ALBERT

Description: 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.

Description: Published

Description: 117819

Description: 1T. Struttura della Terra

Description: JCR Journal

Description: Understanding the interactions between surface and deep Earth processes is important for research in many diverse scientific areas including climate, environment, energy, georesources and biosphere. The TOPO-EUROPE initiative of the International Lithosphere Program serves as a pan-European platform for integrated surface and deep Earth sciences, synergizing observational studies of the Earth structure and fluxes on all spatial and temporal scales with modelling of Earth processes. This review provides a survey of scientific developments in our quantitative understanding of coupled surface-deep Earth processes achieved through TOPO-EUROPE. The most notable innovations include (1) a process-based understanding of the connection of upper mantle dynamics and absolute plate motion frames; (2) integrated models for sediment source-to-sink dynamics, demonstrating the importance of mass transfer from mountains to basins and from basin to basin; (3) demonstration of the key role of polyphase evolution of sedimentary basins, the impact of pre-rift and pre-orogenic structures, and the evolution of subsequent lithosphere and landscape dynamics; (4) improved conceptual understanding of the temporal evolution from back-arc extension to tectonic inversion and onset of subduction; (5) models to explain the integrated strength of Europe's lithosphere; (6) concepts governing the interplay between thermal upper mantle processes and stress-induced intraplate deformation; (7) constraints on the record of vertical motions from high-resolution data sets obtained from geo-thermochronology for Europe's topographic evolution; (8) recognition and quantifications of the forcing by erosional and/or glacial-interglacial surface mass transfer on the regional magmatism, with major implications for our understanding of the carbon cycle on geological timescales and the emerging field of biogeodynamics; and (9) the transfer of insights obtained on the coupling of deep Earth and surface processes to the domain of geothermal energy exploration. Concerning the future research agenda of TOPO-EUROPE, we also discuss the rich potential for further advances, multidisciplinary research and community building across many scientific frontiers, including research on the biosphere, climate and energy. These will focus on obtaining a better insight into the initiation and evolution of subduction systems, the role of mantle plumes in continental rifting and (super)continent break-up, and the deformation and tectonic reactivation of cratons; the interaction between geodynamic, surface and climate processes, such as interactions between glaciation, sea level change and deep Earth processes; the sensitivity, tipping points, and spatio-temporal evolution of the interactions between climate and tectonics as well as the role of rock melting and outgassing in affecting such interactions; the emerging field of biogeodynamics, that is the impact of coupled deep Earth – surface processes on the evolution of life on Earth; and tightening the connection between societal challenges regarding renewable georesources, climate change, natural geohazards, and novel process-understanding of the Earth system.

Description: Published

Description: 104140

Description: OST1 Alla ricerca dei Motori Geodinamici

Description: OSA5: Energia e georisorse

Description: JCR Journal