4791492
Tectonic significance of changes in post-subduction Pliocene–Quaternary magmatism in the south east part of the Carpathian–Pannonian Region
The south-eastern part of the Carpathian–Pannonian region records the cessation of convergence between the European platform/Moesia and the Tisza–Dacia microplate. Plio-Quaternary magmatic activity in this area, in close proximity to the ‘Vrancea zone’, shows a shift from normal calc-alkaline to much more diverse compositions (adakite-like calc-alkaline, K-alkalic, mafic Na-alkalic and ultrapotassic), suggesting a significant change in geodynamic processes at approximately 3 Ma. We review the tectonic setting, timing, petrology and geochemistry of the post-collisional volcanism to constrain the role of orogenic building processes such as subduction or collision on melt production and migration. The calc-alkaline volcanism (5.3–3.9 Ma) marks the end of normal subduction-related magmatism along the post-collisional Călimani–Gurghiu–Harghita volcanic chain in front of the European convergent plate margin. At ca. 3 Ma in South Harghita magma compositions changed to adakite-like calc-alkaline and continued until recent times (< 0.03 Ma) interrupted at 1.6–1.2 Ma by generation of Na and K-alkalic magmas, signifying changes in the source and melting mechanism. We attribute the changes in magma composition in front of the Moesian platform to two main geodynamic events: (1) slab-pull and steepening with opening of a tear window (adakite-like calc-alkaline magmas) and (2) renewed contraction associated with deep mantle processes such as slab steepening during post-collisional times (Na and K-alkalic magmas). Contemporaneous post-collisional volcanism at the eastern edge of the Pannonian Basin at 2.6–1.3 Ma was dominated by Na-alkalic and ultrapotassic magmas, suggesting a close relationship with thermal asthenospheric doming and strain partitioning related to the Adriatic indentation. Similar timing, magma chamber processes and volume for K-alkalic (shoshonitic) magmas in the South Apuseni Mountains (1.6 Ma) and South Harghita area at a distance of ca. 200 km imply a regional connection with the inversion tectonics.
129720526
Tertiary palaeomagnetic data for the Carpatho-Pannonian region in the light of Miocene rotation kinematics
Abstract The tectonic interpretation of the palaeomagnetic data for the Neogene history of the Carpatho-Pannonian region has usually been based on the palaeomagnetic data for the pre-Cenozoic complexes. Here a review of the Tertiary palaeomagnetic data is given. For the sites with two or more sets of data new site-mean directions are calculated. For most areas new area-mean directions are given with a uniform criterion for the limitation of the normally distributed sub-populations. Based on radiometric data some Neogene volcanic sequences are subdivided into two complexes with separate area-mean directions. The possible influence of the areal tilts on the area-mean palaeomagnetic directions is analysed and conclusions on the horizontal rotations are drawn. The palaeomagnetic rotations are interpreted in the light of the author's kinematic model for the Neogene history of the Carpatho-Pannonian region. The rotation of both the southeastern unit by about 100° clockwise and the northwestern unit by about 35° anti-clockwise are supported by palaeomagnetic data. In addition, some rotations predicted by the model are documented by palaeomagnetic data as follows: (1) the anti-clockwise rotation of the flanks of the Darno line (Gemer-Bukk area) with sinistral displacements in the Early Miocene, (2) the anti-clockwise rotations along the southeastern margin of the Northwestern unit with sinistral displacements before 10 Ma, (3) the anti-clockwise rotation of the Ukrainian Carpathians before 12 Ma. Some palaeomagnetic rotations have not been predicted by the kinematic model but occur in the regions where deformations are quite probable. These unexpected palaeomagnetic rotations throw a new light on some details of the kinematics: (1) the advance of the Outer West Carpathian nappes later than 14 Ma is documented by the increased palaeomagnetic inclination of the Pieniny andesites; (2) the movement of the Central and Inner West Carpathians later than 12 Ma is recorded in the palaeomagnetic rotations of the Central and East Slovakian volcanites. This movement seems to reflect a bay of thin crust within the underthrust European plate margin, or, more precisely, the reaction of the eastern contour of the bay on the drag of the Northwestern unit towards the northeast by the still rotating Southeastern unit. The rotation and deformation of the Northwestern unit in the Miocene have to be taken into account in the reconstructions of the pre-Neogene situations since they intensely influenced the arrangement of all older palaeotectonic and palaeogeographic zones. The Southeastern unit also suffered intense rotation and deformation in the Miocene. Unfortunately, there are almost no palaeomagnetic data available for its Tertiary complexes.
129578533
The Western Accretionary Margin of the East European Craton: an overview
Abstract Multidisciplinary investigations of the western margin of the East European Craton (EEC) by EUROPROBE projects since 1992 have confirmed that the Trans-European Suture Zone (TESZ) is the most fundamental lithospheric boundary in Europe, extending 2000 km from the North Sea to the Black Sea-Crimean region. The crust of the EEC is thicker and denser than that of Phanerozoic-accreted Europe, and the base of the lithospheric mantle significantly deeper. These characteristics persist throughout the length of the TESZ, despite the variation in age of the accreted crust along strike. Geological studies of key deep borehole cores and the limited outcrop data confirm that the crust of Phanerozoic-accreted Central Europe comprises a number of terranes, each thought to be derived from Gondwana during several episodes of rifting, ocean formation, ocean destruction and sequential accretion to the EEC throughout Palaeozoic time. There is still much discussion about the identity, provenance and history of these orogenic terranes. The process of accretion led to the formation of terrane-bounding orogenic sutures, which may be marked in outcrop by ophiolitic and eclogitic relics. Recognition of concealed sutures is obviously more difficult, and relies on a variety of geophysical techniques, used in an integrated way by multidisciplinary teams; the evidence from deep seismic reflection and refraction surveys, teleseismic tomography, magnetotelluric experiments and from geophysical potential-field modelling is crucial for such studies. Since the European Geotraverse, much has been learnt about the geometry of the Thor, Iapetus, Rheic, Saxo-Thuringian and Moldanubian oceanic sutures, through the crust and sometimes into the mantle. This has led to a much better understanding of the 3D crustal structure of the Western Accretionary Margin of the EEC, and the lithospheric processes that have shaped it. From this, the influence of tectonic heterogeneities within the orogenic crust on the development of post-orogenic structures and basins can be much better constrained.
128752390
Models for relative motion of crustal blocks within the Carpathian region, based on restorations of the outer Carpathian thrust sheets
Details of the Oligocene-present-day motion of the Adriatic block with respect to Europe can be determined by palinspastic restorations of the outer Carpathians thrust sheets. The arcuate nature of the Carpathians poses problems for simple restorations of sections because they create converging restoration paths which require large amounts of strike-parallel extension (40–50%). Such large amounts of extension are not seen on maps or in the field. A combination of thrust transport directions changing with time between and within thrust sheets and divergent transport directions helps minimise the arc-parallel extension necessary (18–25%). The Pannonian basin can be treated either as an area dominated by strike-slip motion (rigid block movements) or as an area of back arc extension. The differences in restoration geometry produced by these two scenarios help to indicate which of the two mechanisms was dominant. The consequences of the rigid block restoration indicate the model is inappropriate because it requires approximately 20° clockwise rotation of the Adriatic block during the late Tertiary. It also indicates at least 300 km strike-slip motion distributed among the late Tertiary faults of the Dinaride-Balkanide and Hellenide Mountain belts. The back arc extension model alleviates the the 20° clockwise rotation of the Adriatic block and requires about 200 km distributed strike-slip motion in Yugoslavia and Bulgaria.
128519882
Late orogenic vertical movements in the Carpathian Bend Zone ^ seismic constraints on the transition zone from orogen to foredeep
Postcollisional tectonic movements in orogens and their adjacent foreland basins related to intraplate stresses and the presence of a remnant slab are likely to induce significant deformations overprinting the existing patterns of nappe emplacement. In the Carpathian Bend Zone, Romania, vertical motions associated with very limited postorogenic intraplate shortening are of similar magnitude as those generally caused by large orogenic deformations. In the Latest Miocene-Pliocene, up to 6 km of postcollisional sediments of remarkably parallel stratification were deposited in a basin extending over a large part of the present-day orogen. The Early Quaternary featured a dramatical change as the orogen was uplifted while subsidence continued in the basin, tilting the basin flank adjacent to the orogen to a vertical position. The remnant slab presently below the Bend zone in Vrancea is the prime mechanism to have driven the Pliocene subsidence. The Quaternary changes and the eastwards migration of the pattern of vertical motions can be explained by large-scale folding, in response to the overall compressive regime that is recorded in the whole Pannonian-Carpathian area. © 2006 Blackwell Publishing Ltd.
53497744
Dynamics of intra-plate compressional deformation: the Alpine foreland and other examples
Abstract Intra-plate compressional structures, such as inverted extensional basins and upthrusted basement blocks, play an important role in the tectonic framework of the European Alpine foreland. Similar structures are observed on many continental cratons but occur also in oceanic basins and more rarely along passive continental margins. The World Stress Map shows that horizontal compressional stresses can be transmitted over great distances through continental and oceanic lithosphere. Although a number of geodynamic processes contribute to the build-up of intra-plate horizontal compressional stresses, forces related to collisional plate interaction appear to be responsible for the most important intra-plate compressional deformations. Such deformations can involve whole-lithosphere buckling and folding, crustal folding and, by reactivation of pre-existing crustal discontinuities, upthrusting of basement blocks and inversion of tensional hanging-wall basins. Mechanical aspects of basin inversion depend on the interplay of stresses and rheology of the lithosphere. Pre-existing crustal discontinuities weaken the lithosphere and play a crucial role in localizing intra-plate compressional deformations. Reactivation of relatively steeply dipping normal faults occurs when the angle between their strike and the compressional stress trajectory is smaller than 45°. Compressional deformations restricted to crustal levels involve ‘simple-shear’-type detachment of the crust at the level of the rheologically weak lower crust from the mantle-lithosphere; whole-lithospheric ‘pure-shear’-type compressional deformation is indicated for certain inverted basins. A distinction must be made between collision-related and anorogenic compressional/transpressional intra-plate deformations. The hypothesis is advanced that the stratigraphic record of collision-related intra-plate compressional deformations can contribute to the dating of orogenic events affecting the margin of the respective craton.
73609220
Seismic crustal structure between the Transylvanian Basin and the Black Sea, Romania
Abstract In order to study the lithospheric structure in Romania a 450 km long WNW–ESE trending seismic refraction project was carried out in August/September 2001. It runs from the Transylvanian Basin across the East Carpathian Orogen and the Vrancea seismic region to the foreland areas with the very deep Neogene Focsani Basin and the North Dobrogea Orogen on the Black Sea. A total of ten shots with charge sizes 300–1500 kg were recorded by over 700 geophones. The data quality of the experiment was variable, depending primarily on charge size but also on local geological conditions. The data interpretation indicates a multi-layered structure with variable thicknesses and velocities. The sedimentary stack comprises up to 7 layers with seismic velocities of 2.0–5.9 km/s. It reaches a maximum thickness of about 22 km within the Focsani Basin area. The sedimentary succession is composed of (1) the Carpathian nappe pile, (2) the post-collisional Neogene Transylvanian Basin, which covers the local Late Cretaceous to Paleogene Tarnava Basin, (3) the Neogene Focsani Basin in the foredeep area, which covers autochthonous Mesozoic and Palaeozoic sedimentary rocks as well as a probably Permo-Triassic graben structure of the Moesian Platform, and (4) the Palaeozoic and Mesozoic rocks of the North Dobrogea Orogen. The underlying crystalline crust shows considerable thickness variations in total as well as in its individual subdivisions, which correlate well with the Tisza-Dacia, Moesian and North Dobrogea crustal blocks. The lateral velocity structure of these blocks along the seismic line remains constant with about 6.0 km/s along the basement top and 7.0 km/s above the Moho. The Tisza-Dacia block is about 33 to 37 km thick and shows low velocity zones in its uppermost 15 km, which are presumably due to basement thrusts imbricated with sedimentary successions related to the Carpathian Orogen. The crystalline crust of Moesia does not exceed 25 km and is covered by up to 22 km of sedimentary rocks. The North Dobrogea crust reaches a thickness of about 44 km and is probably composed of thick Eastern European crust overthrusted by a thin 1–2 km thick wedge of the North Dobrogea Orogen.
129108819
Lithospheric structure of the Pannonian basin derived from seismic, gravity and geothermal data
Abstract The structure of the Pannonian basin is the result of distinct modes of Mid-Late Miocene extension exerting a profound effect on the lithospheric configuration, which continues even today. As the first manifestation of extensional collapse, large magnitude, metamorphic core complex style extension took place at the beginning of the Mid-Miocene in certain parts of the basin. Extrapolation of the present-day high heat flow in the basin, corrected for the blanketing effect of the basin fill, indicates a hot and thin lithosphere at the onset of extension. This initial condition, combined with the relatively thick crust inherited from earlier Alpine compressional episodes, appears to be responsible for the core complex type extension at the beginning of the syn-rift period. This type of extension is well documented in the northwestern Pannonian basin. Newly obtained deep reflection seismic and fission-track data integrated with well data from the southeastern part of the basin suggests that it developed in a similar fashion. Shortly after the initial period, the style of syn-rift extension changed to a wide-rift style, covering an area of much larger geographic extent. The associated normal faults revealed by industry reflection seismic data tend to dominate within the upper crust, obscuring pre-existing structures. However, several deep seismic profiles, constrained by gravity and geothermal modeling, image the entire lithosphere beneath the basin. It is the Mid-Miocene synrift extension which is still reflected in the structure of the Pannonian lithosphere, on the scale of the whole basin system. The gradually diminishing extension during the Late Miocene/Pliocene could not advance to the localization of extension into narrow rift zones in the Pannonian region, except some deep subbasins such as the Makó/Békés and Danube basins. These basins are underlain coincidently by anomalously thin crust (22–25 km) and lithosphere (45–60 km). Significant departures (up to 130 mW m−2) from the average present-day surface heat flow (c. 90 mW m−2) and intensive Pliocene alkaline magmatism are also regarded as evidence for the initiation of two newly defined narrow rift zones (Tisza and Duna) in the Pannonian basin system. However, both of these narrow rifts failed since the final docking of the Eastern Carpathians onto the European foreland excluded any further extension of the back-arc region.
140203789
Three-dimensional numerical modeling of contemporary mantle flow and tectonic stress beneath the earthquake-prone southeastern Carpathians based on integrated analysis of seismic, heat flow, and gravity data
The principal purpose of the study is to understand the interplay between intermediate-depth large earthquakes in the southeastern Carpathians (Vrancea) and tectonic stress induced by a high-velocity body (lithospheric slab) descending into the mantle beneath the region. To analyze processes of stress generation and localization in and around the descending slab, we develop a three-dimensional (3D) numerical model of contemporary mantle flow and stress beneath the Vrancea region. The input data of the model consist of: (i) temperatures derived from seismic P-wave velocity anomalies and surface heat flow, (ii) crustal and uppermost mantle densities converted from P-wave velocities obtained from seismic refraction studies, (iii) geometry of the Vrancea crust and slab from tomography and refraction seismic data, and (iv) the estimated strain rate in the slab (as a result of earthquakes) to constrain the model viscosity. We find that major crustal uplifts predicted by the model coincide with the East Carpathian orogen and surround the Transylvanian basin and that predicted areas of subsidence are associated with the Moesian and East European platforms. We show a correlation between the location of intermediate-depth earthquakes and the predicted localization of maximum shear stress. Modeled tectonic stresses predict large horizontal compression at depths of about 70–220 km beneath the Vrancea region, which coincides with the stress regime defined from fault-plane solutions for the intermediate-depth earthquakes. This implies that buoyancy-driven descent of the lithospheric slab beneath the Vrancea region is directly linked to intermediate-depth seismicity. © 2004 Elsevier B.V. All rights reserved.
140636554
Seismic attenuation in the Carpathian bend zone and surroundings
We use measurements of crustal and upper mantle seismic attenuation in the southeastern Carpathian Arc and surroundings to test mantle responses to Tethys closure in this region. Active seismicity at the Carpathians’ Vrancea bend zone can delimit lithosphere and asthenosphere distributions through attenuation observations at overlying seismic stations. We measure frequency-independent attenuation via an iterative spectral ratio method which compares P and S spectra for evolving time windows of both arrivals, yielding 400 individual estimates of apparent differential QS and one composite measurement based on a normalized sum of the spectral ratios determined for the individual Q estimates. The procedure allows exclusion of subtle multipathed phases with attenuation different from that of the direct arrivals and yields a robust estimate of the measurement uncertainty. Measurements are retained for interpretation if the mean of the 400 individual Q estimates and the composite spectra Q estimate fall within the standard deviation of the 400 measurements. Results for 65 earthquakes recorded at the German–Romanian K2 accelerometer network during 1999 fall into clear groups: attenuation is low (high QS) at stations east and north of the Vrancea zone on the East European platform, the Scythian Platform, and in the eastern portion of the Moesian Platform. Inconsistent results at stations west of the Intramoesian fault, including those in and around Bucharest, probably reflect strong site effects at several locales. Attenuation at stations above and near the Vrancea zone, and at stations in the Transylvanian Basin, is high (low QS), most likely due to the presence of hot, shallow asthenosphere in these areas. The technique we developed may ultimately yield a strong test of slab detachment and continental lithosphere delamination hypotheses put forth to explain the unusual seismicity and volcanism of the Carpathian arc. D 2005 Elsevier B.V. All rights reserved.
128958324
Attenuation in Southeastern Carpathians area: Result of upper mantle inhomogeneity
The systematic analysis of seismograms recorded on the Romanian territory using Vrancea intermediate-depth earthquakes shows a strong asymmetric pattern relative to the epicentral area: on one side, in the Transylvanian Basin and the Eastern Carpathians (approximately along the inner volcanic chain), the amplitudes are reduced by a factor of 20 on average and the high frequencies are attenuated, in contrast with the other side, in the foreland platform. This pattern is explained by a significant attenuation increase caused by a strong lateral variation of the structure in the upper mantle, immediately towards NW of the Vrancea seismic active volume. This region corresponds to the most recent volcanic activity in the Persani Mountains and with the low-velocity body adjacent toward NW to the high-velocity body subducted beneath Vrancea area as indicated by seismic tomography and heat flow results. The CALIXTO'99 tomography experiment, deployed for 6 months in 1999, provides the largest number of observations for Vrancea earthquakes ever recorded on the Romanian territory. We select data from 8 earthquakes generated in this time interval in the Vrancea nest, which were recorded with signal / noise ratio greater than 5 by at least 25 stations. All of them are small- to moderate-magnitude events (3.6 ≤ Mw ≤ 4.2). The attenuation is much more important in the high-frequency range (> 1 Hz), than at low frequencies. Since the large Vrancea earthquakes can radiate significant energy in the low-frequency range (< 1 Hz), our results show that the seismic hazard level is much more uniform all over the Romanian territory in the low-frequency range than in the high-frequency range.
129040198
High‐resolution teleseismic body wave tomography beneath SE‐Romania – II. Imaging of a slab detachment scenario
SUMMARY 
 
Non-linear teleseismic bodywave tomography with data of the 1999 CALIXTO field experiment (Carpathian Arc Lithosphere X-Tomography) in Romania provides high-resolution imaging of the upper-mantle structure. In this paper, we present the relative P-wave velocity distribution of the lithosphere/asthenosphere system. Smearing from strong crustal velocity anomalies into the upper mantle is successfully suppressed by traveltime corrections with an a priori 3-D regional crustal velocity model (see Martin et al. 2005, herein referenced as paper 1). 
 
 
 
Our high-resolution image shows a high-velocity body beneath Vrancea and the Moesian platform with a NE–SW orientation between 70 and 200 km depth. Beneath 200 km a change in the orientation from NE–SW to N–S can be observed. The body reaches a maximum depth of about 350–370 km. The velocity perturbation is maximal between 110 and 150 km depth (5.2–5.8 per cent) and almost constant for depths beneath 200 km (3.2–3.8 per cent). As most authors of previous studies agree on Miocene subduction along the arc followed by soft continental collision we interpret the high-velocity body as the subducted, yet not fully detached slab. The NE-part of the slab appears to be mechanically coupled to the Moesian lithosphere and hosts the intermediate depth seismicity. In contrast the aseismic SW-part is interpreted as decoupled from the overlying lithosphere and torn off from the underlying lithospheric material beneath 200 km depth. 
 
 
 
Low velocity anomalies NW of the slab above 110 km depth are interpreted as a shallow asthenospheric upwelling. Further low-velocity anomalies are in agreement with a lithosphere-asthenosphere boundary at 110–150 km depth below the Moesian platform and deeper than 200 km under the East European platform (EEP). The tomographic images support models proposing slab rollback during subduction/collision, followed by slab steepening and lithospheric delamination. The different degrees of mechanical coupling of the slab to the overlying lithosphere allow to understand the loci of seismicity as volumes of stress concentration. 
 
 
 
Independent on the specifics of data interpretation our high-resolution image is a novel contribution to understand the process of ongoing lithospheric detachment associated with strong intermediate-depth seismicity in SE-Romania.
129852602
A note on the depth recurrence and strain release of large Vrancea earthquakes
The large 1940 Vrancea event with body wave magnitude mB = 7.3 was investigated in terms of the depth of rupture initiation and extent. It was found that the rupture started at 150 km depth and propagated downwards. The ruptured zones of the 1977, 1986 and 1990 Vrancea events were estimated from the distribution of aftershocks located with the joint hypocentre determination method. Their depth ranges are 90–110 km, 130–150 km and 70–90 km, respectively. Because the body wave magnitudes mb were saturated for the last three events and the surface wave magnitudes MS were underestimated (not being corrected for depth) we chose the moment magnitudes to quantify the four events: 7.7 (1940), 7.4 (1977), 7.1 (1986) and 6.9 (1990), respectively. The depth interval 110–130 km is found to be unbroken since at least 1838 or 1802 and therefore is expected to accommodate the next large moment release (Mw = 7.0 to 7.4). The strain in the vertical and in the SE-NW directions is about 0.0003, giving a moderate strain rate of about 10−13 s−1. A correlation between the depth interval of the large events and the year of occurrence in a century is suggested, offering a physical basis to the observed quasi-cyclicity.
56456717
The Transylvanian Basin (Romania) and its relation to the Carpathian fold and thrust belt: Insights in gravitational salt tectonics
Abstract Interpretation of regional seismic profiles, stratigraphic and sedimentologic data improved insights in the evolution of the Transylvanian Basin. The basin evolution was coeval with the post-Mid-Cretaceous to recent deformation of the Carpathian Mts. Four tectonostratigraphic megasequences are differentiated: Upper Cretaceous (rift), Paleogene (sag), Lower Miocene (flexural basin) and Middle to Upper Miocene (backarc sequence dominated by gravitational tectonics). The Mid-Miocene continental collision in the Eastern Carpathians is associated with the rising Carpathians. This uplift enhanced the differential load, which, together with the high heat flow induced by Late Miocene to Pliocene arc volcanism, triggered large-scale Mio-Pliocene gravity spreading of the salt overburden. This ‘mega-slide’ comprises three structural domains, as follows: extensional weld (upslope), contractional folds (central) and contractional toe thrust (downslope). The diapirs in the east indicate a pre-shortening reactive/passive growth stage. The central folds are mostly the result of late shortening. Basement involved thrusting uplifted the toe thrust domain by the Late Pliocene. The Late Neogene to recent Carpathians uplift, backarc volcanism and gravity spreading are largely coeval.
129741480
On the thermal regime of some tectonic units in a continental collision environment in Romania
An analysis of the evolution of the main tectonic units in Romania shows that the thermal regime of the lithosphere should be derived according, on the one hand, to the particular tectonic interactions the various tectonic units have been involved in and, on the other hand, to the investigated depth interval. A steady-state conduction model of the crustal temperature field based on the heat flow distribution and information on the structure is presented for the Romanian territory. It shows large lateral thermal variations between tectonic units, as a result of different geological and thermal histories. Within the frame of a complex modelling of the thermal evolution of the lithosphere in the East Carpathians, as proposed in this study, the zero-order thermal effects of the pre-Miocene oceanic subduction of the Eurasian plate are evaluated. The deep thermal structure of the subducted slab is derived and shown to be compatible with the velocity structure of the lithosphere and the intermediate-depth seismicity of the Vrancea area.
96475266
Lithosphere thermal structure and evolution of the Transylvanian Depression — insights from new geothermal measurements and modelling results
Abstract The surface heat flow density pattern of the Transylvanian Depression (TD) represents a marked high amplitude short wavelength low in a region of elevated heat flow. Detailed temperature–depth profiles obtained by continuous temperature logging, combined with a finite element modelling of topographic and fluid flow effects, support the conclusion that the observed thermal gradient in the TD truly represents the rate of heat loss of the subsurface. The surface heat flux is 30 mW m−2 in the centre of the depression, increasing to about 60 mW m−2 at margins. Climatic correction is of the order of 2–10 mW m−2 depending on the investigated depth interval. The measured temperatures are compatible with the cooling of the Earth surface during the Weichselian glaciation followed by the climate warming which started 10–11,000 years ago. The transient effects of Neogene sedimentation and erosion mean an overall 2–3 mW m−2 reduction in surface heat flux. A low mantle heat flux (30 mW m−2) and a low crustal heat production rate in the TD (0.5 μW m−3 in the centre) are necessary to explain the heat flux anomaly. The surface heat flux pattern of the TD and the extreme low value in the centre of the depression point to an exceptionally cold and strong lithosphere in the Transylvanian region, as shown by strength envelopes characteristic to the entire depression. The evolution of the TD generally can be understood in terms of an exceptionally strong lithosphere block caught in a compressive tectonic environment.
126826129
Thermo-mechanical controls on the mode of continental collision in the SE Carpathians (Romania) S.A.P.L. Cloetingh, E. Burov, L. Matenco, G. Toussaint, G. Bertotti,
Abstract The Carpathians orogenic system, with its along-arc variations in topography developed in the aftermath of continental collision, is associated with unusual foredeep basins, large-scale strain and seismicity concentration and high-velocity mantle bodies. The East Carpathians continental collision was non-cylindrical, leading to large-scale variations in thrust nappe kinematics, orogenic uplift patterns and foredeep subsidence, controlled by the mechanics and geometry of the lower plate. Thermo-mechanical modelling demonstrates that in this low-rate convergence regime, the subducted lithosphere had enough time to interact with the mantle to advance towards a thermal resettlement. This is favored by the low degree of metamorphism, mechanical weakness of the lower plate and the lack of active surface processes at the contact with and in the upper plate. In contrast, low-buoyant, thick lower crust and active surface processes keep the continuity of the slab intact and promote the development of typical foredeep basins. The model explains in a self-consistent manner the unusual geometry of the Vrancea seismogenic slab in the bend zone of the Romanian Carpathians. The model is also consistent with the presence of two high-velocity bodies inferred from seismic tomography studies and explains the depth zonation of seismicity in the Vrancea area. Differences between the northern part of East Carpathians and the southeastern bend of the Carpathians arc are largely controlled by lateral variations in crustal structure, topography emplacement and surface processes along the arc. Mechanical heterogeneity of the Carpathians subduction leads to the development of two end member modes of collision, allowing a study of these states and their transition. Lithospheric configuration and tectonic topography appear to be prime factors controlling variations in slab behavior. In the SE Carpathians, at the terminal phase of continental convergence, slab delamination, roll-back and depocenter migration appear to play a more limited role at shallow and lithospheric levels.
129264912
Tertiary cooling and exhumation history in the Maramures area (internal eastern Carpathians, northern Romania): thermochronology and structural data
Abstract The Tertiary kinematic history of the Maramures area is constrained by integrating thermochronological (fission track and (U–Th)/He analysis) data with field-based structural investigations. This study focuses on the tectonic evolution of the northern rim of the Tisza–Dacia block during collision with the European margin. Cretaceous nappe stacking, related metamorphism as well as Late Cretaceous exhumation are evidenced by zircon fission track data. Subsequent Palaeogene to Early Miocene sedimentation led to burial heating and annealing of fission tracks in apatite. Final tectonic uplift was initiated during the convergence of Tisza–Dacia with the European margin, associated with transpressional deformation (16 to 12 Ma). This led to Mid-Miocene exhumation, recorded by apatite fission track cooling ages in the western part of the study area. Transtension between 12 and 10 Ma caused brittle deformation along E–W trending strike-slip faults and SW–NE trending normal faults, delimiting blocks that were tilted towards the SW. This fragmentation of the crust led to enhanced exhumation at rates of 1 mm/a in the central part of the study area, as is documented by Middle to Late Miocene cooling ages (13 to 7 Ma). The outside estimate for the total amount of exhumation since Middle Miocene times is 7 km.
129932200
Are systematic variations in thrust belt style related to plate boundary processes? (The western Alps versus the Carpathians)
Within the Mediterranean region, Cenozoic deformation of the Western Alps and the West to East Carpathians has resulted in two different styles of foreland fold and thrust belt. The most prominent difference between the two belts is the presence (Carpathians) or absence (Western Alps) of contemporaneous back-arc extension, but other important differences in structure, topography and metamorphism also exist. These differences in thrust belt style developed mainly during the final stages of thrust belt evolution and appear to reflect fundamental differences in the tectonic settings of the Western Alps and the Carpathians in middle and late Cenozoic time. In particular, they appear to be the result of convergence that is in the first case driven primarily by major plate motions and in the second case only by local motions of small lithospheric flakes or fragments. We suggest that the structural styles developed in these two mountain belts may be useful in identifying mountain belts that have evolved in similar tectonic settings elsewhere in the world. In this respect, the Western Alps and the Carpathians can be regarded as typical examples of two different styles of foreland fold and thrust belt (or more properly as end-member examples within a broad spectrum of foreland fold and thrust belt styles). We propose that continental subduction zones and orogenic belts can be loosely divided into segments that show no major back-arc extensional deformation adjacent to the belt (the Western Alps) and segments that exhibit back-arc extension contemporaneously with thrusting (the Carpathians). The former are found in areas where the rate of overall plate convergence exceeds the rate of subduction, and are commonly typified by extensive involvement of crystalline basement in thrusting, exposure of high grade metamorphic rocks at the surface, high topographic elevation, and large amounts of erosion (tens of kilometers). The latter are found in areas where the rate of subduction exceeds the rate of overall plate convergence and are commonly typified by thrust belts with little to no involvement of crystalline basement in thrusting, low grade to no metamorphism, low topographic elevation, little erosion and, in some instances, an anomalously deep foredeep basin system.
128552362
Kinematic evolution of the Romanian Carpathians
Abstract The regional pattern of contraction and extension directions and the evolution of the strain field from Paleogene to Neogene times enabled a reconstruction of the migration path of the Carpathian collision front. The Carpathian nappes were thrust around the Moesian Plate during Paleogene and Early Neogene times and protruded into a small oceanic embayment between the Moesian and European plates. The arc structure of the Carpathian fold-thrust belt was formed in Late Neogene times as a result of the eastward-escaping Tisza–Dacia block, due to N-directed convergence of the Adriatic plate and the retreating subduction of an oceanic slab. Brittle deformation structures in the Romanian Carpathians suggest three tectonic events related to major plate motions: (1) Paleogene to Middle Miocene NE to ENE contraction caused right-lateral curved strike-slip faults; (2) Middle Miocene to Pliocene fan-shaped orientations of contraction directions were caused by right-lateral oblique convergence in the Southern Carpathians, frontal convergence in the southern Eastern Carpathians and left-lateral convergence in the northern Eastern Carpathians; (3) Pleistocene to Holocene general E–W extension and N–S contraction in the Carpathian arc and local ESE–WNW contraction in the Vrancea area is related to the late roll back stage and break-off of the subducted slab in the bend area.
129655559
Tertiary subduction and slab break-off model of the Carpathian–Pannonian region
Abstract This paper illustrates the application of multidisciplinary data analysis to the Carpathian–Pannonian region and presents a new Tertiary development model that incorporates all multidisciplinary parameters. During the Late Cretaceous–Eocene, the future Carpathian orogen was part of the larger Alpine–Carpathian orogen formed by the southeastward subduction (135–55 Ma) of the Penninic Ocean and the ultimate collision (55–40 Ma) of the European and Adriatic continents. The subduction in the Alpine region ended by the slab break-off of the subducting oceanic lithosphere from the continental one and by the related magmatism (43–24 Ma). While the Eocene Alps were under continental collision, the Eocene remnant Carpathian Flysch Basin (rCFB) was still subducting. The Carpathians and eastern parts of the Alps started to occupy the region of the present Carpathians during the Early Miocene. The oceanic plate underlying the rCFB subducted southwestwards, later westwards, while the northeastward and eastward migration velocity of the accreting plate boundary decreased through time. The slower subduction rate caused: a steeper dip of the subducting slab; the beginning of the Eggenburgian (22–19 Ma) and following duration of extension in the orogenic hinterland accompanied by the asthenosphere upwelling; the onset of the crustally derived volcanism above the risen asthenosphere and the younger mantle-derived volcanism, progressively less contaminated by the crustal material, all contemporaneous with a shortening in the Carpathian accretionary wedge. The subduction of the rCFB finally led, at the end of the Early Miocene, to a collision with the continental margin along the westernmost part of the present Carpathian Arc. The subduction roll-back of the subducting slab of the rCFB under the advancing Inner Carpathians, the oblique closure of the basin, the progressive change of the subduction to collision from the west to the east along the Carpathian Arc drove a scissors-like break-off of the subducting oceanic slab along the West Carpathians. The break-off in the East Carpathians was driven by the weight of a subducting oceanic slab and buoyancy of the attached continental slab. The break-off started in the west of the Carpathian Arc in the Early Miocene, ran along the arc to its present position in the bend area between the East and South Carpathians and separated the oceanic slab, that subducted passively under its own weight, from the European continental margin. The lateral propagation rate of the slab tear decreased with time. The break-off-related volcanism was synchronous with the final stages of the collision.
34595609
Subduction and slab detachment in the Mediterranean-Carpathian region.
Seismic tomography models of the three-dimensional upper mantle velocity structure of the Mediterranean-Carpathian region provide a better understanding of the lithospheric processes governing its geodynamical evolution. Slab detachment, in particular lateral migration of this process along the plate boundary, is a key element in the lithospheric dynamics of the region during the last 20 to 30 million years. It strongly affects arc and trench migration, and causes along-strike variations in vertical motions, stress fields, and magmatism. In a terminal-stage subduction zone, involving collision and suturing, slab detachment is the natural last stage in the gravitational settling of subducted lithosphere.
129306782
Delamination in collisional orogens
During continental collision, the weight of the downgoing slab may lead to extensional shearing in the descending plate, permitting separation of the downdip, dense oceanic lithosphere from the adjacent lighter continental lithospher. Separation may occur by means of a lithosphere-penetrating normal-sense shear zone, by means of pure shear necking of the lithosphere, or by some combination of these mechanisms. During separation, the continental crust attached to the lower plate may undergo an episode of extensional tectonics. The proximity of asthenosphere to crust may result in syntectonic regional metamorphism and plutonism. If the continents continue to converge following delamination, a compressive tectonic regime will be reestablished in the crust. The subsequent cooling of asthenosphere at the base of the crust may lead to the establishment of a continuous flat Moho. The likely imbrication of crustal and mantle lithologies during delamination and during the subsequent compressive tectonic regime, as well as underplating associated with syntectonic plutonism, may account for the seismic complexities observed at Moho depths beneath some mountain belts.
129951351
Crustal constraints on the origin of mantle seismicity in the Vrancea Zone, Romania: The case for active continental lithospheric delamination
Abstract The Vrancea zone of Romania constitutes one of the most active seismic zones in Europe, where intermediate-depth (70–200 km) earthquakes of magnitude in excess of M w  = 7.0 occur with relative frequency in a geographically restricted area within the 110° bend region of the southeastern Carpathian orogen. Geologically, the Vrancea zone is characterized by (a) a laterally restricted, steeply NW-dipping seismogenic volume (30 × 70 × 200 km), situated beneath (b) thickened continental crust within the highly arcuate bend region of the Carpathian orocline, and (c) miscorrelation of hypocenters with the position of known or inferred suture zones in the Carpathian orogenic system. Geologic data from petroleum exploration in the Eastern Carpathians, published palinspastic reconstructions, and reprocessing of industry seismic data from the Carpathian foreland indicate that (1) crust of continental affinity extends significantly westward beneath the external thrust nappes (Sub-Carpathian, Marginal Folds, and Tarcau) of the Eastern Carpathians, (2) Cretaceous to Miocene strata of continental affinity can be reconstructed westward to a position now occupied by the Transylvanian basin, and (3) geologic structure in the Carpathian foreland (including the Moho) is sub-horizontal directly to the east and above the Vrancea seismogenic zone. Taken together, these geologic relationships imply that the Vrancea zone occupies a region overlain by continental crust and upper mantle, and does not appear to originate from a subducted oceanic slab along the length of the Carpathian orogen. Accordingly, the Vrancea zone appears to potentially be an important place to establish evidence for active lithospheric delamination.
128503630
Intra-orogenic extension driven by gravitational instability: Carpathian-Pannonian orogeny
The extensional Pannonian Basin was formed in a few million years during Miocene time synchronously 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 (mountain-forming) 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. This mechanism provides a mechanically self-consistent explanation for all of the main structural features of the Pannonian-Carpathian system and presents a plausible alternative to the popular view that subduction and slab rollback have driven the development of this basin.
128806982
Late Miocene-Quaternary volcanism, tectonics and drainage system evolution in the East Carpathians, Romania
Abstract Middle Miocene (Sarmatian) convergence created the fold and thrust belt of the Eastern Carpathians of Romania, which subsequently experienced post-collisional crustal deformation combined with calc-alkaline and alkalic-basaltic volcanism in late Miocene–Quaternary time. This deformation led to the rise of the Cǎlimani–Gurghiu–Harghita volcanic mountains and to the subsidence of the N–S-oriented intramontane Borsec/Bilbor–Gheorgheni–Ciuc and Brasov pull-apart basins, and the E-oriented monocline-related Fǎgǎras basin. The regional drainage network is the composite of: (1) Older E-, SE- and S-flowing rivers, which cross the Carpathians, radiate towards the foreland and were probably established during the Middle Miocene (Sarmatian) collision event. (2) A more recent drainage system related to the contemporaneous development of the volcanoes and intramontaneous basins, which generally drains westward into the Transylvanian Basin since late Miocene time and has been capturing the older river system. The older river drainage system has also been modified by Late Pliocene–Quaternary folding, thrusting and monoclinal tilting along the Pericarpathian orogenic front and by reactivated transverse high angle basement faults, which cross the Eastern Carpathian foreland.
35136478
Neogene kinematics of the Transylvanian basin (Romania)
The Transylvanian basin is a major sedimentary basin located in the eastern part of the European Alpine orogenic system. It has a sedimentary fill more than 5 km (up to 8 km in some small areas) thick of Upper Cretaceous to upper Miocene deposits. It represents the main gas-producing province in Romania and central, eastern Europe.

In this article we analyze seismic lines and structural data from the basin as well as from its northern, eastern, and southeastern borders. These data indicate a tectonic origin for the Neogene structures from the Transylvanian basin. These structures include (1) northeast- and southwest-dipping thrust faults, and (2) east-northeast- and west-northwest-striking strike-slip faults having normal or reverse slip. Secondary structures such as salt diapirs and folds are related to these faults.

Structural data from the basin and its border indicate a Neogene overall compressional/transpressional regime having maximum principal stress oriented north to northeast.

Daniel Ciulavu received a diploma in geology and geophysics at the University of Bucharest in 1989 and his Ph.D. in geology at the Vrije Universiteit Amsterdam (Netherlands) in 1999. He worked two years for Geasol S.A. (Romania) in hydrogeology, coal, and alluvial gold exploration. Since 1991 he has been on the staff of the University of Bucharest, where he teaches the courses on structural geology in the Department of Geophysics and kinematic analysis for master's students.Corneliu Dinu received a diploma in geology in 1966 and his Ph.D. in 1976 at the University of Bucharest (Romania). After graduation, he worked as field geologist for Prospectiuni S.A. (Romania). Since 1970 he has been on the staff of the University of Bucharest, where he is professor of structural geology and basin analysis. Since 1990 he has served as the dean of sciences at the Faculty of Geology and Geophysics, University of Bucharest. Alexandru Szakacs received a diploma in geology in 1974 and his Ph.D. in 2000 at the University of Bucharest (Romania). He is senior geologist at the Romanian Institute of Geology. He has 25 years of experience in studying the Neogene volcanism of the Carpathian-Pannonian area. He has also worked on the Neogene volcanism of the Cordillera Betica (Spain). Dorin Dordea received a diploma in geology in 1974 at the University of Cluj (Romania). His field of activity is remote sensing. He has worked in several areas in Africa and Romania. Since 1999, he has served as the chief geologist of Prospectiuni S.A. (Bucharest, Romania). He is now working on the application of remote sensing in mining exploration.
55909762
Neogene–Quaternary magmatism and geodynamics in the Carpathian–Pannonian region: a synthesis
In the Carpathian–Pannonian region in Neogene times, westward-dipping subduction in a land-locked basin caused collision of two lithospheric blocks (Alcapa and Tisia) with the southeastern border of the European plate. Calc-alkaline and alkaline magmatism was closely related to subduction, rollback, collision and extension. From the spatial distribution of the magmatic activity, four segments can be defined: Western Segment (magmatism occurring on the Alcapa block), Central Segment (magmatism occurring on both Alcapa and the Tisia blocks), South-Eastern Segment and Interior Segment (both on the Tisia block). Most calc-alkaline magmatism in the region resulted from melting of a heterogeneous asthenospheric mantle source modified by addition of fluids and sediment. Assimilation and fractionation processes at shallow crustal levels occurred in most of the segments, strongly masking the deeper source processes. Long-term subduction, rollback and/or delamination led to contamination of the asthenosphere beneath the Western Segment. Here, large-volume partial melts of the contaminated mantle caused underplating and crustal anatexis, leading to mixing of mantle-derived calc-alkaline magmas with crustal melts. In the Central Segment, calc-alkaline magmas were formed by subduction and rollback, followed by back-arc extension and slab breakoff. Avariable mantle source is indicated in the back-arc setting and larger amount of fluid-induced metasomatism, source enrichment and assimilation nearer to the trench. In the Interior Segment, evolution from typical calc-alkaline magmas to adakite-like ones was related to extension due to fast rotations and transtensional tectonics. Here, calc-alkaline magmas formed by decompression melting of a heterogeneous crust–mantle lithosphere, while adakite-like melts resulted from fliud-dominated melting of the lithosphere. Along the South-Eastern Segment, slab breakoff was responsible for the generation of typical calcalkaline magmas, but in the extreme south of the segment, shallow level tearing of the slab followed breakoff. Strike–slip tectonics allowed the rise of hot asthenosphere and generation of adakite-like magmas, via slab-melting, along the torn edge of the East European Plate. Alkalic basaltic volcanism with an OIB-like asthenosphere source followed the calc-alkaline stage
129712045
Extension-related Miocene calc-alkaline magmatism in the Apuseni Mountains, Romania: Origin of magmas
The Miocene magmatism of the Apuseni Mountains in the Carpatho-Pannonian area hosts some of Europe’s largest porphyry epithermal Cu–Au ore systems associated with shallow subvolcanic intrusions. Detailed field observations combined with K–Ar ages, geochemical analyses, Sr–Nd isotopes and paleomagnetic data constrain a model for the geotectonic evolution and processes of melt generation that may account for the exceptional mineralizing potential of the magmatic activity in this region. The magmatic activity developed mainly between 14.7 and 7.4 Ma and after a gap ceased at around 1.6 Ma. Geotectonic conditions do not support contemporaneous subduction processes, but were represented by transtensional and rotational tectonics, which generated horst and graben structures and favoured the generation and ascent of magmas. The “subduction signature” of the magmas emphasizes the significant involvement of fluids (mantle lithosphere and/or lower crust) inherited during previous geodynamic events. The mechanism of magmagenesis is considered to be related to decompressional melting (various degrees of) of a heterogeneous source situated at the crust-lithosphere mantle boundary. Mixing with asthenospheric melts generated during the extension-related attenuation of the lithosphere may also be implied. The evolution from normal to adakiticlike calc-alkaline and alkaline magmas generally is time-dependent as a consequence of variable fluid-present melting. Fractional crystallization-assimilation processes in shallow magma chambers are suggested for early magmatism but were almost absent from later magmatism, which related to an increasingly extensional regime. The youngest alkalic (shoshonitic) magmatism (1.6 Ma) is asthenosphere-derived, but in a different extensional event, being almost coeval with the OIB-like alkali-basaltic magmatism (2.5 Ma) occurring along the South Transylvanian fault. The fluid-present melting of the source seems to be the critical factor for the presence of the copper-gold-bearing mineralizing fluids.
132528414
K-Ar datings of Neogene-Quaternary calc-alkaline volcanic rocks in Romania
Neogene-Quaternary plate convergence-related calc-alkaline magmatic rocks from Romania have been dated using the K-Ar radiometric technique. The magmatic rocks occur in the East Carpathians and the Apuseni Mts. In the -East Carpathians, the discontinuous magmatic arc is segmented into two main volcanic areas' Oaq-Gutai (oG) and Calimani-Gurghiu-Harghita (CGH) at the extremities and an intrusive (subvolcanic) segment (Jibles-Toroiaga-RodnaBargau: TTRB) in the middle. According to biostratigraphical data, volcanic activity started in the,Badenian' but the oldest rocks are dated atL3.4 Ma. The volcanic activity ceased at about 0.2Ma. The range of apparent ages during Pannonian (9-11 Ma) in TTRB is partly coeval with that of OG, reflecting the paroxysm of the magmatic activity. The longest interval of activity was detected in the Gutai Mts. (13.5-6.9 Ma)-. An obvious age progression along the arc was pointed out for CGH volcanic chain, enhanced along the terminal 40 km of South Harghita Mts. (4.3-0.2 Ma). Preliminary data from the Apuseni Mts. suggest the Sarmatian as the main interval for magmatic activity in that region (13.4-12.4 Ma). l. Introduction
131098177
The Gataia Pleistocene lamproite: a new occurrence at the southeastern edge of the Pannonian Basin, Romania
Abstract The petrological identity of the lamproite occurrence situated c. 5 km south of Gătaia (Banat, western Romania), until now considered to be an alkali basalt, has been revealed by exploration drilling. This drilling programme pierced a slightly vesicular lava flow inside the Şumiga hill (198 m above sea level), revealing a sequence of vesicular lava intercalated with fallout scoria deposits. The isolated lamproite volcano, dated at 1.32±0.06 Ma (whole-rock K/Ar method), is situated at the southeastern margin of the Pannonian Basin and at the western margin of the South Carpathians, along an important NE–SW fault system. The lamproite magma erupted through flat-lying Miocene sedimentary rocks, which overlie older crystalline basement that experienced intense lithospheric deformation and orogeny during Cretaceous times. The lamproite is associated with contemporaneous volcanic activity that lies 50–150 km to the NNE, along the South Transylvanian fault system (Lucareţ alkali basalts, Uroiu shoshonites); these rocks, however, are not consanguineous, and derive from different mantle sources. There are, however, similarities to Oligocene lamproites from Serbia (Bogovina), generated on similar basement. The lamproite is fresh and has a slightly porphyritic texture with phenocrysts of high-Mg olivine and microphenocrysts of euhedral leucite in a glassy matrix. The matrix also contains microcrysts of olivine, armalcolite, apatite, sanidine, low Al-diopside, fluorine-bearing titanium phlogopite, fluorine-bearing amphibole and accessory chrome spinels. Ba-sulphate aggregates fill small vesicles. Very rare clots of corroded Al-phlogopite surrounded by secondary spinels are enclosed by leucite aggregates, suggesting formation during an earlier event. Major and trace element geochemistry and Sr and Nd isotopes show that the rock is a typical lamproite, close to the compositions of Leucite Hills and Gaussberg lamproites. The source for the Gătaia lamproite was probably a garnet harzburgite lithospheric mantle, metasomatized by alkaline mafic melts, most probably active at the Cretaceous–Palaeogene boundary. Metasomatism by alkaline melts is indicated by high abundances of incompatible trace elements, such as Ba, Sr, Rb and Zr. The Gătaia lamproite probably had a limited available source volume for melting that reflects the ambient thermal regime in the typical post-collisional tectonic setting active during Late Neogene to Quaternary time. Emplacement of this lamproite was probably a result of surface uplift and erosion at the base of the lithosphere, marking the collapse of the Alpine orogen.
140681719
Petrology and geochemistry of late Tertiary/Quaternary mafic alkaline volcanism in Romania
Abstract Alkaline volcanic activity occurred in the Persani Mountains (eastern Transylvanian Basin) and Banat (eastern Pannonian Basin) regions of Romania between 2.5 Ma and 0.7 Ma. This volcanism followed an extended period of subduction-related mostly andesitic and dacitic magmatism in the Eastern Carpathian arc. The Persani Mts. alkaline activity coincided with the last phase of subduction-related activity. Several lava flows and pyroclastic deposits in the Persani Mts. carry peridotitic mantle xenoliths and amphibole megacrysts. Major- and trace-element geochemistry indicates that the alkaline magmas are primitive, silica-undersaturated alkali basalts and trachybasalts (7.8–12.3 wt.% MgO; 119–207 ppm Ni; 210–488 ppm Cr) which are LREE-enriched. Mantle-normalised trace-element diagrams reveal an overall similarity to continental intraplate alkali basalts, but when compared with a global average of ocean island basalts (OIB), the Banat lavas are similar to average OIB, whereas the Persani Mts. basalts have higher Rb, Ba, K and Pb and lower Nb, Zr and Ti. These features slightly resemble those of subduction-related magmas, particularly those of a basaltic andesite related to the nearby older arc magmas. With 87 Sr 86 Sr varying from 0.7035-0.7045 and 143 Nd 144 Nd from 0.51273-0.51289, the Romania basalts are indistinguishable from those of the western Pannonian basin (Hungary and Austria) and Neogene alkali basalts throughout Europe. Amphibole megacrysts have similar isotopic signatures, and their REE patterns indicate derivation by crystallisation from a mafic alkaline magma. The age-corrected Sr and Nd isotopic compositions of a calc-alkaline basaltic andesite related to the preceeding period of subduction also lies within the field of the younger alkaline magmas. Pb isotopic ratios of the Romanian alkali basalts do not lie on the NHRL, but overlap the field of Tertiary alkali basalts from the western Pannonian basin, and have unusually high 207 Pb 204 Pb at a given 206 Pb 204 Pb . Thus it is probable that, although the Romanian alkali basalts have a strong asthenospheric (i.e. OIB-type mantle source) component, their Pb isotopic characteristics were derived from mantle which was affected by the earlier subduction.
129752475
Rare earth elements in East Carpathian volcanic rocks
Abstract REE, Y, Rb, Sr, Cs, Ba, Pb, Th, U, Zr, Hf, and Sn are reported for a basalt, low-Si andesite, andesite, high-K andesite, dacite and rhyolite from the calc-alkaline volcanic belt of Calimani-Harghita Mountains (Rumenian Carpathians). The basalt, low-Si andesite and andesite show identical chondrite-normalized REE patterns with fractionated light REE (La-Sa) and unfractionated heavy REE (Gd-Yb). The dacite shows similar pattern but lower ΣREE. The high-K andesite and rhyolite have a distinctively different REE pattern strongly fractionated for both light and heavy REE. These differences point to different genetical mechanism for the high-K andesite-rhyolite and basalt-low-Si andesite-andesite-dacite magmas. The high-K andesite and rhyolite magmas are believed to represent primary melts of an undergoing oceanic slab; the basalt, low-Si andesite, andesite and dacite magmas are considered to be produced by partial melting of garnet pyroxenite bodies derived by reaction between the primary melts of the undergoing oceanic slab and the peridotitic mantle overlying the Benioff zone.
98513412
Boron concentration measurements by prompt gamma activation analysis: Application on miocene-quaternary volcanics of the Carpathian-Pannonian Region
Prompt gamma activation analysis is a highly powerful analytical method in geology, due to its applicability to determine the concentration of all major and few trace elements in whole rock samples. Furthermore, the boron concentration can be determined with proper accuracy without time consuming sample preparation. The reliability of this method was checked on geological standards and on other volcanic rocks, which were analyzed previously by XRF and TIMS for many major and trace element components and Sr-isotopes. Boron concentrations of volcanic rock samples from the East Carpathian Volcanic Field (Eastern-Central Europe) are reported here for the first time. The boron concentrations were measured for an improved definition of the petrogenezis of these rocks and to understand the fluid addition processes during subduction-related volcanism in this region.
102488833
Generation of normal and adakite-like calc-alkaline magmas in a non-subductional environment: An Sr–O–H isotopic study of the Apuseni Mountains neogene magmatic province, Romania
Abstract Neogene magmatism in the Apuseni Mountains of Romania was active between 15 and 7 Ma, with an isolated final eruption at 1.6 Ma. Several groups of magmatic rocks can be distinguished in the province on the basis of ages, trace elements and isotopic compositions. Most are of calc-alkaline affinity, despite the fact that the region is located 200 km from the postulated Carpathian subduction trench. However, adakite-like calc-alkaline magmas were also erupted and the youngest eruptions were of alkaline affinity. Magmatic rocks older than 13.5 Ma are characterised by the highest 87Sr/86Sr, δ18O and δD values in their phenocryst phases. This early magmatism is considered to be a result of crustal melting related to the fast rotation of small crustal blocks. Volcanic rocks younger than 13.5 Ma have lower 87Sr/86Sr and δ18O ratios, with a narrow range for pyroxene and amphibole mineral separates, indicating closed system fractional crystallization. A larger scatter of 87Sr/86Sr and δ18O values is found in plagioclase phenocrysts and groundmasses, indicating that a small amount of crustal assimilation also occurred. The δD values for hydrogen-bearing phases such as amphibole, biotite and groundmass indicate fractional crystallisation in a closed system and a trend of decreasing δD in the source with time. The magma source of normal calc-alkaline adakite-like magmas was not related to contemporaneous subduction, but was likely due to melting of delaminated eclogitic mafic lower crust. In contrast, the late-stage alkaline magmas were related to asthenospheric upwelling. Petrological analysis of the complex succession of magmas in the Apuseni Mountains province demonstrates that normal calc-alkaline and adakite-like magmatism can be generated in a non-subductional environment, in this case associated with an unusual extensional setting.
128932175
Post-collisional Tertiary–Quaternary mafic alkalic magmatism in the Carpathian–Pannonian region: a review
Mafic alkalic volcanism was widespread in the Carpathian–Pannonian region (CPR) between 11 and 0.2 Ma. It followed the Miocene continental collision of the Alcapa and Tisia blocks with the European plate, as subduction-related calc-alkaline magmatism was waning. Several groups of mafic alkalic rocks from different regions within the CPR have been distinguished on the basis of ages and/or trace-element compositions. Their trace element and Sr–Nd–Pb isotope systematics are consistent with derivation from complex mantle-source regions, which included both depleted asthenosphere and metasomatized lithosphere. The mixing of DMM-HIMU-EMII mantle components within asthenosphere-derived magmas indicates variable contamination of the shallow asthenosphere and/or thermal boundary layer of the lithosphere by a HIMU-like component prior to and following the introduction of subduction components. Various mantle sources have been identified: Lower lithospheric mantle modified by several ancient asthenospheric enrichments (source A); Young asthenospheric plumes with OIB-like trace element signatures that are either isotopically enriched (source B) or variably depleted (source C); Old upper asthenosphere heterogeneously contaminated by DM-HIMUEMII-EMI components and slightly influenced by Miocene subduction-related enrichment (source D); Old upper asthenosphere heterogeneously contaminated by DM-HIMU-EMII components and significantly influenced by Miocene subduction-related enrichment (source E). Melt generation was initiated either by: (i) finger-like young asthenospheric plumes rising to and heating up the base of the lithosphere (below the Alcapa block), or (ii) decompressional melting of old asthenosphere upwelling to replace any lower lithosphere or heating and melting former subducted slabs (the Tisia block). D 2004 Published by Elsevier B.V.
128133086
Plio-Quaternary magmatism in Italy
Plio-Quaternary magmatism in Italy exhibits an extremely variable composition, which spans almost entirely the spectrum of magmatic rocks occurring worldwide. Petrological and geochemical data provide a basis for distinguishing various magmatic provinces, which show different major element and/or trace element and/or isotopic compositions. The Tuscany province (14–0.2 Ma) consists of silicic magmas generated through crustal anatexis, and of mantlederived calcalkaline to ultrapotassic mafic rocks. The Roman, Umbria, Ernici-Roccamonfina and Neapolitan provinces (0.8 Ma to present) are formed by mantlederived potassic to ultrapotassic rocks having variable trace element and isotopic compositions. The Aeolian arc (?1 Ma to present) mainly consists of calcalkaline to shoshonitic rocks. The Sicily province contains young to active centers (notably Etna) with a tholeiitic to Na-alkaline affinity. Finally, volcanoes of variable composition occur in Sardinia and, as seamounts, on the Tyrrhenian Sea floor. Magmas in the Aeolian arc and along the Italian peninsula have a subductionrelated geochemical character, whereas the Sicily and Sardinia provinces display intraplate signatures. Intraplate and orogenic volcanics coexist on the Tyrrhenian Sea floor. The geochemical and isotopic complexities of PlioQuaternary magmatism reveal that the upper mantle beneath Italy consists of various domains, spanning both orogenic and anorogenic compositions. Isotopic data suggest that compositional heterogeneity originated from mixing between various mantle reservoirs, and between these and subduction-related crustal material. This probably occurred during the Cenozoic-Quaternary geodynamic evolution of the western Mediterranean.
131727580
Ultramafic xenoliths in plio-pleistocene alkali basalts from the eastern transylvanian basin: Depleted mantle enriched by vein metasomatism
Ultramafic xenoliths from alkali basalts in the Per§ani Mountains in the Eastern Transylvanian Basin (ETB) of Romania are mainly spinel Iherzolites, although spinel harzburgites, websterites, clinopyroxenites and amphibole pyroxenites are also present. Amphibole veins cut some spinel peridotite samples. All are derived from the shallow lithospheric upper mantle. In general, textural variations are restricted to protogranular and porphyroclastic types, compared with the more varied textures found in mantle xenoliths from the alkali basalts of the neighbouring Pannonian Basin. Also, ETB peridotites are richer in amphibole. Thus, the mantle beneath the edge of the ETB is less deformed but more strongly metasomatized than the mantle closer to the centre of the Pannonian Basin. Mineralogical and bulk-rock geochemical variations resemble those of spinel Iherzolites from other sub-continental shallow mantle xenolith suites. There is no apparent correlation between deformation and geochemistry, and much of the major and trace element variation is due to variable extraction of picritic melts. The REE patterns of separated clinopyroxenes from the peridotite xenoliths are mostly LREE depleted, although clinopyroxenes from regions adjacent to amphibole veins have experienced an enrichment in La and Ce and a change in their Sr and Nd isotopic values towards those of the vein, while still retaining an overall LREE depletion. Clinopyroxenes from the websterites and clinopyroxenites are more variable. Amphibole in the hydrous pyroxenites and amphibole veins is strongly LREE enriched and is considered to be metasomatic in origin. 87Sr/86Sr and
55730555
Geochemical response of magmas to Neogene–Quaternary continental collision in the Carpathian–Pannonian region: A review
The Carpathian–Pannonian Region contains Neogene to Quaternary magmatic rocks of highly diverse composition (calcalkaline, shoshonitic and mafic alkalic) that were generated in response to complex microplate tectonics including subduction followed by roll-back, collision, subducted slab break-off, rotations and extension. Major element, trace element and isotopic geochemical data of representative parental lavas and mantle xenoliths suggests that subduction components were preserved in the mantle following the cessation of subduction, and were reactivated by asthenosphere uprise via subduction roll-back, slab detachment, slab-break-off or slab-tearing. Changes in the composition of the mantle through time are evident in the geochemistry, supporting established geodynamic models. Magmatism occurred in a back-arc setting in the Western Carpathians and Pannonian Basin (Western Segment), producing felsic volcaniclastic rocks between 21 to 18 Ma ago, followed by younger felsic and intermediate calc-alkaline lavas (18–8 Ma) and finished with alkalic-mafic basaltic volcanism (10–0.1 Ma). Volcanic rocks become younger in this segment towards the north. Geochemical data for the felsic and calc-alkaline rocks suggest a decrease in the subduction component through time and a change in source from a crustal one, through a mixed crustal/mantle source to a mantle source. Block rotation, subducted roll-back and continental collision triggered partial melting by either delamination and/or asthenosphere upwelling that also generated the younger alkalic-mafic magmatism. In the westernmost East Carpathians (Central Segment) calc-alkaline volcanism was simultaneously spread across ca. 100 km in several lineaments, parallel or perpendicular to the plane of continental collision, from 15 to 9 Ma. Geochemical studies indicate a heterogeneous mantle toward the back-arc with a larger degree of fluid-induced metasomatism, source enrichment and assimilation on moving north-eastward toward the presumed trench. Subduction-related roll-back may have triggered melting, although there may have been a role for back-arc extension and asthenosphere uprise related to slab break-off. Calc-alkaline and adakite-like magmas were erupted in the Apuseni Mountains volcanic area (Interior Segment) from15–9 Ma, without any apparent relationship with the coeval roll-back processes in the front of the orogen. Magmatic activity ended with OIBlike alkali basaltic (2.5 Ma) and shoshonitic magmatism (1.6 Ma). Lithosphere breakup may have been an important process during extreme block rotations (~608) between 14 and 12 Ma, leading to decompressional melting of the lithospheric and asthenospheric sources. Eruption of alkali basalts suggests decompressional melting of an OIB-source asthenosphere. Mixing of asthenospheric
129201636
Partial delamination of continental mantle lithosphere, uplift-related crust mantle decoupling, volcanism and basin formation: a new model for the Pliocene Quaternary evolution of the southern East-Carpathians, Romania
Abstract A geodynamic model is proposed for the Mid-Miocene to Quaternary evolution of the southern East-Carpathians in order to explain the relationships between shallow and deep geological phenomena that occurred synchronously during late-collision tectonics. In this area, an active volcanic zone cross-cuts since 2 My the suture between the overriding Tisza–Dacia and subducting European continental plates. Mafic calc-alkaline and alkaline magmas (south Harghita and Persani volcanoes) erupted contemporaneously. These magmas were supplied by partial melting of the mantle lithosphere of the subducting, and not of the overriding, plate. In an effort to decipher this geodynamically a-typical setting of magma generation, the spatial and temporal distribution of shallow and deep phenomena was successively examined in order to establish the degree of their interdependence. Our model indicates that intra-mantle delamination of the subducting European plate is the principal cause of a succession of events. It caused upwelling of the hot asthenosphere below a thinned continental lithosphere of the Carpathians, inducing the uplift of the lithosphere and its internal decoupling at the Moho level by isostatic and mostly thermal effects. During this uplift, the crust deformed flexurally whilst the mantle deformed in a ductile way. This triggered decompressional partial melting of the uppermost mantle lithosphere. Flexural deformation of the crust induced its fracturing, allowing for the rapid ascent of magmas to the surface, as well as reactivation of an older detachment horizon at the base of the Carpathian nappe stack above which the Brasov, Ciuc and Gheorghieni hinterland basins formed by extension and gravity spreading. The rapid subsidence of the Focsani foreland basin is controlled by the load exerted on the lithosphere by the delaminated mantle slab that is still attached to it. In this model, crust–mantle decoupling, magma genesis and volcanism, local near-surface hinterland extension are consequences of uplift, induced by asthenospheric upwelling triggered by intra-mantle delamination. This model enables to conceive that delamination-induced decoupling began to be efficient 9.4 My ago at the northern end of the East-Carpathians, when the mantle slab dipped westwards. Since then, intra-mantle delamination migrated laterally, normal to the slab strike, and follows the arcuate shape (NW→SE→SW) of the Carpathians. Nowadays, whereas the mantle slab is still actively foundering below the Vrancea seismic zone to the SE of the most recent volcanic area (South Harghita–Persani), a significant southwestward shift of the delamination process can be discerned.
140597925
A map-view restoration of the Alpine-Carpathian-Dinaridic system for the Early Miocene
A map-view palinspastic restoration of tectonic units in the Alps, Carpathians and Dinarides reveals the plate tectonic configuration before the onset of Miocene to recent deformations. Estimates of shortening and extension from the entire orogenic system allow for a semi-quantitative restoration of translations and rotations of tectonic units during the last 20 Ma. Our restoration yielded the following results: (1) The Balaton Fault and its eastern extension along the northern margin of the Mid-Hungarian Fault Zone align with the Periadriatic Fault, a geometry that allows for the eastward lateral extrusion of the Alpine-Carpathian-Pannonian (ALCAPA) Mega-Unit. The Mid-Hungarian Fault Zone accommodated simultaneous strike-perpendicular shortening and strike-slip movements, concomitant with strike-parallel extension. (2) The Mid-Hungarian Fault Zone is also the locus of a former plate boundary transforming opposed subduction polarities between Alps (including Western Carpathians) and Dinarides. (3) The ALCAPA Mega-Unit was affected by 290 km extension and fits into an area W of present-day Budapest in its restored position, while the Tisza-Dacia Mega-Unit was affected by up to 180 km extension during its emplacement into the Carpathian embayment. (4) The external Dinarides experienced Neogene shortening of over 200 km in the south, contemporaneous with dextral wrench movements in the internal Dinarides and the easterly adjacent Carpatho-Balkan orogen. (5) N–S convergence between the European and Adriatic plates amounts to some 200 km at a longitude of 14° E, in line with post-20 Ma subduction of Adriatic lithosphere underneath the Eastern Alps, corroborating the discussion of results based on high-resolution teleseismic tomography.The displacement of the Adriatic Plate indenter led to a change in subduction polarity along a transect through the easternmost Alps and to substantial Neogene shortening in the eastern Southern Alps and external Dinarides. While we confirm that slab-pull and rollback of oceanic lithosphere subducted beneath the Carpathians triggered back-arc extension in the Pannonian Basin and much of the concomitant folding and thrusting in the Carpathians, we propose that the rotational displacement of this indenter provided a second important driving force for the severe Neogene modifications of the Alpine-Carpathian-Dinaridic orogenic system.
129026565
Neogene evolution of the Carpatho-Pannonian region: an interplay of subduction and back-arc diapiric uprise in the mantle
Geodynamic evolution of the Carpathian arc and Pannonian basin during the Neogene times is presented as a set of palinspastic reconstructions. The structural evolution is modeled in terms of a coupled system of: (1) Alpine (Atype) subduction and compressive orogene belt development owing to compression by the Adriatic microplate, (2) lateral extrusion of Alcapa lithosphere from the Alpine collision assisted by transform faults, (3) Carpathian gravity driven (Btype) subduction of oceanic or suboceanic lithosphere underlying former flysch basins and (4) back arc extension associated with the diapiric uprise of asthenospheric mantle. The variable timing of accretionary prism and back arc basin evolution in the Western Carpathians, the NW part of the Eastern Carpathians, and the SE part of the Eastern Carpathians confirms that the final Tertiary evolution of the Carpathian arc and Pannonian basin was not a uniform process. Rather, it took place successively in three segments, reflecting gravity driven subductions compensated by return asthenospheric flows (involving the back-arc diapiric uprise of asthenospheric mantle). The observed low subduction rate implies obstacles to the compensating asthenosphere flow, perhaps represented by confining thick lithosphere at the NW and SE sides of the arc. This segmentation may arise from a gravity driven process allowing asthenospheric side flow to take place speeding up the gravity driven overturn (subduction). Structural evolution as well as the timing and spatial distribution of the arc-type (subduction-related) andesite volcanics suggests that subduction halted because the subducting plate became nearly vertical, followed closely by the detachment of the sinking lithosphere slab from the continental margin. Late stage alkali basalt volcanic rocks imply that during the final stage of back arc basin evolution the related diapiric uprise of asthenospheric mantle incorporated unmetasomatized mantle material, brought possibly into the area of the diapiric uprise by compensating athenosheric mantle counterflows. Correspondence to: J. Lexa (lexa@gssr.sk)
129087284
Origin of potassic (C-type) adakite magmas: Experimental and field constraints
The postcollisional, Mesozoic, C-type or high-K adakitic intrusions (K-adakites) of China lack either temporal or spatial association with subduction and have K2O/Na2O around unity. Otherwise, their geochemistry is very similar to ordinary adakites. New experimental data, geological observations and theoretical considerations lead us to suggest that these K-adakites were high-T (> 1050 and probably > 1075 °C), rather hydrous magmas ( 6 wt.% H2O) produced by fluid-absent partial melting of metatonalites, meta-andesites, or possibly potassic metabasalts at pressures exceeding 2 GPa. Their peculiar chemistry is a consequence of both the elevated K2O/Na2O in the protolith and the very high pressure of partial melting. The most likely tectonic setting is one of extreme crustal thickening followed by delamination of the eclogitic keel and partial melting of this continental crustal material at mantle depths, with high mantle heat flow, during orogenic collapse.
130453769
Kinematics of slab tear faults during subduction segmentation and implications for Italian magmatism
Tectonic activity in convergent plate boundaries commonly involves backward migration (rollback) of narrow subducting slabs and segmentation of subduction zones through slab tearing. Here we investigate this process in the Italian region by integrating seismic tomography data with spatiotemporal analysis of magmatic rocks and kinematic reconstructions. Seismic tomography results show gaps within the subducting lithosphere, which are interpreted as deep (100–500 km) subvertical tear faults. The development of such tear faults is consistent with proposed kinematic reconstructions, in which different rates of subduction rollback affected different parts of the subduction zone. We further suggest a possible link between the development of tear faults and the occurrence of regional magmatic activity with transitional geochemical signatures between arc type and OIB type, associated with slab tearing and slab breakoff. We conclude that lithospheric-scale tear faults play a fundamental role in the destruction of subduction zones. As such, they should be incorporated into reconstructions of ancient convergent margins, where tear faults are possibly represented by continental lineaments linked with magmatism and mineralization.
129580061
Constraints on mantle circulation around the deforming Calabrian slab
[1] Combining tectonics, with seismological and geochemical data, we reconstruct the deformation history of the presently narrow Calabrian slab and the path of mantle circulation during the last 10 Ma. We show that during the slab deformation the mantle laterally flowed inside the back arc region permitting its retrograde motion and giving a seismological and volcanological record after 1–2 myr.
131348637
Modes of basin (de)formation, lithospheric strength and vertical motions in the Pannonian-Carpathian system: inferences from thermo-mechanical modelling
Abstract After a rapid multiphase evolution and a transition from passive to active rifting during late Early Miocene to Pliocene times, the Pannonian Basin has been subjected to compressional stresses leading to gradual basin inversion during Quaternary times. Stress modelling demonstrates the significance of the interaction of external plate-boundary forces and the effect of gravitational stresses caused by continental topography and crustal thickness variation. Flexural modelling and fission-track studies have elucidated the complex interplay of flexural downloading during collision, followed by rapid unroofing by unflexing and isostatic rebound of the lithosphere. The stretching and subsidence history of the Pannonian Basin, the temporal and spatial evolution of the flexure of the Carpathian lithosphere, and the lithospheric strength of the region reflect a complex history of this segment of the Eurasia-Africa collision zone. The polyphase evolution of the Pannonian-Carpathian system has resulted in strong lateral and temporal variation in thermo-mechanical properties in the area. Modelling results suggest that, as a whole, the Pannonian Basin has been an area of pronounced lithospheric weakness since Cretaceous time, shedding light on the high degree of strain localization in this region. This basin, the hottest in continental Europe, has a lithosphere of extremely low rigidity, making it prone to multiple tectonic reactivations. Another feature is the noticeable absence of lithospheric strength in the mantle lithosphere of the Pannonian Basin. Modelling studies suggest pronounced lateral variations in lithospheric strength along the Carpathians and their foreland, which have influenced the thrust load kinematics and post-collisional tectonic history. The inferences and models discussed in this paper are constrained by a large geophysical database, including seismic profiles, gravity and heat-flow data.
128939940
The circum-Mediterranean anorogenic Cenozoic igneous province
Abstract During the Cenozoic widespread anorogenic magmatism, unrelated to recent supra-subduction zone modification of its mantle source, developed within the Mediterranean and surrounding regions; this is referred to collectively as the CiMACI (Circum-Mediterranean Anorogenic Cenozoic Igneous) province. On the basis of a comprehensive review of published and new major and trace element and Sr–Nd–Pb isotopic data (more than 7800 samples) for the magmatic rocks, a common sub-lithospheric mantle source component is identified for most of the region. This has geochemical affinities to the source of HIMU oceanic island basalts and to the European Asthenospheric Reservoir (EAR) and the Low Velocity Component (LVC) of previous workers; we refer to this as the Common Mantle Reservoir (CMR). Global and local seismic tomography studies of the mantle beneath the CiMACI province have revealed a range of P- and S-wave velocity anomalies, some of which have been related to the presence of mantle plumes. Detailed local tomography experiments in the Massif Central of France and the Eifel region of central Germany suggest that, locally, there are diapiric upwellings rooted within the upper mantle which induce adiabatic decompression melting and magma generation. These velocity anomalies can be interpreted as evidence of mantle temperatures up to 150 °C hotter than the ambient mantle. However, the seismic attenuation could also be attributable to the presence of fluid or partial melt and significant thermal anomalies are not necessary to explain the petrogenesis of the magmas. A model is proposed in which the geochemical and isotopic characteristics of the sub-lithospheric mantle beneath the CiMACI province reflect the introduction of recycled crustal components (derived from both oceanic and continental lithosphere) into the ambient depleted upper mantle. This sub-lithospheric mantle is subsequently partially melted in a variety of geodynamic settings related to lithospheric extension, continental collision and orogenic collapse, and contemporaneous subduction, slab roll-back and slab-window formation. On the basis of this in-depth geochemical and petrological study of the CiMACI province, we consider that there is no need to invoke the involvement of anomalously hot mantle (i.e., the presence of a single or multiple deep mantle plumes) in the petrogenesis of the magmas. If, however, we adopt a more permissive definition of “mantle plume”, allowing it to encompass passive, diapiric upwellings of the upper mantle, then we can relate the CiMACI province magmatism to multiple upper mantle plumes upwelling at various times during the Cenozoic. To avoid confusion we recommend that such upper mantle plumes are referred to as diapiric instabilities.
55108896
The Alpine-Carpathian-Dinaridic orogenic system: correlation and evolution of tectonic units
A correlation of tectonic units of the Alpine-Carpathian-Dinaridic system of orogens, including the substrate of the Pannonian and Transylvanian basins, is presented in the form of a map. Combined with a series of crustal-scale cross sections this correlation of tectonic units yields a clearer picture of the three-dimensional architecture of this system of orogens that owes its considerable complexity to multiple overprinting of earlier by younger deformations.The synthesis advanced here indicates that none of the branches of the Alpine Tethys and Neotethys extended eastward into the Dobrogea Orogen. Instead, the main branch of the Alpine Tethys linked up with the Meliata-Maliac-Vardar branch of the Neotethys into the area of the present-day Inner Dinarides. More easterly and subsidiary branches of the Alpine Tethys separated Tisza completely, and Dacia partially, from the European continent. Remnants of the Triassic parts of Neotethys (Meliata-Maliac) are preserved only as ophiolitic mélanges present below obducted Jurassic Neotethyan (Vardar) ophiolites. The opening of the Alpine Tethys was largely contemporaneous with the Latest Jurassic to Early Cretaceous obduction of parts of the Jurassic Vardar ophiolites. Closure of the Meliata-Maliac Ocean in the Alps and West Carpathians led to Cretaceous-age orogeny associated with an eclogitic overprint of the adjacent continental margin. The Triassic Meliata-Maliac and Jurassic Western and Eastern Vardar ophiolites were derived from one single branch of Neotethys: the Meliata-Maliac-Vardar Ocean. Complex geometries resulting from out-of-sequence thrusting during Cretaceous and Cenozoic orogenic phases underlay a variety of multi-ocean hypotheses, that were advanced in the literature and that we regard as incompatible with the field evidence.The present-day configuration of tectonic units suggests that a former connection between ophiolitic units in West Carpathians and Dinarides was disrupted by substantial Miocene-age dislocations along the Mid-Hungarian Fault Zone, hiding a former lateral change in subduction polarity between West Carpathians and Dinarides. The SW-facing Dinaridic Orogen, mainly structured in Cretaceous and Palaeogene times, was juxtaposed with the Tisza and Dacia Mega-Units along a NW-dipping suture (Sava Zone) in latest Cretaceous to Palaeogene times. The Dacia Mega-Unit (East and South Carpathian Orogen, including the Carpatho-Balkan Orogen and the Biharia nappe system of the Apuseni Mountains), was essentially consolidated by E-facing nappe stacking during an Early Cretaceous orogeny, while the adjacent Tisza Mega-Unit formed by NW-directed thrusting (in present-day coordinates) in Late Cretaceous times. The polyphase and multi-directional Cretaceous to Neogene deformation history of the Dinarides was preceded by the obduction of Vardar ophiolites onto to the Adriatic margin (Western Vardar Ophiolitic Unit) and parts of the European margin (Eastern Vardar Ophiolitic Unit) during Late Jurassic to Early Cretaceous times.
55060597
Present-day stress field and tectonic inversion in the Pannonian basin.
Abstract This paper presents a latest compilation of data on the present-day stress pattern in the Pannonian basin, and its tectonic environment, the Alpine–Dinaric orogens. Extensional formation of the basin system commenced in the early Miocene, whereas its structural reactivation, in the form of gradual basin inversion, has been taking place since Pliocene to recent times. Reconstructed compression and associated horizontal contraction are mainly governed by the convergence between Adria and its buffer, the Alpine belt of orogens. The resulting contemporaneous stress field exhibits important lateral variation resulting in a complex pattern of ongoing tectonic activity. In the Friuli zone of the Southern Alps, where thrust faulting prevails, compression is orthogonal to the strike of the mountain belt. More to the southeast, intense contraction is combined with active strike–slip faulting constituting the dextral Dinaric transpressional corridor. Stresses are transferred far from Adria into the Pannonian basin, and the dominant style of deformation gradually changes from pure contraction through transpression to strike–slip faulting. The importance of late-stage inversion in the Pannonian basin is interpreted in a more general context of structural reactivation of back-arc basins where the sources of compression driving basin inversion are also identified and discussed. The state of recent stress and deformation in the Pannonian basin, particularly in its western and southern part, is governed by the complex interaction of plate boundary and intra-plate forces. The counterclockwise rotation and north-northeast-directed indentation of the Adriatic microplate appears to be of key importance as the dominant source of compression (“Adria-push”). Intra-plate stress sources, such as buoyancy forces associated with an elevated topography, and crustal as well as lithospheric inhomogeneities can also play essential, yet rather local role.
131182406
Plume head–lithosphere interactions near intra-continental plate boundaries
Plume–lithosphere interactions (PLI) have important consequences both for tectonic and mineralogical evolution of the lithosphere: for example, Archean metallogenic crises at the boundaries of the West African and Australian cratons coincide with postulated plume events.Incontinents,PLIareoftenlocatednearboundariesbetweenyoungerplates(e.g.,orogenic)andolderstableplates(e.g.,cratons), which represent important geometrical, thermal and rheological barriers that interact with the emplacement of the plume head (e.g., Archean West Africa, East Africa, Pannonian–Carpathian system). The observable PLI signatures are conditioned by plume dynamics but alsobylithosphere rheology and structure. We address the latterproblem by considering a free-surface numerical model ofPLI with two stratified elasto-viscous–plastic (EVP) lithospheric plates, one of which is older and thicker than another. The results show that: (1) plume head flattening is asymmetric, it is blocked from one side by the cold vertical boundary of the older plate, which leads to the mechanical decoupling of the crust from the mantle lithosphere, and to localized faulting at the cratonic margin; (2) the returnflow from the plume head results in sub-vertical down-thrusting (delamination) of the lithosphere at the margin, producing sharp vertical cold boundary down to the 400 km depth; (3) plume head flattening and migration towards the younger plate results in concurrent surface extension above the centre of the plume and in compression (pushing), down-thrusting and magmatic events at the cratonic margin (down-thrusting is also produced at the opposite border of the younger plate); these processes may result in continental growth at the “craton side”; (4) topographic signatures of PLI show basin-scale uplifts and subsidences preferentially located at cratonic margins. Negative Rayleigh–Taylor instabilities in the lithosphere above the plume head provide a mechanism for crustal delamination. Inferred consequences of PLI near intra-continental plate boundaries, such as faulting at cratonic edges and enhanced magmatic activity, could explain plume-related metallogenic crises, as suggested for West Africa and Australia. © 2007 Elsevier B.V. All rights reserved.