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To repιace page 81 ofio|iti, 1995, 2ο (2)' 81.96 ULTRAMAFIC RocKs AND AssoclATED cl.|RoM!τE M|NERALISAT|oN FRoM NEA RoDA (ΕASτERΝ CHALK|DIK| PENINSυLA, NoRτHERN GREECE} KIeopas M. Michai|ldis*, Τriangafy|los C. Soldatos* and c, Christodou]oυ** * Depaιtment of Mineralogy-Petrology.Εconomic Geology, Thessaloniki Uniνersity, Ihessa/o- niki, Greece. "* Department of Geology and Geophysics, University of Adelaide, Adelaide, Australia. Keywords: ultramafics, chromite mineralisation, chemistry, subduction zone. Nea Roda, Chal- kidikΙ pen sin sula, Greece. ABSτRACT The Νea Roda u|tramafic body in the eastern part of Chalkidiki peninsυ|a (Northern Greeοe) is a fauιt bound segment of variabiy serpentinised dunite with podifοrm chromitites. The chromitites range from massive to disseminated type. Sheared serpentinites and talc schists mark the contact zones to the basement meta- morphic rocks. Primary minera|s of serpentinised dunites are olivine (Fo39.6-94.ρ) and chromite (Cηo3=46-62,1o6, Al2o3=$-1$nηo6). Τhe Mg/(Mg+ρg2+1 and crl(cr+A|)-ratios of chromites range from 0-30 to 0.68 and from σ.?+jo o.sη respective|y. C.hrδmite has exchanged Fe2+ and Mg with o|iνine down to temperature of |ess than 7oo"ο. chromite displays restricted rim, patchy and fracture alteration into Mg-Al-poor and Cr+ich ferrit- chromιte, aοcompanied by the formation of chromian ch|orite. The studied dυnites and assοciated chromitites disp|ay microstructura| and compositional similarities to those of the western Chalkidiki ophiolites. A subduοtion-zone re|ated spreading system was interred for the Nea Roda u|tramafics on the basis of the hosted chromite chemistry. A younger (PosιTriassic) emp|acement of the Νea Roda u|tramafics οompared to the vertiskos Formation Pa|eozoiο ultramafics is proposed. tNTRoDUcτ|oN 1 976). Τhe Serbo-Macedonian Massif itself is Τhe Νea Roda u|tramafic body corps out composed of two formations, the Kerdilia near the Nea Roda village, on the isthmus of Formation to the east and the Vertiskοs For- the Athos peninsula in eastern Chalkidiki mation to the west (Fig. 1). The Kerdilia For- (Fig. 1). This ultramafic body occurs in the mation is older (Early Paleozoic) than the core of the Serbo-Macedonian Massif, a ma- Vertiskos Formation (Kockel et al., 1977). jor geotectonic zone of northern Greece. The The Νea Roda u|tramafic body is thrust on Serbo-Macedonian Massif overthrusts the Ri- the metamorphic basement rocks of the Ver- |a Rhodope Massif to the east. Τo the west, tiskos Formation. Two-mica gneisses and its boundary with the Innermost l-lellenides is amphibolites οonstitute the crysta||ine base- defined by reverse thrust faults of its base- ment rocks of the Vertiskos Formatιon. ment metamorphic roοks on the Mesozoic Mu|tidiscip|ine studies and isοtopic data formations of the Circum Rhodope Belt on the οrysta|line rocks of the Serbo.Mace- (Kockel et al., 1971 , 1977', Kauffman et al., donian Massif suggest the following sequen- 81 ofio|iti' 1995, 2ο (2), 81 -96 ULτRAMAFIC RocKs AND ASSocIATED cHRoMlτE MlΝERALlsATloN FRoM NEA RoDA (EASTERN CHALK|DIK! PENINSULA, NORTHERN GREECE) K|eopas M. MichaiIidis and τriangafyllos C. Soldatos Department of Mineralogy.Petrology.ΕconomiC Geology, Thessaloniki Universiξ, Thessa|aniki, Greece. Keywords: ultramafics, chromite mineralΙsation, chemΙstry, s;ubduction zone' Νea Roda, Cha|. ki d i ki pens i nsul a,G reece. ABSTRAOΤ The Nea Roda ultramafic body in the eastern part of Cha|kidiki peninsu|a (Νorthern Greece) is a fault bound segment ol variably serpentinised dunite with podiform chromitites. The chromitites range from massiνe to disseminated type. Sheared serpentinites and ta|c schists mark the contaαt zones to the basemenι meta. morphic rocks. Primary minera|s of serpentinised dunites are o|ivine (Foεg.ε-s+.o) and chromite (Cr2o3=4θ.62wflo, Al2O3=g-19e1"7.). The Mg/(Mg+Fe2+) and.Crl(Cr+Al) ratios of chromites range from 0.30 to 0.68 and from 0|.64 to o.θ4 respectively. Chromite has exchanged Fe2+ and Mg with olivine down to temperature of |ess than 7OO"C. Chromite disp|ays restricted rim, patοhy and fracture alteration into Mg.A|.poor and Crτich ferrit. chromite, accompanied by the formation of chromian chlorite. The sfudied dunites and associated chromitites disp|ay miοrostruc1ural and compositiona| similarities to those of the \,γestern Cha|kidiki ophio|ites. A subduction.zone re|ated spreading system νγas interred fοr the Nea Roda ultramafics on the basis of the hosted chromite chemistry. A younger (post-Triassic) emp|acement of the Νea Roda u|tramafics compared to the Vertiskos Formation Paleozoic ultramafics is proposed. |ΝTRoDUcτloN 1 976). The Serbo-Macedonian Massif itself is Τhe Νea Roda ultramafic body οorps out composed of tνγo formations, the Kerdi|ia near the Nea Roda vιlιage, on the ιSthmuS of Formation to the east and the VertΙskos For- the Athos peninsula in eastern Chalkidiki mation to the west (Fig. 1). Τhe Kerdi|ia For- (Fig. 1). This u|tramafic body oοcurs in the mation is older (Εar|y Paleozoic) than the οore of the Serbo-Macedonian Massif. a ma. Vertiskos Formation (Kocke| et aι., 1977). jor geotectonic zone of northern Greece. The The Νea Roda ultramafic body is thrust on Serbo-Macedonian Massif overthrusts the Ri- the metamorphic basement rocks of the Ver- |a Rhodope Massif to the east. Τo the west, tiskos Formation. Two-mica gneisses and its boundary with the Innermost Hellenides is amphibo|ites οonstΙtute the crysta||ine base. defined by reverse thrust faults of its base- ment rocks of the Vertiskos Formation. ment metamorohιc rocks on the Mesozoiο Multidiscip|Ιne studies and isotopic data formations of the Cirοum Rhodope Be|t on the crystalline rocks of the Serbo-Mace- (Kockelet al., 1971; 1977; Kauffman et al,, donian Massif suggest the following sequen- 82 *αl α) (, + ιr + t! σ + o + ιn (, 0) +J ρ Φ ..1 Ξ Fi +) ι) + ο .ri τ, + .}J .Η (! 4J o 0) t,ι υ Ξ .i ο) aE 'dΣ Σ li (σ ι Φ Φ .Ξ 1 Ξ o ΞI 2 Ξ fi1 ο) βl +J ιιι Ι .io O : I υ$|-tdd99Ψ qΙ &:. 16 OC d t! Φ I 'H tro η, E U) o 6Ι Lt > oE O d t |υ -. .5 Φr{ tr ιr Α Ξ 1 -9 Α oΦ Φ q a Φ i (6 I Ξ ο)Θ ιr Ξ i 4 z ul ι, D tι I I t_ c t oJ .Ξ i Ξ EffiIE i o Φ o ! Φσ) a! Ξ δΕ φ μ t Ψ ι) δ Ξ jξ U) l{ €9δ o x .Ξ(σ(dφ ,.θE,ε,π1 U) Φl9 ..{ ;iz +J Ρ ;ιυ.' fuΚ Η . (υ μ EE# i1,φi[irΙ}π,fΙl :i ?.ιΣ <Ξo :6θ ,,!' i#ffiftf1; ;"',) Ψ.^?=ξeμ;iΞ Et-9 χ,: ο (σ^.9 }. ισ z c'- .Y ii,Ψf)/.''} :Xσ) U) δ: Χ 0jΦ o ΞΦ;+. ElΦ c o o.i ΦΦ-, o+J ..t +J ,i ιr TΙi:'ffid;; - .:: ; 0) O-{ NO (6O +Jtr l oμ o o oα μΦΞ HΞ r ι:Φ Ξμ|;μ/;ξ,# Σo o. Z >.λ ffi i I'i;-?,r6,fe'A\-^ |Πl||||t .l illllllil l ιΙ 83 οe of metamorphiο and deformation events nera|ogic and chemica| data from the Νea from pre-Carboniferous to post-Jurassiο (e. Roda ultramafic rocks and associated chrom- ..|971,, g., Koοke| et a|,, 1977', De Wet et a|,, ite mineralisation. Τhe tectonic environment 1989, Kourou,1991). of formation is investigated and a compari- An l-lercynian event produced migmatites son is made with the ophiolites of western by partia! me|ting at Τ=650-750.C, P=3'5-8.5 Cha|kidiki. Final|y, the teοtoniο evoIution of kbar' Fol|owing the Herοynian migmatization the Νea Roda ultramafiοs and the imp|ic- three metamorphic eνents can be distin. ations on the geological history of the Verti- guished (Kourou, 1991). A Permo-Triassiο skos Formation are discussed. medium- to high-pressure amphibolite.faοies event (Τ=500-64O.c, P=5-8 kbar), a Late Ju. rassic greensοhist-facies event (Τ=440- GEOLOGY 520'C, P=5-6 kbar) and finally, a series of post-Jurassic retrogressive eVents (Τ=300. Τhe outcrop of the Νea Roda u|tramafic 550'C, P<5 kbar) affected the mineralogy of rοοks is bound by the οoast |ine and by the the Vertiskos Formation. Τertiary granites in- Vertiskos Formation metamorphic roοks (Fig. trude the metamorphic rocks in the broader 1B). area of Νea Roda; the Ierissos granite ts The minera|ogy of the surroυnding amphi- about 55 Ma old and the Ouranoupolis gra- bolites, migmatites and mica schists point to nite about 45 Ma (De Wet et al., 1989; Frei, high P-T metamorphic conditions (amphibo- 1992). Serpentinised u|tramafic rocks oοcur lite facies) during Permian-Τriassic (Kourou, throughout the Vertiskos Formation. Τhe big. 1991) and subsequent retrogression to gest ones are near the Gomati village (Gt in greenschist facies during Jurassiο or |ater Fig. 1), |ake Volvi and the town of Νigrita. orogenic events. Τhese u|tramafics are οharacterized by pred- The exposed ultramafics of Νea Roda are ominantly antigorite serpentinites and highly thrust upon the amphibolites of the Vertiskos altered chromites. ln most cases chromΙte is Formation to the south, and migmatites to replaced by ferritchromite and magnetite, the west. Τhe thrust zones are marked by whereas original chromite relics (always en- sheared serpentinite and ta|c sοhists. Τhe ob- ve|oped by ferritοhromtie and magnetite) are served thicknesses of ta|c sοhist zones ex- only preserved in massive chromitites (Chri- ceed 2 m in width, reaching up to 15 m. stodoulou, 1980; Michailidis, 1991 , 1995). The Νea Roda u|tramafic body consists of Τhese ultramafiο bodies were tncorporated in massive dunite and some bands of hazburg- the Vertiskos Formation before the Τriassiο ite.