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The constantly improving resolution of geophysical data, seismic tomography and seismicity in particular, shows that the lithosphere does not subduct as a slab of uniform thickness but is rather thinned in the upper mantle and thickened around the transition zone between the upper and lower mantle. This observation has traditionally been interpreted as evidence for the buckling and piling of slabs at the boundary between the upper and lower mantle, where a strong contrast in viscosity may exist and cause resistance to the penetration of slabs into the lower mantle. The distribution and character of seismicity reveal, however, that slabs undergo vertical extension in the upper mantle and compression near the transition zone. In this paper, we demonstrate that during the subduction process, the shape of low viscosity slabs (1 to 100 times more viscous than the surrounding mantle) evolves toward an inverted plume shape that we coin jellyfish. Results of a 3D numerical model show that the leading tip of slabs deform toward a rounded head skirted by lateral tentacles that emerge from the sides of the jellyfish head. The head is linked to the body of the subducting slab by a thin tail. A complete parametric study reveals that subducting slabs may achieve a variety of shapes, in good agreement with the diversity of natural slab shapes evidenced by seismic tomography. Our work also suggests that the slab to mantle viscosity ratio in the Earth is most likely to be lower than 100. However, the sensitivity of slab shapes to upper and lower mantle viscosities and densities, which remain poorly constrained by independent evidence, precludes any systematic deciphering of the observations.

International audience; Glaciers and rivers control the shape of the high relief topography of mountain ranges. However, their relative contribution in response to climatic oscillations and tectonic forcing and whether landscapes can reach equilibrium conditions during the Quaternary are still unclear. Here we introduce a new thermochronometer of exceptionally low closure temperature (ca. 30-35 °C) based on Optically Stimulated Luminescence (OSL) dating and illustrate how it may be used to measure relief evolution and exhumation rates within the last glacial cycle in the Southern Alps of New Zealand, one of the most tectonically active orogens and an area that has experienced rapid, high magnitude climate changes. We find that exhumation rates have remained steady over the last glacial cycle and match rates observed at a million year timescale. This suggests that, despite an extreme exhumation rate of the order of 800 m in 100 ka, and the fact that in the last ca. 11-18 ka most hillslope sides have changed from U to V-shape valleys and have been dissected by debris-flows, landslides and rock avalanches, the mean exhumation rates have remained nearly constant. This may imply that tectonics, not climate, has a primary control on the rates of exhumation in tectonically active and wet mountain belts. On the contrary, tectonically active mountain ranges might not attain equilibrium on similar timescales in weathering and/or transport limited landscapes as, for example, in arid regions.

International audience; Thermochronologic data collected along age-elevation profiles are commonly interpreted as recording temporally variant but spatially constant exhumation rates. However, thermochronologic age-elevation relationships are known to be perturbed by topographic effects and potential changes in relief, which are neglected in the inherently 1-D interpretation commonly applied. Such data thus potentially record both the denudation and relief history of the sampled region but extracting this information is challenging. In a companion paper, we develop a methodology for rigorously interpreting thermochronologic age-elevation profiles in terms of exhumation rates and relief development through time, and to independently quantify the resolution of these constraints. Here we test this approach using a thermochronological dataset consisting of apatite and zircon fission-track and (U-Th)/He data, collected at La Meije Peak in the Pelvoux-Ecrins massif (French Western Alps). Our data and models suggest a three-phase exhumation history in the Pelvoux-Ecrins massif, including a pulse of rapid exhumation at ˜ 6-5.5 Ma, preceded and followed by more moderate rates of denudation in the order of 0.3-0.4 km Myr‑ 1. This rapid exhumation event appears to occur coevally in other external crystalline massifs in the Alps but is not detected by qualitative inspection of the age-elevation relationships. Both our synthetic results and inversion of the La Meije data strongly suggest that apatite fission-track age-elevation relationships alone cannot resolve both denudation and relief histories independently and that multiple thermochronometers are required. Combining apatite fission-track and (U-Th)/He ages and, particularly, including fission-track-length data greatly improves the resolution of the inferred exhumation histories. Although denudation rates through time and the timing of rate changes are generally well resolved, our data have insufficient resolution to satisfactorily constrain the relief history. Synthetic results reported in the companion paper suggest that the reason for this limitation is that relief increase through valley carving has been insufficient with respect to the regional denudation rates to be unambiguously extracted from the data.

International audience; We present the results of three-dimensional numerical experiments designed to study the response of a layer of crustal material subjected to convergence through an imposed basal velocity discontinuity and to surface processes (erosion/sedimentation). We focus on the three-dimensional response of the system arising from the finite width of the imposed velocity discontinuity. In particular, we describe the complex structures that develop around the wedge and their interactions with the loading/unloading produced by the surface processes. We show that the pro- and retro-shear zones that develop in a doubly-vergent two-dimensional wedge curve around the end of the velocity line-discontinuity to merge into the strike-slip structure that naturally develop, i.e. as a consequence of the imposed boundary conditions, along the edge of the wedge. Along the retro-shear zone the stress orientation rotates along a vertical axis, which implies that the retro-shear zone is a pure thrust along all of its curved length, whereas, along the pro-shear zone stresses rotate along a horizontal axis, which, in turn, implies that the pro-shear zone progressively evolves towards an oblique thrust in its curved section. Furthermore, the outward motion (i.e. perpendicular to the direction of imposed shortening) along the curved section of the retro-shear zone is accommodated by oblique extension along a secondary, kinked structure antithetic to the retro-shear zone. We also show the complex evolution of the wedge when ductile flow and ductile strain softening is activated by increasing the imposed basal temperature. In this situation, the wedge is broader as structures develop at finite distances on either side of the line-discontinuity and its dynamics resembles more that of a ‘vise-like' orogen. At the surface, a flat plateau forms that accumulates sediment from the surrounding actively deforming mountain ranges until a channel breaks through one of the sides and flushes the inward-draining basin of its sedimentary content. The complex numerical models provide a detailed insight into the geometry and complex three-dimensional structures within and at the margins of an orogen, and how they can be affected by erosional processes at the surface.

International audience; We determine to what extent low-temperature thermochronology data, in particular from age-elevation profiles, provide independent and quantitative estimates on denudation rates and relief development. Thermochronological age-elevation profiles have been widely used to infer exhumation histories. However, their interpretation has remained inherently one-dimensional, neglecting potential effects of lateral offsets between samples. Furthermore, the potential effects of transient topography on crustal isotherms and consequently on thermochronological data have not yet been addressed in detail. We investigate this problem with the aim of deriving independent estimates of both denudation rates and relief history from low-temperature thermochronometers, measuring the relative uncertainties on these parameters and finally constraining the timing of potential variations in denudation rate and/or relief development. We adopt a non-linear inversion method combining the three-dimensional thermal-kinematic model Pecube, which predicts thermal histories and thermochronological ages from an input denudation and relief history, with an inversion scheme based on the Neighbourhood Algorithm. We use synthetic data predicted from imposed denudation and relief histories and quantitatively assess the resolution of thermochronological data collected along an age-elevation profile. Our results show that apatite fission-track (AFT) ages alone do not provide sufficient quantitative information to independently constrain denudation and relief histories. Multiple thermochronometers (apatite (U-Th)/He (AHe) ages and/or track-length measurements combined with AFT ages) are generally successful in constraining denudation rates and timing of rate changes, the optimum combination of thermochronometers varying with the input scenario (relief change or varying denudation rates). However, relief changes can only be quantified and precisely constrained from thermochronological age-elevation profiles if the rate of relief growth is at least 2-3 times higher than the background denudation rate. This limited resolution is due to the depth of the closure isotherm (between ˜ 70 and 110 °C) for the AFT and AHe systems, which only partly record topographic change. New thermochronometers (such as 4He/3He or OSL) that are sensitive to lower temperatures may be the key for resolving this issue.

[1] Our 3D modelling study shows that the presence of lithospheric plates around a subducting plate has a significant influence on subduction dynamics, in particular on trench retreat rate, slab dip, and lateral shortening of the subducting plate. Neighbouring plates prevent unrealistic plate behaviour with no need for complex rheologies. Because, at the Earth's surface, plates form a continuous shell, they should not be neglected.

International audience; Detrital thermochronometer data collected from modern rivers or sedimentary basins have the potential to record the evolution of topographic relief, fault kinematics and erosion within drainage basins. However, few studies have addressed the effects of these different factors on detrital thermochronometer age distributions. Here we use transient 3-D thermokinematic and landform evolution models to simulate the effects of time-varying topography and fault kinematics on the thermal field through which detrital samples cool. Cooling-rate-dependent apatite (U-Th)/He (AHe), zircon fission track and muscovite 40Ar/39Ar (MAr) grain age distributions are predicted for samples collected from modern river and basin sediments. These distributions are interpreted to determine the sensitivity of different thermochronometer systems to denudation and deformation histories in drainage basins of varying size. We find that detrital thermochronometers in rapidly eroding regions have a strong sensitivity to the kinematics of exhumation, but lack sensitivity to changes in topographic relief under most conditions. In addition, we find potential for significant overestimation of denudation rates derived from conventional 1-D age-elevation relationships as compared to 3-D model-prescribed rates. At rapid (~2.5 mm/y) model-prescribed denudation rates, 1-D techniques predict rates that are ~5 and ~2 times greater than the 3-D model rate for the AHe and MAr systems, respectively. In models that explore age distributions in foreland basin sediments, we confirm that the lag time concept is a useful and reliable means for identifying denudation rate changes as no significant change in lag time occurs for changing topographic relief scenarios.

International audience; The curvature of a subducting lithosphere is chiefly controlled by the viscosity ratio between the slab and the surrounding mantle. On the basis of a semi-analytical flow model, we explore the rheological dependence of the geometrical response of a viscous slab subjected to toroidal mantle flow. Mantle flow is excited by slab retreat at a prescribed mean velocity and is iteratively solved for by using a stream function approach, in turn providing the stresses that bend the slab. Comparison between model predictions and geophysical observations of slab curvature gives an average slab-to-mantle viscosity ratio of 45.

The South African plateau is bordered by passive margin basins preserving the terrigeneous sediment produced during onshore erosion. As such, these basins potentially provide a record of the variation in onshore elevation and relief over time. Here we bring new constraints on the uplift and erosion of the Southern African plateau over the last 150 Ma from the perspective of the stratigraphic architecture of these basins. We review published data to quantify the terrigeneous supply eroded in the drainage area and preserved in the basins. The novel aspect of our approach is the integration of the evolution of the whole domain in sedimentation (i.e. not only the platform) as well as the onshore eroding region. Along the South African and Namibian Atlantic margins, we determined the long-term signal of sedimentary supply (at the 10 Ma scale) from 3D mass balance calculations comparing sedimentary volumes deduced from offshore isopach maps (with a particular attention to associated uncertainties) on one hand and denudation volumes deduced from thermochronology data on the other. We show that, in this case, the volumes of denudation and of sediments preserved in the basin are consistent both in total and incremental amount. The latter is therefore a reliable estimation of the denudation in the associated continental domain, subject to certain assumptions such as the drainage area over time. The long-term signal of sedimentary supply of the South African and Namibian Atlantic margins shows that the major part of the denudation occurred during the post-rift Lower Cretaceous and the Upper Cretaceous and subsequently decreased. This is not the expected behavior for the simple relaxation of topography acquired during rifting that would show a progressive decrease of the sediment supply over time. This suggests a significant rejuvenation of relief during the Upper Cretaceous, 50 Ma after the rifting event. If erosion is directly linked to elevation or relief variation, this implies 2 generations, the first before break-up (i.e. before 130 Ma; presumably during rifting) and the second during the Upper Cretaceous.

This paper investigates a simple model for the evolution of the central Australian (Amadeus, Officer and Ngalia) basins and the adjacent Canning and Bonaparte Gulf basins at the time of the Alice S...

The goal of this project is to quantify the growth of long wavelength (x1000 km) topography over the last 250 My at the scale of a continent - Africa - and to understand (1) their relationship with the underlying mantle dynamics over such a time period and (2) their consequence over some Earth surface processes. Most studies of past topography reconstruction have focused on orogenic areas. Few efforts have been devoted to characterizing the more subtle long wavelength topography, such as the doming or plateau uplift of continental areas at the 1000 km wavelength, with a paleoelevation of few hundreds of meters to a maximum of 1000-2000m. A direct inversion of the geological data into estimates of paleotopography is difficult. Quantification of past topographies of a continent requires coupling of geological data with a sediment production (erosion) and transport numerical model. The quantification of the Meso-Cenozoic topographies of the African continent is based on uplift (mean time interval 10 my) and paleoprecipitation maps (input of the model) and siliciclastic sedimentary fluxes and thermochronological data. One of the advance of this project is to draw new-style paleogeographic reconstructions focussed on the continental environments yielding the geometry of paleocatchments, the lacustrine baselevel, the type and the flow direction of the fluvial systems? All those data are registered in database and GIS (ArcGis). Uncertainties are quantified. The uplift maps, in a first step semi-quantitative, are based on the paleogeographical changes and on synthesis of the tectonically induced-unconformities both onland and offhore (seismic) and their consequences (incised valleys, forced-regression wedges, changes of weathering types?). The paleoprecipitation maps are product by coupling climatic numerical models with a geological database (GIS) including all the climate recorders (lithology, type of clays, paleosoils; woods, pollens?). The measure of the siliciclastic sediment flux is based on a geometrical, chronostratigraphical and lithological synthesis of the peri-African (margins) and intra-African (SAG) basins. The thermochronological database is a compilation of all the data available in Africa, plus some new field collections. The new numerical model of sediment production and transport at the continental scale, TOPOSED, will form the basis of the quantitative inversion of the geological data to yield estimates of past topography. Its original aspect consists in investigating separately erosion and transport processes, and in assuming that both are controlled by slope and discharge. Studied time interval: Triassic (Induan, Ladinian, Norian), Jurassic (Sinemurian, Bajocian, Late Kimmeridgian), Cretaceous (Valanginian, Barremian, Middle Aptian, Lower to Middle Albian, Late Cenomanian, Late Coniacian-Early Santonian, Maastrichtian), Paleogene (Thanetian, Lutetian, Chattian), Neogene (Early Miocene, Early Pliocene).

International audience; We present a new finite element code for the solution of the Stokes and energy (or heat transport) equationsthat has been purposely designed to address crustal-scale to mantle-scale flow problems in three dimensions. Although it is based on an Eulerian description of deformation and flow, the code, which we named DOUAR ('Earth' in Breton language), has the ability to track interfaces and, in particular, the free surface, by using a dual representation based on a set of particles placed on the interface and the computation of a level set function on the nodes of the finite element grid, thus ensuring accuracy and efficiency.The code also makes use of a newmethod to compute the dynamic Delaunay triangulation connecting the particles based on non-Euclidian, curvilinear measure of distance, ensuring that the density of particles remains uniform and/or dynamically adapted to the curvature of the interface. The finite element discretization is based on a non-uniform, yet regular octree division of space within a unit cube that allows efficient adaptation of the finite element discretization, i.e. in regions of strong velocity gradient or high interface curvature. The finite elements are cubes (the leaves of the octree) in which a q1­p0 interpolation scheme is used. Nodal incompatibilities across faces separating elements of differing size are dealt with by introducing linear constraints among nodal degrees of freedom. Discontinuities in material properties across the interfaces are accommodated by the use of a novel method (which we called divFEM) to integrate the finite element equations in which the elemental volume is divided by a local octree to an appropriate depth (resolution).Avariety of rheologies have beenimplemented including linear, non-linear and thermally activated creep and brittle (or plastic) frictional deformation. A simple smoothing operator has been defined to avoid checkerboard oscillations in pressure that tend to develop when using a highly irregular octree discretization and the tri-linear (or q1­p0) finite element. A three-dimensional cloud of particles is used to track material properties that depend on the integrated history of deformation (the integrated strain, for example); its density is variable and dynamically adapted to the computed flow. The large system of algebraic equations that results fromthe finite element discretization and linearization of the basic partial differential equations is solved using a multi-frontal massively parallel direct solver that can efficiently factorize poorly conditioned systems resulting from the highly non-linear rheology and the presence of the free surface. The code is almost entirely parallelized.We present example results including the onset of a Rayleigh­Taylor instability, the indentation of a rigid-plastic material and the formation of a fold beneath a free eroding surface, that demonstrate the accuracy, efficiency and appropriateness of the new code to solve complex geodynamical problems in three dimensions.

International audience; In recent years, much has been done to develop numerical tools to study the three-dimensional nature of the Earth's lithosphere deformation. DOUAR is one of them: it is a new ALE Finite Element code that is based on an adaptive grid, a key feature in the capture of localized deformation. In order to illustrate this, various simulations of punch experiments have been performed on rigid plastic materials with von Mises and Drucker-Prager type of rheologies. We present the grid refinement algorithm based on strain rate measurements and rederive the plane strain punch analytical solution which allows us to test the accuracy of our results. Various 3-D strip punches experiments with different aspect ratios show DOUAR's ability to capture complex fault patterns. We also discuss the degree to which the incompressibility and rigid plasticity constraints are satisfied. Finally, we show the results of a crustal-scale deformation experiment demonstrating the potential of the octree-based mesh refinement algorithm to solve complex three-dimensional geodynamical problems with great efficiency and accuracy.

International audience; We study the recent dynamics of the central Nepal Himalaya, focusing on possible reactivation of the footwall of the Main Central thrust, which is marked by an abrupt topographic transition. Different tectonic mechanisms, such as overthrusting of a major crustal ramp, underplating, or out-of-sequence thrusting, have been suggested to explain the morphology and exhumation patterns in this area. We present 25 new apatite fission-track ages collected along a north-south transect in central Nepal, as well as two age-elevation profiles. Ages are consistently younger than 3 Ma old in the Main Central thrust zone and increase continuously to 4-6 Ma old in the south. No jump in apatite fission-track ages is observed across the topographic transition. Apparent exhumation rates from age-elevation relationships vary from 0.46 + 0.13/-0.09 km/Ma in the Palung granite south of Kathmandu to 4.4 + 4.8/-1.5 km/Ma in the Main Central thrust zone; the latter rate is probably overestimated by a factor of two due to topographic effects. As shown by a new numerical model, these strongly varying exhumation rates can be explained by overthrusting of a crustal ramp, which exerts a primary control on age patterns, and do not require out-of-sequence reactivation of thrusts in the Main Central thrust zone.

International audience; A new version of a landscape evolution model that includes the evolution of an ice cap at a 103 to 105 year timescale and its associated erosion patterns is presented and applied to the Southern Alps of New Zealand. Modeling of the ice cap evolution is performed on a higher-resolution grid (i.e., 100 m) than previously (Braun et al., 1998). It predicts which parts of the landscape are, and have been, affected by glacial erosion. The model results highlight the complexity of the erosion patterns induced by ice caps and glaciers. Glacial erosion in a tectonically active area is, as suggested by the model, not uniform across the mountain range. Furthermore, high rock uplift rates, heavy precipitation, and climatic oscillations constantly interact. The feedback mechanisms are such that they render the landform very dynamic and transient. However, under conditions of reduced rock uplift rate and precipitation, the landform becomes more stable at the timescale of the glacial cycle. Finally, the modeling results favor a tectonic model in the Southern Alps in which the maximum rock uplift is offset from the Alpine Fault.

[1] Temperature-time histories of rocks are often used to constrain the kinematics of tectonic events, the evolution of landforms, erosion rates, and/or amount of faulting in tectonically active areas. However, interpretations based on thermal histories are not always straightforward as they rely on several interdependent mechanisms such as heat conduction, heat advection, or the presence of transient topography that must be taken into account. Using a three-dimensional finite element code recently developed by one of the authors, we have calculated temperature-time histories to interpret an existing thermochronological data set (K-Ar and FT) complemented by new low-T thermochronometer data ((U-Th)/He and FT) from the Southern Alps of New Zealand. Combined with inversion methods (Genetic Algorithm and Neighbourhood Algorithm), the model is used to derive from the data information on the tectonomorphic development of the orogen during the Pliocene and Pleistocene epochs. Assuming a quasi-geomorphic steady state, we can constrain the rate of tectonic horizontal advection and vertical uplift as well as the geometry of the main structural boundary, i.e., the Alpine Fault. We can also explain the along-strike geometry of the metamorphic isograds and thermochrons in relationship to surface topography. Furthermore, we show that if one assumes that the landscape has not been horizontally transported by tectonic movement, the relief on the west coast of the Southern Alps has increased. This relief increase could have been initiated at any time between 1.5 Ma and 100 ka. Any relief reduction during this period is ruled out by our modeling. Alternatively, if the landscape is advected horizontally in the direction normal to the trace of the Alpine Fault, a relief increase is not required to explain the thermochronological data.

International audience; (U­Th)/He ages reflect the combined effects of He (á particles) loss due to diffusion and He ingrowth due to radioactive decay of U and Th series. Furthermore, the á particles are emitted with sufficient kinetic energy that they can travel, in theory, up to 20 ìm and as a result, á particles may be ejected beyond the crystal edges. To circumvent this problem a correction factor must be applied, which is essentially based on the geometry of the crystals [Farley, K. A., Wolf, R., and Silver, L. (1996). The effect of long alpha-stopping distances on (U­Th)/He dates. Geochimica et Cosmochimica Acta, 60:4223­4229]. This strongly limits the application of the technique to crystals of appropriate geometries. We present here a method to compute the effects of á-ejection for (U­Th)/He dating by taking into account the 3D morphology of individual crystals determined with micro-X-ray tomography. We also develop a model which solves the diffusion equation for the crystals that have been imaged. We then couple this model with an inversion algorithm to extract the range of thermal histories that the rocks may have experienced. This technique is applied to detrital samples from rocks collected in the Southern Alps of New Zealand, a region of high exhumation rate.

Cytogenetic analysis is invaluable for the detection of chromosome abnormalities in tumor samples and is the "gold standard" technique (unique in providing a complete overview of the chromosome complement). Cytogenetic studies of lymph node specimens (LN) can be challenging due to progressively smaller biopsies being procured, low viability, and low proliferative rates. Typically, the initial laboratory evaluation of LN includes flow cytometry and/or immunohistochemistry. Due to overlapping immunophenotypic and morphologic features of some lymphomas, these studies can be insufficient to properly classify a lymphoid neoplasm. Interphase FISH is the test most frequently utilized for LN genetic evaluation. Although FISH has higher sensitivity than conventional cytogenetics, there is vast literature on the existence of cytogenetic abnormalities that are not targeted by the FISH probe(s) used in most laboratories. This is predominantly true for CLL/SLL, but it is also seen in other lymphomas, particularly those characterized by variant translocations involving closely related genes, such as mantle cell lymphoma with alternate translocations involving the CCND2 or CCND3 genes, or lymphomas carrying MYC rearrangements where the partner is not IGH (translocation partners other than Ig genes might merit less aggressive therapy). To achieve the same information obtained from an abnormal karyotype, it is usually necessary to perform multiple FISH tests with significantly increased costs. Genomic microarray and sequencing also have limitations. Microarray can only detect DNA unbalances (missing the balanced translocations that characterize most lymphomas). These whole genomic tests cannot detect multiple related clones indicative of clonal evolution, or unrelated clonal populations indicative of distinct lymphoid neoplasms in the same specimen. Successful cytogenetics offers the best visual representation of the whole chromosome complement and often yields information making it unnecessary to perform additional genetic tests. It should be noted that alternative genetic tests are extremely useful for cases with normal chromosome results or those that lack metaphase cells for analysis, as well as those with cytogenetically cryptic rearrangements or mutations. Recent studies indicate that complex karyotypes in lymphomas are, in general, indicative of transformation and/or worse prognosis. In the present study, for example, several follicular lymphoma cases displayed other abnormalities in addition to the typical t(14;18), some of which are known to be associated with transformation, i.e., deletions 1p, 6q, and 10q. We present our experience with 362 LN received over a 15 month period during 2014 and 2015. See Table below. Through correlation with all diagnostic test results from our laboratory, we demonstrate the unique value of cytogenetic evaluation of lymphoid tissues, optimizing diagnostic/prognostic assessment and, thereby, improving patient management/therapeutic decisions, while achieving cost reduction. Table. A) Summary of cases and subdivision based on successful cytogenetics and normal or abnormal flow/morphology versus normal or abnormal cytogenetics; B) Detailed information on the number of the various lymphoid neoplasms included in our study. Total Cases: 362 No metaphases: 67 (19%) With metaphases: 295 (81%) Normal flow/morphology and normal cytogenetics 74 (25%) Abnormal flow and/or morphology 221 (75%) Normal cytogenetics: 59 (27%) Abnormal Cytogenetics: 162 (73%) Table. Final Diagnosis (Abnormal cytogenetic cases) # cases Sex (M/F) # FISH FISH Abnormal/normal FL 56 25/31 43 43/0 SLL/CLL 32 20/12 21 20/1 HGL 14 7/7 0 0 TCL 14 7/7 5 3/2 MZBCL 13 8/5 8 5/3 DH/THL 10 6/4 10 10/0 DLBCL 8 4/4 8 7/1 MCL 7 4/3 5 4/1 CD30+ 2 0/2 2 1/1 NGCL 2 0/2 2 1/1 BL 1 1/0 1 1/0 LPL 1 1/0 0 0 B-ALL/LBL 1 0/1 1 1/0 HL 1 1/0 1 1/0 Totals 162 84/78 107 (66%) 97/10 Abbreviations: FL, follicular lymphoma; SLL/CLL, small lymphocytic lymphoma/chronic lymphocytic leukemia; HGL, high-grade lymphoma; TCL, T-cell lymphoma; MZBCL, marginal zone B-cell lymphoma; DH/THL, double hit/triple-hit lymphoma; DLBCL, diffuse large B-cell lymphoma; MCL, mantle cell lymphoma,; CD30+, CD30-positive large B-cell lymphoma; NGCL, non-germinal center lymphoma; BL, Burkitt lymphoma; LPL, lymphoplasmacytic lymphoma; B-ALL/LBL, B-cell acute lymphoblastic leukemia/lymphoblastic lymphoma; HL, Hodgkin lymphoma. Disclosures No relevant conflicts of interest to declare.

This chapter investigates the effect of isostatic rebound caused by surface erosion on the distribution of thermochronological ages at the surface of the Earth. We demonstrate that age–elevation relationships contain information on the nature of this isostatic response, i.e. on the degree of flexural compensation, and can, in effect, be used to provide constraints on the effective elastic thickness of the continental lithosphere. Local isostasy The post-orogenic phase of most mountain belts is characterised by a gradual erosion of the topography created during the active tectonic phase. This erosion results in unloading of the underlying lithosphere and consequent isostatic adjustment. The principle of isostasy assumes that there is a region beneath the lithosphere (the compensation depth ) where rocks are so weak that they cannot sustain any horizontal stress gradient over geological times, and hence the region adjusts to imposed loads by deformation. This implies that, at isostatic equilibrium, the weight of adjacent lithospheric columns must be equal. Erosion of surface topography results in a local reduction of the weight of the underlying lithospheric column and must therefore be compensated by vertical uplift. As shown in Figure 11.1, surface erosion by an amount E 0 (panel (b)) of a reference lithospheric column (panel (a)) of crustal thickness h c and total thickness h c + L results in an isostatic surface uplift by an amount u (panel (c)) such that the weights of the two columns ((a) and (c)) down to the compensation depth h c + L are identical.

In our quest to extract information on exhumation from thermochronological data, we now turn our attention to the effects that exhumation itself, i.e. the advection of rocks towards the Earth's surface, may have on the temperature structure of the crust. It is important to realise that the process that we are trying to quantify, namely rock exhumation, is strongly non-linear: it perturbs the system that we propose to use to measure it, i.e. the temperature history of the rock. Steady-state solution We first provide a means of determining the perturbation caused by advection under the assumption of steady-state exhumation, i.e. for situations in which rock uplift is balanced by erosion over a long period of time. Although this is an idealised scenario, it is worth considering, in order to assess the magnitude of the perturbation and the conditions under which it is likely to be significant. Furthermore, thermal steady state is not an unlikely scenario when considered on the scale of an entire, mature orogen, such as in the Southern Alps of New Zealand or in the Taiwan orogen (Willett and Brandon, 2002). Uplift and exhumation As already mentioned in Section 1.2, it is very important always to keep in mind that the cooling that is documented by thermochronology during exhumation is related to the advection of rocks towards the cold upper surface of the Earth.

Numerical models are used to help constrain empirical parameterizations of soil production and transport mechanisms on soil-mantled hillslopes. The neighbourhood algorithm is used to invert soil thickness versus surface curvature data to provide not only more rigorous estimates of model parameter values but determine which of the model parameters are constrained by cosmogenic exposure ages (Heimsath et al., 2000). We show that linear and depth-dependent creep constants can be constrained by simple geomorphometric measurements, such as the distribution of soil thickness on the landform and its relationship to surface curvature. We also show that this unique data set cannot be used on its own to constrain the parameterization of overland flow, another transport mechanism that is thought to play an important role on soil-mantled hillslopes, or to determine if a soil distribution has reached local steady state. We also demonstrate that, to explain the data, soil production must be a function of soil thickness. These conclusions have important implications for our understanding of landscape evolution on medium to long time scales.

Thermochronology, the study of the thermal history of rocks, enables us to quantify the nature and timing of tectonic processes. First published in 2006, Quantitative Thermochronology is a robust review of isotopic ages, and presents a range of numerical modeling techniques to allow the physical implications of isotopic age data to be explored. The authors provide analytical, semi-analytical and numerical solutions to the heat transfer equation in a range of tectonic settings and under varying boundary conditions. They then illustrate their modeling approach built around a large number of case studies. The benefits of different thermochronological techniques are also described. Computer programs on an accompanying website at www.cambridge.org/9781107407152 are introduced through the text and provide a means of solving the heat transport equation in the deforming Earth to predict the ages of rocks and compare them directly to geological and geochronological data. Several short tutorials, with hints and solutions, are also included.

It has been postulated that a steady state between erosional and tectonic processes may develop in continental collision. However, it is not clear whether steady state conditions can be reached for all components of the landscape. Here we show, using landscape evolution models and field evidence, that a true geomorphic steady state may never be reached in the Southern Alps of New Zealand. The strong asymmetries in tectonic uplift and tectonic advection and the onset of glaciations constantly interact to prevent the landscape from reaching a topographic steady state. Evidence suggests that the first-order geomorphology on the western side of the Southern Alps is controlled by orographic precipitation combined with extreme rates of tectonic uplift, whereas the development of deep glacial valleys on the eastern side is initiated by differential uplift along large faults. We also develop a first-order equation, governing the dynamics of the Main Divide, to show that both tectonic advection and fluvial erosion efficiency control the position and the height of the main drainage divide. Using a two-dimensional landscape evolution model, we demonstrate that the transition from glacial to fluvial conditions at the end of the last glaciation led to substantial modifications of the landscape: While the main trunk channels get slowly uplifted, ridges are leveled down, causing the relief to decrease. Hillslopes appear to be affected by fluvial processes which seem to be driven by incision of river tributaries. This reduction of relief will probably never reach a steady state since warmer interglacial periods are substantially shorter than glacial periods.

In recent years, the nature of the complex interactions between the solid earth and the overlying atmosphere has been the subject of much debate (England and Molnar 1990; Whipple et al. 1999; Braun et al. 1999). Does erosion play an important role in the dynamics of mountain building? Is there a strong feedback into the balance of forces at the crustal scale from mass transport by erosional and depositional processes at the Earth’s surface? Or does erosion passively react to changes in the Earth’s surface topography to shape mountains with tectonic forces, originating in the underlying convecting mantle, dominating the dynamics of plate interactions and crustal deformation at convergent plate margins? The answers to these fundamental questions lie in our ability to determine the rate at which surface processes can react to tectonic forcing (Whipple et al. 1999). Where erosion is efficient, the coupling will be strong as the rate of change of surface loading by mass transport will be similar to the rate of creation of topography by crustal deformation. This may lead to a concentration of deformation and thus exhumation in regions of intense erosion (Koons 1990; Willett et al. 1993; Beaumont et al. 2001; Koons et al. 2002, 2003; Braun and Pauselli 2004). Where erosion is relatively inefficient, mountain building is the result of a balance between internal driving forces and those originating from the deflection of an upper free surface; there is no feedback from erosional processes. Low-temperature thermochronology, such as (U-Th)/He (He) or fission track (FT) dating in apatite and zircon, provides information on the rate at which rocks cool as they are exhumed towards the “cold” Earth surface (Duddy et al. 1988; Warnock et al. 1997; Farley 2000; Reiners and Farley 1999). Because the …

Collision tectonics and the associated transformation of continental crust to high-pressure rocks (eclogites) are generally well-understood processes, but important contradictions remain between tectonothermal models and petrological–isotopic data obtained from such rocks. Here we use 40Ar–39Ar data coupled with a thermal model to constrain the time-integrated duration of an orogenic cycle (the burial and exhumation of a particular segment of the crust) to be less than 13 Myr. We also determine the total duration of associated metamorphic events to be ∼20 kyr, and of individual heat pulses experienced by the rocks to be as short as 10 years. Such short timescales are indicative of rapid tectonic processes associated with catastrophic deformation events (earthquakes). Such events triggered transient heat advection by hot fluid along deformation (shear) zones, which cut relatively cool and dry subducted crust. In contrast to current thermal models that assume thermal equilibrium and invoke high ambient temperatures in the thickened crust, our non-steady-state cold-crust model satisfactorily explains several otherwise contradictory geological observations. The duration of the geological processes that shape the Earth generates vigorous debate. Mountain-building, where crust is consumed continuously by burial and recycled as buried remnants rise to the surface, is one process where new dating methods can resolve the issue. High-precision dating of rock remnants left by continental collision in the Caledonides of southern Norway shows that the entire cycle can happen quickly, in about 13 million years. In addition, the rapid transport of hot fluid zones through the cold crust may explain many puzzling geological observations.

We have investigated whether low temperature thermochronological datasets can be used to constrain the rate of surface evolution during the post-orogenic phase of a mountain belt. We use a numerical method to solve the heat transport equation in the Earth’s crust, including the effects of a changing, finite-amplitude topography and the resulting flexural isostatic rebound. We demonstrate that accurate estimates of the amount of relief loss can be obtained by applying a recently developed spectral method that is based on estimates of the relationship between age and surface elevation as a function of topographic wavelength. We also show that the rate at which topography decays with time following cessation of tectonic activity can be constrained from estimates of exhumation rate derived from the slope of age‐ elevation profiles collected across short wavelength topography. Using the Neighbourhood Algorithm to perform a thorough search through parameter space, we are able to find a tectonomorphic scenario that predicts age distributions compatible with a thermochronological dataset collected in the Dabie Shan of eastern China by Reiners et al. (American Journal of Science 2003, vol. 303, pp. 489 ‐518). We demonstrate that, in the Dabie Shan, the mean topographic relief has decreased by a factor of 2·5 to 4·5 during the last 60‐80 Ma, while the mountain belt experienced a mean exhumation rate of 0·01 to 0·04 km Ma −1 . We confirm the

Recent studies integrating geomorphology, thermochronology, cosmogenic erosion rate estimates, and numerical modeling suggest that escarpment evolution may take place following two dramatically different modes: (1) parallel retreat from the escarpment's original position at the continent-ocean boundary to its present-day inland position and (2) formation-in-place by progressive downwearing of a plateau initially located between the coast and a preexisting inland drainage divide. Using a three-dimensional finite element model to solve the heat transfer equation, we show that the mode of migration of a passive margin escarpment can be constrained by low-temperature (apatite (U-Th)/He) thermochronology. We first couple the heat equation solver to a surface processes model that predicts the two different escarpment evolution modes from only slightly different initial conditions. We predict (U-Th)/He age distributions that are markedly different for the two scenarios. We perform a thorough investigation of the model behavior to determine under which circumstances thermochronological data can be used to constrain passive margin escarpment dynamics. These conditions include (a) a tall escarpment, (b) a high geothermal gradient, and/or (c) a low flexural rigidity of the lithosphere. We demonstrate that to determine the rate and mode of escarpment migration from low-temperature thermochronology, one needs to collect samples along transects perpendicular as well as parallel to the escarpment. Tightest constraints on escarpment development are provided by (in ascending order) the minimum (U-Th)/He age encountered seaward of the escarpment, the location of where the minimum age is found, the slope of the age-distance relationship (in a direction perpendicular to the coast), and the slope of the age-elevation relationship (from a transect parallel to the escarpment). We finally demonstrate that there are situations where thermochronological data sets do not provide constraints on the mode of escarpment migration, such as along the escarpment of southeastern Australia, where migration has possibly been very rapid. Using the Neighborhood Algorithm method, we are, however, able to extract from an existing apatite (U-Th)/He data set very useful constraints on the evolution of the southeastern Australian escarpment, including the duration of the migration event (

We have used a coupled thermo-mechanical finite-element (FE) model of crustal deformation driven by mantle/oceanic subduction to demonstrate that the tectonic evolution of the Lachlan Fold Belt (LFB) during the Mid-Palaeozoic (Late Ordovician to Early Carboniferous) can be linked to continuous subduction along a single subduction zone. This contrasts with most models proposed to date which assume that separate subduction zones were active beneath the western, central and eastern sections of the Lachlan Orogen. We demonstrate how the existing data on the structural, volcanic and erosional evolution of the Lachlan Fold Belt can be accounted for by our model. We focus particularly on the timing of fault movement in the various sectors of the orogen. We demonstrate that the presence of the weak basal decollement on which most of the Lachlan Fold Belt is constructed effectively decouples crustal structures from those in the underlying mantle. The patterns of faulting in the upper crust appears therefore to be controlled by lateral strength contrasts inherited from previous orogenic events rather than the location of one or several subduction zones. The model also predicts that the uplift and deep exhumation of the Wagga–Omeo Metamorphic Belt (WOMB) is associated with the advection of this terrane above the subduction point and is the only tectonic event that gives us direct constraints on the location of the subduction zone. We also discuss the implications of our model for the nature of the basement underlying the present-day orogen.

We present the results of simple numerical experiments in which we study the evolution with time of fluid flow around and within a permeable fault embedded in a less permeable porous medium. Fluid movement is driven by an imposed vertical pressure gradient. The results show that fluid flow is controlled by two timescales: τf = Sl2/κF and τF = Sl2/κM, where S is the specific storage of the porous material, l the length of the fault, and κM and κF are the hydraulic conductivities of the porous material and the fault, respectively. Fluid flow and the associated fluid pressure field evolve through three temporal stages: an early phase [t

We employ a numerical surface processes model to study the controls on postbreakup landscape development and denudational history of the southeast African margin. Apatite fission track data, presented in the companion paper, suggest that the Drakensberg Escarpment formed by rapid postbreakup river incision seaward of a preexisting drainage divide, located close to its present position, and subsequently retreated at rates of only ∼100 m m.y.−1. Numerical modeling results support such a scenario and show that the prebreakup topography of the margin has exerted a fundamental control on subsequent margin evolution. The rheology of the lithosphere, lithological variations in the eroding upper crust, and inland base level falls provided secondary controls. A relatively low flexural rigidity of the lithosphere (Te ≈ 10 km) is required to explain the observed pattern of denudation as well as the observed geological structure of the southeast African margin. Lithological variations have contributed to the formation of flat-topped ridges buttressing the main escarpment, as well as major fluvial knickpoints. Both these features have previously been interpreted as supporting significant Cenozoic uplift of the margin. An inland base level fall, possibly related to back-cutting of the Orange River drainage system and occurring 40–50 m.y. after breakup, explains the observed denudation inland of the escarpment as well as the development of inland drainage parallel to the escarpment. Our model results suggest that in contrast to widely accepted inferences from classical geomorphic studies, the southeast African margin has remained tectonically stable since breakup and escarpment retreat has been minimal (

The effect that recent relief changes may have on the distribution of rock ages with elevation is investigated for a range of thermochronometers. From the solution of the heat transport equation in a crustal block undergoing uplift and surface erosion, the temperature history of rock particles that are exhumed at the Earth’s surface today is computed. These T-t paths are then used to calculate apparent isotopic ages for the (U–Th)/He system in apatite, characterized by a low (≈70°C) closure temperature. The results show that recent relief changes strongly affect the distribution of ages with elevation (notably the slope of the age–elevation relationship). The calculations presented here predict that, in most situations, regions that have undergone a steady decrease in surface relief in the recent past should be characterized by an inverted age–elevation relationship, that is older ages should be found near valley bottoms and younger ages near summit tops. It is also shown how the wavelength of the topography, the geothermal gradient, the exhumation rate and the duration of the relief reduction event affect this result.

This study examines the effect of a training program on long-term-care (LTC) surveyors' knowledge of factors affecting oral health and their behavior in citing oral health deficiencies of LTC residents. Twenty surveyors were recruited for the experimental group, along with a non-equivalent comparison group of 31 surveyors. The experimental group participated in a three-hour interactive, case-based training program. The experimental group had a significant increase in total knowledge (p < 0.002) post-test scores with a moderate effect size, eta 2 = 0.115. The training program resulted in a statistically significant increase (p < 0.0001) in oral health citation behavior for the experimental group for six months following training. This study provides evidence that an interactive case-based training program can affect participants' knowledge regarding oral health of LTC residents and participants' oral health citation behavior. As the elderly population experiences an increased life expectancy with increased need for assistance with Activities of Daily Living (ADL), similar training programs will become an important factor in assessing the quality of care provided to LTC residents.

Dipping reflectors in the upper mantle are observed on reflection seismic data and, in some cases, have been interpreted to represent mantle shear zones. It is not clear, however, how these shear zones develop and under what circumstances. Previous attempts to model strain localisation by strain softening in the ductile regime have failed to show the development of mantle shear zones. We present here results from a numerical model of lithospheric extension. The model uses an elasto-visco-plastic rheology dependent on temperature, pressure, deviatoric stress and composition. Strain softening is incorporated into the mechanical model via a simple ad hoc strain–viscosity relationship. The results demonstrate that strain localisation can dominate lithospheric deformation in an extensional regime. We illustrate the effects of varying the parameters, which define the strain–viscosity relationship on the geometry of lithospheric-scale shear zones and the rift basin. We also investigate the effects on shear zone development of introducing a variety of pre-extension weak zones in the crust and/or mantle. Our results suggest that if dipping reflectors observed on deep seismic data around the world are evidence of the existence of mantle shear zones, there is a need to review our conceptual models of strain/strength evolution during the development of continental rifts.

We compare explicit differential operators for unstructured grids and their accuracy with the aim of solving time-dependent partial differential equations in geophysical applications. As many problems suggest the use of staggered grids we investigate different schemes for the calculation of space derivatives on two separate grids. The differential operators are explicit and local in the sense that they use only information of the function in their nearest neighborhood, so that no matrix inversion is necessary. This makes this approach well-suited for parallelization. Differential weights are obtained either with the finite-volume method or using natural neighbor coordinates. Unstructured grids have advantages concerning the simulation of complex geometries and boundaries. Our results show that while in general triangular (hexagonal) grids perform worse than standard finite-difference approaches, the effects of grid irregularities on the accuracy of the space derivatives are comparably small for realistic grids. This suggests that such a finite-difference-like approach to unstructured grids may be an alternative to other irregular grid methods such as the finite-element technique.

The phenomenon of shear-heating is generally difficult to recognise from petrologic evidence alone. Establishing that shear zones attain higher temperatures than the surrounding country rocks requires independent evidence for temperature gradients. In the Musgrave Block, central Australia, there is a clear spatial association between shear zones and interpreted elevated temperatures. Eclogite facies shear zones that formed at ∼550 Ma record temperatures of ∼650–700°C. Outside the high-pressure shear zones, minerals with low closure temperatures such as biotite (∼450°C in the 40Ar–39Ar and Rb–Sr systems), preserve ages >800 Ma, suggesting that these rocks did not experience temperatures greater than about 450°C at ∼550 Ma for any extended period. Thus, the shear zones record temperatures that are ∼200°C higher than the surrounding country rocks. Simple calculations show that the combination of relatively high shear stresses (∼100 MPa) and high strain rates (∼10−11 s−1) for short durations (

Glaciers frozen to bedrock may have protected the southernmost Andes from erosion, providing an explanation for the mountains' topography and fresh constraints on possible links between climate and tectonics.