Orogenesis from bottom to top – Investigating the geodynamics of mountain building using coupled thermo-mechanical-surface-process models

Postponed access: the file will be available after 2022-10-22The objective of this project is to The objective of this project is to advance our understanding of mountain building processes in different plate tectonic settings and with specific focus on the interaction between surface processes and tectonics. Three topics are investigated: 1. The factors controlling overriding plate extension or shortening in ocean-continent subduction systems. 2. The evolution of continent-continent collision orogens from small to large, their typical distribution of shortening, variable structural style, and associated controlling factors. 3. The relation between surface processes and tectonics during orogenic growth and decay and the factors controlling height, width, and longevity of collisional mountain belts. The three research aspects are investigated with the help of numerical models and comparison to natural examples. The newly developed models allow for the first time to efficiently model the coupling between tectonic deformation, erosion and deposition. Results are synthesized in published or submitted articles, provide new geodynamic relationships, ideas, and theory, and simplify understanding of mountain building on Earth. For topic 1, we use two-dimensional thermo-mechanical models, and show that back-arc extension or shortening of the overriding plate in ocean-continent subduction systems is determined by absolute plate velocities on Earth: Overriding plate movement towards the trench inhibits backarc extension and promotes overriding plate shortening, and a stable overriding plate or absolute plate movement away from the trench promote backarc extension. Additionally, a weak backarc lithospheric mantle, removed through Rayleigh-Taylor instabilities induced by the subduction process, is required for backarc extension and facilitates overriding plate shortening. Computation of driving and resisting forces during orogenesis shows near-balance of forces and explains why a weak and thinned backarc lithospheric mantle is pivotal for backarc extension and shortening. Comparison of model results with the Andes and Hellenic subduction zones corroborates that a weak and thinned backarc lithospheric mantle and absolute plate velocities determine overriding plate deformation. In topic 2, we use two-dimensional thermo-mechanical continent-continent collision models tightly coupled to a 2D surface process model and show that distribution of shortening during orogen growth follows a typical evolutionary pattern from a pro-side-dominated cold wedge to an orogenic plateau. Internal crustal loading is the main factor controlling the large scale deformation, while lithospheric pull only modulates the plate driving forces to sustain orogenesis. To first order surface processes delay orogenic growth, and modulate the structural style during growth. Utilizing a force-balance analysis, we show how inherited structures, surface processes, and decoupling between thick-and thin-skinned deformation influence the structures during orogenic growth. Comparison of generic model results with the Pyrenees, Alps, and Himalaya-Tibet shows applicability and limitations of model inferences. For topic 3, we use two-dimensional thermo-mechanical continent-continent collision models tightly coupled to a 2D surface process model and show that orogenic growth and decay depend on crustal rheology and surface process efficiency, and can be subdivided into two phases each. In growth-phase one, orogens grow primarily in height, followed by lateral growth in phase 2. Depending on surface process efficiency, phase-2-orogens can be classified into three types (Type 1, 2a, 2b): Type 1 orogens are not in flux-steady state, and are characterised by longitudinal valleys in the orogen core and low uplift and erosion rates. Flux-steady state, pre-dominantly transverse river flow in the orogen core and high uplift and erosion rates are characteristic for type 2 orogens. These orogens can furthermore be subdivided into types 2a and 2b, depending on whether the pro-side of the mountain belt produces significant thrust sheets. Based on model results, we derive an analytical scaling relationship of mountain belt growth and present a new non-dimensional number, $Be$, that describes the interaction between surface processes and tectonics during orogenic growth, and allows approximation of crustal strength and average fluvial erodibility of orogens on Earth. Finally, we use our scaling relationship and model inferences to compare to several orogens on Earth, specifically the Southern Alps of New Zealand, Taiwan, and Himalaya-Tibet. Our model inferences imply that the height of most growing orogens on Earth is controlled by the crustal strength of the foreland, and not by surface processes efficiency. In contrast, orogenic decay is primarily dependent on surface process efficiency. In decay-phase one, short-wavelength "tectonic" topography is quickly removed within few Myrs, before an effectively local-isostatic rebound creates slow decay of topography, with a timescale depending on surface process efficiency. We conclude that survival of orogenic topography for several tens to hundreds of Myrs is likely the default behaviour on Earth.Doktorgradsavhandlin

Links Between Faulting, Topography, and Sediment Production During Continental Rifting: Insights From Coupled Surface Process, Thermomechanical Modeling

Continental rifts form by extension, and their subsequent evolution depends on the tectonic and climatic boundary conditions. We investigate how faulting, topography, and the evolution of the sediment flux during rifting are affected by these boundary conditions, in particular whether it is possible to correlate tectonic activity, topography, and sediment flux on long timescales (40 Myr). We use a thermomechanical model coupled with a landscape evolution model and present a series of 14 models, testing the sensitivity of the models to crustal strength, extension rate, and fluvial erodibility. The degree of strain localization drives the structural evolution of the modeled rifts: slow extension, high crustal strength, and efficient surface processes promote a high degree of strain localization, resulting in fewer active faults with larger offset. Overall, the magnitude of sediment production correlates with the degree of strain localization. In case of unchanged erosional power and similar amount of extension, systems with slower extension produce more sediment owing to a stronger positive feedback between erosion and fault offset. We observe a characteristic sequence of events, reflecting the morpho-tectonic evolution of rifts: the highest rock uplift rates are observed before the maximum elevation, and the highest sediment flux postdates the peak in elevation. Our results indicate that for natural systems, the evolution of the sediment flux is a good proxy for the evolution of topography, and that a time lag of 2–5 Myr between the peaks in main tectonic activity and sediment flux can exist.publishedVersio

The Role of Subduction Interface and Upper Plate Strength on Back-Arc Extension: Application to Mediterranean Back-Arc Basins

While there has been a lot of work focusing on improving our understanding of divergent and convergent plate boundaries, the intricate nature of back-arc extension, where subduction and large-scale extension occur and interact in close, is yet to be explored properly. It has long been proposed that the strength of the subduction interface, which depends among others on the amount of subducted sediments, plays a pivotal role in subduction dynamics. Here, we investigate the role of back-arc rheology and subduction interface strength on the deformation style of the overriding plate. Using two-dimensional thermomechanical model experiments, we demonstrate, that the presence of a weak mantle–lithospheric domain in the overriding plate can result in back-arc breakup even during the subduction of narrow, land-locked oceanic basins such as those found in the Mediterranean region. The thinning of the back-arc mantle–lithosphere results in a weaker overriding plate, hence a lower slab-pull force is sufficient to initiate back-arc extension. Convective thinning at the subduction interface also reduces the length of the interface, reducing the portion of slab-pull lost as energy dissipation. A weak plate interface, can also reduce the energy dissipated along the subduction zone, leading to earlier extension. A detailed analysis of the forces shaping the overriding plate stress field shows that transmission of slab-pull force has a predominant role while viscous basal drag has a negligible effect in our experiments. Our results compare favorably with large-scale characteristics of land-locked Mediterranean back-arc basins such as the North Tyrrhenian basin and the Pannonian basin.publishedVersio

Evolution of Rift Architecture and Fault Linkage During Continental Rifting: Investigating the Effects of Tectonics and Surface Processes Using Lithosphere-Scale 3D Coupled Numerical Models

Continental rifts grow by propagation, overlap and linkage of individual fault segments. These processes are influenced by erosion and sedimentation and generate complex three-dimensional fault-interaction patterns. We use a 3D thermo-mechanical model of lithosphere deformation coupled with surface processes to investigate the coupling between erosion and tectonics, fault interaction and rift linkage, and evaluate the respective characteristics of crustal strength, inherited structures and erosional efficiency. We find that (a) weaker crust limits interactions between individual rift segments, (b) inherited structures are a major control for fault overlap and linkage except if they are too far apart and prevent interaction, and (c) efficient surface processes prolong fault activity, increase accommodated offset and in doing so, limit fault segment propagation and interactions. From these individual feedbacks, we identify five types of characteristic rift architectures: (a) for strong crust and intermediate erosional efficiency, fault segments link and form a horst between the propagating rifts. (b) Decreasing notch offset leads to segmentation of the central horst. (c) In case of reduced crustal strength no fault linkage occurs and a continuous central horst is promoted. (d) If inherited structures are too far apart, irrespective of crustal strength and erosional efficiency, rift basins do not link and a wide plateau-like horst forms between the propagating rifts. (e) In case of efficient erosion, fault linkage is achieved by the formation of strike-slip faults connecting the individual rift segments. Several of these simulated rift architectures can be identified in the western branch of the East African Rift.publishedVersio

Spatio-temporal patterns of Pyrenean exhumation revealed by inverse thermo-kinematic modeling of a large thermochronologic data set

Large thermochronologic data sets enable orogen-scale investigations into spatio-temporal patterns of erosion and deformation. We present the results of a thermo-kinematic modeling study that examines large-scale controls on spatio-temporal variations in exhumation as recorded by multiple low-temperature thermochronometers in the Pyrenees mountains (France/Spain). Using 264 compiled cooling ages spanning ∼200 km of the orogen, a recent model for its topographic evolution, and the thermo-kinematic modeling code Pecube, we evaluated two models for Axial Zone (AZ) exhumation: (1) thrust sheet–controlled (north-south) exhumation, and (2) along-strike (east-west) variable exhumation. We also measured the degree to which spatially variable post-orogenic erosion influenced the cooling ages. We found the best fit for a model of along-strike variable exhumation. In the eastern AZ, rock uplift rates peak at ≥1 mm/yr between 40 and 30 Ma, whereas in the western AZ, they peak between 30 and 20 Ma. The amount of post-orogenic (2.5 km in the west. The data reveal a pattern of exhumation that is primarily controlled by structural inheritance, with ancillary patterns reflecting growth and erosion of the antiformal stack and post-orogenic surface processes.publishedVersio

Extracellular invertase is involved in the regulation of clubroot disease in Arabidopsis thaliana

Clubroot disease of Brassicaceae is caused by an obligatebiotrophic protist,Plasmodiophora brassicae. During root galldevelopment, a strong sink for assimilates is developed. Amongother genes involved in sucrose and starch synthesis and degra-dation, the increased expression of invertases has been observedin a microarray experiment, and invertase and invertase inhibitorexpression was confirmed using promoter::GUS lines ofArabi-dopsis thaliana. A functional approach demonstrates that inver-tases are important for gall development. Different transgeniclines expressing an invertase inhibitor under the control of tworoot-specific promoters,Pyk10andCrypticT80, which results inthe reduction of invertase activity, showed clearly reduced clu-broot symptoms in root tissue with highest promoter expression,whereas hypocotyl galls developed normally. These resultspresent the first evidence that invertases are important factorsduring gall development, most probably in supplying sugars tothe pathogen. In addition, root-specific repression of invertaseactivity could be used as a tool to reduce clubroot symptoms

Femtosecond formation dynamics of the spin Seebeck effect revealed by terahertz spectroscopy.

Understanding the transfer of spin angular momentum is essential in modern magnetism research. A model case is the generation of magnons in magnetic insulators by heating an adjacent metal film. Here, we reveal the initial steps of this spin Seebeck effect with <27 fs time resolution using terahertz spectroscopy on bilayers of ferrimagnetic yttrium iron garnet and platinum. Upon exciting the metal with an infrared laser pulse, a spin Seebeck current js arises on the same ~100 fs time scale on which the metal electrons thermalize. This observation highlights that efficient spin transfer critically relies on carrier multiplication and is driven by conduction electrons scattering off the metal-insulator interface. Analytical modeling shows that the electrons' dynamics are almost instantaneously imprinted onto js because their spins have a correlation time of only ~4 fs and deflect the ferrimagnetic moments without inertia. Applications in material characterization, interface probing, spin-noise spectroscopy and terahertz spin pumping emerge

Vedolizumab use after failure of TNF- antagonists in children and adolescents with inflammatory bowel disease

BACKGROUND: Vedolizumab is safe and effective in adult patients with Crohn's disease (CD) and ulcerative colitis (UC); however, data in children with inflammatory bowel disease (IBD) are scarce. Therefore, we evaluated vedolizumab use in a cohort of Austrian paediatric patients with IBD. METHODS: Twelve patients (7 female; 7 CD; 5 UC), aged 8-17 years (median, 15 years), with severe IBD who received vedolizumab after tumour necrosis factor antagonist treatment were retrospectively analysed. Clinical activity scores, relevant laboratory parameters, and auxological measures were obtained at infusion visits. RESULTS: In the CD group, 1/7 patient discontinued therapy due to a severe systemic allergic reaction; 1/7 and 2/7 patients achieved complete and partial response, respectively, at week 14; and 3/7 patients discontinued therapy due to a primary non-response or loss of response. In the UC group, complete clinical remission was achieved at weeks 2, 6, and 14 in 2/5, 1/5 and 1/5 patients respectively; partial response was observed in one patient at week 2. CD activity scores did not significantly change from baseline to week 38 (median 47.5 vs. 40 points, p=1,0), while median UC activity scores changed from 70 to 5 points (p<0,001). Substantial weight gain and increased albumin and haemoglobin levels were observed in both groups. CONCLUSION: These results demonstrate that vedolizumab can be an effective treatment for individual paediatric patients with IBD who are unresponsive, intolerant, or experience a loss of efficacy in other therapies. However, vedolizumab appears to be more effective in paediatric UC than in paediatric CD.(VLID)286504

Terahertz spin-to-charge conversion by interfacial skew scattering in metallic bilayers

The efficient conversion of spin to charge transport and vice versa is of major relevance for the detection and generation of spin currents in spin‐based electronics. Interfaces of heterostructures are known to have a marked impact on this process. Here, terahertz (THz) emission spectroscopy is used to study ultrafast spin‐to‐charge‐current conversion (S2C) in about 50 prototypical F|N bilayers consisting of a ferromagnetic layer F (e.g., Ni81Fe19, Co, or Fe) and a nonmagnetic layer N with strong (Pt) or weak (Cu and Al) spin‐orbit coupling. Varying the structure of the F/N interface leads to a drastic change in the amplitude and even inversion of the polarity of the THz charge current. Remarkably, when N is a material with small spin Hall angle, a dominant interface contribution to the ultrafast charge current is found. Its magnitude amounts to as much as about 20% of that found in the F|Pt reference sample. Symmetry arguments and first‐principles calculations strongly suggest that the interfacial S2C arises from skew scattering of spin‐polarized electrons at interface imperfections. The results highlight the potential of skew scattering for interfacial S2C and propose a promising route to enhanced S2C by tailored interfaces at all frequencies from DC to terahertz