Cenozoic uplift of Variscan Massifs in the Alpine foreland: Timing and controlling mechanisms

The European Cenozoic Rift System (ECRIS) and associated fault systems transect all Variscan Massifs in the foreland of the Alps. ECRIS was activated during the Eocene in the foreland of the Pyrenees and Alps in response to the build-up of collision-related intraplate stresses. During Oligocene and Neogene times ECRIS evolved by passive rifting under changing stress fields, reflecting end Oligocene consolidation of the Pyrenees and increasing coupling of the Alpine Orogen with its foreland. ECRIS is presently still active, as evidenced by its seismicity and geodetic data.Uplift of the Massif Central and the Rhenish Massif, commencing at the Oligocene–Miocene transition, is mainly attributed to plume-related thermal thinning of the mantle–lithosphere. Mid-Burdigalian uplift of the SW–NE-striking Vosges–Black Forest Arch, that has the geometry of a doubly plunging anticline breached by the Upper Rhine Graben, involved folding of the lithosphere. Late Burdigalian broad uplift of the northern parts of the Bohemian Massif reflects lithospheric buckling whereas late Miocene–Pliocene uplift of its marginal blocks involved transpressional reactivation of pre-existing crustal discontinuities. Crustal extension across ECRIS, amounting to no more than 7 km, was compensated by a finite clockwise rotation of the Paris Basin block, up warping of the Weald–Artois axis and reactivation of the Armorican shear zones. Intermittent, though progressive uplift of the Armorican Massif, commencing in the Miocene, is attributed to transpressional deformation of the lithosphere.Under the present-day NW-directed compressional stress field, that came into evidence during the early Miocene and further intensified during the Pliocene, the Armorican Massif, the Massif Central, the western parts of the Rhenish Massif and the northern parts of the Bohemian Massif continue to rise at rates of up to 1.75 mm/y whilst the Vosges–Black Forest arch is relatively stable.Uplift of the Variscan Massifs and development of ECRIS exerted strong controls on the Neogene evolution of drainage systems in the Alpine foreland.     

Geo-mechanical and rheological modelling of upper crustal faults and their near-surface expression in the Netherlands

The pattern of fault reactivation, basin deformation and concentration of seismicity along the main trans-Netherlands fault zone, located NW–SE across the centre of the Netherlands, indicates that this zone is a major zone of weakness. Gravity modelling reveals after back-stripping of the sedimentary succession a distinctive continuous positive anomaly that can be explained by lithospheric sources. This zone of weakness is therefore likely to have a major influence on the tectonic processes currently active in the Netherlands region. We give a review of the tectonic history of the Netherlands and then present the results of a quantitative study of the reactivation of basin boundary faults and the influence on the surrounding basin. Well-data, balanced and back-stripped cross-sections are used to constrain the lithosphere rheology. The lithosphere rheology modelling results show a weak coupling between upper crustal deformation and the subcrustal lithosphere. A finite element modelling approach focussing on the upper crust is carried out in which the basin boundary faults are assigned various dips. The modelling results indicate that, for continuous reactivation of basin boundary faults, the presence of both a pre-existing weakness and a reduced friction angle is required. The latter implies that large displacements accommodated by primary faults cannot be directly attributed to the relative weakness of these faults compared to the secondary faults, which is in close accordance with inferences from trenching. A reduced friction angle has a significant effect on lithospheric strength and appears to be the major controlling factor in the reactivation of basin boundary faults.     

Cenozoic sediment distribution and tectonic movements in the Faroe region

A complex history of Cenozoic vertical movements in the Faroe region has been revealed from interpretation of geophysical and geological data, mainly offshore reflection seismic data, side-scan images, shallow cores, and onshore mapping. The history comprises several phases of tectonic disturbances observed at different scales. On the eastern margin of the Faroe Platform a late Eocene–early Oligocene phase of doming of the Faroe Platform has caused a postdepositional tilting of Eocene strata along the southern margin of the platform; a mid-Miocene phase of compressional tectonics is evidenced on seismic transects as gentle anticlines and associated reverse faults; and possible Pliocene uplift of the Faroe Islands is indicated by a progradational wedge of sediments deposited on the eastern Faroe Platform. At the continental margin/slope north of the Faroe Platform, reflection seismic data imaging the postbasalt sedimentary strata indicate three distinct tectonic events phases in the Eocene–Oligocene, Miocene and Pliocene, respectively. In contrast to the Faroe Platform the Faroe–Shetland Channel was characterised by more or less continuous subsidence dominated throughout the Cenozoic. During the Eocene, sediments deposited in the Faroe–Shetland Channel was mostly derived from a source area on the British shelf.     

Late orogenic rebound and oblique Alpine convergence: New constraints from subsidence analysis of the Austrian Molasse basin

Subsidence analysis of 16 wells in the Austrian Molasse basin documents major spatial and temporal changes in tectonic subsidence as well as a late-stage surface uplift. The timing of the main phase of tectonic subsidence shifted from early Oligocene in the western part of the peripheral foreland to the early Miocene in the eastern part. These temporal and spatial changes in tectonic subsidence reflect a change from oblique dextral to sinistral convergence between the Alpine nappe stack and its foreland. The main phase of sediment accumulation was delayed to the early Miocene and led to the infill of the basin and a major second, sediment-load driven phase of basement subsidence. Sediment accumulation rates in the basin reflect the build-up of topography in the Alpine mountain chain. Since approximately 6 Ma a pronounced regional uplift of the entire Molasse basin has taken place, marking the transition from lateral extrusion to orthogonal contraction within the Alpine system and deep-seated changes in geodynamic boundary conditions, possibly due to delamination of previously thickened lithosphere. Surface uplift is contemporaneous with similar processes in extra-Alpine Central Europe, where it is interpreted to reflect intra-plate stress changes.     

Contemporary kinematics of the Upper Rhine Graben: A 3D finite element approach

The Upper Rhine Graben (URG), a Cenozoic intra-plate rift situated in the Alpine foreland, is presently characterised by relative slow tectonic deformation and low to medium seismicity. Concurrently, it is a region with a significant amount of ongoing subsidence in two recent depocentres (0.1 to 0.2 mm/a geological, 1 mm/a geodetical rate). In this paper, the recent kinematic behaviour of the URG is simulated using a 3D finite element model, containing three lithospheric layers (upper mantle, lower crust and upper crust) with different rheological properties. First order fault structures (e.g. border faults) are implemented as frictional contact surfaces within the upper crustal layer. The stresses generated by applying lateral displacements over a time period of 10 ka are insufficient to obtain a match between predicted and observed stress magnitudes. Therefore, a technique of “combined pre-stressing” has been developed to avoid unrealistic deformation and unrealistic stress magnitudes within the model. The stress magnitudes and stress directions predicted are calibrated against in-situ stress measurements and stress indicator data. For benchmarking of the modelling results, the vertical surface displacements predicted are compared to surface uplift derived from geological and geomorphological data. Furthermore, predicted fault slip rates are compared to available geological and geodetical data. Parameters derived from the calculated stress tensor, such as fracture potential and the regime stress ratio are also analysed in order to describe the possible kinematic behaviour of the URG. The modelling results suggest that the URG is currently being reactivated as a sinistral strike–slip system with the central segment of the URG forming a restraining bend and the two recent depocentres situated in releasing bend settings. The modelling results suggest that both sinistral shearing and mantle uplift are active mechanisms driving the recent kinematics of the URG and that the recent subsidence within the two depocentres is re-enforced by ongoing mantle uplift additionally.     

Late Tertiary tectonic evolution of northern Iran: A case for simple crustal folding

Here we present a crustal folding or buckling mechanism to explain the rootless 3–5 km high Alborz Mountains in northern Iran as well as  10 km of Late Miocene to recent subsidence in the south Caspian basin and  3–6 km of subsidence in the central Iranian basin in the context of the middle Miocene to recent Arabia–Eurasia collision. A key element of the mechanism is the presence of lateral and vertical lithospheric strength contrasts between the north Iranian continental and south Caspian oceanic crusts: when compression from the collision is applied across the region, the strong south Caspian oceanic crust, buried under > 10 km of premiddle Miocene sediment, interacts with the bottom of the mechanically strong continental upper crust of northern Iran, resulting in upward buckling of the continental crust and downward buckling of the oceanic crust. We test this mechanism using a finite-element numerical model with a Maxwell rheology and obtain results that are consistent with the geological and geophysical observations. The observations compiled here and the model results demonstrate the potential for using this region as a natural laboratory for studying the early stages of continent–oceanic collision, including processes like basin inversion, fault localization and, potentially, subduction initiation.     

Tectonics of Venus: A review

The article presents a new tectonic scheme of Venus and gives the following interpretation of the planet's main structural units: (1) plains — areas of flood volcanism over stretched crust; (2) dome-like uplifts — areas of uplifting and volcanic activity above the mantle hot-spots; (3) coronae —former dome-like uplifts, partially subsided and diffused by gravity; (4) ridge belts — fold zones; (5) tesserae — fragments of ductile compression and shortening of crust; (6) supercoronae — coronae formed in the course of further evolution and relaxation of Beta-type uplifts. Ishtar Terra is considered to be a fragment of an ancient tessera paleocontinent, on the edge of which the Lakshmi supercorona is superimposed. Aphrodite Terra is considered as a belt of mantle hot-spot structures (dome-like uplifts, coronae, supercoronae, volcanoes, rifts).Three types of planetary belts have been distinguished on Venus: uplifted 'weakened' belts with an abundance of mantle hot-spot structures; a northern fan of ridge belts; and belts of low basalt plains. The center of the planetary system of uplifted weakened belts is situated in Atla Regio.The present tectonic structure of Venus is inferred to have formed during two stages of evolution characterized by different tectonic regimes. Stage I is a regime of soft ductile plates (formation of tessera uplifts and volcanic plains). Stage II is a formation of 'weakened' uplifted planetary belts, various tectonic regimes of mantle hot-spots, and plains-forming volcanism.'Geology and Tectonics of Venus', special issue edited by Alexander T. Basilevsky (USSR Acad. of Sci. Moscow), James W. Head (Brown University, Providence), Gordon H. Pettengill (MIT, Cambridge, Massachusetts) and R. S. Saunders (J.P.L., Pasadena).     

Crustal tectonic zone on Venus

Various tectonic structures to the south and southeast of Ishtar Terra indicate areal stresses. Compression from east-southeast against Ishtar Terra has resulted in ridge belt formation and surface bending at Salme Dorsa, probably along the seam between two crustal units. En echelon fault zone indicates dextral strike-slip shear(s) resulted in the westward movement of planitia crust related to Ishtar Terra. Meshkenet Tessera displays differential dextral strike-slip faulting where the southernmost bar-like blocks have had largest relative movements. Compression against Tusholi Corona has resulted in foreland surface bending similar to that of Salme Dorsa. The tectonic zone as a whole resembles a dextral transform fault extending from a concave arc in the west to another concave arc in the east. The Cytherean surface, crust or uppermost lithosphere seems to be able to transmit stresses over distances. Deeper understanding of these processes is needed to gain a new idea of the crustal deformation on terrestrial planets.     

Late Cenozoic fluvial development within the Sea of Azov and Black Sea coastal plains

Late Cenozoic terrestrial deposits are widespread across the northern coastal regions of the Black Sea and the Sea of Azov and represent diverse fluvial, estuarine and deltaic environments. The dating and correlation of these deposits rely on stratigraphically-associated marine index beds, mammalian and molluscan faunas and magnetostratigraphy. In detail the geometries of these sediment bodies are extremely complex, typically varying between localities and representing many cycles of incision and aggradation. However, the overall disposition of the sediments reflects the transition from the uplifting sediment source region to the north and the subsiding depocentre in the interior of the Black Sea to the south. Since the Middle Miocene the area of the Paratethys/Black Sea depocentre has decreased significantly, but since the Middle Pliocene the hinge zone between uplift and subsidence has been located close to the modern coastline. A combination of regional and local differential crustal movements has given rise to the great variety of fluvial sediment bodies, to the erosion–aggradation cycles, different phases and river activity and to the various fluvial landforms that have all been important in landscape development in this region during the past 12 Ma. The fluvial erosion–accumulation cycles (during the upper Serravillian–Messinian, the Zanclean–late Gelasian, and the Pleistocene) and corresponding cycles of relief dissection and planation are reconstructed against a background of local sea-level changes and climatic variations determined from palaeobotanical data. The maximum fluvial incision occurred in the early Zanclean time with alluvial coastal plains, unique in this area, developing in the Gelasian. Increased climatic aridity during the Pleistocene caused a reduction of fluvial activity in comparison with the Late Miocene and Pliocene. The sea-level oscillations and Pleistocene glaciations affected fluvial processes in different ways. The most remarkable events were the substantial reduction of fluvial activity during the Messinian dessication in the Black Sea and drainage of the shelf, with intensive dissection, coeval with the Last Glaciation.     

Surface processes and tectonics: Forcing of continental subduction and deep processes

It is now well accepted that surface processes provide a critical feedback on the surface tectonic deformation, whatever it is, orogenic building or basin evolution. However, the idea that the influence of these processes may go below the crustal levels, is less common. In this preliminary study, we use coupled thermo-mechanical numerical models to investigate the possible influence of surface processes on the styles of continental collision, in particular, continental subduction. For that, we further exploit the recent successful model of continental subduction of the early stages of India–Asia collision by Toussaint et al. [Toussaint G., Burov, E., and J.-P. Avouac, Tectonic evolution of a continental collision zone: a thermo-mechanical numerical model, Tectonics, 23, TC6003, doi:10.1029/2003TC001604, 2004b.]. On the example of India–Asia-like settings, we show that not only the surface topography but also the total amount of subduction may largely vary as function of denudation rate (controlled by the coefficient of erosion, k). Erosion provides a dynamic discharge of the hanging wall of the major thrust zone, whereas the sedimentation increases loading on the footwall and this helps down-thrusting of the lower plate. Both processes reduce the resistance of the major thrust and subduction channel to subduction. However, very strong or very slow erosion/sedimentation enhance the possibility of plate coupling and promote whole-scale thickening or buckling. The maximal amount of subduction is thus achieved for some intermediate values of erosion rates when the tectonic uplift rate is fine-balanced by the denudation rate. In our case the optimal balance is reached for the values of k on the order of 3000 m²/yr. We then extended our model beyond the conditions of India–Asia collision, in terms of the tested range of k and convergence rates. The experiments suggest that for provided settings, both extra slow (k < 50–100 m²/yr) and extra rapid erosion (k > 6000–8000 m²/yr) limit, by up to 50%, the total amount of subduction, if not totally prevent it. The model demonstrates the large capability of surface processes to adopt to different deformation styles: the orogenic building and subduction successfully develop (subduction number, S > 0.5) in the range of k between 500 m²/yr and 6000 m²/yr at convergence rates ranging from 1 cm/yr to 6 cm/yr. Within this range, some peculiar features of orogenic style such as the geometry of the accretion prism, amount of upper crustal subduction, horizontal progression of the mountain range/thrust fault and the amount of exhumation of metamorphic facies are sometimes quite different. We conclude that surface processes may control deep, mantle level tectonic evolution.     

Active crustal deformation beyond the SE margin of the Tibetan Plateau: Constraints from the evolution of fluvial systems

An integrated explanation is proposed for the Late Cenozoic crustal deformation in Yunnan, SW China, using sedimentary and geomorphological evidence from the Yangtze and Red River systems. The observed fluvial incision indicates up to ~ 15 km of crustal thickening, associated with ~ 3 km of uplift, apparently triggered at ~ 8 Ma by monsoon-induced erosion drawing mobile lower crust from beneath Tibet to the northwest. The mobile lower-crustal layer beneath Yunnan was initially very thin, but a positive feedback loop developed, whereby each incremental influx of lower-crust widened and heated this layer, facilitating the next increment. At ~ 5 Ma, the shear tractions exerted on the brittle upper-crust by this flowing lower crust became sufficient to reactivate pre-existing lines of weakness, dragging blocks of the brittle layer southward and creating the region′s modern active fault systems. This region thus provides a dramatic example of crustal deformation induced by Late Cenozoic climate change, notwithstanding its location adjoining the India–Eurasia plate boundary.     

Tectonic geomorphology of the northern Upper Rhine Graben, Germany

This paper focuses on the northern Upper Rhine Graben (URG), which experienced low tectonic deformation and multiple climate changes during Quaternary times. Recently, human modifications have been high. The paper presents the results of a study into the effects of fault activity on the landscape evolution of the area. The study aims to detect active faults and to determine the last phase of tectonic activity. Information on the long-term tectonic activity is gained from the geological record (drainage system, sediment distributions, fluvial terraces, fault mapping). Previous studies are reviewed and supplemented with new data on tectonic activity. The compilation of all data is presented as a series of paleogeographic maps from Late Miocene to present. It is demonstrated that differential uplift of the western margin of the northern URG had significant impact on the drainage system, the formation of fluvial terraces and the landscape of the western graben shoulder. In a second part of the paper, the imprint of tectonics on the present-day landscape is investigated at the regional scale in order to determine the location of fault scarps and tectonically influenced parts of the drainage system. This study uses an integrated analysis of topography, drainage patterns and fault network. The comparison of features suggests a structural control by numerous NNE- and NNW-oriented intra-graben faults on the flow directions of streams in the Rhine Valley. Several scarps in the Rhine Valley are identified and interpreted to result from intra-graben faulting activity, which in turn controlled fluvial dissection. The third part of the paper presents quantitative measurements of the present-day landscape shape. Calculations of geomorphic indices are used to determine the balance between erosional and tectonic processes and to identify active fault segments. The mountain-front sinuosity and valley shape indices measured along the border faults and in the footwall area are used to determine the level of activity of the faults. Stream profiles of the western and eastern catchments of the River Rhine are investigated for gradient changes at the crossing of the border faults. The combined interpretation of geomorphic indices points to active border fault segments on both sides of the graben. Based on the integration of all results it is concluded that the tectonic morphology identified for the northern URG formed in response to long-term, low level tectonic processes. Due to a significant decrease in erosional and depositional activity during the last 15,000 years, the tectonic morphology has probably been preserved until present.     

Tectonic and kinematic study of a strike-slip zone along the southern margin of Central Ovda Regio, Venus: Geodynamical implications for crustal plateaux formation and evolution

The tectonic system of the southern margin of Central Ovda Regio, a crustal plateau which straddles Venus equator, has been interpreted as a dextral strike-slip array, on the basis of evidence clearly identifiable, as are Riedel fracture patterns of different scales, en échelon folds and brittle strike-slip faults. This transcurrent regime developed two main shear belts (Inner and Outer, on respectively thicker and thinner crust), whose minimum dextral displacement has been estimated in 30-50 km. Since the up or downwelling models for plateau formation cannot easily explain tectonic shears of this magnitude along their margins, an alternative hypothesis has been built, which stands on the proposed collisional belt which could form Ovda northern border (King et al., 1998, Lunar Planet. Sci. Conf. 29, Abstract 1209; Tuckwell and Ghail, 2002, Lunar Planet. Sci. Conf. 33, Abstract 1566). Within this framework, the shear would represent a transcollisional transcurrent zone, similar to the strike-slip zones produced in the foreland of the Himalayas-Tibet collision front. Eastern Ovda would be an independent area of thickened crust, pushed to the SSE by the northern collision, with the deformation concentrated at its margins, and experiencing a shear strain on its southern margin. None of the data, however, either supports nor helps to discard theoretical subduction events as a cause of the collision. On the contrary, image relationships could be interpreted as evidence that the main shear deformation took place during the last global resurfacing event on the planet.     

Ridge belt tectonics of Ganiki Planitia on Venus

The main major ridge belts of Ganiki Planitia on Venus (Lama, Ahsonnutli and Pandrosos Dorsa) are part of the fan-shaped ridge belt complex along the 200 parallel of longitude. These ridge belts with evidence of crustal shortening support the idea of a large-scale E-W compression. The ridge belt patterns indicate a N-S shear component. These forces are explained by a triangular planitia area which compressed by surrounding terrains. The crustal shortening and ridge belt formation indicates compressional plate movement stresses in the uppermost lithosphere.Three sizes of ridge belt structure are to be found within Ganiki Planitia. (1) The ridge belt spacing of 200–400 km can be used to estimate the depth of the major uppermost homogeneous layer of Venus. There are numerous volcanic coronae, paterae and montes located along the main ridge belts or at their junctions. (2) Mid-size ridge groups or subbelts are to be found within the major ridge belts. These are formed by more local responses to tectonic stresses in the stratified uppermost crust. A wavelength of 40–70 km can be seen as a result of bending of the crustal strata and may relate to its thickness. (3) Small individual ridges are connected with most local stresses, defining places where the surface layers broke along the crests of large ridge belts or mid-scale subbelts. Radial and concentric mare ridge-like structures around coronae indicate that corona formation was effective at a sufficiently close vicinity to fault the surface.     

Pleistocene northwards fold propagation of the Jura within the southern Upper Rhine Graben: seismotectonic implications

On the basis of the geophysical (seismic profiles and electric tomography), geomorphic and geological data, we re-evaluate the post-Pliocene structural interpretation of the southern Upper Rhine graben (Basel–Mulhouse area): we demonstrate a Plio–Pleistocene northward propagation of the Jura thrust and fold belt up to Mulhouse proceeding from a succession of four 10 km apart ramps (from north to south Ferrette, Muespach, Magstatt and Rixheim) rooted within the late Triassic evaporitic marls acting as a decollement. This domain was previously considered as having undergone an on-going continuous extension (horst of Mulhouse bounded by the Quaternary Sirentz and Dannemarie grabens).The Quaternary activity of this thin-skinned tectonics induces the growth of a sedimentary wedge whose regional slope, which comprised between 1.4° and 1° to the north, also attests to a low friction basal detachment. More into details, these ramps correspond to 40–50-m high jumps within the forward topographic slope. Pleistocene activity is suggested just above the Muespach ramp by the presence of a 5–10-m north-facing scarp corresponding in depth to a 3-m vertical offset of early Pleistocene alluvial deposits. Farther to the north, a stronger incision of the Rhine Würm terrace can be interpreted as the result of the growth of the Mulhouse–Rixheim frontal ramp.This northward propagation of the Jura thrust and fold belt is strongly controlled by the Oligocene structural inheritage. The development of the frontal ramp in Mulhouse has to be related to the Oligocene significant vertical offset of the Triassic evaporite along the Mulhouse Railway Station fault preventing a propagation of the decollement farther to the north. In the same way, the fold propagation is laterally segmented by the N20°E trending Oligocene fabrics (from East to West, Rhine Valley flexure fault, Allschwil–Istein fault system and Illfurth fault) which acts above the decollement as lateral ramps. To the west, the development of a shallow anticline along the Illfurth fault suggests that the thin-skinned propagation is oblique with respect to the Oligocene fabrics. It results in spacial contrast between a left-lateral-reverse and a right-lateral–normal shallow kinematics along the western and eastern lateral ramps, respectively. In depth to the east, it also induces a vertical contrast between shallow (right-lateral–normal) and deep (left-lateral given by fault plane solutions) kinematics along the Istein–Allschwill–Rhine Valley fault system.Few arguments supporting a nucleation of the Basel-1356 earthquake, the strongest event in NW Europe in the last thousand years, onto the Rhine Valley fault system beneath the decollement have been given. However, we emphasize that the above mentioned coeval thin (aseismic)- and thick (seismic)-skinned tectonics along the Istein–Allschwill–Rhine Valley fault system would make difficult both the identification and the interpretation of the surface rupture of the Basel-1356 earthquake.     

The Late Miocene climate response to a modern Sahara desert

The climate cooling and vegetation changes in the Miocene/Pliocene are generally well documented by various proxy data. Some important ecosystem changes occurred at that time. Palaeobotanical evidence suggests that the Sahara desert first appeared in the Pliocene, whereas in the Miocene North Africa was green. In the present study, we investigate the Late Miocene climate response to the appearance of the Sahara desert from a climate modelling sensitivity experiment. We compare a model experiment, which includes a full set of Late Miocene boundary conditions, with another one using the same boundary conditions except that the North African vegetation refers to the present-day situation. Our sensitivity study demonstrates that the introduction of the Sahara desert leads to a cooling and an aridification in Africa. In addition, we observe teleconnection patterns related to the North African desertification at around the Miocene/Pliocene boundary. From our sensitivity experiment, we observe that the Sahara contributes to a cooling in Central Asia and in North America. As compared to hypsodonty data for Central Asia, an increased aridity is underestimated in the Sahara experiment. Finally, we observe that the introduction of the Sahara leads to a cooling in the northern high latitudes. Hence, our sensitivity experiment indicates that the appearance of the Sahara desert is one piece to better understand Late Cenozoic climate cooling being most pronounced in the high latitudes.     

Dynamic topography of the East European craton: Shedding light upon lithospheric structure, composition and mantle dynamics

Most of the East European Craton lacks surface relief; however, the amplitude of topography at the top of the basement exceeds 20 km, the amplitude of topography undulations at the crustal base reaches almost 30 km with an amazing amplitude of ca. 50 km in variation in the thickness of the crystalline crust, and the amplitude of topography variations at the lithosphere–asthenosphere boundary exceeds 200 km. This paper examines the relative contributions of the crust, the subcrustal lithosphere, and the dynamic support of the sublithospheric mantle to maintain surface topography, using regional seismic data on the structure of the crystalline crust and the sedimentary cover, and thermal and large-scale P- and S-wave seismic tomography data on the structure of the lithospheric mantle. For the Precambrian lithosphere, an analysis of Vp/Vs ratio at 100, 150, 200, and 250 km depths does not show any age-dependence, suggesting that while Vp/Vs ratio can be effectively used to outline the cratonic margins, it is not sensitive to compositional variations within the cratonic lithosphere.Statistical analysis of age-dependence of velocity, density, and thermal structure of the continental crust and subcrustal lithosphere in the study area (0–62E, 45–72N) allows to link lithospheric structure with the tectonic evolution of the region since the Archean. Crustal thickness decreases systematically with age from 42–44 km in regions older than 1.6 Ga to 37–40 km in the Paleozoic–Mesoproterozoic structures, and to ca. 31 km in the Meso-Cenozoic regions. However, the isostatic contribution of the crust to the surface topography of the East European Craton is almost independent of age (ca. 4.5 km) due to an interplay of age-dependent crustal and sedimentary thicknesses and lithospheric temperatures.On the contrary, the contribution of the subcrustal lithosphere to the surface topography strongly depends on the age, being slightly positive (+ 0.3 + 0.7 km) for the regions older than 1.6 Ga and negative (− 0.5–1 km) for younger structures. This leads to age-dependent variations in the residual topography, i.e. the topography which cannot be explained by the assumed thermal and density structure of the lithosphere, and which can (at least partly) originate from the dynamic component caused by the mantle flow. Positive dynamic topography at the cratonic margins, which exceeds 2 km in the Norwegian Caledonides and in the Urals, clearly links their on-going uplift with deep mantle processes. Negative residual topography beneath the Archean-Paleoproterozoic cratons (− 1–2 km) indicates either a smaller density deficit (ca. 0.9%) in their subcrustal lithosphere than predicted by global petrologic data on mantle-derived xenoliths or the presence of a strong convective downwelling in the mantle. Such mantle downflows can effectively divert heat from the lithospheric base, leading to a long-term survival of the Archean-Paleoproterozoic lithosphere.     

Late Miocene paleoenvironment of the Lambert Graben embayment, East Antarctica, evident from: Mollusc paleontology, sedimentology and geochemistry

The Upper Miocene (10.7–9.0 Ma) Battye Glacier Formation was deposited 250 km inland from the modern Amery Ice Shelf edge in Prydz Bay, East Antarctica. The composition of clay minerals distinguishes a Lower Member, which reflects regional erosion of Precambrian metamorphic basement, from an Upper Member, which records increased erosion of local Permian–Triassic Amery Group strata. The Upper Member was deposited in an ice-proximal environment akin to the modern fjords of East Greenland, with substantial diamict deposition resulting from melting iceberg discharge. The Lower Member was deposited in an ice-distal environment and included the accumulation of the fossil-bearing McLeod Beds. The McLeod Beds contain much siliceous biogenic sediment (≤ 15% opal), which is rare to absent in the predominantly hemipelagic mud of modern East Greenland fjords. The McLeod Beds also contain largely monospecific in situ Hiatella sp. mollusc assemblages suggestive of environmental stress, potentially caused by low salinity melt-water and a high input of terrigenous sediment, which excluded most other benthic taxa. Geochemical results from primary aragonite in Hiatella shells imply large freshwater input into the marine environment during mollusc growth, causing low δ¹⁸O, Na, Mg and high Fe values. The present study indicates that iceberg melt-water influence entering the marine environment was greater during the Late Miocene than today around Antarctica, and documents the paleoenvironment associated with a discrete period of ice margin retreat and marine incursion into the Lambert embayment.     

Present-day stress field and tectonic inversion in the Pannonian basin

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.     

Coronal interconnection of two active regions observed in 3.5–8.0 keV X-rays

Using HXIS data, we have studied the further development of the coronal arch extending towards the SE above active region No. 17255 in November 1980. The arch, studied originally by vestka (1984) disappeared on 10 November (after pronounced revival), but since 9 November HXIS revealed another arch-like structure towards the SW. We have studied the development of this new structure which appeared to be most likely an arch interconnecting AR 17255 with AR 17251, located nearly 30° to the west. This interconnection revived many times during the following days with intensity varying with the activity in both active regions. We have estimated the physical characteristics in this coronal structure and compared them with observations of interconnecting loops made at lower energies by Skylab in 1973. The temperature (maximum values 7.5–14 × 10⁶ K) and the density (1.1–5.0 × 10⁹ cm^–3) are found to be higher than in the Skylab loops (a result that could be expected because the HXIS energy range was harder than that of Skylab) and similar to the values deduced for the earlier arch system extending to the SE. However, much shorter decay times of the brightness variations indicate the presence of conduction in contrast to the SE arch in which conduction was clearly inhibited. This supports the assumption that the SE and SW coronal structures were two different phenomena.Presently at Delft Institute of Technology, Landbergstraat 3, 2628 CE Delft, The Netherlands.