Geochemistry of the Jurassic Mirdita Ophiolite (Albania) and the … et... · 2012. 8. 21. · dualism, particularly those in Albania. Dede et al. (1966) recognized first a petrographic

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Lithos 100 (2008

Geochemistry of the Jurassic Mirdita Ophiolite (Albania) and theMORB to SSZ evolution of a marginal basin oceanic crust

Yildirim Dilek a,⁎, Harald Furnes b, Minella Shallo c

a Department of Geology, Miami University, Oxford, OH 45056, USAb Centre for Geobiology and Department of Earth Science, University of Bergen, Allegaten 41, 5007 Bergen, Norway

c Fakulteti i Gjeologjise dhe Minierave, Universiteti Politeknik, Tirana, Albania

Received 20 December 2006; accepted 8 June 2007Available online 15 August 2007

Abstract

The Middle Jurassic Mirdita Ophiolite in northern Albania is part of an ophiolite belt occurring between the Apulian andPelagonian subcontinents in the Balkan Peninsula. The upper mantle and crustal units of the Mirdita Ophiolite show major changesin thickness, rock types, and chemical compositions from west to east as a result of its complex evolution in a suprasubduction zone(SSZ) environment. The ∼3–4-km-thick Western Mirdita Ophiolite (WMO) includes lherzolite–harzburgite, plagioclase–lherzolite, plagioclase–dunite in its upper mantle units and a plutonic complex composed of olivine gabbro, troctolite, ferrogabbro,and gabbro. These peridotites and gabbroic rocks are overlain directly by a ∼600-m-thick extrusive sequence containing basalticpillow lavas and hyaloclastites. Sheeted dikes are rare in the WMO. The ∼12-km-thick Eastern Mirdita Ophiolite (EMO) includestectonized harzburgite and dunite with extensive chromite deposits, as well as ultramafic cumulates including olivineclinopyroxenite, wehrlite, olivine websterite, and dunite forming a transitional Moho with the overlying lower crustal section. Theplutonic rocks are made of pyroxenite, gabbronorite, gabbro, amphibole gabbro, diorite, quartz diorite, and plagiogranite. A well-developed sheeted dike complex has mutually intrusive relations with the underlying isotropic gabbros and plagiogranites andfeeds into the overlying pillow lavas. Dike compositions change from older basalt to basaltic andesite, andesite, dacite, quartzdiorite, to late-stage andesitic and boninitic dikes as constrained by crosscutting relations. The ∼1.1-km-thick extrusive sequencecomprises basaltic and basaltic andesitic pillow lavas in the lower 700 m, and andesitic, dacitic and rhyodacitic massive sheet flowsin the upper 400 m. Rare boninitic dikes and lavas occur as the youngest igneous products within the EMO. The basaltic andbasaltic andesitic rocks of the WMO extrusive sequence display MORB affinities with Ti and Zr contents decreasing upsection(TiO2=3.5–0.5%, Zr=300–50 ppm), while ɛNd(T) (+8 to +6.5) varies little. These magmas were derived from partial melting offertile MORB-type mantle. Fractional crystallization was important in the evolution of WMO magmas. The low Ti and HREEabundances and Cs and Ba enrichments in the uppermost basaltic andesites may indicate an increased subduction influence in theevolution of the late-stage WMO magmas. Basaltic andesites in the lower 700 m of the EMO volcanic sequence have lower TiO2

(∼0.5%) and Zr (∼50 ppm) contents but ɛNd(T) values (+7 to +6.5) are similar to those of the WMO lavas. These rocks showvariable enrichment in subduction-enriched incompatible elements (Cs, Ba, Th, U, LREE). The basaltic andesites through dacitesand boninites within the upper 400 meters of EMO lavas show low TiO2 (∼0.8–0.3%) and ɛNd(T) (+6.5 to +3.0). The mantlesource of these rocks was variably enriched in Th by melts derived from subducted sediments as indicated by the large variations inBa, K, and Pb contents. EMO boninitic dikes and lavas and some gabbroic intrusions with negative ɛNd (T) values (−1.4 and −4.0,respectively) suggest that these magmas were produced from partial melting of previously depleted, ultra-refractory mantle. TheMORB to SSZ transition (from west to east and stratigraphically upwards in the Mirdita Ophiolite and the progression of the ɛNd(T)

⁎ Corresponding author. Tel.: +1 513 529 2212; fax: +1 513 529 1542.E-mail address: [email protected] (Y. Dilek).

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175Y. Dilek et al. / Lithos 100 (2008) 174–209

values from +8.0 to −4.0 towards the east resulted from an eastward shift in protoarc–forearc magmatism, keeping pace with slabrollback in this direction. The mantle flow above the retreating slab and in the arc-wedge corner played a major role in theevolution of the melting column, in which melt generation, aggregation/mixing and differentiation occurred at all levels of the sub-arc/forearc mantle. The SSZ Mirdita Ophiolite evolved during the intra-oceanic collapse and closure of the Pindos marginal basin,which had a protracted tectonic history involving seafloor spreading, protoarc rifting, and trench-continent collision.© 2007 Elsevier B.V. All rights reserved.

Keywords: Jurassic oceanic crust and Tethyan ophiolites; Suprasubduction zone magmatism; MORB volcanism; Boninites; Slab contamination ofmantle source; Slab rollback and extension

1. Introduction

The Tethyan ophiolites in the Alpine orogenic systemoccur along curvilinear suture zones bounding a seriesof Gondwana-derived continental fragments (i.e., Apu-lia, Pelagonia, Central Anatolian crystalline complex;Fig. 1) and represent the remnants of Tethyan marginalbasins that evolved between these microcontinents.Rifting of the northern edge of Gondwana started in thePermo-Triassic and led to the formation of Triassicvolcano-sedimentary units, displaying within-plate al-kaline basalt (WPB) to transitional and mid-ocean ridgebasalt (MORB) chemical affinities (Pamic, 1984; Dilekand Rowland, 1993; Malpas et al., 1993; Pe-Piper, 1998;Saccani et al., 2003). The ophiolites show an ageprogression from Jurassic in the Alpine–Apennine andthe Dinaride–Albanide–Hellenide mountain belts in thewest to Cretaceous in the Anatolide–Tauride (Turkey),the Zagros (Iran), and the Tibetan–Himalayan (China–India–Pakistan) mountain belts in the east. Thegeochemical character of these Tethyan ophiolites alsochanges from MORB-like in the Alps–Apennines(Hébert et al., 1989; Tribuzio et al., 1999; Ramponeand Piccardo, 2000) to island arc affinities (suprasub-duction zone — SSZ ophiolites) in Cyprus, Turkey andbeyond in the east (Pearce, 1980; Pearce et al., 1984;Robinson and Malpas, 1990; Dilek et al., 1999;Hassanipak and Ghazi, 2000; Hébert et al., 2003;Malpas et al., 2003; Parlak et al., 2006). Middle Jurassicophiolites in the Dinaride–Albanide–Hellenide moun-tain system in the Balkan Peninsula display both MORBand SSZ affinities (Smith, 1993; Robertson andKaramata, 1994; Rassios and Smith, 2000; Pamicet al., 2002; Shallo and Dilek, 2003; Saccani et al.,2004), marking a critical transition between the westernand eastern segments of the Neo-Tethyan ophiolites inthe eastern Mediterranean region.

The MORB to SSZ shift in the geochemical affinityof the Middle Jurassic ophiolites of the BalkanPeninsula appears to be a lateral, west-to-east change.Relatively thin (∼3–4 km) and incomplete ophiolite

sequences displaying MORB affinities occur in the westand thicker (∼10–12 km), more complete ones showingcalc-alkaline SSZ affinities occur in the east within theDinarides, Albanides, and Hellenides (Pamic, 1983;Beccaluva et al., 1984; Shallo et al., 1990; Jones et al.,1991; Kodra et al., 1993a; Beccaluva et al., 1994;Bortolotti et al., 1996; Bébien et al., 1998; Clift andDixon, 1998; Rassios and Smith, 2000; Hoeck et al.,2002; Pamic et al., 2002; Pe-Piper and Piper, 2002;Bazylev et al., 2003; Dilek and Flower, 2003; Saccaniand Photiades, 2004; Saccani et al., 2004; Beccaluvaet al., 2005; Bortolotti et al., 2005). Different inter-pretations have been suggested for this geochemicaldualism, particularly those in Albania. Dede et al.(1966) recognized first a petrographic distinctionbetween the upper mantle rocks of the Albanianophiolites marked by the existence of plagioclase-bearing lherzolitic peridotites in the western ophiolitesand by more abundant chromite in the harzburgiticperidotites of the eastern ophiolites. This led to therecognition of the “lherzolitic” western-type vs. “harz-burgitic” eastern-type ophiolites in Albania (e.g., Bébienet al., 1998). Nicolas et al. (1999) ascribed the contrastbetween the western and eastern peridotite massifs tosuccessive episodes of amagmatic and magmaticspreading (respectively) in a slow spreading mid-ocean ridge environment. The observed geochemicaland petrological differences between the two types havebeen explained by an initial seafloor spreading phasethat produced the MORB crust, followed by theinception of an intraoceanic subduction zone thatresulted in the development of the SSZ crust (Shallo,1992; Bortolotti et al., 1996; Robertson and Shallo,2000; Bortolotti et al., 2002; Shallo and Dilek, 2003;Dilek and Flower, 2003; Flower and Dilek, 2003;Bortolotti et al., 2005). All these models infer distinctlydifferent timing and tectonic environments of formationof the Middle Jurassic ophiolites in Albania.

Our recent studies in the northern ophiolite belt inAlbania, known as the Mirdita zone, have shown thatthe geochemical dualism here is an artifact of complex

Fig. 1. Simplified tectonic map of the Mediterranean region showing the main plate boundaries, orogenic belts, and tectonic units of Eurasian, Neo-Tethyan and Gondwana-Land affinities. Neo-Tethyan ophiolites range in age from Jurassic in the Alps and the Balkan Peninsula to Late Jurassic–Cretaceous in the eastern Mediterranean region (mainly in Anatolia and farther east) and are associated with ocean floor sediments and flysch deposits(shown in red). The Mirdita Ophiolite in Albania (north of Tirane) occurs along a sharp NE-SW bend in the generally NW-SE-oriented Dinaride–Hellenide ophiolite belt. The Pelagonian continental fragment in the Balkan Peninsula separates the partly coeval Pindos–Mirdita (west) and theVardar Zone (east) ophiolite belts.

176 Y. Dilek et al. / Lithos 100 (2008) 174–209

melt evolution in a single suprasubduction zoneenvironment and that the observed MORB and SSZaffinities of the Albanian ophiolites do not requireseparate tectonic settings and significantly differenttimes of formation. In this paper, we present newgeochemical and Sm–Nd isotopic data from the uppercrustal units (mainly the extrusive and dike rocks) of the

western and eastern parts of the Mirdita Ophiolite inorder to constrain its petrogenesis and the geochemicalevolution of its magmas. Our geochemistry is based ondetailed and systematic documentation of the structureand volcanic stratigraphy of the extrusive sequences andof the crosscutting relations of different dike generationsand plutons in the western and eastern parts of the

Fig. 2. Geological map of the Albanian ophiolites and surrounding units (modified from Dilek et al. 2005). The dashed line depicts the approximateboundary between the western- and eastern-type ophiolites, based mainly on the apparent changes in the chemical affinities of the crustal and uppermantle rocks fromMORB to SSZ (respectively). 40Ar/39Ar ages (in Ma) of intrusive and metamorphic rocks are from Vergély et al. (1998) and Dimo-Lahitte et al. (2001). Key to lettering for different peridotite massifs (from north to south): Trp— Tropoja, Krb— Krrabi, Gom— Gomsiqe, Puk—Puke, Kuk— Kukesi, Lur— Lure, Skd— Skenderbeu, Blq— Bulqize, She— Shebenik, Shp— Shpati, Dv— Devolli, Vm— Vallamara, Vo—Voskopoja, Mr — Morava.



Mirdita Ophiolite. We use our petrogenetic andgeochemical interpretations to develop a regionalgeodynamic model for the tectonomagmatic evolutionof the Mirdita Ophiolite within the Mesozoic Neo-Tethys. Collectively, our new data and petrogeneticmodel provide a testable hypothesis for the tectonomag-matic evolution of SSZ oceanic crust in restrictedmarginal basins within broader zones of continentalcollision within the Tethyan realm.

Fig. 3. A. Geological map of the Mirdita Ophiolite in northern Albania. A-A′shown in B (modified from ISPGJ-IGJN, 1983, Geological Map of Albaniageological map shown in Fig. 4. WMP and EMP represent the western and earefer to western and eastern subprofiles, along which additional systematic sathe numbers show the localities of plagiogranite and quartz diorite intrusioMirdita Ophiolite. Profile A-A′ runs NNE mainly within the Western-type oarchitecture of both the Western- and Eastern-type and their contact relation

2. Geology of the Mirdita Ophiolite

The Jurassic Mirdita Ophiolite occurs in a ∼30–40-km-wide belt bounded by the conjugate passive marginsequences of Apulia in the west and Korabi-Pelagonia inthe east (Figs. 2 and 3; Dilek et al., 2005). Largeperidotite massifs of the upper mantle units are exposedin the western and eastern parts of this ophiolite belt.The massifs adjacent to the Apulian margin sequences in

, B-B′ and C-C’ depict the profile lines for the structural cross-sections, scale 1:200,000). The polygon marks the boundaries of the detailedstern main profiles for our chemostratigraphic sampling. WSP and ESPmpling of the extrusive and dike rocks was carried out. The circles withns with new U/Pb zircon ages. B. Structural cross-sections across thephiolite, whereas Profiles B-B′ and C-C′ show the internal structurals.

Fig.3(contin

ued).


Fig. 4. Detailed geological map of the central part of the Mirdita Ophiolite in northern Albania. The SWand NE composite columnar sections depictthe internal structure and stratigraphy of the Western- and Eastern-type ophiolites in general. The WMP and EMP sections show the volcanicstratigraphy and the sample numbers and locations along the western and eastern main profiles, respectively. Key to town/village names: A —Aramire, B — Bardhaj, Bu — Bulshar, D — Domgjon, Da — Dardhe, Gj — Gjegjan, H — Helshan, K — Kimez, Kr — Kryez, Ks — Kushnen,M — Mollkuge, P — Paluçe, Pr — Perlat, Rp — Reps, Sh — Shëngjergi, Sp — Spaç.



the west (i.e., Krabbi, Gomsiqe, Skenderbeu) are mainlyplagioclase lherzolites, whereas those close to Pelagoniain the east (i.e., Tropoja, Kukesi, Lura) are harzburgiteswith major chromite deposits (Nicolas et al., 1999;Hoxha and Boullier, 1995). The western lherzolitesshow a pervasive mylonitic fabric, caused by high-temperature (∼1000–800 °C) plastic deformation underlithospheric conditions and spatially associated withmelt impregnation patches (Nicolas et al., 1999). Theseupper mantle rocks are overlain by plastically deformedflaser gabbros. Isotropic gabbros and sheeted dikes arerare in crustal sections, and mylonitic peridotites anddeformed gabbros are locally overlain by basaltic lavas(Fig. 3B) and intruded by diabasic dikes and sills.Nicolas et al. (1999) suggest that the western lherzolitestransition into tectonized harzburgites a few km belowthe lower crustal gabbros.

Based on differences between upper mantle perido-tites and the internal stratigraphy and chemical compo-sitions of crustal units, previous studies have recognizedtwo types of ophiolites in the Mirdita zone (Shallo et al.,1985; Shallo, 1990; Shallo et al., 1990; Kodra et al.,1993b; Beccaluva et al., 1994; Shallo, 1994; Bortolottiet al., 1996; Tashko, 1996; Bébien et al., 1998; Nicolaset al., 1999; Bébien et al., 2000; Insergueix-Filippi et al.,2000; Hoeck et al., 2002; Shallo and Dilek, 2003;Beccaluva et al., 2005; Bortolotti et al., 2005). Thesewill subsequently be referred to as the Western MirditaOphiolite (WMO) and the Eastern Mirdita Ophiolite(EMO). The WMO has much thinner crust (∼ 2–3 km)and shows mainly MORB affinities, whereas the EMOis up to 10–12-km- thick and shows predominantly SSZgeochemical affinities (Fig. 3B). The boundary betweenthese two types is an irregular contact (Fig. 2) alongwhich the Eastern-type plutonic and hypabyssal rocksintrude Western-type peridotites and gabbros. EMOsubunits are locally juxtaposed tectonically against theWestern-type peridotites and gabbros along west-directed, Late Cenozoic thrust faults (Fig. 3B; Dileket al., 2005).

The WMO contains upper mantle peridotites, mafic-ultramafic cumulates and mylonitic gabbros, sparsesheeted dikes, and extrusive rocks that collectively forma ∼3-km-thick composite sequence. Peridotites includelherzolite–harzburgite, plagioclase lherzolite, plagio-clase dunite, and rare amphibole peridotites (olivinehornblendite). The plutonic sequence, which locallyintrudes into and/or overlies the peridotites, consists oftroctolite, olivine gabbro, ferrogabbro, gabbro, and rareamphibole gabbro and generally displays an ol–pl–pxcrystallization order (Beccaluva et al., 1994; Saccaniet al., 2004; Beccaluva et al., 2005). Extrusive rocks,

composed mainly of massive to pillow lavas andhyaloclastites, form a nearly 600-m-thick sequencethat rests directly on serpentinized peridotites andgabbroic rocks along primary contacts (Figs. 4 and 5;Dilek et al., 2005). These contact relations suggest thatthe lavas erupted directly on the upper mantle peridotitesand lower crustal rocks exposed on the seafloor. Isolateddikes crosscut these extrusive rocks and feed youngerlava flows. Normal faults truncate and displace dikesand flows for as much as several meters and are spatiallyassociated with quartz and epidote mineralization(Banerjee et al., 2002; Dilek et al., 2005). The lavasare stratigraphically overlain by 5- to 20-m-thickradiolarian cherts that are late Bajocian-early Bathonian(∼168–166 Ma) to late Bathonian-early Callovian(∼165–163Ma) in age (Marcucci et al., 1994; Marcucciand Prela, 1996).

The EMO commonly includes all subunits of atypical Penrose-type ophiolite pseudostratigraphy(Figs. 3B and 4) with thicknesses up to 10–12 km(Shallo and Dilek, 2003, and references therein). Theperidotite massifs of this type (Tropoja, Kukesi, Lura)are composed of harzburgite tectonite, interlayeredharzburgite and dunite, and dunite with extensivechromite deposits. The harzburgites are composed ofolivine (∼80% forsterite), orthopyroxene (∼17% ensta-tite), clinopyroxene (b3% diopside), and spinel (∼2%)(Hoxha and Boullier, 1995). Dunites are massive andcomposed of olivine, chrome spinel, orthopyroxene, andinterstitial clinopyroxene. Massive dunite in the upperperidotite section transitions upward into ultramaficcumulates (0.5 to b2 km-thick), which consist of olivineclinopyroxenite, wehrlite, olivine websterite, and du-nite, forming a transitional Moho (Dilek et al., 2007).The EMO plutonic section comprises pyroxenite,gabbronorite, gabbro, amphibole gabbro, diorite, quartzdiorite, and plagiogranite intrusions. Late-stage harz-burgite–wehrlite intrusions crosscut the lower crustalrocks in both the WMO and EMO (Dilek et al., 2005).

Sheeted dikes have mutually intrusive relations withunderlying isotropic gabbros, plagiogranites, and quartzdiorites, and feed the overlying pillow lavas (Fig. 3B).Sheeted dikes generally dip ∼80°–60°, except wherethey have been rotated into more gentle dips (40°–30°)along low-angle normal faults. Dikes are extensivelymineralized along these faults and around the late-stagequartz diorite intrusions that are widespread throughoutthe EMO (Fig. 3A). Dike swarms locally intrude theoverlying lava flows causing hydrothermal alterationand mineralization (epidosite and pyrite) in theirvolcanic host rocks. Hydrothermal brecciation andaccompanying mineralization are also common along

Fig. 5. (A). Basaltic pillow lavas of the Western-type ophiolite near the base of the WMP; (B). altered basaltic pillow lavas at the top of the extrusivesection beneath the chert cover along the WMP.


these dike swarms in the extrusive rocks. Epidote,quartz, and pyrite–chalcopyrite mineralization andhydrothermal alteration are common in the sheeteddike rocks hosting the quartz diorite intrusions. Both thesheeted dikes and quartz diorites are oriented NNE,parallel to the main trend of the Mirdita Zone, implyingthat EMO spreading was directed WNW-ESE (Fig. 4).

The EMO extrusive sequence is nearly 1.1-km-thickand consists of pillowed to massive flows ranging incomposition from basalt and basaltic andesite in thelower sections to andesite, dacite, and rhyodacite in theupper part (Figs. 4 and 6; Shallo et al., 1987; Shallo,1990; Beccaluva et al., 1994; Shallo, 1995; Bortolottiet al., 1996, 2002; Shallo and Dilek, 2003; Saccani et al.,2004; Bortolotti et al., 2005). Rare boninitic dikes andlavas in the easternmost Mirdita zone crosscut and/oroverlie earlier extrusive rocks, indicating that theyrepresent the youngest magmatic products during crustal

accretion of the EMO (Dilek et al., 2005). UpperBathonian–Oxfordian radiolarian cherts stratigraphi-cally overlie the extrusive sequence of the Eastern-type ophiolites (Marcucci et al., 1994; Chiari et al.,1994; Marcucci and Prela, 1996).

3. Volcanic stratigraphy

Most analyzed samples were collected along twoprofiles, WMP and EMP for the Western and Easternmain profiles, respectively, shown on the geologicalmap in Fig. 3A. Additional rock samples were alsocollected along the Western (WSP) and Eastern sub-profiles (ESP) (Fig. 3A).

The volcanic rocks along the WMP consist mainly ofpillow lavas with minor sheet flows and hyaloclasticbreccias (Figs. 4 and 5). The extrusive sequence along thisprofile is ∼650-m-thick and rests directly on

Fig. 6. (A). Basaltic andesite pillow lavas at the bottom of the EMP extrusive sequence showing a progression from mega-pillows at the bottom tomini-pillows on top. The white line marks the boundary between two eruptive cycles. (B). Andesitic massive lava flows about 600 m above the baseof the volcanic section along the EMP. An E-dipping high-angle normal fault (F-F′) crosscuts the lava units (C) Andesitic massive lavas andhyaloclastites about 850 m above the base of the volcanic section along the EMP. (D) Dacitic (rhyodacitic) lavas near the top of the extrusive sequencealong the EMP.


serpentinized lherzolites and/or gabbroic rocks (Fig. 4).The basaltic lavas that make up a large part of thesequence are non-amygdaloidal and predominantlyaphyric or slightly phyric (∼90% contain b2% pheno-crysts). In the lower 100 m of the section minor pillowbreccias and hyaloclastites occur at discrete stratigraphichorizons. At the stratigraphic height of 250 m, there areseveral 2–3-m-thick massive flows (Fig. 4). The pillowsimmediately overlying these massive flows are large(∼2 m in diameter) but become progressively smallerupwards. Pillow lavas composed of slightly amygdaloidalbasaltic andesite occur at the top of the WMP. Weanalyzed a total of 26 rock samples collected along theWMP.

The Western sub-profile (WSP) is a discontinuoussection of non-amygdaloidal basaltic pillow lavasestimated to be ∼660-m-thick (Fig. 3A). We collectednine samples along this profile at 5 to 60 m intervals,beginning ∼180 m above the base of the extrusivesequence.

The volcanic sequence along the EMP, which islocated ∼5–7 km NNE of the WMP (Fig. 4), is about

1.1-km-thick and overlies a sheeted dike complex alonga transitional zone consisting of lavas intruded by dikeswarms and microgabbros. The uppermost part of thissequence is overlain by several tens of meters of redchert, intercalated with black shales. The lower 400 m ofthe sequence consists of non-amygdaloidal to slightlyamygdaloidal (0 to ∼2% vesicles) basaltic andesites.Stratigraphically upward and between 400 m and 650 mabove the base of the extrusive sequence the rocksconsist dominantly of pillow lavas, massive flows,pillow breccias and hyaloclastites (Figs. 4 and 6), all ofwhich are made of basaltic andesite. These lavas aremoderately to highly amygdaloidal (N2% to ∼10%).Farther up, between 650 m and 700 m, the rocks aremoderately amygdaloidal basaltic andesitic pillow lavas.From 700m to the top of the extrusive sequence, massiveflows dominate with minor pillow lavas and pillowbreccias (Figs. 4 and 6). These rocks are mostly non- tohighly amygdaloidal andesite with minor amounts ofhighly amygdaloidal (up to 25%) basalt and dacite. Thephenocrysts in the andesites consist of plagioclase andclinopyroxene, whereas in the dacites the phenocryst

Table 1Major- and trace-element analyses (XRF and ICP-MS) of lavas, dikes and plutonic rocks of the Mirdita Ophiolite

Samplenumber

Rock type SiO2 TiO2 Al2O3 FeOt MnO MgO CaO Na2O K2O P2O5 L.O.I SUM Sc V Cr Co Ni Cu Zn

Lava flows of the western main profile4-Al-00 Bas.pl.lava 50.30 1.10 14.88 10.27 0.19 8.00 12.51 1.89 0.11 0.06 1.60 100.91 293 381 48 109 100 835-Al-00 B.and.pl.lava 53.37 0.57 15.57 9.92 0.17 6.08 7.45 3.78 0.01 0.04 3.11 100.07 35.8 262 82 53 47 102 8062a-Al-01 Bas.pl.lava 47.44 1.76 14.04 13.39 0.21 6.61 9.91 2.04 0.06 0.21 4.24 99.92 41.9 341 238 74 121 59 12344-Al-00 Bas.pl.lava 48.18 1.54 14.66 13.29 0.21 7.05 10.02 2.16 0.18 0.11 3.31 100.71 49.7 400 84 65 47 80 12361-Al-01 Bas.pl.lava 48.94 2.37 12.85 15.01 0.24 6.28 8.44 2.27 0.24 0.21 2.44 99.28 385 102 76 53 47 13258-Al-01 Bas.pl.lava 47.89 2.40 13.45 15.59 0.23 5.68 8.90 2.43 0.25 0.24 2.86 99.90 411 150 79 57 45 15442-Al-00 Bas.pl.lava 49.45 2.47 13.74 15.64 0.20 5.51 9.56 2.14 0.18 0.20 1.97 101.06 435 95 71 52 53 14952-Al-01 Bas.pl.lava 42.91 2.08 11.7 12.85 0.21 4.85 8.17 2.55 0.21 0.21 13.97 99.71 440 107 81 52 60 15248-Al-01 Bas.pl.lava 49.90 2.42 13.17 15.28 0.23 6.17 8.04 2.15 0.22 0.24 2.55 99.77 431 96 81 52 52 14945-Al-01 Bas.pl.lava 48.59 2.42 13.43 15.44 0.21 5.72 9.49 1.93 0.22 0.26 2.58 100.28 44.6 482 102 80 55 57 15041-Al-01 Bas.pl.lava 48.60 2.45 13.60 15.63 0.20 5.52 9.92 1.56 0.06 0.27 2.65 100.44 492 92 83 54 57 15038-Al-01 Bas.pl.lava 49.18 1.49 14.33 12.98 0.21 7.06 9.09 2.42 0.30 0.12 2.46 99.63 44.7 341 128 62 57 68 11935-Al-01 Bas.pl.lava 50.95 1.40 13.49 12.31 0.19 6.69 7.43 2.78 0.06 0.13 3.74 99.18 327 125 70 56 74 11640-Al-00 Bas.ms.lava 48.70 3.55 12.51 16.04 0.24 4.76 8.54 3.02 0.37 0.37 1.95 100.05 46.4 448 41 66 32 58 15332-Al-01 Bas.pl.lava 48.91 1.51 14.54 13.14 0.19 7.32 9.81 2.03 0.15 0.12 2.67 100.40 384 110 65 53 69 11031-Al-01 Bas.ms.lava 46.03 1.96 14.22 13.68 0.22 6.31 11.74 1.54 0.07 0.18 4.68 100.67 46.9 495 198 74 78 80 12129-Al-01 Bas.pl.lava 41.11 1.98 14.84 12.32 0.18 4.81 14.08 1.44 0.08 0.17 9.64 100.66 511 237 71 83 98 11539-Al-00 Bas.pl.lava 49.63 1.95 13.11 13.10 0.21 6.96 8.16 3.14 0.05 0.15 3.31 99.77 366 179 66 75 68 13225-Al-01 Bas.pl.lava 47.01 3.42 13.32 15.64 0.26 6.00 7.52 2.40 0.03 0.43 3.50 99.55 50.10 474 70 86 46 59 17436-Al-00 Bas.pl.lava 49.62 1.92 13.85 13.42 0.21 6.91 9.42 2.61 0.27 0.14 2.14 100.51 369 185 63 77 71 12324-Al-01 Bas.pl.lava 48.82 1.97 14.17 13.85 0.19 6.93 11.44 1.65 0.06 0.19 1.43 100.69 403 178 64 68 69 11720-Al-01 Bas.ms.lava 47.51 1.97 14.45 13.84 0.22 6.90 10.73 2.06 0.14 0.17 2.13 100.11 403 164 66 67 76 10117-Al-01 Bas.pl.lava 47.79 2.08 14.02 13.74 0.22 7.08 10.23 2.31 0.10 0.2 2.54 100.30 418 166 74 89 81 12133-Al-00 Bas.pl.lava 48.79 2.71 13.67 15.45 0.20 5.52 8.46 2.72 0.35 0.24 2.5 100.61 442 52 71 38 71 14614-Al-01 Bas.pl.lava 47.77 1.97 14.24 13.41 0.20 7.06 10.50 2.26 0.14 0.17 2.62 100.35 418 203 72 94 83 1112-Al-00 Bas.pl.lava 50.23 2.34 13.21 13.81 0.22 6.21 8.65 3.08 0.07 0.21 2.42 100.45 37.8 364 113 66 55 55 136

Lava flows of the western sub-profile98-Al-01 Bas.pl.lava 48.99 0.66 17.55 8.07 0.17 7.13 12.44 3.04 0.48 0.02 1.69 100.25 293 335 49 132 146 7096-Al-01 Bas.pl.lava 49.01 0.72 17.18 8.21 0.13 7.18 9.44 2.11 1.10 0.02 4.40 99.51 303 306 47 154 123 8195-Al-01 Bas.pl.lava 47.81 0.65 18.43 8.79 0.16 4.89 14.39 1.75 0.58 0.03 3.69 101.17 287 390 38 70 86 7794-Al-01 Bas.pl.lava 46.38 0.61 18.15 7.56 0.14 6.79 15.47 1.16 0.12 0.03 4.74 101.15 311 287 52 123 141 7593-Al-01 Bas.pl.lava 48.47 1.62 13.93 12.28 0.17 6.26 10.85 2.09 0.14 0.12 4.43 100.35 427 157 66 70 88 10488-Al-01 Bas.pl.lava 49.45 1.09 14.51 10.06 0.14 5.55 14.82 1.76 0.25 0.07 3.44 101.16 324 321 49 93 85 10884-Al-01 Bas.pl.lava 45.23 0.47 10.78 9.71 0.21 17.45 7.24 0.27 0.01 0.01 7.72 99.10 139 1295 85 1354 57 6383-Al-01 Bas.pl.lava 50.83 1.60 13.43 11.14 0.16 5.04 12.51 2.26 0.06 0.16 3.91 101.11 279 133 52 58 67 9076-Al-01 Bas.pl.lava 50.05 2.02 13.3 13.61 0.19 6.76 7.91 3.25 0.07 0.18 2.67 100.01 350 172 77 84 59 12798-Al-15 Bas.pl.lava 50.77 2.39 13.52 11.42 0.23 6.44 8.96 4.40 0.20 0.20 1.85 100.38 47.6 411 122 51 47 106

Lava flows of the eastern main profile31-Al-00 And.ms.lava 55.70 0.32 14.62 7.95 0.15 4.36 5.54 4.36 0.06 0.03 6.61 99.7 217 57 41 25 143 6530-Al-00 And.ms.lava 60.03 0.57 14.37 6.03 0.09 2.72 5.14 5.38 0.04 0.04 5.36 99.77 137 54 31 21 72 6663-Al-01 B.and.ms.lava 56.46 0.34 14.23 8.64 0.14 5.07 4.25 3.81 0.07 0.03 5.99 99.03 33.40 265 180 50 31 103 7064-Al-01 Bas.pl.lava 50.25 0.57 14.70 9.43 0.14 7.50 4.97 2.80 0.09 0.04 8.11 98.61 42.10 368 166 60 48 51 7829-Al-00 And.ms.lava 57.71 0.46 15.43 8.60 0.12 4.99 4.05 4.39 0.52 0.04 2.78 99.09 247 60 41 42 25 5365-Al-01 B.and.ms.lava 53.36 0.36 15.10 8.97 0.14 7.16 5.00 2.17 0.26 0.03 5.42 97.97 343 146 49 54 62 6128-Al-00 B.and.ms.lava 52.95 0.84 15.22 11.04 0.15 5.99 5.67 3.76 0.18 0.06 3.25 99.11 41.10 318 37 56 27 102 7726-Al-00 Dac./And.pl.lava 66.44 0.49 11.38 7.17 0.13 2.47 3.46 5.17 0.04 0.04 1.72 98.51 92 33 38 29 55 7925-Al-00 And./B.and.ms.lava 60.1 0.57 14.22 9.64 0.17 4.18 4.37 3.83 0.13 0.04 2.95 100.20 305 30 49 18 137 8266-Al-01 And.ms.lava 57.82 0.47 15.38 8.55 0.14 5.16 3.87 4.31 0.38 0.04 2.52 98.65 245 85 41 44 30 5568-Al-01 B.and.ms.lava 52.60 0.54 15.09 9.35 0.16 7.41 5.03 3.75 0.28 0.06 4.42 98.67 404 139 53 44 130 7769-Al-01 B.and./Bas.pl.lava 54.38 0.52 14.85 9.54 0.14 7.45 2 3.61 0.17 0.04 5.56 98.27 324 99 55 49 78 8423-Al-00 B.and.ms.lava 52.91 0.61 15.26 10.21 0.18 6.89 5.93 3.00 0.63 0.03 3.63 99.28 38.9 279 72 50 38 98 7722-Al-00 B.and./And.pl.lava 58.67 0.46 14.19 8.73 0.16 5.68 5.02 4.10 0.07 0.02 2.12 99.22 194 69 47 38 67 7870-Al-01 And./B.and.pl.lava 60.42 0.36 11.09 6.73 0.17 7.64 6.42 3.73 0.03 0.02 2.65 99.26 39.6 108 404 35 64 225 52


Rb Sr Y Zr Nb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Pb Th U

nd 75 31 582 11 17 44 1.01 0.01 3 1.62 3.29 0.56 3.07 1.32 0.49 1.98 0.40 2.82 0.63 1.79 0.27 1.73 0.28 0.99 0.06 1.08 0.24 0.132 74 64 168 1.71 0.01 3 4.00 12.83 2.25 13.36 5.51 1.76 7.78 1.49 10.14 2.13 6.11 0.89 5.57 0.88 4.01 0.13 0.34 0.15 0.072 92 43 91 0.74 0.03 5 1.95 6.65 1.23 7.68 3.52 1.32 5.16 1.04 7.09 1.55 4.32 0.62 3.89 0.61 2.38 0.06 0.45 0.11 0.043 99 70 1743 106 69 1732 117 70 1662 102 73 1882 98 72 1791 97 68 182 1.9 0.06 6 4.56 14.79 2.63 15.36 6.37 2.25 8.83 1.70 11.52 2.46 6.87 1.00 6.26 0.97 4.62 0.15 0.48 0.17 0.07

85 71 1883 92 49 97 0.75 0.05 17 2.04 6.96 1.30 8.22 3.74 1.37 5.57 1.11 7.54 1.65 4.63 0.68 4.28 0.67 2.55 0.06 0.2 0.09 0.061 57 47 100nd 126 91 284 5.49 0.02 11 9.47 27.69 4.45 23.93 8.69 2.86 11.51 2.16 14.34 3.07 8.64 1.24 7.67 1.20 6.81 0.44 0.92 0.38 0.171 72 46 1011 77 55 148 1.18 0.02 3 2.97 10.36 1.89 11.28 4.79 1.77 6.78 1.31 8.93 1.92 5.29 0.78 4.85 0.76 3.34 0.09 0.36 0.14 0.04

86 61 162nd 47 51 1381 104 79 273 5.47 0.01 3 8.99 26.59 4.27 23.33 8.49 2.71 10.93 2.07 13.23 2.81 7.66 1.11 6.95 1.08 6.66 0.42 0.76 0.37 0.38nd 115 51 1292 71 50 1351 82 52 1351 137 53 156

149 64 199141 54 154

nd 104 63 172 2.3 0.01 8 4.74 14.66 2.51 14.39 5.8 1.97 7.84 1.52 10.18 2.22 6.17 0.89 5.48 0.86 4.28 0.19 2.78 0.29 0.13

10 240 24 3121 135 24 3213 54 20 422 59 20 322 64 50 1117 97 37 812 14 17 29

20 46 1292 35 58 1422.3 85 56 140 1.95 0.01 10 4.39 13.85 2.41 13.95 5.62 1.96 7.86 1.49 10.04 2.16 6.02 0.87 5.43 0.84 4.23 0.17 0.64 0.23 0.12

nd 78 16 44nd 59 20 461 71 13 47 0.6 0.02 12 1.07 2.49 0.35 1.88 0.80 0.28 1.22 0.24 1.70 0.38 1.11 0.17 1.16 0.19 0.84 0.04 0.13 0.18 0.073 33 24 56 0.54 0.03 6 1.03 3.12 0.55 3.37 1.58 0.62 2.49 0.51 3.63 0.81 2.29 0.34 2.12 0.33 1.07 0.04 0.21 0.07 0.115 123 15 434 64 16 39nd 79 26 61 0.69 0.03 12 1.72 4.12 0.71 4.36 2.01 0.75 3.10 0.61 4.29 0.94 2.69 0.40 2.57 0.41 1.46 0.05 0.35 0.16 0.07nd 55 23 45nd 85 19 444 104 17 446 75 21 461 34 21 438 99 18 45 0.57 0.24 50 1.17 3.09 0.52 3.19 1.46 0.61 2.28 0.48 3.22 0.74 2.06 0.31 1.94 0.32 1.04 0.04 0.49 0.13 0.06nd 86 16 36

20 14 37 0.27 0.04 2 0.64 1.84 0.32 1.93 0.89 0.35 1.35 0.26 1.84 0.41 1.15 0.17 1.08 0.17 0.56 0.02 0.25 0.04 0.03

(continued on next page)


Table 1 (continued )

Samplenumber


Lava flows of the eastern main profile72-Al-01 Dac./And.pl.lava 64.64 0.52 12.86 6.85 0.08 4.05 1.61 4.46 0.12 0.05 3.66 98.91 129 44 35 31 99 7017-Al-00 B.and.ms.lava 53.20 0.68 15.51 11.00 0.18 5.99 6.34 3.81 0.23 0.05 2.55 99.54 276 42 55 31 94 8016-Al-00 B.and./Bas.pl.lava 56.66 0.41 13.55 8.05 0.15 5.96 8.40 3.42 0.01 0.02 3.57 100.20 33.90 199 138 43 64 70 6113-Al-00 B.and./Bon.pl.lava 53.87 0.43 13.27 9.5 0.15 8.13 8.09 3.17 0.01 0.02 3.49 100.13 228 337 51 93 84 7573-Al-01 B.and./Bas.pl.lava 52.96 0.38 13.53 8.13 0.17 7.52 11.16 3.19 0.02 0.03 3.04 100.13 185 407 41 91 110 5274-Al-01 B.and./Bas.ms.lava 52.23 0.57 15.37 10.31 0.16 7.12 6.18 3.55 0.16 0.05 3.05 98.75 43.2 270 78 60 38 22 8312-Al-00 B.and.pl.lava 53.81 0.55 14.54 9.29 0.15 6.98 5.74 4.13 0.05 0.05 3.75 99.04 238 153 49 51 63 7611-Al-00 B.and.pl.lava 56.37 0.49 14.55 9.10 0.16 6.84 4.75 3.86 0.05 0.03 3.53 99.73 38.80 237 86 50 44 81 769-Al-00 B.and./Bas.pl.lava 53.99 0.48 14.80 9.26 0.15 6.81 6.04 3.84 0.01 0.02 3.7 99.10 252 129 50 51 69 79105-Al-01 And.ms.lava 62.63 0.47 12.05 6.66 0.11 1.50 5.30 0.94 0.38 0.06 11.12 101.22 3 33 4 35 91104-Al-01 Rhy.ms.lava 70.55 0.39 11.82 6.25 0.05 1.12 1.68 3.70 0.57 0.08 2.04 98.25 9 7 22 4 21 89102-Al-01 B.and.ms.lava 55.88 0.87 14.65 11.99 0.16 6.07 3.27 2.19 0.14 0.07 4.00 99.30 460 36 56 13 739 48101-Al-01 B.and./Bas.ms.lava 53.64 0.74 14.45 14.95 0.16 6.34 1.89 2.37 0.10 0.05 4.20 98.90 528 204 90 36 92100-Al-01 Bon./Bas.pl.lava 53.21 0.29 13.16 10.88 0.18 9.83 3.58 2.27 0.01 0.01 5.68 99.12 291 351 61 75 35 66

Lava flows from the eastern part52-Al-00 Bon./Bas.pl.lava 56.33 0.53 14.17 9.36 0.25 8.55 3.43 2.75 n.d 0.02 3.78 99.17 287 218 52 55 5 13558-Al-00 Bas.ms.lava 49.55 0.61 16.03 12.54 0.11 6.62 4.89 3.11 0.02 n.d 5.70 99.18 440 52 71 29 73 120YDKA99–9 Bas.ms.lava 48.14 1.10 14.45 9.31 0.18 7.47 12.81 2.64 0.50 0.06 96.66 45.5 285 377 98 75 77YDKA99–1 B.and.ms.lava 54.81 0.61 15.16 9.44 0.16 6.21 5.84 5.10 0.04 0.05 97.42 40.6 257 71 38 109 77YDKA99–2 And.ms.lava 57.71 0.45 13.71 9.13 0.10 3.41 5.62 5.43 0.13 0.03 95.72 35 336 18 5 100 65YDKA99–3 And. Ms.lava 56.4 0.70 14.64 10.15 0.12 7.67 2.16 4.79 0.10 0.06 96.78 38.7 300 16 18 139 77YDKA99–8 Dac.ms.lava 67.48 0.44 11.61 6.06 0.12 0.83 5.12 1.71 0.57 0.08 93.73 20.7 13 0 3 29 8960-Al-00 Dac.br.lava 65.26 0.35 11.16 5.92 0.11 0.69 5.03 0.81 0.3 0.06 11.81 101.5 2 2 23 3 65 8961-Al-00 Rhy.ms.lava 83.92 0.26 8.07 3.06 0.04 0.16 2.04 2.28 0.41 0.21 1.42 101.87 8 17 9 3 7 3763-Al-00 And.ms.lava 57.36 0.80 14.64 12.11 0.15 3.12 6.04 0.87 2.53 0.04 3.51 101.17 772 27 40 8 54 12265-Al-00 Rhy./Dac.ms.lava 70.94 0.36 12.27 5.64 0.27 2.38 2.24 2.53 0.30 0.07 3.48 100.48 1 13 22 4 41 95

Dikes and sills from the western part35-Al-00 Bas.dike 49.92 2.24 13.16 14.37 0.21 5.45 9.61 3.03 0.04 0.17 2.26 100.46 43.2 339 66 61 42 53 9770-Al-00 Bas.dike 48.75 0.84 16.20 9.93 0.15 8.94 10.05 1.74 0.04 0.02 3.33 99.99 278 494 52 150 99 6955-Al-01 Bas.dike 47.54 0.62 15.86 8.82 0.16 9.54 12.88 1.05 0.05 0.02 3.21 99.74 37.4 251 470 46 215 101 6462-Al-01 Bas.dike 49.03 2.38 13.35 15.47 0.30 5.89 10.47 1.59 0.04 0.25 1.61 100.37 43.9 438 90 76 52 55 14398-Al-12 Bas.sill 48.54 0.83 16.70 9.65 0.21 10.42 8.46 2.99 1.20 0.04 4.52 103.56 53.4 229 274 157 113 6298-Al-11 Bas.sill 49.78 0.87 20.25 7.45 0.18 7.84 7.16 3.50 2.16 0.05 4.67 103.91 38.7 183 260 117 99 5198-Al-03 Bas.m.gb. 44.83 0.19 9.94 5.41 0.14 12.36 23.51 2.91 0.02 0.06 6.29 105.66 35.3 167 342 335 49 37

Dikes and sills from the eastern partYDKA99–4 Bon.sill 52.38 0.32 12.58 7.78 0.22 12.31 8.95 2.33 0.61 0.02 97.52 48.4 222 671 130 15 11187-Al-00 Bas.dike 55.48 0.25 15.75 10.16 0.17 7.17 9.86 0.40 0.08 n.d 1.52 100.84 275 303 49 97 37 86YDKA99–5 B.and.dike 57.33 0.84 14.57 10.99 0.20 5.26 5.56 1.18 1.47 0.06 97.46 44.1 310 25 7 127 56YDKA99–6 B.and.dike 55.31 0.69 15.45 10.02 0.17 6.89 5.87 2.75 0.60 0.06 97.8 43.3 345 47 31 126 67YDKA99–7 B.and.dike 55.28 0.71 13.95 8.66 0.09 7.16 8.24 2.32 0.40 0.07 96.87 35.1 245 41 29 36 3778-Al-00 Bon./Bas.dike 54.89 0.36 13.64 8.80 0.14 7.95 5.16 2.21 0.28 n.d 5.84 99.27 50.8 294 467 49 117 10 5590-Al-00 Bon.dike 53.21 0.12 10.35 8.87 0.15 15.56 9.28 0.05 0.01 0.01 1.81 99.42 51.8 191 1319 56 410 5 3548-Al-00 And.dike 61.82 1.07 13.75 12.01 0.05 1.28 4.03 4.79 0.03 0.28 0.95 100.06 23.4 7 6 50 2 nd 1950-Al-00 And./Dac.dike 63.82 0.97 13.87 10.13 0.05 1.23 3.89 4.88 0.02 0.23 0.84 99.93 19 20 7 39 8 nd 1455-Al-00 And.dike 61.82 1.30 14.07 11.05 0.11 2.61 3.69 3.17 0.36 0.08 2.07 100.33 31.5 116 10 49 6 1118 7972-Al-00 And.dike 59.60 1.17 15.16 12.34 0.14 3.06 8.14 1.24 0.13 0.05 0.87 101.90 40.8 192 29 47 9 9 2375-Al-00 And.dike 58.27 0.66 14.51 10.61 0.14 4.32 4.94 3.26 0.64 0.04 2.49 99.88 44.3 348 24 50 18 7 3279-Al-00 B.and.dike 56.71 0.61 15.14 11.42 0.14 4.60 6.04 2.16 0.06 0.02 3.86 100.76 375 40 56 23 10 6976-Al-00 Rhy.dike 73.00 0.43 11.86 6.48 0.04 0.83 0.93 4.82 0.03 0.07 1.23 99.72 11 5 27 2 nd 1580-Al-00 Rhy.dike 74.61 0.44 11.68 6.35 0.07 0.74 1.41 4.69 0.09 0.07 0.87 101.02 20.8 10 7 27 2 nd 1967-Al-01 B.and./Bas.dike 53.39 0.62 15.54 10.14 0.12 7.51 5.95 1.62 0.63 0.05 3.82 99.40 264 122 50 49 72 7271-Al-01 Bas.dike 51.96 0.57 15.22 10.06 0.17 8.04 5.37 2.61 0.51 0.05 4.11 98.66 294 86 53 40 104 72




51 22 51nd 106 19 45nd 18 16 35 0.44 0 4 0.93 2.20 0.37 2.10 0.96 0.37 1.46 0.30 2.12 0.47 1.35 0.20 1.24 0.20 0.66 0.03 0.38 0.15 0.09nd 11 12 34

16 15 402 73 21 47 0.47 0.03 20 1.01 2.83 0.50 3.03 1.44 0.58 2.25 0.45 3.13 0.69 1.93 0.30 1.87 0.30 0.99 0.03 0.32 0.06 0.05nd 64 17 46nd 44 13 43 0.65 0.02 10 1.18 2.87 0.45 2.53 1.12 0.43 1.66 0.34 2.42 0.53 1.54 0.23 1.48 0.23 0.84 0.05 0.54 0.18 0.05nd 15 15 4616 154 40 903 56 40 742 65 29 532 56 22 431 21 9 29

2 25 11 39nd 105 11 306.9 155 30 47 1.15 0.2 36 1.63 4.26 0.76 4.65 2.39 0.93 3.75 0.77 5.35 1.18 3.38 0.49 2.98 0.47 1.48 0.08 0.26 0.22 0.080.5 18 18 36 1.2 0.01 5 1.82 4.54 0.69 3.73 1.54 0.51 2.11 0.46 3.15 0.70 2.04 0.30 1.93 0.30 1.11 0.09 0.6 0.3 0.111.6 25 10 24 0.89 0.04 7 1.16 2.58 0.35 1.84 0.73 0.26 1.03 0.22 1.59 0.36 1.08 0.17 1.13 0.19 0.76 0.08 0.4 0.26 0.11.1 33 17 34 0.63 0.05 7 1.13 2.89 0.48 2.85 1.31 0.45 1.88 0.42 2.89 0.66 1.82 0.27 1.71 0.26 1 0.05 0.43 0.17 0.0614.5 70 33 60 1.09 2.06 50 3.54 8.59 1.20 6.46 2.70 0.87 3.91 0.77 5.36 1.21 3.46 0.52 3.40 0.56 1.87 0.09 5 0.98 0.458 391 53 919 57 67 5154 78 14 368 78 41 94

nd 73 59 150 1.29 0 3 3.39 11.50 2.10 12.45 5.34 2.00 7.49 1.47 9.79 2.13 5.90 0.86 5.34 0.82 3.78 0.11 0.21 0.15 0.05nd 104 23 351 90 21 36 0.06 0.01 5 0.41 1.24 0.30 2.25 1.33 0.61 2.35 0.49 3.51 0.76 2.16 0.32 2.03 0.31 0.77 0 0.01 0 0

85 67 183 1.94 0.01 5 4.60 14.61 2.54 15.20 6.18 2.12 8.77 1.68 11.27 2.43 6.73 0.99 6.22 0.96 4.55 0.15 0.51 0.18 0.0725.9 723 24 50 1.47 2.26 378 2.14 5.43 0.91 5.08 1.97 0.80 3.06 0.60 4.20 0.93 2.64 0.39 2.44 0.40 1.32 0.11 0.33 0.2 0.0539.7 29 20 55 1.35 1.1 480 2.23 5.94 0.96 5.11 1.84 0.91 2.73 0.52 3.47 0.77 2.12 0.32 1.99 0.31 1.32 0.1 0.35 0.15 0.040.6 251 9 6 0.19 0.03 2 0.65 0.46 0.12 0.33 0.26 0.21 0.65 0.16 1.23 0.30 0.85 0.13 0.84 0.13 0.1 0.01 0 0.05 0.01

2.7 58 11 15 0.29 0.01 19 0.74 1.90 0.28 1.55 0.71 0.27 1.10 0.21 1.54 0.36 1.01 0.15 1.01 0.16 0.42 0.03 1.19 0.17 0.072 39 8 196.2 96 20 33 0.59 0.01 13 2.15 5.19 0.75 3.95 1.66 0.66 2.38 0.47 3.35 0.75 2.28 0.33 2.13 0.35 1.05 0.05 1.36 0.55 0.242.8 83 17 29 0.43 0.02 22 1.54 3.78 0.58 3.18 1.36 0.56 1.96 0.40 2.85 0.64 1.88 0.29 1.83 0.30 0.88 0.04 1 0.36 0.175.8 85 18 37 0.98 0.04 13 1.66 4.06 0.64 3.57 1.54 0.67 2.25 0.45 3.18 0.58 1.92 0.28 1.79 0.29 0.98 0.07 2.05 0.18 0.375 42 11 25 0.33 0.06 6 0.73 1.55 0.22 1.30 0.62 0.29 1.13 0.25 1.82 0.44 1.32 0.2 1.31 0.22 0.41 0.02 1.49 0.21 0.121 21 4 21 0.58 0.01 3 1.19 2.18 0.24 0.93 0.27 0.10 0.34 0.07 0.56 0.14 0.44 0.08 0.55 0.10 0.25 0.05 0.26 0.42 0.25nd 66 103 147 2.99 0 4 6.12 16.74 2.79 16.31 6.93 2.26 10.04 1.94 13.09 2.88 8.10 1.17 7.31 1.16 4.73 0.2 0.11 0.53 0.152 62 116 189 3.53 0 4 7.72 21.19 3.43 19.58 7.84 2.08 11.12 2.17 14.56 3.14 8.95 1.29 8.14 1.27 6.21 0.25 0.15 0.77 0.242 98 38 79 1.35 0.1 29 3.69 8.87 1.33 7.18 2.90 1.13 4.13 0.82 5.78 1.28 3.67 0.55 3.47 0.55 2.16 0.09 0.56 0.41 0.21 91 35 54 0.47 0.02 9 3.33 8.03 1.19 6.51 2.57 0.97 3.77 0.76 5.24 1.18 3.43 0.5 3.19 0.52 1.6 0.04 0.18 0.35 0.193 90 23 42 0.48 0.06 20 2.05 4.81 0.68 3.63 1.48 0.53 2.20 0.44 3.20 0.73 2.12 0.32 2.08 0.35 0.99 0.03 0.35 0.64 0.26nd 76 18 381 39 50 561 54 57 53 0.96 0.01 9 4.11 9.62 1.34 7.17 2.87 0.80 4.03 0.82 5.73 1.31 3.79 0.58 3.73 0.61 1.93 0.06 0.24 1.2 0.523 91 19 388 80 20 44

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Samplenumber


Sheeted dike complex from the eastern part108-Al-01 B.and. 56.24 0.82 15.34 12.03 0.17 5.03 8.03 1.65 0.15 0.05 1.69 101.18 438 76 57 37 249 58109-Al-01 B.and. 53.89 0.76 15.41 12.75 0.17 5.82 7.65 1.45 0.19 0.05 2.5 100.65 482 61 61 29 47 54110-Al-01 And. 57.18 1.21 15.31 12.52 0.14 3.97 8.63 1.97 0.13 0.07 0.43 101.56 41.9 432 36 50 21 21 33111-Al-01 Bon. 54.21 0.29 13.59 8.91 0.16 9.38 8.72 1.33 0.11 0.01 3.57 100.29 268 353 50 108 85 73112-Al-01 Bon. 57.36 0.28 12.34 8.67 0.16 8.48 7.02 3.75 0.17 0.02 1.33 99.57 51.5 140 306 44 72 6 58116-Al-01 B.and. 55.92 0.48 16.25 10.34 0.17 5.09 4.39 4.42 0.17 0.04 2.13 99.44 44.2 269 28 52 26 112 64117-Al-01 And. 58.92 0.82 14.41 11.39 0.17 4.13 4.06 2.47 0.73 0.09 2.72 99.92 322 22 54 14 39 99118-Al-01 And. 57.2 0.75 14.43 11.05 0.17 4.04 10.3 0 0 0.08 3.63 101.61 427 28 57 13 26 59119-Al-01 B.and. 56.76 0.8 14.38 11.71 0.19 5.95 3.65 0.89 1.15 0.08 4.86 100.41 43.2 455 24 61 13 18 89120-Al-01 B.and. 54.85 0.94 14.53 13.46 0.14 6.82 3.64 1.7 0.14 0.07 3.68 99.98 513 36 72 25 88 44122-Al-01 Dac. 65.57 0.76 13.33 9.45 0.12 2.86 2.28 3.07 0.22 0.11 2.66 100.44 30.8 25 8 41 5 52 109125-Al-01 And. 57.68 0.98 14.05 12.9 0.16 4.87 3.62 2.16 0.18 0.06 3.32 99.98 509 24 69 13 177 76126-Al-01 B.and. 56.61 0.92 14.54 12.39 0.13 5.56 4.56 0.91 0.48 0.08 3.86 100.06 568 22 65 14 30 54

Abbreviations: FeOt= total iron as FeO; L.O.I.= loss on ignition; Bas.=basalt; B.and.=basaltic andesite; Bon.=boninite; And.=andesite; Dac.=dacite; Rhy.= rhyolite; pl.=pillow lava; ms.=massive lava; m.gb.=microgabbro.


phases include plagioclase, quartz, hornblende, andclinopyroxene.

EMO sheeted dikes are rooted in gabbroic rocks. Acomplete transition from isolated dikes crosscuttinggabbroic rocks into the overlying sheeted dike complexcan be traced in the field. The sheeted dikes are generallysubvertical to moderately dipping and are orientedNNE–SSW, again indicating that spreading was directedWNW-ESE. They vary from ∼1 m up to ∼7-m-wide,with average dike width of ∼2 m. Dike margins arecommonly marked by extensive networks of epidote andquartz veins. Crosscutting relations suggest that the earlybasaltic dikes were intruded by basaltic andesite,andesite, dacite, and quartz diorite-dacite dike swarms,which are in turn cut by andesitic, quartz-microdioritic,and boninitic dikes (Dilek et al., 2007).

4. Petrography

About 100 thin sections have been studied for thepetrographic characterization of various volcanic anddike rocks. For the classification of these rocks, we usedthe following geochemical criteria, mainly after LeBas(2000): Basalt (b52 wt.% SiO2); basaltic andesite(N52 wt.% and b57 wt.% SiO2); boninite (N52 wt.%SiO2, N8 wt.% MgO, b0.5 wt.% TiO2); andesite(N57 wt.% and b63 wt.% SiO2); dacite (N63 wt.%and b70 wt.% SiO2); rhyolite (N70 wt.% SiO2).

Basalts comprise nearly all of the extrusive rocks of theWMPand theWSP aswell as some dikes in theWMO, butare rare in the lava succession of the EMP and the sheeteddike complex of the EMO.WMPpillowbasalts andWMObasaltic dikes are predominantly aphyric or slightly phyric

(∼90% contain b2% phenocrysts), whereas the WSPpillow basalts vary frommoderately to highly plagioclase-phyric (2–10% and N10% phenocrysts, respectively). Theglassy rim of the basaltic pillows shows a variolitic texture,which grades inwards into plumose to branching quenchtextures, and the rock eventually becomes fully crystalline(plagioclase, clinopyroxene and Fe-oxides) with anequigranular texture in the centers of pillows. Equigranulartexture is typical of the massive flows. In the porphyriticsamples, plagioclase and clinopyroxene are the dominantphenocrysts (50–70% and 30–50%, respectively), andolivine pseudomorphs rarely occur. The sequence ofcrystallization in these rocks is: olivine–plagioclase–clinopyroxene. The phenocrysts may occur individually,but more commonly plagioclase is glomeroporphyritic.The basaltic lavas and dikes exhibit an incipient tocomplete alteration. Thus, plagioclase in the lavas containsvariable amounts of smectite, whereas clinopyroxene andFe-oxides are variably altered to clay minerals/chlorite andvery fine-grained leucoxene, respectively.

Boninites have been found only in the EMO and occurboth in the lava pile and the dike complex. Of the 40 lavasamples and the 30 dike samples analyzed, boninitescomprise two and four samples, respectively. The twolava samples are aphyric and vary from slightly to highlyaltered. They are medium- (∼5%) to highly-amygdaloi-dal (∼25%); the vesicle-filling minerals consist of quartz,calcite, epidote, and chlorite. Two of the four dikesamples are aphyric, whereas the other two vary frommoderately-phyric (∼7% phenocrysts) to highly-phyric(∼20% phenocrysts). Phenocrysts are clinopyroxene,orthopyroxene, and plagioclase, appearing in the propor-tions of 60%, 30% and 10%, respectively.



1 80 22 442 93 21 421 94 28 60 0.69 0.01 24 1.80 4.95 0.82 4.75 2.08 0.86 3.16 0.63 4.42 0.96 2.80 0.42 2.70 0.43 1.41 0.05 0.12 0.21 0.153 75 11 293 78 10 27 0.32 0.05 16 0.55 1.30 0.19 1.06 0.52 0.17 0.85 0.19 1.40 0.32 0.96 0.16 1.00 0.17 0.43 0.02 0.19 0.09 0.051 47 19 36 0.47 0.05 9 1.11 2.66 0.39 2.16 1.00 0.39 1.70 0.35 2.51 0.60 1.73 0.27 1.82 0.29 0.73 0.03 0.44 0.25 0.186 71 23 491 258 28 447 73 22 47 0.51 0.02 11 2.12 5.12 0.72 3.84 1.62 0.62 2.34 0.47 3.44 0.76 2.23 0.33 2.19 0.35 1.03 0.03 0.92 0.48 0.241 72 24 501 60 36 73 0.95 0.01 11 2.87 7.50 1.12 6.3 2.62 0.89 3.82 0.75 5.34 1.20 3.46 0.52 3.43 0.54 1.96 0.07 0.51 0.63 0.322 66 25 503 79 25 54


Basaltic andesites comprise ∼60% of the lavas and∼35% of the dikes of the EMP. About 80% of thebasaltic andesites are aphyric, and the rest are slightly(1–2%) phyric. Texturally, these rocks are similar to thebasalts (described above) and vary from slightly tohighly altered. Their groundmass consists of plagioclase(variably altered to smectite and/or epidote in dikes),amphibole (variably altered to chlorite), minor clinopyr-oxene and Fe-oxides (variably altered to leucoxene),and less commonly quartz. The phenocrysts areclinopyroxene and plagioclase.

Andesites are common in both EMO lavas and dikes.In the EMP lava sequence andesites occur from about600 m above the base all the way to the top, andconstitute ∼30% of the sequence. This is also theproportion in which they appear as dikes within theEMO. Andesitic rocks in the sheeted dike complex areaphyric, whereas those of the lava sequence vary frompredominantly aphyric/slightly phyric to highly porphy-ritic. The groundmass is composed of plagioclase(variably altered to smectite), quartz, colorless or palegreen amphibole, fine-grained Fe-oxide (variably al-tered to leucoxene), zeolite and chlorite. The pheno-crysts consist of plagioclase and clinopyroxene.

Dacites and rhyolites appear only in the EMO andcomprise ∼10% of the lava pile and the dike complex.Dacitic to rhyolitic lavas and dikes occur as glassy toholocrystalline rocks (Fig. 6). In some glassy samplesspherulitic texture is well developed. Both dacites andrhyolites vary from aphyric to moderately phyric (∼5%),with phenocrysts composed of plagioclase, quartz, greenamphibole, and clinopyroxene. The groundmass consistspredominantly of quartz and feldspar, and minorbrownish-green amphibole (as slender needles) and Fe-oxide.

5. Analytical techniques

Major- and trace-element (V, Cr, Co, Ni, Cu, Zn, Rb,Sr, Y, Zr) analyses were performed on an X-rayfluorescence spectrometer (XRF) at the University ofBergen (Norway). The glass-bead technique of Padfieldand Gray (1971) was used for the major elements andpressed-powder pellets for the trace elements, utilizinginternational basalt standards and the recommended orcertified concentrations of Govindaraju (1994) forcalibration. Inductively-coupled plasma source massspectrometry (ICP-MS) was used for analysis of Sc, Nb,Cs, Ba, the REEs, Hf, Ta, U, Pb, Th and U. Theseanalyses were carried out at the Department of Geology,Washington State University, USA. The analyticalprocedure for the ICP-MS work has been described indetail by Knaack et al. (1994).

The precision of our analyses is better than 2% formost oxides and trace-elements, better than 10% for Ni,Cr, Sc, and better than 18% for Vand Cu (Johnson et al.,1999). The statistics for a single sample (BCR-P) runover a four-month period indicate that precision for thelanthanides, Rb, Sr, Nb, and Hf is better than 2.5%. Theprecision for Ta and Pb is better than 3.5% and betterthan 10% for Th and U (Knaack et al., 1994).

Electron-microprobe analyses were carried out usingan ARL SEMQ at the University of Bergen (Norway),employing standard wavelength dispersive techniques(Reed, 1975), an accelerating voltage of 15 KV, and abeam current of 10 nA. Well-characterized minerals,synthetic oxides and pure metals were employed asstandards. Net peak intensities, corrected for dead-timeeffects and beam-current drift as monitored from theobjective aperture, were reduced by MAGIC IV (Colby,1968).


Sm and Nd isotopes were analyzed on a Finnegan 262,mass-spectrometer at the University of Bergen (Norway).All chemical processing was carried out in a clean-roomenvironment with HEPA filtered air supply and positivepressure. The reagents were either purified in two-bottleTeflon stills or passed through ion-exchange columns.Samples were dissolved in a mixture of HF and HNO3.REE were separated by specific extraction chromatogra-phy using the method described by Pin et al. (1994). Smand Ndwere subsequently separated using a low-pressureion-exchange chromatographic set-up with HDEHP-coated Teflon powder as the ion-exchange resin (Richardet al., 1976). Sm and Nd were loaded onto a doublefilament and analysed in static mode. Nd isotopic ratioswere corrected for mass fractionation using 146Nd/144Ndof 0.7219. Sm and Nd concentrations were determinedusing a mixed 150Nd/149Sm spike. Repeated measure-ments of the JM Nd-standard yielded an average143Nd/144Nd ratio of 0.511113±15 (2σ) (n=62). Thetypical Nd blank level in the laboratory is 5 pg.

6. Geochemistry

In order to characterize the magmatic evolution oftheMirdita Ophiolite, we analyzed 124 samples for majorand particular trace elements by XRF. Of these samples,35 lavas (26 from the WMP) and four dikes are from theWMO, and 41 lavas (24 fromEMP) and 29 dikes are fromthe EMO. In addition, we analyzed 15 plutonic rocks byXRF (6 from the WMO and 9 from the EMO).Furthermore, 48 samples were analyzed for REE andother low-concentration trace elements by ICP-MS, and71 samples for Sm–Nd isotopes. We present the major-and trace-element analyses (XRF and ICP-MS) and theSm–Nd isotopic data of selected samples of lava, dike andplutonic rock samples in Tables 1 and 2, respectively.

6.1. Alteration effects and element mobility

The mobility of a given element is a function of thepermeability of the rock, the extent of water-rockinteractions, and the elemental solubility under thereaction conditions (Kelley and Delaney, 1987; Bickleand Teagle, 1992). Studies on the behaviour of elementsduring alteration and low-grade metamorphism ofbasaltic to felsic rocks have demonstrated that someelements remain relatively stable, whereas others arelost or enriched relative to the concentration of theoriginal rock (e.g. Cann, 1970; Coish, 1977; Humphrisand Thompson, 1978). The studies of Nicollet andAndribololona (1980) and Weaver and Tarney (1981) onthe element mobility of basaltic rocks show that even at

amphibolite facies metamorphism the elements Ni, Cr,Co, Cu, Zn, Fe, Mg, Mn, Ti, V, Nb, P and the middle toheavy REEs are affected insignificantly. Furthermore,Baker (1985) concluded from the studies of felsic rocksthat Ti, Al, P and Yare immobile elements, whereas Na,Si, Mg, Ni and Zn show enrichment and Fe, Mn, K, Sc,Rb, Cs, Ba, Pb and REEs are leached. Loss of REE'sdoes not change, however, the shape of the REE patternssignificantly (Baker, 1985).

The rocks of the Mirdita Ophiolite underwent up tolower greenschist facies metamorphism. From thepetrographic studies of the geochemically analysedsamples it is evident that the rocks have undergonevariable degrees of alteration. This is also reflected in theloss-of-ignition (L.O.I; anticipated to consist mainly ofH2O) of the samples (Table 1) that may reach values ashigh as 14 wt.%, and can be regarded as highly altered.However, the majority (∼75%) of the samples have L.O.Icontents b4 wt.%, thus giving an indication of only littleto moderate alteration. We plotted all the elementsversus L.O.I (of Table 1) but did not find any correlationthat might indicate enrichment or depletion with variableL.O.I. Thus, on this basis, combinedwith the results of thestudies by other researchers as mentioned above, we haveconcluded that element mobility during alteration andmetamorphism did not change original element concen-trations in our samples to any significant extent.

6.2. Major and trace element characteristics

Fig. 7 shows a SiO2–FeOt/MgO plot of the lavas and

dikes of the Mirdita Ophiolite. All the WMO dikes andlavas plot in the tholeiitic field, but the EMO dikes andlavas straddle the tholeiitic–calc–alkaline boundary.Most of the dikes and lavas in the WMO have a narrowrange of SiO2 (47–50 wt%), whereas those in the EMOhave a much wider range of SiO2 (52–70 wt%) (Fig. 7).Nearly 60% of the WMO basalts are Fe–Ti basalts usingthe criteria of FeOt/MgON1.75 and TiO2b2 wt.%(Melson et al., 1976; Sinton et al., 1983).

The geochemical evolution of the lava and dike rocksof the WMO and EMO display pronounced differences,as demonstrated by the Bowen diagrams (Fig. 8). TheWMO rocks show positive correlations between MgOand Al2O3, CaO, Cr and Ni contents, and a negativecorrelation between MgO and FeOt, TiO2, P2O5, Y andZr contents. The EMO lavas and dikes show differentrelations from those of the WMO. In the MgO vs Al2O3

diagram, the EMO samples define a positive correlationup to ca. 6 wt.% MgO and a negative correlationthereafter, signifying fractionation of plagioclase. Withrespect to MgO vs FeOt, similar relations exist for the

Table 2Nd-isotope analyses of selected samples of lavas, dikes and plutonic rocks of the Mirdita Ophiolite

Sample number Rock type Sm Nd 143Nd/144Nd 2SE 145Nd/144Nd 147Sm/144Nd ɛNd(T) T=160Ma

Lava flows of the western main profile4-Al-00 Bas.pl.lava 2.23 4.91 0.513081 0.000006 0.348404 0.274 6.895-Al-00 B.and.pl.lava 1.24 3.05 0.513035 0.000008 0.348404 0.246 6.5662a-Al-01 Bas.pl.lava 5.22 14.13 0.513041 0.000006 0.348396 0.223 7.1544-Al-00 Bas.pl.lava 3.44 8.54 0.513059 0.000006 0.348399 0.244 7.0761-Al-01 Bas.pl.lava 5.97 16.15 0.513025 0.000007 0.348397 0.223 6.8458-Al-01 Bas.pl.lava 6.05 16.39 0.513022 0.000007 0.348398 0.223 6.7842-Al-00 Bas.pl.lava 6 16.26 0.513024 0.000006 0.348394 0.223 6.8248-Al-01 Bas.pl.lava 5.97 16.13 0.513019 0.000008 0.348401 0.224 6.745-Al-01 Bas.pl.lava 5.97 16.24 0.513014 0.000009 0.348397 0.222 6.6441-Al-01 Bas.pl.lava 6.04 16.4 0.51302 0.000007 0.348396 0.223 6.7438-Al-01 Bas.pl.lava 3.53 8.66 0.513067 0.000007 0.348398 0.246 7.1935-Al-01 Bas.pl.lava 3.41 8.43 0.513055 0.000008 0.348403 0.244 732-Al-01 Bas.pl.lava 3.53 8.66 0.513067 0.000007 0.348397 0.247 7.1731-Al-01 Bas.ms.lava 4.6 12.16 0.513065 0.000007 0.348396 0.229 7.525-Al-01 Bas.pl.lava 8.22 25.18 0.51303 0.000006 0.348395 0.197 7.4736-Al-00 Bas.pl.lava 4.39 11.54 0.513059 0.000006 0.348399 0.23 7.3620-Al-01 Bas.ms.lava 4.39 11.72 0.513048 0.000006 0.3484 0.227 7.2117-Al-01 Bas.pl.lava 4.86 13.28 0.513042 0.000008 0.348399 0.221 7.212-Al-00 Bas.pl.lava 5.46 15.09 0.513044 0.000006 0.348397 0.219 7.29

Lava flows of the eastern main profile31-Al-00 And.ms.lava 0.93 2.96 0.512801 0.000007 0.348407 0.19 3.1463-Al-01 B.and.ms.lava 0.74 1.97 0.512959 0.000007 0.34841 0.226 5.4864-Al-01 Bas.pl.lava 1.66 3.92 0.51305 0.000007 0.348404 0.257 6.6529-Al-00 And.ms.lava 0.98 2.47 0.512956 0.000007 0.348408 0.239 5.1765-Al-01 B.and.ms.lava 0.71 1.75 0.512972 0.000007 0.348413 0.247 5.3228-Al-00 B.and.ms.lava 1.93 4.67 0.513044 0.000006 0.348403 0.25 6.6625-Al-00 And./B.and.ms.lava 1.1 2.76 0.512996 0.000008 0.348402 0.241 5.9166-Al-01 And.ms.lava 1.03 2.61 0.512965 0.000007 0.348404 0.238 5.3768-Al-01 B.and.ms.lava 1.22 2.83 0.513045 0.000007 0.348404 0.261 6.4569-Al-01 B.and./Bas.pl.lava 1.19 2.82 0.51304 0.00001 0.348403 0.254 6.4923-Al-00 B.and.ms.lava 1.43 3.41 0.51306 0.000012 0.348402 0.253 6.9170-Al-01 And./B.and.pl.lava 0.78 1.94 0.513035 0.000006 0.348401 0.243 6.6172-Al-01 Dac./And.pl.lava 1.12 2.96 0.513021 0.000007 0.348403 0.229 6.6517-Al-00 B.and.ms.lava 1.48 3.56 0.513045 0.000006 0.348401 0.251 6.6616-Al-00 B.and./Bas.pl.lava 0.91 2.21 0.513034 0.000008 0.34841 0.249 6.4813-Al-00 B.and./Bon.pl.lava 0.92 2.21 0.513026 0.000007 0.348407 0.251 6.2973-Al-01 B.and./Bas.pl.lava 0.94 2.28 0.513034 0.000007 0.348407 0.248 6.5174-Al-01 B.and./Bas.pl.lava 1.42 3.38 0.51305 0.000007 0.348403 0.254 6.7111-Al-00 B.and.pl.lava 1.03 2.57 0.513031 0.000011 0.348405 0.243 6.55

Lava flows from the eastern part52-Al-00 Bon./Bas.pl.lava 1.11 2.67 0.513046 0.000008 0.348409 0.251 6.6860-Al-00 Dac.breccia 2.91 8 0.512866 0.000006 0.348399 0.22 3.865-Al-00 Rhy./Dac.ms.lava 3.08 8.76 0.512853 0.000006 0.3484 0.213 3.69

Dikes from the western part35-Al-00 Bas. 5.1 13.6 0.513052 0.000006 0.348402 0.227 7.2870-Al-00 Bas. 1.7 3.17 0.513193 0.000006 0.348402 0.325 8.0362-Al-01 Bas. 5.92 16.1 0.513027 0.000006 0.348397 0.223 6.8855-Al-01 Bas. 1.26 2.36 0.513172 0.000007 0.348409 0.323 7.67

Dikes from the eastern part87-Al-00 Bas. 0.32 0.79 0.512644 0.00001 0.348415 0.246 −1.0778-Al-00 Bon./Bas. 0.25 1 0.512398 0.000009 0.34841 0.152 −3.9548-Al-00 And. 6.64 17.61 0.513016 0.000006 0.3484 0.228 6.5655-Al-00 And. 2.79 7.95 0.512985 0.000006 0.348398 0.212 6.28

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)


Sample number Rock type Sm Nd 143Nd/144Nd 2SE 145Nd/144Nd 147Sm/144Nd ɛNd(T) T=160Ma

Dikes from the eastern part72-Al-00 And. 2.52 7.13 0.512948 0.000006 0.348401 0.213 5.5480-Al-00 Rhy. 2.71 7.57 0.512849 0.000006 0.348397 0.216 3.5567-Al-01 B.and./Bas. 1.22 2.85 0.513057 0.000006 0.348401 0.259 6.7471-Al-01 Bas. 1.45 3.46 0.513043 0.000006 0.348405 0.254 6.57

Sheeted dikes from the eastern part108-Al-01 B.and. 1.51 3.97 0.512922 0.000006 0.3484 0.229 4.7109-Al-01 B.and. 1.32 3.44 0.512906 0.000007 0.348506 0.232 4.33110-Al-01 And. 2.06 5.27 0.513005 0.000007 0.3484 0.236 6.18111-Al-01 Bon. 0.57 1.4 0.512906 0.000009 0.348409 0.244 4.09112-Al-01 Bon. 0.48 1.13 0.51299 0.000009 0.348414 0.258 5.44116-Al-01 B.and. 1.02 2.5 0.512916 0.000007 0.348405 0.247 4.22117-Al-01 And. 1.61 4.42 0.512883 0.000007 0.348402 0.221 4.11118-Al-01 And. 1.65 4.3 0.51292 0.000007 0.348403 0.233 4.6119-Al-01 B.and. 1.56 4.26 0.512875 0.000007 0.348404 0.221 3.97120-Al-01 B.and. 1.73 4.43 0.512983 0.000006 0.348399 0.236 5.75122-Al-01 Dac. 2.62 7.07 0.512937 0.000006 0.348402 0.224 5.11125-Al-01 And. 1.74 4.57 0.512909 0.000007 0.348405 0.231 4.41126-Al-01 B.and. 5.43 15.54 0.513103 0.000006 0.3484 0.211 8.61

Plutonic rocks from the western part1-Al-00 Gabbro 0.75 1.84 0.513089 0.000006 0.348407 0.247 7.641-Al-00 Gabbro 5.34 16.04 0.513035 0.000006 0.348399 0.201 7.4869-Al-00 Gabbro 1.73 4.1 0.513098 0.000006 0.348399 0.255 7.61

Plutonic rocks from the eastern part73-Al-00 Q.diorite 1.83 5.09 0.512847 0.000007 0.348401 0.217 3.4992-Al-00 Q.diorite 1.23 2.59 0.512928 0.000005 0.348404 0.288 3.6286-Al-00 Gabbro 0.25 0.62 0.51262 0.000011 0.348422 0.24 −1.41

Abbreviations are as in Table 1.


EMO lavas, whereas the EMO dikes show no correlationat all. In theMgO vs CaO diagram, the EMO lavas definea poor positive relationship, and at a given MgO valuetheir CaO contents are significantly lower than those ofthe WMO. However, EMO dikes show no correlation intheMgO vs. CaO diagram. In theMgO vs. TiO2 diagram,the EMO lavas define a flat array with decreasing MgOcontents, whereas the dikes show an increase in the TiO2

and occupy (in particular the andesite dikes) anintermediate position between the EMO and WMOlavas. In the MgO vs. Zr and Y diagrams, the data fromthe EMO display a slight increase in Zr and Y withdecreasing MgO contents. Two of the andesite dikesstrongly diverge, however, from the rest of the EMOdikes. Similarly, as with the lavas and the dikes of theWMO, those of the EMO show positive MgO vs. Ni andMgO vs. Cr correlations. At a givenMgO content, the Niand Cr contents of the EMO lavas and dikes are lowerthan those of the WMO.

The N-MORB-normalized geochemical patterns ofWMO and EMO lavas and dikes are shown in Figs. 9and 10, respectively. In addition to the incompatibleelements (i.e., Cs, Ba, Th, Ta, Nb, K, Pb, Sr, P, Zr, Hf,Ti, Y, REE), the compatible elements Ca, Al, Mg, Mn,V, Sc, Cr and Ni have been included in these diagrams.The elements have been placed in order of their relativeincompatibility in a silicate melt in equilibrium withfertile spinel-lherzolite mantle (Pearce and Parkinson,1993), i.e. with Cs as the most incompatible and Ni asthe most compatible element.

In characterizing the normalized concentration pat-terns, it is convenient to split the incompatible elementsinto two groups. One group comprises elements ofmantle derivation (Ta, Nb, Zr, Hf, Ti, Y, and HREE).The other group includes Cs, Ba, Th, U, and LREE thatare enriched in the mantle to variable degrees as a resultof fluid transfer from the subducted slab and sediments.In the following, we refer to these two groups as mantle-


derived (MDE) and subduction-enriched elements(SEE), respectively.

The normalized element patterns of the basaltic lavasof the WMO are shown by three representative rocksamples, the least evolved (44-Al-00), the most evolved(40-Al-00), and the average basalt sample (Fig. 9A).Drawing a line through the MDE of the least evolvedsample defines a rather flat and then a slightly enrichedpattern from Lu through Zr, and a depleted patternrelative to N-MORB from Zr through Ta. The SEE arevariably enriched above the MDE base-line. The pat-tern of the most evolved sample is parallel to that of theleast evolved, and the difference in elemental concen-trations can be ascribed to fractional crystallization.The basaltic andesite lava (5-Al-00) that occurs in theuppermost part of the WMO is depleted in MDE anddefines a flat pattern relative to N-MORB, although theSEE show variable relative concentrations (Fig. 9A).The basaltic WMO dikes display the same patterns asthe WMO lavas, but two of the samples (98-Al-11 and98-Al-12) show an extreme enrichment in the Cs andBa (Fig. 9B).

The N-MORB normalized patterns of the EMO lavasare shown in Fig. 10A. EMO MDE define flat, depletedpatterns relative to N-MORB. The andesites are mostdepleted, whereas the dacite sample (YDKA99-8) isthe most enriched in MDE, defining a pattern similar toN-MORB. The SEE are variably enriched, but Cs isstrongly enriched in all samples (Fig. 10A). The EMO

Fig. 7. Plot of SiO2 versus FeOt/MgO for lavas and dikes of the WMO and EM

fromMiyashiro (1974). Some of the lava flows of the upper part of the volcanof the samples (lavas and dikes of both WMO and EMO) there are thin qua

basaltic to dacitic/rhyolitic dikes show the same MDEpatterns as the EMO lavas, but they are more variablyenriched in the SEE (Fig. 10B).

6.3. Sm–Nd isotope characteristics

Weanalyzed 71 samples from theMirdita Ophiolite forSm–Nd isotopes. Of these samples, 19 lava, 4 dike and 2gabbro samples were from the WMO, and 22 lava sam-ples, 21 dike, 1 gabbro, and 2 quartz diorite samples werefrom the EMO (Table 2). WMO and EMO ɛNd(T=160 Ma)

are shown as histograms in Fig. 11A. WMO ɛNd shows asmall range (mostly between +7.5 and +6.5), whereas theEMO rocks display a larger range from +8.6 to −4,mostly between +7 and +3.5. This suggests derivation ofWMO melts from isotopically homogeneous mantlesources, whereas the large differences exhibited by theEMO indicate rather heterogeneous mantle sources.Fig. 11B shows ɛNd(T=160 Ma) versus Sm/Nd for thesame rocks. The ɛNd(T=160 Ma) of EMO lavas range from+7 to +3 (basaltic andesites: +7 to +5; andesites: +7 to+3; dacites/rhyolites: ca. +3.5), and the dikes from +8.5to −4 (basaltic andesites: +8.6 to −1; andesites: +6.5 to3.5; dacites/rhyolites: +5 to +3.5; boninites: +5.5 to −4).There is a gap in EMO ɛNd(T=160 Ma) between +3 and −1.From Fig. 11B it appears that WMO magmas wereaffected mainly by crystal fractionation and partialmelting processes as inferred from the limited rangein Sm/Nd, whereas the magmas of the EMO crustal

O. The boundary line between tholeiitic and calc-alkaline rock types isic sequence of the EMO contain quartz-bearing amygdales, and in somertz-filled fractures. We omitted these samples from the diagram.

Fig. 8. Bowen diagrams showing the geochemical relationships between the lavas and dikes of the WMO and EMO. Values are in ppm for elementsand in wt.% for oxides.


rocks were also affected by various degrees of crustalcontamination.

6.4. Variations in chemo-stratigraphy

Fifty lava sampleswere collected through the twomainprofiles (see Fig. 4 for location), representing typicalWMO (26 samples of basalts) and EMO (24 samples of

basalts/basaltic andesites, andesites and dacites) litholo-gies. We refer to these two profiles, shown in Fig. 12, asthe WMP (western main profile) and EMP (eastern mainprofile) in the following sections. Three elements, twoconservative incompatible (Zr and TiO2) and one com-patible (Cr) element, together with the TiO2 contents ofpyroxenes and ɛNd(T=160 Ma) are plotted in a stratigraphiccontext in these profiles (Fig. 12).

Fig. 9. MORB-normalized multi-element diagrams of Western-type lavas (A), and dikes and sills (B) of the Mirdita Ophiolite. Normalizing values (inppm for elements and in wt.% for oxides) (after Pearce and Parkinson 1993) are: Cs (0.007), Rb (0.56), Ba (6.3), Th (0.12), U (0.047), Ta (0.13), Nb(2.33), K (1079), La (2.5), Ce (7.5), Pb (0.3), Pr (1.32), Sr (90), P (314), Nd (7.3), Zr (74), Hf (2.05), Sm (2.63), Eu (1.02), Gd (3.68), Ti (7620), Tb(0.67), Dy (4.55), Y (28), Ho (1.01), Er (2.97), Tm (0.456), Yb (3.05), Lu (0.455), CaO (12), Al2O3 (16), V (300), Sc (40), MnO (0.13), Co (40), MgO(7.5), Cr (275), Ni (100).


From the bottom of the WMP upwards, we seevariations in Zr concentrations between 100 to 300 ppmup to a stratigraphic height of 500 m. The Zr contentdrops to 50 ppm further upward, and TiO2 shows similartrends. The Cr profile largely mirrors the Zr variations(Fig. 12). Compositional change towards the top of theWMP is also reflected in clinopyroxene compositions,which show a significant decrease in TiO2 contents. TheɛNd(T=160 Ma) values show only small variations throughthe WMP, though the highest values (7.5) occur in thelower 300 m of the profile.

Zr contents through the EMP are remarkablyconstant (around 50 ppm), even though the lavas varyfrom basaltic andesite to dacite, whereas the Cr contentshows large variations (Fig. 12). Pyroxene TiO2 content

is low (b0.3 wt.%) (Fig. 12). The ɛNd(T= 160 Ma) valuesare around +6.5 in the lower 800 m of the EMP, morevariable (+6.5 to +5) between 800 and 1050 m, anddrop to ∼ +3 for the uppermost sample at 1100 m abovethe base of the section (Fig. 12).

7. Discussion of geochemical andpetrological evolution

7.1. Nature of the mantle source

In order to characterize the mantle sources ofthe magmas that formed the upper crustal units of theMirdita Ophiolite, it is necessary to examine the con-centrations of highly incompatible to compatible ele-ments where the mantle contribution greatly exceeds


any kind of subduction-related contribution. Pearce andParkinson (1993) compiled bulk distribution coefficientsfor such elements for melting of fertile spinel lherzolite.Their results are as follows: Nb and Zr (very highlyincompatible, VHI), Ti, Y and Yb (highly incompatible,HI), Ca, Al, Vand Sc (moderately incompatible,MI),Mnand Fe (slightly compatible), Co and Mg (moderatelycompatible, MC), and Cr and Ni (highly compatible,HC). By normalizing primitive basalts against a fertile

Fig. 10. MORB-normalized multi-element diagrams of the eastern type lavasin Fig. 9.

MORB mantle (FMM), Pearce and Parkinson (1993)showed patterns characteristic of mid-ocean ridge ba-salts, ocean island basalts, and supra-subduction basalts,reflecting melting and depletion or enrichment events inthe mantle.

We have applied this method to the boninites, basalts,and basaltic andesites of theWMOand EMO, as shown inFig. 13A and B. The abundances of the VHI and HIelements are in general higher for WMO basaltic lavas

(A), and dikes and sills (B) of the MO. Normalizing values are given

Fig. 10 (continued ).


and dikes than for EMObasaltic andesites. However, theirFMM-normalized patterns are similar (Fig. 13B), withthe exception of a boninitic dike (90-Al-00). Typically,the patterns of the basalts and basaltic andesites havethe following incompatible element characteristics:VHIbHINMI, or VHI=HINMI. According to Pearceand Parkinson (1993), such patterns indicate moderate tohigh degrees of melting of an un-enriched to slightly

depleted FMM source. Particularly, with respect to thelavas and dikes of theWMO, the most comparable FMM-normalized patterns are those of basaltic rocks from theMid-Atlantic Ridge and/or the Costa Rica Rift oceaniccrust, whereas those of the EMO are comparable tothe Tonga and/or the Marianas suprasubduction crust(Fig. 13C). We emphasise, however, that the differencesbetween the patterns of the Rock/FMM normalized

Fig. 11. Histogram showing the distribution of ɛNd(T= 160 Ma) (A), and a plot of Sm/Nd — ɛNd (T=160 Ma) (B) for the Mirdita Ophiolite.


diagrams of the Tonga, Marianas, Costa Rica Rift, andAtlanticMORB are subtle. The boninite sample 90-Al-00showsVHINHIbMI, a pattern that indicates high degreesof melting of a depleted source, but with enrichmentin the VHI elements. These considerations are in agree-ment with estimates of the degree of partial melting byBortolotti et al. (2002). These authors concluded thathigh-Ti,MORB-type basalts of theWMOwere generatedby 10% partial melting of fertile MORB-type mantle,whereas the low-Ti basalts and basaltic andesites of theEMO represent the same degree of partial melting of amantle that was previously depleted by 7–17% melting.

7.2. Subduction influence

A hybrid mixture between MORB-like and arc-likeelement signatures is characteristic of ophiolitic basaltsequences (e.g., Pearce, 1980; Stern and Bloomer, 1992;

Shervais, 2001; Ishikawa et al., 2002; Dilek and Flower,2003; Harris, 2003; Pe-Piper et al., 2004; Saccani andPhotiades, 2004; Dilek et al., 2007). This is generallyconsidered to reflect melting of a MORB mantle sourcethat has been contaminated with fluids released from thesubducting slab and/or sediment-derived melts. Theidentification of this character in ophiolitic rocks thusindicates generation above a subduction zone.

To investigate subduction influence on the magmagenesis of the most primitive lavas and dikes of theMirdita Ophiolite, we evaluated the element patternsin MORB-normalized multi-element diagrams (Figs. 9and 10). For this purpose, the elements are subdivided intoconservative and non-conservative types. The concentra-tions of elements of the conservative type (Ta, Nb, Zr, Hf,Ti, Tb, Dy, Y, Ho, Er, Tm, Yb, Lu, V, Sc, Cr, Ni) are littleaffected by subduction, whereas those of the non-conservative type (Cs, Rb, Ba, Th, U, K, La, Ce, Pb, Pr,

Fig. 12. Relationships between various geochemical parameters and the stratigraphy of (A) the eastern main profile (EMP), and (B) the western mainprofile (WMP).


Sr, P, Nd, Sm, Eu, Gd) show various degrees of sub-duction-zone contribution to the magma source (Pearce,1983, Pearce and Peate, 1995). Following the method of(Pearce 1983) and Pearce and Peate (1995), we estimatethe contribution to the source from a subduction zone bydrawing a baseline through the MORB-normalized,conservative elements Ta, Nb, Zr, Hf, Ti, HREE and Y.We have done this for the most primitive basalts andbasaltic andesites from the WMO and EMO, and theresults are shown in Fig. 14A and B. For the samples ofboth the WMO and EMO, there is a general decrease inthe percentage subduction component for Cs (nearly100%) through Gd (∼0%), i.e. from the most to the leastincompatible elements. In WMO samples, there arepronounced variations in the Ba, K, and Pb concentra-tions, a feature that is not seen in EMO samples with theexception of Pb in sample YDKA99-9. This heterogene-ity may be due to: (1) element mobility during alteration,and/or (2) generation of melts from variably subduction-influenced mantle domains. It is well known that Cs, Rb,Ba, K, and Sr are mobile during seafloor alteration (e.g.,

Thompson, 1973; Coish, 1977; Staudigel andHart, 1983).However, if alterationwas responsible for the Ba-, K-, andPb-variations in the WMO basalts (Fig. 14A), one mightexpect the same phenomenon for the rocks of the EMO(Fig. 14B) since they are equally altered. The EMO lavasshow a much more consistent pattern, and it is thereforemore likely that the Ba-, K-, and Pb-variations can bemainly attributed to the generation of melts from aheterogeneously subduction-influenced mantle.

Enrichment of the mantle in slab-derived non-conservative elements is a complex process that mayinclude fluid release from subducted altered oceanic crustand/or sediments, and from felsic magmas generated bypartial melting of sediments (Saunders et al., 1991; Pearceand Parkinson, 1993; Pearce and Peate, 1995; Gribbleet al., 1996; Hawkesworth et al., 1997; Macdonald et al.,2000; Elburg et al., 2002). The transport of incompatibleelements in hydrous fluids differs significantly, e.g. whileU and Ba are highly mobile, Th is less mobile (e.g.,Hawkesworth et al., 1997), and thus fluids released fromsubducted material and their interaction with mantle

Fig. 13. FMM (fertile MORB mantle)-normalized patterns for (A) basalt and basaltic andesite lavas, and (B) Basalt, basaltic andesite and boninitedikes of the WMO and EMO, (C) Basaltic lavas from Tonga, Marianas, Costa Rica Rift and Atlantic MORB oceanic crust. Normalizing values, takenfrom Pearce and Parkinson (1993), are: Nb (0.2), Zr (9.2), TiO2 (0.175), Y (3.9), CaO (3.25), Al2O3 (3.75), V (78), Sc (15.5), MnO 0.13), FeOt (8.8),Co (106), MgO (38.4), Cr (2500), Ni (2020). Oxides in wt.%, elements in ppm.


sources will result in high U/Th and Ba/Th in producedmagmas. At low Th concentrations, lavas and dikes ofboth the WMO and EMO (in particular) show a largespread in U/Th and Ba/Th (Fig. 14C and D), suggestingthat they were generated from a MORB-type mantlesource that was enriched in Ba and U, as well as in otherfluid-mobilized elements. However, Th contents that are

significantly higher than those of MORB, are restrictedto the andesites and rhyodacites of the EMO (Fig. 14Cand D), i.e. the stratigraphically highest volcanic rocks(Fig. 4). Since Th is little mobilized in a fluid phase,this enrichment has to be explained in a different way. Agenerally high-Th source (up to ca. 20 ppmTh), comparedto the Th contents of MORB, is thought to be subducted

Fig. 14. Subduction effect upon dikes and lavas of the Western and Eastern Mirdita Ophiolite. Diagrams A and B show calculated changes (in %) ofnon-conservative elements due to subduction processes (see text for further explanation). Note the strong enrichment of the highly non-conservativeelements (Cs, Ba, K, Pb, Th, U, Sr) compared to that of the moderate non-conservative elements (P, La, Ce, Pr, Nd) and the slightly non-conservativeelements (Sm, Eu, Gd). Diagrams C and D show that the majority of the samples from the WMO are close to MORB compositions with respect to U/Th–Th and Ba/Th–Th relationships. High Th and U/Th and Ba/Th ratios in some of the samples from the EMO indicate sediment and fluidincorporation (see text for further explanation).


sediments (Plank and Langmuir, 1998). Thus, the high Thvalues of the andesitic and rhyodacitic rocks arecompatible with magmas derived from a source that hasbeen enriched in Th by melts derived from subductedsediments.

7.3. Magma evolution in time and space: petrogeneticmodel

Based on our geochemical data and interpretationsand our well-constrained chemostratigraphy of WMOand EMO extrusive sequences, we propose a newpetrogenetic model in which subduction was importantfor the magmatic evolution of the Mirdita Ophiolite(Fig. 15). This model differs from previous interpreta-tions (Robertson and Shallo, 2000; Bortolotti et al.,2002; Dilek and Flower, 2003; Flower and Dilek, 2003;Bortolotti et al., 2005) in which the MORB-type lavas

and dikes of the WMO are attributed to an earlier phaseof oceanic spreading, whereas the heterogeneousigneous sequence of the EMO and its dominant IAT-character have been interpreted to have resulted fromsubsequent intra-oceanic subduction zone magmatism.In our model, the WMO and EMO developed through aprogressive evolution of MORB to IAT to boniniticmagmas above a west-dipping subduction zone, whichexperienced rapid slab retreat during and after itsinitiation (Fig. 15 A, B). Slab rollback exceeding theconvergence rates resulted in upper plate extension(Dilek and Flower, 2003; Garfunkel, 2006) that causedspreading with a well-developed sheeted dike complexin the EMO (Fig. 15C, D). During the evolution ofthe WMO and EMO, melt generation, aggregation/mixing, and differentiation probably occurred in multi-ple levels in the subarc/forearc mantle, and pressureranges of aggregation/mixing and differentiation might

Fig. 15. Summary of the magmatic development in time and space of the Mirdita Ophiolite (trench-slab rollback model adapted from Stern andBloomer, 1992; Dilek et al., 2005).


have overlapped (Fig. 15D). Thus, aggregation ofmelts may have involved melt production and subse-quent modification, similar to the model suggested byGrove et al. (1992). The return mantle flow facilitated byretrograde slab motion and the arc-wedge corner flow

played a major role in the evolution of the meltingcolumn above the subducting slab (Kincaid and Hall,2003). Late-stage boninitic magmas in the MirditaOphiolite were produced from partial melting of rela-tively hot, hydrous and repeatedly depleted, ultra-


refractory peridotite in the rapidly evolving suprasub-duction mantle wedge (Fig. 15D).

The FMM-normalized patterns (defined by theincompatible to compatible conservative elements Nbthrough Ni) of the lavas and dikes of the WMO andEMO (Fig. 13) indicate melting from a rather homoge-neous source region with respect to the conservativeelements. Furthermore, the high abundance of the mostnon-conservative elements (e.g. Cs, Ba, K, Pb, Th, U, P,La) suggests that the mantle source from which the lavasof the WMO and EMO were generated had beenenriched in these elements through subduction process-es (Fig. 14A and B). The variable enrichment patternsthroughout the WMP lava sequence (Fig. 14A) point toa slightly, but heterogeneously enriched mantle wedgein which melting occurred. On the other hand, theconsistent enrichment of non-conservative elements inthe EMP lavas indicates that the mantle from whichthese lavas were generated was homogeneouslyenriched. The relationships between the fluid-mobilizedelements Ba and U and the less-fluid-mobilized elementTh suggest that the mantle source experienced enrich-ment of highly-mobile elements at or prior to the time ofWMO melt extraction, as shown by some samples withhigher U/Th and Ba/Th than MORB (Fig. 14C and D).Andesitic and dacitic/rhyolitic lavas and dikes of theEMO show relatively large Th variations and generallyhigher concentrations than in the more mafic rocks(Fig. 14C and D). Since rocks of more felsic composi-tions occur at a higher stratigraphic level of the EMP(Fig. 12), the Th-enrichment of the source region can beconsidered as a relatively late phenomenon, related tomelting of sediments on the subducting slab.

Up to a stratigraphic level of ca. 500 m above the baseof the WMP lavas, Zr contents vary principally between100–200 ppm. Higher in the section lavas becometransitional between basaltic and basaltic andesite, andZr contents decrease to about 50 ppm. Throughout theformation of the EMP lavas, particularly in the lower800 m, basaltic andesites dominate with Zr contentsvarying approximately between 30 to 50 ppm (Fig. 12).Similar trends can also be observed for the TiO2-contentsof clinopyroxenes (Fig. 12). The pronounced decrease inthe Zr content may indicate that repeatedmelting depletedthe mantle source in incompatible trace elements.Alternatively, increased degrees of partial meltingwould also give lower contents of incompatible traceelements. However, regardless of the relevant mantleprocesses, an important feature demonstrated by thesepatterns is the clear geochemical affinity between thewestern and eastern parts of the ophiolite. A notablefeature of WMP chemostratigraphy is the change in the

geochemical character of the lavas in the upper 100 m ofthe profile from typical “Western” type to typical“Eastern” type, i.e. from MORB-like to IAT-like(Figs. 9, 14 and 15). It is important to note that thischange occurs without any unconformity or other tectonicor structural break. This relationship demonstrates that thewestern and eastern geochemical affinities represent notonly a west-to-east transition, but also a stratigraphic,vertical gradation into more subduction-influenced rocks.This is further substantiated by the ɛNd data that show ageochemical continuation from the upper part of theWMP into the lower part of the EMP (Figs. 12 and 15).

This relationship further questions the previousproposals that the subduction-related EMO magmaticrocks were built upon an older MORB oceanic crust.Such a model implies two fundamental relationships: (1)the MORB-like lavas of the WMO are older than theEMO lavas, and (2) there is a major hiatus between thesetwo lava sequences. However, neither of these twofeatures is supported by our field observations andgeochemical data. Indeed, radiometric ages of theplagiogranite and quartz-diorite intrusions both in theWMO and EMO show rather similar ages of 160 to165 Ma (Dilek et al. 2001, 2007).

Pronounced compositional changes occur in the upper300 m of the EMP. The composition of the lavas changesfrom mainly basaltic andesites to predominantly ande-sites. Contemporaneous with this compositional change,we also observe pronounced isotopic changes such thatɛNd decreases from +6.5 to +3 (Figs. 12 and 15).

The ɛNd values change significantly from west to theeast in the Mirdita Ophiolite (Figs. 11 and 12). The ɛNdof the gabbros vary from +7.6 in the west to −1.4 in theeast. Similarly, the highest (+8) and the lowest (−4) ɛNdare registered in a basaltic dike crosscutting a WMOgabbro and a boninite dike intruding an EMO gabbro,respectively (Fig. 15). This shift in the ɛNd from +8 in thewest to −4 in the east and the documented changes in thechemical compositions of the rocks frommore basaltic tomore evolved and felsic types stratigraphically upwardand toward the east suggest that subduction influencedmagmatism shifted generally eastward in time. This isconsistent with our petrogenetic model in that arc-protoarc magmatism in the upper plate of the subductionzone migrated eastward keeping pace with the slabrollback (Fig. 15). However, the presence of a low-Tibasaltic dike (sample 55-Al-01) (Table 1) in the WMOand a basaltic andesite dike (sample 126-Al-01) withinthe EMO sheeted dike complex showing high ɛNd(+8.61) (Table 2), typical of the WMO rocks, suggeststhat both the WMO and EMO evolved within the sametectonic environment (i.e. an arc-protoarc setting).

Fig. 16. (A) The inferred paleogeography of the western end of Neo-Tethys and the continental reconstruction of Western Gondwana and Laurasia around 200 Ma (modified from Stampfli and Borel,2004). The Pindos Ocean is one of several marginal basins developed between Gondwana-derived continental fragments following the Permo–Triassic rifting. (B) Collapse of the Pindos and Vardarbasins through intra-oceanic subduction around 170Ma. Consumption of the pre-existing ocean floor and slab retreat associated with these subduction zones produced the Jurassic suprasubduction zoneoceanic crust now preserved in the Mirdita and Western Hellenic ophiolites and in the Vardar Zone ophiolites. X–Y show the cross-section line depicted in C. (C) Geodynamic cross-section across theNeo-Tethyan marginal basins, continental fragments, and the bounding supercontinents during the Jurassic (170–160Ma). The Southern Neo-Tethys and the Alpine Tethys are opening up at this stage,as the Pindos and Vardar basins are collapsing. Ophiolite emplacement onto the Pelagonian continent in the Late Jurassic was followed by the collision of Apulia and Pelagonia in the Eocene. Key tolettering for different continents: Afr — Africa, Ap — Apulia, Eur — Eurasia, Pel — Pelagonia.

204Y.

Dilek

etal.

/Lithos

100(2008)

174–209


8. Geodynamic model

The suprasubduction zone signatures in the MirditaOphiolite require an intra-oceanic subduction zonewithin the Neo-Tethyan basin in which the Jurassicophiolites of the Albanides and the western Hellenidesformed. We suggest that this was the Pindos marginalbasin, which evolved between the Apulia (and itseastward extension into Turkey, the Tauride platform)and the Pelagonia subcontinents in the western termina-tion of the larger Neo-Tethyan ocean (Fig. 16A). Recentpaleogeographic reconstructions of the Tethyan systemsuggest that there were a series of marginal basins thatopened up as back-arc basins during the closure of Paleo-Tethys in the Permo-Triassic (Stampfli et al., 2001;Stampfli and Borel, 2004). Some researchers suggestthat the Mirdita and other Albanian ophiolites and theWestern Hellenic ophiolites (i.e., Pindos, Vourinos,Othris) were derived from the Vardar basin east ofPelagonia (Collaku et al., 1992; Bortolotti et al., 1996,2002, 2005).We find these models incompatible with theregional geological constraints, as discussed in detailelsewhere (Dilek et al., 2007).

The Pindos basin was floored with Triassic oceaniccrust prior to its collapse in the Middle Jurassic. ATriassic–Jurassic volcanosedimentary unit is discontinu-ously exposed along the Apulian and Korabi-Pelagoniancontinental margins and contains Middle-Upper Triassicalkaline basalt and radiolarian cherts (Shallo, 1992;Marcucci et al., 1994; Chiari et al., 1994; Dilek et al.2005). Widespread Middle Triassic volcanism associatedwith the Apulia–Pelagonia rifting and the subsequentseafloor spreading in the Pindos basin should have createda Red Sea-type restricted basin with its conjugate passivemargins preserved structurally beneath the thrust sheets ofthe Mirdita and other Albanian ophiolites (Robertson andShallo, 2000; Dilek et al., 2005). This Pindos basin andthe Vardar basin to the north (in present coordinatesystem) started collapsing via intra-oceanic subductionbecause of a regional compressional stress regime causedby the continental collisions that occurred farther north inthe European side of Laurasia (i.e. the Sakarya collision;Fig. 16B). Thus, the closing Pindos and Vardar basinsmarked a “zone of contraction” within the western end ofthe Neo-Tethys, while the Alpine Tethys and the SouthernNeo-Tethys were experiencing seafloor spreading around170–160 Ma (Fig. 16C).

The polarity of the intra-oceanic subduction zonewithin the Pindos basin was west-southwest-dipping (inthe present coordinate system) as constrained by ourchemostratigraphic and isotopic data from the extrusivesequences and the observed variations in the chemical

compositions of different dike generations. The docu-mented geochemical and age progression of the MORB-IAT-boninitic magmatism in the Mirdita Ophiolite is anartifact of subduction zone magmatism that propagatedeastward in time, keeping pace with the trench-slabrollback in this direction.

The inferred suprasubduction evolution and thetectonomagmatic development of the Neo-Tethyanophiolites in the eastern Mediterranean region indicatethat the restricted marginal basins in which theseophiolites had formed were nested in older, pre-existingocean basins (Dilek et al., 2005; Garfunkel, 2006; Dileket al., 2007). The collapse of these older basins and theconsumption of their ocean floor gave way to ophiolitedevelopment in relatively short time spans (b10my). Thecrust of older ocean basins was probably recycled backinto themantlewithout any surficial trace of it, as has beenthe case for most mid-ocean ridge generated oceanic crustthroughout the Phanerozoic (Cloos, 1993). The trench-slab rollback cycles and the arc-protoarcmagmatismwerearrested by trench-continent collisions, effectively termi-nating the igneous accretion of ophiolites and resulting intheir emplacement. The arrival of the Pelagonian passivemargin at the Pindos trenchmarked the end of the igneousevolution of the Mirdita Ophiolite in the Late Jurassic.

9. Conclusions

The Jurassic Mirdita Ophiolite in northern Albaniahad a progressive geochemical evolution in a suprasub-duction zone setting within a Tethyan marginal basin.The spatial, temporal and geochemical relations betweenthe extrusive and dike rocks of the western and easternparts of the ophiolite show that the shift from MORB toSSZ affinities, respectively, is both lateral and strati-graphic (vertical), indicating changes in the melt com-positions and mantle sources through time. Both theMORB and SSZ components of the Mirdita Ophiolitewere produced in the same protoarc-forearc tectonicenvironment.

In the∼650-m-thick extrusive sequence of theWMO,the basaltic pillow lavas in the lower 300 m have highTiO2 (3.5–1.5%) and Zr contents and high ɛNd values(+8–+7.5) with no discernible subduction influence.Stratigraphically upwards the basaltic lavas transition intobasaltic andesites, which acquire lower TiO2 (2.5–0.5%)and Zr contents and lower ɛNd values (+7 to +6.5)suggesting appearance of subduction influence in theirmelt evolution. The small range of the ɛNd values of theselavas and dikes in the WMO indicates derivation of theirmagmas from isotopically homogeneous MORB mantlesources.


The nearly 1.1-km-thick extrusive sequence of theEMO contains mostly pillowed basaltic andesites withinthe lower 700 m. The upper 400 m of the sequenceconsist predominantly of massive flows with minorpillow lavas and pillow breccias with compositionschanging from basaltic andesite, to andesite, dacite, andboninite. The basaltic andesites in the lower 700 m havelow Ti (∼0.5) and Zr contents with ɛNd (+7 to +6.5)similar to those of the WMO lavas. These rocks show aweak subduction influence displayed by their variableenrichment in certain incompatible elements (Cs, Ba,Th, U, LREE). The basaltic andesites, dacites andboninites within the upper 400 m have low Ti and ɛNd(+6.5 to +3.0) and high Th contents (up to 1.2 ppm),suggesting a strong subduction influence. The low Zrcontents of the lavas remain constant (∼50 ppm)whereas the Cr contents show large variations through-out the EMO extrusive sequence. The high Th contentsof more evolved lavas in the upper volcanic sequenceindicate a mantle source that was enriched in Th bymelts derived from subducted sediments. The generallyhigh Ba, K, and Pb contents of these rocks also suggestmagma generation from a homogeneously subduction-influenced mantle. Boninitic dikes and gabbroic intru-sions in the EMO with negative ɛNd (−1.4 and −4.0,respectively) were produced from partial melting ofrepeatedly depleted, ultra-refractory harzburgitic peri-dotites in the mantle wedge.

The geochemical progression from MORB basaltswith high ɛNd (+8.0) in the west to more evolved rocksshowing negative ɛNd (−4.0) in the east in the MirditaOphiolite and stratigraphically upwards within the EMOextrusive sequence was a result of an eastward shift inthe protoarc-forearc magmatism. Slab rollback wasresponsible for this inferred eastward propagation ofsubduction zone magmatism and for rapid extension inthe upper plate that resulted in the development of theEMO sheeted dike complex. These features, combinedwith a relatively higher level of Th-enrichment of thesource mantle due to melting of sediments on thesubducting slab, indicate westward dipping (in thepresent coordinate system) subduction with an east-facing infant intra-oceanic arc system.

The Mirdita Ophiolite and its counterparts in thewestern Hellenides of Greece developed in a marginalbasin (Pindos basin) between Apulia and Pelagonia. TheSSZ evolution of these ophiolites occurred during theclosing stages of the Pindos basin, which had a protractedgeodynamic history involving initial continental rifting,seafloor spreading, protoarc rifting, and trench–continentcollision. Emplacement of the Mirdita and the WesternHellenic ophiolites onto the Pelagonian passive margin in

the Late Jurassic marked the end of igneous accretion ofSSZoceanic crust in the Pindos basin and the beginning ofthe closure of this marginal basin in the westerntermination of the Mesozoic Neo-Tethys.

Acknowledgements

This study was funded by a NATO Science Programresearch grant (EST.CLG-97617) and the Miami Univer-sityCommittee on FacultyResearch.Wewish to thank thedirectors of the Albanian Geological Survey (M. Zaçayand H. Beshku) for their logistical support during ourfieldwork, and our Albanian colleagues (S. Bushati, E.Gjani, A. Meshi, I. Milushi, and A. Vranaj) for providingus with valuable information and discussions on thegeology of Albania. Constructive and thorough journalreviews by Ron Harris, Brian Robins, Paul T. Robinsonand Robert J. Stern helped us improve the paper.

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Geochemistry of the Jurassic Mirdita Ophiolite (Albania) and the … et... · 2012. 8. 21. · dualism, particularly those in Albania. Dede et al. (1966) recognized first a petrographic