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Abstract Tectonics exerts a strong control over the morphology of Earth's surface that is apparent in active mountain belts. In lowland areas, subtle processes like lithospheric flexure and isostatic rebound can impact Earth surface dynamics, hydrologic connectivity, and topography, suggesting that geomorphic and hydrologic analyses can shed light on underlying lithospheric properties. Here we examine the effect of lithospheric flexure on the geomorphology, hydrology, and river water chemistry of the Rio Bermejo fluvial system in the east Andean foreland basin of northern Argentina. Results show that proximal to the mountain front, foredeep basin subsidence causes sedimentation along a braided channel belt that is superelevated relative to the surrounding flood basin. During floods, water flows from the superelevated channel into the groundwater reservoir, causing a net loss of discharge with distance downstream. Further downstream, forebulge uplift forces channel narrowing, high lateral migration rates, and incision up to 13 m into older river deposits. This incision locally allows groundwater flow into the river, causing a ∼20% increase in river solute load. Groundwater emerges from the forebulge into the backbulge, predominantly as spring‐fed channels. Here, channel migration rates decrease, suggesting a switch from net uplift to subsidence that reduces the depth to the groundwater table. This analysis shows that subtle lithospheric flexure can have significant effects on river channel morphology that determine hydrologic flow paths, and ultimately influence geochemical and ecological patterns. We suggest that these effects may elucidate lithospheric properties that are otherwise inferred from bulk geophysical observations.

Density instabilities in the lithosphere can founder gravitationally via viscous dripping and decoupling from overlying crust. The lithospheric dripping concept has been invoked across the globe, but the diversity of crustal effects, observable evidence, and tectonic settings involved in dripping remain underexplored. Here, we synthesize numerical and analogue modeling studies and geologic data from the literature, including all proposed lithospheric dripping events to‐date. We argue that two distinct styles of dripping can occur depending on crustal strength (relative to that of the mantle lithosphere). Near‐surface contraction and subsidence of strong crusts contrasts with near‐surface extension and uplift of weak crusts. We discuss these events in terms of tectonic setting, timing, size, and the main types of data associated with each event. We also find that lithospheric dripping is associated with a distinct suite of geological observations including sedimentological, structural, volcanic, and geophysical data, which can be used to distinguish strong crusts from weak crusts. We find 27 events for which lithospheric dripping is a key hypothesis, including 9 with clear evidence for strong‐crust dripping and 3 with clear evidence of weak‐crust dripping. We review emerging research methods have the potential to detect the signals of dripping in the geologic and geophysical record, and we suggest additional techniques in light of our strong‐crust versus weak‐crust framework. The diverse tectonic settings and inferred consequences of these lithospheric drips, if confirmed, would demand a shift in our understanding of continental geology to emphasize the role of vertical removal of continental lithosphere. Plain Language Summary: If part of the lithosphere (Earth's crust and the rigid upper part of the mantle) increases in density, it may become heavier than the underlying mantle and sink, or founder. Foundering results in the removal of blobs of lithosphere from overlying crust, a process called dripping. Dripping may have occurred in several locations across the globe, but the effects it is capable of producing are not well understood. We synthesize numerical models of dripping with studies of real‐world locations and compile available evidence to better understand the dripping process. We suggest that key observable effects are driven by the strength of the crust relative to the foundering lithosphere. In particular, when the crust is weak and able to flow in response to a lithospheric drip, complex patterns of deformation and sedimentation can result. For the 27 events that have been discussed to date, 9 have clear evidence for strong‐crust behavior, and 3 for a weak‐crust behavior. This framework will help researchers understand what lithospheric dripping looks like in geological and geophysical data, and we discuss avenues for further research on this topic. Key Points: Lithospheric dripping has been proposed for 27 locations throughout the globe and may be responsible for a wide range of observable effectsA synthesis of modeling studies suggests two distinct types of dripping depending on crustal strength relative to mantle lithosphereExisting data support the strong‐crust versus weak‐crust drip framework and suggest future research opportunities [ABSTRACT FROM AUTHOR]

Abstract Density instabilities in the lithosphere can founder gravitationally via viscous dripping and decoupling from overlying crust. The lithospheric dripping concept has been invoked across the globe, but the diversity of crustal effects, observable evidence, and tectonic settings involved in dripping remain underexplored. Here, we synthesize numerical and analogue modeling studies and geologic data from the literature, including all proposed lithospheric dripping events to‐date. We argue that two distinct styles of dripping can occur depending on crustal strength (relative to that of the mantle lithosphere). Near‐surface contraction and subsidence of strong crusts contrasts with near‐surface extension and uplift of weak crusts. We discuss these events in terms of tectonic setting, timing, size, and the main types of data associated with each event. We also find that lithospheric dripping is associated with a distinct suite of geological observations including sedimentological, structural, volcanic, and geophysical data, which can be used to distinguish strong crusts from weak crusts. We find 27 events for which lithospheric dripping is a key hypothesis, including 9 with clear evidence for strong‐crust dripping and 3 with clear evidence of weak‐crust dripping. We review emerging research methods have the potential to detect the signals of dripping in the geologic and geophysical record, and we suggest additional techniques in light of our strong‐crust versus weak‐crust framework. The diverse tectonic settings and inferred consequences of these lithospheric drips, if confirmed, would demand a shift in our understanding of continental geology to emphasize the role of vertical removal of continental lithosphere.

The physics of rock deformation in the lithosphere governs the formation of tectonic plates, which are characterized by strong, broad plate interiors, separated by weak, localized plate boundaries. The size of mineral grains in particular controls rock strength and grain reduction can lead to shear localization and weakening in the strong ductile portion of the lithosphere. Grain damage theory describes the competition between grain growth and grain size reduction as a result of deformation, and the effect of grain size evolution on the rheology of lithospheric rocks. The self‐weakening feedback predicted by grain damage theory can explain the formation of mylonites, typically found in deep ductile lithospheric shear zones, which are characteristic of localized tectonic plate boundaries. The amplification of damage is most effective when minerallic phases, like olivine and pyroxene, are well mixed on the grain scale. Grain mixing theory predicts two coexisting deformation states of unmixed materials undergoing slow strain rate, and well‐mixed materials with large strain rate; this is in agreement with recent laboratory experiments, and is analogous to Earth's plate‐like state. A new theory for the role of dislocations in grain size evolution resolves the rapid timescale of dynamic recrystallization. In particular, a toy model for the competition between normal grain growth and dynamic recrystallization predicts oscillations in grain size with periods comparable to earthquake cycles and postseismic recovery, thus connecting plate boundary formation processes to the human timescale. Key Points: Shear localization and weakening is imperative to the formation of tectonics plate boundariesGrain damage theory provides a framework for the microphysics of strain localization in the lithosphereThe newest developments of grain damage theory include grain scale mixing of different mineral phases and effect of intragranular defects [ABSTRACT FROM AUTHOR]

Permanent deformations in the lithosphere can occur in the brittle as well as in the ductile domain. For this reason, the inclusion of viscous creep and frictional plastic deformation is essential for geodynamic models. However, most currently available models of frictional plasticity are rate independent and therefore do not incorporate an internal length scale, which is an indispensible element for imposing a finite width of localized shear zones. Therefore, in computations of localization, either analytical or numerical, resulting shear zone widths tend to zero. In numerical computations, this manifests itself in a severe mesh sensitivity. Moreover, convergence of the global iterative procedure to solve the nonlinear processes is adversely affected, which negatively affects the reliability and the quality of predictions. The viscosity that is inherent in deformation processes in the lithosphere can, in principle, remedy this mesh sensitivity. However, elasto‐viscoplastic models that are commonly used in geodynamics assume a series arrangement of rheological elements (Maxwell‐type approach), which does not introduce an internal length scale. Here, we confirm that a different rheological arrangement that puts a damper in parallel to the plastic slider (Kelvin‐type approach) introduces an internal length scale. As a result, pressure and strain and strain rate profiles across the shear bands converge to finite values upon decreasing the grid spacing. We demonstrate that this holds for nonassociated plasticity with constant frictional properties and with material softening with respect to cohesion. Finally, the introduction of Kelvin‐type viscoplasticity also significantly improves the global convergence of nonlinear solvers. Key Points: We study shear banding using a Kelvin‐type elasto‐viscoplastic rheologyShear band thickness converges upon mesh refinementThis approach remedies mesh sensitivity of nonassociated plasticity and/or strain weakening [ABSTRACT FROM AUTHOR]

With the Late Cretaceous onset of Africa‐Iberia‐Europe convergence Central Europe experienced a pulse of intraplate shortening lasting some 15–20 Myr. This deformation event documents area‐wide deviatoric compression of Europe and has been interpreted as a far‐field response to Africa‐Iberia‐Europe convergence. However, the factors that governed the compression of Europe and conditioned the transient character of the deformation event have remained unclear. Based on mechanical considerations, numerical simulations, and geological reconstructions, we examine how the dynamics of intraplate deformation were governed by the formation of a convergent plate boundary fault between Iberia and Europe. During the Late Cretaceous, plate convergence was accommodated by the inversion of a young hyperextended rift system separating Iberia from Europe. Our analysis shows that the strength of the lithosphere beneath this rift was initially sufficient to transmit large compressive stresses far into Europe, though the lithosphere beneath the rift was thinned and thermally weakened. Continued convergence forced the formation of the plate boundary fault between Iberia and Europe. The fault evolved progressively and constituted a lithospheric‐scale structure at the southern margin of Europe that weakened rheologically. This development caused a decrease in mechanical coupling between Iberia and Europe and a reduction of compressional far field stresses, which eventually terminated intraplate deformation in Central Europe. Taken together, our findings suggest that the Late Cretaceous intraplate deformation event records a high force transient that relates to the earliest strength evolution of a lithospheric‐scale plate boundary fault. Key Points: Late Cretaceous Iberia‐Europe convergence caused the formation of a convergent plate boundary fault between the continentsThe rheological strength of the fault governed plate coupling and the transmission of compressive stress into EuropeInitially strong plate coupling drove deformation in Europe, which ceased after ~15–20 Myr due to a weakening of the fault [ABSTRACT FROM AUTHOR]

Earth's cratonic mantle lithosphere is distinguished by high seismic wave velocities that extend to depths greater than 200 km, but recent studies disagree on the magnitude and depth extent of the velocity gradient at their lower boundary. Here we analyze and model the frequency dependence of S p waves to constrain the lithosphere-asthenosphere velocity gradient at long-lived stations on cratons in North America, Africa, Australia, and Eurasia. Beneath 33 of 44 stations, negative velocity gradients at depths greater than 150 km are less than a 2-3% velocity drop distributed over more than 80 km. In these regions the base of the typical cratonic lithosphere is gradual enough to be explained by a thermal transition. Vertically sharper lithosphere-asthenosphere transitions are permitted beneath 11 stations, but these zones are spatially intermittent. These results demonstrate that lithosphere-asthenosphere viscosity contrasts and coupling fundamentally differ between cratons and younger continents. [ABSTRACT FROM AUTHOR]

We present a tectonic map of the Tauern Window and surrounding units (Eastern Alps, Austria), combined with a series of crustal-scale cross-sections parallel and perpendicular to the Alpine orogen. This compilation, largely based on literature data and completed by own investigations, reveals that the present-day structure of the Tauern Window is primarily characterized by a crustal-scale duplex, the Venediger Duplex (Venediger Nappe system), formed during the Oligocene, and overprinted by doming and lateral extrusion during the Miocene. This severe Miocene overprint was most probably triggered by the indentation of the Southalpine Units east of the Giudicarie Belt, initiating at 23-21 Ma and linked to a lithosphere-scale reorganization of the geometry of mantle slabs. A kinematic reconstruction shows that accretion of European lithosphere and oceanic domains to the Adriatic (Austroalpine) upper plate, accompanied by high-pressure overprint of some of the units of the Tauern Window, has a long history, starting in Turonian time (around 90 Ma) and culminating in Lutetian to Bartonian time (45-37 Ma). [ABSTRACT FROM AUTHOR]

Abstract: The coupling/decoupling between the lithosphere and asthenosphere has significant implications for understanding many important aspects of plate tectonics and geodynamics. To drive plate motion, mantle convection requires coupling at the lithosphere–asthenosphere (LA) interface. Meanwhile a low viscosity layer in the asthenosphere is indicative of possible LA decoupling. Here we present an analytical model of a stratified uppermost mantle structure disturbed by a long-wavelength perturbation (such as the body tide) to analyse the influence of LA viscosity contrast on the growth (or decay) rates of the perturbation. We show that the viscosity contrast of 8–10 orders of magnitude would allow a relative motion of the lithosphere over the asthenosphere due to the long-wavelength perturbations at the rate of about 10cmyr−1. These constrains on the viscosity contrast can allow to discriminate between the LA coupling and decoupling. The growing seismic and mineralogical evidences of a possible ultra low viscosity asthenospheric layer may be indicative of the LA decoupling and their relative motions due to long-wavelength perturbations, and a contribution of the tidal drag on the plate motion should not be neglected in the regions of high viscosity contrasts. [Copyright &y& Elsevier]

Abstract: Previous models of subduction (both analogue and numerical) have observed a number of distinct styles of subduction, each with particular subduction motions (partitioned between slab rollback and forward plate advance) and associated slab morphologies. We use 3-D numerical models to investigate subduction dynamics by varying the strength of slabs as well as the buoyancy, and propose a new classification based on these parameters. The slab strength is specified both through the ratio of viscosities between the subducting plate and upper mantle (η plate/η um) as well as the plate thickness, h plate. Only a very restrictive range of plates (“strong” plates with smaller buoyancy) tend to favor modes of subduction which are exclusively advancing. Plates which have greater negative buoyancy will eventually transition into a retreating style. We find that the flexural strength and the buoyancy determine the subduction style (as distinguished by a characteristic slab morphology), and control several subduction characteristics including the partitioning between slab rollback and plate advance, the trench curvature, and the slab''s radius of curvature. Plates that are 80–100km thick with η plate/η um ~100–300 are classified here as “weak” and are the only plates to exhibit slab geometry with several recumbent folds atop the more viscous lower mantle. This regime of weak plates with their associated slab morphologies (predominant folding) is argued to be most similar to slabs on Earth based on the presence of folded slab piles in Earth''s upper mantle (as interpreted from seismic tomography). [Copyright &y& Elsevier]

Abstract: Modelling subduction involves solving the dynamic interaction between a rigid (solid yet deformable) plate and the fluid (easily deformable) mantle. Previous approaches neglected the solid-like behavior of the lithosphere by only considering a purely fluid description. However, over the past 5 years, a more self-consistent description of a mechanically differentiated subducting plate has emerged. The key feature in this mechanical description is incorporation of a strong core which provides small resistance to plate bending at subduction zones while simultaneously providing adequate stretching resistance such that slab pull drives forward plate motion. Additionally, the accompanying numerical approaches for simulating large-scale lithospheric deformation processes coupled to the underlying viscous mantle flow, have been become available. Here we put forward three fundamentally different numerical strategies, each of which is capabable of treating the advection of mechanically distinct materials that describe the subducting plate. We demonstrate their robustness by calculating the numerically challenging problem of subduction of a 6000km wide slab at high-resolution in three-dimensions, the successfuly achievement of which only a few codes in the world can presently even attempt. In spite of the differences of the approaches, all three codes pass the simple qualitative test of developing an “S-bend” trench curvature previously observed in similar models. While reproducing this emergent feature validates that the lithosphere–mantle interaction has been correctly modelled, this is not a numerical benchmark in the traditional sense where the objective is for all codes to achieve exact agreement on a unique numerical solution. However, we do provide some quantitative comparisons such as trench and plate kinematics in addition to discussing the strength and weaknesses of the individual approaches. Consequently, we believe these developed algorithms can now be applied to study the parameters involved in the dynamics of subduction and offer a toolbox to be used by the entire geoscience community. [Copyright &y& Elsevier]

The numerical block-model of the lithosphere dynamics is used to simulate seismicity in Italy and its surroundings, based on the available structural and geodynamics information. The purpose of the study is to understand which are the tectonic processes that control the main features of the observed seismicity and the kinematics of the region. The influence of the rheology of the fault systems is studied as well. The model we use differs from other modeling approaches in that it simulates earthquakes and hence it possibly relates to seismicity and geodynamics. The model provides an effective capability to include the set of documented constraints supplied by widely available earthquake catalogs. This is done by means of the comparison of the GR relation, of the focal mechanisms and of the space distribution for observed and computed seismicity. The region is modeled as a system of perfectly rigid blocks, separated by infinitely thin fault planes, in viscoelastic interaction between themselves and with the underlying medium. The movement of the boundary blocks and of the underlying medium determines the motion of the blocks. The synthetic seismicity obtained with the defined block-model is similar to the observed one for the most seismically active areas. A linear frequency-magnitude (FM) relation (Gutenberg-Richter law) is obtained for synthetic earthquakes; the slope ( b-value) of the FM plot appears larger for the synthetic seismicity than for the observed one. Nevertheless, the b-value is essentially larger in northern and central Italy than that in southern Italy, both in the model and in the observations. The analysis of the source mechanisms of the synthetic earthquakes shows a good agreement with the observations. In the model normal faulting is typical for the Apennines, the eastern edge of Sicily and the Calabrian arc, while reverse faulting takes place at the northwestern boundary of the Adriatic Sea, in the southern Alps and along the eastern edge of the Adria, along the Dinarides. The model correctly reproduces the extension zone along the Apennines and the contraction zone along the northwestern boundary of the Adriatic Sea; the counter-clockwise rotation of the Adria is mimed. The resulting movements of the blocks are in overall agreement with GPS (Global Positioning System) observations. The results of the modeling experiments suggest that the main features of dynamics and seismicity in the central Mediterranean region cannot be satisfactorily explained as a consequence of Africa and Eurasia convergence only; the passive subduction in the Calabrian arc and the different rheology of faults are essential as well. [ABSTRACT FROM AUTHOR]

Abstract: We explore the impact of fluids migrating through a fault network on the dynamics of lithosphere, both on slow movements and seismicity. For that purpose fluids in the fault zones are incorporated into modelling of blocks-and-faults systems, which takes into account driving forces and the system''s geometry. Simulations have been performed for two-dimensional models: an idealised “brick wall” structure, and a coarse image of Sinai Subplate. Migrating fluids originating in different locations are considered, as well as fluids trapped in closed pockets. Basic features of the modelled and observed seismicity are in good accord, as shown by comparison with the earthquake catalog compiled by Geophysical Institute of Israel. [Copyright &y& Elsevier]

Abstract: The Carpathians–Pannonian Basin system provides a natural laboratory for analysing lithospheric to surface controls on tectonic topography development in a coupled source-to-sink environment. To link processes taking place at depth and at the surface, recent research focused on the interplay between basin evolution, active tectonics, topography evolution and intraplate folding mechanisms. Neotectonic processes control landscape development and natural hazards, in particular the seismicity, during the late-stage (Late Neogene–Quaternary) evolution of both the Carpathians–Pannonian Basin system and its interaction with the adjacent Dinarides and Balkans. The deep structure of the SE Carpathians exerts a strong control on the post-collisional evolution of the system. New constraints are available from seismic tomography, deep seismic reflection and refraction profiling and detailed studies of the Vreancea seismicity. Inherited orogenic fabric and structure of the active Black Sea sink has a strong influence on the localisation of the Neogene sediment pathways. A close relationship has been established between the timing and mechanisms of stress changes in the Pannonian and Transylvania basins and structural episodes in the surrounding thrust belts, pointing to an intrinsic mechanical coupling with these basins, the orogen and its foredeep. Basin inversion taking place during the Pliocene–Quaternary times in the entire Carpathians–Pannonian system is related to changes in the regional stress field leading to differential vertical movements associated with a laterally variable folding mechanism active in the entire system. Short, crustal folding patterns alternate with lithospheric wavelengths in the SE Carpathians foreland, East and South Carpathians, Transylvania and Pannonian basins. The lateral variability is the result of a marked contrast in rheology between these areas, directly related to the crustal configuration, thermal properties and late-stage collision kinematics with the Carpathians foreland. Lateral variations in the properties of the downgoing plates largely control the collision mode in the Carpathians and the post-collisional evolution of the entire system. [Copyright &y& Elsevier]

Recent research in the Himalayan fold-thrust belt provides two new sets of observations that are crucial to understanding the evolution of the Himalayan-Tibetan orogenic system. First, U-Pb zircon ages and Sm-Nd isotopic studies demonstrate that (1) Greater Himalayan medium- to high-grade metasedimentary rocks are much younger than true Indian cratonic basement; and (2) these rocks were tectonically mobilized and consolidated with the northern margin of Gondwana during early Paleozoic orogenic activity. These observations require that Greater Himalayan rocks be treated as supracrustal material in restorations of the Himalayan fold-thrust belt, rather than as Indian cratonic basement. In turn, this implies the existence of Greater Himalayan lower crust that is not exposed anywhere in the fold-thrust belt. Second, a regional compilation of shortening estimates along the Himalayan arc from Pakistan to Sikkim reveals that (1) total minimum shortening in the fold-thrust belt is up to ∼670 km; (2) total shortening is greatest in western Nepal and northern India, near the apex of the Himalayan salient; and (3) the amount of Himalayan shortening is equal to the present width of the Tibetan Plateau measured in an arc-normal direction north of the Indus-Yalu suture zone. This information suggests that a slab of Greater Indian lower crust (composed of both Indian cratonic lower crust and Greater Himalayan lower crust) with a north-south length of ∼700 km may have been inserted beneath the Tibetan crust during the Cenozoic orogeny. We present a modified version of the crustal underthrusting model for Himalayan-Tibetan orogenesis that integrates surface geological data, recent results of mantle tomographic studies, and broadband seismic studies of the crust and upper mantle beneath the Tibetan Plateau. Previous studies have shown that incremental Mesozoic and early Cenozoic shortening had probably thickened Tibetan crust to ∼45-55 km before the onset of the main Cenozoic orogenic event. Thus, the insertion of a slab of Greater Indian lower crust with maximum thickness of ∼20 km (tapering northward) could explain the Cenozoic uplift of the Tibetan Plateau. The need for Tibetan crust to stretch laterally as the Greater Indian lower crust was inserted may explain the widespread east-west extension in the southern half of the Plateau. Our reconstruction of the Himalayan fold-thrust belt suggests that Indian cratonic lower crust, of presumed mafic composition and high strength, should extend approximately halfway across the Tibetan Plateau, to the Banggong suture. From there northward, we predict that the Tibetan Plateau is underlain by more felsic, and therefore weaker, lower crust of Greater Himalayan affinity. Two slab break-off events are predicted by the model: the first involved Neotethyan oceanic lithosphere that foundered ∼45-35 Ma, and the second consisted of Greater Indian lithosphere (most likely composed of Greater Himalayan material) that delaminated and foundered ∼20-10 Ma. Asthenospheric upwelling associated with the break-off events may explain patterns of Cenozoic volcanism on the Tibetan Plateau. Although the model predicts a northward migrating topographic front due solely to insertion of Greater Indian lower crust, the actual uplift history of the Plateau was complicated by early-middle Tertiary shortening of Tibetan crust. [ABSTRACT FROM AUTHOR]

Glacial Isostatic Adjustment (GIA), or postglacial rebound refers to the crustal response to glacial loading and unloading processes. In this investigation, we run numerical simulations using different rheological parameters and ice loading histories to obtain models of the glacial isostatic response for the Grand Banks of Newfoundland. The objective is to assess in general the potential impact of GIA on hydrocarbon reservoirs and trapping structures in terms of tilting, deformation, fault activity or geochemical implications on the trapped fluids. Comparisons may be drawn to related studies, including analogous impacts on reservoirs in the Barents Sea, as well as validation of GIA model predictions of vertical crustal motion using GNSS stations, levelling networks and relative sea level (RSL) observations at numerous sites across eastern Canada. By running a series of GIA models, a range of vertical motion rates are output through time to determine displacement amounts, and calculations are performed on these outputs to disseminate other valuable data attributes such as the displacement gradient and differences in time and space. In general, the vertical motion rate is seen to change drastically over time for certain points, as the lag in response of regions near the ice periphery leads to a distinct pattern of uplift and subsidence. The Grand Banks generally experienced between 57 m of subsidence to 34 m of uplift since the last glacial maximum, depending on the specific location and the GIA model parameters. At the reservoir scale, model results along a 10 km baseline show up to −1.0–1.5 m of differential vertical displacement, which could have led to reservoir tilting or even hydrocarbon migration. As a result of this study, it is clear that there are implications of GIA on hydrocarbon reservoirs since the Last Glacial Maximum, and these effects are ongoing. [ABSTRACT FROM AUTHOR]