Ultramafic rocks of the Eastern Alps represent slices of suboceanic or subcontinental mantle tectonically incorporated into the orogenic belt. These comprise: 1) Ultramafics of the Stubach and Habach Groups are part of the Prealpine Penninic domain (Tauern Window). 2) The Speik complex represents a dismembered early Paleozoic (?) ophiolite complex within the Austroalpine Crystalline basement (Styria). 3) Serpentinites in the Mesozoic Cover units of the Penninic realm (Tauern & Engadin Windows) and the Austroalpine basement (Reckner Complex).Geochemical and petrological investigations reveal considerable differences between these mantle slices, e.g. concerning the degree of partial melting and metamorphic history .The primary silicate assemblages of the peridotites have been mostly replaced by metamorphic parageneses as a result of regional metamorphism and serpentinization. Ultramafics of the Stubach Group (1) are dunites, harzburgites, wehrlites and websterites. They are moderately depleted in magmaphile elements (Al2O3 up to 2.8 wt.% in pyroxenites). In spite of the significant modal amounts, up to 70%, of clinopyroxene (the main carrier of REE), the HREE abundances (0.1 times chondrite) reflect high degrees of melt depletion. Therefore pyroxenite layers are interpreted as small scale mantle segregations and do not represent ultramafic cumulates. Most of the samples show LREE metasomatism to variable degrees. REE distributions of associated metabasaltic rocks define flat MORB-type patterns. All these data call for remnants of oceanic crust generated in a spreading center.The dominant rock types of the Speik Complex (2) are dunites and harzburgites. Boudinaged layers and crosscutting stocks of olivine-orthopyroxenites are noteworthy. The strongly depleted character of all samples is confirmed by relatively low Al2O3- and CaO-contents (<1 wt.%) and generally low REE abundances (0.01-0.1 times chondrite). Several samples have U-shaped patterns and characteristics of residual harzburgites and dunites that have been re-enriched in LREE during a second melting event. Mafic and ultramafic cumulates as well as the presence of fertile peridotites underline the heterogeneous character of the Speik Complex. Trace elements from associated mafic rocks display island-arc-type signatures. High PGE-contents and scattering 187Os/188Os values from podiform chromitites suggest a subduction-related origin.In contrast fertile lherzolites and harzburgites are characteristic of the Mesozoic Cover units (3). The high abundances of Al2O3 (up to 4.6 wt.%) and TiO2 (up to 0.22 wt.%) are generally consistent with estimates of primitive mantle.The samples display high HREE concentrations (up to 2.5 times chondrite) and a significant LREE depletion. Similar REE patterns are common in undepleted subcontinental spinel lherzolites from pre-oceanic rifts. Mesozoic samples from the Eastern Alpine nappes as well from the Penninic domain show the same geochemical features and may represent similar subcontinental mantle material. This project is funded by the Austrian Science Foundation (P12323-CHE).
Mesozoic blueschist facies rocks occur along two east-west trending suture zones (the Meliata unit and the Pieniny Klippen Belt) in the Western Carpathians. According to geochemical and petrological characteristics, the blueschist were formed by subduction of geological units different in geotectonic positions. The Meliata unit contains blueschist facies marbles, quartz phyllites, metabasites and older amphibolite facies rocks. Ultramafic rocks, radiolarites and charts, representing oceanic crust material are known from this unit, but they are unmetamorphosed or indicate very low-grade conditions. Most of the blueschist facies rocks were derived from continental crust material, which are represented by basement rocks and shallow-water clastic sediments of continental margin. Small amounts of basaltic rocks that are intercalated in marbles have composition between Arc-MORB basalts and show enrichment of LREE. Composition of primary amphibole of richterite composition and REE distribution in metagabbro, found as slices in evaporite melange, have affinity with alkaline rocks. In contrast to the Meliata unit, the Klippen Belt blueschists, which occur as pebbles in conglomerates, reveal typical N-MORB composition and have flat REE distribution.
There is no significant difference in metamorphic conditions between the Meliata and Klippen Belt blueschist facies rocks. In both cases pressure and temperature were about 1.2 GPa and 460. Typical blueschist facies minerals are glaucophane, phengite and sodic clinopyroxene of jadeite, omphacite and aegirine composition. Mineral assemblages in metabasites from the Meliata unit indicate an early low-pressure assemblage (< 0.5 GPa at 350°C), characterized by muscovite and zoisite followed by high-pressure glaucophane, phengite, Na-pyroxene, chlorite and clinozoisite, indicating pressures of > 1.2 GPa at 450°C. Ar-Ar age from phengitic white mica in the Meliata unit and from glaucophane in the Klippen Belt indicated Middle Jurassic age of high-pressure metamorphism, however early Jurassic to late Triassic ages for phengite in the Meliata unit were obtained as well. Differences in lithology and geochemical composition of blueschist facies rocks suggest that source of pebbles in the Klippen Belt was a terrain different from that exposed in the Meliata unit.
Hungary is essentially a huge low-lying basin, encircled by the mountains of the Carpathians to the north and east, the Eastern Alps to the west, and the Dinarides to the south. The tectonic and magmatic evolution of this country reflects its position in the Intra-Carpathian Area (ICA). The ICA, with its three major blocks Alcapa, Tisza, and Dacia, shows a very complex tectonic structure and various temporal magmatic associations that has been formed before the Cenozoic and then juxtaposed afterwards by large lateral displacements (Csontos et al., 1992; Harangi et al., 1996). One of the most eminent expression of those Cenozoic tectonic events, was certainly the eastward escape of the Alcapa block from the compressive Alpine area (Csontos et al., 1992). On the other hand, some ophiolites or ophiolitic-like bodies situated within the ICA delineate decisive stages of the Mesozoic magmatic evolution of the northwestern part of the Tethys, as in the case of the rise and fate of the prominent Vardar ocean.
Ophiolites are thought to represent a section through the oceanic lithosphere. The current interpretation coming from petrological studies is that ophiolites have formed either in mid-ocean ridge-like environments, or formed above subduction zones (Elthon, 1991; Pearce, 1991; Searle, 1992; Taylor et al., 1992). An increasing number of supra subduction zone ophiolites have been assigned to various ophiolites worldwide. This assignment is based especially on geochemical grounds, which often show elemental anomalies in lavas and gabbros of ophiolite complexes.
In this work we examine and review the geochemistry of the magmatic rocks of the Szarvaskö complex. Situated in the SW Bükk Mountains and occupying an area of about 8 km long and 3 km wide, this complex forms one of the largest Jurassic mafic bodies within the Carpathian chain. The main objectives of the study are to constraint the long-standing problem of the petrologic controls on the Szarvaskö magmatism, to delineate the nature of the Szarvaskö crust giving insight into the magma sources, and to compare the complex with other ancient and modern oceanic analogues. Since ocean magmatism in the ICA is related to the opening, subduction, and reopening of the oceanic branch of the NW-Tethys, their mantle sources should be not unique. Accordingly, the study of these igneous rocks provide an opportunity to evaluate the geochemistry characteristics of an ophiolite originated along an ocean ridge behind a subduction zone.
Csontos L, Nagymarosy A, Horváth F & Kovác, M, Tectonophysics, 208, 221-241, (1992).
Elthon D, Nature, 354, 140-143, (1991).
Harangi S, Szabó C, Józsa S, Szoldán Z, Arva-Sos E, Balla M & Kubovics I, International Geology, 38, 336-360, (1996).
Pearce J, Nature, 354, 110-111, (1991).
Searle RC, Geological Society Special Publication, 60, 65-79, (1992).
Taylor RN, Murton BJ & Nesbitt RW, Geological Society Special Publication, 60, 117-132, (1992).
In the area of Thrace, Greece the incomplete and dismembered ophiolite of Evros has been developed in the upper stratigraphic levels of the Circum-Rhodope Belt. Its age, although not clearly defined, is considered to be of Jurassic to Lower Cretaceous. The geotectonic setting of the ophiolite was a volcanic arc-marginal basin system in the Palaeotethyan oceanic realm (Magganas et al., 1991).
The ophiolitic rocks have been involved to deformation and low grade metamorphic events during and after their emplacement. In the uppermost level of the ophiolitic sequence massive and pillow lavas and few pyroclastics are found. These lavas were also extensively recrystallized to metavolcanics by ocean floor metamorphism. The protoliths of the metavolcanics have been affected from complex differentiation procedures, as that implied from their geochemistry and primary mineralogical constituents.
Both subducted and obducted slabs were parts of the Vardar micro-ocean. Aqueous fluids from the sediment carrying subducted slab reduced the melting point of the heterogeneous mantle wedge and caused its partial melting, during their diapiric ascent. The protoliths of the metavolcanics produced by about 30% partial melting of an already depleted mantle source in a place close to the trench. The composition of this newly formed high-depleted magma was of boninitic type and generated at low pressure (about 7 - 8 kbars) and temperature of 1200 - 1300°C.
REE data suggest that the primary magma on route to the surface by diapiric uplift underwent open system fractional crystallization in pressures 2 to 3 kbars lower than the pressure of the partial melting. Tholeiitic basalts and mainly basaltic andesites to andesites were formed at the initial stages of the differentiation by crystal fractionation, which involved olivine, Cr-spinel, clinopyroxene and occasionally plagioclase. Some of these minerals may have been crystallized into the upper mantle. Subordinate dacites and rhyolites were created when plagioclase became the main fractionated phase. The oxygen fugasity remained nearly stable during the formation of the main volume of the rock association, but it notably changed when rhyolitic rocks started to crystallize. The viscosity of the pillow-lavas was greater than that of the massive lavas. In opposite, the cooling rate of the pillows was faster.
Magganas A, Sideris C & Kokkinakis A, Mineralogy & Petrology, 44, 235-252, (1991).
New data obtained from the three tectonic zones of the Vardar previously defined by Mercier (1968) (i.e. from W to E the Almopias, Païkon and Peonias units) allow us to present a new scheme of the tectonic evolution of this major neotethyan remnant.Rifting began in the early-middle Triassic in all this realm. It was followed by oceanisation in the W (Almopias) during upper Triassic to lower Jurassic responsible for a wide track of the tethys ocean. Probably by upper-mid Jurassic an East dipping subduction began in the western ocean, being responsible for the creation of the calc-alcaline insular arc and the opening of the narrow "oceanic" back arc bassin of Peonias. By the end of Jurassic, huge obduction of the western part of the Almopias ocean occured onto the pelagonian microcontinent leaving part of it as a deep basin floored with oceanic crust. At the same time, volcanism ceased in the Païkon arc and the eastern oceanic crust was locally obducted to the E onto the Serbo-macedonian. During the Cretaceous strike-slips occured and the carbonate platform of the Païkon subsided (upper Cretaceous). Then in the earliest tertiary, general compressional tectonics gave the present situation. The Païkon former island arc was partly "subducted" below the Peonias (Guevgeli) "ophiolite" and cut into two huge tectonic sheets. The remnants of the western Tethyan ocean was mainly thrust to the W in a number of sheets, but was also partly back-thrust onto the Païkon platform.
The eastern part of the Vardarian area in Greece comprises discontinuous Jurassic ophiolites of the Guevgueli and Chalkidiki complexes (Innermost Hellenic Ophiolite Belt or IMHOB). To the North, the Paikon Massif, which consists of thick carbonate series containing several intercalations of basic and acidic volcanic rocks, separates the Guevgueli complex from the ophiolites of the western part of the Vardarian area. The Guevgueli complex is made up of three groups of rocks. The first one corresponds to the upper part of an ophiolite and comprises gabbroic cumulates, plagiogranites, hypabyssal rocks and lavas showing a clear affinity to MORB magmatism. The second one is made up of amphibole-rich ultramafic and mafic cumulates and of magmatic breccias; the third one includes the Fanos granite and the Piyi migmatites. The amphibole-rich cumulates and the Fanos granite present calc-alkaline characteristics. Structural considerations indicate transcurrent movements in which the minimum and maximum stresses are both horizontal and strike west-northwest - east-southeast and north-northeast - south-southwest respectively. Therefore, the Guevgueli complex probably represents a backarc basin formed during the Upper Jurassic in a continental active margin affected by spreading and wrench faulting. In central Chalkidiki (between Thessaloniki and Metamorphosis), ophiolites constitute a discontinuous northwest - southeast trending belt. Along this belt, lavas are rare, whereas peridotites, pyroxenites, gabbronorites, diorites and quartz diorites are abundant. The peridotites are composed of harzburgites, dunites, and chromitites that are texturally and chemically identical to the tectonic units of most ophiolites. The cumulate sequence ranges from websterite to norite, orthopyroxene is a common cumulus phase. Hypabyssal rocks locally appear as dyke swarms: relatively high MgO- and SiO2-contents, associated with low to very low TiO2-contents in some of these dykes are typical of boninites. All these characteristics shown by central Chalkidiki ophiolites are observed in modern forearc regions.It is worth noting that boninites and low Ti-basalts, associated with dacites, are also abundant to the west of the Guevgueli complex in the Paikon massif, and are probably present in ophiolites from the western part of the Vardarian area. A model proposed to explain the petrogenesis of modern boninite suites invokes ascending diapirs caused by the propagation of a back-arc spreading system into a forearc, as a source of heat required to produce these melts from depleted, cold, H2O-bearing, metasomatized shallow mantle wedge. Duality of ophiolites in the Vardarian area could therefore testify to interactions between subduction and backarc spreading, in a region probably dominated by wrench faulting, and including both continental and oceanic areas.
Mesozoic ophiolites contribute to fundamental concepts of oceanic lithosphere genesis and emplacement (e.g. Troodos Ophiolite) and are critical to regional tectonic understanding. Two main ages of ophiolite exist: mid-Jurassic in the western region (former Yugoslavia, Albania, Greece), and Late Cretaceous in the east (Turkey, Cyprus, Syria, Iran). However, processes of ophiolite formation and emplacement are very similar throughout the orogen regardless of age (Robertson, l994). Numerous fragmentary ophiolites (e.g. Balkan region) can best be understood by reference to the best preserved examples (i.e. the Jurassic Albanian ophiolites; Shallo, l990) and Cretaceous Troodos Ophiolite; Robinson and Malpas, l990; Robertson and Xenophontos, l993) The message from the modern oceans is that the lithosphere shows greater diversity than hitherto believed. However, it appears that the East Mediterranean ophiolites are divisible into two types: mid-ocean ridge (MORB) and subduction related (SSZ), based on geochemistry, mineralogy, associated sediments and regional tectonic setting. The most intact MORB-type ophiolite is the "western" Albanian ophiolite (Shallo, l990). Fragmentary counterparts include the ophiolites in Croatia and Greece (e.g. Othris). Fragments of alkaline or MORB extrusives within melanges beneath both Jurassic ophiolites (e.g. Pindos-Vourinos, N Greece; Smith, l993) and Cretaceous ophiolites (e.g. Lycian Ophiolite, W Turkey; Baer-Bassit Ophiolite, N Syria) are interpreted as accreted fragments of oceanic crust formed during rifting-initial spreading, including seamounts and related sediments (e.g. Avdella Melange, N Greece). Otherwise, all the main Jurassic and Cretaceous ophiolites originated in subduction-related settings. The Jurassic Eastern Albanian ophiolite include chemically depleted andesitic extrusives and arc-type intrusives, and records a transition from the adjacent MORB ophiolite. The Cretaceous Troodos Ophiolite includes very depleted high-magnesian (boninite-type) lavas that appear to fingerprint SSZ settings. The ultramafics (i.e. harzburgitic) of these ophiolite are correspondingly depleted (e.g. chromites). Most of the Jurassic ophiolites (e.g. Evvia) and the Turkish Cretaceous ophiolites (e.g. Lycian, Hoyran-Beysehir, W Turkey; Guleman Ophiolite, E Turkey) survive only as harzburgitic thrust sheets, of inferred SSZ origin. Two types of subduction-related ophiolite are recognised. First, ophiolites formed in relatively small back-arc basins i.e. mid-Jurassic Guevgueli Ophiolite (N Greece); also the Late Triassic? Kure Ophiolite (Central Pontides). Secondly, there are intra-oceanic SSZ ophiolites, locally with pelagic sedimentary covers (e.g. Troodos). Such SSZ-ophiolites relate to regional plate boundary re-organisation events and may involve collapse of former spreading ridges. Most Jurassic and Cretaceous ophiolites are underlain by metamorphic soles recording overthrusting of hot, young oceanic lithosphere over marginal subduction-accretion complexes. The SSZ-type ophiolites were mainly emplaced in response to trench-margin collision. However, obduction of the Troodos Ophiolite was delayed until onset of Plio-Quaternary continental collision. Also, the Jurassic Guevgueli Ophiolite (N Greece) was intruded into a continental rift and subsequently remained in situ relative to adjacent units.
Robertson AHF, Earth Science Reviews, 37, 139-213, (1994).
Robinson PT & Malpas J, Ophiolites: Oceanic Crust Anaolgues, Cyprus Geol Surv Dept, 13-36, (l990).
Robertson AHF & Xenophontos, C, Spec Pub Geol Soc London, 70, 85-120, (l993).
Shallo, M, Kodra A & Gjata K, Ophiolites: Oceanic Crust Anaolgues, Cyprus Geol Surv Dept, 265-270, (l990).
Smith, AG, Spec Publ Geol Soc London, 76, 213-244, (l993).
The Eastern Albanide terrains characterized by the large development of the ophiolites and their continental margins offer excellent opportunities to investigate the tectonic history of Mirdita oceanic basin from its break-up to the definitive closure.
The thinning of the continental crust registered during Permian - Verfenian leads to two stages continental break-up: a. Tensions operate in a continental plate during the Anisian. They cause the installation of the small graben basins in which deposition and volcanism take place (Porphyrite-radiolarite formation), b. Starting from Ladinian and especially during T3 and J1, the break-up progressed. Basalts and associated radiolarites are largely located in the middle part of the Qerret - Miliska thin continental crust basin, which definitively separate Apulian microplate in the West from Korab - Pelagonian microcontinent in the East. This megagraben structure is named Mirdita oceanic basin. In this early stage, ultramafic manifestations, associated with eufotide gabbros are formed as well.
Oceanic spreading, followed by the installation of the intraoceanic subduction and charriage led to the formation of the huge complete and incomplete ophiolitic sequences. Isotopic and biostratigraphic (radiolarian) data on the ophiolites, their metamorphic soles and primary radiolarite cover argue a similar and very short age span: Late Bajocian to Early Callovian. During the Late Callovian and Early Malm, ophiolite massifs together with metamorphic soles and volcano-sedimentary formation are emplaced onto continental margins.
NE - SW and NW vector polarity showing the ophiolite emplacement are in contradiction with tectonic models supporting only Vardarian or Cukali (Pindi) ophiolite origin.
Toward the Late Eocene, ophiolites and their continental margins are thrusted southward on the Krasta-Cukali zone.
The ophiolitic associations within Mirdita zone show a progressive evolution from continental rifting and passive margin development to oceanic basin formation. The rifting activity developed during T3-J1 produced volcanics, mantle peridotites and sedimentary rocks. The volcanism is documented by the extrusions of a range of within plate basalts, transitional and mainly of mid-ocean ridge basic volcanics. Two types of mantle ultramafics are distinguished: a.) Marginal peridotites within carbonate margins represented of cpx-rich spinel harzburgites and lherzolites. Their sp facies contain high concentrations of Na2O in cpx (0,45-1,35%), b) Preoceanic rift peridotites in small massifs, relatively rich in cpx and their spinel bearing associations. The cpx is characterized by high content of fusible components. Interesting spinel pyroxenites and garnet pyroxenite facies are found in the contact of this peridotites and the Western ophiolite belt.
The early spreading stage produced incomplete MOR-type ophiolites. Later, during the oceanic extension, the intraoceanic subduction occurred. On its top, the forearc spreading centers seems to be installed. Huge and complete ophiolite sequences (Eastern ophiolite belt) are formed. These ophiolites are composite in origin. They have components that are both MOR and SSZ related. Complex intrusive relations in plutonic units and intermittent magmatic activities are characteristic. IAT and MORB type magmatic series are recognized. Several dike generations of IAT, MORB affinity and Boninites are distinguished. The extrusives show a mixing nature as well. In the Easternmost parts of the Western belt ophiolites, MORB-type crust is intruded by the products of later subducted-related magmatism (boninites etc.) Late intrusions are largely developed. Contractional deformation led to the intraoceanic displacement and the formation of granulite, amphibolite and green schist facies. The ophiolites are set also on the volcano-sedimentary formation and the metamorphic soles are formed. To the closing stage belong the trachyte-rhyolite volcanism. Small diorite intrusions of the collision type cut the Westernmost areas of ophiolites as well. This moment shows the end of ophiolitc magmatism from its onset to oceanic crust continental emplacement.
F04 : 4A/13 : F6
In the Dinaride-Hellenide realm Mesozoic Jurassic ophiolites form a large belt ranging from former Yugoslavia across Albania to Greece. Conventionally they are divided into a western belt and an eastern belt bordering the Serbo-Macedonian massif and ranging from Central Serbia across the Vardar zone to Northern Greece (Smith, 1993). It is called Vardar or Axios zone. The western belt, often termed Mirdita or Pindos zone, is in turn divided into two zones with different geology, lithology and geochemistry. Both belts, which are situated E and W of the Pelagonian and Drina-Ivanica Massifs resp., or at least some of their segments were thought to be characterized in their ultramafic portion either by harzburgite (eastern belt and central to southern part of the western belt) or lherzolite (western belt N of the Scutari - Pec line).
More recent studies on Albanian ophiolites however, suggested a separation of the western belt into a western lherzolite bearing and a eastern harzburgite bearing zone each with a characteristic ophiolite sequence (Shallo, 1992). This separation is not only indicated by the lithology but also by the geochemistry of basalts (Bortolli et al, 1996). The former are dominated by MORB characteristics, the latter show affinities to SSZ or island arc volcanics. Further to the south the separation of the western belt vanishes and no distinction can be made any more between the western and eastern zone, instead geological profiles across the ophiolites contains elements of both zones.
Obviously there is a wide variety in lithology and geochemistry of the ophiolite across and along strike over the whole western belt from southern Croatia to central Greece. The variation within the western belt is probably as large as between the western and the eastern belts. The same mid-to upper Jurassic formation age, the occurrence of metamorphic soles and comparable sediments on top indicate a common formation and emplacement history.
Bortolotti Vet al, Ofioliti, 21, 3-20, (1996).
Shallo M, Geol. Rdsch, 81, 681-692, (1992).
Smith AG, Geol. Soc. Spec. Pub, 76, 213-243, (1993).
The Albanian ophiolites outcrop in the Mirdita zone and extend southward in the Sub-Pelagonian zone (Hellenides) and Northward in the Serbian zone (Dinarides). They consist of two NNW-SSE trending belts, showing East-West and North-South diversities. Two types of metamorphic rocks are distinguished in the ophiolitic domain: metamorphic soles and intra-ophiolitic metamorphics. The first type is developed at the base of ophiolites, at the contact with a volcano-detritic series which in turn overlains a sedimentary platform. The sole rocks are less than 700 m in thickness, strongly deformed and disturbed by late faulting. The protolith of this sole is likely to be a volcano-sedimentary series made of N-MORB basalts and sediments derived from the continental margin, probably contaminated by biogenic sediments (radiolarians). These soles display an inverted metamorphic gradient that evolves from amphibolite (rarely granulite) facies at the top decreasing to greenchist facies at the bottom. The maximum pressure-temperature conditions calculated for the granulite facies rocks are close to 800-850°C for 1 Gpa. Twenty 40Ar/39Ar dates have been obtained on mineral separates and single grains from this sole. The ages vary from 160 to 174 Ma, corresponding to middle Jurassic (Bajocian-Bathonian). Ages are younger in the North than in the South, with an age difference of 14 Ma along strike.The second type of metamorphics (intra-ophiolitic) is mostly developed in the Northern ophiolite massifs. They are located in the upper ophiolitic sequence, between the intrusive formations (troctolite, gabbro) and the volcanics. They only consist of amphibolites and amphibolitic schists, unlike the metamorphic soles which offer more diversified assemblages. The maximum pressure-temperature conditions are in the range 500-600°C and < 0,4 GPa. Geochimical characteristics and relic textures suggest that the protolith of these rocks are the volcanics of the ophiolitic complex. Due to their low K content, 40Ar/39Ar ages from these metamorphics are not well constrained. However, they do not appear to be significantly older than the sole ages. The development of these metamorphic rocks units is controlled by different processes. Metamorphic soles were formed during the closure of the ophiolitic basin through the succession of two events, first by burying along the subduction zone and then by intra-oceanic thrusting. The formation of intra-ophiolitic metamorphics is likely to be related with dynamic and hydrothermal activity during oceanisation. In this respect, the different types of metamorphic rocks in the Mirdita zone record the following phases of ophiolitic evolution: oceanisation (opening), subduction and intra-oceanic thrusting (shortening), before final obduction and collision. 40Ar/39Ar data suggest that these events occurred within a short time interval.
Eastern Mediterranean ophiolites form three principal belts, the Jurassic western Dinaride-Hellenide complexes, the Jurassic-Cretaceous bodies in eastern Greece and central Turkey, and the late Cretaceous occurrences of southern Turkey, Cyprus and further east. Many complete ophiolite sequences are prime examples of the "ophiolite conundrum"geochemical compositions similar to present-day "supra-subduction zone" settings contrasted with stratigraphic and structural evidence of formation at an oceanic spreading center well separated from an island arc.
Mantle isotopic analyses suggest that km-scale mantle compositional inhomogeneities are widespread and can last for 100's to 1000's of m.y. Ophiolite-producing melts may arise from previously subducted mantle, but there is no a priori need to invoke active subduction during melting. The composition of magmas at spreading centers depends upon a complex tectonic history lasting millions of years.
Mantle seismic tomography, isotopic signatures of mid-ocean ridge and oceanic island basalts, and the mantle geothermal budget together suggest a model of compositional stratification in the deep mantle, wherein a deep layer of more dense, undepleted mantle, up to 1000 km thick, underlies an upper depleted zone of mantle that includes source regions for normal mid-ocean ridge basalts and more depleted magmas found in both supra-subduction and mid-oceanic environments. The boundary between these layers is located at approximately 2000 km depth, but there is likely large scale topography (100 km to 1000 km) on this interface. Some slabs penetrate nearly to the core-mantle boundary. Dynamical models show that subducting slabs deflect a compositional boundary by an amount depending on both the age of the slab and the density gradient across the interface. As the density difference is slight, the topography on the interface will be large. Major episodes of subduction, e.g. supercontinent formation, would depress the interface in some regions, causing it to rise elsewhere. Mantle plumes may arise from these high points on the interface. Thus the dynamics of the deep interior of the mantle are integrally linked to surface geology.
Compositional differences between many eastern Mediterranean ophiolites and standard mid-oceanic ridge lavas may result from a "suprasubduction" environment of ophiolite formation; from continued spreading during conversion of ridge-parallel or ridge-perpendicular faults to incipient subduction zones (intraoceanic thrusts) during plate motion changes leading to ophiolite emplacement; or from differences through time in composition of mantle source regions of mid-oceanic spreading center lavas. As strict uniformitarianism clearly does not apply to patterns of continental assembly and fragmentation, so it need not apply to the composition of mantle source regions for oceanic spreading centers through time. Geochemical indicators need to be used integrally with geologic information to obtain the most robust tectonic interpretation of a given ophiolite. Eastern Mediterraneal ophiolites may have formed from mantle previously subducted during Hercynian and/or Pan-African times.
Despite their status as some of the world's largest and best-exposed ophiolites, the ophiolites of the Eastern Mediterranean remain enigmatic in terms of their tectonic settings of formation. Recent detailed land- and ocean-based studies of the Western Pacific have, however, revealed some good analogues in terms of both geochemistry and crustal structure. The two most significant are:
1. Subduction initiation terranes. The present-day subduction system initiated in the Eocene throughout the Western Pacific from Japan to Tonga, possibly as a consequence of the India-Tibet collision. It led to the formation of a complex 'protoarc terrane' containing two types of lithosphere. One is post-initiation oceanic lithosphere of boninite and island arc tholeiite composition. The other is pre-initiation lithosphere of mid-ocean ridge composition, commonly strongly attenuated. Magma of boninite and island arc tholeiite composition subsequently invaded and erupted onto both types of lithosphere to produce island arc volcanic edifices.
2. Ridge-trench intersections. These are common at the ends of subduction systems, such as Vanuatu, Tonga and the Marianas, where back-arc basin spreading centres intersect the trench or its transform continuation. They are characterised by oceanic-type crust with an island arc tholeiite to boninite composition. Slab retreat can cause mantle from outside the subduction zone to be 'sucked into' the mantle wedge in these areas. If this mantle has a plume influence, as in North Tonga, the volcanic rocks may contain a distinctive plume component in their geochemistry.
In the Eastern Mediterranean, both the Jurassic and Cretaceous ophiolite belts contain complexes that are contemporaneous with plate reorganisations linked to episodes of Atlantic break-up, and thus could have been formed by processes associated with subduction initiation. Thus, similarities to the Western Pacific Eocene protoarc terrane may be expected. Of the Jurassic ophiolite belt, the complexes from Albania through Greece show many similarities with the Eocene terranes of the Izu-Bonin-Mariana region. The Pindos ophiolite may be a type example with its complex juxtaposition of MORB, island arc tholeiites and boninite lavas. Of the Cretaceous belt, the Troodos Massif is one of many that has compositional analogues in the Eocene of the Tonga-Fiji region. The significance of ridge-trench intersections is less clear, although the southern part of the Troodos Massif exhibits many compositional similarities with Western Pacific analogues.
Several independent lines of research have suggested that the Vourinos and Pindos ophiolites were part of a single oceanic slab. Now these investigations can be unified and Vourinos re-fit with the Pindos as for two pieces of a jigsaw puzzle.
Structural evidence has previously shown that rock fabrics are similarly orientated within the two ophiolites. These fabrics are generally more mylonitic in the Pindos and higher temperature in Vourinos. The distribution/abundance of mantle -> ductile -> brittle fabrics suggest that Vourinos was at the leading edge of the emplacing slab. Major ductile transcurrent-shear systems appear to be matchable between the two complexes. If so, these predict that remnants of Vourinos might be located within one of these zones well into Pindos "territory".
Geochemically and petrologically, the two ophiolites can be characterised as follows : Vourinos has an extremely depleted mantle restite suite, as shown in compositions of harzburgites, spinels in harzburgites and of dunites and chromitites derived from melting of a depleted mantle source. The mantle suite of the Pindos varies from similar exrtremely depleted material, to depleted, to relatively fertile lherzolites and plagioclase lherzolite more similar in chemistry to those of the Othris ophiolite. The area in the Pindos in which are found the most extremely depleted mantle rocks, that is, those which have a distinctive "Vourinos" style chemistry, coincides in position with the ductile transcurrent system which structurally connects south Vourinos with the Mavrovouni massif of the Pindos.
In general, chromite mineralisation is scattered and sub-economic in the Pindos in comparison to chrome-rich Vourinos, even in mantle areas of depleted rocks. Probable metalliferous zones in the Pindos occur in Mesovouni and the highly deformed Mavrovouni massifs. The Mavrovouni occurrences crop out within a ductile transcurrent system and the Mesovouni massif to the south of the system. We speculate that both these massifs are remnants of Vourinos, structurally detached during ductile eplacement, and preserved in what is today the area of the Pindos ophiolite.
Dismembered ophiolites on the Southern Aegean islands of Crete, Karpathos and Rhodes link the Jurassic ophiolites of the Hellenides (eg. Pindos, Vourinos) and the Cretaceous ophiolites of the Taurides in Southern Turkey (eg. Antalya). The ophiolites of these islands do not form a continuous belt. There are significant differences in composition and age between the ophiolites of Crete in the west and those of Karpathos and Rhodes in the east.
Crete: Peridotite relics in serpentinites are lherzolitic, with mean Al2O3 concentrations of 1.8 wt% and CaO concentrations of 2.4 wt%. Spinels in these rocks are as rich in Al2O3 as those from orogenic lherzolite massifs (eg. Ronda, Beni Bousera, Lizard). Thus, these rocks represent primitive, undepleted mantle material, indicating an origin at a slow-spreading ridge (similar to the modern day Atlantic Ridge). The Cretan peridotites are intruded by gabbroic dikes ranging in composition from hornblende diorite to plagiogranite. These rocks are characterized by trace element patterns typical for a calc-alkaline trend. K-Ar dating of hornblendites from the ultramafic sequence leads to Middle/Upper Jurassic ages (around 160 Ma), indicating that these ophiolites are a part of the Jurassic ophiolite belt of the Balkan peninsula. Around 20 - 30 Ma younger K-Ar ages are derived from the gabbroic dikes within the peridotites. This suggests that the intrusion of these dikes took place after the spreading event, probably following the movement of the oceanic lithosphere into an environment above a subduction zone.
Karphathos and Rhodes: The peridotite relics in serpentinites from Karphathos and Rhodes are very low in Al2O3 and CaO and correspond to depleted harzburgites. The ultramafics are intruded by doleritic dikes which are very monotonous in composition. The dikes show the trace element signature of island arc basalts. Both the depleted nature of the peridotites and the geochemical character of the dikes are typical of supra-subduction zone ophiolites. K-Ar dating of hornblendes from the dolerites reveals a minimum age of early Late Cretaceous (around 90 Ma) for the ophiolites of the two islands. The age as well as the remarkable similarity in composition and structure to ophiolite occurences in Southern Turkey demonstrate that the ophiolites of Karpathos and Rhodes belong to the Cretaceous ophiolite belt of the Eastern Mediterranean and Middle-East.
The Mesozoic carbonates of the Arabian platform in N. Syria are overlain by a series of thrust sheets consisting of Neotethyan deep-sea, passive margin and ophiolitic sequences. The thrust sheet assemblage was emplaced upon the Arabian margin in the middle Maastrichtian and was transgressed by late Maastrichtian to Early Tertiary marine carbonates. We have sampled the allochthonous ophiolitic and autochthonous cover sequences in order to provide palaeomagnetic constraints on the timing and nature of tectonic rotations which have potentially occurred during both emplacement and subsequent deformation episodes.
Single components of magnetisation have been recovered by both alternating field and thermal demagnetisation. Layered gabbros, sheeted dykes, sills and pillow lavas of the ophiolitic complex all carry stable remanent magnetisations which are unrelated to the present geomagnetic field direction. Inclinations become more tightly clustered following tilt correction, suggesting that primary remanences are being isolated. Declinations are consistent within sampled sites and localities but vary widely across the sampled region, suggesting that the ophiolitic thrust sheets have undergone significant differential rotation. The presence of both positive and negative inclinations suggests that the sampled units are not precisely coeval, but were formed during both normal and reversed polarity periods. This excludes formation entirely within the long Cretaceous normal polarity period (118-84 Ma), placing restrictions on the range of potential ages for formation of the Baër Bassit ophiolite in the Late Cretaceous. In this respect, the ophiolite differs from the extensively studied Troodos ophiolite of Cyprus, which formed entirely during the long Cretaceous normal polarity interval.
The Cyprus arc lies on the boundary between African and Anatolian plates, linking with the Hellenic arc to the west and the East Anatolian transform margin to the east. The arc has only diffuse seismicity and no active volcanism: subduction is being overtaken by collision. We present results of 4,500 km of multi-channel seismic reflecton data collected by us and integrated with a database of 10,000 km of additional seismic profiles. Interpretation focuses here on the Iskenderun-Latakia-Mesaoria and Cyprus basins. Each has a distinctive Neogene history related to its position in the arc complex, and the changing direction of the plate convergence vector. Oblique convergence is partitioned between compressional and strike-slip faulting in different ways, and extensional fault systems accompany shelf and crestal collapse. Drilling offshore Turkey shows ophiolitic basement covered by a thin veneer of Miocene and younger sediments. Our mapping indicates that the ophiolites form the cores of large Miocene thrust culminations which reimbricate the earlier Maastrichtian to late Eocene ophiolitic sutures. One culmination extends from the Hatay ophiolite across the southern fringes of the Latakia basin, into the Paralimni melange and the Trouli inlier of the Troodos complex of Cyprus. Another links the Baer Bassit ophiolite, through the Cyprus basin and Yerasa fold belt, with the Mamonia complex of southern Cyprus. The broadly asymmetric form of the basins attests to their evolution as piggy-backs on the underlying thrust ophiolitic basement.
Isolated outcrops of ophiolitic rocks, termed the Central Anatolian Ophiolites, are found as allochthonous bodies in the Central Anatolian Crystaline Complex, that represents the metamorphosed passive northern edge of the Tauride-Anatolide Platform. In terms of pseudostratigraphic relationships of the magmatic units and their chemical designation, the Central Anatolian Ophiolites exhibit a supra-subduction zone (fore arc) setting within the Vardar-Izmir-Ankara-Erzincan segment of the Neotethys. The epi-ophiolitic sedimentary cover of the Central Anatolian Ophiolites is characterized by epiclastic volcanogenic deep-sea sediments and debris-flow intercalated with pelagic units. The marked high volume of epiclastic volcanogenic sediments is suggestive of rifting in a marginal sea adjacent to an immature volcanic arc. The richest and most significant planktonic foraminiferal association recorded from the lowest pelagic members infer an formation age of early middle Turonian to early Santonian. Latest Maastrichtian sediments unconformably overlying the Central Anatolian Ophiolites and the underlying platform units suggests a post early Santonian-pre middle Campanian emplacement age. Correlating the rock-units, and formation/obduction ages of the supra-subduction zone type Central Anatolian Ophiolites with further ophiolites in the western part (Greece and NW Anatolia) of the Vardar-Izmir-Ankara-Erzincan segment of the Neotethys it is concluded that the intraoceanic subduction in the east is definitely younger and associated with the involvement of an immature island-arc during early late Cretaceous.
Late Cretaceous Pozanti-Karsanti ophiolite in southern Turkey displays well-preserved ultramafic and mafic cumulates. The ultramafic cumulate rocks are represented by dunite, chromite, websterite and wehrlite whereas the mafic cumulate rocks are represented exclusively by low-Ti gabbronorites. These rocks exhibits adcumulate-mesocumulate textures and show magmatic accumulation features such as igneous lamination, size grading and rhytmic layering. Major-trace element and mineral chemistry of the cumulate rocks indicate that the Pozanti-Karsanti ophiolite formed in a supra-subduction zone tectonic setting. Mg numbers of olivine, clinopyroxene and orthopyroxene in the ultramafic cumulates are (Mg# 90-84), (Mg# 93-88) and (Mg# 90-85) respectively whereas Mg numbers of clinopyroxene and orthopyroxene in the mafic cumulates are (Mg# 89-73) and (Mg# 80-66). Highly magnesian olivines, clinopyroxenes, orthopyroxenes and absence of plagioclase in the ultramafic cumulates suggest a high-pressure (~10kbar) crystal fractionation of primary basaltic melts beneath an island arc. The gabbroic cumulates of the Pozanti-Karsanti ophiolite differ from the basal cumulates in the same arc. Covariation of Al2O3 versus Mg numbers of clinopyroxene and orthopyroxene shows typical features of low-pressure igneous intrusions such as Skaergaard and Tonsina complex (Alaska). These gabbronorites probably represent the remains of a magma chamber formed at shallower levels in the arc than the basal ultramafic rocks. These gabbronorites were juxtaposed against ultramafic cumulates (deep-level) during either accretion or later faulting.
The Central Anatolian Crystalline Complex (CACC) or Kirsehir Block is part of the metamorphosed leading edge of the Tauride-Anatolide carbonate platform and contains oceanic remnants derived from the Neotethys Ocean (Izmir-Ankara-Erzincan branch). Two tectonic units are distinguished: an amphibolite-facies Mesozoic basement, dominated by platform-derived marbles, over which is thrust a younger fragmented Upper Cretaceous ophiolite sequence. Three metabasite horizons were sampled to reflect the development of the oceanic segment: (a) fragmented and stratiform ophiolitic members of Upper Cretaceous (90-85 Ma) formation age, (b) a tectonized Upper Cretaceous ophiolitic melange, and (c) amphibolites concordant with marbles from the largely (?)Trias Kaleboynu Formation in the lower part of the carbonate platform. Metabasalts and metagabbros from isolated fragments of the stratiform ophiolites form geochemically coherent groups and indicate the influence of a subduction component during their development. However, some late ophiolitic dykes and pillow lava sequences, especially those from the Cankiri Basin, have transitional chemical features towards MORBs. It is considered that the SSZ ophiolites record the association of a tholeiitic arc and adjacent back-arc basin with more MORB-like compositions. Metabasite blocks within the tectonized ophiolitic melange slice are dominated by MORB compositions, together with minor OIB and IAB. This can be compared with ophiolitic units within the accretionary wedge of the Ankara melange, which records dominant seamount-derived OIB, but no IAB fragments. The different block populations relate to the downgoing slab (MORB-dominated) relative to material scraped off and accreted (OIB-dominated). Minor IAB was probably derived by tectonic erosion of the arc root zone. Concordant amphibolites of the Kaleboynu Formation are largely OIB-types and reflect an early ensialic rifting stage of the Tauride-Anatolide carbonate platform. That small ocean basins were also developing at this time is recorded by the presence of MORB-types and associated pelagics. In summary, the metabasite geochemical data from the CACC records early rifting (within-plate OIB, some MORB), major spreading centre ocean crust development (MORB, with OIB seamounts) and finally subduction-related crust formation (arc and back-arc SSZ basalts). The various metabasite compositions are finally mixed in the melange units of an accretion/subduction complex. The CACC block, together with the contents of the Ankara melange, are considered to represent oceanic lithosphere and continental carbonate platform that were subsequently ejected from the accretionary/subduction complex on collision with the Sakarya microcontinent.
The Yzmir-Ankara-Erzincan suture zone, formed by the closure of the northern branch of Neotethys, is approximately prolonged E-W direction in central Anatolia and resulted from N-S convergence between Pontides and Anatolides-Taurides since the Late Cretaceous. This lineament and/or ancient suture zone is the remnant of Neotethyan ocean, and represented by tectonostratigraphic sequences into two main thrust zones developed by the polyphase deformations. The North Anatolian thrust zone (NATZ) is an imbricated thrust zone of ophiolitic mélange and its cover rocks in the northern part of the Sivas Tertiary basin. Whereas, the Sakardag-Çavusdagi thrust zone (SÇTZ) is formed by deformation of continental metamorphites and basin deposits between Sakardag and Sivas Tertiary basin in the southern border of this continental collision zone.
Three tectonic units have been defined from the foreland (south) to hinterland (north) in the NATZ. These thrust units are mainly composed of the ophiolitic mélange, such as serpentinite, diabases, radiolarites, Pre-Liassic metamorphites, Lower Cretaceous limestones, dolerit dykes, the Cenomanian-Campanian volcano sedimentary sequences-limestones and Lower Paleocene limestones. Thus, the inital melangé is the pre-Cenomanian aged. These basement tectonic units are unconformably overlain by Lower-Middle Eocene (Kuizian-Lütetian) shallow marine detritics and Upper Miocene-Pliocene continental deposits in the NATZ.
The Sakardag-Çavusdagi thrust zone (SÇTZ) is defined as Sakarda_ unit, Paleozoic continental metamorphites, Paleocene aged alcaline syenites which intruded to the metamorphites. These alcaline plutons are related to post- collisional process in the northern central Anatolia. All above units unconformably overlies by Lower-Middle Eocene (Kuizian-Lütetian) aged shallow marine carbonates. Whereas, This formation was unconformably overlined by Oligocene gypsium, a part of the Sivas Tertiary basin deposits. The middle Miocene (K-Ar radiometric dating, 15 Ma) continental basalts that cuts the Karaçayyr syenite. Upper Miocene-Pliocene continental facies, Quaternary travertine and allivium are the youngest units that unconformably overlies all of the units in the SÇTZ.
The Late Post Cretaceous tectonic deformation in Paleozoic metamorphics show ductile (D1,), ductile-brittle (D2) and brittle (D3) phases. (D1,) is a Late Cretaceous-Pre Paleocene ductile deformation phase with NNW-SSE direction. (D2) covers Paleocene and Upper Eocene period with NNE-SSW extensional regime. (D3) is a dominant brittle deformation phase formed under the compressive regime in NNW-SSE direction at Upper-Post Eocene time interval.
Two tectonic phases have been defined by kinematic analysis of striations measured on fault planes affecting the Tertiary cover units. Those phases are Pre-Upper Eocene and Upper-Post Eocene. The first tectonic phase (P1) was developed under extensional regime with NNE trending (N194°E) <sigma>3 axis. This phase is consistent with N-S and/or NNE-SSW extensional regime of the metamorphites (D2), and probably occured at the same time interval. The second tectonic phase (P2) is giving compressional regime in NNW trending (K150°E) <sigma>1 and axis. However, this phase is consistent with brittle deformation (D3,) of metamorphites in NNW-SSE direction.
NATZ has shown piggy-back and/or over-step thrust sequences and characterized by imbricated thrust systems, and formed on the fore-arc accretionary (prism) basin. All of the deformations of the continental metamorphites and its cover rocks, are indicating an imbricated stack which moved from north to south in Late Cretaceous-Pliocene and, reverse movement occured in Post Pliocene.
The uppermost parts of the eastern Rhodope metamorphic domain are represented by a high grade HP-metamorphic complex (Kimi complex), which is composed of migmatitc gneisses that contain abundant boudins of metaultramafic rocks and eclogite amphibolitess interpreted to be remnants of a dismembered ophiolitic sequence. Geochonological data suggest a prolonged metamorphic history involving early Cretaceous HP-metamorphism and Paleocene metamorphism at intermediate crustal level (Wawrzenitz and Mposkos, 1997). The Kimi complex is tectonically overlain by weakly metamorphosed Mesozoic sequences, and both were overlain by a transgressive contact by unmetamorphosed Eocene to Oligocene sediments. Stratigraphic relationships indicate exhumation and emplacement of the Kimi complex before the Lutetian. Mineral assemblages and microstructures of this complex preserve the record of successive early-Alpine tectonometamorphic events that are not observed in the lower tectonic units of the Rhodope zone.
Boudins of (ultra-)basites preserve P-T stages and strain fabrics that developed at high pressures and temperatures. Pressures higher than 16 kbar at temperatures of around 750-800°C are estimated in the ultrabasites from the mineral assemblage Grt (Grs13-15 Prp58-66 Alm 21-39 Sps 0.4-1.0) -Cpx-Ol (Fo0.9)-Cr Spl, and in the eclogite ambhibolites with relics of the HP assemblage Grt-Cpx-Ky-Qtz-Rt. This was followed by a granulitic stage at about 10-12 kbar observed in both, gneisses and (ultra-)basites. Impressive shearing of the (ultra-)basites at high temperatures during both stages was accumulated by pervasive crystal plastic flow of clinopyroxene and is interpreted as to reflect deep lithospheric detachment of the ophiolitic still in the Lower Cretaceous. Subsequent migmatization of gneisses and formation of muscovite pegmatites in the Paleocene at about 8-10 kbar was associated with access of water probably reflecting deeper level subduction beneath the Kimi complex associated with juxtaposition of Apulia against Europe. Strain at that stage transformed (ultra-)basites to boudins but was not such extensive to erase the earlier recored entirely. We consider the Kimi complex as a part of an Eo-Alpine suture, which can be traced to the N into the Austroalpine.
Wawrzenitz N, & Mposkos E, Europ J Mineral, 9, 659-664, (1997).
Northwestern edge of the Arabian platform (i.e. Amanos Mountains - Turkey) consists mainly of thick autochthonous sedimentary succession. Onto the platform, ophiolites were obducted during the late Mesozoic and Tertiary periods. Therefore within the platform sequence are ordered and dismembered ophiolite slices. In the northern and central Amanos Mountain, which is situated to the northwestern edge of the Arabian platform, the ophiolites outcrop extensively. In the region thirteen different ophiolite slices have been differentiated according to the internal ordering, lithological and structural characteristics, and timing of generation and emplacement. They were emplaced onto the Arabian platform in three main stages: These are a) Late Cretaceous, b) Eocene, and c) Miocene. The ordered ophiolites and the associated mélanges were emplaced first during the late Cretaceous. The ophiolite stack formed a structural high, lying sub-parallel to the continental margin, separating internally located sea realm (The Kastel basin) from the oceanic realm, locating northwest. The Eocene ophiolite obduction caused thin - skin deformation in the Arabian platform. In the Miocene stage, a huge nappe package consisting mainly of ophiolitic and metamorphic nappes emplaced on top of the Arabian platform.
In this talk, the ophiolitic associations of the Amanos Mountain will be detailed, and their tectonic significance will be discussed.
The Southeast Anatolian orogen is a part of the eastern Mediterranean-Himalayan orogenic belt. The eastern parts of the Southeast Anatolian orogenic belt may be divided into two roughly east-west trending structural zones. These are the nappe region to the north and the Arabian platform to the south.
The Arabian platform includes a sedimentary succession deposited from Early Paleozoic to Miocene time. The nappe region represented by the Jurassic-Cretaceous aged ophiolite at the base. The ophiolitic units are overlain by the Campanian-Danian calcalkaline island arc volcanics and Campanian-Lutetian deposits. The metamorphic equivalents of ophiolitic unit at the base and Upper Cretaceous volcanics were thrusted onto the Lutetian deposits as a nappe package.
The Upper Lutetian-Upper Oligocene aged olistostromal-turbiditic units which are intercalated with the calcalkaline volcanics, were developed on and in front of the allocthonous units. The calcalkaline volcanics are products of an island arc which reactivated in the Late Lutetian-Late Oligocene period after Danian.
The continental and shallow marine sedimentary rocks which were developed in a molasse basin during the Late Oligocene-Early Miocene period, overlie the tectonic units. The tectonic emplacement continued at the more southern areas. All of the units in the area had thrusted onto the Arap platform after the Late Miocene.
In West Bulgaria two types of old ophiolites have been established. Their features, such as stratigraphy, composition, relationship with the associated island arc, genesis, and age, are comparatively well characterized.
The Balkan ophiolite, comprising large bodies such as South Banat (Rumania), Zaglavac and Deli Jovan (E. Serbia), Tcherni Vrach and others (Bulgaria), is formed of a relatively well-preserved block of ocean crust (Haydoutov, 1989). The section of the Tcherni Vrach massif starts with layered gabbro followed by massive gabbro over which sheeted dikes are situated, and ends with pillow lavas covered by umbers. Combined REE and Sm-Nd isotope data document that the Balkan ophiolite is similar to the transitional middle ocean ridge basalts extracted from depleted mantle (Haydoutov, Pin, 1993). The age of the Balkan ophiolite is Late Precambrian - 563+5 Ma - zircons from massive gabbro ( Quadt et al., 1998).
The Sredna Gora ophiolite forms small, intenselv dislocated lenses along the northern edge of the Thracian microplate. This ophiolite is formed mainly by metaigneous rocks - diabases, diabasic lavabreccias, gabbrodiabases, gabbro. The established geological data, composition, including sediment components, the relationship with the island-arc igneous rocks, and the age of the ophiolite, indicate that this is a back-arc ophiolite (Haydoutov et al., 1997).
The Balkan island-arc association, connected genetically and spatially with the described above ophiolites, is formed of sedimentary-volcanic and intrusive complexes. The age of the association is determined by Cambrian Archaeocyathus, discovered in the carbonate horizon of the sedimentary-volcanic complex.
The relationship between the Balkan ophiolite and the superimposed island arc is variable. In general it is tectonic. In some localities, inconformable relation of he island arc over the ophiolites has been observed. The ophiolite association is also intersected all over by the island-arc magmatites. The Sredna Gora ophiolites are intersected by the late impulses of the island-arc intrusive complex and is considered of Cambrian age.
The considered disposition of the back-arc basin - to the south of the arc - is important for establishing the direction of subduction to which the formation of the arc is related. The subduction zone was disposed to the north of Tcherni Vrach massif and inclined to the south.
Haydoutov I, Geology, 17, 905-908(1989)
Haydoutov I, Pin C, Geologica Balcanica, 23, 51-59 (1993)
Haydoutov I, Kolcheva K & Daieva L, Rev. Bulg. Geol. Soc, 58, 71-82 (1997)
Quadt A, Peytcheva I & Haydoutov I, Compt. rend. Acad. Bulg. Sci, 97, in press
The Kutahya-Bolkardag Belt (KBB) includes imbricated tectonic slivers of the passive continental margin sequences of the Tauride-Anatolide Platform together with allochthonous ophiolite-bearing assemblages. The Kocyaka Metamorphic Complex (KMC) is a HP/LT sliver within the KBB. In the study area, KMC starts with pelagic carbonates that yielded Late Jurassic-early Cretaceous fossils in further slices of the KBB. The pelagic sediments are transitional to an allolistostrome with diverse ophiolitic blocks in a turbiditic matrix. The allolistostrome comprises a matrix-dominated lower and a block-dominated upper part. KMC is unconformably overlain by continental clastics of Danian age. The blocks (blueschists, incipient metabasalts, greenstones, subophiolitic amphibolites, metaserpentinites, metacherts and metavolcanoclastics) of the allolistostrome include inequilibrium assemblages indicating a wide range of HP/LT conditions. The matrix rock units (pelitic schists and metacalci-turbidites interlayered with metavolcanics-volcanoclastics, and metacherts) exhibiting also HP/LT assemblages are devoid of Na-pyroxene and/or lawsonite. Petrographic data from some blocks suggests that the peak P conditions around the upper limit of blueschist facies were arrived prior to their incorporation into the olistostrome. The last stage of the metamorphic overprint both in the blocks and the matrix is represented by glaucophanitic-greenschist facies assemblages. Geochemical data reveal that the KMC metabasalt blocks display both IAT-MORB and MORB affinities. The IAT-MORB transitional features are: a- high abundance of LIL and b-low abundance of HFSE (Nb, Ti, Zr, Y). The LIL enrichment and HFSE depletion relative to MORB distinguish these rocks from the N-MORB and also indicate the influence of a subduction component in their source. Another group of samples display features (lower Rb/Zr and Ba/Zr ratios, and higher Ti, V, Y, and Zr contents) that suggest a MORB type origin. A few metabasalt knockers have the geochemical fingerprints of OIB and characterized by the enrichment of incompatible elements (e.g. Nb) relative to MORB. The preliminary geochemical data reveals the existance of a variety of magma types ranging in composition from IAT-MORB; MORB and OIB, which are typical for an intraoceanic supra-subduction zone tectonic setting.A proposed geodynamic model considers that during the Early Cretaceous northward subduction of the Yzmir-Ankara branch of Neotethys, blocks and slices of the HP/LT metamorphic accretionary complex were transported into the olistostromal deposits of the passive continental margin sequence. This was followed by the subduction of the KMC-type marginal sequences resulting in HP/LT metamorphism of the entire slab. The decrease in the subduction velocity caused by the buoyancy of the subducted continental margin has very probably resulted in the restoration of the geothermal gradients and produced the late-stage glaucophanitic-greenschist facies overprint. Due to the terminal closure of the Yzmir-Ankara branch of Neotethys and collision with the Sakarya Microcontinent the metamorphosed continental margin sequences were imbricated and thrusted to the south prior to Danian.
Eclogitized serpentinites are present in the Rhodope Ophiolitic Association from the Precambrian metamorphic basement of the Rhodope massif - Southern Bulgaria. The Ophiolitic Association marks a stable stratigraphic level in the metamorphic basement, which is divided in two sequential-stratigraphic supergroups - Prarhodopian and Rhodopian. It is considered that the ophiolites represent ocean crust fragments, obduced over the active edge of an ancient continent, covered by pelite-carbonate sediments of Riphean age and later folded and metamorphosed together with the whole rock complex. The primary ophiolite components of basic volcanites, gabbros, gabbronorites and serpentinized peridotites had undergone a continuous metamorphic-structural evolution and as result pyroxenites, talc-chlorite-actinolite schists, various amphibolites and metasomatic gabbrodiorites were formed.
Eclogitization is displayed along local shear zones. They are most often observed in deeply sunk and compressed synclines and are usually situated along the lithological boundaries of rocks with different rheological properties. The eclogitization zones are always in conformity with the general stratification and metamorphic schistosity of the rocks. Eclogitized serpentinites are found in the strongly folded Avren syncline. They possess layered structure at the peripheral parts of lenticular bodies, demonstrated by alternation of non-altered serpentinite stripes with thin 1-2 cm eclogite zones. The closer to the contacts eclogite zones have a zonal structure. Their central parts are occupied by garnet (Prp50-56Alm27-29 Grs16-18Sps1-2) with sporadic pyroxene and spinel grains, followed by stripe built mainly of olivine (Fo88Fa12), enstatite (En80-84Fs14-16), diopside (Wo49-50En46-47Wo4) and spinel (Cr pleonast). An transitional zone of criptocrystalline talc-chlorite aggregate is formed between the eclogite minerals and serpentinite. The myrmekite-like simplectites built of diopside and spinel, or diopside, enstatite and magnetite are very characteristic reaction products in this transitional zone. The stripes gradually disappear towards the central parts of the serpentinite bodies. The PT conditions of mineral crystallization in the eclogite zones vary within the range 560-811°C and 8-15 kbar. The formation of garnet-bipyroxene-olivine-spinel banded segregations is due to deformation of the serpentinites during synmetamorphic folding of the metamorphic basement in the Avren syncline. Then, thin shear zones were formed at the peripheral parts of the serpentinite bodies, where interlaminar friction took place. As a result, temperature and pressure increased and serpentine was dehydrated and replaced by talc, chlorite, ortho- and clinopyroxenes, olivine, spinel and garnet.
Within the eastern Mediterranean ophiolites the Albanian portion forms very well developed sections. They are part of the western ophiolitic belt, ranging from Croatia in the north to Greece in the south. Generally the Albanian ophiolites are divided in a western and eastern zone, were the former show MORB and the latter SSZ signature (Shallo, 1992; Bortolotti, 1996).
The ophiolite complex of Voskopoja is located in the southernmost part of the Albanian ophiolites and forms together with the complexes of Shpati, Devolli, Vallamara, Morava, Shebeniku, and Bitincka the southern Mirdita ophiolites. Except for the latter two complexes they are interpreted as continuation of the western zone, the Shebeniku and Bitincka are compared to the ophiolites of the eastern zone. The contrast between the western and the eastern ophiolites, well developed in northern Albania, is not so clearly recognizable in southern Albania.
Most of the ophiolitic mantle sections contain harzburgite together with a subordinate amount of lherzolite and dunite. Lherzolites, plagioclase lherzolites and dunites form the ultramafic cumulate section. Pyroxenites and wherlites are restricted to the Shebeniku and Spati Massif. Troctolites, besides pyroxene gabbros are common in Devolli and Voskopoja, but occur also in Morava. Sheeted dikes are missing in all profiles. Only four ophiolites (Shpati, Devolli, Vallamare, and Voskopoja) contain a volcanic section directly overlying the ultramafic and/or mafic cumulate sequence. Geochemical data of lavas of the Voskopoja massif indicate a relatively wide range of geochemistry intermediate between typical MORB and island arc tholeiites erupted in a SSZ environment. For example, the Zr/Y ratio varies from 2.5 to 3.5, the Ti/V ratio between 20 to 45. In the spider diagrams variations can be observed from typical MORB to island arc compositions. This variation in element ratios can not be explained by crystal fractionation processes but requires most probably a tapping of geochemical heterogeneous mantle portions.
The Pindos ophiolite in Greece, a continuation of the western zone of the south Albanian ophiolites, shows a SSZ genesis indicating that a geochemical variation from MORB to SSZ tholeiites not only exists between the eastern and the western zone, but also in a north-south direction along the main axis of the ophiolites on a regional scale.
Bortolotti Vet al, Ofioliti, 21, 3-20, (1996).
Shallo M, Geol. Rdsch, 81, 681-692, (1992).
The Meso-Hellenic Basin of northern to central Greece is a long, excceedingly narrow and deep Tertiary basin:
* at its narrowest, the Meso-Hellenic is only 20 km wide.
* up to 5000 m of molasse sediments fill the basin.
The basin separates the Vourinos, Pindos and Othris ophiolites; a reconstruction of these ophiolites show they were once part of a single obduction oceanic slab. Break-up of the slab is Cretaceous to Tertiary and possibly coincides with the birth of the Meso-Hellenic.
The basin occludes the margin between a Pelagonian metamorphic basement with a younger flysch or Ionian basement.
Tectonism along the east of the basin between molasse and basement formations is absent except in the area of neotectonic faults. The morphology on the east of the basin thus is apparently little changed since its formation. The distribution of molasse sediments to the west occurs over a much broader area than that of the Meso-Hellenic, suggesting that the original morphology of the molasse "basin" was much broadeer in area.
Several "windows" of basement formations along the Meso-Hellenic present the most complex structural geology of the Pindos (and one is glad that the molasse covers these structures everywhere else).
The western margin of the Meso-Hellenic displays a complex tectonic history which includes:
*"Warping" of the basement rocks (ophiolites, flysch) and the base of the molasse to a near-vertical dip into the Meso-Hellenic.
* Large boulders of Cretaceous carbonates are synformationally incorporated into the molasse, implying a pre-existing high topography present during the "warping" period.
The western margin of the Meso-Hellenic is lined by a series of NW-SE trending steep faults. These faults are near vertical, and extend over 40 km length. Molasse is steeply over-turned along these faults, implying they are steep reverse faults. Inward of the margin, a zone only 1-3 km wide contains at least four of these faults and each uplifts increasing deep basement formations. Short decoupling faults between imply some strike-slick motion. Then, several faults further inward of the Meso-Hellenic juxtapose molasse with fysch: folding in the molasse between these faults is antiformal, again implying a major compressional "squeeze". A cross-section of the margin connecting ophiolitic and melange stratigraphic intervals requires that the closure of the molasse basin was much more "violently" compressive event than previously recognised.
Albania is part of the Alpine Mediterranean shrivelled belt in the Dinarido-Albano-Helenic branch. Depending to the Jurassic-Cretaceous fold-formation stages, the outer and inner Albanides are distinguished. The huge ophiolitic complex, the Mirdita zone, with about of 4200 km2 extension, is the main feature of the inner Albanides.
The gravity map compiling for all the Albanide territory urged a great contribution to settling some significant problems, for the compilation of the: new Geological Map, Tectonical Map and Metallogenic Map, of Albania at 1:200000 scale and especially on the interpretation of the geotectonical position of the ophiolitic complex.
The ultramafic rocks occupy the main place in the ophiolitic complex both in superficial distribution and especially in to the depth, therefore the density taken for Bouguer anomaly calculation made possible to acquire some clear anomalies of the gravity, above ultramafic massifs. The interpretation of the gravity anomaly made possible to judge about their continuity in deeper strata and to have an idea of their relationships to the surrounding rocks. The gravity anomaly with the high intensity, in the Mirdita zone, outlines the form, dimensions and the general characteristics of the ophiolites of this tectonical area. Five high positive gravity anomalies, epicentres which are set after one another in a chain-form according to the anomaly belt, beginning from ultrabasic massif of Tropoja-Kukes north-east area to that of Lura, Bulqiza areas to the Morava south-east sector, are fixed within area. Therefore, this belt has a submeridional direction in accordance with the general structure of the ophiolitic extension. This belt is nearly 220 km long, and from 10 to 50 km wide. The maximum intensity of the gravity anomalies is ~ 105 mGal. In the upper part, this belt takes a powerful turn of 60º-70º in the form of a north-eastern-ward incline, going on beyond our border, in Yugoslavian territory, while in the south, it continues to the Greek territory. The gravity positive anomalies acquired within this belt, are generally asymmetric, and in all the cases, their eastern flank has a higher gradient than the western one, that has an irregular outline. It is most marked especially in the sectors continuing southward of Tropoja- Kukes ultrabasic massif.
The gravity Bouguer anomaly of the Bulqiza ultrabasic massif has an outline nearly similar to the massif frameworks, except it's in northern-western part, in Burrel basin direction. Such a precise outlining of the anomaly, fits perfectly with that of the massif one, and reflects as well the structural features of the massif itself and of its relationships to the adjacent rocks. In the north and southwards, the thickness of this massif is increasingly reduced. The Bulqiza massif is related northward to that Lura according to a very slim thickness of ultrabasic rocks localized in the western sector, while southwards, it is considerably reduced up to a closure.
The gravity anomaly form of the Lura massif and its westward continuation helps us to judge about the continuity of the ophiolitic formation under the limestone deposits. A gravity anomaly is acquired further southward Bulqiza ultrabasic massif and it is caused by the presence of the Shebenik ultrabasic massif.
The anomaly acquired in the Shebenik massif is extended beyond its border, in west, in the direction of the Kuturman massif. This reveals an extension of rocks with higher density under the Neogenic deposits in the west and further in the south. The magnetic observations above the Neogenic sediments reveal that the ophiolitic formations continue further under these deposits up to the Kuturman and Shpat massif further in the south.
The most powerful anomaly acquired over the ophiolitic belt of the Mirdita zone in Albanides, is on the north-eastern margin of the territory on the Kam-Tropoja ultrabasic massif. The gravity anomaly in Kam-Tropoja massif (with 70 mGal amplitude) continues in the ex Yugoslavia, southwest-northeastward.
According to the gravity data, the southern part of the Albanides ophiolitic belt, has a more limited thickness and it keeps developing southwards in Helenide.
The anomaly of gravity field in Mirdita tectonic zone of Albanides reflects the ophiolitic complex development in this zone. The changing anomaly intensity is related to their changing extension thickness. Proceeding from this fact, we come to the conclusion that the highest ophiolite thickness is localised in the east and it is reduced westwards. These reductions of the ophiolitic thickness are not uniform. Thus, even based on this gravity inversion in various sections, a reduced trend of the ophiolitic thickness southward can be judged. While, in some southern sectors, the ophiolites situated on the surface cause no distinct gravity anomaly.
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