Journal of the Geological Society, London, Vol. 146, 1989, pp. 53-59, 10 figs, 1 Table. Printed in Northern Ireland

A geophysical investigation of post-Alpine granites and Tertiary sedimentary basins in northern

F. MALTEZOU’ & M. BROOKS2 l Department of Geology, The University, Southampton S09 SNH, UK 2Department of Geology, University College, PO BOX 78, Cardiff CFl lXL, UK

Ab-& The geology of the Rhodope region of northern Greece consists of crystalline basement rocks of the Rhodope Massif in which Tertiary extensional basins and granitic intrusions of Oligocene age occur widely. Geophysical modelling has highlighted the close spatial relationship of the Tertiary sedimentary basins and post-tectonic granites of closely similar age. Geochemical data for selected granites are used to support the suggestion that there is a close genetic relationship between the episodeof granite intrusion and the tectonic development of extensional basins.

Regional geology Granitic intrusions of varying composition and age are also widespread in the Rhodope region. Bitzios et al. (1981) The Rhodope Massif is a crystalline basement area which classified theseintrusions into Pre-Alpine, Alpine and occupies a large part of southern and north-western Post-Alpinegranites. Radiometric dating of anumber of Greece and a small part of north-western Turkey (Fig. 1). Post-Alpine intrusions consistently gives an Oliogocene age Thismassif, together with theSerbomacedonian Massif, (Britzios1973; Kronberg 1974; Britzios et al. 1981; abutsthe Vardar zone and the Pelagonian and sub- Kyriakopoulos 1987). A K-Ar age of 27.9 Ma was given by Pelagonian zones of the Internal Hellenides (Marinos 1982). Kronberg (1974) forthe granite. Kyriakopoulos The western boundary of the Rhodope Massif in Greece is (1987) gave Rb-Sr ages of 31.9 f 0.5 Ma and 31.8 f 0.6 Ma delineated by the ‘Strimon line’, a major fault zone which for the same granite. The Leptokarya granite has yielded a separates it from the Serbomacedonian Massif. The surface K-Ar age of 28Ma (Bitzios1973) and Rb-Srages of geology of the Greek Rhodope region comprises crystalline 31.9 f 0.5 Ma and 31.8 f 0.6 Ma (Kyriakopoulos 1987). The basementrocks of theRhodope Massif,which are of age of the Philippi granite (Fig. 2) is given by Bitzios et al. uncertain age,the MesozoicCircum-Rhodope Belt and a (1981) as28Ma. For the Maronia monzodiorite, in the number of Tertiary sedimentary basins. Granitic intrusions eastern part of the Rhodope region (not shown in Fig. 2), a occur widely throughout the area. Ultramafic rocks are also Rb-Sr age of 29.8 f 1.3 or 28.9 f 0.1 Ma (Kyriakopoulos present in the Eastern Rhodope region. 1987) tends to discount the Mid-Miocene age given on the Themetamorphic basement of theRhodope Massif geological map of the area. Overall, a dateof approximately consists of a variety of medium- to high-grade metamorphic 28 Ma is considered to be a realistic age for many of the rocksincluding marble,granite gneiss, amphibolite and unmetamorphosed, undeformed granites. It is also possible serpentinite.In the Eastern Rhodope the metamorphic that earlier intrusive ages may have been reset by elevated basement is structurally overlain by a sequence of low-grade temperatures during the Alpine orogeny. metasedimentsand meta-igneous rocks of Mesozoic age. In addition to acid plutonic rocks, the Rhodope region Thisunit is knownas theCircum-Rhodope Belt and contains a large number of rhyolitic and rhyodacitic dykes comprises the Phyllite (orMakri) Series and the Drimou

Melia Series. The Circum-Rhodope Beltis considered to be 200 2 8O equivalent to the Peonias unit of the Vardar zone (cited in Papanikolaou 1984). Yugoslavia ’; Bulgaria The Tertiarysedimentary basins often contain interca- -42O lated volcanics of mainly acidic composition. These basins are fault-controlled and of large area1 extent. Their trends differ across the region. The Strimon and Philippi basins in the west (Fig. 2) have a NW-SE orientation, parallel to the Hellenidestructural elements. The Prinosbasin, which is the western part of the basin (Fig. 2), has a NE-SW -40° orientation cross-cutting the Hellenide elements. The above three basins areconsidered to havebeen initiated in Miocenetimes. All other major basins to the east of the Prinosbasin (-Xanthi basin, Kirki-Essimi basin, Orestiasbasin) have approximately an E-W orientation (Fig. 2) andwere initiated in Eocenetimes. A phase of Fig. 1. Main geotectonic divisionsof the Internal Hellenides and Oligocene volcanism characterizes the latter basins. adjacent areasof northern Greece. 53

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24*00' 26.00'

BULGARIA Fig. 2. Map of the Greek Rhodope region showing the main Tertiary basins and major intrusions.The Komotini-Xanthi- fault is also shown. B1, Strimon basin; B2, Philippi basin; B3, Prinos basin; B4, Nestos basin; B5, Komotini-Xanthi basin; B6, Kirki- Essimi basin; B7, Orestias basin; G1, Phillipi granite; G2, Xanthi granite; G3, Granite at the eastern flankof Nestos basin; G4, Leptokarya granite. The Komotini-Xanthi- Kavala and Avdhira faults are also shown.

and sills. These rocks, which belong the the havenot produced majorsedimentary basins in the volcanic province, are of Eocene-Oligocene age (Fytikas et Rhodope region. al. 1984) andappear tobedirectly related tothe Post-Alpine granitic rocks. Geophysical studies Geophysical data, in the form of gravity and aeromagnetic Tectonic evolution maps of theRhodope region, were made available by Theformation of earlyTertiary basins in theRhodope IGME.The regionalgravity maps areata scale of regionmight be relatedto extension in amarginal basin 1:25OOOO andare contoured at a 50 gu interval. The associated with a subduction zone earlier than the present average density of gravity observation points is approxim- subductionregime of theOuter Hellenic arc. Ithas ately one station every 3-4 km'. previouslybeen suggested that sucha subduction zone, Additionalgravity information was obtainedfrom a whereoceanic lithosphere was consumed, existed in the marineBouguer anomaly map of theNE Aegean area NorthAegean (Papazachos 1976; Papazachos & Papado- (Morelli et al. 1975). This map covers an area to the east poulos 1977; Fytikas et al. 1984) and this might therefore be and south of island (Fig. 2), up to a small distance theexplanation for the extensional basinsand associated (approximately 15 km) from the coastline of the Rhodope volcanicity of earlyTertiary age in theRhodope region. region. Thecontour interval is 100 gu andthe scale Robertson & Dixon (1984) also considered the possibility of 1:75OOOO. By merging the two datasets a homogenized separate oceanic tracts, in order to explain the magmatism gravitymap of theRhodope and NE Aegean regionwas in both the and the southern Aegean areas, pointing produced(Maltezou 1987), whichcovers an area of outthat Papavassiliou & Sideris (1982) attributedthe 30 000 km2. This map has a 50 gu contour interval, but only Tertiarylavas of westernThrace to north-eastward the 100 gu interval contours are shown in Fig. 3. subduction of Vardarian oceanic crust. DetailedBouguer anomaly maps of the Phillippiand Fytikas et al. (1984) related the early Tertiary volcanicity Nestos basin areas were also made available by IGME for to subduction of theAfrican plate beneath the Eurasian studying the individualanomalies associated with these margin.In this model, asubsequent phase of collision basins. between Eurasia and a microcontinental block at the leading Theabove data sets were used in the construction of edge of the African plate resulted in the southward jump of gravity profiles across theelongate anomalies associated the volcanicity to its present location in the arc. with the basins, which were interpreted by 2D modelling. Most information about the age of initiation of extension 3D modelling was also carried out in the case of the Philippi in eachbasin comes fromthe age of thesedimentary formations involved. The oldest sediments described in the Strimon, Prinos and Philippi basins (Fig. 2) are of Miocene age. The oldestsedimentary formations in the Komotini- Xanthibasin are of Eoceneage, whilst theMiocene is absent. In the Orestias and Kirki-Essimi basins, the Public PetroleumCorporation of Greece(DEP) and the Greek Institute of MineralExploration (IGME) boreholes show thatUpper Eocene sediments lie directly theon metamorphic basement. Neogene sediments are absent from the Orestias basin. Normal faults of early Tertiary age exist throughout the Rhodope region andbound the extensional sedimentary basins. As anexample the Komotini-Xanthi-Kavalafault (Fig. 2), whichdefines thenorthern boundaries of the Nestos basin and the Komotini-Xanthi basin, is known to haveexisted since the Eo-Oligiocene (LybCris 1984). - Eocene basins aredistributed through the eastern part of 20 km the area and are separated by a major fault zone (Avdhira Fig. 3. Bouguer anomaly gravity mapof the Rhodope fault) (Fig. 2) from the Miocenebasins in thewestern and NE Aegean area. Contour interval is 100 gu. P2,P1, Rhodoperegion. Extension has continued through the P3, P4: Profiles acrossthe Philippi, Prinos, Komotini- Neogene and Quaternary, but the later phases of extension Xanthi and Orestias basins respectively.

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24" 26"

41" 00

40"30'

Fi. 4. Aeromagnetic map of the Rhodope and NE Aegean region. Contour interval is 100 nT. Dashed line identifies the anomaly associated with the Phillippi granite reproduced in Fig. 8. M1, M2: Interpretation profiles across the Xanthi granite and Philippi granite respectively.

basin, where the detailed regional coverage of gravity data region. Table 1 summarizes the magnetic properties of the allowed this approach. two intrusions. Borehole information from the Prinos, Komotini-Xanthi The low Q valuessuggest thedominance of induced andOrestias basins was used to constrainthe gravity magnetization,and initial modelling tookno account of modelling by means of fixedbasement depths and remanentmagnetization. A more detailed interpretation, density-depthfunctions. The density-depthfunction p = considering remanent magnetization as well as induced, was p. X exp(At) (Cordell 1973), with A in the range of 0.40 to madefor the Leptokarya intrusion. The direction of the 0.45 km-', was established for the basins of the region by remanent component, for which no reliable estimate exists usinginformation from individual well logs. Aconstant due to the large scatterof the results obtained from oriented density contrast within the range of -0.35 to -0.40 Mg m-3 samples (Spais 1987), was allowed to vary. The inclination has also been used in the modelling. This range of density and declination of the NRM vector, together with the body contrasts was assumed to span reasonable estimates of the coordinates,were the variable parameters in anon-linear averagedensity contrast between the sedimentary infill of optimization interpretation (Al-Chalabi1971; James 1972) the basins andthe surrounding metamorphic rocks. The employed for this purpose. The minimization was performed models producedby using a density contrast withinthe above rangewere very similar tothose produced by assuming exponentially increasing densities. An aeromagnetic survey carried out by ABEM-Elektrisk Table 1. Magnetic properties of the Leptokarya and Xanthi granites Malmetning,Stockholm in 1966 led tothe production of aeromagneticmaps for the Rhodope region at ascale of Volume Range of NRM Koenigsberger 1: 50 OOO. These maps were used to construct profiles across susceptibility intensity ratio Q the individualaeromagnetic anomalies associated with the (W @/m) Tertiary granitic intrusions (Fig. 4). Leptokarya (38.5 f 10.4) X 106' (26 - 2259) X 10c3 0.30 f 0.13 Susceptibility andNRM intensity valuesmeasured for granite (N = 135) (N = 43) (N = 36) samples from the Leptokarya intrusion (Spais 1987) and the (42.5 6.7) X 106' (65 - 1708) X 10-' 0.15 f 0.08 Xanthi granite (this study)were found to besimilar, and Xanthi f (N = 22) (N = 20) may well be representative of all the Tertiary granites in the granite (N = 22)

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300 The results obtained from the aeromagnetic interpreta- NNW tion of the Philippi, Xanthi and Leptokarya granites reveal maximum depths to base of 5.0, 4.5 and 1.2 km respectively c CALC (Figs 5, 6 and 7), showing a progressive decrease in granite thickness from west to east. These results were obtained by 2D modellingexcept in the case of the Philippigranite where the shape of the anomalydoes not justify suchan approach. A 3Dinterpretation modelobtained by the method of Talwani (1965) for this anomaly (Fig. 8) is shown in Fig. 6. It appears that all these intrusions have the form of sheet-like or laccolithic bodies.

Discussion

Distance (km) Granite batholiths may extend down to about one third of - theaverage thickness of the crust(Pitcher 1979). Leake pE -Il-.c_i (1978) notedthat there is tendency a forgravity interpretation to favourrather thin granites, but he P speculated that suchgeometries possibly result fromthe g 1.2 transportation of magma laterally, when upward motion of Fig. 5. Interpretation model for the Leptokarya intrusion produced blobsand pipes of magma is arrestedin the more rigid by non-linear optimization modelling. k = 38.5 X W3SI, NRM = upper crust. This 'transportation geometry' rather than the 620 X 10-3 A/m, I = - 23', D = 1.56'. 'consolidationgeometry' explains the outward-sloping contactsexhibited by most exposed granites. The conven- by accessing the program MINUIT installed on the CFUY tional model of bubble consolidation would require inward computer of the University of London Computer Centre. A sloping contacts to be more common. The geometriesof the range of possiblesolutions for the body geometry, all Rhodope granites revealed by the aeromagnetic interpreta- similar, was obtained by this method (Fig. 5). tion (Figs 5, 6 and 7) could therefore be interpreted toresult

41010'

Fig. 6. Interpretation model for the Philippi granite and calculated anomaly. The model ,oo56, consists of a number of prisms, the depth to the 24'

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800i - - OBS G 600. b 0 CALC OB’ 2 400. -

.-100

- -150

.-200

Distance (., km ) 10 20 3p 40 Fig. 7. Combined interpretation h oo , E 2. models of the Xanthi granite Y (magnetics, crosses) and the 4. r” Komotini-Xanthi basin (gravity, P 6. dots). k = X 10-3 SI, p = 9) 38.5 0 -0.40 Mg m-3.

from magma rising and spreading out at a common shallow This is anuncertain estimate because of theabsence of level in the crust (butsee later discussion). There are no borehole information or other control of the modelling. The gravityanomalies associated with the Tertiary granites. maximumthickness in thePrinos, Komotini-Xanthiand Densitymeasurements revealed similar densities between Orestiasbasins (Fig. 2) was found, by 2D modelling the granites and their surrounding metamorphic rocks. As constrained by boreholeinformation, to be 4.5, 2.8 and anexample, the average density obtained from measure- 2.0 km respectively. ments onsamples from theLeptokarya granite is Superposition of the gravity interpretation model of the 2.73 Mgni3, identicalwith the average density value of Komotini-Xanthi basin on the aeromagnetic interpretation 2.75 Mg m-3 found for basement rocks (leucocratic augen model of theXanthi granite emphasizes the closespatial gneiss andbiotite gneiss) from the same area (Maltezou relationship between these geological units of closely similar 1987). age (Fig. 7). In the case of the Kirki-Essimi basin (Eocene) Modelling of residual gravity anomalies associated with and the Leptokarya granite (Oligocene) (Fig. 2), the basin majorTertiary sedimentary basins in theRhodope region fill is thin (only 2.50111 of sediments were found by drilling, has produced estimates of the shape and thickness of each cited in Innocenti et al. 1984) and does not give rise to a basin. The maximum thickness in the Phillipi basin (Fig. 2) pronouncedgravity anomaly. A representativemodel was found, by 3D modelling, to be approximately 5.0 km. producedalong a profile running SSE-NNW across the Leptokaryaintrusion is shown in Fig. 5, suggesting the continuation of the granite under the basinto the south. The surface geology in the area of the Orestias basin does not indicate the presence of a granite, but drilling has revealed Oligocene volcanics at depth. The common characteristics of the above threebasins are their age of initiation (Eocene) and their close association with Oliogocenegranites and/or contemporaneous volcanics. The area occupied by the aeromagnetic anomaly of the Oligocene Philippi granite (Fig. 8) is shown in Fig. 2 and a 3D interpretation model is shown in Fig. 6. It appears that the granite, although it has a small surface outcrop, occupies a large volume immediately below the basin fill (of Miocene age). The Miocene Nestos basin is similarly associated with an earlier Tertiary granite on its eastern flank (Fig. 2), although modellinghas not been carried outto reveal the exact relationship. The closeassociation, in time and space, of Eocene- Miocenebasins andOligocene granites and volcanics suggests thatthe emplacement of thesepost-tectonic granites and the formation of the basins may be intimately related within the same overall crustal extensional regime. Inconsidering the possibility of acausal link between Fig. 8. Aeromagnetic anomalyof the Phillippi granite. Contour extensional tectonics and the emplacement of granites at a intervale is 100 nT. high crustal level, twounresolved problems of Rhodope

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regionalgeology arehighlighted. Firstly, if theearly Tertiarygranites were emplaced above the brittle-ductile 0.5 8 Leptokarya granite transitiontheir intrusion could not have been accommod- 00 Xanthi granite ated by ductiledeformation in thesurrounding envelope (e.g. by ballooning) but must, rather, have been accompanied by large-scalebrittle deformation.Detailed geological mapping aroundthe peripheries of unroofedgranites is - required to investigate in detailthe actual nature of the E intrusionmechanism. Secondly, theunroofing of early + 0.0 Tertiary granites implies subsequent localized crustal uplift with an amplitude of at least a few kilometres and this is 3z \ difficult to reconcilewith modela of simplecrustal Y extension. Moreover, some of this crustal uplift appears to am 0 be Miocene in age, synchronous with episodesof subsidence v ’\ e. in theStrimon, Philippi andPrinos basins. The overall 8. tectonic regime therefore seems to have been similar to that -0” - 0.5 which characterizespresent-day mainland Greece, with localized zones of major subsidence separated by interven- ing zones of major uplift. Hence the uplift and unroofing of the young granites of Rhodope maybe attributableto crustal mechanisms that are operativein the Aegean domain at the present day. In pursuance of the idea of a common tectonic regime -1.0 for the basins and granites, some limited trace element data55 45 65 75 from the Leptokarya and Xanthi granites have been used wt% SiO, to determineto the likely tectonicsetting of granite emplacement.Pearce et al.’s (1984) methodindicates a Fig. 10. A discriminant plot to separate calc-alkaline from alkaline volcanic arc environment for both granites (Fig. 9). Major suites (Brown 1981). Open circles and solid squares, data from Kyriakopoulos (1987);solid circles, data from Christophidis (1977). element analysis of geochemical data (Kyriakopoulos 1987; Christophidis 1977 and this study) were used to characterize the magmatic character of the Oliogocene granites (Xanthi Themetaluminous character is suggested by the negative andLeptokarya granites) and contemporaneous volcanics. values of the quantity A1 - (K + Na + 2Ca) obtained on These belong mostly to the calc-alkaline suite (Brown 1981) samples from both granites. Such granites (calc-alkaline and andare metaluminous (Debon & LeFort 1983). A dis- metaluminous) may have been intruded into a volcanic arc criminant plot to separate calc-alkaline from alkaline suites setting(Pearce et al. 1984) ora within-plate attenuated is shown in Fig. 10 for the Leptokarya and Xanthi granites. continentallithosphere setting. The closespatial and temporalrelationship between the development of the Tertiarybasins and the intrusion of thegranites together with the presence of contemporaneous volcanics within the 1000 basinsthemselves is particularlysuggestive of thelatter environment. The Miocene basins in the western part of the region are alsorelated in space with post-Alpinegranites, which appear to be older than thebasin fill. These granites belong 100 to the same group as the Oligocene intrusionsin the east but a differenta explanation is neededfortheir tectonic E n relationship to the Miocene basins. The available informa- n tion is not sufficient to establish thenature of this relationship and further studies are required. The model of P the Philippigranite (Fig. 6) suggestsa shallow depthto = 10 base, whichis alsoa common feature of theXanthi and Leptokarya granites in the eastern part of the area. Thereare interesting points of similaritybetween the Rhodope granites and the post-orogenic granites described from south Greenland (Bridgwater et al. 1974). The latter are high-level intrusions which, also, have a sheet-like form 1 (from 0.5-5.0 kmthick) and are associated with contem- 1 100010 100 poraneoussedimentary basins which sometimesinvolve Y+Nb ppm volcanicity, but of alkaline character. Apossible analogue tothe Rhodope basins(Levi & Fig. 9. Rb - (Y + Nb) discriminant diagram for the Leptokarya (0) Aguirre 1981) mightbe that of the volcano-sedimentary and Xanthi (0)granites. VAC, volcanic arc granites,ORG, basins in Central Chile initiated in the Jurassicin a tensional Ocean ridge granites, WPG, within-plate granites;COLG, at- regime thatpersisted to end-Mesozoictimes following tenuated continental lithosphere granites. subduction of an oceanic plate below a continental margin.

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Shallow marine to continental sediments and large quanti- INNOCENTI,F., KOLIOS,N., MENETTI,P,, MAZZVOLI,R., PECCERILLO,G., ties of calc-alkalineacid andintermediate volcanicswere REA, F. & VILLARI,1. 1984. Evolution and geodynamic significance of depositedwithin NNW-elongated basins, bordered by the Tertiary orogenicvolcanism in Northeastern Greece. Bulletin Volcanologique, 17(1), 25-37. Palaeozoic (pre-Andean) basement. Shallow to very shallow JAMES,F. 1972. Function minimization. Report of the European orgaization calc-alkalinegranitic bodies were intrudedduring the for nuclear research. CERN, Geneva, Switzerland. Jurassic to Palaeogene. It appears that the development of KRONBERG,P. 1974. l :500Wgeological map. Krinidhes sheet. IGME Athens. the basins and the emplacement of the intrusions took place KRYIAKOPOULOS,K. 1987. Geochronological, geochemical and mineralogical study of some Tertiary plutonic rocks of the Rhodope massif and their during thesame extensional regime, under the coupled isotopic characteristics. PhD thesis, University of Athens. action of plate subduction and spreading-subsidence. This is LEAKE,B. E. 1978. Granite emplacement: the granites of Ireland and their a possibility which must be investigated in the case of the origin. In: BOWES,D. R. & LEAKE,B. E. (eds) Cmtal evolution in Rhodope basins. northwestern Britain and adjacent regions, 221-248. LEVI,B. & AGUIRE,L. 1981. Ensialic spreadingsubsidence in the Mesozoic This study reveals the sheet-like form of the Oliogocene andPalaeogene Andes of central Chile. Journal of fhe Geological granitesin the Rhodope region andpostulates a close Society, London, 138, 75-81. genetic relationship between the episode of granite intrusion LYBERIS,N. 1984. Tectonic evolution of the north Aegean trough. In: DIXON, and the tectonic development of the contiguous extensional J. E. & ROBERTSON,A. H. F. (eds) The geological evolution of the Eastern Mediterrean. GeologicalSociety, London, Special Publication, basins. Further geological investigations, including detailed 17, 709-25. mapping, are required to establish the detailed natureof this MALTEZOU,F., 1987. Gravity and magnetic studies of the Rhodope region, NE relationship. Greece. PhD thesis, University of Southampton. MARINOS,G., 1982. Southeast Europe. In: DUNNING, F. W. MYKURA,W. & Wewish to thankthe Director General of IGME, Athens, C. SLATER,D. (eds) Mineral deposits of Europe. IMMand Mineralogical Papavassiliouand R. W.Nesbitt for their help in obtaining the Society, London, 233-53. gravity and aeromagnetic data. Fotini Maltezou thanks N. Hamilton MORELLI,C., PISANI, M. & GANTAR,C. 1975.Geophysical studies in the for helpful discussions and I. Croudace and S. Kalogeropoulos for AegeanSea and in the Eastern Mediterranean. Bolletino Geojisika Teorica and Applicata, 18, 127-68. their help in the geochemical interpretation. Data collection trips to PAPANIKOLAOU,1984. D. The three metamorphic belts of the Hellenides: a Greecewere funded bythe Commission of theEuropean review and a kinematic interpretation. In: DIXON,J. E. & ROBERTSON, Communities (EEC Project No 124 UK). A. H. F. (eds) The geological evolution of the Eastern Mediterranean. Geological Society, London, Special Publication, 17, 551-61. PAPAVASSILIOU,C. T. & SIDERIS,C. 1982. Geochemistry and mineralogy of References Tertiary lavas of Sappai-Ferrai area (W. Thrace), Greece. Implications AL-CHALABI,M. 1971. Some studies relating to non-uniqueness in gravity and on their origin. In: DIXON,J. E. & ROBERTSON,A. H. F. (eds). The magnetic inverse problems. Geophysics, 36, 835-55. Geological Evolution of the Eastern Mediterrean, Abstracts, Edinburgh, Bm~os,D. 1973. La geologie et metallogenie de la region de Kirki (Thrace 1982, 85. Occidentale-Greece). PhD thesis, University of Pans VI. PAPAZACHOS,B. C. 1976. Evidence of crustal shortening in the North Aegean -, CONSTANTINIDES,C., DIMADIS, E., DEMETRIADES,A., KATIRTZOCLOU, region. Bolletino Geojisika Teorica and Applicata, 19, 66-71. C. & ZACHOS,S. 1981. Mixed sulphide mineralization of the Greek - & PAPADOPOULOS,G. A. 1977. Deep tectonlc andassoclated ore Rhodope. Report forthe Greek-Soviet scienttj5c cooperation in the field of deposits in the Aegean area. In: KALLERGIS, G. (ed.) Proceedings of the geology. IGME, Athens. VI Colloquim on the Geology of the Aegean Region, 2, 1071-81. BRIDGWATER,D., SUITON, J. & WATTERSON,J. 1974. Crustal downfolding F’EARCE,J. A.,HARRIS, N. B. W. & TINDLE,A. G. 1984. Trace element associated with igneous activity. Tectonophysics, 21, 57-77. discriminationdiagrams for tectonic interpretation of graniticrocks. BROWN,G. C. 1981.Space and time in granite plutonism. Philosphical Journal of Petrology, 25(4), 956-83. Transactions of the Royal Society, London, AM1, 321-36. PITCHER,W. S. 1979. The nature, ascentand emplacement of granitic CORDELL,L.1973. Gravity analysis using an exponential density-depth magmas. Journal of the Geological Society, London, 136,627-62. functionSan Janito graben, California. Geophysics, 38, 684-90. ROBERTSON,A. H. F. & DIXON,J. E. 1984. Introduction: aspects of the CHRISTOPHIDIS,G. 1977. Contribution in the investigation of plutonic rocks of geologicalevolution of the Eastern Mediterrean: In: DIXON,J. E. & the Xanthi area. PhD thesis, University of Thessaloniki. ROBERTSON,A. H. F. (eds) The geological evolution ofthe Eastern DEBON,F. & LE FORT,P. 1983. A chemical-mineralogicalclassification of Mediterrean. Geological Society, London, Special Publication, 17, 1-74. common plutonic rocksand associations. Transactions of the Royal SPAIS,C. 1987. Palaeomagnetic and magnetic fabric investigations of Tertiary Society of Edinburgh, Earth Sciences, 73, 135-49. rocks from the Alexandroupolisarea, N.E. Greece. PhD thesis, FYTIKAS,M,, INNOCENTI, F., MANNEITI,P., MAZZUOLI,R., PECCERILLO,A. & University of Southampton. VILLARI,L. 1984. Tertiary to Quaternary evolution of volcanism in the TALWANI,M.1965. Computation with the help of a digital computer of Aegean region. In: DIXON,J. E. & ROBERTSON,A. H. F. (eds) The magnetic anomalies caused by bodies of arbitrary shape. Geophysics, 30, geological evolution of the Eastern Mediterranean. Geological Society, 797-817. London Special Publication, 17, 687-99.

Received 7 May 1987; revised typescript accepted 14 July 1988.

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