Long‐Term Coupling and Feedback Between Tectonics and Surface Processes During Non‐Volcanic Rifted Margin Formation

Here we present high‐resolution 2‐D coupled tectonic‐surface processes modeling of extensional basin formation. We focus on understanding feedbacks between erosion and deposition and tectonics during rift and passive margin formation. We test the combined effects of crustal rheology and varying surface process efficiency on structural style of rift and passive margin formation. The forward models presented here allow to identify the following four feedback relations between surface processes and tectonic deformation during rifted margin formation. (1) Erosion and deposition promote strain localization and enhance large offset asymmetric normal fault growth. (2) Progressive infill from proximal to more distal half grabens promotes the formation of synthetic sets of basinward dipping normal faults for intermediate crustal strength cases. (3) Sediment loading on top of undeformed crustal rafts in weak crust cases enhances middle and lower crustal flow resulting in sag basin subsidence. (4) Interaction of high sediment supply to the distal margin in very weak crust cases results in detachment‐based rollover sedimentary basins. Our models further show that erosion efficiency and drainage area provide a first‐order control on sediment supply during rifting where rift‐related topography is relatively quickly eroded. Long‐term sustained sediment supply to the rift basins requires elevated onshore drainage basins. We discuss similar variations in structural style observed in natural systems and compare them with the feedbacks identified here.publishedVersio

PrAGMATiC: a Probabilistic and Generative Model of Areas Tiling the Cortex

Much of the human cortex seems to be organized into topographic cortical maps. Yet few quantitative methods exist for characterizing these maps. To address this issue we developed a modeling framework that can reveal group-level cortical maps based on neuroimaging data. PrAGMATiC, a probabilistic and generative model of areas tiling the cortex, is a hierarchical Bayesian generative model of cortical maps. This model assumes that the cortical map in each individual subject is a sample from a single underlying probability distribution. Learning the parameters of this distribution reveals the properties of a cortical map that are common across a group of subjects while avoiding the potentially lossy step of co-registering each subject into a group anatomical space. In this report we give a mathematical description of PrAGMATiC, describe approximations that make it practical to use, show preliminary results from its application to a real dataset, and describe a number of possible future extensions

Mantle exhumation at magma-poor rifted margins controlled by frictional shear zones

The transition zone from continental crust to the mature mid-ocean ridge spreading center of the Iberia-Newfoundland magma-poor rifted margins is mostly composed of exhumed mantle characterized by highs and domes with varying elevation, spacing and shape. The mechanism controlling strain localization and fault migration explaining the geometry of these peridotite ridges is poorly understood. Here we show using forward geodynamic models that multiple out-of-sequence detachments with recurring dip reversal form during magma-poor rifting and mantle exhumation as a consequence of the strength competition between weak frictional-plastic shear zones and the thermally weakened necking domain beneath the exhuming footwall explaining geometry of these peridotite ridges. Model behaviour also shows that fault types and detachment styles vary with spreading rate and fault strength and confirm that these results can be compared to other magma poor passive margins such as along Antarctica-Australia and to ultra-slow mid-ocean spreading systems as the South-West Indian Ridge.publishedVersio

Relative continent - mid-ocean ridge elevation: a reference case for isostasy in geodynamics

The choice of crustal and mantle densities in numerical geodynamic models is usually based on convention. The isostatic component of the topography is not calibrated to fit observations resulting in not very well constrained elevations. The density distribution on Earth is not easy to constrain because it involves multiple variables (temperature, pressure, composition, and deformation). We aim in this study to provide a reference case for geodynamic modelling where crustal and mantle densities are calibrated to fit the relative continent/mid-ocean ridge elevation in agreement with observations. We first review observed Earth topography of stable continents and of active mid-ocean ridges and define the characteristic average elevation of these domains. We use self-consistent thermodynamic calculations of dry mantle rocks that include partial melting to calibrate densities of the continental lithospheric mantle and beneath the mid-ocean ridge. The thermodynamic solutions are coupled with a 2-D incompressible plane strain finite element method for viscous-plastic creeping flows to solve for the dynamic evolution during extension from continental rifting to mid-ocean spreading. The combined results from 2-D thermo-mechanical models and 1-D isostatic calculations show that the relative elevation difference between mid-ocean ridges and continents depends on crustal density, mantle composition, and the degree of depletion of the lithospheric mantle. Based on these results we calibrate the reference density that only depends on temperature, which can be used in classic thermo-mechanical models based on the Boussinesq approximation. Finally the model calibration provides a solution that fits (1) the elevation of active mid-ocean ridges far from hotspots (-2750 ± 250 m), (2) the elevation of stable continents far from hotspots (+400 ± 400 m), (3) the average depletion buoyancy of the continental lithospheric mantle (between -20 and -50 ± 15 kg/m3 depending on lithospheric thickness) and (4) the average continental crust density (2835 ± 35 kg/m3 for a 35 km thick crust).publishedVersio

Late-syn- to post-rift salt tectonics on wide rifted margins—Insights from geodynamic modeling

Rifted margins are often associated with widespread and thick evaporite (salt) deposits and pronounced salt tectonics. The largest salt basins formed during the latest stages of rifting, immediately prior to continental breakup. Salt tectonics along these rifted margins commonly exhibit structural domains characterized by gravity-driven updip extension, translation, downdip shortening, and salt nappe advance. The precise spatial and temporal links between these structural processes, their relative contributions and dynamics are still a topic of debate on many margins. We use 2D thermo-mechanically coupled finite-element modeling of lithospheric extension to investigate the evolution of salt tectonics along wide rifted margins and the interplay between rifting and post-rift deformation. The models integrate lithospheric extension with post-rift salt tectonics using a geodynamically self-consistent approach where the geometries of the lithosphere and salt basins are not prescribed. They confirm that wide salt-bearing rifted margins are characterized by gravity-driven updip extension and downdip shortening, but also that syn-depositional salt flow and salt stretching occurs in their distal portions prior to and during continental breakup. This produces widening of the basin and emplacement of a salt nappe over newly formed oceanic crust. Post-rift updip extension is mostly balanced by downdip diapir shortening, all related to Couette flow. The salt nappe initiated by late syn-rift stretching advances further by post-rift pressure-driven Poiseuille salt flow so that its final width is a product of both processes. The results can be directly compared to examples from various salt-bearing rifted margins and improve our understanding of their enigmatic genesis and evolution.publishedVersio

Coupling Crustal-Scale Rift Architecture With Passive Margin Salt Tectonics: A Geodynamic Modeling Approach

Continental rifted margins are often associated with widespread, thick evaporite (i.e., salt) deposits and pronounced salt tectonics. The majority of salt basins formed during the latest stages of rifting, prior to continental breakup. We use 2D thermo-mechanical finite element modeling of lithospheric extension to investigate the interplay between rifted margin architecture, late syn-rift salt deposition, and post-rift salt tectonics. We focus on four different types of continental margins: (a) narrow, (b) intermediate, (c) wide, and (d) ultra-wide margins. We evaluate the: (a) interplay between laterally variable syn-rift extension, salt deposition and salt tectonics, (b) influence of syn-rift basin architecture on post-rift salt flow, (c) spatial and temporal distribution of salt-related structural domains, and (d) contrasting styles of salt tectonics for different margin types. Narrow and intermediate margins form partially isolated salt basins associated with prominent base-salt relief, limited translation but significant diapirism, and minibasin development. Wide and ultra-wide margins form wide salt basins with subtle base-salt relief that results in significant seaward salt expulsion and overburden translation. These wide margins demonstrate significant updip extension with the development of post-rift normal faults and rollovers, mid-margin translation associated with complex diapirism and downdip diapir shortening. All margins contain a distal salt nappe that varies in width and complexity. We also test the effect of different salt viscosities, relative post-salt progradation rates, and pre-salt sediment thicknesses. The results are comparable to several examples of salt-bearing rifted margins and improve our understanding of their dynamics and on the controls on their salt tectonics variability.publishedVersio

Specific MRI Abnormalities Reveal Severe Perrault Syndrome due to CLPP Defects

In establishing a genetic diagnosis in heterogeneous neurological disease, clinical characterization and whole exome sequencing (WES) go hand-in-hand. Clinical data are essential, not only to guide WES variant selection and define the clinical severity of a genetic defect but also to identify other patients with defects in the same gene. In an infant patient with sensorineural hearing loss, psychomotor retardation, and epilepsy, WES resulted in identification of a novel homozygous CLPP frameshift mutation (c.21delA). Based on the gene defect and clinical symptoms, the diagnosis Perrault syndrome type 3 (PRLTS3) was established. The patient's brain-MRI revealed specific abnormalities of the subcortical and deep cerebral white matter and the middle blade of the corpus callosum, which was used to identify similar patients in the Amsterdam brain-MRI database, containing over 3000 unclassified leukoencephalopathy cases. In three unrelated patients with similar MRI abnormalities the CLPP gene was sequenced, and in two of them novel missense mutations were identified together with a large deletion that covered part of the CLPP gene on the other allele. The severe neurological and MRI abnormalities in these young patients were due to the drastic impact of the CLPP mutations, correlating with the variation in clinical manifestations among previously reported patients. Our data show that similarity in brain-MRI patterns can be used to identify novel PRLTS3 patients, especially during early disease stages, when only part of the disease manifestations are present. This seems especially applicable to the severely affected cases in which CLPP function is drastically affected and MRI abnormalities are pronounce

Low-dose folic acid supplementation does not influence plasma methionine concentrations in young non-pregnant women

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Specific MRI abnormalities reveal severe perrault syndrome due to CLPP defects

In establishing a genetic diagnosis in heterogeneous neurological disease, clinical characterization and whole exome sequencing (WES) go hand-in-hand. Clinical data are essential, not only to guide WES variant selection and define the clinical severity of a genetic defect but also to identify other patients with defects in the same gene. In an infant patient with sensorineural hearing loss, psychomotor retardation, and epilepsy, WES resulted in identification of a novel homozygous CLPP frameshift mutation (c.21delA). Based on the gene defect and clinical symptoms, the diagnosis Perrault syndrome type 3 (PRLTS3) was established. The patient's brain-MRI revealed specific abnormalities of the subcortical and deep cerebral white matter and the middle blade of the corpus callosum, which was used to identify similar patients in the Amsterdam brain-MRI database, containing over 3000 unclassified leukoencephalopathy cases. In three unrelated patients with similar MRI abnormalities the CLPP gene was sequenced, and in two of them novel missense mutations were identified together with a large deletion that covered part of the CLPP gene on the other allele. The severe neurological and MRI abnormalities in these young patients were due to the drastic impact of the CLPP mutations, correlating with the variation in clinical manifestations among previously reported patients. Our data show that similarity in brain-MRI patterns can be used to identify novel PRLTS3 patients, especially during early disease stages, when only part of the disease manifestations are present. This seems especially applicable to the severely affected cases in which CLPP function is drastically affected and MRI abnormalities are pronounced