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  • 2020-2023  (11,262)
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  • 1
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    A user-friendly, multi-parameter protocol for monitoring permafrost thaw (2021)
    In:  EPIC3AGU Fall Meeting, New Orleans, LA, USA/Online, 2021-12-13-2021-12-17
    Details
    Publication Date: 2022-01-09
    Description: There is an urgent need for standardized data collection to better understand permafrost thaw and its interaction with vegetation, hydrology, soil and snow. To enable this, the Permafrost Thaw Action Group of T-MOSAiC have developed a protocol for gathering integrated observations of multiple connected components of permafrost landscapes. It is integrated with a user-friendly app aimed at non-experts to facilitate collection and synthesis of data from across the Arctic. Recognizing the fundamental role of interactions between the different components of the permafrost system, we provide measurement guidelines for variables pertaining to snow, vegetation, hydrology, soil and permafrost in a single protocol. The measured variables include snow depth, vegetation height, water level, soil type, and thaw depth. The protocol locates all measurements on transects that are revisited throughout the year. The co-located measurements of multiple variables facilitate quantification of interactions between these variables and model–data integration. The protocol is geared toward non-experts, including citizen scientists. We provide video tutorials and a user-friendly app. The protocol uses simple measurements that do not require specialist equipment or skills. While variables that are more difficult to measure could not be included, we believe that the simplicity of the protocols will enable greater participation in data collection and thus an improved coverage of the permafrost region. Along with the protocol and app, we present the first results from the data collection which has been live now for several months, and details of how to get involved.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Format: application/pdf
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  • 2
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    Debris cover on thaw slumps and its insulative role in a warming climate (2020)
    Wiley
    In:  EPIC3Earth Surface Processes and Landforms, Wiley, ISSN: 0197-9337
    Details
    Publication Date: 2022-10-21
    Description: Thaw slumps in ice‐rich permafrost can retreat tens of metres per summer, driven by the melt of subaerially exposed ground ice. However, some slumps retain an ice‐veneering debris cover as they retreat. A quantitative understanding of the thermal regime and geomorphic evolution of debris‐covered slumps in a warming climate is largely lacking. To characterize the thermal regime, we instrumented four debris‐covered slumps in the Canadian Low Arctic and developed a numerical conduction‐based model. The observed surface temperatures 20°C and steep thermal gradients indicate that debris insulates the ice by shifting the energy balance towards radiative and turbulent losses. After the model was calibrated and validated with field observations, it predicted sub‐debris ice melt to decrease four‐fold from 1.9 to 0.5 m as the thickness of the fine‐grained debris quadruples from 0.1 to 0.4 m. With warming temperatures, melt is predicted to increase most rapidly, in relative terms, for thick (~0.5‐1.0 m) debris covers. The morphology and evolution of the debris‐covered slumps were characterized using field and remote sensing observations, which revealed differences in association with morphology and debris composition. Two low‐angle slumps retreated continually despite their persistent fine‐grained debris covers. The observed elevation losses decreased from ~1.0 m/yr where debris thickness ~.2 m to 0.1 m/yr where thickness ~1.0 m. Conversely, a steep slump with a coarse‐grained debris veneer underwent short‐lived bursts of retreat, hinting at a complex interplay of positive and negative feedback processes. The insulative protection and behaviour of debris vary significantly with factors such as thickness, grain size and climate: debris thus exerts a fundamental, spatially variable influence on slump trajectories in a warming climate.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
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    Images and videos of analogue centrifuge models exploring marginal flexure during rifting in Afar, East Africa (2020)
    GFZ Data Services
    Details
    Publication Date: 2022-01-28
    Description: Abstract
    Description: This data set includes images and videos depicting the evolution of deformation and topography of 17 analogue experiments c passive margin development, to better understand the ongoing tectonics along the western margin of Afar, East Africa. The tectonic background that forms the basis for the experimental design is found in Zwaan et al. 2019 and 2020a-b, and references therein. The experiments, in an enhanced gravity field in a large-capacity centrifuge, examined the influence of brittle layer thickness, strength contrast, syn-rift sedimentation and oblique extension on a brittle-viscous system with a strong and weak viscous domain. All experiments were performed at the Tectonic Modelling Laboratory of of the Istituto di Geoscience e Georisorse - Consiglio Nazionale delle Ricerche (CNR-IGG) and of the Earth Sciences Department of the University of Florence (CNR/UF). The brittle layer (sand) thickness ranged between 6 and 20 mm, the underlying viscous layer, split in a competent and weak domain (both viscous mixtures), was always 10 mm thick. Asymmetric extension was applied by removing a 1.5 mm thick spacer at the side of the model at every time step, allowing the analogue materials to spread when enhanced gravity was applied during a centrifuge run. Differential stretching of the viscous material creates flexure and faulting in the overlying brittle layer. Total extension amounted to 10.5 mm over 7 intervals for Series 1 models that aimed at understanding generic passive margin development in a generic orthogonal extension setting, whereas up to 16.5 mm of extension was applied for the additional Series 2 models aiming at reproducing the tectonic phases in Afar. In models involving sedimentation, sand was filled in at time steps 2, 4 and 6 (i.e. after 3, 6 and 9 mm of extension). Detailed descriptions of the experiments, monitoring techniques and tectonic interpretation of the model results are presented in Zwaan et al. (2020c) to which these data are supplementary.
    Keywords: EPOS ; Analogue modelling results ; multi-scale laboratories ; Rifting ; Passive margin ; antiform ; deformation 〉 ductile flow ; deformation 〉 folding ; deformation 〉 fracturing ; depression ; EARTH SCIENCE 〉 SOLID EARTH 〉 TECTONICS 〉 PLATE TECTONICS 〉 CRUSTAL MOTION 〉 CRUSTAL MOTION DIRECTION ; EARTH SCIENCE 〉 SOLID EARTH 〉 TECTONICS 〉 PLATE TECTONICS 〉 FAULT MOVEMENT 〉 FAULT MOVEMENT DIRECTION ; EARTH SCIENCE 〉 SOLID EARTH 〉 TECTONICS 〉 PLATE TECTONICS 〉 PLATE BOUNDARIES ; EARTH SCIENCE 〉 SOLID EARTH 〉 TECTONICS 〉 PLATE TECTONICS 〉 STRAIN ; EARTH SCIENCE 〉 SOLID EARTH 〉 TECTONICS 〉 PLATE TECTONICS 〉 STRESS ; flexure/buckle ; geologic process ; graben ; graben ; normal fault ; plateau ; rift valley ; rifting ; sedimentary process 〉 deposition ; tectonic and structural features ; tectonic process 〉 continental_breakup 〉 rifting ; tectonic setting 〉 extended terrane setting 〉 continental rift setting ; tectonic setting 〉 plate margin setting 〉 active continental margin setting ; tectonic setting 〉 plate spreading center setting
    Type: Dataset , Dataset
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  • 4
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    Competition between 3D structural inheritance and kinematics during rifting: Insights from analogue models (2022)
    In:  Basin Research
    Details
    Publication Date: 2022-04-11
    Description: he competition between the impact of inherited weaknesses and plate kinematics determines the location and style of deformation during rifting, yet the relative impacts of these ‘internal’ and ‘external’ factors remain poorly understood, especially in 3D. In this study, we used brittle-viscous analogue models to assess how multiphase rifting, that is changes in plate divergence rate or direction, and the presence and orientation of weaknesses in the competent mantle and crust, influences rift evolution. We find that the combined reactivation of mantle and crustal weaknesses without any kinematic changes already creates complex rift structures. Divergence rates affect the strength of the weak lower crustal layer and hence the degree of mantle-crustal coupling; slow rifting decreases coupling, so that crustal weaknesses can dominate deformation localisation and surface structures, whereas fast rifting increases coupling and deformation related to mantle weaknesses can have a dominant surface expression. Through a change from slow to fast rifting mantle-related deformation can overprint structures that previously formed along (differently oriented) crustal weaknesses. Conversely, a change from fast to slow rifting may shift deformation from mantle-controlled towards crust-controlled. When changing divergence directions, structures from the first rifting phase may control where subsequent deformation occurs, but only when they are sufficiently well developed. We furthermore place our results in a larger framework of brittle-viscous rift modelling results from previous experimental studies, showing the importance of general lithospheric layering, divergence rate, the type of deformation in the mantle, and finally upper crustal structural inheritance. The interaction between these parameters can produce a variety of deformation styles that may, however, lead to comparable end products. Therefore, careful investigation of the distribution of strain localisation, and to an equal extent of basin depocenter locations over time is required to properly determine the evolution of complex rift systems, providing an incentive to revisit various natural examples.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 5
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    Ring-shear test data of feldspar sand FS900S used in the Tectonic Modelling Laboratory at the University of Bern (Switzerland) (2022)
    GFZ Data Services
    Details
    Publication Date: 2022-12-20
    Description: This dataset provides friction data from ring-shear tests on feldspar sand FS900S used for the simulation of brittle behaviour in crust- and lithosphere-scale analogue experiments at the Tectonic Modelling Laboratory of the University of Bern (Zwaan et al. in prep; Richetti et al. in prep). The materials have been characterized by means of internal friction parameters as a remote service by the Helmholtz Laboratory for Tectonic Modelling (HelTec) at the GFZ German Research Centre for Geosciences in Potsdam (Germany). According to our analysis both materials show a Mohr-Coulomb behaviour characterized by a linear failure envelope. Peak, dynamic and reactivation friction coefficients of the feldspar sand are μP = 0.65, μD = 0.57, and μR = 0.62, respectively, and the Cohesion of the feldspar sand is in the order of 5-20 Pa. An insignificant rate-weakening of less than 1% per ten-fold rate change is registered for the feldspar sand. Granular healing is also minor.
    Language: English
    Type: info:eu-repo/semantics/workingPaper
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  • 6
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    A review of tectonic models for the rifted margin of Afar: Implications for continental break-up and passive margin formation (2020)
    In:  Journal of African Earth Sciences
    Details
    Publication Date: 2022-03-18
    Description: The Afar region represents a unique opportunity for the study of ongoing rift development and the various phases of continental break-up. In this work we discuss the geological and geomorphological characteristics of the Western Afar Margin (WAM) and the various scenarios proposed for its evolution. A drastic decline in topography and crustal thickness from the Ethiopian Plateau into the Afar Depression, as well as a series of marginal grabens and a general presence of antithetic faulting characterize the WAM. Present-day extension is mostly accommodated at the rift axis in Afar, yet the margin is still undergoing significant deformation. Models for the evolution of the WAM involve either isostatic loading effects due to erosion, rifting-induced block rollover, large-scale detachment fault development or crustal flexure due to lithospheric stretching or magmatic loading. This wide variation of potential mechanisms for WAM development may reflect a general structural variation along the margin and in Afar, involving different stages of rift formation and possibly indicating two distinct pathways leading to continental break-up. In order to better understand the rifting mechanisms and to fully exploit the research potential of the region, further assessment of the WAM and its relation to Afar will be necessary. The findings of such future work, combined with data from rifts and passive margins from around the globe will be of great importance to assess the processes involved in continental breakup and to better constrain the sequence of events leading from initial rifting to break-up and oceanic spreading.
    Language: English
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  • 7
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    Structural Analysis of the Western Afar Margin, East Africa: Evidence for Multiphase Rotational Rifting (2020)
    In:  Tectonics
    Details
    Publication Date: 2022-03-18
    Description: The Afar region in East Africa represents a key location to study continental breakup. We present an integrated structural analysis of the Western Afar Margin (WAM) aiming to better understand rifted margin development and the role of plate rotation during rifting. New structural information from remote sensing, fieldwork, and earthquake data sets reveals that the N-S striking WAM is still actively deforming and is characterized by NNW-SSE normal faulting as well as a series of marginal grabens. Seismicity distribution analysis and the first-ever borehole-calibrated sections of this developing passive margin show recent slip concentrated along antithetic faults. Tectonic stress parameters derived from earthquake focal mechanisms reveal different extension directions along the WAM (82°N), in Afar (66°N) and in the Main Ethiopian Rift (108°N). Fault slip analysis along the WAM yields the same extension direction. Combined with GPS data, this shows that current tectonics in Afar is dominated by the local rotation of the Danakil Block, considered to have occurred since 11 Ma. Earlier stages of Afar development (since 31–25 Ma) were most likely related to the large-scale rotation of the Arabian plate. Various authors have proposed scenarios for the evolution of the WAM. Any complete model should consider, among other factors, the multiphase tectonic history and antithetic fault activity of the margin. The findings of this study are not only relevant for a better understanding of the WAM but also provide insights into the role of multiphase rotational extension during rifting and passive margin formation in general.
    Language: English
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  • 8
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    Analogue modelling of marginal flexure in Afar, East Africa: Implications for passive margin formation (2020)
    In:  Tectonophysics
    Details
    Publication Date: 2022-03-18
    Description: The Afar region in East Africa is a key locality for studying continental break-up. Within Afar, passive margins are developing, of which the Southern Afar Margin (SAM) contains synthetic (basinward) faulting, whereas crustal flexure, antithetic faulting and marginal grabens occur along the Western Afar Margin (WAM). Numerous conflicting scenarios for the evolution of the WAM exist. In this analogue modelling study we test various factors that may affect the development of a WAM-style passive margin: brittle crustal thickness, (en echelon) rheological contrasts, sedimentation and oblique extension. Our experimental results illustrate how marginal flexure due to a weak lower crust below Afar can elegantly account for the structural features of the WAM. Brittle crustal thickness controls what structures occur: a thinner brittle crust accommodates flexure internally, whereas increasing brittle thicknesses lead to faulting. Large escarpment faults develop early on, followed by late-stage antithetic faulting and marginal grabens. A thicker brittle crust also causes enhanced subsidence, and increased strength contrasts between lower crustal domains leads to more localized deformation. Basin-wide sedimentation causes enhanced subsidence, as well as longer activity along large synthetic (escarpment) faults. Finally, oblique extension clearly prevents the development of marginal grabens, which only form in near-orthogonal extension. These results support a tectonic scenario involving initial oblique extension due to Arabian plate motion, creating echelon synthetic escarpment faults along the WAM. After the Danakil Block started its independent rotation, near-orthogonal extension conditions were established, allowing (enhanced) marginal flexure, antithetic faulting and marginal graben formation along the older en echelon escarpment. Differences in extension obliquity may also explain the differences in structural architectures between the WAM and SAM. The characteristics of the WAM are typical of magma-rich passive margins, and the margin has great potential for studying continental break-up and (magma-rich) passive margin formation.
    Language: English
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  • 9
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    Rift propagation in rotational versus orthogonal extension: Insights from 4D analogue models (2020)
    In:  Journal of Structural Geology
    Details
    Publication Date: 2022-03-18
    Description: In rift settings, extension rates often vary along strike, due to rotation about a vertical axis or Euler pole, yet tectonic modelers traditionally apply constant along-strike deformation rates. Here we compare rift development and propagation under traditional orthogonal extension versus rotational extension conditions. The set-ups involve brittle-viscous layering and localize deformation through structural weaknesses (seeds). Our models provide first-order insights into the differences in rift development between both boundary conditions: orthogonal extension produces a rift basin with constant synchronous along-strike features, whereas rotational extension induces along-strike structural gradients, diachronous rift development causing rift propagation and the development of V-shaped basins. We observe important viscous flow associated with differential pressure gradients in rotational extension. We also describe the important effects of strain partitioning between rift axis and model boundaries, the quantifying of which is crucial to avoid incorrect model interpretations. Although our model results are first-order only, they are in good agreement with various natural examples and previous modeling studies and highlight the importance of considering the third dimension when studying tectonic systems.
    Language: English
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  • 10
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    Rift segment interaction in orthogonal and rotational extension experiments: Implications for the large-scale development of rift systems (2020)
    In:  Journal of Structural Geology
    Details
    Publication Date: 2022-03-18
    Description: During extension of the continental lithosphere, rift basins develop. These are often initially offset, and must interact and connect in order to create a continuous rift system that may ultimately achieve break-up. When simulating extensional tectonics and rift interaction structures, analogue and numerical modellers often apply a continuous extension rate along the strike of a rift or rift system. Yet in nature significant extension velocity variations occur along rifts and plate boundaries as a natural consequence of tectonic plates moving apart about a pole of rotation, resulting in rotational extension, and associated rift propagation and structural gradients. Here we present various analogue tectonic experiments to assess rift interaction structures forming in orthogonal extension settings versus rotational extension settings. Our modelling efforts show that rotational extension and orthogonal extension produce significantly different large-scale structures. Rotational extension can cause important variations in rift maturity between rift segments, delay rift interaction zone development, and make rift segments propagate in opposite directions. Still, local features in a rotational extension system can often be regarded as evolving in an orthogonal extension setting. Furthermore, we find that various degrees of rift underlap produce three basic modes of rift linkage structures. Low underlap distance (high angle φ) experiments develop rift pass structures. With increasing underlap distance (φ = ca. 40°), transfer zone basins develop. High degrees of underlap (φ ≤ 30°) tend to result in en echelon sub-basins. Our results match with data from previous modelling efforts and natural examples. We furthermore propose a large-scale tectonic scenario for the East African Rift System based on rotational extension and associated rift propagation. These insights may also be applicable when studying other large-scale rift systems.
    Language: English
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