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E. Carminati M. J. R. Wortel W. Spakman R. Sabadini 《Earth and Planetary Science Letters》1998,160(3-4):651-665
A review of the geological and geophysical data from the central and western Mediterranean region and the present-day upper mantle structure derived from tomographic studies are utilized in order to define the Oligocene–Recent geodynamic evolution for the area. In line with previous work, we suggest that the Miocene–Quaternary opening of the western and central Mediterranean basins is the result of back-arc extension due to the roll back toward the southeast of a northwestward subducting African slab in a geodynamic setting pinned between the Alpine and Betic collisional zones. We find, however, that this general pattern is complicated by four different detachment events which occurred beneath the Alps (Early Oligocene), the Betic chain (Aquitanian), northern Africa (Langhian) and the Apennines (Late Miocene?–Pliocene). We show that each of these events determines a major tectonic reorganization within the European plate. 相似文献
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We develop and present an approach for gaining insight into the thermal structure of the upper mantle in a tectonically active region. As a starting point for the analysis we use regional geological reconstructions, based on data from surface geology, shallow seismics and paleomagnetism. For these reconstructions we determine the necessarily associated upper mantle processes, such as subduction. We then forwardly model the thermal structure of upper mantle corresponding with the geological reconstruction used. In this way we obtain an estimate of a very important characteristic – the temperature distribution of the upper mantle–that is independent from those estimates from the usual deep seismic methods. If sufficient detailed information on the seismological structure of the region is available, a quantitative test of our modelling results is possible, via the temperature dependence of seismic velocities. We apply our approach to the Mediterranean area, for which we will test the reconstruction published by Dercourt et al. (1986). 相似文献
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Structure and seismicity of the Aegean subduction zone 总被引：1，自引：0，他引：1
Tomographic results show the presence of a high-velocity anomaly dipping north beneath the Aegean Sea (Hellenic arc), down to a depth of at least 600 km. This anomaly is interpreted as the image of the subducting lithosphere of the African plate. No deep seismicity, however, is associated with this downgoing slab, although this would be expected on the basis of the age of the downbending lithosphere (approximately 100 Myr) and the inferred duration of the present ongoing episode of subduction. Using a thermo-mechanical model for the subduction zone we find that the non-stationary input of the subduction zone-both in convergence rate and in thermal structure of the downgoing lithosphere - adequately accounts for both the presence of a velocity anomaly associated with a slab and the absence of deep seismicity. The non-stationarity follows from the large-scale tectonic setting of the Eastern Mediterranean basin. 相似文献
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The subduction behaviour of oceanic lithosphere in relation to its age is studied in detail.It is shown that the penetration depth of subducted lithosphere increases with increasing lithospheric age. In all cases where sufficient data are available, the relation proves to be unique.The controlling property appears to be the amount of gravitational instability of the part of the lithosphere concerned with respect to the surrounding upper mantle. The instability depends, through the density and temperature, on the time elapsed between creation and subduction.It is concluded that gravitational instability of the oceanic lithosphere—upper mantle system is a major cause of plate tectonics.The structure of individual subduction zones is interpreted accordingly. 相似文献
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A recently established relation between the penetration depth of oceanic lithosphere and the lithospheric age appears to be of special interest to the understanding of the South American subduction zone. The main characteristics of this complicated zone, such as the absence of deep-focus earthquakes south of 30°S, the variations in the dip angle of the descending Nazca plate and the gap in seismic activity between depths of approximately 300 and 525 km, can be understood if the spatial and temporal variations in the age of the descending oceanic lithosphere are taken into account. In view of the significance of local aspects of the subduction process the South American-Nazca plate interaction cannot simply be considered as a type-example of the interaction between a continental and an oceanic plate. 相似文献
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E Carminati M.J.R Wortel P.Th Meijer R Sabadini 《Earth and Planetary Science Letters》1998,160(3-4):667-679
The Algero–Provençal and the Tyrrhenian extensional basins developed in two stages in a geodynamic setting characterized by the nearly N–S convergence between Africa and Eurasia. The spreading of the Provençal basin occurred in the early Miocene following a long period of rifting in the western Mediterranean area. A dramatic eastward shift of the active extensional deformation resulted in the Tortonian to Quaternary opening of the Tyrrhenian basin. In a companion paper, Carminati et al. propose that: a trench retreat process in a geodynamic setting locked by the continental collisions in the Alps and in the Betic chain is a viable mechanism for the late Oligocene–early Langhian opening of the western Mediterranean; a Langhian slab detachment episode along the north African margin is likely to have caused the end of the trench retreat along this part of the boundary determining the end of active expansion in the western Mediterranean and the beginning of active extension in the Tyrrhenian basin. The objective of the present paper is to quantitatively test this proposed scenario. We calculate, by means of a thin shell model, the effects of these plate boundary reorganizations on the European stress and strain field. We show that the two-stage opening of the western and central Mediterranean can be explained by the evolution proposed by Carminati et al. and that, in particular, the eastward shift of the active extension which produced the termination of the first opening stage and the beginning of the second is likely to have been triggered by the slab detachment episode along the north African margin. 相似文献
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Subduction zone seismicity and the thermo-mechanical evolution of downgoing lithosphere 总被引：1，自引：0，他引：1
In this paper we discuss characteristic features of subduction zone seismicity at depths between about 100 km and 700 km, with emphasis on the role of temperature and rheology in controlling the deformation of, and the seismic energy release in downgoing lithosphere. This is done in two steps. After a brief review of earlier developments, we first show that the depth distribution of hypocentres at depths between 100 km and 700 km in subducted lithosphere can be explained by a model in which seismic activity is confined to those parts of the slab which have temperatures below a depth-dependent critical valueT
cr.Second, the variation of seismic energy release (frequency of events, magnitude) with depth is addressed by inferring a rheological evolution from the slab's thermal evolution and by combining this with models for the system of forces acting on the subducting lithosphere. It is found that considerable stress concentration occurs in a reheating slab in the depth range of 400 to 650–700 km: the slab weakens, but the stress level strongly increases. On the basis of this stress concentration a model is formulated for earthquake generation within subducting slabs. The model predicts a maximum depth of seismic activity in the depth range of 635 to 760 km and, for deep earthquake zones, a relative maximum in seismic energy release near the maximum depth of earthquakes. From our modelling it follows that, whereas such a maximum is indeed likely to develop in deep earthquake zones, zones with a maximum depth around 300 km (such as the Aleutians) are expected to exhibit a smooth decay in seismic energy release with depth. This is in excellent agreement with observational data. In conclusion, the incoroporation of both depth-dependent forces and depth-dependent rheology provides new insight into the generation of intermediate and deep earthquakes and into the variation of seismic activity with depth.Our results imply that no barrier to slab penetration at a depth of 650–700 km is required to explain the maximum depth of seismic activity and the pattern of seismic energy release in deep earthquake zones. 相似文献
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Seth Stein Sierd Cloetingh Douglas A. Wiens Rinus Wortel 《Earth and Planetary Science Letters》1987,82(1-2)
The possibility that thermoelastic stresses due to plate cooling contribute significantly to the stress field and seismicity in young oceanic lithosphere has been a subject of considerable recent interest. This effect is suggested by three key observations: a decrease in seismicity with lithospheric age, the fact that focal mechanisms show extension perpendicular to the spreading direction, and a depth stratification of mechanism types. A difficulty with this idea is that although thermoelastic stresses should be comparable in different regions, the intraplate seismicity seems to occur in local concentrations. In particular, the ridge-parallel extensional seismicity occurs preferentially in the Central Indian Ocean region.We explore the possibility that much of the data favoring thermoelastic stresses can be interpreted in terms of stresses resulting from individual plate geometry and local boundary effects. In particular, the dramatic concentration of extensional seismicity in the Central Indian Ocean region is consistent with finite element results for the intraplate stress incorporating the effects of the Himalayan collision and the various subduction zones. The ridge parallel extensional stresses show a decrease with age similar to that of the seismicity. As earthquakes in this area provide a major portion of the data for both ridge-parallel extension and depth stratification, these effects may be due more to the regional stress. We thus propose that thermoelastic stresses provide a low level “background” in all plates, but that the dominant effect is that of individual plate geometry and local boundary effects. 相似文献