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Large-scale diapiric salt movements affect the architecture of sedimentary basins and often prevent the understanding of their mechanics by hiding or distorting subsidence patterns. One good example is the evolution of the Transylvanian Basin, which formed during Miocene times in an area located in between the rapid slab rollback and continental collision recorded at the exterior of the Carpathians and the extension of the neighbouring Pannonian Basin. In the absence of major genetic fault systems, quantifying these external tectonic forcing factors requires an accurate reconstruction of subsidence evolution. Having the advent of a detailed 3D geometrical model of the Transylvanian Basin, we apply a 3D numerical modelling technique that couples salt re-distribution and subsidence evolution to quantify and understand the basin kinematics and vertical motions. Two techniques, backward and forward modelling are coupled in order to discriminate between salt migration driven by overburden and the influence of external tectonic forcing factors. The results show that salt kinematics was more complex than simple unidirectional migration, suggesting the existence of areas with significant subsidence hidden by the inward salt migration and areas with apparent large subsidence that are in reality artefacts of outwards salt migration. Additionally, the results suggest that parts of the basin have been successively affected by in- and out-ward salt migration events, an effect of localising subsidence and overburden. Furthermore, accelerated moments of salt migration took place during the main Miocene contraction events recorded at the exterior of the Carpathians, demonstrating that salt migration is enhanced by intraplate stresses. Our study also infers that the subsidence of the Transylvanian Basin is the result of the superposition of the contraction at the exterior of the orogenic chain and the back-arc extension

Ocean-continent subduction cannot be initiated without preceding intra-oceanic subduction!

The formation of new subduction zones is a key element of plate tectonics and the Wilson cycle, and many different controlling mechanisms have been proposed to initiate subduction. Here, we provide a brief overview of the known scenarios of subduction initiation in intra-oceanic and ocean-continent tectonic settings. Intra-oceanic subduction is most commonly associated with mechanical heterogeneities within the oceanic lithosphere, such as pre-existing fracture zones, spreading ridges, and transform faults. Numerous and well-recognized examples of new active subduction zones formed in intra-oceanic environments during the Cenozoic, suggesting that the initiation of ocean-ocean subduction must be a routine process that occurs “easily and frequently” in the mode of plate tectonics currently operating on Earth. On the contrary, the most traditional mechanisms for the establishment of classic self-sustaining ocean-continent subduction—passive margin collapse and subduction transference—are surprisingly rare in observations and difficult to reproduce in numerical models. Two alternative scenarios—polarity reversal and lateral propagation-induced subduction initiation—are in contrast much better documented in nature and experimentally. However, switching of subduction polarity due to arc-continent collision and lateral transmission of subducting plate boundaries are both inextricably linked to pre-existing intra-oceanic convergence. We, therefore, conclude that the onset of classic ocean-continent subduction zones is possible only through the transition from a former intra-oceanic subduction system. This transition is likely facilitated by the ductile damage accumulation and stress concentration across the aging continental margin. From this perspective, the future closure of the Atlantic Ocean can be viewed as an archetypal example of the role of transitional process between intra-oceanic subduction (Lesser Antilles) and the development of a new subduction zone at a passive continental margin (eastern North America)

Thermo-mechanical controls on geothermal energy resources: case studies in the Pannonian Basin and other natural laboratories

Geothermal energy is an important renewable energy resource, whose share is growing rapidly in the energy mix. Geosciences provide fundamental knowledge on Earth system processes and properties, required for the development of new methods to identify prospective geothermal resources suitable for exploitation. Through robust prediction and detection of critical reservoir parameters, including rock fabric, temperature, in situ stress, flow properties and fluid geochemistry, it is possible to reduce pre-drilling risks for geothermal exploratio

Fingerprinting secondary mantle plumes

Many vertical seismic velocity anomalies observed below different parts of the Eurasian plate are rooted in the transition zone between the upper and lower mantle (410–660 km), forming so-called secondary plumes. These anomalies are interpreted as the result of thermal effects of large-scale thermal upwelling (primary plume) in the lower mantle or deep dehydration of fluid-rich subducting oceanic plates. We present the results of thermo-mechanical numerical modelling to investigate the dynamics of such small-scale thermal and chemical (hydrous) anomalies rising from the lower part of the Earth's upper mantle. Our objective is to determine the conditions that allow thermo-chemical secondary plumes of moderate size (initial radius of 50 km) to penetrate the continental lithosphere, as often detected in seismo-tomographic studies. To this end, we examine the effect of the following parameters: (1) the compositional deficit of the plume density due to the presence of water and hydrous silicate melts, (2) the width of the weak zone in the overlying lithosphere formed because of plume-induced magmatic weakening and/or previous tectonic events, and (3) a tectonic regime varied from neutral to extensional. In our models, secondary plumes of purely thermal origin do not penetrate the overlying plate, but flatten at its base, forming “mushroom”-shaped structures at the level of the lithosphere-asthenosphere boundary. On the contrary, plumes with enhanced density contrast due to a chemical (hydrous) component are shown to be able to pass upwards through the lithospheric mantle to shallow depths near the Moho when (1) the compositional density contrast is ≥ 100 kg m−3 and (2) the width of the lithospheric weakness zone above the plume is ≥ 100 km. An extensional tectonic regime facilitates plume penetration into the lithosphere but is not mandatory. Our findings can explain observations that have long remained enigmatic, such as the “arrow”-shaped zone of low seismic velocities below the Tengchong volcano in south-western China and the columnar (“finger”-shaped) anomaly within the lithospheric mantle discovered more than two decades ago beneath the Eifel volcanic fields in north-western Germany. It appears that a chemical component is a characteristic feature not only of conventional hydrous plumes located over presently downgoing oceanic slabs, but also of upper mantle plumes in other tectonic settings

Late-Cantabrian orocline fault systems: modelling of their influence in the Iberian alpine evolution

La península ibérica constituye un laboratorio natural para el conocimiento de la deformación intraplaca alpina. Aunque la actual topografía es el resultado de los últimos eventos tectónicos ocurridos entre el Eoceno y el Mioceno inferior, la evolución de la fracturación que lo acompaña no es del todo bien conocida. Hasta ahora, la denominación tardi-varisco ofrecía una ventana temporal donde quedaban incluidos procesos tectónicos escasamente definidos. Presentamos una serie de modelos litosféricos en los que se investiga el control que ejercen estructuras posteriores al desarrollo del orógeno Varisco, en las postrimerías de la formación del oroclinal Cantábrico (Arco Ibero Armoricano, 310-295 Ma), y su evolución posterior durante gran parte del ciclo alpino. La superficie de los modelos es analizada mediante el estudio de velocimetría de partículas que permite establecer el análisis de la deformación y la cinemática de las estructuras producidas durante todo el proceso de deformación. Los resultados indican que la configuración actual de la topografía se ve fuertemente controlada por la presencia de las fallas producidas en los estadios finales de la formación del oroclinal y fueron posteriormente reactivadas durante el ciclo alpino. Estas estructuras son responsables del levantamiento topográfico que da lugar a la configuración de cadenas intraplaca y cuencas asociadas durante el acortamiento pirenaico.Iberia provides a natural laboratory for documentation of intraplate alpine deformation. Although presentday topography is the result of the latest tectonic events occurred during the Eocene and Lower Miocene, the former evolution of related structures is not well documented. Hirtherto, the late-Variscan term offered a vague and wide temporal window, where most of the tectonic processes not well understood were included. We present an analogue modelling study where the control and alpine evolution of structures postdating the Variscan orogeny, originated during the formation of the Cantabrian Orocline (Ibero-Armorican Arc, 310-295 Ma), is investigated. The models surface was analyzed through the particle image velocimetry method, which provides useful information about the evolution and kinematics of structures developed during deformation. The results show that the present-day configuration of topography is strongly controlled by the presence of faults formed during the final stages of the orocline development and were subsequently reactivated during the Alpine cycle. These structures are responsible for topographic uplift leading to the evolution of intraplate reliefs and associated basins during the Pyrenean shortening.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEpu

Plume‐Induced Sinking of Intracontinental Lithospheric Mantle: An Overlooked Mechanism of Subduction Initiation?

Although many different mechanisms for subduction initiation have been proposed, only few of them are viable in terms of consistency with observations and reproducibility in numerical experiments. In particular, it has recently been demonstrated that intra-oceanic subduction triggered by an upwelling mantle plume could greatly contribute to the onset and operation of plate tectonics in the early and, to a lesser degree, modern Earth. On the contrary, the initiation of intra-continental subduction still remains underappreciated. Here we provide an overview of 1) observational evidence for upwelling of hot mantle material flanked by downgoing proto-slabs of sinking continental mantle lithosphere, and 2) previously published and new numerical models of plume-induced subduction initiation. Numerical modeling shows that under the condition of a sufficiently thick (>100 km) continental plate, incipient downthrusting at the level of the lowermost lithospheric mantle can be triggered by plume anomalies of moderate temperatures and without significant strain- and/or melt-related weakening of overlying rocks. This finding is in contrast with the requirements for plume-induced subduction initiation within oceanic or thinner continental lithosphere. As a result, plume-lithosphere interactions within continental interiors of Paleozoic-Proterozoic-(Archean) platforms are the least demanding (and thus potentially very common) mechanism for initiation of subduction-like foundering in the Phanerozoic Earth. Our findings are supported by a growing body of new geophysical data collected in various intra-continental areas. A better understanding of the role of intra-continental mantle downthrusting and foundering in global plate tectonics and, particularly, in the initiation of “classic” ocean-continent subduction will benefit from more detailed follow-up investigations