REl\'UlCONn SUl;IETA IT.... L1A.'lA ()l ...tl:'olERAI.OGIA E. PtXROI.OGIA, 1986. vu!. ~1 (2). pp. 1~5-255

The harzburgite xenoliths in a quaternary basanitoid lava near Scordia (Hyblean Plateau, )

VITTORIO SCRIBANO , Istituto di Scientt della TerrR dell'Universira, Corso halia ", 95129 (halia)

A.ST....CT. - In a quaternary qe basanitoid lava ddormazioni, indicanti una c:omplcssa stotia • me­ flow, cropping out in the l..oddiero Valley (Scordis lamor.fica .. di queue harzburgiti prima dcIla Ioro area, Hyblean Plateau), upper tnlIJltle derived ulm­ incorpotUionc ne! magma OrJpite. Cib uovcrebbe mafic xcnoliths occur; these mosdy consist of riscontro ndIe !time gcotcrmomctrichc cbe indicaoo hanburgites, which exhibit a C'Oal$JC equant (rardy una ri-cquilibrazionc di qucste toCC'C a temperature WJu1at) texture due to olivine (FOoo.• ) and ottho­ rdativamcntc balSC (T < 730" C). pyroxene (EnooFSoWo.) grWls, with scarce Cr-spind Qucsti indusi harzbwgitici prescmano inoItre 'Cr/(Cr + Al)=O.+{l.7) and Cr-

The olivine phenocrysts are zoned from FOg~ to F073 with CaD ranging from 0.25 up to OA5 (wt%). The pyroxene microlites plot in the salite field in the En-Fs-Wo quadrilateral and exhibit rather high Ti content (Ti~ = 3.5 %) (tab. 5, analysis 11. er P It; fig. 5). The opaque micrograins are Ti.magnetite (X... t = OA) where a low va· sw nadium content was found (V~lI = 0.36 " wt7e). The glass is enriched in the feldspar 81g components for some microprobe analyses []]2 indicate Na-sanidine compositions. TABLE 1 ~3 CMm;ctrl trna/ysis of tM host f#vII find its CIPW normflti~ composition. All d~m~nts wt!,~ found by XRF, ~xetpt F~ that ~s d~tt',mint'd by Titrlltion ~4 and M"O by AAS Fi~. I. - ~llon of the xenolith beanng laya .., and its slraugraphic relationshIps with the sur­ roundina rocks. The full lines in the upper sketch, 51°2 .2.13 represent roads, the light dolled ones, $lreams. 1be T10 3 ••5 arrow indicates thc: slIxlied outcrop. Lcgmd of the 2 I) sl.rlI.tigtllphic skelch: quat(rn.ry calcncniles .nd 41:r03 ' •.2' marls; 2) massive basaniloid lava; }) ba~nitoid pillow.fragment breccia; 4) lholciile pilloll' 1.1,". F_ 0 6.U a 3 Bolh 2 .nd } are xenoJith bearing. ,., fi.32 ." Geological u/ting and petrological outlines - ..It 01 the host IttvQ ... ~ H.Dt In the Valley of the Loddiero river, between the villages of Soordia and MWtello, "-:r0 3.02 80 m thick alternating volcanic rocks and ',' 1.33 shallow water marine sediments crop out; P:rO, ... their quaternary age was already suggested L.1. 2.01 (CARTA GEOLlxacA DELLA StCtLIA SUD­ ORIENTALE, 1984). The x~olith bearing Tote! tOD.OD rocks belong to a 10 ID thick lava sheet resting on white marls and interfingered with "" ~ 12." 40 m thick lens of pillow.fragment breccia M 21. 5. (fig. I). ,. 7.'5 7.23 This lava is a massive basanitoid, with "" 22.10 ca. 7 % normative nepheline. This rock plots " 14 .•S "U 6.S6 close to the boundary line between the •.21 basahs and the basanites fields in the total .."' 2.27 alkalies Over silka diagram proposed by Cox et al. (1984) (tab. 1). This lava exhibits (Analyliall facilities at Istitltto di $cienze della an oligo-mkroporphyritic texture (P.I.=20) Terra, Catania). due to skeletal olivine microphenocrysts plunged into a viuophyric groundmass, where acicular A~ plagioclase feldspar, It should be stressed this lava was mostly purplish dinopyroxenes, olivine and opaque liquid when emplaced as indicated by the mkrolites can be distinguished within the low P.I. and the skeletal character of the glass patches. olivine microphenocrysts. THE HARZBURGITF XENOLITHS IN A QUATERNARY I'IASANITOID ETC. 247

Th~ x~noUth! TABLE 2 R~pr~senlQlilJ~ miNoprOM QnalYJ~J 01 coaTSt oliv;nt Both mantle. and deep cruSt derived ~rQinJ i" tIN Jllldi~d IHlnbllrgitt JC~"olilbJ xeno1iths occur In the considered lava, the former being the dominant type. The size of these inclusions varies from few centi­ < metres down to the Size of isolated xeno­ -n., •.n •.n ".a p.n cryStS; the largest ones exhibit rounded •.n on On '.n on shapes, whereas the small ones generally - ., •• .n an~ular edges. For these xenoliths are not ...... 0 .n uniformely distributed In the host lava, it - .n .n .n .n IS impossible to evaluate preeisely their - .n .• .n .n .n volume percentagc, which somewhere IS •• .n _.. n.n more than 15 val.'i' ...... " The ultramafic assemblages are typified on .. '.0" ,.- '."" I ...... mincnlogic lmd textural basis following the ,. .,n .,. .,. .,. ..• ..>0, ,.- 1.>0' lUGS recommendlllion~ (1973) and HARTE .. ,.­ ..­ (1977). Coarse hllrzburgites and minor ..• .­ .­ - .- .­ oHvine.c1inopyroxenites where thus recogni­ .- .­.= .­.= .-.010 .­ zed, the first constituting the subject of this " .- .- n .• n.' paper. n.' n.' •.. (f..licroprobe facilities at Centro cli Studio delle The IUlrzburgite xenolith8 Formazioni Igncc dcll'halia Cemralc, CNR, Roma).

P~troRrtJphy earth's surface (ROEDDER, 1965; WRSWELL, The harzburgite xenoliths here found 1975; MITCHELL, 1984) (fig. 2c). exhibit a coarse (both equant and tabular) It must be remarked the enstatite often c granoblastic ... texture due to olivine grains appears more clouded by Ouid inclusions than wh

at b) THE HARZBURGITE XENOLlTHS IN A QUATERNARY BASANITOID ETC. 24Q below the microprobe's detection limit. but TA.BLE 3 a little Mn content was sometimes revealed R(pru(n/Ilt;w m;cropro~ IlnalyuI 01 ortbopyrOJC~ ("b. 2). n~ in /~ s/udi(d bIlnburc;te xenotiths. Formutll~ The orthopyroxene exhibits a rather woe ~id~u/tlud tIIsumin, .u Fe tII di""'ent constant Mg/(Mg+Fe> value (=0.908). but •._.- its aluminium content varies from 0.64 up to 2.70 (wt%) (x = 1.56). CaD varies from ... • ••0. - _. 0.19 up to 0.73 (x = 0.38). Cr203 from "-D' ...... 0.1 up to 0.5 (x = 0.31) (wt%). Some ~'.o. •• .... •• .... ,... representative analyses are shown in tab. 3 '_'1 •.n •.n ..•. ..n .n Cd. also fig. 5). The other minor elements ...... always result below the detection limits. - .fl .n .u .fl .n The spinel is a chromian variety exhibiting -"D. .fl .n .n n n heterogeneous compositions even within a ••••• ... .n ." .u .n single grain. the Cr/(Cr+Al) atomic ratio ,n ... .n ." .• ." varying from 0.20 up to 0.70 (x = 0.53) ',' .fl .fl .n .fl .n and Mg/CMg+ Fe) from 0.35 to 0.60 (x = '0'.' n." ...... -., 0.48). The Ni and V contents are too low to be detected by the used analytical .." .... '" '0_" .0_' • equipmeRl. It must be emphasized the lowesl , ...... l.". 1_'" ..... Cr/(Cr+AI) value (= 0.20) was found in ..- ••1I_' -... .0" .... few anhedral spinels iRlerfingered with. or ~ .- .- ...... n...... fl' .n• 4; .•- rimmed by, a diopsidic pyroxene (tab. ,-. .". ..n ., 6g. 6)...... • ...... 0 ...... 1.'" ..... The primary clinopyroxene (to be distin­ • "TO' guished from a neogenetic one occurring in .- .- .- .- - the vitrophyric blebs: see below) plots in .. .- .- .- .- ,. .." .- .•.• .fl' the lower limit of the diopside field in the - - . n' Ca.Mg.Fe diagram shown in 6g. 5; the • .- ...... atomic ratio Ca/(Ca + Mg) varies from 0.46 • .- .- • • .-• .. .-. - up to 0.48 the Mg/(Mg+Fe) from 0.86 to • • • • fl • 0.88. The AI(vl) per fonnula unit (0 = 6) .. • ... '.' •• .. is 0.1:5. computed on stoichiometric basis Evidence lOT partial melting within the according to PAPllCE et a1. (1974). Cr~:I harzhurgi/e xenolilhs ranges between 0.8 and 1..5 (wt%) and Na~O CORlent is about 2 (wt%), that can Patches consisting of a selvage of fine account for about 8 mol% of jadeite end grained mane minerals. seldom occur in the term calculated following CAWTHORN and above described mineral assemblages. These CoLLERSON (1974) (tab. 5; fig. 5). are here called • blebs It' (MAALOE and PRINTZLAU. 1979) and exhibit varying shape and size; in faCt they appear stretched ( .) The: analyses were performed using a JEOL between the edges of two coarse grains but electron microanalyser fitted with a LINK E.D.S.; exhibit roughly equant shapes at the junction 1.5 was the operative voltage:. 100 seconds the of three or more crystals (fig. 3, a-h). Some rountinM time:. (') 1lle atomic Fe: in formulae:, if not specified, blebs appear quite isolated from the host would be: tlken as Fe:"' total. lava; some others. on the contrary, are joined

Fig. 2. - 11) Photomicrograph of I coarse harzburgile: xe:nolith occurring in the: studied laVI. Equanl fosle:rite: (OL) and emu-lile: (OP) grains Ire: evidenl; lhe: Iff'OW$ indieate some: virrophyric blebs. Pume po/Ilr;ud liCh/,- scll1e bM = mm 0.5. h) Harzburgite:, where heavily fractured forslerite: grains (OLI and minor disrupled emu-lile (OP) Ire: permeated by I dark ro1ourc:d micro-cryptocristalline: 5C:lvagc and glass. Pltrne pol. lit,ht; J~tlle bill' = 1 mm. c) Magnification of I coarse c:nstatite: grain exhibiting I rc:roarkable: pallc:rn of fractures Ind fluid inclusions Ullils. Note: the: corona rim where .1 contaa with the host IaVI (Uppermosl edge of lhe: photo. HWlUcite. pUne pol. liCht; utile bM = 0.19 mm. d) I-hrzburgite:. where: the: olivine: grains Ire: crossed by serpentine: vei.nlets (c~r in the: photo), whereas a microfra<:ture: is filled by the: host lava (duk). Pwne pol. li,bt. sctlle Hr = 0.' mm. 250 v. SCRIBANO

Fig. 4. - ,,) Photomicrograph showing the reaction· corona in enstatite (OP) at contact with the host b) lava (H). This rim consists of a selvage of olivine microlites (facing to the host lava) and a thinner Fig. 3. - Rather high magnification of two .. blebs» shell of cryptocrystalline material gradually passing in onc of the studied harzburgite xenoliths. The to the umransformcd pyroxene. (Sce the text for different shape the two blebs exhibit can account further explanation). Note the olivine grain in the for the different degree of partial melting. The upper right corner of the photo is not affected by blebs are both surrounded by coarse olivine ami any reaction rim. Plane pol. light, scale bar = they consist of diopsidic pyroxene and spine! micro­ 0.3 mm. h) Another reaction rim as the precedent, grains plus olivine relics, plunged into cryptocrystal­ looked at hip;her magnification; the points indicate line material and glass. Plane fJfJI. light, scale as .. V, Z, X, W» correspond to the analyses in bars: a) = 0.15 mm; b) = 0.07 mm. tab. 7. Plane pol. light, scale bar = 0.085 mm. THE IIARZBUkGITE XE,'i'OUTIfS IN A QUATERNARY BASANITOID ETC. 25\

Ca TABLE 4 Rtprt!tlltlltl~ m;cropro~ .1lalYStI of spilltls in 7:'------'\ the hIInburgi/t xtlloliths. Ft'· in formulllt was tstimattd impoling Jtoichiomttry .~-,~-'" ...,--,._,,, ••,••e , ..... _",_...... • • ,• g -...... ,_, ...... • .• .. .. .• 0_ ..-.' _ ..- • "'.0. 0"" ,...... " • • '" ._") ...... - .. ..." ... OIl." Mg Fe .. .• .• .•- .. Il _., , , - ..... Il." "." ... Fig. 5. - Ca.Mg.Fe diagram where pyroxene in -<••0, .,." ..... » .•• ..... ".1. harzburRite are plotted together with analyses re· ..,., ...... " ..... •••x> .0 .•• presenting glass and microcryslS in the blebs, poinn In the c:nstatite IeaClion rims and the clinoo ...l_ ,. f._I. '0.'" pyroXet'll: OC'OJrring in the host lava's groundmal$. .. .- .- .- .- " ...... - ...... - ...- ..,.., '.011' ..... ,.- ..- MgjMg.Fe' ..,.. ,."0 .-...... ,. ,-... 0.70 .- ..• .- a b c • .....- .....- ..0•• ...... 0;,0 "\ .. ...,. ••••• ...... , ..,.. • ., • <,,,c.·.,) .•. .,. .- .,. ..• 0,50 " .... • !- 0.<0 , • ;. brownish isotropic material and, when large - - enough, filled with the selvage itself. Some· 0.30 Cr/Cr'AI where else the coarse minerals appear largely 0.20 0.30 OAO 0.50 0.60 0.70 o.ao disrupted (fig. 2 b). The positive volume change due to the liquid produced by partial Fi~. 6. - Cr/tCr+Al) over Mg/Mg+I:Fel atomic melting which forced the sorrounding solids, I1IliO$ in lhe spinels OC'CUrring in the harzburgites. and the shock for t}}(: pressure release during .. 11,. represents the upper Iimil of the Ahpinel. peridOfile field dtllwn on the u/AI ratio in spincls the xenoliths ascent, might account for such basis ronforms C.U.SWUL (1980); .. b,. is the « sheared ... textures. Cr-spinel·peridolites and .. C''' the mromitc-paidoLile field. 1be square symbols indicate anhedral spind narely OC'CUrring in the sludied hanburgites inler. Chemistry 01 the bleb! finRe~ with diopside; the full dOIS represent the Numerous microprobe analyses were car· more commonly OC'CUrring spind compositions. Note that lhe entire compositional interval could be found ried out both in the microcrysts and in the in any single. scmicoarse spine! grain. glass patches which constitute the blebs. The former consist of chromian diopsidic pyroxene whose averaged composition is with the host Java by channel·like fractures reported in tab. 6 (the analyses. N _, .. 0 ... eitber crossing the coarse crystals or fol. in tab. 5 instead rep~nt single points). lowing their rims. Such blebs must be related It must be firstly emphasized these din" partial melting episodes inside the previous pyroxene micrograins differ from the primary holocrystalline assemblages (e.g. MAALOE ones (cf. the mineral cbemistry section) by and PRINTZLAU, 1979). their lower AI, Fe and Na, but higher Si In a few of the studied xenoliths, the 6ne and Mg contents. It is also note worthy that grained selvage and the glass exceed 30 % AI(VI) in these quench.minerals ranges from of the modal occurrence; the coarse minerals 0.02 to 0.06 atoms per formula unit that here ~hibit numerous fractures marked by is much less than in the originaty diopside 252 V. SCRlBANO

TABLE 5 the conuary marked by rather thick reaction Repruentative microprobe analyses of primary rims where an onhopyroxene is (fig. 4 a). clinopyroxene occurrin? in tbe harzburgile xenoliths These coronas consist of a thin shell (5­ (an. 1, Lj, analyses of the quench cryslals in the 30 !-Lm) of pale coloured cryptocrystalline blebs (N, 0) and tbe bosl lal.:ll clinopyroxene (P). ~ Formu14t wtre computed following PAPIICE Cl material (zones« x, z in fig. 4 b) mantled by al. (1974) a selvage of olivine microutes which some­ where appear stretched and aUigned normally ." , • to the contact surface (zone «w~ in fig. 4 b); "0...... • an interstitial film of glass is also present A'.O, .. " ...... " ...... " between these microcrysts. '0.0...... • •. ~I Numerous microprobe analyses through '" ...... • the onhopyroxene outer rim show the Ca, ..... IO." ...... ".", U . ..., - .• • .• .. ... Cr and Na contents increase, Mg and Si -TlO...... • .... decrease while AI and Fe remain roughly Cr••• 0 •• ...... OO ...... •. constant; in few points this trend is drt­ --,' '.--'.0' ...... • maticaly emphasized yelding a dinopyroxene T....' ...... lOO." 100.... '0'"11 stoichiometry (analysis", X .. in tab. 7). The olivine of the selvage exhibits a rather constant Mg/(Mg+Fe) value (=0.77) and ...,,- i. <0._1. 10." "'W~ , ,. I ...~ , I ..... some ri, Mn and Ca contents (analysis ..'.Il,.) ""0 ...... ,C." .,..- .-.'0' .•. .-... .•. in tab. 7)...... , ..• ...... - ..,.-, .... .-•.. .-.... .-O• ..• ...... -... .- h .- .-.... .-.OO' .- .- Discussion aO(I concluding remarks .. .on .•...... ".- ... ..oo .-...... -.... " .,.. .". ..., .•. .... The harzburgite orthopyroxene low CaO and AbOJ contents as well as the rather ca/le-·...} ...... vl...•••·, • ... .• .. .. high Cr!(Cr+Al) values in the spineIs, sug­ gest these peridotites suffered a rather high depletion by partial melting processes, pro­ (Al(vl) = 0.16-0.14 a.u.£.). It is also stressed bably more than 20 % (DICK and FISHER., that these microcrystalline pyroxene com­ 1984; HERVIG er al., 1980) (fig. 7). It is positions span over wide interval (6g. 5); also note worthy that the Cr content in these variations' seem to be related the spind never exceeds the limits CARSWELL glass/crystals proportion in the blebs. (1980) puts for Cr-spinel in garnet free as- The analyses performed in the glass and cryptocrystalline zones give composition TABLE 6 much more variable than the microcrysts; A~tlged hfebs composition (t:alt:1l1tlud on tlN Ixzsis some of them fit in a wide range of suO­ 0/ mit:roproln flnal,St!!. both in tht miaot:r'Jsts, calcic pyroxene compositions (fig. 5); the the cryptocr)'sfalfine materiaf and flN gl6ss1 tlnd averaged composition calculated on the avtraged quench cl\'nopyro"ene composition bleb's modal occurrence basis, is shown in ••. .,coocnns ...... TI(* tab. 6. In spite of the Si02 (= 465 wtro) and total alkalies (= 2.8 %) so obtained plot dose to the boundary line between the alkalic .',- •.• ....., and subalkaline fields in the MACDoNALD o.l20. 11.03 ,.. and KATSURA (1964) diagram, the whole '001-' ... ,.• analysis does not fit in any natural occurring .~ .OO primary magma composition. - lO." 17.00 Tln .U -2 ." n , , Corona rims in enstatite ""2 • .. .. ~ lI.n 21 ••' The boundary surfaces of the studied .,' ,." .n xenoliths are rather sharp where oHvine is ',' .. .OO in contact with the host lava, they a~ on _. ...., ... THE HARZBURGlTE XENOLITHS IN A QUATERNARY BASANITOID ETC. 253

TABLE 7 calculations the averaged Cr, AI, Mg, Fe Microprobe analyses taken across a reaction rim contents in these minerals, a temperature in enstafite; the analyses V, Z, X, W correspond value of about 8000 C was found according to the points shown in fig. 4 b). to the above qUOted Author (the T interval being between 600 and 850° C). The more ~11lS 'tUCTIOI' IN "..sf_TlTE aluminous spine! here rarely occurring inter­ , , fingered with diopside was not considered ... • • for these computations. Considering the equilibration pressure s.o~ 57.0ll ~ "." .. 39.10 values, the lack of garnet in these mineral A'.03 .." 1.6' 1.65 .00 assemblages provides an upper pressure limit at about 1.5 GPa (for T = 7000 C) (MAc FoOlol .." 6.76 '.M >0.49 GREGOR, 1974; GASPARIK, 1984). On tbe .... 33.67 205.37 17.'

semblages; but few spinels found in the studied rocks interfingered with clinopyroxe­ ne (rab. 4, analysis «U ») exhibit the same Cr content as the spinels occurring in Al­ ..... spine! lherzolites and in some garnet lherzo­ ...... lites (CARSWELL, 1980) (6g. 6). Concerning the estimate of equilibrium ...../ temperatures and pressures it must be stres­ le"'" ..., sed that only few published geothermometers , . \. ' and no geobarometers are reliable for mantle us .... -io-~::~·~·_·.. ..·_,,·- • derived mineral assemblages (e.g. FUJIl and .'-.0: ... ~~ ~ • SCARFE, 1982). Nevertheless an attempt to /b.,··--_·_;-_··--·.... i estimate P, T intervals was done. Using the AI,O, AJ content in enstatite at equilibrium with forsterite and spine! as geothermometer, an upper limit of T = 7300 C was found for Fig. 7. - Al.a. over CaD and CrA (wt%) equilibration temperature following MAC variations in Ihe studied ortnopyroxe:nes. The field « a" in the bottom diagram is for ortnopyroxene GREGOR (1974); this upper limit should be occurring in spine1.lherzoliles, «b,. in barren­ dropped down to C'V 650" C using the hari;burgites, «c» in CQaI'Se garnet Iherzolites, GASPARIK'S (1984) experimental data on « d" in porphyrodastic garnet Iherzolites, «e .. in the CMAS system. On the other hand, the fertile harzbmgites. In the upper diagl"llm «g,. is the field for onnopyroxene in barren harzburgite olivine-spinel geothermometer that should and in the porphyroclastic garnet-lherzolites, «f .. give reliable results for such low-aluminous in spine! lherzolites. The field where the ortho­ spine! compositions (FABRIES, 1979) is pyroxenes occurring in the fertile harzburgites plot however rather obstructed by the chemical is not represented in the figure (see HEIl.VIG et al., 1980). Note for both the diagl"llms the compositions zoning shown by the studied spinel. of Ihe studied pyroxene plot in the barren­ Nevertheless, taking to account for this harzbmgites fields. 25. V. SCRIBANO the studied xenoliths it is however difficult metasomalizing effect on the barzburgite to speculate whether the partial melting in body. the blebs occurred in the mantle or after To conclude, in spite of Ihe discrepancies the incorporation into the host magma. The between the equilibration temperature values latter hyporesis seems suitable, since the here estimated by different geothermometers, adiabatic pressure drop these minerals suf. it seems Ihat the studied harzburgites re· fered during their (rapid) ascent to the equilibrated at rather low temperature. For earth's surface could have favoured such the estimated pressure interval is too wide minor partial melting episodes, particularly for any interpretative purpose, thus two in that zones where different minerals are different petrogenetic hypotheses are for­ each other touching. It seems also possible mulated. that some metasomatizing effects wefe exerted The former hypotesis suggests that a deep­ on them by the magmatic fluids, which scated harzburgite body (produced by im· penetrated into the xenoliths' microcracks portant partial melting episodes of primitive and locally altered the «barren» character fertile peridorites) ascended along an ocean· of these harzburgires. This is consistent with type geotherm to the uppermost top of the ~ relatively long residence time of the xeno­ mantle (or 10 the lowest crustal level) where liths in the host liquid as deduced by their it re-equilibrated prior to partial disruption rather smaU size (which could imply the and incorporation into the host magma. It fragmentation of previous larger blocks), rhe must be hypothized thal the Fe-depleted zonal variation of chromium in their spinels character of the harzburgites provided for (e.g. FUll! and SCAR fE, 1982) and by the their diapiric upwelling through the denser, thick reaction rims Ihe enstatite exhibilS less depleted other peridotites. On the other where ar the contact with Ihe host lava (see hand, neither pressure (depth) changes nor hefore). mass transfer, but a dropping-rlown of the On the other hand, the lack of olivine thermal gradient in the Hyblean area could microcrysts among the quench crystals in have produced the same effect on the these blebs, better fit in the before quoted harzburgite «body», wathever level it oc· Author's hypotesis: in fact, considering the cupied in the upper mantle. averaged bleb composition here reported In all the cases the considered xenoliths (tab. 6) and the PRESNALL. et al. (1978) and are believed to be accidental inclusions in GASPARIK'S (1984) experimental results on the host basanitoid lava. the CMAS system, the appearance of diopsi­ Acknowledgements. - This work was financially de liS only quench mineral phase should supported by Ministero della Pubblica lstruzione. indicate high pressure conditions. In this The microprobe analyses were performed at Centro case the postulated «fluids» could have CNR per 10 Studio delle Formazioni Ignee dd­ aete<.l in the mantle, too, producing their 1'1 talia Centro-Meridionale. Noma ().

REFERENCES

BARBERI F., CI.... EITA L., GASPARlNI P., INNo­ Tbe interpretation of igneous rocks. London, CENTI F., SCANOONf. R, (1974) - Evolution of a 450 pp. seC/ion of the Africa-Europe plate boundary: CRlSTOFOLlNI R., BATIAGLIA M. (1974) - Le mani· paleomagnetic and VQlcanological evidence from festazioni basalticbe deifa zona di Sicily. Earth. Plane!. Sci. Lell., 22, 123-132. nel quadro del vulcanismo dell'altipiano lbleo. CARSWELL D.A. (1980) . Mantle derived Iherzolite Boil. Soc. Cool. It., 94, 185·207, , nodules associated witb kimberlites, carbona/eite DICK 1-1.),8., FISHER R.L. (1984) - Mineralogic "and basalt magmatism: a review. Lilhos, 13, studies of the resiJues of mantle melting: abYJJal 121-138. . and alpine.type peridotites. In: Kornprobst ). CAWTHORN R.C., CoLLERSON K.O. (1974) _ Tbe (Editor), Kimberlites If; The Manlle and Crust­ recalculation of pyroxene end member parameten Mantle Relationships, Elsevier, Amsterdam, 1984. and the estimation of ferrous and ferric iron FABRIES ). (1979) . Spinel·Olivine Geothermometry . content from electron microprobe analyses. Am. in Peridotite From UltramaPc Complexes, Contr. . Miner., 59, 1203·1208. Miner. Petr., 69, 329-336. Cox K.C., BEll. ).0., PANKUR:>T R.}. (1984) _ FUJII T., ScARFE C.M. (1982) - Pe/roloS'.}' of Ultra· THE HARZBURGITE XENOLITHS IN A QUATERNARY BASANITOID ETC, 255

mafic Nodules from West Kettle River, near MAcOoNALD G.A., KATSURA T. (1964) Chemical Kelowna, 50uthern British Columbia. Comr. Mi­ composition of Hawaiian lavas. ]. Petrol., 5, ner. Petr., BO, 297-306. 82-133. GASPARIK T, (1984) - Twa-pyroxene thermobara­ MACGREGOR 1.0. (1974) - The system MgO.AI.or metry with new experimental data in the system SiO.: solubility of AI.O. in enstatite for spinel CaO·MgO-AI.orSiO•. Conn. Miner. Pelt., 87, and garnet peridotite compositions. Am. Miner., n87. 59, 1l0-1l9. HARTE B. (1977) - Rock nomenclature with par­ MITCHELL RH. (1984) - Garnet Ihm:.olites from ticular relation to deformation and recrystallisation the Hanaus-l and Louwremia Kimberlites of textures in olivine.bearing xenoliths. }. of Gool., Namibia. Contr. Miner. Pelt., 86, 178-188. 85, 279·288. PAPIKE }.}" CAMERON K., BALDWIN K. (1974) . HERVIG R.L., SMITH }V., STEELE I.M., DAWSON Amphiboles and pyroxenes: characterization of }.B. (1980) - Fertile and barren AI.cr spinel the other than quadrilater components and efti­ har..burgites from the upper mantlt: ion and mates of ferric iron from microprobe data. Gool. electron probe analyses of trace elements in olivine Soc. of Am. Abm., 6, 1053-1064. and orthopyroxene: relation to Iherzolites. Earth PRESNALL D.C., DlxoN S.A., DlxoN } .R., O'DoN­ Planet. Sei. Lw., 50, 41·58. NEL TH., BRENNER N.L., SCHROCK R.L., Dycus HERZBERG C.T. (1978) - P)'roxene geothermometry and geobarometry: experimental and thermcr D.W, (1978) . Uquidus Phase Relations on the Join Diopside·Forsterite-Anorthite From J atm. dynamic evaluation of $Ome SUb$Olidus phase to 20 Kbar: Their Bearing on the Generation relations involving p)'roxenef in the systemCaO­ and Crystallization of Basaltic Magma. Conlr. MgO·AI.OrSiO•. Geoc:h, Cosm. Acta, 42, 945­ 958, Miner. Pw., 66, 190-203. lUGS SU8COMMlSSION ON THE SYSTEMATICS OF ROEDDER E. (1965) - Liquid CO. inclusion in olivine­ IGNEOUS ROCKS (1973) - Recommendations. N.]b. bearing nodules and phenocryus from basa/tr. Miner. Mh., 3, 149·164. Am. Miner., 50, 1746-1782. MAALOR $., PRlNTZLAU I. (1979) _ Natural Partial VARIOUS AUTHORS (1984) . Carta Geologica della Melting of Spinel Lherwlite. }. of Petrol., 20, Sicilia md·orientale a scala 1: 100.000. Regione 727-742. Siciliana, .