1,721,322 research outputs found
Topographic expressions of mantle dynamics in the Mediterranean
No full textThe surface of the Earth is the ever-changing expression of the dynamic processes occurring at depth and at or above its surface. However, our ability to “read” landscapes in terms of their underlying tectonic or climatic forcing remains rudimentary. During the last decade, particular attention has been drawn to the deep dynamic contributions to topography, related to the stresses that are produced at the base of the lithosphere by mantle convection, and their relevance compared to the (iso)static component of topography. Here, we use examples from the Mediterranean and estimate residual and dynamic topography. We then compare those with surface uplift from geology for specific regions to disentangle the dynamic from the static components. Considering the different topographic signatures of tectonic processes (e.g. actual, residual, and dynamic topography as well as uplift rates) jointly provides a powerful way to distinguish between the contributions of mantle, crustal, and surface processes. Such an approach might bring us closer to reading topographic expressions in terms of their geological cause
Interplays Between Mantle Flow and Slab Pull at Subduction Zones in 3D
No full textThe understanding of the interactions between subduction-induced mantle flow and background mantle flow (being global or regional) remains incomplete despite its potential impact on subduction dynamics and associated deformation. Here we present the results of three-dimensional laboratory models of subduction zones at the scale of the upper mantle in which we systematically vary the plate's width and trench perpendicular background mantle flow. In particular, we test different mantle flow magnitudes and directions of flow, and evaluate their impact on the slab geometry in the vertical plane, trench shape evolution, and the superficial horizontal mantle deformation. While the chosen viscosity ratio between the convective mantle and the subducting plate in our models (∼100) is favorable to the deformation of the slab through mantle displacement, we show that the geometry of the slab in the vertical plane is only marginally affected by the imposed background flow. Instead, the background flow has a larger impact on the horizontal kinematics and deformation of the trench. It reduces along-trench variations of trench kinematics, which in turn decreases trench curvature, and it largely disturbs the pattern of mantle deformation at slab edges, inhibiting the development of toroidal cells. We also show that the thickness of the convective layer (here, the upper mantle) controls the toroidal component of the mantle flow and the length scale of trench curvature for large subduction zones
Thermal structure of a vanishing subduction system: An example of seismically-derived crustal temperature along the Italian peninsula
No full textThe active tectonic processes in convergent margins confer a high degree of complexity to the crust. Determining the thermal structure is, therefore, key to better elucidate the nature of those processes. In order to reconstruct the thermal structure of the crust beneath the Italian peninsula, we combine the most recent and accurate shear-wave velocity model that is currently available with thermodynamic modelling, assuming a global average crustal composition with no lateral variations. Our model, presented in terms of Moho temperature and crustal thermal gradients, shows a very good agreement with the known thermal anomalies associated with the backarc spreading related to the Apennine subduction. Importantly, we envisage a new anomalous region of high Moho temperatures in NW Italy (T > 800 °C at 30 km), at the transition between the Alps and Apennine orogens. The lowest temperatures of our model, corresponding to geothermal gradients <19 °C km-1, are obtained in the still active but slow-convergent portion of the northern Apennine. Moho temperatures increase moving southwards along the Apennine chain, an observation that is coherent with the evidence of ceasing subduction and consequent rebalancing of the depressed isotherms along the slab. Our results suggest that a thermal structure in different tectonic settings can be inferred with acceptable uncertainties based on absolute seismic velocity models. In this sense, our approach can be extended to any other region
Styles and regimes of orogenic thickening in the Peloritani Mountains (Sicily, Italy): new constraints on the tectono-metamorphic evolution of the Apennine belt
No full textThe Peloritani Mountains constitute the Sicilian portion of the Calabria–Peloritani Arc (Italy), a tectono-metamorphic edifice recording the history of the subduction–exhumation cycle during Tertiary convergence between the African and European plates. Here, we describe the kinematic and the petrological characteristics of the major shear zones bounding the lowermost continental-derived metamorphic units cropping out in the eastern portion of the Peloritani Mountains. Both meso- and micro-scale shear sense criteria indicate a top-to-the-SSE tectonic transport, during a general evolution from ductile to brittle deformation conditions. Quantitative thermobarometry on texturally equilibrated phengite–chlorite pairs crystallized along the shear bands indicates pressure of 6–8 kbar at temperatures of 360–440 °C for the structurally highest units and 3–4 kbar at 380–440 °C for the lowest ones. This documents an overall inverse-type nappe arrangement within the tectonic edifice and a transition from an Alpine- (13–18 °C km−1) to a Barrovian-type (28–36 °C km−1) geothermal gradient during the progress of the Alpine orogenic metamorphism in the Peloritani Mountains. The integration of these results allows the Peloritani Mountains to be considered as a constituent element of the Apennine orogenic domain formed during the progressive space–time transition from oceanic to continental subduction at the active convergent margin
Role of Lateral Mantle Flow in the Evolution of Subduction Systems: Insights from Laboratory Experiments
No full textRheological properties of paraffin as an analogue material for viscous crustal deformation
No full textGeological Map of the Cape Adare Quadrangle, north Victoria Land, Antarctica (Scale 1:250.000)
No full textStructural and hydrogeological features of Pleistocene shear zones in the area of Rome (Central Italy)
No full textThe last tectonic episode observed in the Latium Tyrrhenian margin (Central Italy), few km cast of Rome, is represented by a set of middIe-upper Pleistocene N-S shear zones, characterised by complex geometric and kinematic setting. The easternmost of these shear zones displays a strike-slip component of motion and is located at the boundary between the Apennine carbonate chain and the volcanic areas. The distribution of travertine deposits and hydrothermal springs suggests that this fault zone acts as an impermeable barrier for lateral flow derived from superficial karstic circuit, and as a preferential upwelling surface for deep hydrothermal fluids. We propose that high fluid pressure could develop inside these fault zones favouring the reactivation of buried pre-existing crustal discontinuities and the local re-orientation of the stress field, as testified by the geometry and the kinematics of the surface fault pattern.JCR Journalope
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