Eastern Rhodope Research Articles

Trace element and isotopic composition of mafic and ultramafic cumulate xenoliths in alkaline basalts from the Eastern Rhodopes, Bulgaria: Inferences on deep processes under the metamorphic core complexes

Oligocene within-plate alkaline basalts, intruded in the Eastern Rhodope metamorphic core complexes Kesebir and Biala Reka, carry ultramafic and mafic xenoliths, consisting of clinopyroxenites, websterites, orthopyroxenites, 2-pyroxene- and clinopyroxene gabbros. These xenoliths are interpreted as samples of layered intrusions formed at upper mantle-lower crustal depths. Calculated parental liquids from LA ICP-MS analyses of clinopyroxene in the ultramafic clinopyroxenites, orthopyroxenite and websterite indicate that they may have formed from melts similar in composition to their host basanitic magma. The clinopyroxene REE patterns of least magnesian websterites suggest amphibole and clinopyroxene fractionation. Trace element compositions of gabbros and high-Fe clinopyroxenites indicate that they are the most differentiated product from the same parent. Calculated parental liquids for some of them, however, show geochemical features typical for subduction-related rocks. In addition, Sr and Nd isotopic compositions of evolved websterites and gabbros are more radiogenic than those of the host basanites. This transition from within-plate to subduction-related signature can be related to fractionation of amphibole, accompanied by crustal contamination of the basanitic magma with more radiogenic lower crustal material.

Structural and 40Ar/39Ar age constraints on the Kulidjik nappe: A record of an early Alpine thrust tectonics in the northeastern Rhodope Massif, Bulgaria

In the northeastern Rhodope Massif, a unique juxtaposition of assumed high-grade basement allochthon onto a low-grade Mesozoic unit is exposed in the Kulidjik nappe. The thrusting is interpreted as post-Jurassic to pre-Late Eocene. The tectonostratigraphy comprises the following units: (i) an upper unit of high-grade basement of the eastern Rhodope consisting of various amphibolite facies rocks with metaophiolite lenses; (ii) an overlaying Mesozoic (including Jurassic radiolarians) low-grade unit; (iii) a structurally overlaying allochthon of the Kulidjik nappe; and (iv) unconformable Late Eocene sedimentary and Oligocene volcanic cover rocks. The basement unit contains a NNE-SSW oriented lineation rarely associated with top-to-the NNE ductile shearing. Greenschist facies retrogression of this unit is diagnostic of local thrusting of the overlying low-grade unit. The greenschists of the low-grade unit represent arc metavolcanic rocks overlain by phyllites. The structural elements in this unit have similar attitudes as the basement unit. Kinematic indicators in the low-grade unit demonstrate internal top-to-the NNE ductile shearing during greenschist facies conditions. The allochthon consists of klippen composed of muscovite-albite gneisses. The flat-lying thrust contact with ductile-brittle deformation contains mylonites and cataclasites. Previously reported local top-to-the SSW ductile shearing in the allochthon is probably a consequence of shear instabilities. Deformation-crystallization relationships revealed fabrics in the allochthon compatible with greenschist up to lower amphibolite facies conditions without retrogression and similar ENE-verging fold patterns in the low-grade unit and the allochthon at the thrust contact. Two muscovite samples from distinct klippen yielded inverse isochron 40Ar/39Ar ages of 156.07±1.30 Ma and 162.62±2.69 Ma, which reflect cooling below 350°C of the allochthon associated with its exhumation during emplacement after greenschist-lower amphibolite facies metamorphism. Structural data indicate NNE-directed tectonic transport of the low-grade footwall unit, which is consistent with emplacement in comparable metamorphic conditions, and the thrust direction of the allochthon in the hanging wall. The subduction-accretionary origin of the low-grade unit and the new age results allow us to link this tectono-metamorphic event to Late Jurassic thrust imbrication of arc units on the Rhodope basement, which is the first time that early Alpine thrust tectonics in the northeastern Rhodope Massif have been recognized.

Petrogenesis of Ultramafic Rocks from the Ultrahigh-pressure Metamorphic Kimi Complex in Eastern Rhodope (NE Greece)

Widespread bodies of garnet–spinel metaperidotites with pyroxenitic layers occur in the ultrahigh-pressure metamorphic Kimi Complex. In this study we address the origin of such peridotite–pyroxenite associations in the context of polybaric melting regimes. We conduct a detailed geochemical investigation of major and trace element relations and compare them with a range of major element modelling scenarios. With increasing bulk-rock MgO content, the garnet–spinel metaperidotites exhibit decreasing CaO, Al2O3, TiO2, and Na2O along with increasing Ni and a gradually increasing Zr/Zr* anomaly, consistent with an origin as residues after variable degrees of melt extraction. The major element modelling further suggests a polybaric adiabatic decompression melting regime beginning at high to ultrahigh pressure, with an intermediate character between pure batch and fractional melting and a mean extent of melting of 9–11%. The pyroxenites exhibit major element compositions that cannot be reproduced by experimental or calculated melts of peridotite. Moreover, the Kimi pyroxenites have highly variable Ni and Sc contents and a wide range of Mg-number (0· 76–0· 89), inconsistent with an origin as frozen melts or the products of melt–peridotite interaction. However, both the major element systematics and the observed rare earth element patterns, with both convex and concave shapes, can be explained by an origin as clinopyroxene-rich, high-pressure cumulates involving garnet and/or Cr-spinel.

Evolution and relationships between volcanism and tectonics in the central-eastern part of the Oligocene Borovitsa caldera (Eastern Rhodopes, Bulgaria)

The nested Borovitsa caldera emplaced during the collision-related Paleogene volcanism in the Eastern Rhodopes. The pre-caldera succession consists in Priabonian to Early Oligocene sediments and lavas (absarokites, shoshonites, latites). The caldera filling corresponds to an acid volcanism Early Oligocene in age. The tectono-magmatic evolution of the caldera can be divided into six main stages. (1) Ignimbritic units (more than 1.5 km thick) with a trachydacitic to trachytic composition deposited. The K–Ar method yields an age of 34–33.5 Ma. The volcanic products are either strongly or not welded in the western and eastern parts of the caldera, respectively. (2) An initial Murga caldera, 7–10 km in diameter, collapsed. This event was accompanied by the intrusion of a circular body consisting of lenses-bearing rocks of trachyrhyodacitic to rhyolitic composition within the border faults. (3) The emission of pyroclastic rocks continued and a large sub-volcanic body (33 Ma) of trachydacitic to trachyrhyolitic composition intruded in the western part of the circular body. (4) The Borovitsa caldera (15 km × 34 km) collapsed. Rhyolitic and trachydacitic dykes dated at 32.5 Ma intruded along its border faults. (5) High-Si trachyrhyolitic–perlitic domes intruded in the eastern part of the Borovitsa caldera at 30–32 Ma and the Dushka caldera collapsed within the Borovitsa structure. (6) Dykes of various compositions (from shoshonite to rhyolite) and trachydacitic to rhyolitic sub-volcanic stocks finally intruded within the caldera and along its rims at 27.5–29.5 Ma. Observations on radar and optical satellite imagery allowed both a new mapping of the structural pattern in the Borovitsa caldera and the understanding of the relationships between faulting and volcanism in this area. Horse-tail features accommodating the right-lateral throw component at the termination of NW–SE and N–S right-lateral strike–slip faults are superimposed upon the Murga caldera and the eastern part of the Borovitsa caldera respectively. WNW–ESE to NW–SE extension along the horse-tail patterns was responsible for the ascent of pressurized magma through the crust via vertical open fractures leading to volcanic activity and subsequent emplacement of domes and crypto-domes during the fifth magmatic stage. This extension was followed by a compression with various orientations, which may be interpreted as a switch of the tensile stress to a compressive one at the onset of subsidence of the Dushka caldera. The last tectonic event in the area is characterized by a N–S extension that led to the reactivation of part of the previous structures, the formation of NW–SE to E–W normal faults and the emplacement of dykes and stocks during the sixth magmatic stage.

A new species of Aethionema (Brassicaceae) from the Bulgarian flora

Aethionema rhodopaeum D. Pavlova is described as a new species from the eastern Rhodope Mountains. The plant was found growing only on serpentines, in two localities, at an altitude of approximately 400 m. The localities are typical open habitats with sparsely colonized debris. The plant communities, composed mainly of xerophytes with a mosaic distribution, contain a large number of rare and endemic species for the Bulgarian flora. The new species belongs to the Aethionema saxatile group and is quite close to the species A. saxatile (L.) R. Br., in particular to ssp. creticum and ssp. graecum. The following diagnostic features are given for the new species: inner filament length always greater than half the petal length, lack of teeth of the filaments, longer [2‐3(3.5) mm] style than that of A. saxatile subspecies, and dark purple petals. All leaves are broadly elliptical to suborbicular, obtuse, and fleshy. The chromosome number of the new species is 2n = 24. The differences between the new species and related taxa are also discussed. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155, 533‐540. ADDITIONAL KEYWORDS: Rhodope Mountains ‐ serpentine ‐ systematics ‐ taxonomy.

Petrology, geochemistry and geodynamic implications of Jurassic island arc magmatism as revealed by mafic volcanic rocks in the Mesozoic low-grade sequence, eastern Rhodope, Bulgaria

In the eastern Bulgarian Rhodope, mafic extrusive rocks and underlying greenschists are found in the Mesozoic low-grade unit, which represents the northern extension of similar sequences including the Evros ophiolites in Thrace (Greece). Both rock types define a suite of low-Ti tholeiitic basalts to transitional boninitic basaltic andesites and andesites and associated metapyroclastites (greenschists), intruded at its base by diorite dikes of a boninitic affinity. Mafic lavas and greenschists display large ion lithophile element (LILE) enrichment relative to high-field strength elements (HFSE), flat REE patterns of a slight light REE depletion, a strong island arc tholeiite (IAT) and weak MORB-like signature. All these rocks are characterized by negative Nb anomalies ascribed to arc lavas. They have positive ɛNd i values in the range of + 4.87 to + 6.09, approaching the lower limit of MORB-like source, and relatively high ( 207Pb/ 204Pb) i (15.57–15.663) at low ( 206Pb/ 204Pb) i (18.13–18.54) ratios. The Nd isotopic compositions coupled with trace element data imply a dominantly depleted MORB-like mantle source and a contribution of subduction modified LILE-enriched component derived from the mantle wedge. The diorite dike has a low ɛNd i value of − 2.61 and is slightly more Pb radiogenic ( 207Pb/ 204Pb) i (15.64) and ( 206Pb/ 204Pb) i (18.56), respectively, reflecting crustal contamination. Petrologic and geochemical data indicate that the greenschists and mafic extrusive rocks represent a magmatic assemblage formed in an island arc setting. The magmatic suite is interpreted as representing an island arc–accretionary complex related to the southward subduction of the Meliata–Maliac ocean under the supra-subduction back-arc Vardar ocean/island arc system. Magmatic activity appears to have initiated in the north during the inception of the island arc system by the Early–Middle Jurassic time in the eastern Rhodope that most likely graded to back-arc spreading southwards as represented by the Late Jurassic MORB-type Samothraki Island ophiolites. This tectonic scenario is further constrained by paleotectonic reconstructions. The arc–trench system collided with the Rhodope in the Late Jurassic times.

Snow cover variability in Bulgarian mountainous regions, 1931–2000

AbstractPrincipal component (PC) analysis was carried out on annual snow cover series from 15 mountain climate stations in Bulgaria to characterize the spatial and temporal variability in snow cover over the 1931–2000 period. Three distinct snow cover response regions were identified: (1) high elevation sites above 1500 m in the Vitosha and Rila Mountains; (2) low elevation sites below 1000 m in the eastern Rhodope and southern Pirin Mountains and (3) a mid‐mountain zone of 1000–1500 m elevation including stations from several mountain ranges. Snow cover exhibited evidence of significant decadal‐scale variability over the 1931–2000 period but little evidence of long‐term trends linked to climate warming. Over the more recent 1971–2000 period, the mid‐mountain zone has increased in importance and shows a significant trend toward a later start to the snow cover season.Composite analysis of high and low snow accumulation winters showed high accumulation years associated with a negative North Atlantic Oscillation (NAO)/East Atlantic (EA)‐like pattern that favored increased winter precipitation over the Mediterranean and Balkans and anomalous easterly flow across the Black Sea into Bulgaria. Low snow accumulation years were associated with the positive mode of a Scandinavian (SCA)‐like pattern that generated fall warming, a delay to the start of the snow cover season and reduced winter precipitation. Correlation of annual snow cover series with these modes of atmospheric variability revealed few significant correlations but evidence of considerable secular variability in the strength and sign of the relationships. This reflects the complex climate regime of Bulgaria, which is located at the cross‐roads of Mediterranean and Continental climate influences and on the periphery of the main nodes of influence of Northern Hemisphere circulation patterns that play important roles in European snow cover variability. Copyright © 2007 Royal Meteorological Society

From syn- to post-orogenic Tertiary extension in the north Aegean region: constraints on the kinematics in the eastern Rhodope–Thrace, Bulgaria–Greece and the Biga Peninsula, NW Turkey

Abstract The Aegean region experienced back-are extension related to the Hellenic subduction system at least from the latest Oligocene to the present. We document Tertiary extension-related kinematics in the north Aegean, in the eastern Rhodope–Thrace of Bulgaria–Greece and the Biga Peninsula of NW Turkey. A regionally consistent NNE–SSW- to NE–SW-oriented kinematic direction, delineated in both areas by stretching lineations and associated ductile–brittle shear fabrics in exhumed metamorphic domes beneath detachments, suggests that they were kinematically coupled during the Tertiary extension. This kinematic framework, combined with regional geochronological data and the stratigraphic record in hanging-wall supradetachment basins, defines an extensional history that includes syn- and post-orogenic episodes from Paleocene to Miocene times. Paleocene–early Eocene synorogenic extension in the Kemer micaschists of the northern Biga Peninsula and in the Kesebir–Kardamos dome in Rhodope–Thrace accommodated gravitationally induced hinterland-directed exhumation of the orogenic stack, coeval with the closure of the Vardar Ocean. Then, following collision within the region, it was succeeded by latest Oligocene–Early Miocene extension as recorded in the Kazdaǧ Massif in the southern Biga Peninsula, which overlaps the Aegean back-arc post-orogenic extension, widely recognized in the central Aegean and southern Greek Rhodope. The protracted record of extension is interpreted to reflect progressive exhumation of the orogenic wedge along the Eurasian plate margin. Southward migration of extension and magmatism across the study areas accounts for sequential shift and roll-back of the subduction boundary at that margin, from the latest Cretaceous in the Rhodope to its present position at the Hellenic trench. The results allow recognition of the investigated areas as an important extensional domain in the north Aegean region, which underwent Tertiary syn- and post-orogenic extension.

Pressure–temperature–deformation paths of closely associated ultra-high-pressure (diamond-bearing) crustal and mantle rocks of the Kimi complex: implications for the tectonic history of the Rhodope Mountains, northern Greece

The ultra-high-pressure (UHP) Kimi complex (uppermost eastern Rhodope Mountains) is a tectonic mixture of crustal and mantle derived associations. Pressure–temperature (P–T) paths and microtextural and geochronological data reveal that crustal and mantle parts juxtaposed against each other at a depth corresponding to ~15 kbar (1 kbar = 100 MPa) had separate ascend histories. The crustal rocks comprise amphibolitised eclogites, orthogneisses, marbles, and migmatitic pelitic gneisses. The latter document UHP metamorphism within the dehydration-melting range of pelitic gneisses, with maximum P–T conditions of >45 kbar at ~1000 °C, as determined by diamond inclusions in garnet and rutile needle exsolutions in Na-bearing garnet. Decompression was combined with only little cooling before 15 kbar, followed by more significant cooling between 15 and 10 kbar. This P–T path probably reflects ascent of UHP rocks within a subduction channel, followed by accretion in the lower crust of a thickened wedge. Although the first ascend phase was probably rapid, the overall time span for UHP metamorphism and final exhumation may have extended over more than 70 Ma. A U–Pb sensitive high-resolution ion microprobe (SHRIMP) age on zircons of ±149 Ma was suggested to date the UHP metamorphism, whereas Rb–Sr white mica and U–Pb zircon ages from syn-shearing pegmatites of ±65 Ma constrain medium- to low-grade shearing and final exhumation of UHP rocks. Mantle parts consisting of spinel–garnet metaperidotites and garnet pyroxenites reached maximum P–T conditions in the garnet-peridotite field at T > 1200 °C and P > 25 kbar. This was associated with plastic flow and followed by severe near isothermal cooling to T < 800 °C at 15 kbar and static annealing. A garnet–clinopyroxene whole-rock Sm–Nd age from a garnet pyroxenite of ±119 Ma probably reflects the age of metamorphic mantle processes (static annealing following the high P/high T strain episode), rather than constraining the age of UHP metamorphism.

40Ar/39Ar geochronology constraints on the Middle Tertiary basement extensional exhumation, and its relation to ore-forming and magmatic processes in the Eastern Rhodope (Bulgaria)

The interaction of distinct geologic processes involved during late orogenic extensional exhumation history of the metamorphic units in the Eastern Rhodope is refined by new and reviewing 40Ar/39Ar geochronological and structural data. Minerals with different closure temperatures from metamorphic rocks investigated in this study are combined with those from magmatic and ore-forming hydrothermal rocks in two late stage metamorphic domes – the Kesebir-Kardamos and the Biala reka-Kehros domes. The 38-37 Ma muscovite and biotite cooling ages below 350°-300°C characterize basement metamorphic rocks that typified core of the Kesebir-Kardamos dome, constraining their exhumation at shallow crustal levels in the footwall of detachment. These ages are interpreted as reflecting last stage of ductile activity on shear zone below detachment, which continued to operate under low-temperature conditions within the semi-ductile to brittle field. They are close to and overlap with existing cooling ages in southern Bulgaria and northern Greece, indicating supportively that the basement rocks regionally cooled between 42-36 Ma below temperatures 350°-300°C. The spatial distribution of ages shows a southward gradual increase up structural section, suggesting an asymmetrical mode of extension, cooling and exhumation from south to the north at latitude of the Kesebir-Kardamos dome. The slightly younger 36.5-35 Ma crystallization ages of adularia in altered rocks from the ore deposits in the immediate hanging-wall of detachments are attributed to brittle deformation on high-angle normal faults, which further contributed to upper crustal extension, and thus constraining the time when alteration took place and deformation continued at brittle crustal levels. Silicic dykes yielded ages between 32-33 Ma, typically coinciding with the main phase of Palaeogene magmatic activity, which started in Eastern Rhodope region in Late Eocene (Priabonian) times. The 40Ar/39Ar plateau ages from the above distinct rock types span time interval lasting approximately ca. 6 Ma. Consequently, our geochronologic results consistently indicate that extensional tectonics and related exhumation and doming, epithermal mineralizations and volcanic activity are closely spaced in time. These new 40Ar/39Ar age results further contribute to temporal constraints on the timing of tectonic, relative to ore-forming and magmatic events, suggesting in addition that all above mentioned processes interfered during the late orogenic extensional collapse in the Eastern Rhodope region.

Zeolites and zeolitization of acid pyroclastic rocks from paroxysmal Paleogene volcanism, Eastern Rhodopes, Bulgaria

An extensive bimodal volcanic suite developed in the Late Paleogene in the Eastern Rhodopes Mountains, Southern Bulgaria. Most of the widespread and thick rhyolitic tuffs and ignimbrites, erupted during two major Early Oligocene acid phases, were emplaced in a shallow marine environment and subsequently altered. K-rich Ca-clinoptilolite (in some places K-clinoptilolite, mordenite or analcime), clay minerals (celadonite or/and smectite), adularia (or albite) and opal-CT replace the volcanic glass. The zeolitized pyroclastic rocks are strongly depleted in MnO, Na2O, K2O, and enriched in CaO, Fe2O3, TiO2 and MgO. Regional zoning in distribution of the major glass-replacing minerals has been established: quartz + adularia (or albite) ± zeolites in the proximal to the vent area; zeolites in the medial and clay minerals in the distal area. Vertical zoning has been also recognized because only the basal pyroclastic layer is transformed into adularia + quartz whereas clinoptilolite, accompanied by opal-CT and clay minerals, prevails in the rest of the section. The zeolitized glass shards are characteristically zoned: (1) a thin rim (<5μm thick) of celadonite coats the shard surface retaining their original shape; (2) a 30–50μm-thick zone, made of contiguous platy zeolite crystals, oriented perpendicular to the rim and (3) a central zone of large euhedral crystals, surrounding a central hollow area. Phenocrysts are not affected by the zeolitization and some relict glass is found in the top of the pyroclastic section. According to the semiquantitative X-ray analysis and heat of immersion test of Culfaz et al. (1973) the clinoptilolite content in the zeolitized pyroclastic rocks varies from 38 to 72 wt.%. The cation exchange capacity values range between 40 and 153 meq/100 g and show a significant positive correlation with clinoptilolite content obtained by the heat of immersion test (r = 0.71). The lateral zoning and presence of typical hydrothermal minerals such as celadotite indicate that zeolitization of the thick Eastern Rhodopes pyroclastic series results from the operation of a large low temperature hydrothermal system. The hydrothermal solutions consist of marine water heated by the anomalous geothermal gradient of the active volcanic areas or/and by the hot pyroclastic deposits.

Structure of Pinus nigra Arn. populations in Bulgaria revealed by chloroplast microsatellites and terpenes analysis: Provenance tests

Pinus nigra is a forest and low elevation mountain species found around the Mediterranean Sea that has had its distribution reduced and fragmented by anthropogenic disturbance. Due to commercial interest it is currently being replanted, however, the genetic structure of populations is little known and current planting strategies could threaten its genetic diversity. In the present study we investigated the genetic structure and genetic diversity of P. nigra populations in Bulgaria using chloroplast microsatellite markers and terpene analysis. Nine provenances were chosen throughout the species' range in Bulgaria. Following DNA extraction, chloroplast microsatellite (cpSSR) loci were surveyed using three primer pairs. Between 5 and 9 size variants were identified at each locus. A total of 22 size variants at the 3 loci were identified, that were combined in 68 different haplotypes, of which 7 represent 39.81% of the genetic structure. AMOVA analysis revealed that 6.06% of the variation was found among populations, while 93.94% was expressed within populations. The cpSSR analysis divided European Black pine populations into four groups, the first represented by populations located the eastern Rhodopes, Sr. Gora and St. Planina mountains, while the second group is primarily located in the Phodopes and Slavianca mountains. The populations from Pirin and Osogovo mountains show different genetic patterns. Terpene analysis revealed that most of the monoterpene pool in P. nigra was accounted for by α-pinene followed by β-pinene. The presence of four distinct terpene groups is not consistent with physical distances between populations, and a similar non-significant correlation between genetic distance determined by chloroplast microsatellites analysis and chemotype distance (determined by terpenes) was observed. Our results suggest that the structural pattern of genetic diversity of cpDNA in European Black pine populations is the consequence of historical biogeographic processes.

Structural and geochemical studies on amphibolite and greenschist-facies rocks in the Kulidjik river valley, eastern Rhodope, Bulgaria: preliminary results

Structural and geochemical studies on amphibolite and greenschist-facies rocks in the Kulidjik river valley, eastern Rhodope, Bulgaria: preliminary results

Constraints of stable isotopes on the origin of alunite from advanced argillic alteration systems in Bulgaria

Voluminous areas of advanced argillic alteration (AAA) constitute major exploration targets for surficial Cu–Au epithermal and potentially underlying porphyry-type deposits. In Bulgaria, more than 30 alunite occurrences are recognised, few of them being associated with a mineralised system. A mineralogical study combined with a stable isotopic (O, H, S) study has been carried out on nine alunite occurrences of advanced argillic zones hosted by volcanic rocks of Late Cretaceous age in the Srednogorie belt and of Oligocene age in the Rhodopes belt. This work was realised in order to constrain the origin of alunite and to define criteria to discriminate alunite from ore deposits and alunite from large barren alteration systems. Mineralogy of the nine occurrences consists of alunite + quartz + minor alumino-phospho-sulphates, associated with more or less kaolinite, dickite, pyrophyllite, diaspore and zunyite, depending on formation temperature. Alunite generally occurs as tabular crystals but is also present as fine-crystalline pseudocubic phases at Boukovo and Sarnitsa, in Eastern Rhodopes. In the advanced argillic alterations associated with economic ore, the presence of zunyite in the deeper parts indicates acid–fluorine–sulphate hydrothermal systems, whereas it is absent in uneconomic and barren advanced argillic alteration. All occurrences are formed at temperatures between 200 and 300 °C. (H, O, S) isotopic signatures of alunite combined with mineralogical features from all the studied occurrences, whatever their type, show characteristics of magmatic-hydrothermal systems. Sulphur data indicate essentially a magmatic origin for sulphur. Oxygen and hydrogen data suggest that hydrothermal fluids result from a mixing between magmatic fluids and an external component, which is identified as seawater-derived fluids or meteoric water in the vicinity of a sea. In most of the alunite occurrences, magmatic fluids are dominant and H 2S/SO 4 ratios are estimated to be higher than 2. Two exceptions exist in the Rhodopes. At Boukovo and Sarnitsa, where the estimated formation temperatures of alunite are the lowest, the external fluids are dominant and H 2S/SO 4ratios are estimated to be lower than or close to 1. At this stage of the work, the mineralogical and isotopic criteria do not enable a clear distinction between economic and uneconomic systems. However, some features are common in the economic ore deposits: the presence of zunyite in the deeper part of the system, the relatively high temperatures suggested by the zunyite + pyrophyllite + alunite + diaspore assemblages, the (O, H, S) signature of alunite, which is characteristic of dominant magmatic–hydrothermal acid–sulphate–fluorine systems.

2: Hydrothermal ore deposits related to post-orogenic extensional magmatism and core complex formation: The Rhodope Massif of Bulgaria and Greece

The Rhodope Massif in southern Bulgaria and northern Greece hosts a range of Pb–Zn–Ag, Cu–Mo and Au–Ag deposits in high-grade metamorphic, continental sedimentary and igneous rocks. Following a protracted thrusting history as part of the Alpine–Himalayan collision, major late orogenic extension led to the formation of metamorphic core complexes, block faulting, sedimentary basin formation, acid to basic magmatism and hydrothermal activity within a relatively short period of time during the Early Tertiary. Large vein and carbonate replacement Pb–Zn deposits hosted by high-grade metamorphic rocks in the Central Rhodopean Dome (e.g., the Madan ore field) are spatially associated with low-angle detachment faults as well as local silicic dyke swarms and/or ignimbrites. Ore formation is essentially synchronous with post-extensional dome uplift and magmatism, which has a dominant crustal magma component according to Pb and Sr isotope data. Intermediate- and high-sulphidation Pb–Zn–Ag–Au deposits and minor porphyry Cu–Mo mineralization in the Eastern Rhodopes are predominantly hosted by veins in shoshonitic to high-K calc-alkaline volcanic rocks of closely similar age. Base-metal-poor, high-grade gold deposits of low sulphidation character occurring in continental sedimentary rocks of synextensional basins (e.g., Ada Tepe) show a close spatial and temporal relation to detachment faulting prior and during metamorphic core complex formation. Their formation predates local magmatism but may involve fluids from deep mantle magmas. The change in geochemical signatures of Palaeogene magmatic rocks, from predominantly silicic types in the Central Rhodopes to strongly fractionated shoshonitic (Bulgaria) to calc-alkaline and high-K calc-alkaline (Greece) magmas in the Eastern Rhodopes, coincides with the enrichment in Cu and Au relative to Pb and Zn of the associated ore deposits. This trend also correlates with a decrease in the radiogenic Pb and Sr isotope components of the magmatic rocks from west to east, reflecting a reduced crustal contamination of mantle magmas, which in turn correlates with a decreasing crustal thickness that can be observed today. Hydrogen and oxygen isotopic compositions of the related hydrothermal systems show a concomitant increase of magmatic relative to meteoric fluids, from the Pb–Zn–Ag deposits of the Central Rhodopes to the magmatic rock-hosted polymetallic gold deposits of the Eastern Rhodopes.

Natural Opal as a Model System for Studying the Process of Biomineralization

Opal is a natural nanostructure model. It possesses nanosized close packed silica spheres and a regular sublattice of voids, filled with molecular water and accessible for filling by other substances. Using natural opal as a substrate, no complimentary technique is needed to produce a patterned surface as it is present naturally. Thus, the possession of nano-dimensions for efficient influencing of different biological events can be used in the laboratory and biologically integrated multifunctional devices (biomaterials, sensors) could be created. Additionally, biomineralization mechanisms may be studied using model systems. The main purpose of the work is to use nanostructured or other functionalized materials as models to contribute to the study of biomineralization. Particularly this paper reports on the ability of natural opal from Bulgaria's Eastern Rhodopes mountain to induce the deposition of a surface layer of calcium phosphate from simulated body fluid. Raman, infrared spectroscopy and XRD were used to show that opal consists of two main phases: microcrystalline quartz and cristobalite and that the observed with optical microscopy layer deposited from the simulated body fluid on both phases was calcium phosphate.

Mesozoic–Tertiary structural evolution of an extensional gneiss dome—the Kesebir–Kardamos dome, eastern Rhodope (Bulgaria–Greece)

The tectonic evolution of the Rhodope massif involves Mid-Cretaceous contractional deformation and protracted Oligocene and Miocene extension. We present structural, kinematic and strain data on the Kesebir–Kardamos dome in eastern Rhodope, which document early Tertiary extension. The dome consists of three superposed crustal units bounded by a low-angle NNE-dipping detachment on its northern flank in Bulgaria. The detachment separates footwall gneiss and migmatite in a lower unit from intermediate metamorphic and overlying upper sedimentary units in the hanging wall. The high-grade metamorphic rocks of the footwall have recorded isothermal decompression. Direct juxtaposition of the sedimentary unit onto footwall rocks is due to local extensional omission of the intermediate unit. Structural analysis and deformational/metamorphic relationships give evidence for several events. The earliest event corresponds to top-to-the SSE ductile shearing within the intermediate unit, interpreted as reflecting Mid-Late Cretaceous crustal thickening and nappe stacking. Late Cretaceous–Palaeocene/Eocene late-tectonic to post-tectonic granitoids that intruded into the intermediate unit between 70 and 53 Ma constrain at least pre-latest Late Cretaceous age for the crustal-stacking event. Subsequent extension-related deformation caused pervasive mylonitisation of the footwall, with top-to-the NNE ductile, then brittle shear. Ductile flow was dominated by non-coaxial deformation, indicated by quartz c-axis fabrics, but was nearly coaxial in the dome core. Latest events relate to brittle faulting that accommodated extension at shallow crustal levels on high-angle normal faults and additional movement along strike-slip faults. Radiometric and stratigraphic constraints bracket the ductile, then brittle, extensional events at the Kesebir–Kardamos dome between 55 and 35 Ma. Extension began in Paleocene–early Eocene time and displacement on the detachment led to unroofing of the intermediate unit, which supplied material for the syn-detachment deposits in supra-detachment basin. Subsequent cooling and exhumation of the footwall unit from beneath the detachment occurred between 42 and 37 Ma as indicated by mica cooling ages in footwall rocks, and extension proceeded at brittle levels with high-angle faulting constrained at 35 Ma by the age of hydrothermal adularia crystallized in open spaces created along the faults. This was followed by Late Eocene–Oligocene post-detachment overlap successions and volcanic activity. Crustal extension described herein is contemporaneous with the closure of the Vardar Ocean to the southwest. It has accommodated an earlier hinterland-directed unroofing of the Rhodope nappe complex, and may be pre-cursor of, and/or make a transition to the Aegean back-arc extension that further contributed to its exhumation during the Late Miocene. This study underlines the importance of crustal extension at the scale of the Rhodope massif, in particular, in the eastern Rhodope region, as it recognizes an early Tertiary extension that should be considered in future tectonic models of the Rhodope and north Aegean regions.

Foraminifers from the exotic Late Permian limestone pebbles in the Mesozoic low-grade sequence of the eastern Rhodope, Bulgaria: paleogeographic and paleotectonic consequences

Foraminifers from the exotic Late Permian limestone pebbles in the Mesozoic low-grade sequence of the eastern Rhodope, Bulgaria: paleogeographic and paleotectonic consequences

Biostratigraphic data from the Çetmi Melange, northwest Turkey: Palaeogeographic and tectonic implications

The Çetmi accretionary melange is cropping out in the Biga Peninsula of northwest Turkey. It is characterised by an isolated position, relatively far from the accretion complexes of the nearest suture zones, which raises the question of its lateral correlations. A detailed biostratigraphic investigation of the limestone and radiolarite blocks and the matrix of the Çetmi melange allowed to propose a solution for this palaeogeographic problem. Scarce red nodular limestones in the Han Bulog facies represent the oldest lithology in the melange. Their Late Scythian–Ladinian age is based on Chiosella gondolleloides, the co-occurrence of Gladigondolella sp. and Nicoraella cf. kockeli, and Paragondolella fuelopi. Light grey limestone blocks are a characteristic feature of the Çetmi melange. They occur in two distinct facies. Facies A consists of packstone to grainstone, and is characterised by unsorted and poorly washed pelbiosparites. Facies B consists of wackestone to packstone, and is characterised by poorly washed biopelmicrites to biopelsparites. The foraminiferal assemblage of Facies A, containing Triasina hantkeni, is of Late Norian to Rhaetian age. The foraminiferal assemblage of Facies B never contains T. hantkeni, and is characteristic of a Late Triassic (Carnian? to Norian–Rhaetian) age. Radiolarian cherts are widely distributed in the Çetmi melange. They record fully pelagic sedimentation from the Upper Bajocian to the Aptian. The matrix of the Çetmi melange consists of brown to black shales, sometimes silty or siliceous, intercalated with dark grey greywackes. Palynomorphs of one sample of brownish silty shale yielded an Early to Middle Albian age, based on the co-occurrence of several dinoflagellate cysts. The age of the matrix, representing the youngest lithology within the melange, and of the unconformable overlaying section (latest Albian–Cenomanian) indicate that the melange-forming process stopped between the Early Albian and the latest Albian–Cenomanian. At a regional scale, the Çetmi melange has little in common with the melanges from the İzmir–Ankara and Intra–Pontide sutures of northwestern Turkey precluding a direct correlation. On the other hand, the Çetmi melange shares several characteristics with the melange-like units of the eastern Rhodope Zone (Bulgaria and Greece), like a major Cenomanian transgression, the reworking of Triassic limestones and Middle Jurassic–Lower Cretaceous radiolarians, and the absence of Jurassic–Cretaceous passive margin lithologies. The occurrence of Rhodopian units on the Biga Peninsula suggests that the studied units represent an isolated fragment of the Rhodope Zone in NW Turkey.

Compositional diversity of Eocene–Oligocene basaltic magmatism in the Eastern Rhodopes, SE Bulgaria: implications for genesis and tectonic setting

Basaltic magmatism occurred only rarely within the extensive Eocene–Oligocene volcanic activity in the Eastern Rhodope Mts., SE Bulgaria. The earliest mafic volcanism started at ca. 34 Ma with K-rich trachybasalts strongly enriched in large ion lithophile elements (LILE), particularly Ba, Sr, Pb, Th, and light rare earth elements (REE) relative to the high field strength elements (HFSE). They have high 87Sr/ 86Sr ratios (0.70688–0.70756), low 144Nd/ 144Nd (0.51252–0.51243), and very high 207Pb/ 204Pb (15.74–15.76) and 208Pb/ 204Pb (39.07–39.14) at low 206Pb/ 204Pb (18.72–18.73) ratios, reflecting high degrees of crustal contamination. Shoshonitic basalts and absarokites and calc-alkaline and high-K calc-alkaline magmas, which erupted between 33 and 31 Ma, have decreasing Sr isotope initial ratios from west (0.70825) to east (0.70647) at approximately constant 143Nd/ 144Nd isotopic compositions (0.51252–0.51243) and slightly decreasing 207Pb/ 204Pb (15.66–15.72) and 208Pb/ 204Pb (38.80–38.96) and increasing 206Pb/ 204Pb (18.73–18.90) in comparison with the trachybasalts. All these rocks are characterized by negative Nb–Ti and Eu anomalies. They resulted from different degrees of partial melting of enriched asthenosphere, and the magmas were later contaminated by the Rhodopian crust. The end of the magmatic activity (28–26 Ma) was marked by emplacement of alkaline dykes, spatially associated with metamorphic core complexes. They are characterized by low 87Sr/ 86Sr (0.70323–0.70338), high 144Nd/ 144Nd (0.51290–0.51289), and 206Pb/ 204Pb (18.91–19.02) at lower 207Pb/ 204Pb (15.52–15.64) and 208Pb/ 204Pb (38.59–38.87) ratios, consistent with an origin from a source similar to OIB-like European Asthenospheric reservoir contaminated by depleted mantle lithosphere. The Eastern Rhodope Eo-Oligocene mafic magmatism formed as part of the prolonged extensional tectonics of the whole Rhodope region in Late Cretaceous–Paleogene time, similar to those in the U.S. Cordillera and Menderes Massif (Turkey). Initiation of extension is constrained by the formation of metamorphic core complexes, low-angle detachment faults, and supradetachment Maastrichtian–Paleocene sedimentary basins, intimately associated with 70–42 Ma granitoids and metamorphism which record mantle perturbation. The Eo-Oligocene stage started with block faulting, sedimentary basin formation, and extensive acid-intermediate and basic volcanism over the entire Eastern Rhodope area. The order of emplacement of the basalts from high-Ba trachybasalts through shoshonites, calc-alkaline and high-K calc-alkaline basalts, and finally to purely asthenospheric-derived alkaline basalts, with progressively decreasing amount of crustal component, reflects upwelling asthenospheric mantle. Most of the models proposed in the literature to explain extension and magmagenesis in the Rhodopes and the Mediterranean region cannot be applied directly. Critical evaluation of these models suggest that some form of convective removal of the lithosphere and mantle diapirism provide the most satisfactory explanation for the Paleogene structural, metamorphic, and magmatic evolution of the Rhodopes.