Initiation of transform faults at rifted continental margins: 3D petrological-thermomechanical modeling and comparison to the Woodlark Basin

This work presents high-resolution 3D numerical model of transform fault initiation at rifted continental margins. Our petrological-thermomechanical visco-plastic model allows for spontaneous nucleation of oceanic spreading process in a continental rift zone and takes into account new oceanic crust growth driven by decompression melting of the asthenospheric mantle. Numerical model predicts that ridge-transform spreading pattern initiate in several subsequent stages: crustal rifting (0-1.5 Myr), spreading centers nucleation and propagation (1.5-3 Myr), proto-transform fault initiation and rotation (3-5 Myr) and mature ridge-transform spreading (> 5 Myr). Comparison of modeling results with the natural data from the Woodlark Basin suggests that the development of this region closely matches numerical predictions. Similarly to the model, the Moresby (proto-) Transform terminates in the oceanic rather than in the continental crust. This fault associates with a notable topographic depression and formed within 0.5-2 Myr while linking two offset overlapping spreading segments. Model reproduces well characteristic "rounded” contours of the spreading centers as well as the presence of a remnant of the broken continental crustal bridge observed in the Woodlark Basin. Proto-transform fault traces and truncated tip of one spreading center present in the model are also documented in nature. Numerical results are in good agreement with the concept of Taylor et al. (2009) which suggests that spreading segments nucleate en echelon in overlapping rift basins and that transform faults develop as or after spreading nucleates. Our experiments also allow to refine this concept in that (proto)-transform faults may also initiate as oblique rather than only spreading-parallel tectonic features. Subsequent rotation of these faults toward the extension-parallel direction is governed by space accommodation during continued oceanic crust growth within offset ridge-transform intersection

The Dynamics of Forearc – Back‐Arc Basin Subsidence: Numerical Models and Observations From Mediterranean Subduction Zones

The subsidence history of forearc and back-arc basins reflects the relationship between subduction kinematics, mantle dynamics, magmatism, crustal tectonics, and surface processes. The distinct contributions of these processes to the topography variations of active margins during subduction initiation, oceanic subduction, and collision are less understood. We ran 2D elasto-visco-plastic numerical models including surface and hydration processes. The models show the evolution of wedge-top and retro-forearc basins on the continental overriding plate, separated by a forearc high. They are affected by repeated compression and extension phases. Compression-induced subsidence is recorded in the syncline structure of the retro-forearc basin from the onset of subduction. The 2-4 km upper plate negative residual topography is produced by the gradually steepening slab, which drags down the upper plate. Trench retreat leads to slab unbending and decreasing slab dip angle that leads to upper plate trench-ward tilting. Back-arc basins are either formed along inherited weak zones at a large distance from the arc or are created above the hydrated mantle wedge originating from arc rifting. Back-arc subsidence is primarily governed by crustal thinning that is controlled by slab roll-back and supported by the underlying mantle convection. High subduction and mantle convection velocities result in large wavelength negative dynamic topography. Collision and continental subduction are linked to the uplift of the forearc basins; however, the back-arc records ongoing extension during a soft collision. During the hard collision, both the forearc and back-arc basins are ultimately affected by the compression. Our modeling results provide insights into the evolution of Mediterranean subduction zones

The influence of mantle refertilisation on the formation of TTGs in a plume-lid tectonics setting

Orientadora: Profª. Drª. Elisa Souza OrthDissertação (mestrado) - Universidade Federal do Paraná, Setor de Ciências Exatas, Programa de Pós-Graduação em Química. Defesa : Curitiba, 26/02/2019Inclui referências: p.109-121Resumo: A biomassa lignocelulósica é um material barato, amplamente distribuída mundialmente e renovável. Uma dessas fontes de biomassa é a casca de arroz (CA): um resíduo agrícola de uma das maiores culturas agrícolas mundiais e que mais utilizam pesticidas organofosforados. Além dos pesticidas, algumas armas químicas também são compostos organofosforados, que tem como características principais serem altamente estáveis e extremamente tóxicos. Esses compostos podem ser clivados por grupos nucleofílicos como imidazóis e ácidos hidroxâmicos, levando a organofosfatos menos tóxicos. Assim, uma abordagem promissora na degradação de organofosforados é a funcionalização covalente de materiais com grupos nucleofílicos e sua aplicação na degradação desses compostos. O objetivo desse trabalho foi obter catalisadores sustentáveis para a degradação de organofosforados a partir da funcionalização covalente da celulose da CA com grupos imidazol e ácido hidroxâmico. Para isso, a CA após tratamento alcalino teve parte das hidroxilas da celulose oxidadas a ácidos carboxílicos pelo método TEMPO/NaBr/NaClO de duas maneiras: (i) um baixo grau de oxidação, gerando a amostra sólida ICACOOH; e (ii) um alto grau de oxidação, gerando a amostra coloidal SCACOOH. As amostras ICACOOH e SCACOOH foram funcionalizadas covalentemente com 1-(3-aminopropil)imidazol, gerando, respectivamente duas amostras com imidazol: ICAIMZ (sólida) e SCAIMZ (coloidal). De forma análoga, a funcionalização covalente das amostras ICACOOH e SCACOOH com cloridrato de hidroxilamina deu origem as amostras com ácidos hidroxâmicos ICAAHD (sólida) e SCAAHD (coloidal). As amostras foram caracterizadas por diversas técnicas, dentre as quais titulação potenciométrica, microscopia eletrônica de varredura, espectroscopia de infravermelho por transformada de Fourier e ressonância magnética nuclear. O conjunto dessas técnicas comprovou a funcionalização covalente dos materiais, bem como elucidou a composição desses materiais. A atividade catalítica das amostras foi avaliada com os organofosforados 2,4- dinitrofenil fosfato (DEDNPP) e o pesticida Paraoxon. Foram observados incrementos catalíticos entre os maiores já reportados, da ordem de 106-107 vezes na reação entre os biocatalisadores com o DEDNPP e da ordem de 104-105 vezes entre os biocatalisadores e o Paraoxon, em relação às respectivas reações espontâneas. Os biocatalisadores foram reciclados por três ciclos de catálise, sem variação significativa da atividade catalítica, provando ser reutilizável. A fim de compreender o mecanismo, os biocatalisadores foram estudados na reação com cloro-2,4-dinitrobenzeno, não mostrando nenhuma atividade. Esses resultados indicam que os imidazóis e ácidos hidroxâmicos desses materiais são seletivos no ataque ao fósforo dos organofosforados. Assim, foram sintetizados a partir do resíduo agrícola CA dois materiais template (um colóide e um sólido) e quatro biocatalisadores (dois colóides e dois sólidos), sendo que esses últimos mostraram altos incrementos catalíticos na degradação dos organofosforados, seletivos no mecanismo de ataque e reciclados ao fim da reação. Uma abordagem inovadora é mostrada ao aplicar princípios da química verde na modificação química de um resíduo agrícola e utilizá-lo como catalisador na degradação de pesticidas. Palavras-chave: Imidazol. Ácido hidroxâmico. Casca de arroz. Catálise. Armas Químicas. Pesticidas.Abstract: Lignocellulosic biomass is an inexpensive material, widely distributed worldwide and renewable. One of the sources of biomass is rice husk (CA): an agricultural residue from one of the world's largest agricultural crops and one that counts abusive use of organophosphate pesticides. Besides pesticides, some chemical weapons are also organophosphorus compounds, whose main characteristics are the high stability and extreme toxicity. These compounds can be cleaved by nucleophilic groups such as imidazoles and hydroxamic acids, leading to less toxic organophosphates. Thus, a promising approach in the degradation of organophosphates is the covalent functionalization of materials with nucleophilic groups and its application in the degradation of these compounds. The objective of this work was to obtain sustainable biocatalysts for the degradation of organophosphates from the covalent functionalization of cellulose in CA with imidazoles and hydroxamic acids. Therefore, CA after alkaline treatment had part of the cellulose hydroxyls oxidized to carboxylic acids by the TEMPO/NaBr/NaClO method in two ways: (i) a low degree of oxidation, giving the solid sample ICACOOH; and (ii) a high degree of oxidation, giving the colloidal sample SCACOOH. The ICACOOH and SCACOOH samples were then covalently functionalized with 1-(3- aminopropyl) imidazole, generating, respectively, the imidazole samples ICAIMZ (solid) and SCAIMZ (colloidal). Similarly, the covalent functionalization of the samples ICACOOH and SCACOOH with hydroxylamine hydrochloride gave the samples with hydroxamic acids ICAAHD (solid) and SCAAHD (colloidal). The samples were characterized by several techniques, such as potentiometric titration, scanning electron microscopy, Fourier transform infrared spectroscopy and nuclear magnetic resonance. All these techniques proved the covalent functionalization of the materials with imidazoles or hydroxamic acids, as well as it elucidated the composition of these materials. The catalytic activity of the samples was then evaluated with the organophosphates 2,4-dinitrophenyl phosphate (DEDNPP) and the pesticide Paraoxon. Catalytic increments, among the highest reported, in the order of 106-107- fold were observed in the reaction between the biocatalysts with DEDNPP and in the order of 104-105-fold between the biocatalysts and Paraoxon, compared with the respective spontaneous reactions. The biocatalysts were also evaluated in 3 consecutive cycles of catalysis, without a significant variation of the catalytic activity. In order to understand the mechanism, the biocatalysts were studied in the reaction with chloro-2,4-dinitrobenzene, showing no activity. These results indicate that the imidazoles and hydroxamic acids of these materials are selective in the phosphorus attack of organophosphates. Thus, two template materials (one colloid and one solid) and four biocatalysts (two colloids and two solids) were synthesized from the agricultural residue CA, and the latter showed high catalytic increments in the degradation of organophosphates, selective in the attack mechanism and recycled at the end of the reaction. An innovative approach is shown by applying green chemistry principles in the chemical modification of an agricultural residue and using it as a catalyst in the degradation of pesticides. Keywords: Imidazole. Hydroxamic acid. Rice husk. Chemical weapons. Catalysis. Pesticides

Semi-empirical Gibbs free energy formulations for minerals and fluids for use in thermodynamic databases of petrological interest

The P-T partition function in statistical thermodynamics can be used to derive semi-empirical formulations of the Gibbs free energy G for minerals and fluids. Parameterization of these equations includes simultaneous regression of experimental heat capacity and molar volume data, allowing fitting, appraisal and optimization of various data sources, as required in the construction of internally consistent petrological data bases. This approach can also be extended to minerals with λ-transitions and to fluids by considering the Gibbs free energy as a function of pressure P, temperature T and an ordering parameter Xα, so that accurate modelled representation and extrapolation of the thermodynamic properties of large numbers of petrologically significant minerals and coexisting fluids can be attained. The ordering parameter is chosen to denote the equilibrium mole fraction (thermodynamic probability) of ordered clusters (structural units) in a substance when G(T,P, Xα)=min. The procedure is tested on existing experimental data for the system MgO-SiO2-H2O. The proposed Gibbs free energy formulation permits thermodynamic properties of minerals, fluids and phase equilibria to be described and extrapolated over a wide range of pressure (0-800 kbar) and temperature (20-3000 K), thus allowing effective use in thermodynamic data bases of petrological interes

Non-Newtonian rheology of crystal-bearing magmas and implications for magma ascent dynamics

The eruptive dynamics of volcanic systems are largely controlled by the viscosity of deforming magma. Here we report the results of a series of high-temperature, high-pressure experiments at conditions relevant for volcanic conduits (250 MPa confining pressure and temperature between 500 °C and 900 °C) that were undertaken to investigate the rheology of magma with crystal fractions varying between 0.5 and 0.8 (50 to 80 wt.%) at different strain-rate conditions. The experiments demonstrate that the presence of crystals increases the relative viscosity (ratio between the viscosity of the mixture and the viscosity of the melt phase) of magmas and additionally induces a decrease of the relative viscosity with increasing strain-rate (shear thinning, non-Newtonian behavior). The experimental results, combined with existing data at low crystal fractions (0–0.3), were used to develop a semi-empirical parameterization that describes the variations of relative viscosity for crystal fractions between 0 and 0.8 and accounts for the complex non-Newtonian rheology of crystal-bearing magmas. The new parameterization, included into numerical models simulating the magma ascent dynamics, reveals that strain-rate-dependent rheology significantly modifies the dynamic behavior inside volcanic conduits, particularly affecting the magma fragmentation conditions

Tectonics and seismicity in the Northern Apennines driven by slab retreat and lithospheric delamination

Understanding how long-term subduction dynamics relates to the short-term seismicity and crustal tec tonics is a challenging but crucial topic in seismotectonics. We attempt to address this issue by linking long-term geodynamic evolution with short-term seismogenic deformation in the Northern Apennines. This retreating subduction orogen displays tectonic and seismogenic behaviors on various spatiotemporal scales that also characterize other subduction zones in the Mediterranean area. We use visco-elasto-plastic seismo-thermo-mechanical (STM) modeling with a realistic 2D setup based on available geological and geophysical data. The subduction dynamics and seismicity are coupled in the numerical modeling, and driven only by buoyancy forces, i.e., slab pull. Our results suggest that lower crustal rheology and lithospheric mantle temperature modulate the crustal tectonics of the Northern Apennines, as inferred by previous studies. The observed spatial distribution of upper crustal tectonic regimes and surface displacements requires buoyant, highly ductile material in the subduction channel beneath the internal part of the orogen. This allows protrusion of the asthenosphere in the lower crust and lithospheric delamination associated with slab retreat. The resulting surface velocities and principal stress axes generally agree with present-day observations, suggesting that slab delamination and retreat can explain the dynamics of the orogen. Our simulations successfully reproduce the type and overall distribution of seismicity with thrust faulting events in the external part of the orogen and normal faulting in its internal part. Slab temperatures and lithospheric mantle stiffness affect the cumulative seismic moment release and spatial distribution of upper crustal earthquakes. The properties of deep, sub-crustal material are thus shown to influence upper crustal seismicity in an orogen driven by slab retreat, even though the upper crust is largely decoupled from the lithospheric mantle. Our simulations therefore highlight the effect of deep lower crustal rheologies, self-driven subduction dynamics and mantle properties in controlling shallow deformation and seismicity

Practical analytical solutions for benchmarking of 2-D and 3-D geodynamic Stokes problems with variable viscosity

Geodynamic modeling is often related with challenging computations involving solution of the Stokes and continuity equations under the condition of highly variable viscosity. Based on a new analytical approach we have developed particular analytical solutions for 2-D and 3-D incompressible Stokes flows with both linearly and exponentially variable viscosity. We demonstrate how these particular solutions can be converted into 2-D and 3-D test problems suitable for benchmarking numerical codes aimed at modeling various mantle convection and lithospheric dynamics problems. The Main advantage of this new generalized approach is that a large variety of benchmark solutions can be generated, including relatively complex cases with open model boundaries, non-vertical gravity and variable gradients of the viscosity and density fields, which are not parallel to the Cartesian axes. Examples of respective 2-D and 3-D MatLab codes are provided with this paper

3-D multiobservable probabilistic inversion for the compositional and thermal structure of the lithosphere and upper mantle: III. Thermochemical tomography in the Western-Central U.S.

Acknowledgments We are indebted to F. Darbyshire and J. von Hunen for useful comments on earlier versions of this work. This manuscript benefited from thorough and constructive reviews by W. Levandowski and an anonymous reviewer. We also thank J. Connolly, M. Sambridge, B. Kennett, S. Lebedev, B. Shan, U. Faul, and M. Qashqai for insightful discussions about, and contributions to, some of the concepts presented in this paper. The work of J.C.A. has been supported by two Australian Research Council Discovery grants (DP120102372 and DP110104145). Seismic data are from the IRIS DMS. D.L.S. acknowledges support from NSF grant EAR-135866. This is contribution 848 from the ARC Centre of Excellence for Core to Crust Fluid Systems (http://www.ccfs.mq.edu.au) and 1106 in the GEMOC Key Centre (http://www.gemoc.mq.edu.au).Peer reviewedPublisher PD