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Subduction dynamics can be understood as the result of the balance between driving and resisting forces. Previous work has traditionally regarded gravitational slab pull and viscous mantle drag as the main driving and resistive forces for plate motion respectively. However, this paradigm fails to explain many of the observations in subduction zones. For example, subducting plate velocity varies significantly along-strike in many subduction zones and this variation is not correlated to the age of subducting lithosphere. Here we present three-dimensional and time-dependent numerical models of subduction. We show that along-strike variations of the overriding plate thermal structure can lead to along-strike variations in subducting plate velocity. In turn, velocity variations lead to significant migration of the Euler pole over time. Our results show that the subducting plate is slower beneath the colder portion of the overriding plate due to two related mechanisms. First, the mantle wedge beneath the colder portion of the overriding plate is more viscous, which increases mantle drag. Second, where the mantle wedge is more viscous, hydrodynamic suction increases, leading to a lower slab dip. Both factors contribute to decreasing subducting plate velocity in the region; therefore, if the overriding plate is not uniform, the resulting velocity varies significantly along-strike, which causes the Euler pole to migrate closer to the subducting plate. We present a new mechanism to explain observations of subducting plate velocity in the Cocos and Nazca plates. These results shed new light on the balance of forces that control subduction dynamics and prove that future studies should take into consideration the three-dimensional structure of the overriding plate., This work was supported by Spanish Ministry of Economy and Competitiveness projects CGL2012-37222 and CGL2014-58821-C2-1-R. M.I. Billen acknowledges support from NSF grant 1246864. L.G.J. Montesi acknowledges support from NSF grant OCE 10-60878.

Several mechanisms have been suggested for the formation of flat slabs including buoyant features on the subducting plate, trenchward motion and thermal or cratonic structure of the overriding plate. Analysis of episodes of flat subduction indicate that not all flat slabs can be attributed to only one of these mechanisms and it is likely that multiple mechanisms work together to create the necessary conditions for flat slab subduction. In this study we examine the role of localized regions of cratonic lithosphere in the overriding plate in the formation and evolution of flat slabs. We explicitly build on previous models, by using time-dependent simulations with three-dimensional variation in overriding plate structure. We find that there are two modes of flat subduction: permanent underplating occurs when the slab is more buoyant (shorter or younger), while transient flattening occurs when there is more negative buoyancy (longer or older slabs). Our models show how regions of the slab adjacent to the subcratonic flat portion continue to pull the slab into the mantle leading to highly contorted slab shapes with apparent slab gaps beneath the craton. These results show how the interpretation of seismic images of subduction zones can be complicated by the occurrence of either permanent or transient flattening of the slab, and how the signature of a recent flat slab episode may persist as the slab resumes normal subduction. Our models suggest that permanent underplating of slabs may preferentially occur below thick and cold lithosphere providing a built-in mechanism for regeneration of cratons.

© 2014 Elsevier B.V. The GOCE (Gravity field and steady-state Ocean Circulation Explorer) mission, launched on March 2009, included a new type of satellite instrument, an on-board three-axis gradiometer able to measure the Earth's gravity gradients at the satellite height (255 km). The potential of this new type of measurement and its derived products (i.e., global gravity field models), together with other land-based geophysical observables (Bouguer and geoid anomalies), to image sub-lithospheric thermal and compositional anomalies is evaluated in this study. We focus on the Atlantic-Mediterranean Transition Region (AMTR), the diffuse, transpressive contact between the Iberian Peninsula and North Africa. The present-day lithospheric structure in the area is characterized by a wide band of active deformation, large lateral variationsin the lithosphere and the presence of a positive seismic-velocity anomaly in the uppermost mantle beneath the Betics and the westernmost Alboran Basin-Gibraltar Arc. Here, the perturbing effects of deep, sub-lithospheric density anomalies in GOCE gravity gradients and other land-based geophysical data are assessed, and its impact in lithospheric-scale geophysical-petrological modeling within a ther-modynamically consistent framework analyzed. Some of the gravity gradients computed at the satellite altitude are rather sensitive to the presence of even a relatively small sub-lithospheric cold slab, like theone observed in the AMTR, showing the potential of the new GOCE data to map upper mantle anomalies. Lithospheric models ignoring the AMTR sub-lithospheric heterogeneities could be significantly biased. In particular, extreme changes of 4-6 km and 60-70 km in the crustal and lithospheric thickness, respectively, are required to include sub-lithospheric mantle contributions to land-based and satellite gravitydata., JF was supported by the JAE-DOC programme (CSIC-Spain) cofunded by ESF, and by Spanish Ministry of Economy and Competitiveness grants CGL2009-13103 and CGL2012-37222. MC was supported by Spanish Ministry of Economy and Competitiveness-CSIC grant 200930I053 MICINN-CSIC. ZM acknowledges the financial support from the Science Foundation of Ireland under the research program 11/RFP.1/GEO/3309. This is a contribution of the Consolider-Ingenio 2010 project TOPO-IBERIA (CSD2006-00041).

The direction of plate tectonic motion and the direction of mantle flow, as inferred from observations of seismic anisotropy measurements, show a good global correlation far from subduction zones. However, this correlation is poor near subduction zones, where below the slab seismic anisotropy is aligned parallel to the trench and above the slab has a complex pattern, which has not been fully explained. Here we present time-dependent three-dimensional (3D) fully-dynamic simulations of subduction to study the effect of overriding plate structure on the evolution of slab geometry and induced mantle flow. We find that along-strike variation in thermal thickness of the overriding plate causes increased hydrodynamic suction and shallower slab dip beneath the colder portion of the overriding plate; the variation in slab geometry drives strong trench-parallel flow beneath the slab and a complex flow pattern above the slab. This new mechanism for driving trench-parallel flow provides a good explanation for seismic anisotropy observations from the Middle and South America subduction zones, where both slab dip and overriding plate thermal state are strongly variable and correlated, and thus may be an important mechanism in other subduction zones. The location and strength of trench-parallel flow vary with the time-dependent evolution of the slab, suggesting that the global variability in seismic anisotropy observations in subduction zones is in part due to the non-steady-state behavior of these systems.

Mammalian cerebral cortex is accepted as being critical for voluntary motor control, but what functions depend on cortex is still unclear. Here we used rapid, reversible optogenetic inhibition to test the role of cortex during a head-fixed task in which mice reach, grab, and eat a food pellet. Sudden cortical inhibition blocked initiation or froze execution of this skilled prehension behavior, but left untrained forelimb movements unaffected. Unexpectedly, kinematically normal prehension occurred immediately after cortical inhibition, even during rest periods lacking cue and pellet. This 'rebound' prehension was only evoked in trained and food-deprived animals, suggesting that a motivation-gated motor engram sufficient to evoke prehension is activated at inhibition's end. These results demonstrate the necessity and sufficiency of cortical activity for enacting a learned skill.

Isobutene oligomerization on W2O3/Al2O3 and NiO-W2O3/Al2O3 catalysts (20 wt.% W2O3 and 5 wt.% NiO) was studied. The catalysts were prepared by impregnating ammonium tungstanate and nickel nitrate on a γ-alumina sol-gel support. The XRD patterns of the samples calcined at 500°C show the presence of large W2O3 conglomerates on the W2O3/Al2O3 sample and smaller ones on the NiO-W2O3/Al2O3 catalyst. Pyridine-FT-IR absorption spectra study shows a higher acidity on the nickel-containing sample. The isobutene oligomerization was carried out in a gas-phase flow reactor (50°–150°C), and selectivity as high as 100% to the formation of the olefins fraction was obtained. The role of NiO coordinating the π-allyl adsorption of the olefins as well as its role to the high selectivity were discussed.

Mammalian cerebral cortex is accepted as being critical for voluntary motor control, but what functions depend on cortex is still unclear. Here we used rapid, reversible optogenetic inhibition to test the role of cortex during a head-fixed task in which mice reach, grab, and eat a food pellet. Sudden cortical inhibition blocked initiation or froze execution of this skilled prehension behavior, but left untrained forelimb movements unaffected. Unexpectedly, kinematically normal prehension occurred immediately after cortical inhibition, even during rest periods lacking cue and pellet. This ‘rebound’ prehension was only evoked in trained and food-deprived animals, suggesting that a motivation-gated motor engram sufficient to evoke prehension is activated at inhibition’s end. These results demonstrate the necessity and sufficiency of cortical activity for enacting a learned skill. DOI: http://dx.doi.org/10.7554/eLife.10774.001, eLife digest Many of the movements that humans and other animals make every day are deceptively complex and only appear easy because of extensive practice. For example, picking up an object involves several steps that must be precisely controlled, including reaching towards the item and holding it using the right amount of pressure to not crush it or drop it. Part of the brain called the motor cortex is thought to be important for learning and controlling these skilled movements, but its exact role in these processes is not clear. A technique called optogenetics allows the roles of individual parts of the brain to be studied by rapidly altering their activity, whilst minimizing the likelihood that the brain will compensate for these changes. By genetically modifying animals to produce light-sensitive channel proteins in certain brain cells, the activity of particular regions of the brain can be controlled by shining light onto them. Guo et al. have now used optogenetics to control the motor cortex as the mice performed a task they had been trained to do – reaching for and picking up a food pellet. Suddenly shutting down the motor cortex at the start of a trial prevented the mice from starting the task, and shut down part way through the task caused the front limbs of the mice to freeze in midair. However, only the learned, skilled task was frozen by motor cortex shutdown; mice could still move their limbs normally if the motor cortex was instead shut down during routine movements. When the cortex was reactivated, the mice instantly resumed trying to pick up the food pellet. Unexpectedly, even during rest periods when there was no food pellet and the mice were just waiting for the experiment to begin, turning the motor cortex off and then back on again suddenly caused the mice to perform the complete grabbing motion. This implies that the cortical activity evoked at the end of inactivation acts to trigger the full movement sequence. This was particularly likely to occur if the animal had been deprived of food before the test or was particularly well trained, but did not depend on the position of the limb. Overall, Guo et al.’s work opens the question of how the instructions that describe the learned movement are encoded within the motor cortex and its downstream networks. Future studies could also investigate how learning a set of movements affects the structure of cortical neurons and their connections, thus suggesting how these memories are stored. DOI: http://dx.doi.org/10.7554/eLife.10774.002

We investigate the influence of mantle flow relative to the lithosphere on subduction dynamics. We use 2D thermo-mechanical models assuming incompressible non-Newtonian fluid rheology. Different mantle flow velocities consistent with absolute plate motion models are tested, as well as both directions of flow, either sustaining or opposing slab dip. The effects of different inflow/outflow velocity profiles, slab strengths and upper–lower mantle viscosity contrasts are also evaluated. Slab dip deviations between models with opposite mantle flow directions range from 37° for relatively strong slabs (ηmax = 1025 Pa s) to 50° for weaker slabs (ηmax = 1024 Pa s), accounting for a significant amount of natural slab dip variability. For imposed mantle flow supporting the slab, the initial stage of slab steepening is followed by a stage of continuous slab dip decrease. This slab shallowing eventually leads to mantle wedge closure, subduction cessation and slab break-off, possibly driving subduction flips.

[1] Slab dip varies significantly, both between different, and along single subduction zones. Provided that old subducting plates are colder and denser than young plates, variations in the slab dip should correlate with slab age. However, recent statistical analyses do not show this expected correlation. We present the results of non-Newtonian numerical dynamic models where subduction is driven by means of a kinematic boundary condition. We systematically vary the age of both the overriding and subducting plates in order to test these effects on the slab dip at different depth ranges. We find that colder overriding plates result in shallower slab dips and episodes of flat slab subduction, as a result of the increased suction force in the mantle wedge. The influence of the thermal state of the overriding plate on slab dip is shown here to be more important than that of the age of subducting lithosphere. Modeling results are qualitatively compared to the large dip variability of the Cocos slab including a flat-slab segment. We suggest that this variability is likely related to the change of the thermal state of the overriding plates, with flat subduction occurring under cold lithosphere in southwestern Mexico and steep subduction under the warmer lithosphere of the northwestern Caribbean plate.

12 páginas, 11 figuras, 1 tabla., A Matlab tool for archaeomagnetic dating has been developed in this work. Well-dated palaeosecular variation curves (PSVCs) can be used to date archaeological artefacts with unknown ages. The archaeomagnetic direction (declination and/or inclination) and the archaeointensity obtained from the archaeological artefact are compared with a master PSVC. In addition, historical lava flows with controversial ages can be dated using this methodology. The dating process follows the descriptions given by Lanos (2004), which is based on the combination of temporal probability density functions of the three geomagnetic field elements. Here, we develop an interactive tool in Matlab code to carry out archaeomagnetic dating by comparing the undated archaeomagnetic (or lava flow) data with a master PSVC. The master PSVCs included with the Matlab tool are the different European Bayesian curves and those generated using both regional and global geomagnetic field models. A case study using all the PSVCs available in Europe and some undated archaeomagnetic data has been carried out to analyze how the different PSVCs affect the dating process. In addition, the dating uncertainty and the relocation error have been analyzed in the European region. Results show that some regional Bayesian PSVCs and the regional SCHA.DIF.3K archaeomagnetic model are the best choices to obtain an accurate date in Europe. Moreover, when it is available, the full geomagnetic field vector must be used for archaeomagnetic dating., The authors are grateful to the Spanish Research Project CGL2008-02203 and the FPI grant BES-2006-13488.