scholarly journals The role of inheritance in forming rifts and rifted margins and building collisional orogens: a Biscay-Pyrenean perspective

2021 ◽  
Author(s):  
Gianreto Manatschal ◽  
Pauline Chenin ◽  
Rodolphe Lescoutre ◽  
Jordi Miró ◽  
Patricia Cadenas ◽  
...  
Keyword(s):  
Numerical Models ◽  
Rift System ◽  
Rifted Margins ◽  
New Concepts ◽  
The Alps ◽  
Orogenic Cycle ◽  
Work Done ◽  
Collisional Orogens ◽  
Rifted Margin

The aim of this paper is to provide a conceptual framework that integrates the role of inheritance in the study of rifts, rifted margins and collisional orogens based on the work done in the OROGEN project, which focuses on the Biscay-Pyrenean system. The Biscay-Pyrenean rift system resulted from a complex multistage rift evolution that developed over a complex lithosphere pre-structured by the Variscan orogenic cycle. There is a general agreement that the Pyrenean-Cantabrian orogen resulted from the reactivation of an increasingly mature rift system along-strike, ranging from a mature rifted margin in the west to an immature and segmented hyperextended rift in the east. However, different models have been proposed to explain the preceding syn-rift evolution and its influence on the subsequent reactivation. Results from the OROGEN project show a sequential reactivation of rift inherited decoupling horizons and identify the specific role of exhumed mantle, hyperextended and necking domains during reactivation. They also highlight the contrasting fate of segment centres vs. segment boundaries during convergence, explaining the non-cylindricity of internal parts of collisional orogens. Results from the OROGEN project also suggest that the role of inheritance is more important during the initial stages of subduction and collision, which may explain the complexity of internal parts of orogenic systems. In contrast, once tectonic systems get more mature, orogenic evolution becomes mostly controlled by first-order physical processes as described in the Coulomb Wedge theory for instance. This may account for the simpler and more continuous architecture of external parts of collisional orogens. It may also explain why most numerical models can reproduce mature orogenic and rift architectures with better accuracy compared to the initial stages of such systems. Thus, while inheritance may not explain steady-state processes, it is a prerequisite for comprehending the initial stages of tectonic systems. The new concepts developed from the OROGEN research are now ready to be tested at other orogenic systems that result from the reactivation of rifted margins, such as the Alps, the Colombian cordilleras and the Caribbean, Taiwan, Oman, Zagros or Timor.

scholarly journals Melt volume at Atlantic volcanic rifted margins controlled by depth-dependent extension and mantle temperature

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Gang Lu ◽  
Ritske S. Huismans
Keyword(s):  
Numerical Models ◽  
Potential Temperature ◽  
Analytical Prediction ◽  
Natural Systems ◽  
Passive Margins ◽  
Margin Width ◽  
Rifted Margins ◽  
Mantle Potential Temperature ◽  
Mantle Temperature ◽  
Rifted Margin

AbstractBreakup volcanism along rifted passive margins is highly variable in time and space. The factors controlling magmatic activity during continental rifting and breakup are not resolved and controversial. Here we use numerical models to investigate melt generation at rifted margins with contrasting rifting styles corresponding to those observed in natural systems. Our results demonstrate a surprising correlation of enhanced magmatism with margin width. This relationship is explained by depth-dependent extension, during which the lithospheric mantle ruptures earlier than the crust, and is confirmed by a semi-analytical prediction of melt volume over margin width. The results presented here show that the effect of increased mantle temperature at wide volcanic margins is likely over-estimated, and demonstrate that the large volumes of magmatism at volcanic rifted margin can be explained by depth-dependent extension and very moderate excess mantle potential temperature in the order of 50–80 °C, significantly smaller than previously suggested.

scholarly journals Rheological inheritance controls the formation of segmented rifted margins in cratonic lithosphere

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
M. Gouiza ◽  
J. Naliboff
Keyword(s):  
Large Scale ◽  
Labrador Sea ◽  
Structural Domains ◽  
Continental Extension ◽  
Margin Width ◽  
Lithospheric Thickness ◽  
Rifted Margins ◽  
Tectonic History ◽  
Rifted Margin

AbstractObservations from rifted margins reveal that significant structural and crustal variability develops through the process of continental extension and breakup. While a clear link exists between distinct margin structural domains and specific phases of rifting, the origin of strong segmentation along the length of margins remains relatively ambiguous and may reflect multiple competing factors. Given that rifting frequently initiates on heterogenous basements with a complex tectonic history, the role of structural inheritance and shear zone reactivation is frequently examined. However, the link between large-scale variations in lithospheric structure and rheology and 3-D rifted margin geometries remains relatively unconstrained. Here, we use 3-D thermo-mechanical simulations of continental rifting, constrained by observations from the Labrador Sea, to unravel the effects of inherited variable lithospheric properties on margin segmentation. The modelling results demonstrate that variations in the initial crustal and lithospheric thickness, composition, and rheology produce sharp gradients in rifted margin width, the timing of breakup and its magmatic budget, leading to strong margin segmentation.

Role of kinematic thermomechanical modelling on constraining asymmetric continental break up

2021 ◽  
Author(s):  
Paul Perron ◽  
Laetitia Le Pourhiet ◽  
Anthony Jourdon ◽  
Tristan Cornu ◽  
Claude Gout
Keyword(s):  
Numerical Modelling ◽  
Cross Sections ◽  
Initial Conditions ◽  
Numerical Models ◽  
Mechanical Coupling ◽  
Lithospheric Thickness ◽  
Rifted Margins ◽  
Major Player ◽  
Long Time ◽  
Rifted Margin

<p>For a long time, the complexity of the lithosphere was ignored by numerical modelling because the inherited structural and compositional complexity of the “real” lithosphere is indeed mainly unknown to geologists so modeler preferred to understand first order parameters such as rate of extension, lithospheric thickness, mechanical coupling or decoupling at the Moho. These models were not representative of any particular region but they were helpful. As a wider community of geologist became interested in numerical modelling, a growing number of numerical models have attempted to account for a major player in structural geology: inheritance. However, the complexity of “real” Earth has been simplified and “idealized” where inherited “anomalies” (e.g. fault, pluton, craton) or a combination of them has been added without really knowing the exact initial conditions which are the unknown of the problem. Yet another approach has been to add a lot of them in a more or less random mater or to replace them by initial noise in the parameters. None of these approaches actually fulfil the need for end-users community to have predictive models.</p><p>Realizing that structural inheritance is some kind of kinematic forcing in the solution of the models but also that it is not possible to anticipate and identify all the geological structures that can be inherited in rifted margin lithospheres, we have developed a new approach, through the integration of a new kinematic module to pTatin2D thermomechanical code, permitting to understand the kinematics of deformation of the continental lithosphere and asthenosphere through time leading to the establishment of rifted margins. The method is settled and validated by fitting the architecture (i.e. basement, Moho, LAB, Tmax) and by solving the kinematics of a random unknow 2D cross section extracted from 3D thermomechanical rifted margin model.</p><p>This new tool aims to help geologists to better constrain and draw on their 2D geological cross sections the position of the Moho, the Lithosphere-Asthenosphere boundary (LAB), the temperature isotherms and the heat flux.</p><p>Key words: Kinematic thermomechanical modelling, asymmetric rifted margin architecture, modelling method.</p>

The role of the Alps in an integrating Europe : Frameworks for prospective debat

2006 ◽  
Vol 94 (2) ◽  
pp. 21-32 ◽  
Author(s):  
Ruggero Schleicher-Tappeser
Keyword(s):  
The Alps

scholarly journals Trans-lithospheric diapirism explains the presence of ultra-high pressure rocks in the European Variscides

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Petra Maierová ◽  
Karel Schulmann ◽  
Pavla Štípská ◽  
Taras Gerya ◽  
Ondrej Lexa
Keyword(s):  
High Pressure ◽  
Numerical Models ◽  
Classical Concept ◽  
Plate Interface ◽  
Ultra High Pressure ◽  
Common Process ◽  
Mountain Belts ◽  
Collisional Orogens ◽  
Rock Association ◽  
European Variscides

AbstractThe classical concept of collisional orogens suggests that mountain belts form as a crustal wedge between the downgoing and overriding plates. However, this orogenic style is not compatible with the presence of (ultra-)high pressure crustal and mantle rocks far from the plate interface in the Bohemian Massif of Central Europe. Here we use a comparison between geological observations and thermo-mechanical numerical models to explain their formation. We suggest that continental crust was first deeply subducted, then flowed laterally underneath the lithosphere and eventually rose in the form of large partially molten trans-lithospheric diapirs. We further show that trans-lithospheric diapirism produces a specific rock association of (ultra-)high pressure crustal and mantle rocks and ultra-potassic magmas that alternates with the less metamorphosed rocks of the upper plate. Similar rock associations have been described in other convergent zones, both modern and ancient. We speculate that trans-lithospheric diapirism could be a common process.

scholarly journals The idea of community and its practice: Tensions, disruptions and hope in Glasgow’s urban growing projects

2021 ◽  
Vol 69 (2) ◽  
pp. 484-499
Author(s):  
Helen Traill
Keyword(s):  
Social Life ◽  
Participant Observation ◽  
Community Gardening ◽  
Conceptual Approach ◽  
The Everyday ◽  
Community Theory ◽  
Communal Space ◽  
Work Done ◽  
Do So

The question of what community comes to mean has taken on increasing significance in sociological debates and beyond, as an increasingly politicised term and the focus of new theorisations. In this context, it is increasingly necessary to ask what is meant when community is invoked. Building on recent work that positions community as a practice and an ever-present facet of human sociality, this article argues that it is necessary to consider the powerful work that community as an idea does in shaping everyday communal practices, through designating collective space and creating behavioural expectations. To do so, the article draws on participant observation and interviews from a community gardening site in Glasgow that was part of a broader research project investigating the everyday life of communality within growing spaces. This demonstrates the successes but also the difficulties of carving out communal space, and the work done by community organisations to enact it. The article draws on contemporary community theory, but also on ideas from Davina Cooper about the role of ideation in social life. It argues for a conceptual approach to communality that does not situate it as a social form or seek it in everyday practice, but instead considers the vacillation between the ideation and practices of community: illustrated here in a designated community place. In so doing, this approach calls into focus the frictions and boundaries produced in that process, and questions the limits of organisational inclusivity.

Digital forensics and evolving cyber law: case of BIMSTEC countries

2019 ◽  
Vol 22 (4) ◽  
pp. 744-752
Author(s):  
Sisira Dharmasri Jayasekara ◽  
Iroshini Abeysekara
Keyword(s):  
Information Technology ◽  
Design Methodology ◽  
Digital Forensics ◽  
Content Type ◽  
Global Context ◽  
Study Approach ◽  
Legal Frameworks ◽  
Work Done

Purpose The purpose of this paper is to discuss the role of digital forensics in an evolving environment of cyber laws giving attention to Bay of Bengal Initiative for Multi-Sectoral Technical and Economic Cooperation (BIMSTEC) countries, comprising Bangladesh, India, Myanmar, Sri Lanka, Thailand, Nepal and Bhutan, in a dynamic global context. Design/methodology/approach This study uses a case study approach to discuss the digital forensics and cyber laws of BIMSTEC countries. The objective of the study was expected to be achieved by referring to decided cases in different jurisdictions. Cyber laws of BIMSTEC countries were studied for the purpose of this study. Findings The analysis revealed that BIMSTEC countries are required to amend legislation to support the growth of information technology. Most of the legislation are 10-15 years old and have not been amended to resolve issues on cyber jurisdictions. Research limitations/implications This study was limited to the members of the BIMSTEC. Originality/value This paper is an original work done by the authors who have discussed the issues of conducting investigations with respect to digital crimes in a rapidly changing environment of information technology and deficient legal frameworks.

Synconvergent and coherent (ultra)high-pressure crustal rock exhumation

2021 ◽  
Author(s):  
Lorenzo G. Candioti ◽  
Joshua D. Vaughan-Hammon ◽  
Thibault Duretz ◽  
Stefan M. Schmalholz
Keyword(s):  
Numerical Models ◽  
A Priori ◽  
Western Alps ◽  
Ultrahigh Pressure ◽  
Plate Motion ◽  
Crustal Rock ◽  
Plate Boundaries ◽  
Crustal Rocks ◽  
Natural Data ◽  
The Alps

<p>Ultrahigh-pressure (UHP) continental crustal rocks were first discovered in the Western Alps in 1984 and have since then been observed at many convergent plate boundaries worldwide. Unveiling the processes leading to the formation and exhumation of (U)HP metamorphic crustal rocks is key to understand the geodynamic evolution of orogens such as the Alps.</p><p> </p><p>Previous numerical studies investigating (U)HP rock exhumation in the Alps predicted deep (>80 km) subduction of crustal rocks and rapid buoyancy-driven exhumation of mainly incoherent (U)HP units, involving significant tectonic mixing forming so-called mélanges. Furthermore, these predictions often rely on excessive erosion or periods of divergent plate motion as important exhumation mechanism. Inconsistent with field observations and natural data, application of these models to the Western Alps was recently criticised.</p><p> </p><p>Here, we present models with continuous plate convergence, which exhibit local tectonic-driven upper plate extension enabling compressive- and buoyancy-driven exhumation of coherent (U)HP units along the subduction interface, involving feasible erosion.</p><p> </p><p>The two-dimensional petrological-thermo-mechanical numerical models presented here predict both subduction initiation and serpentinite channel formation without any a priori prescription of these two features. The (U)HP units are exhumed coherently, without significant internal deformation. Modelled pressure and temperature trajectories and exhumation velocities of selected crustal units agree with estimates for the Western Alps. The presented models support previous hypotheses of synconvergent exhumation, but do not rely on excessive erosion or divergent plate motion. Thus, our predictions provide new insights into processes leading to the exhumation of coherent (U)HP crustal units consistent with observations and natural data from the Western Alps.</p>

Regulation of the Cerebral Circulation: Role of Endothelium and Potassium Channels

1998 ◽  
Vol 78 (1) ◽  
pp. 53-97 ◽  
Author(s):  
FRANK M. FARACI ◽  
DONALD D. HEISTAD
Keyword(s):  
Potassium Channels ◽  
Cerebral Circulation ◽  
Second Messengers ◽  
Chronic Hypertension ◽  
Major Mechanism ◽  
Disease States ◽  
Vasoactive Factors ◽  
New Concepts ◽  
Intracellular Second Messengers

Faraci, Frank M., and Donald D. Heistad. Regulation of the Cerebral Circulation: Role of Endothelium and Potassium Channels. Physiol. Rev. 78: 53–97, 1998. — Several new concepts have emerged in relation to mechanisms that contribute to regulation of the cerebral circulation. This review focuses on some physiological mechanisms of cerebral vasodilatation and alteration of these mechanisms by disease states. One mechanism involves release of vasoactive factors by the endothelium that affect underlying vascular muscle. These factors include endothelium-derived relaxing factor (nitric oxide), prostacyclin, and endothelium-derived hyperpolarizing factor(s). The normal vasodilator influence of endothelium is impaired by some disease states. Under pathophysiological conditions, endothelium may produce potent contracting factors such as endothelin. Another major mechanism of regulation of cerebral vascular tone relates to potassium channels. Activation of potassium channels appears to mediate relaxation of cerebral vessels to diverse stimuli including receptor-mediated agonists, intracellular second messengers, and hypoxia. Endothelial- and potassium channel-based mechanisms are related because several endothelium-derived factors produce relaxation by activation of potassium channels. The influence of potassium channels may be altered by disease states including chronic hypertension, subarachnoid hemorrhage, and diabetes.

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