70-385c: gamet ari0gite and websterites).

terns show some simiLarities to several Salt lake Craterpyroxenites (FnEY, 1980). The relatively high contentsofLREE cannot be due to the presence ofa trappedliquid. ihese samples are as depleted in total REE andother incompatible trace elements (e.S.Ti,Zr,Hf) rel-ative to basalts as the other pyroxenites (Table 4).

DISCUSSION

Pyroxenite layers in high-temperature alpine peri-dotites and ultr€lmafic xenoliths are generally inter-preted as uppef mantle cumulates or crystal segregates

formed by flow crystallization (KoRNpRoBSr, 1969;

TABLE 4 - UeJor and trace €lment conpositlon of pyroxenltea

1970; InvrNc, 1980; FRev, 1980; Orere et al.,1980;Louser and Arricnr,1979,1982). The presentedgeochemical data including hrgh tMgl values, Cr andCo contents and strong depletion of K, P, Ti, La, Ce,Zr and Hf are consistent with such a process. Fur-thermore, the very low contents of incompatible ele-ments imply that the interstitial liquid was effectivelyexpelled from the pyroxenites.

A question arises regarding the characteristics oftheparental magmas of the pyroxenites. Although somesamples still contain relicts of high P-Z phases, meta-morphism has generally obliterated the magmaticmineral assemblages (CoNqu6pS,1977). Thus, in orderto put constraints on the pyroxenite petrogenesis, it is

sro2(z)ArdrFef g

ItdOu8oCroNa 29K20TtO2PzQsu)I

I [nslRb(ppo)siSc

,v.cr

CoN1btZ^LeCeSoEuTbYLLuYllfZt

Ref: 7O-379 70-379a 7O-379b 7O-379d 72-445 70-291

47.61 49.02 45i85 46.66 44.31 46.84 45.2710.05 8.40 t2.75 tt.35 12.14 t3.47 10.896.90 5.40 7.9A 8.3r 6.lt 1.84 8.090. 14 0. ll 0. t8 0. 13 0. 12 0. 17 0. 12

24.t8 26. r0 20. r8 2r,52 23.96 16. l2 25.507.a2 7.46 10.19 9.89 8.59 13.97 6.840.58 0.51 0.60 0.58 0.73 0.7s 0.620.02 0.02 0.02 0.02 0.02 0.02 0.020.24 0.21 o.2L 0.26 0.30 0.rl 0.410.05 0.04 0.04 0.04 0.03 0.03 0.040.9q r.02 0.7r 0.26 2.4r 0.57 0.92

98.55 99.29 94.72 99.02 98.72 99.89 98.82. E9 .91 .86 .86 .90 .83 .89

48.20 51.049.67 7.907 .t7 7.130.12 0.16

23. l0 22.208.r9 9.300.84 0.790.02 0.020.42 0.460.04 0.040.62 0.73

98.39 99.71.89 .88

46.25 49.EIl r.85 q.807.92 6.480. t4 0. 14

22.37 I8.958:47 13,210.5E 1.050.02 0.02o.47 0.370.03 0,030.82 0.61

98.92 99.47.47 .a7

48.24 45.86 44.6810,26 tr,77 11.908. l0 7 .44 6.520.16 0,r5 0,13

21.00 19.21 17.659.84 11.85 14.350.79 0.80 0.990.02 0.02 0,020.34 0.38 0.630,02 0.03 0,030.23 0.64 2,O4

99.00 99.r5 98.94.86 . E6 .89

46.276.21

10.520. l4

28.006.550.540.02o.290.030.56

99.23.86

lll2lll26 27 15 27 r1 30 68 36 2939 27 56 37 44 30 32 35 37 39 26 43 49 50260 223 408 340 253 27a 204 218 2t6 230 282 164 3tO 267 2gA2025 6538 2255 2990 2445 1652 48t3 2a62 3200 2365 2t72 2855 1385 2t24 t24460 62 57 61 55 58 85 72 56 64 51 91 61 52 541640 1860 2155 1400 1745 2590 2335 2290 2050 t735 2050 2320 1665 1645 13606l ll0r 47 32 46 l0 I59 238 86 73 ll4 79 63 40 ll2?s 74 65 71 189 31 98 74 44 ll3 35 tol 6s 34 450,44 0.67 0.37 0.39 0.33 .O7 0.27 0.05 0.23 0.21 0.52 0.20 o.l8 o.2o 0.541.90 2.t8 r.43 r.65 t.26 .24 l.l3 2.98 0.83 0.90 2.08 0.80 0,76 1.t5 2.470.62 0.64 0.65 0.83 0.65 0.t7 0.56 0.75 0.45 0.72 ,0.97 0.17 0.57 0.69 r.230.26 O.24 O.29 O.29 O.29 O.ll 0.26 0.34 0.20 Oi33 0.39 0.r8 O.27 0.33 0.540.20 0.t7 0.38 0.31 o.27 0.r2 0.I8 0.25 0.16 0.23 0.28 o.l3 0.28 0.22 0.341.08 0.56 3.74 1.74 t.97 1.43 1.00 1.36 t.25 1.00 l.60 0.86 1.90 r.04 1.360.r7 0.ll 0.58 0.27 0.29 0.24 0.r7 0.22 0.20 0.16 0.25 0.t5 0.32 o.r7 0.229t515llll14t7lll4

o.2 0.7 0.4 0.6 0.4 0.1 0.3 0.5 0.4 0.4 0.2 0.3 0.3 0.6l8 ti t8 8 14 16. 19 ll 20

72-364 72-357 7l-262 72-361 7O-385c 72-427a 72-2OZ 72-212

P-Predesi tUSl-Ut/(Mg + Fez+) rtth p63+73s2+ assuned to be 0.1.5.

284 J. L. Bodinrer et al.

xo-o

i10o

FutzE(,

:-- 1

xo.o

equations using the total inverse technique of TAR-ANToLA and VALETTE (1982). In the calculations, allparameteN are considered to be unknown within acertain error range and constrain and adjust each other.The iterative numerical routine requires a given "apriori" solution.

As "a priori" parameters of the composition of themineral phases (Table 5) we took the compositionalranges ofhigh P-Zgarnet and spinel reported by IRVTNG(1974) and the range ofdata on high P-Zpyroxenesgiven by BrNonn et al. ( I 978). The data from BENDERet al. (1978) were selected because the high Ca contentof numerous pyroxenites implies that the primary cli-nopyroxene was Ca-rich. The "a priori" proportionsof the phases were estimated from the normative com-position by recasting whole-rock data as pyroxenes.The results of the calculation, assuming that Al is pres-ent only in the Tschermak's molecule of the pyroxenes,are plotted on Fig. 6 together with the coexisting highP-Tclino- and orthopyroxenes (BrNoen a al., 1978).Samples such as 70-385c andTl-262 which lie veryclose to the clinopyroxene-orthopyroxene tie-line couldhave been composed only of two pyroxenes. On theother hand, samples such as 7O-379b and 70-291 whichplot well above the pyroxene tie-line, towards theTschermak's mole apex probably contain an Al-richphase (gamet or spinel). The normative calculation was

si 02%43s1705153

Frc. 4. Variations of CaO vs. MgO and A12O3 us. SiO2 inthe pyroxenites. Solid lines delineate the fields of high-P cli-nopyroxene (CPX) and orthopyroxene (OPX) after BENDERet al. (1978) and WIlxrNsoN (1976). The arrows show thedirections ofthe tielines between clinopyroxene and, respec-tively orthopyroxene, spinel and garnet. Solid cicles: our data;empty circles: data from ITUBET and Autcnn (1982).

LaCe Nd SmEu Tb Yb Lu

FIc. 3. A: Clinopyroxene/orthopyroxene partition coefr-cients of REE in the pyroxenites. Nd for orthopyroxene wasinterpolated. The range of the values from spinel peridotitexenoliths in alkalic basalts are shown for comparison: small-dashed lines after OroNeLlo (1980) and dashed lines afterSroscn (1982). The heavy solid line represents the partitioncoefficients from lherzolite of the Lizard ultramafic body(Fnrv, 1969). B: Clinopyroxene/gamet partition coefficientsof REE in the pyroxenites. The dashed lines represent therange of values for eclogite inclusions after Pslrporrs el a/.(1972).

first necessary to evaluate the nature, modal propor-tions and composition of the primary mineral phases.

(A) Primary mineral phases

Assuming that the primary magmatic assemblages

were composed of clinopyroxene, orthopyroxene, spi-nel and/or garnet and the recrystallization processes

did not significantly affect the bulk chemical compo-sition, the modal proportions and compositions oftheprimary phases were estimated by petrological mixing

CaO %

l5

also carried out by assuming that all the Al was presentin garnet or spinel. Trace elements were used to identifrthe phase: for example, the samples with distinct HREEfractionation probably contained garnet. These samples(70-379b and 70-291) are also characterized by thelowest TilSc ratios (<25 versus 40-7 5 in other pyrox-enites), and relatively high Mn contents (Table 4). Onthe other hand, the pyroxenites rich in Cr and with aflat REE pattern (e.g. sample 70-379a) probably hadspinel in their mode. The "a priori" modal estimatesfor clino- and orthopyroxene obtained by projectionfrom the Ts apex onto the pyroxene tie-line (Fig. 6)were taken with an error range of 5O7o. The proportionsof the Al-rich phases were taken as the mean values ofuncertainties ranging from l7o to an upper limit ob-tained from a normative calculation assuming all Alin spinel or garnet.

The initial calculations suggested that both spineland garnet are present in several samples. These sam-ples are from the composite layers and integrate dif-ferent zones ofthe layen. Thus, additional calculationswere undertaken, assuming an "a priori" equal distri-bution of Al between these two minerals. The results

285

are reported in Table 5 for sample 70-379b and inTable 6 for the other samples. Samples 70-379a and70-379b are from distinct zones ofthe same layer (Ap.pendix 1) and contain only spinel (70-379a) or garnet(70-379b). Conversely, sample 70-379, which repre-sents the wholeJayer composition, contains both min-eral phases. The calculated pyroxene compositions(Table 5) are close to those given by CoNqutpf(L977)for analyzed primary pyroxenes. The data were testedby an estimation of the temperature of equilibrationof the calculated assemblages (Table 7). The temper-ature obtained, particularly on the two pyroxene geo-thermometer is very similar to that found experimen-tally (1425"C) by KonNpnorsr (1980) for the garnetpyroxenites from Freychindde. The agreement betweenthese two temperature estimates indicates that the cal-culated mineral composition may closely approximatethe primary phase composition.

(B) Composition of coexisting liquids

The major element compositions of a liquid inequilibrium with clinopyroxene at a temperature of

Aridge layered pyroxenites

Sm Eu Tb Sm Eu Tb

Ftc. 5. Chondrite-normalized REE abundances in the pyroxenites from Lherz (A) and Freychindde (B).Dotted lines delineate the range oflight REE depleted pyroxenites ofLouBET and At.r,icne (1982) fromLherz and Freychin0de. The dashed line corresponds to pyroxenite 74-57 ofI-ouser and Arricnr (1982)from FreychinEde.

oE!3o-oI(,

oz(,oC

TABLE 5 - Calculated conpoaltlon of prlnary olnerals

"A prlorL" valueg

sloz (t) 51.5 (0.6)Alzor 7.0 (0.3)cr2o3 0.8 (0.3)Feo 7.3 (0.3)uno 0.1 (0.I)uso 30.0 (0.6)cao 2.5 (0.3)Nazo 0.2 (0.3)T1o2 0.1 (0.1)[ 99.5x (z) 20 (10)

50.63 (.29)7.25 (.22)0.2r (.03)6.92 (.17')0.14 (.0r)

30.s1 (.24)2.52 (.06)0.92 (.07)o.l2 (.02)

99.2217 (3)

"MJueted" values

49.34 (.24)9.69 (.20)0.27 (.0s)s.10 (.14)0.08 (.0r)

17.93 (.18)15.s4 (.18)r.ll (.03)0.33 (.04)

99.3949 (4)

39.03 (.r4)20.r3 (.r3)0.s0 (.08)

r0.40 (.22)0.44 (.04)

20.36 (.20)7.8r (.24)0.00 (.00)0.15 (.04)

98.8234 (4)

48.5 (0.7)9.0 (.03)1.s (0.3)5.0 (0.3)0.r (0.r)

r8.0 (0.6)16.0 (0.6)0.6 (0.3)0.1 (0.r)

99.850 (25,

4r.0 (0.6)22.O @.6)0.1 (0.1)

10.5 (0.3)0.3 (0.1)

18.0 (0.6)7.5 (0.3)0.0 (0.0)0.r (0. l)

99.530 (2s>

X - mdal proportlons; the values ln bracketa are Ipyroxene; CPX - cllnopyroxene, Gl - Sarnet

.t

ataodard devlatlons. OPX - ortho-

286 I.L.Bodinrer et al.

FIc. 6. Whole-rock pyroxenite composition plotted intodiopside-enstatite- (Ca + Mg) Tschermak's component dia-?tamt 2 = 7 0-37 9a, 3 : 7 O-37 9b, 6 : 7 0-29 l, 7 = 7 2-365, 9

= 7l-262, ll : 70-385c, 12 = 72-427a. Tie lines-emptycircles: composition of high P- T clinopyroxene-orthopyroxenepain of BBNpnn et al. (1978); solid circles: pyroxene pairswith the highest Al content from Aridge pyroxenite layers(CoNaufRf, 1977).

about 1400'C and pressure 15-25 kb was calculatedaccording to the procedurc of HaNsoN and LANGMUIR(1978) and is given in Table 8. The calculated liquidhas a composition typical of tholeiitic basalts as indi-cated particularly by the contents of SiO2, TiO2 andNazO. The tholeiitic character of the parental magmaof the pyroxenite is consistent with some other geo-

chemical and petrological data. In contrast to pyrox-enites related to alkalic basalts, (e.g. Fnrv and PRTNZ,

1978; MENzles, 1983) the analyzed rocks have d com-position marked by a depletion of LREE, Ti,K,P,Zrand Hf. The sequence of mineral fractionation (CoN-

au6R6, 1977) indicates that orthopyroxene is a liquidusphase, a feature typical of tholeiitic magma. Likewise,the experimental studies at high pressures (20 + 5 kb)show that the fractionation of picritic tholeiites andtransitional and alkalic basalts cannot account for theabsence of olivine among the cumulate phases (Iro

TABLE 6 - Calculated prlDary Dodal cooposltlon of pyroxen-Ites

Sanple

TABLE 7 - Ibo pyroxene te[peratures (afterItercier and Bertrand, 1984)

15 kb 25 kb

7 O-37 9a70-379b7 2-4277 t-26272-20270-29r

1405"c r42s"c13900c 1410'c1430'c 1450'c1380'c 14000cr4l0'c 1430"c1400"c 1420'c

and KErvxeoy, 1968). On the contrary, the mineralassemblages of the pyroxenites can be derived fromolivine tholeiites (GnreN and RrNGwooD, 1967 t T ltr-suMr et al., 1983't

Tholeiitic basalts occur in several areas in the Pyr-6n6es. Perhaps the most widespread are Triassic tho-leiitic dolerites which were erupted during the earlystage of the opening of the Atlantic Ocean (Momclwet al., 1982). From the recent geochemical data ofAr-IBERr (1985) it appears that they may have character-istics of the parental magma for the Pyr6n6es pyrox-enites. This hypothesis was tested for trace elementsby the application of the inverse method to the equationof equilibrium crystallization. With regard to the "apriori" parameters (Table 9), the composition of theparental liquid was taken as the range of tholeiites givenby ALIBERT ( 1985), while the analysed pyroxenites wereconsidered to be solids. The proportions ofthe phaseswere taken from the calculated modes of the primaryassemblages of the pyroxenites (Tables 5 and 6),whereas the partition coefficients of InvrNc (1980) forpyroxenes and spinel and those ofFnry et al. (1978)for garnet were employed (Table 9).

The calculation was done separately for each sample(calculations for sample 70-379b are shown in Table

TABLE 8 - Calculated conpo6ltlon of 11qutd tn equtllbrlun otthcllnopyroxene

Llquid

7O-379a 7O-379b 7O-379a 7O-379b

slo2 (z)ArPsctf:FeOMtrO

ugoCaO

NafTt0 2tttlgl

49.54 49.348.68 9.690.36 0,274.17 5. l00.09 0.08

t8.57 17.93t6.07 r5.540.98 l. I I0.39 0.33

99.45 99.39

49.54 (0.26)14.7r (0.34)0.05 (0.0r)

r0.16 (0.32)o,22 (o.02)

1r.46 (0.r3)10.79 (0.12)2.39 (0. l2)1.05 (0.11)

100.330. 70

49.34 (0.24)16.40 (0.34)0.03 (0.0r)

10.86 (0,30)0. r9 (0.02)

11.07 (0.11)r0.43 (0.r2)2.7t (O.07)0.E9 (0.1r)

r0r.920.68

70-3797O-379a70-379d72-44570-29172-36472-35172-36170-385c72-20212-21272-t8

44 (3)s8 (3)20 (3)36 (ll)6 (3)

s4 (4)44 (3)37 (3)l7 (3)32 (2)r7 (s)5 (5)

43 (4)38 (3)5e (9)5l (10)60 (14)37 (3)47 (3)45 (3)78 (s)s4 (3)73 (s)86 (r0)

l0 (3)0 (0)

l7 (r0)7 (1)

33 (e)1 (l)6 (4)

l6 (6)5 (r)

14 (4)7 (r)7 (r)

SP

The Dodes of sanples 71-262 atd, 72-427a are not reportedsloce the los A1 cootenta would requlre the presence ofollvlne ln thelr [ode; ollvl.ne la not consldered to be ofpriury MgDatlc orlglo ln the pyroxenltes. The values lnbracketa correapond to I staodard devlatlon. OPX - ortho-pyroxene; CPX - cllnopyroxenel SP - spinel; GT - garnet.

The cooposltlon of the liquid E6 calculated ualog the partttl.oncoefflclent (K) of Bender et al. (1978) for S1O2, MgO aod ofthorpBon (1974) for the ltSo/Feo ratlo. (g. calculateJ fron theregresslon ltne Ink, - -2193 + 1.69 ar T = 1400"K (Elthon and

T'CScarfe 1984, Fujtt and Bougault, 1983, crees and Hlbber6on, 1970,Thonpeon, 1974 dnd B€nder et al. 1978). A slDllar regress{on 11neglves K11 - 0.37 at 1400'K and KAI - 0.59. Stoce XNa tsdffccted by pressure (Tho@on, 1974), the regresslotr llne is asfofl@B: lnKNe - 0.067 P(kb) - 2,236. Thue K11" - 0.41 at 20kb, \rn ' 0.43 and KCr - 8 afrer Schtlllng er al. (1978). Ttecoqotltlona of cllnopyroxene are calculated "adju6ted" values(Tab1e 5) for the irinary clldopyroxene. The values ln bracketsare the errora calculated by the lnverslon rethod representlnguncertalntles ln the prtDary ntneral (Table 5) and nodal (Tabte 6)coEposltlons.

3 (3)4 (l)4 (4)6 (l)I (r)8 (r)3 (3)2 <2)0 (0)0 (0)3 (l)2 (l)

Aridge layered pyroxenites

TAILE 9 - Calculated RBE partltlon coefflclenta and corposltlon of parental llqulil for aaople 70-379b

"A prlorl" vsluea "Adjusted" vslues

Llqutd

287

Ltquld

La (ppo)Ce

SnEuTbrtx (z)

.003 (.001)

.005 (.001)

.020 (.005)

.030 (.006)

.050 (.01)

. 15 (.03)17 (3)

.10 (.02) .00r (.00r)

.1s (.03) .oo3 (.002)

.39 (.07) .08 (.03)

.46 (.08) .20 (.08)

.52 (.12' .8 (.4)

.53 (.r4) 4 (3)49 (4\ 34 (4)

7.5 (1.0)l7.s (2.0)2,8 (.2).e8 (.r).55 (.05)

r.80 (.2)

.003 (,001) .088 (.003) .0014 (.0010) 7.48 (.52)

.006 (.001) .152 (.006) .0038 (.oor9) r8.09 (1.40)

.0i8 (.005) .43 (.02) .060 (.024) 2,66 (.16)

.027 (.006) .50 (.02) .19 (.07) .91 (.06)

.063 (.010) .58 (.03) l.l0 (.31) .61 (.03)

.r5 (.03) .s8 (.04) 6.3 (.e) r.78 (.rr)20 (3) s2 (3) 28 (3)

-A prlorl" values: KD for pyroxeoes and apinel - Ilvlng (1980), KD for garnet - Frey er al. (f978), liquld - Trta88lctholeiltes fron Pyr6n6es (Altbert, f985), x (nodal proportlone) - calculated node6 of the pri@ry asaenblage (Table 5). T'tlevaluea i.n brackets - I standard devlatloo. OPX - orthopyroxene; CPS - clLtropyroxene; CT - garnet.

oUFE

<*G-oG\sg'r0

5s

5

1o5o{sxLooF,zaLU1

_olz' EouFEd

9 as an example) and the results ("adjusted" values)for the REE composition of the parental magma ofpyroxenite are given in Fig. 7 together with the rangeofREE abundances in the Pyr6n6es dolerites obtainedby Almenr ( 1985). The "adjusted" data fall well withinthe range ofthe dolerites. Due to the relatively uniformcomposition ofthe dolerites, the "a priori" compositionof the parental liquid was constrained within a verynarow range during the calculations (Table 9). Con-sequently, the least constrained parameter-partitioncoefficient values-shows the largest spread. The cal-culated partition coefficients for clinopyroxene areshown in Fig. 7. For six samples, the values are withinthe range defined by the two experimental sets of par-tition coefrcients given by InvrNc (1980), in agreement

with the tested model. Exceptions are three samples-'12-357 , 70-379 and 70-291 . The first two samples havehigher partition coefficients for La and Ce. Since onlytwo elements are involved, it seems that these two py-roxenites were either derived from different parentalliquids with higher LREE content or were affected bya secondary proces which preferentially enriched theseelements. The second alternative is preferred as thesamples contain minute amounts of secondary am-phibole (Appendix l) occurring either in the thin layers(72-257) or at the margin of the thick layers (70-379a).

The third sample (70-291) yields very low partitioncoefficients outside ofthe data range oflnvrNc ( 1 980).In fact, the composition, particularly for trace elements,of this pyroxenite differs from that of the other samples.Rock 70-291 was either derived from a different pa-rental magma with adistinct composition characterizedparticularly by a strong depletion of incompatible traceelements or more likely the pyroxenite was modifiedby a subsequent partial melting event as suggested byLouBEr and Arricnr (1982) for some mafic layersfrom high-temperature alpine bodies. Similar invenemethod calculations have been done for pyroxenitesfrom Lherz and Freychindde studied by Louner andAt-LEcns (1982). Their samples can also be suMividedinto the same three groups and provide results whichare consist€nt with the models suggested for our sam-ples.

CONCLUSION

The pyroxenites interlayered with spinel lherzolitesin the three high-temperature alpine peridotite massifsin Aridge have suffered a complex petrogenetic history,marked by a subsolidus recrystallization following earlyemplacement. The distribution of the trace elementsin minerals was partially modified during recrystalli-zation; for instance, the HREE and Sc were prefer-entially incorporated in the secondary garnet, at theexpense ofthe pyroxenes. This process has not signif-icantly modified the whole-rock composition whichhas only been affected by a slight metasomatic enrich-ment near the margins of the layers.

Otherwise, most ofthe pyroxenites have geochemicalfeatures typical ofsegregates. A process involved in themineral-liquid separation could have been dynamic

La Ce Sm Eu Tb Yb

Ftc. 7. A: Calculated composition of liqrrids in equilibriumwith the pyroxenites (heavy line). Dscontinuous lines delineatethe field of data reported by Arnrnr (1985) for \reneantholeiitic dolerites (+l standard deviation). B: "Adjusted"partition coefficients for clinopyroxene/iquid. Discontinuouslines: two experimental sets ofpartition coefficients reportedby Invwc (1980).

288 I.L.Bcdinier et al.

c

72.357

70.385c

72.202

7r.262\\

72.212

72.361

flow crystallization during migration ofbasaltic magmathrough spinel lherzolite, a mechanism described indetail by IRwNG (1980). Contrary to pyroxenite xeno-liths which zre usually assumed to be derived fromalkalic basaltic magma (e.g. FRrv and PnrNz, 1978;

IRvrNG, 1980; MrNzIrs, 1983; FRry, 1984), the stud-ied pyroxenites are related to tholeiitic magma. Thepyroxenites are depleted in the most incompatible ele-ments particularly LREE. In addition, their partition-ing ofREE between clino- and orthopyroxene differsfrom that of the xenoliths and phenocrysts in alkalicbasaltic lavas but resembles that of ultramafic rocks inalpine peridotite bodies. The chemical composition ofthe parental tholeiitic magma is very similar to thecomposition of Triassic dolerites encountered throughthe Pyr6n6es.

The study also strows the importance of high P-Zfractionation in ascending primary magrwu "en routs"to the surface. In particular, it suggests that pyroxeniticsegregation can account at least partially forthe LREEenrichment in continental tholeiites. Consequenfly,parental magmas of continental tholeiites can be de-rived from a source with a flat REE pattern.

Acknowledgements-T\anks are due to Drs. F. A. Frey, M.Polv6, J. W. Shervais, J. Suen and J. Kornprobst for theircritical comments on the manuscript and J. Vernidres for helpin the calculations. We thank J. P. Iorand for his selectionof the samples. The study was financially supported by ATPtransfert and the NSERC ofCanada (operating grant A3782).

Editorial handling: F. A. Frey

72.384lrJlJl l

h;t 2

lr*rl s

Fl;l +

F;t 5

l5o9 e

72.427

72.226

REFERENCES

ALIBERT C. (1985) A Sr-Nd isotopic and REE study of larcTriassic dolerites from the grren€es (France) and the Mes-sejana Dyke (Spain and Portugal). Earth Plana. Sci. Lett.73, 8l-90.

AvE r rttEvlNr H. G. (1967) Structural and petrographicanalysis of an "alpine-type" peridotite. The lherzolirc ofFrench $rren6e s. Leidse Geol. Mededel. 42, l-57.

BENDER J. F., HoDGES F. N. and BENCE A. E. (1978) Pet-rogenesis ofbasalts from the project Famous area: experi-mental study from 0 to 15 kbars. Eanh Plana. Sci. Lett.41,277-302.

Bnerrac{eu S. and Sumr C. H. (1964) Flowage difer-entiation. Science 145, 150-l 53.

CoNeuEnf F. (1977) P6trologie des pyrox6nites lit€es dansles complexes ultramafiques de I'Ari€ge (France) et autr€sgisements de lherzolite i spinelle. Compositions min6ral-ogiques et chimiques, 6volution des conditionsd'equilibredes pyrox6nites. Bull. Soc. Fr. Min6ral. Cristal. lM,42-80.

CoNQUfRf F. ( 1978) P6trologie des complexes ultramaiquesde lherzolites i spinelle de l'Ariige (France). ThEse Doct.Etat, Paris, 333 p.

CoNqu6nf F. and FABRDsJ. (1984) Chemical disequilibriumand its thermal significance in spinel peridotites from theLherz and Freychinde ultramafic bodies (Ariige, Frenchhnen6es). ln Kimberlites. II. The Mantle and Crust-MantleRelationships. (ed. J. KoRNpRoB$r), pp. 319-331. Elsevio,Amsterdam.

DosrAL J., Dupuy C., ClnnoN J. P., DEKERNETZoN L. M,and M,luny R. C. (1983) Partition coefrcients oftrace ele-ments: application to volcanic rocks of St. Vincen! Westlndies. Geochim. Cosmochim. Acta 4il, 525-533.

ELfiIoN D. and Scmru C. M. (1984) High-pressure phaseequilibria ofa high-magnesia basalt and the genesis ofpri-mary oceanic basalts. Amer. Mineral.69, l-15.

70.357

FIc. 8. Four sections of the "layered series" in the Freychinide mascif showing the sample locations(modified afterCoNeuERf, 1977) 1-peridotite, 2-olivine-spinel websterite, 3-spinel orthopyroxene,4-spinel websterite, 5-garnet websterite, 6-garnet clinopyroxenite.

;]

FREY F. A. (1969) Rare earth abundances in a high-temper-ature peridotite intrusion. Geochim. Cosmochim. Acta 33,1429-t447.

FREY F. A. (1970) Rare earth abundances in Alpine ultramaficrocks. Pftys. Earth Planet. Inter.3,323-330.

FREY F. A. (1980) The origin ofpyroxenites and garnet py-roxenites from Salt take Crater, Oahu, Hawaii: Trace ele-ment evidence. Amer. J. Sci. 280-A, 427-449.

FnEv F. A. (1984) Raie earth abundances in upper mantlerock. In Rare Earth Element Geochemistry (ed. P. HnN-DERSoN), pp. 153-203. Elsevier, Amsterdam.

FREY F. A., GREEN D. H. and Roy S. D. (1978) Integratedmodels ofbasalt petrogenesis: a study ofquartz tholeites toolivine melilitites from South Eastern Australia utilizinggeochemical and experimental petrological data. J. Petrol.19, 463-5 I 3.

FREv F. A. and PruNz M. (1978) Ultramafic inclusions fromSan Carlos, Arizona: petrologic and geochemical data bear-ing on their petrogenesis. Earth Planet. Sci. Lett.38,129-t76.

FUJII T. and Bouclurr H. (1983) Melting relations of amagnesian abyssal tholeiite and the origin of MORBs. .Eart&Planet. Sci. Lett. 62, 283-295.

GrnnN D. H. and HIssBrsoN W. (1970) Experimental du-plication of conditions of precipitation of high-pressurephenocrysts in a basaltic magma . Phys. Earth Planet. Inter.3,247-254.

GnEeN D. H. and RncwooD A. E. (1967) An experimentalinvestigation of the gabbro to the eclogite transformationand its petrological application. Geochim. Cosmochim. Acta31,767-833.

HAMELTN B., PoLvE M. and AuicnE C. J. (1985) Orogeniclherzolites, upper mantle heterogeneity and reinjectionprocess€s. Teffa Cognita 5, 27 4.

HaNsoN G. N. and LANcMUIR C. H. (1978) Modelling ofmajor elements in mantle-melt systems using trace elementapproaches. Geochim. Cosmochim. Acta 42, 7 25-'l 42.

InvtNc A. J. (19'74\ Geochemical and high-pressure experi-mental studies ofgarnet pyroxenite and pyroxene granulitexenoliths from the Delegate basaltic pipes. Australia. "/. Pe-trol.15, l-40.

IRvtNc A. J. (1980) Petrology and geochemistry of compositeultramafic xenoliths in alkalic basalts and implications formagmatic process€s within the mantle. Amer. J. Sci. 280-4,389-426.

Iro K. and Knrxeov G. C. ( 1968) Melting and phase relationsin the plane tholeiitelherzolite-nepheline basanite to 40kilobars with geological implications. Contrib. Mineral.Petrol.19,177-211.

JAcKsoN E. D. and THAvER T. P. (1972) Some criteria fordistinguishing between stratiform, concentric and Alpineperidotite-gabbro complexes. 24th Inter. Geol. Congr.Montreal, sr,ct. 2, 289-296.

KoRr.IpRoBsr J. (1969) k massif ultrabasique de Beni-Bouchera (Rif inteme, Maroc): 6tude des p6ridotites dehaute temp€rature et de haute pression et des pyrox6nolitesi grenat et sans grenat qui leur sont associ6es. Contrib.Mineral. Petrol. 23, 283-322.

KoRNpRoBST J. (1970) Les peridotites et les pyrox6noliteS dumassif ultrabasique de Beni Bouchera: une 6tude exp€ri-mentale entre 1100 et 1500'C, sous 15 i 30 kiloban depresion &che. Contrib. M ineral. Petrol. 29, 290-309.

KoRtIpRoBsr J. (1980) A subsolidus high pressure/high tem-perature exprimental study on a garnet-websterite assem-blage exsolved from a sirnple pyroxene accumulate at Frey-chindde (an alpine-type peridotite body, Northern FrenchPyr6nees). ln Orogenic mnfic and ultramafic association.C olloques I nter. C.N. R. S. 27 2, 245 -252.

LAcRolx A. (1901) Sur un nouveau groupe de roches trdsbasiques (lherzolites, aridgites). (Etang de Lherz, Vall6e duSuc, Prades). C.R. Acad. Sci. Paris 132, 358-360.

LAcRoIx A. (1917) ks p6ridotites des Pyr6n6es et les autres

289

roches intrusives non feldspathiques qui les accompagnent.C. R. Acad. Sci. Paris 165,381-387.

IoRAND J. P. (1983) ks min6raux opaques des lherzolites ispinelle et des pyroxenites associ6es: une 6hrde comparativedans les complexes orog6niques et dans les enclaves desbasaltes alcalins, ThEse, Univ. Paris, 254 p.

I-ounnr M. and ArrBcne C. J. (1979) Trace element studiesin the Alpine peridotite of Beni-Bouchera (Morocco). Geo-chem. J. 13,69-75.

I-ouBEr M. and Auianr C. J. (1982) Trace elements inorogenic lherzolites reveal the complex history ofthe uppermantla Nature 298, 809-8 1 4.

MENZTES M. (1983) Mantle ultramafic xenoliths in alkalinemagmas: evidence for mantle heterogeneity modifred bymagmatic activity. ln Continental Basalts and Mantle

, Xenoliths (eds. C. J. HAwKEswoRrH and M. J. NoRRy),pp. 92-l10. Shiva Publishing Cheshire, U.K.

MERCTER J. C. and BERTRAND P. (1984) Thermobarom6triepyrox6nique. Quelques m6thodes bas6es sur des r6actionsde transfert. ln Thetmom4trie et barom4tie gdologique (d.M. LAcAcHE), pp.237-280. Soc. Fr. Min6ral. Cristal. Paris.

MoNTrcr.ry R., tr2aysxB 8., Rossy M. and THuzenr R.(1982) Etude K-Ar du magmatisme basique li6 au TriasSup6rieur des Pyr6n6es. Bull. Min6ral.105, 673-680.

NrcoLAs A., BoucHEz J. L. and BouDrER F. (1972) Inter-pretation cin6matique des d6formations plastiques dans lemassifde lhenolite de Lanzo. Tectonophysics 14, 143-17 l.

Onere M., SUEN J. and Drcrsy J. S., JR. (1980) The originof mafic layers in the Ronda high-temperature peridotiteintrusion, S. Spain: an evidence ofpartial fusion and fac-tional crystallization in the upper manllelnOrogenic Maficand Ultramafic Association. Colloques Inter. C.N.R.S. 272,257-268.

Or.[Jr4A. N., HIcucHr M., Werrra M. and Nacesewe J.( I 968) Trace element partition between two pyroxenes andthe host lava. Earth Planet. Sci. Lett.5,47-51.

Orrowerro G. (1980) Rare earth abundances and distributionin some spinel peridotite xenoliths from Assab (Ethiopia).Geochim. Cosmochim. Acta 44, 1885-1901.

PHrr-porrs J. A., ScnNerzrER C. C. and THoMAS H. H.( 1972) Petrogenetic implications of some new geochemicaldata on eclogitic and ultrabasic inclusions. Geochim. Cos-mochim. Acta 36, I 131-l 166.

Polv6 M. and ArlDcnr C. J. (1980) Orogenic lherzolitecomplexes studied by t?Rb.E7Sr: a clue to understand themantle convection processes? Earth Planet. Sci. Lett.5l,7t-93.

RAvIER J. (1964) Aridgites et Eclogites. Bull. Soc. Fr. Mindral.Cristallogr. 87 , 212-215.

S,c.voya|.rr L., PERSTN F., and Dupuy C. (1984) D6termi-nation de Terres Rares dans certaines roches basiques etultrabasiques. Geostandards Newsletter 8, 1 59- I 6 I .

ScnruNc J. G., Srcunossox H. and KrNsr-ny R. H. (1978)Skagi and Westem neovolcanic zones in Iceland, 2. Geo-chemical variations. J. Geophys. Res. 83,3983-4002:

SHERvAIS J. W. (1979a) Thermal emplacement model forthealpine therzolite massif at Balmuccia, ltzly. J. Petrol. 20,795-820.

SHERvAIS J. W. (1979b) Ultramafic and mafic layers in thealpine-type lherzolite massif at Balmuccia (Italy) . Mem. Soc.Geol. Padova 33, 135-145.

Snu"rrzu N. and Arricne C. J. (1978) Geochemistry of tran-sition elements in garnet lherzolites nodules in kimberlites.Contrib. Mineral. Petrol. 67, 41-50.

SroscH H. G. (1981) Sc, Cr, Co and Ni partitioning betweenminerals from spinel peridotite xenoliths. Contrib. Mineral.Petrol. TE, 166-174.

SroscH H. G. (1982) Rare earth element partitioning betweenminerals from anhydrous spinel peridotite xenoliths. Geachim. Cosmochim. Acta. 46, 793-81 l.

SUN S. S., NEsBrrr R. W. and SHanesKrN A. Y. (1979) Geochemical characteristics of mid ocean idge basalts. EarthPlanet, sci. Lett. 44, I 19-138.

Aridge layered pyroxenites

290 J. L. Bodinier a/ a/.

TARANToLA A. and Vererle B. (1982) Generalized non-linear inverse problems solved using least-squares criterion.Rev. Geophys. Space Phys. 20, 219-232.

Tersunr Y., SAKUyUMA M., FAKUyAMA H. and KusrnnoI. (1983) Generation of arc basalt magmas and thermalstructure of the mantle wedge in suMuction zones..L Geo-phys. Res. 88, 58 l5-5825.

THoMpsoN R. N. ( 1974) Some high pressure pyroxenes. Min-eral. Mag 39,768-787 .

WILKTNsoN J. F. G. (1976) Some subcalcic clinopyroxenitesfrom Salt Lake Crater, Oahu and their petrogenetic signif-icance. Contrib. ivlineral. Parol. 58, 18 l-201.

WrrsHrRE H. G. and Ptx-E J. E. N. (1975) Upper mantle dia-pirism: Evidence from analogous features in alpine peri-dotite and ultramafic inclusions in basalt. Geology 3,467-470.

APPENDIX 1: SAMPLE DESCRIPTION

Lherz

70-379 Symmetrically zoned composite layer of garnetarieeite (20 cm thick).

70-379a: Marginal zone of70.379, grading fiom orthopy-roxene-rich websterite (619o Opx, 34Vo Cpx,4VoSp) near the margin to spinel websterite (43Vo Opx,47Vo Cpx, l07o Sp) toward the centre. Secondaryreactions, relatively frequent, are characterized bythe growth of plagioclase and brown amphibole.

70-379b: Central and thickest 2one of 70-379, consisting ofgamet aridgite (57Vo Cpx, 3l1o Gt, l27o Sp, withminor Opx).

70-379d: Composite sample: spinel websterite with a smallquantity of garnet aridgite.

72-445: Spinel websterite (50Vo Opx, 427o Cpx, 870 Sp)forming the main mass of a symmetrically zonedboudin, 5 to 15 cm thick. Both margins (about 7

mm thick) are composed of orthopyroxene, withintentitial grains of spinel and clinopyroxene.

70-291: Garnet clinopyroxenile (567o Cpx, 427o Gt,29o Sp)from a 40-50 cm thick layer.

Freychinide

The samples of pyroxenites were collected in four profilesexposed along a deep gully in the eastern part of the massif(Fie. 8).

72-364:- Thin layer (up to 3 cm) of spinel websterite (5470

Opx, 3l%o Cpx, lS%o Sp) with fuzzy contacts. Asmall amount of serpentinized olivine is present.

72-357: Thin layer (2 cm thick) ofspinel websterite (5370

Opx,399o Cpx, 87o Sp). Pale brown amphibole isoccasionally present.

7l-262: Symmetrically zoned layer (8 cm thick) gradingfrom orthopyroxenite at the very margin to spinel

websterite with equal proportions of orthopyroxeneand clinopyroxene in the central zone. The abun-dance of spinel increases toward the centre.

72-361: Symmetrically zoned layer (25 cm thick) gradingfrom orthopyroxene-rich websterite near the inar-gin to spinel websterite (499o Opx,40Vo Cpx, ll%Sp) in the central zofle.

70-385c: Gamet websterite (33Vo Opx, 607o Cpx,7% Gt)from the core ofa composite pyroxenite lens (80cm thick and 3 m long). It is separated from theorthopyroxene-rich mdrgins by a transitional spinelwebsterite (50% Opx, 48Vo Cpx, 29o Sp).

72-427a: Thin thyer (3 cm thick) ofspinel websterite. Or-thopyroxene is more abundant than clinopyroxene;olivine occurs as interstitial crystals crowded withtiny opaque veinlets.

72-202: Symmetrically zond layer(I8 cm thick) composedof gamet and spinel-free websterite near the mar-gia, and garnet-spinel bearing websterite in thecentral zone.

72-212: Symmetrically zoired layer (50 crn thick) gradingfrom othopyroxene-rich websterite at the marginto garnet-rich spinel websterite in the central zone.

Prades

72-18: Symmetrically zoned layer (up to 25 cm thick).The contact is marked by a concentration of or-thopyroxene, with minor amounts of clinopyrox-ene and spinel. The margin consists of a spinelwebsterite with clinopyroxene predominating overorthopyroxene and with relatively abundant palebrown amphibole. At 2 cm from the wall, theabundances of ofthopyroxene and spinel decreaseto the benefit of clinopyroxene and garnet. Thecentral part is composed ofa coarse-grained garnetariegite, with spinel always rimmed by gamet. Thisgamet ariegirc type is different from the 70-379type gamet aridgite in its lower content of spineland garnet and its occurrence only in rims aroundspinel.

In addition mineral separates (Tables I and 2) were obtainedfrom three layers from Lherz and Freychindde:

Lherz

70-358: Garnet clinopyroxenite very similar to 70-291,froma I mthickboudin.

Freychinide

70-357: Garnet clinopyroxenite (107o Opx, 459o Cpx;44VoGt, l7o Sp) from the centre of a thick (0.8 to I m)zoned layer (Fig. 8).

72-226: Spinel orthopyroxenite (887o Opx,6Vo Cpx,67" Sp)from a 16 cm thick layer (Fig. 8).

I;

t,