Tertiary-Quaternary subduction processes and related magmatism in the Alpine-Mediterranean region

During Tertiary to Quaternary times, convergence between Eurasia and Africa resulted in a variety of collisional orogens and different styles of subduction in the Alpine-Mediterranean region. Characteristic features of this area include arcuate orogenic belts and extensional basins, both of which can be explained by roll-back of subducted slabs and retreating subduction zones. After cessation of active subduction, slab detachment and post-collisional gravitational collapse of the overthickened lithosphere took place. This complex tectonic history was accompanied by the generation of a wide variety of magmas. Most of these magmas (e.g. low-K tholeiitic, calc-alkaline, shoshonitic and ultrapotassic types) have trace element and isotopic fingerprints that are commonly interpreted to reflect enrichment of their source regions by subduction-related fluids. Thus, they can be considered as ‘subduction-related’ magmas irrespective of their geodynamic relationships. Intraplate alkali basalts are also found in the region generally postdated the ‘subduction-related’ volcanism. These mantle-derived magmas have not been, or only slightly, influenced by subduction-related enrichment. This paper summarises the geodynamic setting of the Tertiary-Quaternary “subduction-related” magmatism in the different segments of the Alpine-Mediterranean region (Betic-Alboran-Rif province, Central Mediterranean, the Alps, Carpathian-Pannonian region, Dinarides and Hellenides, Aegean and Western Anatolia), and discusses the main characteristics and compositional variation of the magmatic rocks. Radiogenic and stable isotope data indicate the importance of continental crustal material in the genesis of these magmas. Interaction with crustal material probably occurred both in the upper mantle during subduction (‘source contamination’) and in the continental crust during ascent of mantle-derived magmas (either by mixing with crustal melts or by crustal contamination). The 87Sr/86Sr and 206Pb/204Pb isotope ratios indicate that an enriched mantle component, akin to the source of intraplate alkali mafic magmas along the Alpine foreland, played a key role in the petrogenesis of the ‘subduction-related’ magmas of the Alpine-Mediterranean region. This enriched mantle component could be related to mantle plumes or to long-term pollution (deflection of the central Atlantic plume and recycling of crustal material during subduction) of the shallow mantle beneath Europe since the late Mesozoic. In the first case, subduction processes could have had an influence in generating asthenospheric flow by deflecting nearby mantle plumes due to slab roll-back or slab break-off. In the second case, the variation in the chemical composition of the volcanic rocks in the Mediterranean region can be explained by “statistical sampling” of the strongly inhomogeneous mantle followed by variable degrees of crustal contamination

Stratigraphy, facies and geodynamic settings of Jurassic formations in the Bükk Mountains, North Hungary: its relations with the other areas of the Neotethyan realm.

Jurassic mélange complexes related to the subduction of the Neotethys Ocean occur in the Bükk Mountains, North Hungary. This paper characterizes the sedimentary sequence of basin and slope facies that occur in the southwestern part of the Bükk Mountains, placing special emphasis on the redeposited sedimentary rocks (olistostromes, olistoliths: Mónosbél Group) in order to obtain information on the provenance of the clasts, and the mode and time of their redeposition. The series of formations studied shows a general coarsening-upwards trend. Based on radiolarians and foraminifera, the Mónosbél Group formed in Early to Late Bathonian time. The lower part of the complex is typified by a predominance of pelagic carbonates, shale and radiolarite with andesitic volcaniclastic intercalations. The higher part of the succession is characterized by polymictic olistostromes. Large olistoliths that are predominantly blocks of Bathonian shallow marine limestone (Bükkzsérc Limestone) appear in the upper part of the sequence. Based on the biostratigraphic and sedimentological data, results of analyses of the redeposited clasts and taking into consideration the concepts of the development of the western Neotethys domain, the evolutionary stages of the sedimentary basins were defined. The onset of the compressional stage led to initiation of nappe stacking that led to the formation of polymict olistostromes and then to the redeposition of large blocks derived from out-of-sequence nappes of the former platform foreland

Birth, life and death of the Pannonian Lake

The Miocene-Pliocene Pannonian Lake formed in an extensional basin system behind the compressional arc of the Carpathians. Its size and depth were comparable to those of the Caspian Sea. Subsidence began in Middle Miocene times, forming deep, pelagic basins, separated by reef-bearing ridges. Clastic influx filled the marginal basins during Middle Miocene time. Prograding deltas dissected the lake and completed the infilling of the basin system by the end of the Pliocene. Basin plain, prodelta, delta front, delta plain, beach, fluviatile, and marsh environments can be recognized. Terminal Miocene uplift of the Carpathians isolated the Pannonian region from the rest of Paratethys. The subsequent decrease of salinity resulted in the evolution of an endemic, freshwater mollusc fauna. Rich nutrient influx from rivers supported high organic productivity (dinoflagellates, diatoms, nannoplankton, foraminifers, ostracods, etc.), yielding organic-rich sediments. Preservation of organic matter was helped by a stratified water column and oxygen deficient bottom conditions. Deep burial, continuing subsidence, and high geothermal flux due to an extremely thin crust, led to the formation of commercially exploitable oil and gas accumulations. Shallow lacustrine zones of basin margins provided suitable environments for a rich Congeria-Melanopsis mollusc fauna. Wave action on beaches produced commercially exploitable pure quartz sand deposits. Taxodium and Alnus forests flourished around the lake producing enormous lignite deposits. Besides a rich land snail and mammal fauna, prehominids lived in the forests. There was a warm, temperate climate, with probably frostfree winters. Basaltic volcanoes overlooked the landscape, and maars hosted minor lakes with rich algal flora forming oil shale. The catchment area included most of the Carpathians and parts of the Alps and Dinarides. The positive water balance resulted in a supposed overflow in the southern margin, supplying exotic fauna to the South Carpathian and Dacian basins of the Eastern Paratethys. The Pannonian Lake was completely filled by the end of Pliocene. Recent lakes in the Carpathian Basin are not descendants of it

Forecasting strong aftershocks in earthquake clusters from northeastern Italy and western Slovenia

In this study, we propose an analysis of the earthquake clusters that occurred in North-Eastern Italy and western Slovenia from 1977 to today. Given a mainshock generating alarm in the population, we are interested in forecasting if a similar magnitude earthquake will follow. We classify the earthquake clusters associated with mainshocks of magnitude Mm into two classes: if the strongest aftershock has a magnitude >=Mm-1 (swarms or large aftershock seismic sequences) as type A, otherwise (smaller aftershocks seismic sequences) as type B. A large aftershock following a main shock can cause significant damages to already weakened buildings and infrastructures, so a timely advisory information to the civil protection is of great interest for effective decision-making. For the first time, we applied to a new catalogue a pattern recognition algorithm for cluster type forecasting that we developed for all Italy (Gentili and Di Giovambattista, 2017). Thanks to the lower completeness magnitude of the local OGS catalogue, compared to the national one, and to a new version of the algorithm, we were able to lower the threshold of the clusters mainshocks magnitude from 4.5 to 3.7. The method has been validated by rigorous statistical tests. We tested the algorithm on the 1976 highly destructive earthquake cluster (mainshock magnitude 6.5 - the strongest in the last 80 years in the region) and we retrospectively forecasted it as an A cluster. Successful results were obtained also on other three smaller earthquake clusters in 2019.Comment: 42 page

The Alpine-Carpathian-Dinaridic orogenic system: correlation and evolution of tectonic units

A correlation of tectonic units of the Alpine-Carpathian-Dinaridic system of orogens, including the substrate of the Pannonian and Transylvanian basins, is presented in the form of a map. Combined with a series of crustal-scale cross sections this correlation of tectonic units yields a clearer picture of the three-dimensional architecture of this system of orogens that owes its considerable complexity to multiple overprinting of earlier by younger deformations. The synthesis advanced here indicates that none of the branches of the Alpine Tethys and Neotethys extended eastward into the Dobrogea Orogen. Instead, the main branch of the Alpine Tethys linked up with the Meliata-Maliac-Vardar branch of the Neotethys into the area of the present-day Inner Dinarides. More easterly and subsidiary branches of the Alpine Tethys separated Tisza completely, and Dacia partially, from the European continent. Remnants of the Triassic parts of Neotethys (Meliata-Maliac) are preserved only as ophiolitic mélanges present below obducted Jurassic Neotethyan (Vardar) ophiolites. The opening of the Alpine Tethys was largely contemporaneous with the Latest Jurassic to Early Cretaceous obduction of parts of the Jurassic Vardar ophiolites. Closure of the Meliata-Maliac Ocean in the Alps and West Carpathians led to Cretaceous-age orogeny associated with an eclogitic overprint of the adjacent continental margin. The Triassic Meliata-Maliac and Jurassic Western and Eastern Vardar ophiolites were derived from one single branch of Neotethys: the Meliata-Maliac-Vardar Ocean. Complex geometries resulting from out-of-sequence thrusting during Cretaceous and Cenozoic orogenic phases underlay a variety of multi-ocean hypotheses, that were advanced in the literature and that we regard as incompatible with the field evidence. The present-day configuration of tectonic units suggests that a former connection between ophiolitic units in West Carpathians and Dinarides was disrupted by substantial Miocene-age dislocations along the Mid-Hungarian Fault Zone, hiding a former lateral change in subduction polarity between West Carpathians and Dinarides. The SW-facing Dinaridic Orogen, mainly structured in Cretaceous and Palaeogene times, was juxtaposed with the Tisza and Dacia Mega-Units along a NW-dipping suture (Sava Zone) in latest Cretaceous to Palaeogene times. The Dacia Mega-Unit (East and South Carpathian Orogen, including the Carpatho-Balkan Orogen and the Biharia nappe system of the Apuseni Mountains), was essentially consolidated by E-facing nappe stacking during an Early Cretaceous orogeny, while the adjacent Tisza Mega-Unit formed by NW-directed thrusting (in present-day coordinates) in Late Cretaceous times. The polyphase and multi-directional Cretaceous to Neogene deformation history of the Dinarides was preceded by the obduction of Vardar ophiolites onto to the Adriatic margin (Western Vardar Ophiolitic Unit) and parts of the European margin (Eastern Vardar Ophiolitic Unit) during Late Jurassic to Early Cretaceous time

Seismotectonically Active Zones in the Dinarides

Seismotectonically active zones are formed due to displacements of segments of the Adriatic micro-plate that differ in size and in their rate of movement, and by the resistance of the rock masses of the Dinarides. The spatial position of these zones can be determined through the locations of earthquake foci. The zones of seismotectonic activity are then correlated with the most important faults on the surface. The seismotectonically active zones are relatively steeply inclined in the shallowest 10-20 km, which is caused by the oblique contacts between the Adriatic micro-plate and the Dinarides. The zones are curved at depth in many cases, which reflects the compression of the area. Curved parts of the zones are characterised by the greatest pressures and also by the most frequent earthquakes. Mildly inclined zones reflect the reverse displacements in the area, also probably the activity on contacts between rock masses of different density, or the extension of the Adriatic micro-plate subduction. The southern part of the plate is the most active. The greatest pressures caused by these movements occur in the area between Mljet island and Dubrovnik. Therefore the majority of earthquakes, and notably the strongest ones, occur in the area between Split, Imotski, Hvar island and Dubrovnik, as well as along the Montenegro coast in a SE direction

Oil and gas bearingness and structural elements of Adriatic islands and peninsulas (Outer Dinarides) with special review of anhydrite – carbonate Mesozoic complex and diapiric belt

Već dugi niz godina evaporitne naslage mezozojske starosti na području jadranskih otoka i poluotoka (vanjski Dinaridi) zaokupljaju pažnju geologa istraživača. Ovim radom su prikazani naftno-geološki podaci, koji omogućuju veću sigurnost kako bi se moglo točnije nego dosad planirati istraživačke radove u cilju lociranja novih, vrlo dubokih istraživačkih bušotina na pojedinim dijelovima jadranskih otoka i poluotoka (slike l, 2, 3, 4 i 5). To je područje anhidritno-karbonatnog kompleksa, a naročito u području južnootočkog mezozojskog bazena, gdje su bušotinom Brač-lß određene pojave ugljikovodika od C1-C5, te izmjeren tlak od 1 100 bara. Time se potvrđuju ranija saznanja, da naslage s anhidritnim pokrivačem (izolator) predstavljaju zatvorene naftno-geološke cjeline s visokim tlakom i temperaturom, te ekonomski značajnim količinama ugljikovodika. Dano je mišljenje o pojavama sumporovodika u anhidritno-karbonatnom kompleksu i njegovom lošem djelovanju na ljudski organizam, a također i na razornu izmjenu kristalne rešetke u čeliku. Prikazani su i dijapiri na južnom rubu južnootočkog mezozojskog bazena, njihov utjecaj na formiranje pojedinih otoka i mogući utjecaj na nafto-plinonosne odnose u tom bazenu (slika 5).Evaporite deposits of Mesozoic age in the area of Adriatic islands and peninsulas (Outer Dinarides) have been attracting attention of exploration geologists for many years. This paper presents petroleum geological data that provide more certainty for more accurate planning of exploration operations that would result in location of new, very deep exploration wells in certain parts of Adriatic islands and peninsulas (Figures l, 2, 3, 4 and 5). This is the area of anhydrite-carbonate complex, especially in the part of Mesozoic basin where certain hydrocarbon shows of C1-C5 were acquired in Brač-1 ß well and where the pressure of 1 100 bar (15 954 psi) was measured. This confirms the previous knowledge that deposits with anhydrite seal represent closed petroleum geological units with high pressure and temperature and commercially significant hydrocarbon quantities. The opinion is presented on hydrogen sulfide shows in anhydrite-carbonate complex and its bad impact on human health and on destructive alteration of crystal lattice in steel. The paper also presents diapirs on the southern edge of Mesozoic basin in the area of southern islands, their impact on formation of certain islands and possible impact on oil and gas bearing relations within this basin (Figure 5)

Detrital pyroxenes in the Eocene flysch of the Istrian Basin (Slovenia, Croatia)

For the first time, few detrital augite and pigeonite crystals have been found in the Eocene flysch basins of Istria (Trieste-Koper basin; Italy, Slovenia, Croatia) and Krk Island (Croatia). Their chemistry suggests that they are related to subalkaline rocks (within-plate tholeiites) crystallized at a pressure between 0 and 5 kbar. As a possible source, the nearby basaltic andesites of Ljubac have been taken into consideration. The argument for a ?Late Tertiary age of the Ljubac volcanics is that no detrital pyroxenes have been found in the Eocene flysch and Oligo- Miocene molasse deposits of the area (Lugovic et al., 1998). Radiometric data are not available until now. The detection of detrital pyroxene could be an indication of an older age of the Ljubac volcanics. The presence of similar pyroxenes in the Trieste-Koper and the Krk Island flysch and their absence in Brkini flysch suggest that the basin of Krk was linked with the Istrian basin rather than the Brkini basin

New Commercial Oil Discovery at Rovesti Structure in South Adriatic and its Importance for Croatian Part of Adriatic Basin

Rad je potaknut najnovijim podacima o uspješnom naftnogeološkom istraživanju i otkriću komercijalnog ležišta u jugozapadnom dijelu Jadranskog bazena u podmorju u blizini gradova Bari i Brindisi. Autori su u više navrata u svojim izlaganjima i člancima u časopisu Nafta isticali da i u hrvatskom dijelu jadranskog podmorja treba očekivati otkriće nafte ako se na odgovarajući način pristupi reinterpretaciji seizmičkih podataka i rezultata istražnog bušenja. Nedavnom analizom takvih podataka ustanovljeno je da prilikom ranijih istraživačkih radova nisu uzeti u obzir svi elementi evolucije paleogeografskih elemenata koji su utjecali na razvoj paleostruktura te stvaranja potencijalno matičnih i ležišnih stijena, te pokrovnih (izolatorskih) naslaga. U daljnjem tekstu bit će posebno istaknuti gore spomenuti elementi i na kraju date preporuke za usmjeravanje daljnjih naftno-geološka istraživanja.This paper has been inspired by the newest data on successful petroleum-geological exploration and the discovery of commercial reservoir in southwestern part of the offshore Adriatic Basin in the vicinity of towns Bari and Brindisi. On several occasions in presentations in Nafta journal, the authors have pointed out that oil discovery could be expected in the Croatian part of Adriatic offshore if the seismic data reinterpretation and exploration drilling results were addressed properly. Recent analyses of such data showed that previous studies did not include all paleo-geographic elements, which affected the development of paleo-structures and creation of potential source and reservoir rocks and cap rocks. Special attention shall be put on the above mentioned elements and at the end, the recommendations for further petroleum-geological exploration shall be given

Possible location of the next major earthquakes in the northern Apennines: present key role of the Romagna-Marche-Umbria wedge

It is argued that in some zones of the Northern Apennines, in particular the Rimini-Ancona thrust system, the Romagna Apennines and the Alta Valtiberina trough, the probability of major earthquakes is now higher than in other Apennine zones. This hypothesis is suggested by the comparison of the present short-term kinematics of the Romagna-Marche-Umbria wedge in the Northern Apennines, deduced by the distribution of major shocks in the last tens of years, with the previous repeated behavior of the same wedge, evidenced by the distribution of major earthquakes in the last seven centuries. The seismotectonics of the Apennine region here considered is closely connected with the larger context that involves the progressive migration (from south to north) of seismicity along the peri-Adriatic zones. The information provided by this study can be used to better manage the resources for prevention in Italy