Sierd Cloetingh

Dynamic processes controlling evolution of rifted basins

Abstract The extension of the lithosphere, controlling the development of rifted basins, is driven by a combination of plate-boundary forces, frictional forces exerted on the base of the lithosphere by the convecting asthenosphere and deviatoric tensional stresses developing over upwelling branches of the asthenospheric convection system. Although mantle plumes are not a primary driving force of rifting, they play an important secondary role by weakening the lithosphere and by controlling the level of rift-related volcanic activity. A distinction between “active” and “passive” rifting is only conditionally justified. The extension of the lithosphere, depending on its rate and magnitude, and the potential temperature of the asthenosphere, can cause by adiabatic decompression partial melting of the lower lithosphere and upper asthenosphere. In rift systems, the level and timing of volcanic activity is highly variable. The lack of volcanic activity implies “passive” rifting. An initial “passive” rifting stage can be followed by a more “active” one during which magmatism plays an increasingly important role. Magmatic destabilization of the Moho may account for the frequently observed discrepancy between upper and lower crustal extension factors. Combined with evidence for thermal thinning of the mantle–lithosphere, this suggest that the volume of the lithosphere is not necessarily preserved during rifting as advocated by conventional stretching models. The structural style of rifts is controlled by the rheological structure of the lithosphere, the availability of crustal discontinuities that can be tensionally reactivated, the mode (orthogonal or oblique) and amount of extension, and the lithological composition of pre- and syn-rift sediments. Simple-shear extension prevails in rifts that subparallel the structural grain of the basement. Pure-shear extension is typical for rifts cross-cutting the basement grain. Pre-existing crustal and mantle–lithospheric discontinuities contribute to the localization of rift systems. The duration of the rifting stage of extensional basins is highly variable. Stress field changes can cause abrupt termination of rifting. In major rift systems, progressive strain concentration on the zone of future crustal separation entails abandonment of lateral rifts. Depending on constraints on lateral block movements, crustal separation can be achieved after as little as 9 My and as much as 280 My of rifting activity. Syn-rift basin subsidence is controlled by isostatic adjustment of the crust to mechanical stretching of the lithosphere, its magmatic inflation and thermal attenuation of the mantle–lithosphere. Post-rift basin subsidence is governed by thermal reequilibration of the lithosphere–asthenosphere system. Deep-seated thermal anomalies related to syn-rift pull-up of the asthenosphere–lithosphere boundary have decayed after 60 My by about 65% and after 180 My by about 95%. The magnitude of post-rift subsidence is a function of the rift-induced thermal anomaly and crustal density changes, the potential temperature of the asthenosphere and initial water depths. Intraplate stresses can have an overprinting effect on post-rift subsidence. Stretching factors derived from post-rift subsidence analyses must be corrected for such effects.

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.

Late Precambrian to Triassic history of the East European Craton: dynamics of sedimentary basin evolution

Abstract During its Riphean to Palaeozoic evolution, the East European Craton was affected by rift phases during Early, Middle and Late Riphean, early Vendian, early Palaeozoic, Early Devonian and Middle-Late Devonian times and again at the transition from the Carboniferous to the Permian and the Permian to the Triassic. These main rifting cycles were separated by phases of intraplate compressional tectonics at the transition from the Early to the Middle Riphean, the Middle to the Late Riphean, the Late Riphean to the Vendian, during the mid-Early Cambrian, at the transition from the Cambrian to the Ordovician, the Silurian to the Early Devonian, the Early to the Middle Devonian, the Carboniferous to Permian and the Triassic to the Jurassic. Main rift cycles are dynamically related to the separation of continental terranes from the margins of the East European Craton and the opening of Atlantic-type palaeo-oceans and/or back-arc basins. Phases of intraplate compression, causing inversion of extensional basins, coincide with the development of collisional belts along the margins of the East European Craton. The origin and evolution of sedimentary basins on the East European Craton was governed by repeatedly changing regional stress fields. Periods of stress field changes coincide with changes in the drift direction, velocity and rotation of the East European plate and its interaction with adjacent plates. Intraplate magmatism was controlled by changes in stress fields and by mantle hot-spot activity. Geodynamically speaking, different types of magmatism occurred simultaneously.

Stress in the Indo-Australian plate

Cloetingh, S. and Wortel, R., 1986. Stress in the Ind~Austr~ian plate. In: B. Johnson and A.W. Bally (Editors), Intraplate Deformation: Characteristics, Processes and Causes. Tectonophysics, 132: 49-67 We modelled the state of stress in the Indo-Australian plate in order to investigate quantitatively variations observed in tectonic style. The numerical procedure incorporates the dependence of slab pull and ridge push on the age of the oceanic lithosphere. Estimates are presented for the average net resistive forces at the Himalayan collision zone, the suction force acting on the overriding Indo-Australian plate segment at the Tonga-Kermadec trench and the drag at the base of the lithosphere. Our modelhng shows a concen~ation of compressive stresses of the order of 3-5 lcbar in the Ninetyeast Ridge area; the effects of the compressive resistance associated with Himalayan collision and subduction of young lithosphere off the northern part of the Sunda arc are focused in this region. The stress field as calculated gives a consistent explanation for the observed concentration of seismic activity (Stein and Okal, 1978) and significant deformation in the oceanic crust (Weissel et al., 1980; McAdoo and Sandwell, 1985) in the area. The calculated stress field in the area adjacent to the Southeast and Central India ridges is characterized by tension parallel to the spreading axis. This explains the concentration of near-ridge normal faulting seismicity (with T-axes subparaIle1 to the spreading ridge) in the Indian Ocean as recently observed by Bergman et al. (1984) and Wiens and Stein (1984). The regional stress field along the strike of the Sunda arc varies from compression seaward of and parallel to the Sumatra trench segment, to tension perpendicular to the Java-Flores segment. This explains the selective occurrence of well developed grabens seaward off the Java-Flores segment of the trench, observed by Hilde (1983). Our modelling shows that the observed rotation of the stress field (Denham et al., 1979) in the Australian continent is mainly the consequence of its geographic position relative to the surrounding trench segments and the variations of the forces acting on the down-going slab in each of these. The state of compression in west and central Australia is induced by the action of resistive forces at the Himalayan and Banda arc collision zones. The joint occurrence of high levels of compression in the plate’s interior and normal faulting seismicity in the near-ridge areas, is a transient feature unique to the present dynamic situation of the Indo-Australian plate.

Stress-induced late stage subsidence anomalies in the Pannonian Basin

Abstract Subsidence, sedimentation and tectonic quiescence of the Pannonian basin was interrupted a few million years ago by tectonic reactivation. This recent activity has manifested itself in uplift of the western and eastern flanks, and continuing subsidence of the central part of the Pannonian basin. Low- to medium-magnitude earthquakes of the Carpathian-Pannonian region are generated mostly in the upper crust by reverse and wrench fault mechanisms. There is no evidence for earthquakes of extensional origin. 2-D model calculation of the subsidence history shows that a recent increase in magnitude of horizontal compressional intraplate stress can explain fairly well the observed Quaternary uplift and subsidence pattern. We propose that this stress increase is caused by the overall Europe/Africa convergence. In Late Pliocene, consumption of subductible lithosphere at the eastern margin of the Pannonian basin was completed, and the lithosphere underlying the Pannonian basin became locked in a stable continental frame. Consequently extensional basin formation has come to an end, and compressional inversion of the Pannonian basin is in progress.

On a tectonic mechanism for regional sealevel variations

Abstract No satisfactory tectonic explanations have yet been offered for the apparent sealevel fluctuations of about 1 cm/1000 years and a magnitude of up to a few hundred meters that have been proposed by Vail et al. [1]. We propose a mechanism that does appear to be able to explain these changes if horizontal stresses of the order of a few kilobars occur in the lithosphere and if changes in these stress fields occur on geological time scales. The proposed model is one of an interaction between these stresses and the deflections of the lithosphere caused by sedimentary loading. Apparent sealevel changes of up to 100 m can be produced at the flanks of the sedimentary basins by this interaction. The mechanism is most effective for young margins that are subject to rapid sediment loading. By its nature, the tectonic model can explain contemporaneous fluctuations in apparent sealevel in neighbouring depositional environments. In principle, it implies the possibility of regional correlations in different basinal settings.

Lithosphere folding: primary response to compression?

We examine the role of lithosphere folding in the large-scale evolution of the continental lithosphere. Analysis of the record of recent vertical motions and the geometry of basin deflection for a number of sites in Europe and worldwide suggests that lithospheric folding is a primary response of the lithosphere to recently induced compressional stress fields. Despite the widespread opinion, folding can persist during long periods of time independently of the presence of many inhomogeneities such as crustal faults and inherited weakness zones. The characteristic wavelengths of folding are determined by the presence of young lithosphere in large parts of Europe and central Asia and by the geometries of the sediment bodies acting as a load on the lithosphere in basins. The proximity of these sites to the areas of active tectonic compression suggests that the tectonically induced horizontal stresses are responsible for the large-scale warping of the lithosphere. Wavelengths and persistence of folding are controlled by many factors such as rheology, faulting, time after the end of the major tectonic compression, nonlinear effects, and initial geometry of the folded area. In particular, the persistence of periodical undulations in central Australia (700 Myr since onset of folding) or in the Paris basin (60 Myr) long after the end of the initial intensive tectonic compression requires a very strong rheology compatible with the effective elastic thickness values of about 100 km in the first case and 50-60 km in the second case.

Mechanical controls on collision related compressional intraplate deformation.

Intraplate compressional features, such as inverted extensional basins, upthrust basement blocks and whole lithospheric folds, play an important role in the structural framework of many cratons. Although compressional intraplate deformation can occur in a number of dynamic settings, stresses related to collisional plate coupling appear to be responsible for the development of the most important compressional intraplate structures. These can occur at distances of up to ±1600 km from a collision front, both in the fore-arc (foreland) and back-arc (hinterland) positions with respect to the subduction system controlling the evolution of the corresponding orogen. Back-arc compression associated with island arcs and Andean-type orogens occurs during periods of increased convergence rates between the subducting and overriding plates. For the build-up of intraplate compressional stresses in fore-arc and foreland domains, four collision-related scenarios are envisaged: (1) during the initiation of a subduction zone along a passive margin or within an oceanic basin; (2) during subduction impediment caused by the arrival of more buoyant crust, such as an oceanic plateau or a microcontinent at a subduction zone; (3) during the initial collision of an orogenic wedge with a passive margin, depending on the lithospheric and crustal configuration of the latter, the presence or absence of a thick passive margin sedimentary prism, and convergence rates and directions; (4) during post-collisional over-thickening and uplift of an orogenic wedge. The build-up of collision-related compressional intraplate stresses is indicative for mechanical coupling between an orogenic wedge and its fore- and/or hinterland. Crustal-scale intraplate deformation reflects mechanical coupling at crustal levels whereas lithosphere-scale deformation indicates mechanical coupling at the level of the mantle-lithosphere, probably in response to collisional lithospheric over-thickening of the orogen, slab detachment and the development of a mantle back-stop. The intensity of collisional coupling between an orogen and its fore- and hinterland is temporally and spatially variable. This can be a function of oblique collision. However, the build-up of high pore fluid pressures in subducted sediments may also account for mechanical decoupling of an orogen and its fore- and/or hinterland. Processes governing mechanical coupling/decoupling of orogens and fore- and hinterlands are still poorly understood and require further research. Localization of collision-related compressional intraplate deformations is controlled by spatial and temporal strength variations of the lithosphere in which the thermal regime, the crustal thickness, the pattern of pre-existing crustal and mantle discontinuities, as well as sedimentary loads and their thermal blanketing effect play an important role. The stratigraphic record of collision-related intraplate compressional deformation can contribute to dating of orogenic activity affecting the respective plate margin.

EuCRUST-07: A new reference model for the European crust

[1] We present a new digital model (EuCRUST-07) for the crust of Western and Central Europe and surroundings (35N–71N, 25W–35E). Available results of seismic reflection, refraction and receiver functions studies are assembled in an integrated model at a uniform grid (15 0 � 15 0 ). The model consists of three layers: sediments and two layers of the crystalline crust. Besides depth to the boundaries, we provide average P-wave velocities in the upper and lower parts of the crystalline crust. The new model demonstrates large differences in the Moho depth compared to previous compilations, over ±10 km in some specific areas (e.g. the Baltic Shield). Furthermore, the velocity structure of the crust is much more heterogeneous than in previous maps. EuCRUST-07 offers a starting point for numerical modeling of deeper structures by allowing correction for crustal effects beforehand and to resolve trade-off with mantle heterogeneities. Citation: Tesauro, M., M. K. Kaban, and S. A. P. L. Cloetingh (2008), EuCRUST-07: A new reference model for the European crust, Geophys. Res. Lett., 35, L05313, doi:10.1029/2007GL032244.

Eastern Pyrenees and related foreland basins: pre-, syn- and post-collisional crustal-scale cross-sections

Abstract A new crustal-scale cross-section through the Eastern Pyrenees shows a minimum of 125 km of total shortening across the belt. Convergence rates of 6 mm/yr (during early and middle Eocene time) between the northern domain of the Iberian plate and Europe can be evaluated from calculated shortening rates in both sides of the orogen. Two stages of orogenic growth can be determined in the Eastern Pyrenean transect. A first stage (from Early Cretaceous to middle Lutetian time) is characterized by a low topography, submarine emplacement of the thrust front, fast rates of south-directed shortening up to 5 mm/yr and widespread marine foreland deposition. This stage is also characterized by equivalent amounts of mountain erosion and detrital foreland accumulation. A second stage (middle Lutetian to late Oligocene) is marked by an increase in structural relief, subaerial emplacement, a decrease in shortening rates and widespread continental sedimentation. This leads towards a non-equilibrium condition in which mountain erosion is almost three times the foreland basin accumulation, leading to a large by-pass of sediments towards the Atlantic before the final endorrheic stage of the basin. Erosion rates based on area conservation between middle Lutetian and present day sections in a two-dimensional calculation indicate an average of 0.15 mm/yr. This rise is lower than middle Lutetian to early Miocene rock uplift rates in the Eastern Pyrenees, which account for 0.2–0.35 mm/yr, suggesting that erosion has been discontinuous through time. Inferred maximum river incision rates since the middle Miocene opening of the Ebro Basin towards the Mediterranean Sea account for less than 0.1 mm/yr.