184 research outputs found
Localization and delocalization of deformation in a bimineralic material
No full textWe investigate how localization and delocalization of deformation occurs in a bimineralic material composed of a strong plagioclase and a weaker quartz phase. We perform numerical, meter-scale shear experiments in which we vary the temperature and the ratio of the two mineral phases. Three micromechanical deformation fields are identified according to the mechanical behavior of the minerals at play (brittle or ductile when both phases are in the brittle or ductile regime, respectively, and semibrittle when one phase is in the brittle and the other in the ductile regime). Besides these micromechanical deformation fields, we identify three deformation types characterizing the degree of localization (type I: localized shear zone, type II: localized anastomosing shear zone, and type III: delocalized shear zone). Type I is expected in the brittle deformation field. In the semibrittle field, all deformation types can be observed depending on the amount of weak phase present. In the ductile field, deformation is dependent on the strength ratio between the two phases. For a low strength ratio, deformation of type III is always observed. For high-strength ratios, deformation of type II can be observed for a moderate amount of weak phase. A small amount of weak phase (This article is published as Jammes, Suzon, Luc L. Lavier, and Jacqueline E. Reber. "Localization and delocalization of deformation in a bimineralic material." Journal of Geophysical Research: Solid Earth 120, no. 5 (2015): 3649-3663. DOI:10.1002/2015JB011890. Posted with permission.</p
Stick-slip and creep behavior in lubricated granular material: Insights into the brittle-ductile transition
No full textCrustal deformation can occur via stick-slip events, viscous creep, or strain transients at variable rates. Here we explore such strain transients with physical experiments comprising a quasi-two-dimensional shear zone with elastic, acrylic discs and interstitial viscous silicone. Experiments of solely elastic discs produce stick-slip events and an overall (constant volume) strengthening. The addition of the viscous silicone enhances localization but does not greatly change the overall pattern of strengthening. It does, however, damp the stick-slip events, leading to transient, creep-like behavior that approaches the behavior of a Maxwell body. There is no gradual transition from frictional to viscous deformation with increasing amounts of silicone, suggesting that the mixed rheology is in effect as soon as an interstitial fluid is present. Our experiments support the hypothesis that a possible cause for strain transients in nature is an interstitial viscous phase in shear zones.This article is published as Reber, Jacqueline E., Nicholas W. Hayman, and Luc L. Lavier. "Stick‐slip and creep behavior in lubricated granular material: Insights into the brittle‐ductile transition." Geophysical Research Letters 41, no. 10 (2014): 3471-3477. DOI:10.1002/2014GL059832. Posted with permission.</p
Modes of continental extension in a crustal wedge
No full text© 2015 Elsevier B.V. We ran numerical experiments of the extension of a crustal wedge as an approximation to extension in an orogenic belt or a continental margin. We study the effects of the strength of the lower crust and of a weak mid-crustal shear zone on the resulting extension styles. A weak mid-crustal shear zone effectively decouples upper crustal extension from lower crustal flow. Without the mid-crustal shear zone, the degree of coupling between the upper and the lower crust increases and extension of the whole crust tends to focus on the thickest part of the wedge. We identify three distinct modes of extension determined by the strength of the lower crust, which are characterized by 1) localized, asymmetric crustal exhumation in a single massif when the lower crust is weak, 2) the formation of rolling-hinge normal faults and the exhumation of lower crust in multiple core complexes with an intermediate strength lower crust, and 3) distributed domino faulting over the weak mid-crustal shear zone when the lower crust is strong. A frictionally stronger mid-crustal shear zone does not change the overall model behaviors but extension occurred over multiple rolling-hinges. The 3 modes of extension share characteristics similar to geological models proposed to explain the formation of metamorphic core complexes: 1) the crustal flow model for the weak lower crust, 2) the rolling-hinge and crustal flow models when the lower crust is intermediate and 3) the flexural uplift model when the lower crust is strong. Finally we show that the intensity of decoupling between the far field extension and lower crustal flow driven by the regional pressure gradient in the wedge control the overall style of extension in the models.We are grateful to Patrice Rey and Loic Labrousse for constructive comments that helped to improve the paper, and Editor Yanick Ricard for helpful assistance. This work was supported in part by the Academic Excellence Alliance program award to Luc L. Lavier from King Abdullah University of Science and Technology (KAUST) Global Collaborative Research under the title "3-D numerical modeling of the tectonic and thermal evolution of continental rifting". This is UTIG contribution 2842
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Continental extension in orogenic belts : modes of extension, origin of core complexes, and two-phase postorogenic extension
No full textContinental extension principally occurs in orogenic belts, however, most of numerical simulations use uniform crust that cannot represent an orogenic belt. We simulate lithospheric extension in an orogenic hinterland approximated by a crustal wedge. We first show that the presence of a preexisting weak mid-crustal shear zone dipping at low angle exerts a critical control on whether crustal and mantle deformation are decoupled or coupled. When the lower crust and the mid-crustal shear zone are weak, decoupling occurs and crustal deformation is compensated by lower crustal flow. When the lower crust is strong or a weak shear zone is absent, coupling occurs and crustal deformation is compensated by flow in the mantle. By varying the strength of the lower crust and the weak shear zone in numerical lithospheric extension experiments, we examine structures developed and compare them with structures observed in extended and collapsed orogenic belts. In models with a weak mid-crustal shear zone, we find that decoupling is particularly effective. In these models, we distinguish three modes of extension: 1) localized, asymmetric crustal exhumation in a single metamorphic massif with a weak lower crust, 2) the formation of rolling-hinge normal faults and the exhumation of lower crust in multiple metamorphic core complexes with an intermediate strength lower crust, and 3) distributed domino faulting over the weak mid-crustal shear zone with a strong lower crust. In models without a mid-crustal shear zone, extension is coupled and structures similar to those observed in continental margins form. We further analyze my model to better explain and understand the core complexes and low-angle normal faults which develop when a preexisting weak mid-crustal shear zone is present. We define three types of detachment systems and present four models which produce core complexes that bear striking resemblance to natural examples: 1) bivergent core complexes, 2) metamorphic core complexes, 3) boudinage structures, and 4) flexural core complexes. We also discuss intracrustal isostasy and the thermal history of material particles sampled in modeled detachment. Finally, based on a geological and geophysical synthesis and using numerical simulations, we propose a two-phase postorogenic extensional scenario that approximates the evolution and the structures observed in the South China Sea margins.Earth and Planetary Science
Mantle Deformation Processes during the Rift-to-Drift Transition at Magma-Poor Margins
No full textThe rift-to-drift transition at rifted margins is an area of active investigation due to the unresolved issues of the the ocean-continent transition. The deep structures that characterize present-day OCTs are often difficult to identify by seismic observations, while terrestrial exposures are preserved only in fragments separated by tectonic discontinuities, such as at some ophiolites. Numerical modeling is a powerful method for contextualizing observations within rifted margin evolution. In this article, we synthesize geological observations from various fossil ocean-continent transitions preserved in ophiolites and from a recent seismic experiment on the Ivorian Margin of West Africa with a novel formulation of GeoFLAC to characterize mantle deformation and melt production for magma-poor margins. Across varied surface heat fluxes, mantle potential temperatures, and extension rates our numerical modeling results show important homologies with geological observations. We propose that the development of large shear zones in the subcontinental mantle, melt infiltration, grain size reduction, and anastomosing detachment faults control the structure of the ocean-continent transition. We also infer, through changes in fault orientation, that the active push of upwelling, melt-rich asthenosphere is an important control on the local stress environment. During the exhumation phase of rifted margin evolution, continentward-dipping shear zones couple with seaward-dipping crustal detachment faults to partially exhume the subcontinental and former asthenospheric mantle. The mantle and crust form lithospheric boudinage that creates core-complex-like domes of peridotite at or near the surface. The faults that exhume these peridotite bodies are largely anastomosing and exhibit magmatic accretion in their footwalls. A combination of magmatic accretion and volcanic activity derived from the shallow melt region constructs the oceanic lithosphere in the footwalls of the out-of-sequence, continentward-dipping detachment faults in the oceanic crust and subcontinental mantle
Erratum to: Review of the nutritional benefits and risks related to intense sweeteners
No full textUnfortunately, the original version of this article [1] contained an error. The author’s names were included incorrectly, the surnames were presented before the forename: Bruyère Olivier, Ahmed H. Serge, Atlan Catherine, Belegaud Jacques, Bortolotti Murielle, Canivenc-Lavier Marie-Chantal, Charrière Sybil, Girardet Jean-Philippe, Houdart Sabine, Kalonji Esther, Nadaud Perrine, Rajas Fabienne, Slama Gérard and Margaritis Irène The author list has been corrected in the original article and is also included correctly below: Olivier Bruyère, Serge H. Ahmed, Catherine Atlan, Jacques Belegaud, Murielle Bortolotti, Marie-Chantal Canivenc-Lavier, Sybil Charrière, Jean-Philippe Girardet, Sabine Houdart, Esther Kalonji, Perrine Nadaud, Fabienne Rajas, Gérard Slama, Irène Margaritis.International audienc
Erratum to: Review of the nutritional benefits and risks related to intense sweeteners
No full textUnfortunately, the original version of this article [1] contained an error. The author’s names were included incorrectly, the surnames were presented before the forename: Bruyère Olivier, Ahmed H. Serge, Atlan Catherine, Belegaud Jacques, Bortolotti Murielle, Canivenc-Lavier Marie-Chantal, Charrière Sybil, Girardet Jean-Philippe, Houdart Sabine, Kalonji Esther, Nadaud Perrine, Rajas Fabienne, Slama Gérard and Margaritis Irène The author list has been corrected in the original article and is also included correctly below: Olivier Bruyère, Serge H. Ahmed, Catherine Atlan, Jacques Belegaud, Murielle Bortolotti, Marie-Chantal Canivenc-Lavier, Sybil Charrière, Jean-Philippe Girardet, Sabine Houdart, Esther Kalonji, Perrine Nadaud, Fabienne Rajas, Gérard Slama, Irène Margaritis.International audienc
Erratum to: Review of the nutritional benefits and risks related to intense sweeteners
No full textUnfortunately, the original version of this article [1] contained an error. The author’s names were included incorrectly, the surnames were presented before the forename: Bruyère Olivier, Ahmed H. Serge, Atlan Catherine, Belegaud Jacques, Bortolotti Murielle, Canivenc-Lavier Marie-Chantal, Charrière Sybil, Girardet Jean-Philippe, Houdart Sabine, Kalonji Esther, Nadaud Perrine, Rajas Fabienne, Slama Gérard and Margaritis Irène The author list has been corrected in the original article and is also included correctly below: Olivier Bruyère, Serge H. Ahmed, Catherine Atlan, Jacques Belegaud, Murielle Bortolotti, Marie-Chantal Canivenc-Lavier, Sybil Charrière, Jean-Philippe Girardet, Sabine Houdart, Esther Kalonji, Perrine Nadaud, Fabienne Rajas, Gérard Slama, Irène Margaritis.International audienc
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An analysis of subduction related tectonics offshore southern and eastern Taiwan
No full texttextArc-continent collision is associated with vigorous mountain building and terrane accretion on relatively short (<10 Ma) geologic timescales. It is believed to be an important mechanism for the growth of continents. Taiwan represents one of the few active examples of this process. As such, is the perfect natural laboratory to investigate the nature of the continent ocean boundary and the uncertain behavior of the accretionary prism and extended, transitional rifted margin crust during the collision process. Taiwan also provides a unique opportunity to investigate structures in the backarc, yielding key insights into the still controversial tectonic conditions that were responsible for the unique subduction-collision system observed today. The obliquity of the collision between the North Luzon Arc and the Chinese rifted margin allows for examination of different temporal stages of collision at different locations. Recently acquired seismic reflection and wide-angle seismic refraction data, offshore Taiwan, document the crustal structure of the incipient mountain belt and of the Philippine Sea Plate in the backarc domain to the east. Geophysical profiles offshore southern Taiwan show evidence for a transition from the subduction of ocean crust to highly extended, transitional continental crust of the northern South China Sea distal margin. During oceanic subduction, accretion and underplating of thick sedimentary cover sequences create a large 13-15 km thick accretionary prism. Prior to the encroachment of the continental shelf, there is evidence for further underplating of transitional distal margin crust to the base of the prism. These findings support a multi-phase collisional model in which early growth of the mountain belt is driven by structural underplating of the previously sedimentary-only accretionary prism with blocks of transitional crust from the distal rifted margin. Geophysical profiles offshore eastern Taiwan show evidence for asymmetric crustal thickening, from 12-18 km, along the entire length of the Gagua Ridge suggesting the West Philippine Basin oceanic crust is underthust beneath that of the Huatung Basin. In this interpretation, the Gagua Ridge was the result of a failed subduction initiation event during the early Miocene that may have existed simultaneously and, for a short time, competed with the Manila subduction zone in accommodating convergence between the Eurasia and Philippine Sea plates.Earth and Planetary Science
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From rifting to collision : the evolution of the Taiwan Mountain Belt
No full texttextArc-continent collisions are believed to be an important mechanism for the growth of continents. Taiwan is one of the modern day examples of this process, and as such, it is an ideal natural laboratories to investigate the uncertain behavior of continental crust during collision. The obliquity of collision between the northern South China Sea (SCS) rifted margin and Luzon arc in the Manila trench subduction zone allows for glimpses into different temporal stages of collision at different spatial locations, from the mature mountain-belt in central-northern Taiwan to the 'pre-collision' rifted margin and subduction zone south of Taiwan. Recently acquired seismic reflection and wide-angle seismic refraction data document the crustal-scale structure of the mountain belt through these different stages. These data reveal a wide rifted margin near Taiwan with half-graben rift basins along the continental shelf and a broad distal margin consisting of highly-extended continental crust modified by post-rift magmatism. Magmatic features in the distal margin include sills in the post-rift sediments, intruded crust, and a high-velocity lower crustal layer that likely represents mafic magmatism. Post-rift magmatism may have been induced by thermal erosion of lithospheric mantle following breakup and the onset of seafloor spreading. Geophysical profiles across the early-stage collision offshore southern Taiwan show evidence the thin crust of the distal margin is subducting at the Manila trench and structurally underplating the growing orogenic wedge ahead of the encroaching continental shelf. Subduction of the distal margin may induce a pre-collision flexural response along the continental shelf as suggested by a recently active major rift fault and a geodynamic model of collision. The weak rift faults may be inverted during the subsequent collision with the continental shelf. These findings support a multi-phase collision model where the early growth of the mountain belt is driven in part by underplating of the accretionary prism by crustal blocks from the distal margin. The wedge is subsequently uplift and deformed during a collision with the continental shelf that involves both thin-skinned and thick-skinned structural styles. This model highlights the importance of rifting styles on mountain-building.Earth and Planetary Science
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