REND/CONTI Soeletcl: Itllllllnll dl Mln.erol0gj4 e Petrologill, JI /J): pp. t7J·9B7Comunleazlone preRntata ..lla Rlunlone dell.. SIMP In Rende·cet..ro (eo.enza) 11 :t'I-l6-lS62

PETROLOGY AND GEODYNAMIC SIGNIFICA CEOF THE CALABRIA-LUCANIA OPHIOLITES

LUIGI BECCALUVAIstilUto di Mineralogia ddl'Universitil., via Mezzocannone 8, 80134 NapoH

GIANPAOLO MACCIOTTAhliluto di Petrogr1llia e Gillcimemi l\tincrari dell'Univcrsita, via Gramsci 9, 43100 Puma

PIERA SPAD£AI5Iitulo di Scienze del1a Terra dell'Universita, viale Ungheria 43, 33100 Udine

RIASSUNTO. ~ Studi recemi hanno moslrato chei complessi ofiolilid fanennoid presemano 1.1 Ioroimerno notevoli differenze $OprattullO per quanlOriguarda i caraneri peuografici e geochimici delleloro sezioni intrusive ed effusive.

La dimibuzionc degli dementi maggiori cd intracce, gli andamemi differenziativi, le fasi di li·quidus cd iI loro ordine di crislaIlizzazione ndleroccc: effusive cd intrusive indicano una corrispon·denza dei comple55i ofiolitici, da un lato, con seg­menli litosferici generali lungo dorsali medi~C1I'niche 0 badni retmarco ben sviluppali, dal!'ahro,con associazioni magmatiche forrnatesi 1.1 limite diplacchc: imJ1lOC'C2niche convttgenti (archi insulari,stadi iniziali di apertun di bacini retroarco).

Le ofioliti mesozoiche della Calabria settentr}o.nale: e ddl'Appennino lucano appanengono a diverseunita lenoniche sovrapposte, interessate d. differentitipi e gradi di metamorfismo.

Nonoslame 1.li differenze tra le varie unitl, lecaraueristic:hc: petmlogiche e geochimiche: indicaooche: tune le olioliti stOOi.te possono essere interpre­hue come un unico originario comples50 di ultra·rnafiti di mantcllo, gabbri cumulitici e basalti tha­leiitia ad affinita oceanica, analoghi ai MORS t~an·sizionali.

La stteua a55OCiazione talora risrontrata tra Orl()­liti e materi.li continent.li di ba55a crosta (similia quelli ddla forrnazione dioritico-kinzigitica) sugge­riscc che: esse rappresentino relitli di IitO$fera ocea·nia. fonruuasi in posmonc: pericomillemale ed inuno S1adio d.i ocanizzazione embrion.le, .n.lop·meme a quanto in precedenu propasto per le ono.liti delle uniti liguridi eslerne dell'Appennino Jet.

tenlriona!e.Tale badllO oceanico dovrebbc: essere SlatO mtle­

teS$&IO da importanti zone di fratturl e faglie tra·sformi, come suggttiscono le C1lr1IttWStichc: tellonico­rnetamorfiche delle orKllili sludiale.

Durante la chiusur. cretacea del bacino le unitlofiolitiche furono coinvolte in pl'OC'e5si di subdu-

zione con sviluppo di paragene:5i metamorfichc: dialta pressione/bassa temperatura indicanti valorimanimi di paniale equilibralUra di 6-8 Kb e350" ± 50" C.

ABSTRACT. - The available petrological and geolo­gical data on the Calabria·Lucania ophiolites indicatethat Ihcy can be considered, like other WesternMediterranean ophiolites, as fragments of the ocea·nic lithosphe:re created du~ing the }ura55ic openingof the Western Tethyan basin and sep.rating theEuropean and African (lllsubrian) conlincmal blocks.

1bey represent oceanic association of; I) tenonitespind·lhenolites, 2) tooleiitic baWlS of transitionalMORB affinilY, 3) g:abbroic cumulilic rocks, re­vealing, on !he whole, the c10sesl magmatic re­sernb1ancl: wilh ophiolites from &lagne (Corsia.)and External Ligurides (Nonhem Apennines).

The: magm.tic and tectono-metamorphic characte­ristics of the whole association sugsest that !heCalabria·Lucania ophiolites may represent Iilhosphe­ric sections generated at .n early oceanic·ridgesystem (and developed in a pericontinental position),subsequently interested, at least in part, by • tectono­metamorphic evolution in fracture zones.

The Cretaceous dosure of t!)is ocean basin tookplace by lIndemusdnll and ,;/ubdlletion processes,with development of high-pressure/Iow temperaturemetamorphic parageneses in the ophiolite lithologiesindicating maximum values of parlial equilibrationof 6-8 kb at 350" ± 50" C.

Introduction

Recently important differences have beenpointed out among Phanerozoic ophioliteswith regard to the geochemical and petro­grnphical charncteristics of their extrusiveand intrusive sections (MIYASHIRO, 1973,1975; PEARCE and CANN, 1973; SMEWING

9i" L. BECCALUVA, G. MACCIOTTA, P. SPADEA

et al., 1975; Roccl et al., 1975; CHURCHand RICCIO, 1977; BECCALUVA et al., 1979.1980; SAUNOERS et al., 1980; CAMERON etal.. 1980; SURI. 1981).

Athough such differences may sometimesbe atlributed to physical-chemical varialionsin a single tectonic setting, recent studiesattribute these penological diversities 10

ophiolile generation in different originaltectonic environments (SUN and NES8IT.1978; PEARCE, 1975, 1980; BECCALUVA etal., 1979; CRAWFORD et al., 1981).

Particularly evident is the geochemical af.finity of some ophiolitic basahs to basahsfrom mid-oceanic ridges and marginal basinson one hand, and of some other ophioliticbasalts to basahs, basahic andesites and ha­ninitic types from island-arc setting, on theother (BECCALUVA et al., 1979). This ismatched by a parallel and sistematically dif­ferent crystallization order in lavas andassociated plutonic complexes, correspondingto different Ti02 contents (BEccALuvA etal., 1980; SERRI. 1981), so that Ihe variousassociations may be classified as high-Ti,low-Ti and very low-Ti ophiolitcs.

Particularly for the Tethyan realm, signi­ncant differences have been demonstrated forthe intrusive and volcanic sequences, as wellas for mantle uhramanc between Eastern andWestern Mediterranean ophiolitcs (Roccl etal., 1975; BEBIEN et al., 1975; BECCALuvAet al.. 1980). The petrological characteristicsof many low-Ti ophiolitic complexes from theEastern Mediterranean area such as Troodos,Vourinos and Pindos indialte an island-arc/back-arc basin ralller than an ocean-ridgeoriginal setting (BECCALUVA et al., 1978,1979,1980; CAPEDRl et al., 1980). Instead,this latter geodynamic envitonment has beengenerally proposed for the high-Ti WesternMediterranean ophiolites (FERRARA et al.,1976; PICCAROO, 1977; BECCALUVA et al.,1975, 1976. 1980; SURI. 1981; SPADEA.1979).

In the Calabrian arc, recently consideredto be a southern fragment of the dismemberedAlpine belt (HACCARD et al., 1972; DIETRICHand ScANOONE. 1972; AMODJo-MORELU etal., 1976), 9phiolites occur in distinct tectonicunits. They may, or may not. show HP-LTmetamorphism and are overthrust by lowercontinental crust tenanes (Diorito-Kinz.igitic

Formalion auct.).Data on the petrological and geological

charscteristics of the Calabria-Lucania ophio­lites were presented in previous works(HOFFMANN, 1970; DE ROVER, 1972; PIC­CARRETA and ZIRPOLI, 1975; SPAOEA et al.,1979; LANZAFAME et al., 1979 a, DoSTALet al., 1979). The aim of this paper is 10review the salient petrological and geologicalfeatures of the Calabria-Lucania ophiolitcsderiving from different occurrences andstructural settings, in an attempt 10 a betterdennition of their original setting and meta­morphism. This should contribute to c1arifingsome aspects of the tectonic-metamorphicevolution of the southern most sector of theAlpine chain.

Geological framework

In the Calabrian Arc Temyan ophiolitescrop out discontinuously from the Calabria­Lucania border zone (Lucanian Apennine andNorthern Calabria) 10 Central Calabria (fig.1). The general ophio!itic sequence consists,in ascending order, of altered ultramancs(mostly mantle tectonites), of gabbro, basaltand chert (AMoDlo-MoltELLI et al., 1976;LANZAFAME et al., 1979 a).

The ophiolitic lithologies are highlydismembered and occur in several tectonicunits which were in the Aquitanian over­thrust eastwards on tOP of the Apenninesedimentary terrains (AMODlo-MoRELLI etaI., 1976). The ophioIite sedimentary coverincludes almost ubiquilOus radiolarian cheetat the base, overlain by predominant calca­reous and argillaceous deposits with abundantterrigenous components. The age of the se­dimentary cover is referred to Tithonian­Neocomian. Together with setpentinites themetabasahs represent the predominant rock·type in the ophiolite sequences. The gab­broic complex is poorly represented by veryrare Mg-gabbro and Fe-gabbro bodies (theselatter are found as fragments in sedimentarybreccias), while a manc sheeted complex isabsent. Basaltic dikes occur as scattered in­trusions into uhramancs. gabbros and pillow­lavas.

The ophiolitic rocks are included in al­lochtonous terrains with a different mode ofoccurrence: as nappes (Northetn and CentralCalabria), as slices and melange (Lucanian

PETROLOGY AND GEODYNAMIC SIGNIFICANCE ETC. 975

Apennine and Northern Calabria), and asolistoliths (Lucanian Apennine).

Based on the occurrence and tectonic p0­sition they can be grouped into: 1) Lot«T

Ophiolitt Unit, composed of milange andtectonic slices (Frido Unit according to LAN·ZAFAME et aI., 1979 a, b) which includes theDiamame-Terranova (pro parte) + Frido

+

c..o

".."

•I2ZJ

en....

,

..+ + +

+ ++ +

++~~+

+ + ++ + + ++~ +

+ + ...,.,-. ++ + +

+ + +

....l/l

•[ill]

,r-:--lL-:.J

-

'",

'.,

'm

oD

o

N

f

,o

Fig. 1. - Generalized geologic map of the Calabria-Lucania atel, Southern Apennines (modi6ed fromAMODIO MOlELLI et al., 1976 and Sl'ADEA et al., 1980).. I. Qualttnary and Ncogene deposiu; 2. Si­cilide uniu (Mesozoic-Tertiary); J. Calabro-lucanian 8ysch (Lale Cretaceous 10 Miocenel (Ci!ento Unitof AMODIO MOIELLI et aI., 1976); 4. Sedimenlary cover of continenlal rocks (Mesozoic); ,. Continenwigneous and metamorphic rock uniu (Palcozoic); 6. Upper Ophiolite Unil (Late ]urassic-Early Cretaceous)(MlIlvito Unit and Gimigliano Unit of AMODto MOlELLI et .1., 1976); 7. Frido Unit (Jurassic-EarlyCretaceous) (Diamante-Terranova Unit and Frido Unil of AMODIO MOlELLI et al., 1976); 8. Carbonaterock units (Mesozoic.Teniary).

976 L. BECCALUVA, G. MACCIOTTA, P. SPAOEA

Unit of AMODIO-MoRELLI et al. (1976);2) Upper Ophiolite Unit which comprisethe MALVITO and GIMIGLlANO units (proparte) of DIETRICH nnd SCANDONE (1972)and AMOOIO-MoRELLI et aI. (1976); 3) ophio­litic olistoliths. The ophiolites of the LowerUnit (i.e. Frido Unit), consisting of dominantultrama6c rocks and metabasalts, composeeither slices or elements of different sizes ina melanges with metasedimentary or serpen­tinitic matrix. The mctasedimentary rocksassociated with ophiolites derive from cal­careous-pelitic sequences, with interbeddedquartz-arenites, of Neocomian-Aptian age(Frido Formation of VEZZANI, 1969; Flyscha quartzites of French authors) representingthe cover of pillow lavas (LANZAFAME et aI.,1979 b).

The Upper Ophiolite Unit, is only about350 m thick, and consists of predominantmetabasalts nnd capping metasedimentswhich were originally radiolarian chert, peliteand Calpionellid limestone of Tithonian­Neocomian age. This unit is tectonicallyoverlain by the Dioriro-Kinzigitic (Polia-Co­panello) Unit, which represents the highesttectonic element of the Calabrian Arc(AMODlO-MoRELLI et al., 1976).

Olistoliths occur in the Lucanian Apen­nine and consist of prevalent basaltic pillow­lavas, minor gabbros and serpentinites for­ming the substratum on which flysch se­quences were deposited, probably since LateAptian.

In the Lucanian Apennine, polymetamor­phic rocks from the lower crust, cor­responding to hhe Diorito-Kinzigitic Unit,and consisting of granofels, garnet gneiss,and amphibolite are in close association withophiolites of the Frido Unit. Field and petro­graphical data indicate that these continentalrocks were already associated with the ophio­lites at the time of the tectonization andHP-LT metamorphism and as far back asthe outpouring of the basalt (SPADEA, inpress).

Primary J)etrological leJllure8

Basalts

The extrusive basaltic rocks are representedby pillow-lavas and pillows-brecdas, and byrare hyaloclastites. The lavas are aphyric and

porphyritic basa1ts (actually metabasahs)mostly olivine-free. Plagioclase phenocrystsoccur in all porphyritic types with stronglyvariable modal abundance (maximum valuesabout 60 % volume), often indicating theintervention of accumulation processes. Ba­saltic rocks, either aphyric or oligophyric, alsooccur as dikes within serpentinite and gab­bro. Similar dike rocks are intruded intogranofeIs and amphibolite referred to theDiorito-Kinzigitic Unit (LANZAFAME et al.,1978; SPADEA, in press).

In spite of the complex metamorphic ef­fects, the above-mentioned rocks still shownprimary features as far as some geochemicalcharacteristics and mineral relics are con­cerned. Magmatic dinopyroxenes are oftenstill preserved. The chemical mobilizationeffects are mainly reRected in the high H~O'

values as well as in erratic variations of Caand alkaline elements.

Due to diffused alteration only relativelyimmobile elements such as Ti, Y, Nb, Zr,P, Cr, REE (HUMPHRIS and THoMPsoN,1978 a, b), and possibly, Mg, Ni, V, Fe, Siand AI (PEARCE, 1975) are used to evaluatethe magmatic nature of the rocks.

The basaltic samples show a remarkablechemical homogeneity and geochemical fea­tures analogous to those of mid-oceanic ridgebasalts (MORB). There are no systematiccompositional differences among the rocks ofdifferent tlXtonic units or of different me­tamorphic fades.

They are characterized by ZrjY, Y/Nb,Zr/Nb and Ti/Zr ratios in the range ofvariations shown by mid·ocean ridge andmarginal basin tholeiites (PEARCE and CANN,1973; ER LANK and KABLE, 1976; KAY andHUBBARD, 1978; PEARCE and NORRY, 1979),as indicated by the distribution of the rocksin the PEARCE and CANN (1973) diagrams.An ocean.floor tholeiile affinity is supportedby the position of samples in Ti/Cr (PURCE,1975; GARCIA, 1978) and Ti/Cr.Ni (BEc­CALUVA et al., 1979) plots proposed for thediscrimination between ocean-floor andisland-arc tholeiites (SPADEA, 1979, and inpress).

They also share petrographic features withMORB and other high-Ti ophiolitic basaltsof pure oceanic affinity, in that they showthe crystallization of plagioclase before dino-

PETROLOGY AND GEOOYNAMIC SIGNIFICANCE ETC.

Gabbro8

Gabbroic rocks are only a few percent ofmafic ophiolites from the Calabria·Lucaniaarea and occur as bodies not exceeding one

Fig. 2. - Chondrite-norma!ized REE patrems forCalabria-Lucania metabasahs (after DoSTAL et al.,1979). For comparison REE patterns of ophioliticmetabasalts from Balagne (Corsica), Northern Apen­nines, Alps and Alpine Corsica are also shown(after VENTUlELLI et aI., 1981).

T.. Vb L..

--, ----- .. /

'.

' .. --.

~ ...

~_....._.---~-'

,

L. c. Nd S.. E.. Od Tb

Model calculations indicate that the Ca­labria and Balagne parental magmas couldhave derived by approximately 15 96 equi­librium partial melting of mantle sourceswith sligthly higher than chondritic Zr/Yand Zr/Ti ratios (fig. ).

Similar conclusions can be drawn fromthe Cr-Y and Cr-Ce/Sr diagrams (fig. 4),where the Calabria basalts fit genetic path­ways characterized by dosed/open systemfractionation from intermediate partial fusiondegrees.

Low-pressure fractionation in the Cala­brian basalts is indicAted by variations ofall refractory elements, which form an overalltholeiitic trend with increased Ti, Fe, V,Zn, Mn, Se. and decreased Ni, Cr and AIas the fraclionation increases. Zr, Y, Nb, Pand REE also increase with the differen­tiation (SPADEA, 1979; DoSTAL et al., 1979;BECCALUVA et al., 1980). This trend is con­sistent with fractional cristallization of olivine± Cr-spinel and plagioclase (which are s0­

metimes still recognizeable as phenocrysts inthe metabasaltsJ, later followed by dino­pyroxene.

•';:'30

I~20

8•

pyroxene which never occurs as phenocryst.In this respect they are strictly comparableto the volcanic sections, or their metamorphicequivalents, of other ophiolit~ from theWestern Mediterranean area, such as Corsica(BECCALUVA et al., 1977; GLOM, 1977), theAlps (BICKLE and PEARCE, 1975; BERTRAND,1970; MEVEL, 197.5; RAITH et al., 1977;LoMBARDO et al., 1978), the Voltti Group(MAzZUCOTELLI et al., 1976; PICCARDO,1977) and the Northern Apennines (BECCA­LUVA et al., 1980, and references therein).

It is worth noting, however, that even ifthe=:y all show a clear ocean·floor affinity, thediffere=:nt ophiolites from the Western Medi­te=:rranean are=:a display some diffe=:re=:nces bothin parental magmas and fractionation trends(cf. BECCALUVA et al., 1980).

This is evidenced by the different REEpatterns (fig. 2) and ratios between incom­patible=: ele=:ments such as Zr/Y, Zr/Nb,Z,/T;, Nb/Y, PlY and La+Co/Y fo< thevarious ophiolitic complexes (BECCALUVA etaI., 1980).

A relatively wide range of rarios betweenincomparable elements can also be observedwithin the Calabrian basalts (6g. 3).

The available REE data on Western Me­diterranean ophiolitic basalts generally showflat HREE chondrite-normalized (about10+3.5 times) patterns associated with bothslightly positive (Balagne=:) and negative (Li­guria, Alps, Alpine, Corsica) LREE fraetic­nation (6g. 2).

Similarly, the=: Calabrian basalts have rela­tivdy Bat chondrite-normalized REE pat­terns with abundances of heavy REE (HREE)about 12+22 times those of chondrites, anda slight LREE enrichment comparable=: tothat of Balagne basahs.

These geochemical characteristics, whichare different from those of the most corn·monly LREE depleted oceanic tboleiites,indicate a closer resemblance of Calabriabasahs with transitional MORB (SUN et al.,1979). Since incompatible element ratiosshow little change during the moouate- orhigh-degree partial melting required to ge­nerate=: ocean-floor type thole=:iitic magmas, theabove-cited geochemical differences suggestvarying degrees of depletion of the soutcemantle from which the patental melts of thevarious ophiolite sequences were generated.

978 L. BECCALUVA, G. MACCIOTTA, P. SPADEA

km3 in volume. Mg-gabbros are cut by fairlyabundant maflc dikes, recalling a typicalgabbro-diabase association. In some occur­rences gabbeD with basaltic dikes, previouslyaffected by oceanic metamorphism, representa subsuatum on which basalt erupted (LAN-

"

ZAFAME et al., 1978).Mg-gabbros are coarse-to medium-grained

and are composed of saussuritized plagioclase,diopside ± olivine. A clear layering, shownby variations in texture and mineral com­position, suggests a cumuli tic origin. The

.eo

o•5

o•

o 0______ 0

S __-:1'5;(: ~r--"L-.:~~·'"o t

o,•

MORB

~'::,

0',1"". 0.5

"z,

5.0

z, / .,/Ti'10

5 '0 '0 so wo 500

,"0

0.5

c*••___ - - - _·O""""'~

-----i1.. - • .Jt:t: •t~:;.

F:O.5 01.'"

•o

o

•

z,

5 '0 so '00 500

Fig. 3. - ZrjY and Zr/Ti vs. Ze plot for Calabria-Lucania metabasalts with different metamorphic fa­des: prehnite-pumpellyite = .; lawsonite-albite = 0; blueschist and &reenschist = *; samples with pIa­&iodase accumulation are not shown (data after SPADEA, 1979). Dashed lines indicate non modalbatch melting (cf. SHAW, 1970) trends and degrees (figures) for the inferred ophiolitic parental magmasfrom hypotetical sources chemically and mineralogically similar to mantle Iherzolite5 of Western Medi­terranean ophiolites (BECCALUVA et al., 1981). The source for Calabrian basalis as been modelled asfollows: S = 01 0.60, Opx 0.20, Cpx 0.16, Sp (Spinel) 0.04 and the assumed eutectic composition:01 0.15, Opx 0.15, Cpx 0.40, Sp 0.30. The modelled vectors indicate fractional cristallization of olivine(DJ), plagiodase (PI), orthopyroxene (Opx), dinopyroxene (Cpx), ilmenite (Urn) and zircon (Zrn);F = 0.5 liquid fraction. Partition coefficients and di~tribution fields of basalts from different tectonicsettings are after PURCE and NORRY (1979): lAB = island·arc basalts, MORB = mid-occanic ridge ba­salts, WPB = within.plate basalts. Asterisk shows chondrite composition.

PETROLOGY AND GEODYNAMIC SIGNIFICANCE ETC. 979

high MgO and low content of residual ele­ments such as Ti, p. Zr and Nb are compa­tible wilh Ihose rather undifferentiated termsof a cumulilic series where the adcumulusprocesses bring about the expulsion. to agreat extent, of the original intercumulus Ii·quid (table 1). Fe-rich gabbros <X'CUr asfragments of sedimentary breccia in the FridoUnit. In spite of advanced metamorphism(in the glaucophane schist facies), primarycumulitic textures and mineral assemblagesare still recognizable in these rocks. Theirchemical composition (table 1) is characte·rized by high Fe, Ti and P contents, reflectingthe nature and proportion of cumulus phases,and by a general increase in residual elementsindicating higher extent of original inter­cumulus liquid (meso- and artho-cumulatetextures).

On the whole the gabbroic rocks have

Manlle ultramaf1c

Serpentinizecl uhramafic occur in the Lu·canian Apennine as large bodies (up to 300 min ticknessl. Minor bodies and scaneredlenses are also present in the Northern andCentral Calabria.

In most occurrences they are serpentinizedIherzolites containing relicts, often well-

chemistry and fractionation trends compa·rable to those of gabbroic intrusives fromother Western Mediterranean ophiolites (fig.5) and from the modern oceanic crust(MIYASHIRO et al., 1970; KAY et al.. 1970;MELSON and THOMPSON, 1970; ENGEL andFISHER. 1975).

Both Mg. and Fe-rich rypes may be inter­preted as cumulates generated from oceanictholeiite magmas by separation of olivine.plagioclase and pyroxene during early stages(Mg-gabbros), later accompanied by Fe·Tioxide and apatite (Fe·gabbros).

c,

1000

100

C3.,,,,''(601

, 40~

. "_~O\'_~O!""*00

* 0

.. * G,.ull.. ku'

T, ••~ ••

C,1000

100

-,-- -<¥-c,, ,, ,I ,, ,L 601. l607., ,

~30T. 51:15:t - _L.. __

••

'" Om...Om""

10 L...~~---=:o-~~~~~___5 10 20 30 50 100 Y

el/s,101-~_~~~~_~~~~

0.01 0.1 0.5

Fig. 4. Cr vs. Y and Cr vs. Ce/Sr plob .5 moddlM by PEAICE (1980) tor derivation of ophioliticparental magmas by diflermt panial. melting degrtts (figures) from Co chondritc source. Ooscd andoyen S)'$tcm fractional Cfy5taJliution ucnds II'C irxl.i.catcd by singlc and doublc l~, respectively. ForCalabria·Lucania IIlCllbasalb in Cr vs. Y plot chta and symbols arc as in 6g. J; in G: vs. Cc/Sr plotdlul arc from DoSTAL et al., 1979. Notc the close rcscmbhDa: of CalabrilUl ophiolitic nugtnltism, bothin panial. melting degree and fractionation trends, with other Western Mediterranean ophiolile5 likc Gt0S5­glockner and Balagne.

980 L. BECCALUVA, G. MACCIOTTA, P. SPADEA

Metamorphic evolution

Generol ospectsThe different metamorphic evolution of

the Calabria-Lucania ophioJites provides acriterion for a major dassi6cation.

A mst order subdivision can be madeconsidering the presence of high-pressuremetamorphism. This metamorphism relatedto an early underthrusting has been exten­sively recognized in the Pennine zone of theAlps, where it is known as an Eo-Alpineevent (DAL PIAZ, 1974), and in the AlpineCorsica (OHNENSTE1TER et al., 1975).

Ophiolites affected by high.pressute meta­morphism occur typicaUy in melange andslices of the Lower Ophiolite Unit in theLucanian Apennines and Northern Calabria,and compose, pro parte, the Upper OphioliteUnit in Northern and Central Calabria. Theyare considered to be of Alpine affinity andto testify a provenantt from a subductedpart of the ocean crust (DIETRlcH and SCAN­DONE, 1972).

A second major group is characterized byweak metamorphism, without penetrativedeformation, unrelated to high-pressure con­ditions. Typically, this group is representedby spilitized pillow-Iavas which either com­pose, pro parte, the Upper Ophiolite Unit inNorthern and Central Calabria, or are in­cluded as olistoliths in Latc Cretaceousdeposits in the Lucanian Apennines. Theseophiolites were considered to be of Ligurideaffinity (DtETRICH and SCANDONE, 1972).Their metamorphism probably developedmainly in an oceanic environment.

The chronology of the metamorphic andtectonic events in which the ophiolites wereinvolved can be inferred from stratigraphicalrelations within different members of thesuite and with different Rysch sequences.Few radiometric ages have recently beenreported (BECCALUVA et al., 1981) whichindicate extensive isotopic re-equilibrationduring Oligocene-Early Miocene times.

A 6rst metamorphic event, markedly poly-

The bulk rock chemistry (table 1) of theCalabrian mantle lherzolites is indistin.guishable from that of comparable peridotitesof other Western Mediterranean ophiolites(cf. BECCALUVA et al., 1980).

preserved, of diopside and chromite. Relictolivine may sometimes be found. Completelybastitized orthopyroxene is often recognizablein rocks still containing fresh diopside. Onthe basis of relict minerals and tectonitetexture most ultramafic can be attributed toprimary mantle lherzolites.

Rare serpentinized dunites, hanburgitesand websterites are represented as centimeter­sized bands within thp. main lhenolitic mas­ses (LANZAFAME et al., 1978).

Fig. ,. - TiO. Rnd FeCI.... vs. FeO,•• ./MgO dia­grams for votcaniteli and gabbros from Calabria­Lucania ophiolites (.... ). Gabbros: A = Mg·gabbros.B = Fe-gabbroids from Northern Apennines andCorsica ophiolites; C = gabbroic rocks from Vou­rinos and Troodos ophiolites (after BECCALUVA etal., 1980). VolcaniUs: A = volcanites from Nor­thern Apennines and Corsica ophiolitcs; B = volca­nites from Vourinos and Troodos ophiolites (afterBECCAt.uVA ct al., 1980). For comparison, fraetio­nation trends for abyssal tholeiites (C), Skaergaardliquid (DJ and island·arc tholeiite suites of M.­caule)' lsland·Kermadccs (El, Miyake-)imalzy.Bonin(F) and Tofua.Tong. (Cl are also shown (afterMIYASlllRO, 1975).

GABBAOS

f.O'ot.. :DTi02 ..• lj•,

• ,.~

, 5 Feolo\

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PETROLOGY AND CEODYNAMIC SIGNIFICANCE ETC. 981

TABLE 1Analyus 01 ophiolitic and relaud rocks Irom the Calabria·Lucania area (Southern Apen­nines): metabasalts grouped according to metamorphic lades (average values, standard de­viations, with number 01 samples in brackets, are reported); metagabbros (Mg- gabbroand Fe·gabbro), urpentiniud ultramaftu (largely serpentinized and completely urpentinizedlberzo[;te, respectively), and basaltic dike rocks intruded in lower continental crust te"anes

"''1' 4.01 1."

r..; 0.19 0.•

'{J5 0.22 0••

l.l. 4.25 1.32

~~

i( 21

47.27

..n

16. "10.28

0.17

'.45

,.",.n0.12

0.21

,."

'.n'.n0.01

12.51

a{ 11

".~

,.",...1.'1

,."~."

0.01

14.05

at 11

"."0.11

'.n7.5'

0.15

33.67

'-"

12.'1

a( 11

".H0.11

'.H,.~

0.19

".".."

at 1) a( 11 a( I)

".iD ".20 "./19

D.n 0.41 ).5'17.93 '5.90 10.49

'.lI 5.70 12.11

0.14 0.12 0.20

'i.72 11.00 4.93

8.41 10.24 12.n

1.57 2." 3.10

2.•1 '.11 '.n0.02 0.02 I."

4.10 4.06 2.51

...""it 7} 10'

41.65 2.02

2.02 0.72

11.38 2.40

1O.8li 2.lO

0.11 O.GlI

7.181.47

'.11 1.!M

2.14 1.10

0•• 1.l8

0.25 0.08

4.43 0.53

Q..""i( tller45.382.25

I.M 0.46

16.') I.'J'J

10.57 1.19

0.18 O.GlI

1.381.7$

'.50 2.22

2.42 0./19

0.8li 0.90

0.20 0.05

5.53 I.U

......".......i(11) UI

47.11' 2.08

1.7$ 0.14

18." 3.'2

9.71 3.25

0.11 0.05

5.50 '.88

7.132.lI

3.2!l 1.50

0.5$ 0.5'

O.lO 0.011

5.15 1.14

10.72 1.71

0.20 0:1lI

5.87 2.03

1.21 3.32

.... f«les It....

i(I1110'

4'i.3I 2.23

'.9:9 0.41

11.31\.11

Sl02 (wtl1

Tl02

AI 20)

"'­"'"..''"

110 11 " 2!lD 50 lSS 74

m 50 lIl1 113

U,. ..:JO

l§ol III zas 124

12,. '12

III 28 122 41

'5 7 5

14 4 ZJ 7

115 .,

'" ,~

no ..

" ~

'" '"16 "

11' R

• •" .

,~ n272 142

... .337 314

214 13&.. ~

'" ... ," "

'"

.."""

'"".,.."..",,

59 1840 1710 2150

"21'W1 2560

24. 67 81 81

Z7I 21 U

3oQ.713

~

'" . .n'~ , ,

'"'"'""",'"•"

phasic, took place in oceanic environmentand developed at first in peridotite and gab­bro, before the eruption of stratigraphica1lyoverlying pillow.lavas. A second phase af­fected the whole ophiolite sequence and ischaracterized by spilitic alteration of thepillow-Iavas. This early metamorphism canbe ascribed to the Jurassic-Early Cretaceous,the earliest Cretaceous minimum age beingindicated by the distribution of the meta­morphism in sediments on top of the se­quence.

The subsequent metamorphic event relatedwith early displacement by subduction isconsidered at least synchronous, or evenolder (pre Upper Albian) (HACCARD et al.,1972; SPADEA in press), with that of theEo-Alpine event, for which a Late Creta~us

age (100+60 Ma) IS known by extensiveradiometric dating.

Later episodes of AJpine metamorphismare related to the main phases of the Apen­nine orogeny, which occurred in Middle Ter­tiary (Oligocene-Miocene) and Miocene times(OGNIBEN, 1969, 1973; HACCARD et al.,1972; AMODto-MORELLI et al., 1976).

Oceanic metamorphismEvidences of alteration related with ocean·

floor metamorphism prior to early tecto·nism are displayed in few cases within theCalabria-Lucania ophiolites. As in mostophiolitic rocks, in fact. the dominant oceanicmetamorphism is of low· to very low-gradeand took place without apparent deformation,making its distinctions from later low-gradeorogenlc metamorphism difficult. Further­more, in the higly dismembered ophiolitesof the Calabria·Lucania area the criterion ofrecognizing an oceanic metamorphism on the

982 L. BECCALUVA, G. MACClOTTA, P. SPADEA

basis of the high gr:tdient infetted by (hevertical distribution of mineral assemblagescannot usually be applied.

Nevertheless, alteration of higher gradethan spilitization can, in some cases, provideclear evidence of oceanic metamorphism.

One instance is represented by gabbro,intruded by basaltic dikes and stratigraphi­cally overlain by pillow-Iavas, which composesolistoliths exposed in few sections of theLucanian Apennines (LANZAFAME et al.,1978). The gabbro and associated basaltshow a complex multiphase retrograde (frommiddle- to low-grade) metamorphism, unlikethe ovetlying pillow-Iavas (as well as dikesintruded in the latter) which wete affectedonly by spilitization.

In metagabbro, assemblages consisting ofcummingtonite followed by brown and greenhornblende, and subsequently by actinoliteare displayed, which suggest a r«rystsl­lization under amphibolite, followed bygreenschist facies conditions. Earlier alte­ration is occasionally testified by recrystal­lization of diopside followed by developmentof reddish hornblende, which could indiC1lteinitial high-grade, quasi·magmatic conditions.The metabasaltic dike rocks display onlyamphibolite and greenschist facies assem­blages (LANZAFAME et al., 1978).

Another favorable circumstance occurs incases of close association (in melange zone)of basic rocks affected by rodingitic alterationwith development of different mineral assem­blages. One group of rocks displays typicalrodingitic assemblages dominated by diopsideand hydrogarnet which are overprinted byyounger ones including pumpellyite as majorphase. Widespread pumpellyte and no relicof older metasomatic assemblages characte­rize another group of rodingitized basic rocks(SPADEA, in press). There are indicationsthat rodingitic alteration, and consequentlyserpentinization, occurred both before andafter the tectonic displacement of the peri­dotite bodies. The older process, duringwhich the diopside-hydrogarnet pair crystal­lized, very likely took place in an oceanicenvironment.

High-pressuu metamorphismHigh-pressure/low-temperature assembla­

ges developed during an early subductionevent are generally wen preserved without

extensive overpnntlng, particularly in thenorthern area (Lucanian Apennine), wherearagonite is widespread in metasedimentaryrocks of the Frido Unit (SPADEA, 1976;LANZAFAME et al., 1979 b; SPADEA, in press).

Ophiolites and associated sedimentaryrocks display different features of the high­pressure metamorphism, either in the degreeof recrystallization, or in the composition ofthe associated minerals in similar primarylithotypes, or in deformation. Two maingroups of high-pressure rocks can be distin­guished and be arranged in a blueschist faciesseries as defined by TURNER. (1981).

A first group includes typical blueschistmetabasites with glaucophane·l.awsonite andalso containing various Na-pyroxenes, eros­site, pbengite, pumpellyite, albite and sphene.

A second group of HP-LT rocks consistsof prevalent metabasalts and capping meta­sediments: mineral assemblages are domi­nated in the fonner by albite-Iawsonite-chlo­rite (plus pumpelIyite, epidote, and ubiqui­tous sphene). Blue amphiboles and sodicpyroxenes rarely occur, and are mainly re­presented by Mg-riebeckite and aegi.rine­augite, respectively.

In terms of facies classification the twogroup of high.pressure rocks are referred tothe blueschist (or glaucophane schist faciesaccording to DE ROEVER, 1972), and to thelawsonite-albite facies, respectively. Detailedreports have been published on the minera-­logy and petrology of these meta-ophiolites,particularly of metabasites (basalt, dolerite,and rare gabbro: HOFFMANN, 1970; DEROEVER, 1972; DE ROEvER et al., 1974;PICCARRETA and ZIRPOLI, 197'; SPADEA etai, 1979).

Mineral assemblages and textures of rocksreferred to both the lawsonite-albite andblueschist facies indicate that the dominantHp·LT metamorphism was polyphase andwas overprinted by a younger metamorphismunder lower pressure conditions. The latterattained greenschist facies during its climax.

The polyphase character of the high-pres­sure metamorphism is clearly shown byzoning of blue amphiboles and Na.pyroxenes,and bv textural relations of Ca·silicates(Iawso~ite, pumpellyite, and epidote).

Widespread mineral assemblages developedin lawsonite-albite facies metabasites include

PETROLOGY AND GEODYNAMIC SIGNIFICANCE ETC. 983

TABI.E 2Minrral al1emblaglS devefo~d during HP/LT me­ttzmorphism (under ftlwso"itNJbitt and glaucophaneschist conditions and during /I lau evmt (mos/lyunder grunschist I/ldes conditions) in metabasitesand metaudimen//lry rocks 01 the Calabria Lucania

arell (Southern A~nnines)

LITIIOTTP£S

"'......UTUw-.. "--sa< "-sa<

~m -- - --U.SOIIlTlf'I.tlr(LUITt - - - --E'IIlOTE ----- -----,"""",ln/_AUN:GIW IIf[-AUGln - - - - - - --- -Gl..o\UCOf'WUOSSl'tCllOSSITtIlC-IIEI(CI - - - - -ACl'1-.lnCll,.llltlTE -----IMITt "ILl - - - -- - - - -- ------>l[T.uE1I11'LIrTAll\' ~u

_n ----- - ----....... nE - - - -- -- - - - - - - -_IlE ---.-'_ITE -----_m - -- -AAIIGOIIITE.....J.EIIITE ----- ___ r-

CALCITl -- - --

as major phases:a} albite-chlorite ± lawsonite ± pumpel­

lyite ± epidote;b) albite-chlorite ± Mg-riebeekite ± aegi-

rine-augite;with ubiquitous sphene, and phengite, cal­cite and hematite as possible additional mi­nerals (DE ROEVER, 1972).

Besides variations in mineral composition,strong differences in metamorphic texturesare displayed, as a result of variable defor­mation.

Metabasites with blueschist assemblagesinclude either pervasively recrystallized, mas­sive or more or less deformed rocks, or partlyrecrystallized rocks in which magmatic textu­res and minerals can survive. They consistmostly of:cl lawsonite ± pumpellyite-glaucophane­

crossite ± albite ± phengite ± chlorite;d) lawsonite ± pumpellyite-jadeite/aegirine­

aegirine/ augite-glaucophane·crossite ±albite ± phengite ± chlorite;

e) lawsonite-omphadte·jadeite/aegirine ±chIorite ± albite.

Sphene is a common additional phase, andsporadic aragonite, represented by relictforms, occurs (HOPFMANN, 1970).

A group of poorly recrystallized metaba­sites, mostly with a basaltic parentage occur­ring within the Frido Unit from the LucanianApennines closely associated to metasedi­mentary rocks with widespread aragonite,displays typical blueschist assemblages, butmainly in small quantities, with aragoniteas a possible additional component.

Metabasites consist£ng of dominant albiteand chlorite, with small amounts of lawso­nite and/or pumpellyites, and in places ofaragonite, are common within the Frido Unitin the same area. They can be consideredeither as representative of transitional con­ditions between lawsonite·a1bite and theblueschist fades, or be assigned to the lawso­nite-a1bite facies according to TURNER (1981).

Mineral assemblages displayed by mera­basites of lawsonite-albite and the blueschistfaeies are compared in tab. 2. Assemblagesdeveloped during a late metamorphic event,which are qualitatively similar in both groupsof high-pressure rocks, are also reported. Theoverall diflerences between metabasites ofrhe two high-pressure facies are also [eAtttedin the composition of both blue amphibolesand sodic pyroxenes, as emphasized byDE ROEVER (1972) and DE ROEVER et al.(1974). Pertinent chemical data are plottedin figs. 6 and 7.

Some poT constraints on the conditionsof the high-pressure metamorphism are pro­vided by the occurrence of lawsonite andaragonite, by the composition of blue amphi­boles and sodic pyroxenes, and by thecoexistence of albite and quartz. Estimatedconditions for the lawsonite·albite fadesmetamorphism are fluid pressure between 3and 4.5 kb, and temperature in the 250"-/­3500 C range. For transitional conditions toblueschist facies, higher pressure (above 5 kb)and probably lower temperature can beestimated by the occurrence of aragonite andthe absence of glaucophane. For blueschistfaeies metamorphism pressure between 6 kband 8 kb, and a possible temperature rangein the order of 3500 ± 50" C can be inferred.

Summary Bud concluaion&

The available petrological and geologicaldata indicate that the Calabria-Lucania ophio­lites may be considered as fra$ments of theoceanic lithosphere developed during the

98' L. BECCALUVA, G. MACCIOTTA, P. SPADEA

90 ,,-GU1JCOf't<AHE

'"UEc,un

70 CIIOSSITE

• ••• •• • •50 •• • ·1 ~•• • ••• •• ••• • •• • •• '"30 • •• •••

MO-

10Gl"UC()O'lo<ANE • IIIEaEC.UTE

••10 30 50 70

Fe~R"'·lOO

90

Fig. 6. - Composition of Na-pyroxencs, in ICrmsof ,he molar proportions of cnd·memben diopsidc+hedcnbergitc.jackile-aegirinc, OC'QIrring in law$Onile­albite facies metabasal! (ll.) and in bluac:hist raciesmClabasalt (Al and melagabbro (.) from the:Calabria·Lucln;. afea (Southern Apennines). Datafrom HOFFMANN (1970); DE ROEVER (1972); SPADUet .1. (1979); SPADEt. (unpublished),

Jurassic opening of the Western Tethyanbasin and separating the European andAfrican (lnsubrian) continental blocks.

They ~pre~nt oceanic associations con­sistuted by: 1) mantle ultramafic generallyshowing a spinel-I~rzolitic character; 2) ocea­nic tholeiitic basalt similar to transitionalMORB, evolving by fractional crystallizationtowards ferrobasaltic compositions; 3) gab­broic rocks produced by cumulus processes,al various fractional crystallization stages,from oceanic tholeiite magmas.

In this regard they are similar and havethe same significance of the other ophioliticcomplexes from the \'Uestern Mediterraneanarea, and reveal the dosest resemblance, asfar as the magmatic characteristics are con­cerned, with those of Balagne and ExternalLigurides. Their basaltic sequences, in fact,show an affinity with undeplepted tholeiitesof transitional MORE type from ExternalLigurides and Balagne.

All the data on the Western MediterraneanophioJites indicate that after initial riftingepisodes (Middle Triassic to Early Jurassic),continental fragmentation and developmentof multiple deep seaways took place (ScAN-

Fig. 7. _ Composilion of Na.amphiboles, in termsof Fe"IFe" + Mg + Mn • 100 VI Fe'''/fe''' +Al + Ti . 100, in metabasalt and mctagabbro fromthe Calabria·Lucania area (Southern Apennines).Data from HOFFMANN (1970), D£ RO£VEl (1972),D£ ROEVER et al. (1974); SPADEA et al. (1979),SPADEA (unpublished).

DONE, 1975), which later evolved to ridgesegment/fracture zone systems (PICCARDO,1977; BECCALUVA and PICCARDO, 1978;BECCALUVA et al., 1980). This was ap­parently related to separation of Africafrom North America, and its eastward m"tion with respet"t to the Euroasiatic plate(DEWEyet aI., 1973) which produced largescale tensional and transcurrent effects withinthe epicontinental and newly-formed oceanicdomains.

As it has been sugge;=sted for the analogoussequences from the External Ligurides andBalagne (BECCALUVA et al., 1980), basahsfrom the Calabria ophiolites might representthe activity of an early oceanic-type magma·!ism developed in a pericontinental position,very close to the new continental margins.This hypothesis can also account for theabundance of terrigenous sediments coveringophiolitic basahs, which require a nearbycontinent (lANzAFAME et al., 1978), andtheir primary association with continentalcrust terranes prior to the tectonic-meta­morphic evolution during orogeny (LAmA­FAME et aI., 1979 a; SPADE", in press).

Since there is no contrasting geologicalor petrological evidence, it is conceivable that

PETROLOGY AND GEODYNAMIC SIGNIFIC.... NCE ETC. 985

Ihis oceanic basin never reached a well­developed stage, resulting in a narrow deepseaway with remnanlS from continental crustmargins. Moreover, the fact that 1) thebrecciation of ophiolitic along with conti­nental material, 2) the serpentinization ofthe mantle lherzolites and 3) the oceanic me­tamorphism in gabbros occurred, in someplaces, before ~nic oosahs extrusion anddikes emplacement, indicates early tectonismand similar characteriSlics to those of oceanicfracture zones as pointed out for someNorthern Apennines ophiolites (cf. ABBATEet al., 1972; GALBIATI et al., 1976; BECC....­LUVA et al., 1980; SERRt, 1980). Such atectonic environment could also account forthe lack of a complete sheeted dike andgabbro complex, and for the general consi­derably reduced thickness of the ophioliticsequences with respect to normal oceaniccrust.

Therefore the Calabria-Lucania ophiolitesmay represent lithospheric sections generatedat an early ocean ridge system, later inte­rested, at least in !,art, by a subsequenttectonic-metamorphic evolution in fracturezones and, eventually, by injection of newoceanic melts at the intervening ridge/transform intersections. An oceanic/pericon.tinental pattern, strongly affected by bothdivergent and transcurrent movements, withdevelopment of short ridge segments and

important fractures and leaky transformzones (cf. CRISTENSEN and SALISBURY,1975), should have characterized theoriginal geodynamic environment of theCalabria-Lucania ophiolites.

Before the end of Early Cretaceous theclosure of this ocean basin took place byconvergence, underthrusting and consumptionof the oceanic Iithosphere, which might havebeen subducted for a short time, due to itsrestricted extension. The age of the earlyHp·LT metamorphic episode is consideredto be post-Aptian and pre-Late Albian, basedon stratigraphical evidence (HACCARD et al.,1972; SPADEA, in press).

Pertinent metamorphic assemblages indi­cate parlial equilibration al different pres­sure conditions, reaching maximum values of6+8 kb at 350" ± 50" C. The widespreadblueschist assemblages and the largely incom­plete equilibria attained suggest a high rateof consumption, resulting in a rapid decreaseof the geothermal gradient and the establish.ment of the blueschi~t facies stability con·ditions. The subsequent exhumation, whichoccurred extensively without overprinting andobliterating the high-pressure assemblages,may also have occurred al high rates. Thisimplies, accotding to the model proposed byDR....PER and BoNE (1981) an early tectonicemplacement of the high.ptessure terrains.

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