collision and extension in the alpine - carpathian...

Collision and Extension in the Alpine - Carpathian - Pannonian

System

A 2-day workshop on the geodynamicevolution of the Alpine – Carpathianorogens and the Pannonian basin, encompassing geophysicsgeochemistry and geology

to take place at:Siófok on the shore of Lake Balatonin Hungary, September 14-16, 2007

For details, contact:Greg Houseman: [email protected] Horvath: [email protected] by the Royal Society and the Eötvös University, Budapest

Collision and Extension in the

Alpine - Carpathian - Pannonian System

September 14-16, 2007

A two day workshop on the geodynamic evolution of the Alpine-Carpathian orogen, encompassing geophysics, geochemistry and geology

at Lake Balaton, Guest House of the Hungarian Academy of Sciences in Siófok, Hungary

The convenors of this meeting thank the Royal Society, the University of Leeds, and Eotvos University (project no. NK60445) for financial support essential to the success of this meeting.

The abstracts in this volume are in the order of presentation, as follows. Presenters' names only are given in this list. See abstracts for co-author names.

SCIENTIFIC PROGRAM

4 to 5 speakers per session, each speaker: 15 mins + 5 mins questions

Session 1: Saturday 09:00 to 10:50Theme: Tectonics and geodynamicsChair: Greg Houseman

09:00-09:05 Greg Houseman: Welcome and introduction09:05-09:30 Horváth, Ferenc: Continental extrusion tectonics revisited (p4)09:30-09:50 Faccenna, Claudio: The Mediterranean arc at the end of subduction (p5)09:50-10:10 Fodor, László: Tertiary evolution of paleostress field and fault pattern in the

Pannonian-Carpathian domain (p6)10:10-10:30 Bada, Gábor: Late-stage tectonic inversion and landscape development of the

Pannonian basin and the Topo-Hungary initiative (p7)10:30-10:50 Decker, Kurt: Miocene to present tectonics at the Alpine-Carpathian-Pannonian

junction (p8)

10:50-11:10 Coffee break

Session 2: Saturday 11:10 to 12:30Theme: Magmatism and mantle processesChair: Dan McKenzie

11:10-11:30 Harangi, Szabolcs: Petrogenesis and geodynamic relationships of the Neogene to Quaternary volcanism in the Carpathian-Pannonian region (p9)

11:30-11:50 Szabó, Csaba: Melt and fluid inclusions from the upper mantle xenoliths and their significance in the Carpathian-Pannonian region (p11)

11:50-12:10 Falus, György: Mechanical processes in the upper mantle during the formation of the Carpathian Pannonian System: a mantle xenolith study from the Southeastern

Alpine - Carpathian - Pannonian Workshop, September 14-16, 2007 1

Carpathians (p12)12:10-12:30 Achauer, Ulrich: The Plume Project : Plume-like instabilities in the Upper Mantle

beneath Europe – ILP task force VIII (p13)

13:00-14:00 Lunch

Session 3: Saturday 14:00 to 15:40Theme: SeismologyChair: Frank Horváth

14:00-14:20 Hegedűs, Endre: Seismic Probing of the Pannonian Lithosphere by Controlled Source Methods: a Review (p14)

14:20-14:40 Behm, Michael and Brueckl, Ewald: Crustal structure of Eastern Alps derived from data of recent WAR/R experiments (p15)

14:40-15:00 Stuart, Graham: Initial seismology results from the Carpathian Basins Project (p16)15:00-15:20 Sumanovac, Franjo / Orešković, Jasna : Lithosphere structure in the area of the

Dinarides and SW part of the Pannonian Basin based on 2-D seismic and gravity modelling (p17)


Session 4: Saturday 16:00 to 17:40Theme: Subduction and deformationChair: Claudio Faccenna

15:40-16:00 McKenzie, Dan: The control of seismicity by temperature (p18)16:00-16:20 Butler, Robert: How pre-existing crustal structure can influence the tectonic

evolution of orogenic belts (p19)16:20-16:40 Royden, Leigh: Subduction dynamics for variable density slabs (p20)16:40-17:00 Husson, Laurent: Dynamic topography in the Aegean and Pannonian basins (p21)17:00-17:20 Brun, Jean-Pierre: Mechanisms of Aegean extension (p22)

Bus leaves at 18:30 ------> Dinner (19:30) in Udvarház Restaurant, Felsőörs

Session 5: Sunday 09:00 to 10:20Theme: Topography and stratigraphy vs. tectonics and climateChair: Jean-Pierre Brun

09:00-09:20 Sztanó, Orsolya: Changes of water depth in the Late Miocene Lake Pannon revisited: the end of an old legend (p23)

09:20-09:40 Horváth, Anita: Detailed anatomy of the Makó Trough, Hungary: implications for the evolution of the Pannonian basin (p24)

09:40-10:00 Nádor, Annamária: Tectonic vs. climatic control on changes in sediment supply and storage: The Quaternary alluvial record of the central Pannonian basin (p25)

10:00-10:20 Stuewe, Kurt and Wagner, Thomas: The western margin of the basin: Highlights of young morphologies formed by basin inversion (p26)



Session 6: Sunday 10:40 to 13:00Theme: Pannonian basin: data and modelsChair: Leigh Royden

10:40-11:00 Lenkey, László: Geothermics of the Pannonian basin and its bearing on the tectonics of basin evolution (p27)

11:00-11:20 Szafián, Péter: Gravity field in the Carpatho-Pannonian region: data and implications on the crustal structure (p29)

11:20-11:40 Tondi, Rosaria: Seismic and density structure beneath the Vrancea seismogenic zone (p30)

11:40-12:00 Lorinczi, Piroska: Geodynamical models of the intermediate depth seismicity of the SE Carpathians (p31)

12:00-12:20 Houseman, Greg: A mechanism for the development of intra-orogenic basins by gravitational instability of the continental lithosphere (p32)

12:20-13:00 General discussion

13:00-14:00 Lunch

Contributed Posters on display throughout the meeting:Dando, Ben: Preliminary results from the Carpathian Basins teleseismic tomography project

(p33) Mitterbauer, Ulrike: ALPASS teleseismic tomography - Status report (p34)Zámolyi, András: Geomorphologic and drainage network analysis at the western end of the

little Hungarian Plain (p35)Zamolyi, András: From Miocene thrusting to post-collisional extension (p36)Szafián, Péter: Neotectonic analysis of high resolution seismic data, Lake Balaton,

Pannonian basin (p37)

14:00 Departure


CONTINENTAL EXTRUSION TECTONICS REVISITED

Frank Horváth1, Gábor Bada,1,2 Csaba Szabó3, Mátyás Herein1, Endre Dombrádi1,2

(1) Dept. of Geophysics, Institute of Geography and Earth SciencesEötvös Loránd University, Budapest, Hungary (ELTE)

(2) Netherlands Research Centre for Integrated Solid Earth Science (ISES)(3) Dept. of Petrology, Institute of Geography and Earth Sciences

Eötvös Loránd University, Budapest, Hungary (ELTE)

It is now well documented that lateral motions of wrench fault-bounded continental fragments are a general process in continental collision zones. McKenzie (1970, 1972) was the first to show that in the Mediterranean region two small plates (Aegean and Turkish) move rapidly westwards and consume oceanic lithosphere. This motion is such as to minimise the deformation work which needs to be done to move the African-Arabian plate further towards Eurasia. He also realised that the whole process resembles the indentation of a rigid die on a soft material, which creates fragments extruding sideways on both sides of the die. This idea of extrusion tectonics during continental collision became so popular that quite a few authors reinvented and applied the mechanism worldwide (e.g. Tapponier and Molnar, Burke and Sengör, Ratschbacher et al.).

In the framework of MIT-ELTE cooperation (1979-86) extrusion of an East Alpine block towards the east and rollback of the oceanic lithosphere in the Carpathian embayment was suggested and related to the formation of the Pannonian basin. It was also inferred that during extension moderate stretching (ß<2.2) occurred on a very thin, practically non-existing mantle lithosphere. The mechanism of this remarkably inhomogeneous stretching was difficult to understand at that time.

This lecture deals with one obvious, still hardly addressed aspect of the continental extrusion and attempts to explain the mechanism of inhomogeneous stretching. The model is very simple: the overthickened orogenic crust is stretched indeed directly on the top of the asthenosphere. We infer that a crustal wedge developed in the Alpine continental collision zone by detachment from the underlying and subducting mantle lithosphere. Extrusion of this wedge superimposed a crustal flake directly onto the asthenosphere as the former oceanic lithosphere retreated by subduction rollback. The dramatic temperature increase at the bottom of the crust led to rapid heating of the crust and cooling of the upper part of the asthenosphere.

This simple model is compatible with the thermal and subsidence history of the Pannonian basin and offers a reasonable explanation for the first phase of magmatic activity during basin formation, characterised by the rapid onset of a vast amount of lower crustal melt (SiO2-rich rhyolites with a high 87Sr/86Sr isotope ratio).


THE MEDITERRANEAN ARC AT THE END OF SUBDUCTION

Claudio Faccenna

Dip. Scienze Geologiche, Università Roma TRE

Plate tectonic history, geological, geochemical (element and isotope ratios), and seismological (P-wave tomography and SKS splitting) data are combined with laboratory modeling to present a three-dimensional reconstruction of the subduction history of the central Mediterranean subduction. We found that the dynamic evolution of the western Mediterranean subduction zone is characterized by a strong episodicity revealed also by the discrete opening of the Tyrrhenian Sea. In particolar, the Calabrian slab has been progressively disrupted by means of mechanical and thermal erosion leading to the formation of large windows, both in the southern Tyrrhenian Sea and in the southern Apennines. Windows at lateral slab edges have caused a dramatic reorganization of mantle convection, permitting inflow of subslab mantle material and causing a complicated pattern of magmatism in the Tyrrhenian region, with coexisting K- and Na-alkaline igneous rocks. Rapid, intermittent avalanches of large amounts of lithospheric material at slab edges progressively reduced the lateral length of the Calabrian slab to a narrow (200 km) slab plunging down into the mantle and enhancing the end of the subduction process.


TERTIARY EVOLUTION OF PALEOSTRESS FIELD AND FAULT PATTERN IN THE PANNONIAN-CARPATHIAN DOMAIN

László I. Fodor

Geological Institute of Hungary ([email protected])

The Pannonian basin and the surrounding Carpathian orogen is one of the best studied areas from the point of view of outcrop-scale fault analysis and reconstruction of paleostress fields. The data set was partly collected by systematic field measurements, partly by local works of M.Sc. and Ph.D. works (Fodor et al.1999, Csontos et al. 2002). Interpretation of paleostress data was combined with paleomagnetic data, which indicated large-scale rotations in the Miocene and probably in the Pliocene (Márton and Fodor 1995, 2003). During the last years, detailed geological mapping permitted the reconstruction of the fault pattern on map-scale (Fodor et al. in prep.). All these data derived from the outcropping mountain ranges; the extrapolation of fault-slip data has been achieved using industrial seismic reflection profiles.

The Paleogene basin formation and the subsequent early Miocene dismembering was characterised by a strike-slip type stress regime, with a compression in WNW–ESE to NW–SE direction. Transtension or pure compression was observed locally.

The first rotation event of the Pannonian basin occurred around 18-17 Ma. This rotation marks the change toward extensional tectonics and indicates the birth of the Pannonian Basin. This rotation was followed by the major (“first”) rifting event (17–15 Ma), which resulted in the formation (or reactivation) of normal faults, tilted blocks and half grabens, mainly in NW–SE direction. Emergence of metamorphic core complexes was also characteristic. Strike-slip faulting with transtensional character remained dominant in areas where displacement transfer was accommodated between blocks having different amount of extension.

A second block rotation event occurred between 15 and 14 Ma, which was followed by a “second phase of rifting”. Outcrop-scale observations permitted the reconstruction of the gradually rotating normal fault pattern from NNW to NNE and tensional stress axis from ENE to ESE direction, respectively. Map-scale faults do not unequivocally show such rotation; they were probably reactivated by gradually changing kinematics. The intensity of faulting was variable across the basin, displacement seem to reach larger values in the east. Extension was locally replaced by transpression, particularly in western Pannonia. All the Miocene structural evolution can be understand in the light of the temporal and spatial changes of the peri-Carpathian subduction and thrust front.

The Late Miocene classical “post-rift phase” was also marked by considerable brittle faulting. Tilting of pre-Late Miocene erosional surfaces, formation of syn-sedimentary fault scarps, local transtensional basins continued up to the early Pliocene (Csillag et al. 2004). Locally, the late Miocene faults dominate the structural pattern and “syn-rift faults” have minor importance.

Csillag, G., Fodor, L., Müller, P. & Benkő, K. 2004: Denudation surfaces, development of Pannonian formations and facies distribution indicate late Miocene to Quaternary deformation of the Transdanubian Range. – Geolines 17, 26–27.

Csontos, L., Benkovics, L., Bergerat, F., Mansy, J-L., Wórum, G. 2002: Tertiary deformation history from seismic sections study and fault analysis in a former European Tethyan margin (the Mecsek-Villány area, SW Hungary). – Tectonophysics 357, 81–102.

Fodor, L., Csontos, L., Bada, G., Györfi, I. & Benkovics, L. 1999: Tertiary tectonic evolution of the Pannonian basin system and neighbouring orogens: a new synthesis of paleostress data. – In: Durand, B., Jolivet, L., Horváth, F. & Séranne, M. (eds): The Mediterranean Basins: Tertiary extension within the Alpine Orogen. Geological Society, London, Special Publications, 156, 295–334.

Márton, E. & Fodor, L. 1995: Combination of paleomagnetic and stress data: a case study from North Hungary. – Tectonophysics 242, 99–114.

Márton, E. & Fodor, L. 2003: Tertiary paleomagnetic results and structural analysis from the Transdanubian Range (Hungary); sign for rotational disintegration of the Alcapa unit. – Tectonophysics 363, 201–224.


LATE-STAGE TECTONIC INVERSION AND LANDSCAPE DEVELOPMENT OF THE PANNONIAN BASIN AND THE TOPO-HUNGARY INITIATIVE

Gábor Bada

Dept. of Geophysics, Eötvös L. University, Budapest, Hungary

This contribution presents data and models on the late-stage inversion of the Pannonian basin, and its bearing on active tectonics and landscape development. Extensional formation of the Pannonian basin system within the Alpine orogenic belt started in the early Miocene, whereas its structural reactivation has been taking place since latest Miocene times due to changes in the regional stress field from tension to compression. As a result of the northward indentation of the Adriatic microplate (“Adria-push”), which is considered as the main driving force of active tectonic processes in the East Alpine-Pannonian region, considerable compressional stresses are concentrated in the Pannonian lithosphere. This has resulted in active faulting, seismicity, and overall contraction that led, eventually, to a gentle folding of the lithosphere. Stress indicators, earthquake focal mechanisms, GPS measurements and the results of neotectonic studies are reviewed, all indicating a well-defined spatial and temporal variation of the stress and strain fields during the last stages of basin evolution. Accordingly, related structural styles of structural inversion in the Pannonian basin vary both in time and space, resulting in a complex pattern of neotectonic activity.

Extensional basin formation led to significant weakening of the Pannonian lithosphere with subsequent deformation localised at crustal discontinuities. The extended, hot, and weak lithosphere is prone to reactivation under relatively low compressional stresses. Due to its low rigidity and the presence of intra-plate compression concentrated in the thin elastic core of the Pannonian lithosphere, the area exhibits large-scale bending manifested in Quaternary subsidence and uplift anomalies. The Pannonian basin has been interpreted as an example of lithospheric folding, with a wavelength spectrum ranging from a few kilometres (local basin inversion) to hundreds of kilometres (whole lithospheric folding). Folding of the Pannonian lithosphere is manifested in differential vertical motions with significant uplift at the basin margins and along some internal basement highs, and subsidence in the basin centre. Reconstruction of related landforms, erosion/deposition processes and drainage pattern development in this closely coupled system is of key importance. In this context, the latest results of the following main research topics are presented: (i) Dynamics of basin inversion: rheology and stress field in the Pannonian lithosphere; (ii) Mapping of active geological structures; (iii) Active tectonics vs. drainage pattern; (iiii) Temporal aspects: reconstruction of vertical vs. horizontal strain rates.


MIOCENE TO PRESENT TECTONICS AT THE ALPINE-CARPATHIAN-PANNONIAN JUNCTION

K. Decker

Department of Geodynamics and Sedimentology, University of Vienna [email protected]

The presentation addresses a review of the post-collisional tectonics of the Eastern Alps and the adjacent Western Carpathians. It attempts to highlight distinct stages during “continental extrusion” towards the Pannonian area, which accordingly may not be regarded a continuous process lasting from the Miocene to the Present.

(1) Oligocene to Early Miocene tectonics include N- to NW-directed thrusting of the Alpine-Carpathian allochthon over the European foreland and contemporaneous lateral extrusion of the central Eastern Alps south of the ENE-striking sinistral SEMP fault system. This early stage of extrusion is related to and dated by the exhumation of the Tauern Window south of the SEMP, which started during the Oligocene.

(2) Middle to Late Miocene extrusion is characterized by the abandonment of the SEMP fault, which is cut by the NE-striking sinistral Vienna Basin fault system. The latter delimits a new-shaped extruding unit referred to as the Styria-West Carpathian Wedge. NE-directed lateral movement of the wedge is accompanied by trailing edge extension (subsidence of the Styrian Basin and tectonic exhumation of the Rechnitz metamorphic core) and out-of-sequence thrusting at its leading edge (West Carpathians, Polish Galicia). Thrusting is directed towards NE, parallel to the Vienna Basin fault system, which therefore may be regarded a tear fault as originally proposed by L. Royden. Extrusion terminates during the Late Micoene (~ 7 – 5 Ma).

(3) Miocene faults of the Vienna Basin fault system are cut by NW-striking normal faults and grabens related to NE-directed extension. Major faults are located in the Kuty-Dobra Voda area and in the Czech Morava graben. Timing of extension is constrained by the Pliocene to Early Quaternary fill of these grabens as well as by fault data from slickensided loess and fossil soils, which are correlated to an Early Pleistocene soil forming period.

(4) Earthquake data, recent stresses, and analyses of active faults indicate that active tectonics at the Alpine-Carpathian-Pannonian junction mimic Middle to Late Miocene extrusion. The active Vienna Basin fault system shows up as a seismically active zone stretching from the Alps into the West Carpathians. Stress data and focal plane solutions prove sinistral strike-slip. By analogy to the Miocene it is suggested that the fault system is linked to active fold-thrusting in the Outer Carpathians. GPS and geological data suggest that the currently “extruding” wedge moves at a velocity of 1 - 2 mm/a with respect to the European foreland.


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PETROGENESIS AND GEODYNAMIC RELATIONSHIPS OF THE NEOGENE TO QUATERNARY VOLCANISM IN THE CARPATHIAN-PANNONIAN REGION

Szabolcs Harangi1, Hilary Downes2, László Lenkey3, Theodoros Ntaflos4

1 Eötvös University, Department of Petrology and Geochemistry, Budapest, Hungary, e-mail: [email protected]

2 School of Earth Sciences, Birkbeck College, University of London, London, U.K.3 Hungarian Academy of Sciences, Research Group of Geophysics and Environmental Physics, Budapest,

Hungary4 Department of Lithospheric Sciences, University of Vienna, Vienna, Austria

Neogene to Quaternary volcanism of the Carpathian-Pannonian Region (CPR) is part of the extensive volcanic activity in the Mediterranean and surrounding regions. Eruptions of magmas with wide range of compositions (basaltic to rhyolitic) are close relationships with the geodynamic evolution of the CPR, yet there has been a continuous debate about the origin of the magmatism. First, we discuss the possible role of subduction, extension and mantle plume in the melt generation. Then, we highlight two hot topics: (1) the nature of the sub-lithospheric mantle beneath the Pannonian basin, as inferred from the geochemistry of the alkaline mafic rocks; (2) characteristics of the youngest volcanism of the CPR in the southeast Carpathians.

Using the spatial and temporal distribution of the magmatic rocks and their major and trace element and Sr-Nd-Pb isotope characteristics, we suggest that lithospheric extension in the Pannonian Basin had a major role in the generation of the magmas. Dehydration of the subducting slab should have resulted in thorough metasomatism in the mantle wedge during Cretaceous to Early Miocene, lowering the melting temperature, and therefore playing an indirect role in the generation of magmas later on. Mixing between mantle-derived magmas and lower crustal melts could have been an important process at the first stage (Middle Miocene) of the silicic and calc-alkaline magmatism in the Northern Pannonian Basin. However, the crustal component gradually decreased with time consistent with a magmatic activity in a continuously thinning continental plate. Calc-alkaline volcanism along the Eastern Carpathians was mostly post-collisional and could be related to slab break-off and/or lithospheric delamination processes. Alkaline basaltic volcanism began at the end of rifting of the Pannonian Basin (11 Ma) and continued until recently. We suggest that a mantle plume beneath the Pannonian Basin is highly unlikely and the mafic magmas were formed by small degree partial melting in a heterogeneous asthenospheric mantle, which has been close to the solidus temperature due to the lithospheric extension in the Miocene. Magmatism appears to have been in a waning phase for the last 2 Ma, but recent volcanic eruptions (<200 Kyr) indicate that the future volcanic activity cannot be unambiguously ruled out.

Composition of the 11-0.1 Ma old alkaline mafic magmas provides important information about the nature of the sub-lithospheric mantle and the melt generation beneath the Pannonian basin. Trace element composition of the most primitive samples suggests that the primary magmas were formed by different degrees (1-6%) of melting of a moderately enriched mantle (1.5- to 4-times primitive mantle values) in the garnet-spinel and garnet-peridotite stability field. A K-bearing hydrous mineral phase (possibly amphibole), which remained in the residuum at low degree melting, is assumed in the mantle source regions. Mantle potential temperature is estimated based on olivine-melt thermometry. Olivine equilibrium temperatures are in the range from 1250 to 1350oC, which corresponds to mantle potential temperature of about 1350±50oC. We suggest that melt generation could be due to mantle flows along lithosphere-asthenosphere irregularities, i.e. mostly at the periphery of the Pannonian basin. The long history of orogenic events (Hercynian and Alpine orogenesis) in Europe could supply vast amount of crustal material into the upper mantle resulting in small-scale geochemical heterogeneity. Partial melting


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of different parts of the shallow asthenospheric mantle such as metasomatized, amphibole-bearing sections with FOZO-like composition at low degree melting and depleted MORB-mantle around them at higher degree of melting and mixing of these melts could explain the isotopic variation in the alkaline mafic magmas of the Pannonian basin.

One of the hottest topics of the magmatism in the CPR is the origin of the latest volcanic eruptions. Our new data (e.g., high-Mg minerals in the dacites, recognition of a new lamproite occurrence) indicate the important role of lamproitic magmas in the magmagenesis along the southeastern part of the CPR. The ultrapotassic melts mixed variably with lower crustal melts providing hybrid, dacitic magmas, which should ascent rapidly to the surface. The temporal history of the <1 Ma volcanism in the Ciomadul with the last eruption at 28 ka and the petrologic and geochemical features of the magmas warn that the volcanic eruptions could continue in the future.

This study has been supported by Hungarian-Austrian research funds (Hungarian-Austrian Action Foundation, ASO) and the OTKA Research grant # K68587.


MELT AND FLUID INCLUSIONS FROM THE UPPER MANTLE XENOLITHS AND THEIR SIGNIFICANCE IN THE CARPATHIAN-PANNONIAN REGION

Csaba Szabó

Dept. of Petrology, Institute of Geography and Earth SciencesEötvös Loránd University, Budapest, Hungary (ELTE)

Melt and fluid inclusions, in general, are small droplets of any kind of melts or fluids enclosed in a host mineral, which were trapped accidentally at high temperatures (±pressures) and subsequently quenched or partially or totally crystallized. In mantle environments CO2 (or CO2-rich) fluid and silicate melt inclusions are the most abundant, however sulfide and extremely rare carbonatite melt inclusions also occur and are relevant to the focus of interest.

CO2-rich fluid inclusions may include H2O, N2, CO, SO2 and noble gases, too. The distribution of minor volatile species in inclusion fluids can provide information on the oxidation state of the mantle, on mantle degassing processes and on recycling of subducted material to the mantle.

Silicate melt accumulations in the mantle occurring as inclusions, melt pockets, interstitial glass patches and veins have been described from several localities of upper mantle xenoliths all over the world. These melt accumulations provide essential information on melting and melt migration related to processes of metasomatism, melt-mantle interaction, and fluid-melt immiscibility, which impart incompatible major, minor and trace elements into depleted regions of otherwise fertile mantle. Also, silicate melt inclusions are key materials to reveal post-entrapment processes such as crystallization on the inclusion walls or immiscibility of volatiles and silicates within the inclusions.

The most important message of MI studies in mantle xenoliths is that they may preserve the composition of high pressure and temperature melts, because the large elastic modulus of their host mantle silicates (e.g., orthopyroxene, clinopyroxene, olivine) prevent them from low-pressure re-equilibration and decompression during ascent to the surface. It is noteworthy that, by contrast, interstitial glass patches, melt pockets or veins in the upper mantle xenoliths significantly re-equilibrate and their chemical composition and/or textural features usually reflect lowering pressure and temperature conditions. Therefore, early-stage or primary silicate melt inclusions from deep lithosphere environments are generally considered to be mantle silicate melts that were trapped at high pressure and temperature in equilibrium with the peridotitic assemblages.

It is generally accepted that sulfide MI can provide insight into geochemical processes such as mantle depletion and enrichment. Petrographic and major element characteristics of sulfide phases in upper mantle xenoliths are consistent with their origin as an immiscible phase formed during partial melting. However, an origin by metasomatic fluid infiltration through the lithospheric mantle has been also suggested. Re-Os isotopes of sulfide inclusions in mantle peridotites have lately contributed much information on ages of the lithospheric mantle.


MECHANICAL PROCESSES IN THE UPPER MANTLE DURING THE FORMATION OF THE CARPATHIAN PANNONIAN SYSTEM: A MANTLE

XENOLITH STUDY FROM THE SOUTHEASTERN CARPATHIANS

Gyorgy Falus

Eötvös Loránd Geophysical Institute

Peridotite mantle xenoliths with a broad textural variation provide evidence for consistent microstructural evolution in a vertical transect of the shallow lithospheric mantle (35-55 km depth) beneath the Persani Mountains, Southeastern Carpathians, Romania, due to ongoing plate convergence in the Carpathian Arc nearby. Recrystallized grain size, crystal preferred orientations strength, and resulting seismic anisotropy vary continuously and display a strong correlation to equilibrium temperatures, suggesting a continuous variation in deformation conditions with depth. The shallowmost xenoliths display microstructures typical of high stress deformation, marked by strong recrystallization to fine grain sizes, which results in weak crystal preferred orientations and anisotropy. The deepest xenoliths show coarse grained prophyroclastic microstructures and strong crystal preferred orientations. Replacive orthopyroxenes, consuming olivine, and high H2O concentrations in the pyroxenes are observed in some xenoliths indicating limited percolation of subduction-related fluids/melts in the sampled upper mantle. Despite high stress deformation and high H2O content in some of the studied xenoliths, analysis of olivine crystallographic orientations indicates that [100] slip systems, rather than "wet" [001] accommodate most of the deformation. Dominant activation of [100] probably results from the low H2O solubility in olivine at spinel peridotite facies, low pressure conditions. These observations raise the question of the conditions necessary to produce ‘wet’ deformation of olivine at shallow depths in the mantle. Seismic anisotropy estimated from the measured olivine and pyroxene crystal preferred orientations suggests that strike-parallel fast SKS polarization directions and ~1s delay times in the southeastern Carpathians are likely the consequence of convergence-driven belt-parallel creep in the lithospheric mantle.


THE PLUME PROJECT : PLUME-LIKE INSTABILITIES IN THE UPPER MANTLE BENEATH EUROPE – ILP TASK FORCE VIII

Ulrich Achauer, Marge Wilson and the PLUME project participants

PLUME brings together an interdisciplinary group of researchers interested in the problem of how convective instabilities in the upper mantle originate and what their relationship is to magma generation processes (“hotspots”) and lithosphere geodynamics.

In recent years a number of high-resolution integrated seismic projects across regions of Tertiary to Recent volcanism in central Europe have, in collaboration with detailed geochemical studies, demonstrated the existence of a number of small-scale, almost cylindrical, upwellings of low-velocity mantle material (~ 100-150 km in diameter). These “diapiric instabilities” have some characteristics in common with those of “classical” mantle plumes (e.g. thermal and geochemical anomalies, associated basement uplift), but a number of distinct differences:

• They are much smaller in size than classical plumes• They do not appear to “have” a plume head• They appear to originate in the Transition Zone (410-660 km depth)

The existence of these small-scale plume structures suggests that there might exist a number of different classes of mantle plume, originating from different depths within the mantle (e.g. the Transition Zone, the lower mantle or the CMB). So far such structures have only been postulated to exist beneath the European continent (e.g. the Massif Central, the Eifel and possibly the Bohemian Massif), but it is highly likely that similar structures exist beneath other continents.

The following observations can be made concerning the origin of these upper mantle plumes:

• They are small-scale convective instabilities within the upper mantle beneath Europe which appear to originate in the Transition Zone (410-660km depth)

• There is a strong correlation between the location of the “upwellings” and lithospheric architecture – suggesting some form of top-down control.

• The upwellings appear to be concentrated around the edge of a region of subducted slabs at the base of the upper mantle.

• Basaltic magmas derived by decompression partial melting of the upwelling mantle “diapirs” have the distinctive geochemical signature of a common mantle source component – the European Asthenospheric Reservoir (EAR).

• The EAR could be the product of outflow from one or more lower mantle plumes.

The location of these upper mantle instabilities could be controlled by a number of factors, such as:

• The regional stress field• Inherited lithospheric structures (e.g. sutures and weak zones)• The upwelling of hot or volatile-rich material from the deep mantle • Dynamic mantle upwelling in response to delamination of subducted (or thickened

continental) lithosphere – so-called “splash plumes”

In this paper we shall present the current state-of-affairs of the project PLUME and outline future research directions.


SEISMIC PROBING OF THE PANNONIAN LITHOSPHERE BY CONTROLLED SOURCE METHODS: A REVIEW

Hegedűs, EndreEötvös Loránd Geophysical Institute

Early results of the lithospheric research by refraction and wide-angle reflection methods.During the first experiments in 1955 seismic arrivals were obtained from the crust-mantle boundary. Those first attempts have revealed that the crust is thinner in the Pannonian Basin than the European average. In the 60’s and early 70’s it became possible to map the crustal thickness in Central Europe by a grid of DSS profiles.

Results of deep seismic reflection investigation of the Earth’s crust and upper mantle: the Pannonian Geotraverse Program.A domal uplift structure of the lithosphere-asthenosphere boundary beneath the Bekes Basin is detected at 40-45 km depth. The existence of displacement zones affecting the whole lithosphere where supposed with magmatic intrusions reaching the upper crust.

New generation of seismic wide-angle reflection and refraction experiments in Central Europe: the CELEBRATION 2000, ALP 2002 and SUDETES 2003 programs.A consortium of European and North American institutions completed a huge active-source seismic experiment focused on Central Europe. In total 230 shots with an average charge of 500 kg were applied as seismic sources detected along 18.000 km long profiles using 3.320 stations. The net of interlocking profiles provided substantial 3D coverage within the Pannonian Basin where unknown structures where detected beneath the thick Cenozoic volcano-sedimentary cover.

Low frequency seismic studies for practical applications: the Nyírség 3D experiment. A 700 sqkm grid survey with 1000 stand-alone low-frequency recording units detected wide-angle signals penetrated through the volcanic blanket revealed significant underlying sedimentary strata – using tomographic inversions.


CRUSTAL STRUCTURE OF EASTERN ALPS DERIVED FROM DATA OF RECENT WAR/R EXPERIMENTS

Michael Behm and Ewald Brückl

Institute of Geodesy and Geophysics, Vienna University of Technology

The Alps are the result of a long and ongoing tectonic evolution, initiated coevally with the opening of the Atlantic Ocean in the early Jurassic. Major geodynamic processes involved in the orogenesis of the Eastern Alps include the subduction of the Meliata ocean in the Jurassic and Cretaceous, the subduction of the Alpine Tethys in the Tertiary and the following continent-continent collision between the European and Adriatic-Apulian plates. In the Miocene, parts of the Eastern Alps were vertically or horizontally extruded or escaped tectonically eastwards into the Pannonian domain along major strike-slip fault systems.

Since 2000 several large WAR/R experiments (CELEBRATON 2000, ALP 2002, SUDETES 2003) covered this area by a dense net of seismic profiles. We present the most recent seismic models of the Eastern Alps and their transition to the surrounding tectonic provinces (Bohemian massif, Southern Alps, Dinarides, Pannonian domain) derived from CELEBRATION 2000 and ALP 2002 data. The seismic data were processed by different 2D and 3D techniques, resulting in P-wave velocity models of the crust and upper mantle, and a new Moho depth map.

P-wave velocity structures of the upper and middle crust correlate well with geologic and tectonic units. Examples of regions with relatively low velocities are sedimentary basins and their basement and granite intrusions in the Bohemian massif. Significant high velocity areas are a deep reaching zone north of the Tauern window, the middle crust of the Tisza unit, and, most pronounced the upper crust of the Adriatic foreland. High velocities in the lower crust are found below the Vienna basin and its north-western and south-eastern surroundings.

The Moho depth map shows a fragmentation of the crust and upper mantle into three parts: the European plate, the Adriatic-Apulian micro-plate, and the newly interpreted Pannonian fragment. The Moho depth map indicates a southward subduction of the European plate below the Adriatic-Apulian plate and below the Pannonian fragment. However, the Adriatic-Apulian Moho dips in north-north-eastern direction below the Pannonian Moho. We interpret that the Pannonian fragment was part of the Adriatic-Apulian plate before and during an early state of the collision. Crustal thinning and Moho uplift of the Pannonian fragment was initiated during the subsequent tectonic escape to the unconstrained margin in the east, represented by the Pannonian basin. Since the Miocene, underthrusting of the Adriatic-Apulian plate below the Pannonian fragment could have been one mechanism of continuing crustal shortening in the region of the Eastern Alps and the most northern Dinarides.

Ongoing studies on crustal structure in the area of the Eastern Alps focus on the interpretation of the S-wave velocity structure. Despite that only vertical component geophones were used in the above mentioned experiments, significant shear wave phases are also regularly observed in the seismic sections, in particular diving waves through the crust (Sg), and reflections from the Moho (SmS). The results so far show significant structures of the Vp/Vs ratio in the upper crust. In case of the Moho, the evaluation of reflected S-waves confirms the results derived by P-wave modelling.


INITIAL SEISMOLOGY RESULTS FROM THE CARPATHIAN BASINS PROJECT

G. Stuart (1), G. Houseman (1), B. Dando (1), E. Hegedüs (2), E. Brückl (3), S. Radovanovic (4), G. Falus (2), A. Kovács (2), H. Hausmann (3), A. Brisbourne (5)

(1) School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK ([email protected]), (2) Eötvös Loránd Geophysical Institute, 1145 Budapest, XIV. ker. Columbus u. 17-23, Hungary, (3) Institute of Geodesy and Geophysics, TU-

Wien, A-1040, Vienna, Austria, (4) Seismological Survey of Serbia, 11000 Beograd, Park Tasmajdan, Serbia, (5) SEIS-UK, University of Leicester, University Road, Leicester,

LE1 7RH, UK

The Carpathian Basins Project (CBP) aims to understand the origin of Miocene-age extensional basins, of which the Pannonian Basin is the largest, within the arc of the Alpine-Carpathian Mountain Ranges – a compressional structure. Analysis of the subsidence history of the Pannonian Basin shows that its mantle lithosphere has undergone a much greater degree of extension than the overlying crust. We describe the results of a temporary seismic deployment to test competing theories of how the continental lithosphere evolved in the region.

We deployed a 46-element seismic network, 450 km x 80 km, oriented in a NW-SE direction, crossing the Vienna and western Pannonian Basins in Austria, Hungary and Serbia. The network ran for 14 months from early May 2006. The stations were broadband to 30s and spaced at ~30 km along 3 parallel lines, which are 40 km apart. The principal object of this network is to use P and S-wave teleseismic tomography to image the upper mantle. P-wave residuals from sources perpendicular to the tectonic grain show a ~1s variation across the Mid-Hungarian High in to the Pannonian Basin. This delay cannot be explained by sedimentary or crustal thickness variations, which are well-controlled by boreholes, deep seismic soundings and our own receiver function analyses. We must infer significant lithospheric thinning and anomalously low asthenospheric velocities underlying the Pannonian Basin to explain our observations. These travel time delays are accompanied by a dramatic change in the orientation of SKS splitting measurements from E-W to NW-SE across the Mid-Hungarian High.

We have also installed a more broadly distributed regional broadband array of 10 instruments (broadband to 120 sec) for 2 years from September 2005, spaced at ~100km within Hungary, Croatia and Serbia to augment the data available from permanent broadband networks in central Europe. Preliminary interstation surface wave dispersion results from across the Pannonian Basin imply lithospheric thicknesses of the order of 60km.


LITHOSPHERE STRUCTURE IN THE AREA OF THE DINARIDES AND SW PART OF THE PANNONIAN BASIN BASED ON 2-D SEISMIC AND GRAVITY

MODELLING

Franjo Šumanovac1, Jasna Orešković1, ALP 2002 Working Group1University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Pierottijeva

6,10000 Zagreb, HR

Deep seismic exploration has been carried out on the profile ALP07 in the framework of the international scientific project ALP 2002-Seismic Exploration of the Alpine Lithospere, whose scientific objective is to acquire fundamental data about deep structures in crust and upper mantle, including Mohorovičić discontinuity. These data are very useful in the seismology and other deep explorations. The ALP07 profile is set up approximately perpendicular to extension of geological structures, respectively to the dinaridic direction. The profile length is 270 km and covers areas of the Dinarides and edge part of the Pannonian basin in Croatia. The profile extends from Istra, across the Krk island, city of Karlovac, beside the Zagreb and ends at the Đurđevac by border with Hungary. Four shots were set on the profile: Koromačno in Istra, Tribalj at Crikvenice, Ivanić Grad and the shot in Hungary, and 72 stations were deployed.

Data quality is much higher from the shots placed in the Pannonian Basin, than from the shots placed in the area of the Dinarides. High quality data can be seen on the measured seismograms of the shots Ivanić Grad (32070) and Hungary (38070), where first and even later arrivals are very clear. The shot in Hungary provides us with the most integral data about deep crustal structures and Mohorovičić discontinuity.

Two-dimensional interpretation has been carried out by the forward modelling software based on the Ray Tracing Method, which consists of two modules: ZPLOT (author Colin Zelt), and SEIS 83 (authors Vlastislav Červeny and Ivan Pšenčik). Automatic inversion by the Seismic Tomography Method has been carried out by the HOLE software (author J. A. Hole). Two-dimensional gravity modelling on the profile ALP07 has been performed by the software GM-SYS in order to reducing of the interpretation ambiguity. The aim was to define better attributes of the layers determined by the seismic modelling. However, new significance has been associated to some events on the seismic profile, so gravity modelling has been more useful than expected.

Depths of the Mohorovičić discontinuity on the seismic model obtained by the forward modelling are the greatest in the area of the Dinarides (40 km). Depths in the area of the Pannonian Basin are in the range 20-30 km with the smallest value at the end of the profile. Depth changes are not smooth and uneven relief of the Mohorovičić discontinuity can be noticed. Seismic tomographic model indicates this event, as well. In the upper crust seismic velocities are generally very low, around 6 km/s, but with lateral variations. Two anomalies of higher velocities can be noticed: shallow anomaly in the beginning and deeper anomaly in the center of the profile. These anomalies can be also seen on the tomographic model. Relatively high seismic velocities characterise the lower crust in the area of the Dinarides (6.6-7.1 km/s), but in the area of the Pannonian Basin velocities are very low, around 6.0 km/s. According to the velocity distribution there is no need to divide the crust on the upper and the lower, but the crust can be considered as unique layer. This conclusion is also confirmed by the gravity modelling. Therefore two types of crust are defined: Pannonian Crust and Dinaridic Crust, which are separated by wide Transition Zone. This zone is characterised by sharp changes of seismic velocities and densities that point to tectonic anomalies and fracturing.


THE CONTROL OF SEISMICITY BY TEMPERATURE

Dan McKenzie

Bullard Labs, Cambridge University

Modern broad band digital records of earthquakes allow the depth of shallow events to be determined to an accuracy of about 5 km. The thickness of the crust beneath the recording station can also be determined to a similar accuracy. Global studies of the depth of earthquakes beneath continents have shown that almost all occur within the crust. Detailed thermal modelling of the temperature structure of the continental crust must take account of the temperature dependence of the thermal conductivity and of the distribution of heat sources with depth. Such modelling shows that only those regions where the crust or mantle is cooler than 600 C are seismic. The same is true of oceanic lithosphere, and of the seismicity in sinking slabs. This result implies that the localised regions of intermediate and deep focus activity, such as those beneath beneath Romania, the Hindu Kush and Myanmar, are also regions where the temperature is below 600 C. Almost all the mantle beneath continents is warmer than 600 C, whereas this isotherm is at a depth of about 60 km within old oceanic lithosphere. It is therefore likely that the intermediate depth seismic activity beneath these regions of the continents results from the subduction of fragments of old oceanic lithosphere, like that which is still present beneath the southern part of the Caspian Sea.


HOW PRE-EXISTING CRUSTAL STRUCTURE CAN INFLUENCE

THE TECTONIC EVOLUTION OF OROGENIC BELTS

Rob Butlera,

and Enrico Tavarnellib

aInstitute of Geophysics and Tectonics, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom. [email protected]

bDipartimento di Scienze della Terra, University of Siena, Siena, Italy

The geological structure of continental lithosphere shows complex variety that is inherited into orogenic belts and influences the localization and amplification of contractional structures during mountain building. The role of basement in thrust belts commonly reflects the propensity of pre-existing faults to reactivate during horizontal compression. However, reactivation styles are hugely variable in nature and may reflect not only orientation and strength variations of pre-existing faults but also of the strength of the crust within which they are embedded. Thus different patterns of basement reactivation may reflect spatially-varying strength-depth profiles in continental lithosphere that are themselves inherited from spatially-distinct geological histories. These are also modified during orogenesis. On a large scale these variations are likely to place limits on the ability of continental crust to deform significantly during the progressive evolution of mountain belts. Different patterns of basement deformation, proxies for larger-scale crustal deformations, are reviewed. While in some areas these inherited faults may simply reactivate under inversion, more commonly faults show complex, partial reactivation structures embedded within tracts of distributed strain that relate to crustal types. Within the volumes of distributed strain, faults may serve to nucleate large-scale buckle folds, for example, along basement-cover interfaces. Segmentation of orogenic belts (e.g. the Apennines) can relate to pre-existing variations in rift basin geometry. On a larger scale, the evolution of slab roll-back and the related growth of overlying extensional basins (e.g. Tyrrhenian Sea) may be modulated by the distribution not only of subductable oceanic lithosphere but also of the rift-related weak zones in the adjacent continental crust. Examples are drawn primarily from the Alpine-Apennine system together with other sectors of the Tethyan orogens. It remains unclear the extent to which continental orogenic belts represent the amplification of inherited geological heterogeneities as opposed to self-ordered phenomena modulated by the syntectonic environment.


SUBDUCTION DYNAMICS FOR VARIABLY BUOYANT SLABS

Leigh Royden

Dept. Earth. Atmos. Planet. Sci., MIT, Cambridge MA 01890 USA

[email protected]

Subduction of variably buoyant lithosphere is a common phenomena in many geologic settings. A semi-analytic three-dimensional subduction model, which incorporates a thin-sheet slab within a viscous upper mantle, provides a dynamically consistent means of computing subduction kinematics. Model results indicate that rates of subduction and trench migration can respond by a factor of two or more in as little as 2 m.y. after anomalously buoyant lithosphere enters the subduction system. Changes in subduction rate are closely correlated with slab dip, with shallower slab dips corresponding to subduction of more negatively buoyant slabs. Subduction rate correlates with distance from the trench to the volcanic arc, which decreases by a factor three following subduction of a continental margin.

The recent evolution of the Apennine, Banda and Hellenic subduction systems provide excellent opportunities to observe how spatial and/or temporal variability in foreland buoyancy is reflected by changes in rates of subduction. Within the Southern Apennine and southwestern Banda Arc regions, entry of buoyant continental crust into the subduction boundary is followed by very rapid cessation of subduction, in reasonable agreement with model predictions. Along the Hellenic subduction boundary, entry of Ionian oceanic lithosphere into the southern part of the subduction system (south of Kephalonia) has resulted in an increase in trench retreat rates from ~10 mm/yr to ~35 mm/yr over a period of less than 10 m.y. This is in excellent agreement with model results and explains evolution of the Kephalonia Transform system the young disruption of the Hellenic thrust belt along a broad belt connecting the Kephalonia Transform to the North Aegean Trough and ultimately to the North Anatolian Fault system.


DYNAMIC TOPOGRAPHY IN THE AEGEAN AND PANNONIAN BASINS

Laurent Husson

CNRS, Université Rennes-1

Large-scale variations of the topography may reflect variations the vertical support of topography from mantle dynamics. For example,small subductions like the Aegean Sea or the Pannonian Basin show important vertical variations of the base level that more likely reflect changes in subduction dynamics rather than isostatic readjustment. Such observations will be discussed on the basis of numerical and analogue modeling.


MECHANISMS OF AEGEAN EXTENSION

Jean-Pierre Brun

Géosciences Rennes, Campus de Beaulieu, 35042 Rennes cedex France

Jean-Pierre.Brun @univ-rennes1.fr

We attempt here an integrated crust-mantle approach of the Aegean extension based on the geometry and timing of crustal ductile flow patterns, directly observed in the metamorphic core complexes (MCC), and those that can be inferred for the mantle from seismology, in particular seismic anisotropy and tomography. Our analysis can be summarised according the three following lines of evidence.

1- Structural, paleomagnetic and geochronological evidence from the Rhodope MCC show that extension starts in the northern Aegean in the Eocene time -i.e. around 45 Ma ago- 15 to 20 Ma before what was believed up to now.

2- Twice during the extensional history, MCC develop synchronous with the exhumation of HP metamorphic rocks: i) in Eocene time, MCC in the Rhodope and blueschist exhumation in the Cyclades, ii) in Oligocene-Lower Miocene times, MCC in the Cyclades and blueschist exhumation in Crete.

3- Stretching lineations in Rhodope and Cyclades MCCs and mantle anisotropy in North Aegean, when plotted on the same map, form a coherent arcuate pattern that suggest a strong kinematical relationship between crust and mantle flow and between ductile flow and large scale dextral block rotation in the upper brittle crust.

The evolution of extension at the scale of the whole Aegean is quantitatively described by a step-by-step restoration of extensional displacements at surface that takes into account the geometry of the most prominent large-scale structures, block rotation, indicated by structural contours and paleomagnetic data, and the directions of principal stretch measured in MCCs.

On the above bases, we propose a model where most of the 45 Ma of Aegean extension is controlled by the rotational retreat of the Hellenic slab toward the S-SW. The model well fits with the flow pattern recorded in crust and mantle, simultaneously. During the last 5 Ma, this simple kinematics is however modified by the westward extrusion of Anatolia.


CHANGES OF WATER DEPTH IN THE LATE MIOCENE LAKE PANNON REVISITED: THE END OF AN OLD LEGEND

O. Sztanó (1), I. Magyar (2) & F. Horváth (1)

(1) Eötvös Loránd University, Budapest, Hungary, (2) MOL Hungarian Oil and Gas Company, ([email protected], [email protected], [email protected])

The large Late Miocene Lake Pannon was a descendant of the Paratethys. The lake inherited a complicated collision- and rift-related bottom topography, which determined variations of subsidence rates and water depth of the individual subbasins. Lake water level was influenced by discharging rivers and precipitation, both controlled by climatic variations. Lake Pannon was surrounded by uplifting mountain chains providing abundant sedimentary influx both from Alpine and Carpathian source regions. This led to the progressive infill of the basin by fluvial-deltaic and turbiditic sediments dominantly from northwesterly (palaeo-Danube) and northeasterly directions (palaeo-Tisza). The variations in rate of progradation to aggradation of the delta-fed shelf-slope systems indicate that relative lake level also varied significantly both in space and time. The geometry of clinoforms can be used to determine the palaeo-water depth. Initial bottom topography and differential subsidence rates determined if “shallow-water” (200-400 m) or “deep-water” (700-900m) developed at certain parts of the basin. The high rate of subsidence coupled with the high rate of sediment input rates resulted in an excellent resolution of the startigraphic record, therefore former studies emphasized that both 3rd, 4th -order depositional sequences can be recognised. At the eastern part of the basin, where the most detailed studies were carried out so far, one of the most spectacular sequence boundaries at about 6.8 Ma was depicted by earlier authors who claimed that it separated the “deep-water” system from the overlying “shallow-water” one. In addition to the remarkable change in the height of the slope, onlaping slump deposits and turbidites at the former slope-toe were among the evidences to postulate a Messinian event.

In our study the same sections have been reinterpreted by using the advantages of the digital processing technology. Since the basin-fill succession was deformed by Late Miocene, Pliocene to Quaternary tectonics it seemed to be neccesary to remove their effects. Therefore a series of snapshots were produced by flattening the seismic image to supposed palaeo-horizontals. The images clearly show, that when the shelf-slope system prograded above a half-graben, the virtual increase of the slope height and length occurred as a consequence of synsedimentary deformation at a basin margin listric fault. Afterwards aggradation and progradation continued at varying rates until a long wavelength synsedimentary folding of the whole area took place. The gradual uplift of the eastern and the ongoing subsidence of the western parts of the study area resulted in again a virtual growth of the slope height particularly along the limb of the fold. The water depth in this segment of Lake Pannon in reality did not changed significantly during these events, it remained in the range of about 4-500 m (un-decompacted thickness).

Based on the analyses of perpendicular sections it can be proved that the onlap surface dividing the virtually “deep-” and “shallow-water” settings, high and low slopes respectively, marks superposition of two distinct feeder systems having a 45o degree difference in their direction of progradation.

These evidences indicate that there was no major lake level drop in the Late Miocene Lake Pannon at about 6.8? Ma, but synsedimentary deformation took place at various scale and duration. Retro-deformation of the basin fill succession is necessary to understand the interplay of sedimentation and tectonics.

It is acknowledged that this study was supported by Norsk Hydro and data was provided by MOL.


DETAILED ANATOMY OF THE MAKÓ TROUGH, HUNGARY:

IMPLICATIONS FOR THE EVOLUTION OF THE PANNONIAN BASIN

Anita Horváth, G. Bada, R. Wallis, Gy. Valcz, P. Szafián, F. Horváth

TXM-Falcon Oil and Gas

Recently, intensive unconventional hydrocarbon exploration has been taking place in the Pannonian Basin, exploring basin-centered gas accumulation (BCGA) potential of the Makó Trough. The project is of enormous economic potential as well as scientific and technological challenge. Exploration risk is very high, due to extreme high temperature/high pressure conditions.

The investigation focuses on one of the deepest sub-basins in the Pannonian basin, which to date has never been considered for unconventional exploration. Great wealth of new geological and geophysical information have been gathered and integrated with existing data. Interpretation of these data is in progress, involving several Hungarian and international industrial and academical institutions. The purpose of this presentation is to highlight the current status of exploration making use of mainly new 3D seismic data covering >1100 km2. These data revealed the regional stratigraphic and tectonic features of the trough and provided insights to the details of the basinal and basement structures at an unprecedented resolution and depth. The well and core data revealed complementary information on the present-day stress field, representing the characteristics of the natural fractures and pressure systems in the trough.

The exploration results obtained so far are of key importance in developing the existing kinematic and dynamic models for the formation and deformation of the Pannonian basin.


TECTONIC VS. CLIMATIC CONTROLS ON CHANGES IN SEDIMENT SUPPLY AND STORAGE: THE QUATERNARY ALLUVIAL RECORD OF THE CENTRAL PANNONIAN

BASIN

A. Nádor, Á. Tóth-Makk, Á. Magyari, E. Thamó-Bozsó, E. Babinszki, Zs. Kercsmár

Geological Institute of Hungary, H-1143 Budapest, Stefánia 14

e-mail: [email protected]

Studies of long-term evolution of Quaternary fluvial systems in the Pannonian Basin and their responses to climate changes and tectonics significantly contribute to the fuller understanding of Late Neogene basin development. About 2 Ma ago a major change from the former extensional to compressional stress field led to basin inversion, which caused uplift of the marginal flanks and the western part of the Pannonian Basin, and increased subsidence of different sub-basins, which became areas of continuous fluvial sedimentation. The drainage pattern development of the Danube and Tisza rivers and their tributaries was primarily controlled by differential subsidence rates at various parts of the basin, thus vertical motions were fundamentally responsible for the accumulation of alluvial strata in diverse thicknesses. The subsiding basins are excellent archives of long-term fluvial records which reflect changes in discharge regimes, sediment supply and sediment storage over time-scales of 103 – 106 years.

The data-base for interpretation of the Quaternary alluvial records includes several thousands of water-prospecting wells with excellent electric logs, 32 fully cored deep boreholes (100-1000 m depth) and fully cored shallow boreholes, too.

Fluvial responses to climate changes have morphological, sedimentological and stratigraphical components, which are highlighted with different examples from the Quaternary fluvial record from the central part of the Pannonian Basin.

Morphological responses are best reflected in changes in channel geometry. Clear and unambiguous recognition of plan-views are limited to Late Quaternary examples from the Tisza river and its tributaries. A clear correlation between fluvial activity and millennial-scale climate changes was detected in a basin margin setting, where altogether six phases of braided and meandering fluvial styles were identified corresponding to stadials and interstadials during the Late Pleistocene, resulting in the formation of different geomorphic levels. This direct response was not demonstrated in a subsiding basin interior setting, where fluvial aggradation, whether it was deposited by meandering or braided rivers, kept pace with subsidence, so different channel planforms could not be preserved as temporally and spatially separated geomorphic surfaces, such as on the basin margin.

Sedimentological responses can be defined in a number of ways: e.g. in the proportions and spatial distribution of different lithofacies and facies associations. Our model on Milankovitch-scale climate changes suggests that an increased sediment flux towards the basin during interglacials was due to an increased discharge and transport capacity of the rivers, while a decreased sediment supply to the distal parts of the basin occurred during glacials. This means a delay between erosion and temporary storage of weathering products near to the source area and subsequent transportation and re-deposition of sediments into the basin interior. The model highlights the importance of variations in sediment flux and storage controlling the spatial distribution of fluvial sub-environments.

Finally, stratigraphic responses pronounced by aggradation, degradation and lateral migration are reflected in the basin scale fluvial architecture. Regional sections across the central Pannonian Basin provide examples for spatial distribution of depositional sequences.


THE WESTERN MARGIN OF THE BASIN: HIGHLIGHTS OF YOUNG MORPHOLOGIES FORMED BY BASIN INVERSION

Kurt Stüwe and Thomas Wagner

Institut für Erdwissenschaften, Heinrichstr. 26 A-8010 Graz, Austria; email: [email protected]; [email protected]; web: http://wegener.uni-graz.at

The western margin of the Pannonian Basin includes: (a) the Vienna Basin and (b) the Styrian Basin. The Vienna Basin is dominated by a large transform fault that extends well into the Carpathian arc and that created an enormous pull-apart basin along its northwest margin. This pull apart basin and the Vienna transform fault clearly also dominated the geometry of basin inversion over the last 10 my. In contrast, in the Styrian Basin, no major transform faults have been mapped and the thickness of the sedimentary pile in the basin increases successively and continuously eastward - bar some north-south striking basement swells (Middle Styrian Swell, South Burgenland Swell). As such, the basin extension and its subsequent inversion are likely to have followed a more ‘normal’ pattern and the Styrian Basin and its bounding regions are an ideal area to study basin inversion processes. In this contribution we highlight three eye catching morphological features of the Styrian Basin and its surroundings that apparently relate to the basin inversion.

• Caves in the Palaeozoic of Graz: The river Mur is the major Alpine drainage that crosses the transition zone from the orogen into the basin in a unit called the Palaeozoic of Graz. This unit is made of karstified carbonates hosting hundreds of caves, many of which include long horizontal stretches. These caves obviously formed at (or below) ground water level, but they occur on various elevations from active caves on the present day elevation of the Mur up to 600 m above the current water table. Many of these caves contain crystalline basement pebbles that are likely to have been deposited during their active time. We are currently dating the burial ages of these sediments to infer the incision history of the river Mur and obtain vertical reference levels for the basin inversion. Preliminary ages show a rough age increase with elevation from zero to about 4 my at 600 m above the current river level corresponding to an incision rate of 0.15 mm per year.

• Pohorje Dome: The Pohorje Dome in Slovenia rises some 1.000 vertical metres above the basin amidst the suture zone between Adriatic and European plates. The river Drava crosses the dome through its centre, apparently indicating an antecedent relationship of dome and river. This implies that the dome is likely to be a very young feature, probably younger than most of the offset along the Lavanttal fault which constrains its uplift to the last 5 my. Preliminary cosmogenic exposure ages have not revealed a systematic pattern, but confirm active tectonics in the region.

• Terraces in the basin: In the Styrian Basin itself, the morphology also indicates active tectonics: The hilly landscape of the Styrian wine growing area fluctuates between 200 m and 500 m above sea level on relatively short length scales and shows – in some regions – a very strict parallel organisation of drainages with asymmetric valley profiles. This asymmetry in the morphology is enhanced by various glacial and interglacial terraces that often occur on side of the valley only. Using channel profiles of streams and displaced young marine deposits (e.g. Leitha Kalk) as reference levels we constrain which landforms were formed by basin inversion and which are formed by drainage incision.


GEOTHERMICS OF THE PANNONIAN BASIN AND ITS BEARING ON THE TECTONICS OF BASIN EVOLUTION

Lenkey1, L., Dövényi2, P. and Horváth2, F.

1Research Group of Geology, Geophysics and Space Science of the Hungarian Academy of Sciences

2Department of Geophysics, Eötvös University

The Pannonian basin is characterized by high heat flow (90-120 mW/m2) in contrast to the surrounding areas, where the heat flow is normal; Ukrainian shield: 40-50 mW/m2, Moesian Platform: 60-70 mW/m2, Bohemian Massif: 50-70 mW/m2, etc. The only exception is the Tauern window in the Eastern Alps, where the heat flow is medium to high (80-100 mW/m2), but due to the scarce data these values might be uncertain. The heat flow reflects the thermal effects of sedimentation and erosion, groundwater flow, Neogene to recent volcanism and tectonic processes. The calc-alkaline volcanic arc along the inner side of the Carpathians is characterized by high heat flow. The main phase of volcanic activity along the Western part of the arc occurred 16-10 Ma, but the heat flow is still high. The high heat flow might be attributed to elevated temperature in the deep crust or lithosphere. The thermal effects of Neogene to Quaternary sedimentation and erosion were modeled. The Pannonian basin was filled up by a large prograding delta system, which advanced into the basin from NW, N and NE. In the northern and southern parts of the basin the observed heat flow is 10 mW/m2 and 20 mW/m2 less, respectively, than it would be in steady state. Erosion in the inner outcrops does not influence the heat flow significantly. Downward flow of meteoric water in the karstic areas (Dinarides, Transdanubian Range, etc.) cools the recharge area. The water seepages to great depth (1-3 km) and after warming up it emerges to the surface or discharges to sediments near the feet of the hills resulting in high heat flow in the discharge areas. The heated areas are always much smaller than the cooled areas. Groundwater flow in the sediments is less vigorous and it is mainly horizontal or subhorizontal due to the layering. There are some spots in Hungary, where the temperature field is disturbed by groundwater flow in sediments, but in the major part of the sedimentary areas the heat is transported by conduction. This hypothesis is supported by temperature-depth logs and groundwater flow models.The high heat flow in the Pannonian basin can be attributed to the tectonic processes related to the formation of the basin. McKenzie (1978) and Royden et al. (1983) suggested that the high heat flow is caused by lithospheric stretching. Thin crust and lithosphere, seismic data on the structure of the basement, and paleostress determinations prove their idea.We calculated crustal and lithospheric mantle stretching factors in a 5 x 5 km grid from the present day basement depth and heat flow applying Royden and Keen’s (1980) non-uniform stretching model, and assuming constant pre-rift crustal thickness. Before the calculation the basement depth was corrected for the late stage (younger than 2.4 My) vertical movements, and the heat flow was smoothed by a low-pass filter with a cutting wavelength of 100 km. The obtained crustal stretching factors are in agreement with the earlier results, but the mantle stretching factors have smaller values. (The mean values of the stretching factors are shown in the Table.) Nevertheless, the mantle stretching everywhere in the basin exceeds the crustal stretching, in qualitative agreement with the earlier models. The stretching factors depend on the pre-rift crustal thickness. Another approach is to assume homogeneous lithospheric stretching, and calculate the stretching factor and the initial crustal thickness (from the basement depth and heat flow as before). According to the results the North-Pannonian block (ALCAPA) had a normal to slightly thickened crust, while the crust of Tisza block was considerably overthickened. (Calculation was not made in the Dacia part of the Tisza-Dacia


block.) This prediction agrees with pre-rift sedimentation history of the blocks. Marine Paleogene sediments are found in the North-Pannonian block, but the few Paleogene sediments in the Tisza block are terrigeneous origin.The crustal stretching factors can be used to estimate the horizontal stretching of the crust, and therefore to calculate its “retrodeformation”. Assuming ENE-WSW directed extension we “pulled back” the outcrops of the Inner Carpathian geological units to their pre-rift position. The mean stretching of the crust was 150-200 km, and the internal deformation of the crust (and lithosphere) can explain about 30°-40° CCW rotation of the Western Carpathians and 35° CW rotation of the Apuseni Mts. in contrast to the observed 80° in both cases.

TableThickness of the

pre-rift crust (km)Mean value of

crustal stretchingMean value of lithospheric

mantle stretching32 1.4 3.335 1.6 3.140 1.8 2.745 2 2.4

Variable (38-65) 2 2

References

McKenzie, D., 1978. Some remarks on the development of sedimentary basins. Earth Planet. Sci. Lett., 40: 25-32.Royden, L. and Keen, C.E., 1980. Rifting process and thermal evolution of the continental margin of Eastern

Canada determined from subsidence curves. Earth Planet. Sci. Lett., 51: 343-361.


GRAVITY FIELD IN THE CARPATHO-PANNONIAN REGION: DATA AND IMPLICATIONS ON THE CRUSTAL STRUCTURE

Peter Szafian (1), Frank Horváth (1), Gábor Tari (2) and Sierd Cloetingh (3)

(1) Dept. of Geophysics, Institute of Geography and Earth SciencesEötvös Loránd University, Budapest, Hungary (ELTE)

(2) Allygabor, Houston, USA(3) Vrije Universiteit, Amsterdam, The Netherlands

The crustal and lithospheric structure of the Carpatho-Pannonian area has been a subject of an extensive research from the 1950’s using three standard geophysical methods: seismic reflection, seismic refraction and gravity surveys. Seismic interpretation was assisted by two-dimensional gravity modelling along specific deep seismic lines. However, lack of unified gravity anomaly maps in addition to the immense computation requirements hindered large-scale three-dimensional density modelling of the whole region. A few years ago these difficulties disappeared and we could compile a unified Bouguer anomaly map of the region, using previously prepared and recently published gravity maps, and carry out two and three dimensional gravity model calculations for the determination of the Moho depth and the identification of the most prominent intra-crustal density heterogeneities.

The different parts of the Carpatho-Pannonian region are characterized by remarkably different gravity anomalies. The dominantly mild positive Bouguer anomalies of the Pannonian basin are primarily controlled by three regional sources: the thick sedimentary fill of the basin, and the elevated positions of the mantle and the asthenosphere. The general picture of the gravity anomalies suggest that the basin is approximately in the stage of Airy-type isostatic equilibrium, however a few striking exceptions can also be found.

The Eastern Alps, the Dinarides and the Carpathians are equally characterized by negative Bouguer anomalies, however, they are far not uniform: they reflect the different tectonic evolution, hence the different lithospheric structure, of certain parts of the mountain ranges.

In order to obtain a large scale view on the major boundaries of significant density changes, the results of 2D and 3D gravity modelling studies are shown, focusing on the Moho configuration. The results reveal that zones of continental collision are characterized by thick crustal roots, while transpressional orogenic segments show a more diverse picture: in the Western Carpathians, the Moho is a flat surface; in the Dinarides a medium Moho root is observed; and the Southern Carpathians are characterized by a thick crustal root.


SEISMIC AND DENSITY STRUCTURE BENEATH THE VRANCEA SEISMOGENIC ZONE

Rosaria Tondi (1), Ulrich Achauer (2), and Lucian Besutiu (3)

1. INGV – Istituto Nazionale di Geofisica, Sezione di Bologna, Via Donato Creti 12, 40128 Bologna, Italy

2. IPGS – Institut de Physique du Globe de Strasbourg, 5 rue René Descartes, 67084 Strasbourg - France

3. Institute of Geodynamics of the Romanian Academy, 19-21 Jean-Louis Calderon St., sector 2, 020032 Bucharest 37 - Romania

Additional constraints on the geodynamic models for the origin of the intermediate depth Vrancea Seismogenic Zone are given by three-dimensional Vp, Vs, Vp/Vs and density images. The reconstructed physical parameters aim to substantiate or eliminate two contrasting models which explain the Vrancea seismicity: the subduction model and the active continental lithospheric delamination model.

For our goal, we apply the tomographic inversion method of sequential integrated inversion proposed by Tondi and de Franco (2006) to shot data collected during the VRANCEA99 (Hauser et al., 2001) and VRANCEA2001 (Landes et al., 2004) seismic refraction experiments, to local earthquake data collected during the CALIXTO (EOS, 1998) experiment and to recent gravity measurements of the studied area.

We first locate P and S wave sources of local events with the NonLinLoc location program (Lomax et al., 2000) and then we consider these events as those originated from shots points.

The mathematical formulation of the seismic travel time inversion algorithm, which regularizes the solution with the minimization of the first and the second partial derivatives of the functionals describing the velocity parameters, enables us to control the proliferation of caustics and arrivals during iterations, which is a common problem when using ray-tracing techniques with realistic and extensive heterogeneous velocity models. This increases the robustness and efficiency of the method and efficiently handles a seismic data set which is severely affected by scattering effects. Furthermore, the density model parametrization which uses polyhedral bodies whose density is linearly dependent on the three coordinates (Pohànka, 1998) leads to a perfect match between the density and the velocity model parametrization and takes into account the presence of geological structures characterized by a gradual increase in density with depth. After each iteration, the events are relocated with the updated velocity model until the discrepancies between two subsequent localizations are sufficiently small. The reliability of the reconstructed models, which explain equally well both travel times and gravity data, is quantified through a restoring test and the estimation of travel times and gravity residuals.


GEODYNAMICAL MODELS OF THE INTERMEDIATE DEPTH SEISMICITY OF THE SE CARPATHIANS

Piroska Lorinczi and Gregory A. Houseman

School of Earth and Environment, University of Leeds, UK

The Carpathians are a major mountain system of the Central and Eastern Europe, which in the South-east surround the Transylvanian basin. Located on the oroclinal bend of the Carpathian mountains, the Vrancea region is characterised by a localised (~30 km x 80 km in the horizontal plane) zone of seismic activity to depths of 200 km. This phenomenon is often attributed to subduction of oceanic lithosphere. However, there is no obvious zone of subduction associated with the Vrancea deep earthquakes. An alternative explanation to this deep seismicity is the downwelling of the continental lithosphere in the form of a Rayleigh Taylor instability. The fault plane solutions, for a time interval of 40 years, indicate maximum vertical extension rates on the order of 14% per Myr in the depth range 50-100 km, decreasing by about an order of magnitude in the depth range 100-150 km. Such rapid rates of deformation clearly represent a recent development, that could not have persisted for a period of time much greater than 5 Myr, and cannot be clearly attributed to recent subduction. Three dimensional finite deformation models of the gravitational instability of the continental lithosphere, based on the finite element method, demonstrate that the Rayleigh Taylor mechanism can explain the present distribution of deformation within the downwelling lithosphere, both in terms of distribution of seismicity and amplitude of strain rates. The spatial width of the high stress zone that corresponds to the seismically active zone is realistically represented when we assume that the viscosity of the lithosphere decreases by an order of magnitude across the lithosphere. The mantle downwelling is balanced by lithospheric thinning in an adjacent area which would correspond to the Transylvanian basin. This type of planform is inherently three dimensional and is triggered in these experiments by a harmonic perturbation in the form of a first order Bessel function (with m = 1 asymmetry). In these models mantle downwelling is associated with crustal thickening but the lithospheric thinning beneath the adjacent basin is associated with only minor crustal thinning.


A MECHANISM FOR THE DEVELOPMENT OF INTRA-OROGENIC BASINS BY GRAVITATIONAL INSTABILITY OF THE CONTINENTAL LITHOSPHERE

Gregory A. Houseman (1) and Lykke Gemmer (2)

(1) Institute of Geophysics and Tectonics, School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK ([email protected])

(2) Statoil ASA, 4035 Stavanger, Norway ([email protected])

The extensional Pannonian Basin formed in a few million years during Miocene time, synchronous with contraction in the surrounding Alpine and Carpathian orogens. This system is characteristic of a class of extensional basins that form in the midst of active orogenic belts. The mechanism that causes this type of geological event is enigmatic but usually has been associated with subduction. We examine a new hypothesis for intra-orogenic extensional basin formation, in which gravitational spreading of previously thickened crust triggers gravitational instability of the mantle lithosphere. A basin is formed by lithospheric extension, as shortening and lithospheric downwelling occur in the surrounding mountain belts.

We have developed a 3D finite deformation solver based on the finite element method, which enables us to examine the way in which such a gravitational instability can develop for an unstably stratified system representing the continental lithosphere. We describe numerical experiments which are necessarily simplified relative to any actual intra-orogenic basin, but which demonstrate that the gravitational instability mechanism is possible.

This mechanism predicts in a natural way that simultaneous extension in the central basin and convergence in the surrounding mountain chains occur. The model predicts greater extension factors in the lithospheric mantle than in the crust. Both of these predictions are consistent with observations from the Pannonian-Carpathian system. This mechanism thus provides a mechanically self-consistent explanation for two of the major structural features of the Pannonian-Carpathian system and presents a plausible alternative to the popular view that subduction of oceanic lithosphere and slab roll-back have driven the development of this basin.


PRELIMINARY RESULTS FROM THE CARPATHIAN BASINS TELESEISMIC TOMOGRAPHY PROJECT

B. Dando (1), G. Houseman (1), G. Stuart (1), E. Hegedus (2), E. Brueckl (3), S. Radovanovic (4)

(1) School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK(2) Eötvös Loránd Geophysical Institute, 1145 Budapest, XIV. ker. Columbus u. 17-23, Hungary

(3) Institute of Geodesy and Geophysics, TU-Wien, A-1040, Vienna, Austria(4) Seismological Survey of Serbia, 11000 Beograd, Park Tasmajdan, Serbia

As part of the Carpathian Basins Project, a 46-element broadband seismic network oriented NW-SE, perpendicular to tectonic strike of the mid-Hungarian line, was deployed across the Vienna and western Pannonian basins through Austria, Hungary and Serbia. Our study aims to resolve the seismic structure of the crust and upper mantle using data from this network. Our initial results consist of P-wave teleseismic travel time residual patterns observed across the array from different azimuths and distances. The residuals are relative to the ak135 reference Earth model. We compare the adaptive stacking (Rawlinson & Kennett, 2004) and multi-channel cross correlation (VanDecar & Crosson, 1990) methods for relative arrival time picking using 23 events (5.4 < Mb < 7.3; 77.9 deg to 80 deg) with back-azimuths almost perpendicular to the length of the array. These residuals vary from fast (-0.8 s) in the Vienna Basin to the north-west, to slow (0.85 s) in the south-west Pannonian Basin. The residuals increase from near zero on the mid-Hungarian line and reach a maximum (0.8 s) in southern Hungary before decreasing in to northern Serbia. This anomaly does not change significantly when the residuals are corrected for known sedimentary thicknesses and estimated crustal thickness variations from controlled source surveys. Thinned lithosphere and low velocities are inferred to the SE under the Pannonian basin. A more three-dimensional lateral velocity structure beneath the seismic network is revealed by examination of travel time residuals from a range of back-azimuths.


ALPASS TELESEISMIC TOMOGRAPHY - STATUS REPORT

U. Mitterbauer, R. Lippitsch, M. Behm, E. Brückl, and ALPASS Working Group

ALPASS (Alpine Lithosphere and Upper Mantle Passive Seismic Monitoring) is a passive seismic monitoring project aiming to reveal the structure of the lower lithosphere and upper mantle beneath the Eastern Alps and their neighbouring tectonic provinces. It was launched to extend the seismic models from controlled source experiments (CELEBRATION 2000 and ALP 2002) to larger depths. Of particular interest is the structure and dip of subducting lithospheric slabs. The layout of ALPASS was designed to fill the gap between the TRANSALP experiment in the west and two other passive seismic experiments (BOHEMA, Carpathian Basin Project) in the east. By cooperation of Austria, Croatia, Finland, Hungary, Poland and USA 57 temporary seismic recording stations were deployed from May 2005 until May 2006. Data from permanent networks were also collected to improve the coverage of the investigated area. 144 events (50% with M > 5.6) from epicentral distances between 30° and 100° were selected for a forthcoming teleseismic inversion. Picking of P-wave arrivals has been done by the application of a semi-automatic correlation technique. Crustal travel time corrections are calculated on the basis of a 3D seismic model which implements the results of CELEBRATION 2000 and ALP 2002. Residual travel time fields were calculated by subtracting the effect of a global reference model and applying crustal corrections. These travel time fields are smooth and show consistent regional anomalies. Therefore we expect significant results from the teleseismic inversion.


GEOMORPHOLOGIC AND DRAINAGE NETWORK ANALYSIS AT THE WESTERN MARGIN OF THE LITTLE HUNGARIAN PLAIN

Zámolyi A.(1), Székely B.(1,2), Timár G.(1), Draganits, E.(3)

(1) Eötvös University Budapest, Department of Geophysics, Space Research Group ([email protected])

(2) Institute of Photogrammetry and Remote Sensing, Vienna University of Technology, Austria

(3) Institute for Engineering Geology, Vienna University of Technology, Austria

The Little Hungarian Plain belongs to the southern part of the Danube Basin, a polyphase intramontane basin similar to the Vienna Basin. Both basins are located at the junction between Eastern Alps and Western Carpathians and had a common evolution up to Middle Miocene times (Kovác et al., 1993). In contrast to adjacent areas, the Little Hungarian Plain preserved its basin characteristics after undergoing a late Miocene extensional and a following convergent deformation phase (Fodor et al., 2005; Horváth & Cloetingh, 1996). This convergent phase, resulting from the inversion of the Pannonian Basin, is also considered as the neotectonic phase of the region (Fodor et al., 2005; Bada et al., 1999; Horváth, 1995). Major structural features are the Rába and Répce, Mojmirovice-Certovica, and the Mur-Mürz-Leitha (Lajta) fault systems (Lenhardt et al., 2007). The dominant strike-slip character of these fault zones changed to a dip-slip mode from Lower Miocene to Upper Miocene accompanied by overall subsidence which, in turn, was followed by the already mentioned neotectonic phase. Recent vertical movements varying between -2.0 and +0.2 mm/year and (Joó, 1992) have a strong influence on the landscape evolution and on the geometry of drainage networks (Ouchi, 1985). Geomorphologic analysis focused on the western margins of the Little Hungarian Plain, on the area of the Parndorfer Platte (Pándorfalvi síkság). Drainage basin analysis included the Leitha (Lajta), Répce, Rábca, Ikva and Wulka rivers. In order to minimize human influence on the channel geometry, calculation of river channel properties (e.g. river sinuosity) were conducted based on the exactly georeferenced historical map sheets of the second military survey of the Habsburg empire recording the morphological situation around 1840 (Timár & Molnár, 2003). Calculated sinuosity values show strong local variations, which are partly linked to fault activity of the most recent basin evolution phase.

ReferencesBada G., Horváth F., Gerner P., Fejes I. (1999): Review of the present-day geodynamics of the Pannonian

basin: progress and problems. Geodynamics, 27, 501-527.Fodor L., Bada G., Csillag G., Horváth E., Ruszkiczay-Rüdiger Zs., Palotás, K., Síkhegy, F., Timár G.,

Cloetingh S., Horváth F. (2005): An outline of neotectonic structures and morphotectonics of the western and central Pannonian Basin. Tectonophysics, 410, 15-41.

Horváth F. (1995): Phases of compression during the evolution of the Pannonian Basin and its bearing on hydrocarbon exploration. Marine and Petroleum Geology, 12(8), 837-844.

Horváth F., Cloetingh S. (1996): Stress-induced late-stage subidence anomalies in the Pannonian basin. Tectonophysics, 266, 287-300.

Joó I. (1992): Recent vertical surface movements in the Carpathian Basin. Tectonophysics, 202, 129-134.Kovác P., Hók J. (1993): The Central Slovak Fault System — the field evidence of strike slip. Geol.

Carpath., 44, 155-159.Lenhardt W., Svancara J., Melichar P., Pazdírková J., Havír J., Sykorová Z. (2007): Seismic activity of

the Alpine-Carpathian-Bohemian Massif region with regard to geological and potential field data. Geologica Carpathica, 58(4), 397-412.

Ouchi S. (1985): Response of alluvial rivers to slow active tectonic movement. Geological society of America Bulletin, 96, 504-515.

Timár G., Molnár G. (2003): A második katonai felmérés térképeinek közelítő vetületi és alapfelületi leírása a térinformatikai alkalmazások számára. Geodézia és Kartográfia, 55(5), 27-31.


FROM MIOCENE THRUSTING TO POST COLLISIONAL EXTENSION

A. Zamolyi (1) K. Decker (2), M. Hölzel (2), P. Strauss (3) & M. Wagreich (2)

(1) Eötvös University Budapest, Space Research Group ([email protected])

(2) Department of Geodynamics and Sedimentology, University of Vienna

(3) OMV Exploration & Production GmbH, Vienna

Structural elements related to the differential movement between the Alpine and the Carpathian nappes are investigated at the junction between the Eastern Alps and the Carpathian orogen. Several phases of deformation are recognized from seismic interpretation. The first one includes Early Miocene thrusting of the Waschberg-Zdanice unit, which is dated by growth strata of the Laa Fm. (Karpatium) overlying fault propagation folds of blind thrusts. These thrusts are cut by post-Karpatian surface breaking out-of-sequence thrusts. The second main stage of deformation is characterized by the extensional reactivation of the former thrust faults and by the formation of piggy-back half grabens on top of the allochthon. These basins are filled with up to 750 mS (TWT) thick Middle to Late Miocene sediments (Badenium to Pannonium). Extension also triggered normal faults cutting the Karpatian growth strata. Based on seismic evidence and biostratigraphic data the change from foreland-directed thrusting to post-collisional extension occurred between the Upper Karpatium and the Lower Badenium. The observed deformation history matches data recorded by earlier studies (e.g. Nemcok et al., 1989; Fodor, 1995; Seifert, 1996; Peresson & Decker, 1997;). Accordingly, the first phase (? Oligocene to Lower Miocene) is characterized by constantly NW-directed thrusting (Nemcok et al., 1989). The younger extensional basins are related to ESE-WNW extension reconstructed for the Middle to Late Miocene (Fodor, 1995).

ReferencesFodor L. (1995): From transpression to transtension: Oligocene-Miocene structural evolution of the

Vienna basin and the East Alpine-Western Carpathian junction. Tectonophysics, 242, 151-182.Nemcok M., Marko F., Kovac M., Fodor L. (1989): Neogene tectonics and paleostress field changes in

the Czechoslovakian part of the Vienna basin. Jahrbuch der Geologischen Bundesanstalt, 132, 443-458.

Peresson H., Decker K. (1997): The Tertiary dynamics of the northern Eastern Alps (Austria): changing paleostresses in a collisional plate boundary. Tectonophysics, 272, 125-157.

Seifert P. (1996): Sedimentary-tectonic development and Austrian hydrocarbon potential of the Vienna Basin. in: Wessely G., Liebl W. (eds.): Oil and Gas in Alpidic Thrustbelts and Basins of Central and Eastern Europe, EAGE Special Publication No. 5, pp.331-341.


NEOTECTONIC ANALYSIS OF HIGH RESOLUTION SEISMIC DATA, LAKE BALATON, PANNONIAN BASIN

P. Szafián (1), G. Bada (1), O. Vincze (1), B. Székely (1), V. Spiess (2)

(1) Dept. of Geophysics and Space Sciences, Eötvös University, Budapest, Hungary (2) Marine Technology – Environmental Research, University of Bremen, Germany

([email protected])

High resolution multichannel and ultra high resolution single channel seismic data acquired on Lake Balaton during the last decade provide an outstanding data set for detailed analysis of neotectonics in the central Pannonian basin. The two data sets image different depth intervals. Single channel data have a 20-50 metres penetration with a decimetre scale resolution. Since a large portion the single channel data were measured in a dense grid, fine details of the different styles of neotectonic deformation can be identified and laterally correlated. Multichannel data provide information down to a depth of 150-200 metres, with a smaller resolving power, and allow identification of larger scale structural features. Combined analysis of the two data sets permits (1) detailed mapping and kinematic interpretation of different neotectonic features and (2) analysis of the connection between older (Miocene) and younger (post-Miocene, i.e. neotectonic) structures, and the reactivation of existing older faults. The neotectonic features identified below Lake Balaton are discussed within the context of active tectonics of Transdanubia in central Pannonia. A special emphasis is put on the timing of fault activity and the kinematics and style of the reconstructed deformation pattern. The results are compared to the present-day stress field and geodynamic habitat of the Pannonian basin. This study was supported by the Hungarian Scientific Research Fund OTKA no. TS044765, K37724, F043715, NK60445.


List of Participants


Name Country Affiliation E-mailAchauer Ulrich Germany EOST Strasbourg [email protected] Gábor Hungary ELTE [email protected] Hrvoje Croatia ZagrebBehm Michael Austria TU-Wien [email protected]ückl Ewald Austria TU-WienBrückl Johanna Austria TU-WienBrun Jean-Pierre France CNRS Rennes [email protected] Rob UK LeedsDando Ben UK Leeds [email protected] Kurt Austria Vienna [email protected]ádi Endre Hungary ELTE [email protected]övényi Peter Hungary ELTE [email protected] Claudio Italy Roma-TRE [email protected] György Hungary ELGI [email protected] László Hungary MAFI [email protected]örfi István Hungary Hungarian Horizon [email protected] Szabolcs Hungary ELTE [email protected]űs Endre Hungary ELGI [email protected] Mátyás Hungary ELTEHidas Károly Hungary ELTEHorváth Anita Hungary TXM Ltd. [email protected]áth Ferenc Hungary ELTE [email protected] Greg UK Leeds [email protected] Laurent France CNRS Rennes [email protected] Sasa Croatia ZagrebKonc Zoltán Hungary ELTE [email protected] László Hungary ELTE [email protected] Piroska UK Leeds [email protected] Dan UK CambridgeMitterbauer Ulrike Austria TU-Wien [email protected]ádor Annamária Hungary MAFI [email protected]šković Jasna Croatia ZagrebRoyden Leigh USA MITStuart Graham UK Leeds [email protected] Kurt Austria GrazSumanovac Franjo Croatia ZagrebSzabó Csaba Hungary ELTE [email protected]án Péter Hungary ELTE [email protected]ékely Balázs Hungary ELTE [email protected]ó Orsolya Hungary ELTE [email protected]ár Gábor Hungary ELTE [email protected] Rosaria Italy INGVWagner Tom Austria Graz [email protected]ámolyi András Hungary ELTE [email protected]

[email protected]

[email protected]@mail.tuwien.ac.at

[email protected]

[email protected]

[email protected]

[email protected]

[email protected]@mit.edu

[email protected]@rgn.hr

[email protected]

collision and extension in the alpine - carpathian...

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