147 research outputs found
Magma wagging and whirling : excitation by gas flux
No full textAuthor Posting. © The Authors, 2018. This article is posted here by permission of The Royal Astronomical Society for personal use, not for redistribution. The definitive version was published in Geophysical Journal International 215 (2018): 713–735, doi:10.1093/gji/ggy313.Gas flux in volcanic conduits is often associated with long-period oscillations known as seismic tremor (Lesage et al.; Nadeau et al.). In this study, we revisit and extend the ‘magma wagging’and ‘whirling’models for seismic tremor, in order to explore the effects of gas flux on the motion of a magma column surrounded by a permeable vesicular annulus (Jellinek & Bercovici; Bercovici et al.; Liao et al.). We find that gas flux flowing through the annulus leads to a Bernoulli effect, which causes waves on the magma column to become unstable and grow. Specifically, the Bernoulli effects are associated with torques and forces acting on the magma column, increasing its angular momentum and energy. As the displacement of the magma column becomes large due to the Bernoulli effect, frictional drag on the conduit wall decelerates the motions of the column, restoring them to small amplitude. Together, the Bernoulli effect and the damping effect contribute to a self-sustained wagging-and-whirling mechanism that help explain the longevity of long-period seismic tremor.This work was supported by National Science Foundation grants EAR-1344538 and EAR-164505
Generation of plate tectonics with two-phase grain-damage and pinning: Source-sink model and toroidal flow
No full textInternational audienceThe grain-damage and pinning mechanism of Bercovici and Ricard (2012) for lithospheric shear-localization is employed in two-dimensional flow calculations to test its ability to generate toroidal (strike-slip) motion and influence plate evolution. This mechanism posits that damage to the interface between phases in a polycrystalline material like peridotite (composed primarily of olivine and pyroxene) increases the number of small Zener pinning surfaces, which then constrain mineral grains to ever smaller sizes, regardless of creep mechanism. This effect allows a self-softening feedback in which damage and grain-reduction can co-exist with a grain-size dependent diffusion creep rheology; moreover, grain growth and weak-zone healing are greatly impeded by Zener pinning thereby leading to long-lived relic weak zones. The fluid dynamical calculations employ source-sink driven flow as a proxy for convective poloidal flow (upwelling/downwelling and divergent/convergent motion), and the coupling of this flow with non-linear rheological mechanisms excites toroidal or strike-slip motion. The numerical experiments show that pure dislocation-creep rheology, and grain-damage without Zener pinning (as occurs in a single-phase assemblages) permit only weak localization and toroidal flow; however, the full grain-damage with pinning readily allows focussed localization and intense, plate-like toroidal motion and strike-slip deformation. Rapid plate motion changes are also tested with abrupt rotations of the source-sink field after a plate-like configuration is developed; the post-rotation flow and material property fields retain memory of the original configuration for extensive periods, leading to suboptimally aligned plate boundaries (e.g., strike-slip margins non-parallel to plate motion), oblique subduction, and highly localized, weak and long lived acute plate-boundary junctions such as at what is observed at the Aleutian-Kurile intersection. The grain-damage and pinning theory therefore readily satisfies key plate-tectonic metrics of localized toroidal motion and plate-boundary inheritance, and thus provides a predictive theory for the generation of plate tectonics on Earth and other planets
Reactive infiltration of hydrous melt above the mantle transition zone
No full text[1] Seismic studies repeatedly image a low-velocity layer overlying the mantle transition zone in tectonic settings ranging from subduction zones to continental cratons. This layer has been hypothesized to result from the presence of a dense partial melt formed by dehydration melting as relatively wet transition zone material is advected by convection currents into the low-water-solubility upper mantle. Here we examine this hypothesis by considering the dynamic infiltration of a low-viscosity reactive hydrous melt into a high-viscosity ambient solid. The thickness of the melt layer is strongly controlled by return flow induced in the surrounding viscous solid, and in steady state a dynamic equilibrium is achieved where the melt lens is restrained from collapse by the exterior mantle. Melt layers with thicknesses in excess of 10 km develop for a wide range of mantle parameters and develop on timescales equivalent to the lifespan of an ocean basin. Citation: Leahy, G. M., and D. Bercovici (2010), Reactive infiltration of hydrous melt above the mantle transition zone
Energetics of a two-phase model of lithospheric damage, shear localization and plate-boundary formation
No full textcited By 102International audienceThe two-phase theory for compaction and damage proposed by Bercovici et al. (2001a, J. Geophys. Res., 106, 8887-8906) employs a nonequilibrium relation between interfacial surface energy, pressure and viscous deformation, thereby providing a model for damage (void generation and microcraking) and a continuum description of weakening, failure and shear localization. Here we examine further variations of the model which consider (1) how interfacial surface energy, when averaged over the mixture, appears to be partitioned between phases; (2) how variability in deformational-work partitioning greatly facilitates localization; and (3) how damage and localization are manifested in heat output and bulk energy exchange. Microphysical considerations of molecular bonding and activation energy suggest that the apparent partitioning of surface energy between phases goes as the viscosity of the phases. When such partitioning is used in the two-phase theory, it captures the melt-compaction theory of McKenzie (1984, J. Petrol., 25, 713-765) exactly, as well as the void-damage theory proposed in a companion paper (Ricard & Bercovici, submitted). Calculations of 1-D shear localization with this variation of the theory still show at least three possible regimes of damage and localization: at low stress is weak localization with diffuse slowly evolving shear bands; at higher stress strong localization with narrow rapidly growing bands exists; and at yet higher shear stress it is possible for the system to undergo broadly distributed damage and no localization. However, the intensity of localization is strongly controlled by the variability of the deformational-work partitioning with dilation rate, represented by the parameter γ. For γ ≫ 1, extreme localization is allowed, with sharp profiles in porosity (weak zones), nearly discontinuous separation velocities and effectively singular dilation rates. Finally, the bulk heat output is examined for the 1-D system to discern how much deformational work is effectively stored as surface energy. In the high-stress, distributed-damage cases, heat output is reduced as more interfacial surface energy is created. Yet, in either the weak or strong localizing cases, the system always releases surface energy, regardless of the presence of damage or not, and thus slightly more heat is in fact released than energy is input through external work. Moreover, increased levels of damage (represented by the maximum work-partitioning f*) make the localizing system release surface energy faster as damage enhances phase separation and focusing of the porosity field, thus yielding more rapid loss of net interfacial surface area. However, when cases with different levels of damage are compared at similar stages of development (say, the peak porosity of the localization) it is apparent that increased damage causes smaller relative heat release and retards loss of net interfacial surface energy. The energetics and energy partitioning of this damage and shear-localization model are applied to estimating the energy costs of forming plate boundaries and generating plates from mantle convection
Local content: perspectives of Brazilian sovereignty and economic development in the context of the Pré-Sal
No full textEsta dissertação trata de política industrial conhecida como Conteúdo Local, ou Política de Conteúdo Local, que obriga empresas a comprarem bens e serviços produzidos no local ou país em que sua atividade é desenvolvida. A pesquisa buscou enquadrar o Conteúdo Local como espécie de Política Industrial, realizando uma breve revisão bibliográfica. Entre os elementos do Conteúdo Local destaca-se a necessidade da aprendizagem e da experiência na formação ou desenvolvimento de uma indústria, motivo pelo qual abordamos a teoria desenvolvida por Alice Amsden sobre a industrialização de países subdesenvolvidos. Após ser realizada a definição de Conteúdo Local, são listados casos internacionais, sendo descrita a conjuntura nacional e internacional em que a política que é aplicada. O caso do setor de Petróleo e Gás Natural é analisado em específico, para o qual descrevemos antes a atuação do BNDES e da Petrobrás, além da utilização de Conteúdo Local nas políticas de Compras Públicas. Analisamos então a aplicação do Conteúdo Local pela ANP a partir de 1997 até os dias atuais. A pesquisa tenta apontar que a política é uma importante ferramenta para industrialização, especialmente no contexto de país subdesenvolvido, e poderia ter se consolidado como importante motor de crescimento e desenvolvimento tecnológico no Brasil, que detém grande porção de recursos minerais, especialmente após a descoberta do Pré-Sal. Conclui-se que importantes resultados derivaram de sua aplicação, sendo que o ordenamento jurídico brasileiro autoriza e exige aplicação de políticas industriais nesse sentido. Por fim, o desmonte da política no setor de Petróleo e Gás Natural se deu de maneira precipitada.This dissertation investigates the industrial policy known as Local Content, or Local Content Policy, in which companies are required to contract local or national services and goods. The research sought to frame Local Content as a kind of Industrial Policy, conducting a brief bibliographic review. Among the elements of Local Content, manufacturing learning and experience stands out in the industrialization process, which is why we examine the theory developed by Alice Amsden about the industrialization of underdeveloped countries. After the definition of Local Content is set, international cases are listed and the national and international conjunctures in which the policy is applied is described. The case of the Brazilian Oil and Natural Gas sector is analyzed, for which we have previously discussed the activities of the Brazilian Development Bank (BNDES) and Petrobrás, as well the application of Local Content in Public Procurement policies. We then analyze the application of Local Content by the Brazilian National Agency for Petroleum, Natural Gas and Bio fuels (ANP) from 1997 to present. The research attempts to point out that the policy of Local Content is an important instrument to promote industrialization, especially in underdeveloped countries, and it could have consolidated itself as an important engine of growth and technological development in Brazil, because of the country\'s significant amount of hydrocarbons resources, especially after \'Pré-Sal\' was discovered. The work concludes that important results were derived from the application of such policy, that the Brazilian legal system authorizes and requires the application of industrial policies in this sense, and that the dismantling of the Local Content policy in the Oil and Natural Gas sector occurred in a hasty manner
Courier Volume IV, Number 1, Whole number 21, March 1964
No full textArticle about Konrad Bercovici, author of Roumanian tales and novels. His daughter gave his books, papers, manuscripys, published and unpublished and extensive corrospondence to Syracuse University. Also given to the Library was one of the most beautiful Book of Hours ever seen in this part of the world .
Other recent additions of Special Collections material are described
Dissolved organic matter molecular composition data and supporting metadata for multiple oceanographic cruises with RV SONNE (SO254, SO245, SO248) and RV POLARSTERN (PS79), Bermuda Atlantic Time-series Study and Hawaii Ocean Time-series
No full textThis data includes the dissolved organic matter (DOM) molecular composition data obtained via Fourier-transform ion cyclotron resonance mass spectrometry and the accompanying metadata (cruise, station number, geographic coordinates, water depth, temperature, salinity and solid-phase extracted dissolved organic carbon concentrations (SPE-DOC)) for multiple oceanographic cruises (HOTS, BATS, SO254, SO245, SO248, ANT 28-II, ANT 28-IV, and 28-V). This data was analyzed in Bercovici et al., 2023 (https://doi.org/10.1029/2023GB007740). DOM composition data for the cruise SO245 was previously published in Osterholz et al., 2021 (https://doi.org/10.1016/j.marchem.2021.103955). In order to maximize comparability among data, we reanalyzed the same set of samples from SO245 on the FT-ICR-MS together with the samples from the other cruises and sites. SPE-DOC concentrations were determined on a Shimadzu TOC-VPCH total organic carbon analyzer. DOM composition was determined on a SolariX XR FT-ICR-MS (Bruker Daltonik GmbH, Bremen, Germany) equipped with a 15 Tesla superconducting magnet and an electrospray ionization source (ESI; Bruker Apollo II ion source). The metadata were compiled from the CTD bottle data of multiple cruises, some of which are available on PANGAEA at the following links: SO248: https://doi.org/10.1594/PANGAEA.864673, SO245: https://doi.org/10.1594/PANGAEA.890394, SO254: https://doi.org/10.1594/PANGAEA.890453
Generation of plate tectonics from lithosphere-mantle flow and void-volatile self-lubrication,
No full textAbstract The formation of plate tectonics from mantle convection necessarily requires nonlinear rheological behavior. Recent studies suggest that self-lubricating rheological mechanisms are most capable of generating plate-like motion out of fluid flows. The basic paradigm of self-lubrication is nominally derived from the feedback between viscous heating and Ž temperature-dependent viscosity. Here, we propose a new idealized self-lubrication mechanism based on void e.g., pore . Ž . andror microcrack generation and volatile e.g., water ingestion. We test this void-volatile self-lubrication mechanism in Ž . a source-sink flow model; this leads to a basic nonlinear system which permits the excitation of strike-slip toroidal motion Ž . Ž . a necessary ingredient of plate-like motion out of purely divergent i.e., poloidal or characteristically convective flow. Ž With relatively inviscid void-filling volatiles, the void-volatile mechanism yields a state of highly plate-like motion i.e., . with uniformly strong ''plate'' interiors, weak margins, and extremely focussed strike-slip shear zones . Moreover, the void-volatile model obeys a chemical diffusion time scale that is typically much longer than the thermal convection time scale; the model thus complies with the observation that plate boundaries are long lived and survive even while inactive. The void-volatile model of self-lubrication therefore predicts self-focussing shear zones, plate generation, and plate-boundary longevity through what has long been suspected to be a key ingredient for the existence of plate tectonics, i.e., water. q 1998 Elsevier Science B.V
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