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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.earscirev.2010.06.002 Byline: Mark R. Handy (a), Stefan M. Schmid (a)(c), Romain Bousquet (b), Eduard Kissling (c), Daniel Bernoulli (d) Keywords: Tethys; Alps; Mediterranean; plate motion; subduction Abstract: A new reconstruction of Alpine Tethys combines plate-kinematic modelling with a wealth of geological data and seismic tomography to shed light on its evolution, from sea-floor spreading through subduction to collision in the Alps. Unlike previous models, which relate the fate of Alpine Tethys solely to relative motions of Africa, Iberia and Europe during opening of the Atlantic, our reconstruction additionally invokes independent microplates whose motions are constrained primarily by the geological record. The motions of these microplates (Adria, Iberia, Alcapia, Alkapecia, and Tiszia) relative to both Africa and Europe during Late Cretaceous to Cenozoic time involved the subduction of remnant Tethyan basins during the following three stages that are characterized by contrasting plate motions and driving forces: (1) 131-84Ma intra-oceanic subduction of the Ligurian part of Alpine Tethys attached to Iberia coincided with Eo-alpine orogenesis in the Alcapia microplate, north of Africa. These events were triggered primarily by foundering of the older (170-131Ma) Neotethyan subduction slab along the NE margin of the composite African-Adriatic plate; subduction was linked by a sinistral transform system to E-W opening of the Valais part of Alpine Tethys; (2) 84-35Ma subduction of primarily the Piemont and Valais parts of Alpine Tethys which were then attached to the European plate beneath the overriding African and later Adriatic plates. NW translation of Adria with respect to Africa was accommodated primarily by slow widening of the Ionian Sea; (3) 35Ma-Recent rollback subduction of the Ligurian part of Alpine Tethys coincided with Western Alpine orogenesis and involved the formation of the Gibraltar and Calabrian arcs. Rapid subduction and arc formation were driven primarily by the pull of the gravitationally unstable, retreating Adriatic and African slabs during slow convergence of Africa and Europe. The upper European-Iberian plate stretched to accommodate this slab retreat in a very mobile fashion, while the continental core of the Adriatic microplate acted as a rigid indenter within the Alpine collisional zone. The subducted lithosphere in this reconstruction can be correlated with slab material imaged by seismic tomography beneath the Alps and Apennines, as well as beneath parts of the Pannonian Basin, the Adriatic Sea, the Ligurian Sea, and the Western Mediterranean. The predicted amount of subducted lithosphere exceeds the estimated volume of slab material residing at depth by some 10-30%, indicating that parts of slabs may be superposed within the mantle transition zone and/or that some of this subducted lithosphere became seismically transparent. Author Affiliation: (a) Institut fur Geologische Wissenschaften, Freie Universitat Berlin, Malteserstrasse 74-100, D-12249 Berlin, Germany (b) Institut fur Geowissenschaften, Universitat Potsdam, Postfach 601553, D-14415 Potsdam, Germany (c) Institut fur Geophysik, ETH-Zentrum, Sonneggstrasse 5, CH-8092 Zurich, Switzerland (d) Geologisch-Palaontologisches Institut, Universitat Basel, Bernoullistrasse 32, CH-4056 Basel, Switzerland Article History: Received 23 November 2008; Accepted 1 June 2010

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.12.025 Byline: Bernhard Steinberger (a)(b)(c), Stephanie C. Werner (c), Trond H. Torsvik (a)(c)(d) Keywords: Earth; Venus, Interior; Mars, Interior; Volcanism Abstract: The relation between gravity anomalies, topography and volcanism can yield important insights about the internal dynamics of planets. From the power spectra of gravity and topography on Earth, Venus and Mars we infer that gravity anomalies have likely predominantly sources below the lithosphere up to about spherical harmonic degree l=30 for Earth, 40 for Venus and 5 for Mars. To interpret the low-degree part of the gravity spectrum in terms of possible sublithospheric density anomalies we derive radial mantle viscosity profiles consistent with mineral physics. For these viscosity profiles we then compute gravity and topography kernels, which indicate how much gravity anomaly and how much topography is caused by a density anomaly at a given depth. With these kernels, we firstly compute an expected gravity-topography ratio. Good agreement with the observed ratio indicates that for Venus, in contrast to Earth and Mars, long-wavelength topography is largely dynamically supported from the sublithospheric mantle. Secondly, we combine an empirical power spectrum of density anomalies inferred from seismic tomography in Earth's mantle with gravity kernels to model the gravity power spectrum. We find a good match between modeled and observed gravity power spectrum for all three planets, except for 2a[c]1/2la[c]1/24 on Venus. Density anomalies in the Venusian mantle for these low degrees thus appear to be very small. We combine gravity kernels and the gravity field to derive radially averaged density anomaly models for the Martian and Venusian mantles. Gravity kernels for l[greater than or equal to]5 are very small on Venus below [approximately equal to]800km depth. Thus our inferences on Venusian mantle density are basically restricted to the upper 800km. On Mars, gravity anomalies for 2a[c]1/2la[c]1/25 may originate from density anomalies anywhere within its mantle. For Mars as for Earth, inferred density anomalies are dominated by l=2 structure, but we cannot infer whether there are features in the lowermost mantle of Mars that correspond to Earth's Large Low Shear Velocity Provinces (LLSVPs). We find that volcanism on Mars tends to occur primarily in regions above inferred low mantle density, but our model cannot distinguish whether or not there is a Martian analog for the finding that Earth's Large Igneous Provinces mainly originate above the margins of LLSVPs. Author Affiliation: (a) Center for Geodynamics, Geological Survey of Norway, NO-7491 Trondheim, Norway (b) Helmholtz Centre Potsdam, German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany (c) Physics of Geological Processes, Univ. of Oslo, NO-0316 Oslo, Norway (d) School of Geosciences, Univ. of the Witwatersrand, Wits 2050, South Africa Article History: Received 5 February 2009; Revised 16 October 2009; Accepted 22 December 2009

Combined analysis of high-resolution seismic images of the Alaska and Cascadia subduction zones reveals where metamorphic fluids are released. Both images show the subducted oceanic crust as a dipping low-velocity layer with a clear termination depth. However, in Alaska the crust is thicker (15-20 km compared to 8 km) and terminates at greater depth (120 km compared to 40 km) than in Cascadia. Based on metamorphic reaction estimates and geodynamic models, we demonstrate that the termination depth corresponds to eclogitization of the crust triggered by dehydration of water-bearing minerals, and that the location of this reaction is dependent on the thermal structure of the subducted slab. Keywords: subduction, oceanic crust, seismic studies, metamorphism, eclogite, water.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.earscirev.2005.06.001 Byline: S. Cloetingh (a), T. Cornu (a), P.A. Ziegler (b), F. Beekman (a) Keywords: neotectonics; intraplate deformation; seismicity; topography; European continental rift system; geomorphology Abstract: Research on neotectonics and related seismicity has hitherto been mostly focused on active plate boundaries that are characterized by generally high levels of earthquake activity. Current seismic hazard estimates for intraplate domains are mainly based on probabilistic analyses of historical and instrumental earthquake catalogues. The accuracy of such hazard estimates is limited by the fact that available catalogues are restricted to a few hundred years, which, on geological time scales, is insignificant and not suitable for the assessment of tectonic processes controlling the observed earthquake activity. More reliable hazard prediction requires access to high quality data sets covering a geologically significant time span in order to obtain a better understanding of processes controlling on-going intraplate deformation. The Alpine Orogen and the intraplate sedimentary basins and rifts in its northern foreland are associated with a much higher level of neotectonic activity than hitherto assumed. Seismicity and stress indicator data, combined with geodetic and geomorphologic observations, demonstrate that deformation of the Northern Alpine foreland is still on-going and will continue in the future. This has major implications for the assessment of natural hazards and the environmental degradation potential of this densely populated area. We examine relationships between deeper lithospheric processes, neotectonics and surface processes in the northern Alpine Foreland, and their implications for tectonically induced topography. For the Environmental Tectonics Project (ENTEC), the Upper and Lower Rhine Graben (URG and LRG) and the Vienna Basin (VB) were selected as natural laboratories. The Vienna Basin developed during the middle Miocene as a sinistral pull-apart structure on top of the East Alpine nappe stack, whereas the Upper and Lower Rhine grabens are typical intracontinental rifts. The Upper Rhine Graben opened during its Late Eocene and Oligocene initial rifting phase by nearly orthogonal crustal extension, whereas its Neogene evolution was controlled by oblique extension. Seismic tomography suggests that during extension the mantle-lithosphere was partially decoupled from the upper crust at the level of the lower crust. However, whole lithospheric folding controlled the mid-Miocene to Pliocene uplift of the Vosges-Black Forest Arch, whereas thermal thinning of the mantle-lithosphere above a mantle plume contributed substantially to the past and present uplift of the Rhenish Massif. By contrast, oblique crustal extension, controlling the late Oligocene initial subsidence stage of the Lower Rhine Graben, gave way to orthogonal extension at the transition to the Neogene. The ENTEC Project integrated geological, geophysical, geomorphologic, geodetic and seismological data and developed dynamic models to quantify the societal impact of neotectonics in areas hosting major urban and industrial activity concentrations. The response of Europe's intraplate lithosphere to Late Neogene compressional stresses depends largely on its thermo-mechanical structure, which, in turn, controls vertical motions, topography evolution and related surface processes. Author Affiliation: (a) Netherlands Research Centre for Integrated Solid Earth Sciences, Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands (b) Department of Earth Sciences, University of Basel, Bernoullistrasse 32, 4056 Basel, Switzerland (c) Department of Geological Sciences, Geo-Center, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria (d) Ecole et Observatoire des Sciences de la Terre, Institut de Physique du Globe de Strasbourg, 5 rue Rene Descartes, 67084 Strasbourg, France (e) Geologisches Institut, Albert Ludwigs Universitat, Freiburg i.Br., Albertstrasse 23-B, 79104 Freiburg i.Br., Germany (f) Netherlands Institute of Applied Geosciences, Princetonlaan 63584 CB Utrecht, The Netherlands (g) Geodatisches Institut, Universitat Fredericiana Karlsruhe, Englerstrasse 7, 76128 Karlsruhe, Germany (h) Geodesy and Geodynamics Laboratory, ETH-Honggerberg HPV G53, 8093 Zurich, Switzerland (i) Bureau de Recherches Geologiques et Minieres, Land Use Planning and Natural Risk Division, 3 Avenue Claude Guillemin, 45060 Orleans, France (j) Royal Netherlands Meteorological Institute (KNMI), P.O. Box 201, 3730AE De Bilt, The Netherlands Article History: Received 1 July 2004; Accepted 2 June 2005

Buried circular collapse structures above a tabular evaporitic body are recorded by recently acquired 3D seismic data on the Levant Basin and continental margin, offshore Israel (Eastern Mediterranean). The structures formed during the Pliocene as buried Messinian (late Miocene) evaporites underwent extensive dissolution in a submarine, deep-water setting. Three-dimensional seismic analysis is used to describe the detailed morphology of the structures and the associated overburden, allowing the reconstruction of their origin and development. It is proposed that evaporite dissolution led to the collapse of the weakly lithified overburden, and this deformed with a series of concentric extensional faults. From the structural analysis of the overburden, the estimated maximum duration of the dissolution event is 0.75-1 Ma. The mechanism proposed for the creation of the circular collapse structures is subjacent dissolution of the more soluble evaporites in the Messinian evaporites, as a result of focused vertical fluid flow at the base of the evaporitic series. Rapid release of overpressured fluids, as, for example, during an earthquake, is thought to have initiated the focused fluid flow, which impinged on the evaporitic seal to the point where dissolution occurred, creating the localized circular collapse structures in the overburden. Keywords: Eastern Mediterranean, evaporites, solution, collapse structures, seismic methods.

The development of affordable digital technologies that allow the collection and analysis of georeferenced field data represents one of the most significant changes in field-based geoscientific study since the invention of the geological map. Digital methods make it easier to re-use pre-existing data (e.g. previous field data, geophysical survey, satellite images) during renewed phases of fieldwork. Increased spatial accuracy from satellite and laser positioning systems provides access to geostatistical and geospatial analyses that can inform hypothesis testing during fieldwork. High-resolution geomatic surveys, including laser scanning methods, allow 3D photorealistic outcrop images to be captured and interpreted using novel visualization and analysis methods. In addition, better data management on projects is possible using geospatially referenced databases that match agreed international data standards. Collectively, the new techniques allow 3D models of geological architectures to be constructed directly from field data in ways that are more robust compared with the abstract models constructed traditionally by geoscientists. This development will permit explicit information on uncertainty to be carried forward from field data to the final product. Current work is focused upon the development and implementation of a more streamlined digital workflow from the initial data acquisition stage to the final project output. Keywords: geospatial data, field studies, digital cartography, surveys, three-dimensional models.

The Iceland plume has had an important influence on vertical motions in the North Atlantic. The convecting mantle in this region contains a large-scale low-velocity seismic anomaly, which correlates with a long-wavelength gravity high and bathymetric feature. This suggests that an arm of plume material has extended, or is extending, from Iceland, in a direction perpendicular to the Mid-Atlantic Ridge. Here we present the results of a detailed teleseismic traveltime study that reveals the high-resolution morphology of this low-velocity anomaly beneath the British Isles. Our images provide insights into the nature of plume-lithosphere interactions. The low-velocity anomaly imaged in this study correlates geographically with a region of high gravity anomalies and high topography that was associated with Paleogene magmatism and phases of epeirogenic uplift during the Cenozoic Era. There is evidence that the distribution of British earthquakes is also related to the low-velocity anomaly. The low-velocity anomaly is interpreted to represent hot material from the original Iceland plume head that became trapped beneath thinned regions of lithosphere ca. 60 Ma. Keywords: plume-lithosphere interactions, North Atlantic Igneous Province, seismic tomography.

A tomographic analysis of the seismic events in the Dead Sea region indicates the presence of large magmatic diapirs. The magmatic diapirs extend as 10 to 13 km high domal structures that are elliptical in shape. The domal structures stretch from the lower crust to the overlying intermediate crust. The presence of the magmatic diapirs under the Dead Sea basin indicates abnormally high temperature, magmatic upwelling, and metastable stratification in the lower crust.

We used seismic tomography to investigate the complex structure of the upper mantle below northwestern South America. Images of slab structure not delineated by previous seismicity studies help us to refine existing tectonic models of subducted Caribbean-Pacific lithosphere beneath the study area. Beneath western Venezuela and Colombia we distinguish two slabs: a Maracaibo and a (redefined) Bucaramanga slab. The Maracaibo slab, coinciding with most of the Bucaramanga slab previously defined by W.D. Pennington, dips in a direction of 150 degrees at an angle of 17 degrees to a depth of 275 km and correlates to the subducted Late Cretaceous oceanic plateau of the Caribbean plate. Farther south, a second slab dips at an angle of 50 degrees in a direction of 125 degrees to a depth of at least 500 km and correlates to the subducted oceanic crust of the Nazca plate and the downdip extension of the Panama island arc. We refer to this slab as the redefined Bucaramanga slab, because it is different from the Bucaramanga slab segment defined by Pennington. The area of the South American plate overriding both slabs is characterized by the absence of an active volcanic arc, an anomalously wide topographically uplifted and tectonically active area, and the northward escape of the Maracaibo block along active strike-slip faults. In support of earlier studies, we attribute this to the underthrusting of the Caribbean oceanic plateau (our shallowly dipping Maracaibo slab) along the base of the South American lithosphere and to the recent collision of the Panama island arc rafted in on more steeply dipping crust of the Nazca plate (our redefined Bucaramanga slab).

The Mantle Electromagnetic and Tomography (MELT) experiment was developed to collect both seismic waves and electromagnetic data on the ocean floor spanning the East Pacific Rise. Data on electric and magnetic fields gave insight on the electrical conductivity of the upper mantle.

GLobal Positioning System (GPS) measurements across the New Madrid seismic zone (NMSZ) in the central United States show Little, if any, motion. These data are consistent with platewide continuous GPS data away from the NMSZ, which show no motion within uncertainties. Both these data and the frequency-magnitude relation for seismicity imply that had the largest shocks in the series of earthquakes that occurred in 1811 and 1812 been magnitude 8, their recurrence interval should well exceed 2500 years, Longer than has been assumed. Alternatively, the Largest 1811 and 1812 earthquakes and those in the paleoseismic record may have been much smaller than typically assumed. Hence, the hazard posed by great earthquakes in the NMSZ appears to be overestimated., During the years 1811 and 1812 a long sequence of earthquakes (1), including three large shocks thought to have had surface wave magnitudes near or exceeding 8 (2), was centered [...]