An extinct,Late Mesoproterozoic,Sveconorwegian mantle wedge beneath SW Fennoscandia,reflected in seismic tomography and assessed by thermal modelling          下载免费PDF全文

Trond Slagstad  Yuriy Maystrenko  Valerie Maupin  Sofie Gradmann 《地学学报》2018,30(1):72-77

A channel‐like, low‐velocity zone in the lithospheric mantle beneath W Norway coincides spatially with the extension of a recently discovered 200 × 50 km granite batholith, which formed as a result of oceanic subduction beneath the SW Fennoscandian margin between 1.07 and 1.01 Ga. Based on results from numerical modelling, we argue that the low‐velocity zone, at least in part, reflects the thermal (radioactive) effects of the refertilized mantle wedge of this magmatic arc. The geological record in SW Fennoscandia suggests that active‐margin magmatism terminated as a result of rapid slab rollback and trench retreat starting at ca. 1 Ga. The rapid shift from active‐ to passive‐margin processes was probably critical in preserving the mantle wedge, and its identification can therefore shed light on how active‐margin processes terminated in ancient orogens.  相似文献   

Breaking the Grenville–Sveconorwegian link in Rodinia reconstructions     

Trond Slagstad  Evgeniy Kulakov  Christopher L. Kirkland  Nick M. W. Roberts  Morgan Ganerd 《地学学报》2019,31(5):430-437

The Grenville, Sveconorwegian, and Sunsas orogens are typically inferred to reflect collision between Laurentia, Baltica, and Amazonia at ca. 1.0 Ga, forming a central portion of the Rodinia supercontinent. This triple‐junction configuration is often nearly identical in otherwise diverse Rodinia reconstructions. However, available geological data suggest that although the Grenville and Sveconorwegian provinces shared a similar tectonic evolution from pre‐1.8 to ca. 1.5 Ga, they record distinctly different tectonic histories leading up to, during, and possibly following Grenville–Sveconorwegian orogenesis. Moreover, palaeomagnetic data suggest the two continents were separated at peak orogenesis, further invalidating any direct correlation. A number of possible interpretations are permissible with available geological and palaeomagnetic data, of which a “classic” triple‐junction configuration appears least likely. In contrast to the commonly inferred intertwined Proterozoic evolution of Baltica and Laurentia, the possibility remains that they were unrelated for a billion years between 1.5 and 0.45 Ga.  相似文献   

4D Arctic: A Glimpse into the Structure and Evolution of the Arctic in the Light of New Geophysical Maps,Plate Tectonics and Tomographic Models     

Carmen Gaina  Sergei Medvedev  Trond H. Torsvik  Ivan Koulakov  Stephanie C. Werner 《Surveys in Geophysics》2014,35(5):1095-1122

Knowledge about the Arctic tectonic structure has changed in the last decade as a large number of new datasets have been collected and systematized. Here, we review the most updated, publicly available Circum-Arctic digital compilations of magnetic and gravity data together with new models of the Arctic’s crust. Available tomographic models have also been scrutinized and evaluated for their potential to reveal the deeper structure of the Arctic region. Although the age and opening mechanisms of the Amerasia Basin are still difficult to establish in detail, interpreted subducted slabs that reside in the High Arctic’s lower mantle point to one or two episodes of subduction that consumed crust of possibly Late Cretaceous–Jurassic age. The origin of major igneous activity during the Cretaceous in the central Arctic (the Alpha–Mendeleev Ridge) and in the proximity of rifted margins (the so-called High Arctic Large Igneous Province—HALIP) is still debated. Models of global plate circuits and the connection with the deep mantle are used here to re-evaluate a possible link between Arctic volcanism and mantle plumes.  相似文献   

Coarse-scale data assimilation as a generic alternative to localization     

Kristian Fossum  Trond Mannseth 《Computational Geosciences》2017,21(1):167-186

Coarse-scale data assimilation (DA) with large ensemble size is proposed as a robust alternative to standard DA with localization for reservoir history matching problems. With coarse-scale DA, the unknown property function associated with each ensemble member is upscaled to a grid significantly coarser than the original reservoir simulator grid. The grid coarsening is automatic, ensemble-specific and non-uniform. The selection of regions where the grid can be coarsened without introducing too large modelling errors is performed using a second-generation wavelet transform allowing for seamless handling of non-dyadic grids and inactive grid cells. An inexpensive local-local upscaling is performed on each ensemble member. A DA algorithm that restarts from initial time is utilized, which avoids the need for downscaling. Since the DA computational cost roughly equals the number of ensemble members times the cost of a single forward simulation, coarse-scale DA allows for a significant increase in the number of ensemble members at the same computational cost as standard DA with localization. Fixing the computational cost for both approaches, the quality of coarse-scale DA is compared to that of standard DA with localization (using state-of-the-art localization techniques) on examples spanning a large degree of variability. It is found that coarse-scale DA is more robust with respect to variation in example type than each of the localization techniques considered with standard DA. Although the paper is concerned with two spatial dimensions, coarse-scale DA is easily extendible to three spatial dimensions, where it is expected that its advantage with respect to standard DA with localization will increase.  相似文献   

The Lower Palaeozoic apparent polar wander path for Baltica: palaeomagnetic data from Silurian limestones of Gotland, Sweden     

Allan Trench  Trond H. Torsvik 《Geophysical Journal International》1991,107(2):373-379

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Existence of the frequentistic estimate for power-law regression with a location parameter, with applications for making discharge rating curves     

Trond Reitan  Asgeir Petersen-Øverleir 《Stochastic Environmental Research and Risk Assessment (SERRA)》2006,20(6):445-453

Practical application of the power-law regression model with an unknown location parameter can be plagued by non-finite least squares parameter estimates. This presents a serious problem in hydrology, since stream flow data is mainly obtained using an estimated stage–discharge power-law rating curve. This study provides a set of sufficient requirements for the data to ensure the existence of finite least squares parameter estimates for a power-law regression with an unknown location parameter. It is shown that in practice, these requirements act as necessary for having a finite least squares solution, in most cases. Furthermore, it is proved that there is a finite probability for the model to produce data having non-finite least squares parameter estimates. The implications of this result are discussed in the context of asymptotic predictions, inference and experimental design. A Bayesian approach to the actual regression problem is recommended.  相似文献   

The distribution of snow accumulation across the Austfonna ice cap, Svalbard: direct measurements and modelling     

Andrea Taurisano  Thomas V. Schuler  Jon Ove Hagen  Trond Eiken  Even Loe  Kjetil Melvold  & Jack Kohler 《Polar research》2007,26(1):7-13

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Analysis and comparison of mixed finite element and multipoint flux approximation methods for homogeneous media     

Trond Mannseth 《Computational Geosciences》2007,11(1):59-72

We consider discretization on quadrilateral grids of an elliptic operator occurring, for example, in the pressure equation for porous-media flow. In a realistic setting – with non-orthogonal grid, and anisotropic, heterogeneous permeability – special discretization techniques are required. Mixed finite element (MFE) and multipoint flux approximation (MPFA) are two methods that can handle such situations. Previously, a framework for analytical comparison of MFE and MPFA in special cases has been suggested. A comparison of MFE and MPFA-O (one of two main variants of MPFA) for isotropic, homogeneous permeability on a uniformly distorted grid was also performed. In the current paper, we utilize the suggested framework in a slightly different manner to analyze and compare MFE, MPFA-O and MPFA-U (the second main variant of MPFA). We reconsider the case previously analyzed. We also consider the case of generally anisotropic, homogeneous permeability on an orthogonal grid.  相似文献   

A multi-dimensional assessment of urban vulnerability to climate change in Sub-Saharan Africa     

Herslund  Lise Byskov  Jalayer  Fatemeh  Jean-Baptiste  Nathalie  J&#;rgensen  Gertrud  Kabisch  Sigrun  Kombe  Wilbard  Lindley  Sarah  Nyed  Patrik Karlsson  Pauleit  Stephan  Printz  Andreas  Vedeld  Trond 《Natural Hazards》2015,82(2):149-172

In this paper, we develop and apply a multi-dimensional vulnerability assessment framework for understanding the impacts of climate change-induced hazards in Sub-Saharan African cities. The research was carried out within the European/African FP7 project CLimate change and Urban Vulnerability in Africa, which investigated climate change-induced risks, assessed vulnerability and proposed policy initiatives in five African cities. Dar es Salaam (Tanzania) was used as a main case with a particular focus on urban flooding. The multi-dimensional assessment covered the physical, institutional, attitudinal and asset factors influencing urban vulnerability. Multiple methods were applied to cover the full range of vulnerabilities and to identify potential response strategies, including: model-based forecasts, spatial analyses, document studies, interviews and stakeholder workshops. We demonstrate the potential of the approach to assessing several dimensions of vulnerability and illustrate the complexity of urban vulnerability at different scales: households (e.g., lacking assets); communities (e.g., situated in low-lying areas, lacking urban services and green areas); and entire cities (e.g., facing encroachment on green and flood-prone land). Scenario modeling suggests that vulnerability will continue to increase strongly due to the expected loss of agricultural land at the urban fringes and loss of green space within the city. However, weak institutional commitment and capacity limit the potential for strategic coordination and action. To better adapt to urban flooding and thereby reduce vulnerability and build resilience, we suggest working across dimensions and scales, integrating climate change issues in city-level plans and strategies and enabling local actions to initiate a ‘learning-by-doing’ process of adaptation.

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Timing of collision initiation and location of the Scandian orogenic suture in the Scandinavian Caledonides          下载免费PDF全文

Trond Slagstad  Christopher L. Kirkland 《地学学报》2018,30(3):179-188

The Scandinavian Caledonides represent a classical example of a deeply eroded Himalayan‐style orogen formed during Baltica–Laurentia continent collision. We propose that initial contact along continental‐margin promontories led to a drop in convergence rate, resulting in increased slab rollback along parts of the margin still undergoing oceanic subduction. Slab rollback caused extension of the overlying lithosphere with orogen‐wide emplacement of mafic layered intrusions, ophiolite formation and bimodal magmatism at 438–434 Ma, in what immediately thereafter became the upper plate (Laurentia) in the Scandian continent–continent collision. A compilation of magmatic ages provides evidence of long‐lived, Ordovician arc magmatism in units above the suture, which is essentially absent below the suture. This model provides a tight constraint on the timing of collision initiation, and provides a framework by which tectonic units comprising the Scandinavian Caledonides can be assigned a Baltican or more exotic heritage.  相似文献