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Johannes C. Vrijmoed - One of the best experts on this subject based on the ideXlab platform.
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evidence for non Lithostatic Pressure in subducted continental crust
Contributions to Mineralogy and Petrology, 2020Co-Authors: Jamie Cutts, Matthijs A. Smit, Johannes C. VrijmoedAbstract:Continental crust buried during collisional orogeny typically records Pressures of 3 GPa or lower; however, Pressures much higher than this are recorded locally, which would suggest burial to mantle depths. Deep continental subduction is not observed in active orogens and should be hindered by the positive buoyancy of sialic crust relative to the mantle. Non-Lithostatic Pressure caused by mechanical contrasts between rock types provides an alternative explanation for extreme Pressures recorded in buried continental crust; however, its occurrence and significance in natural systems is debated. Mechanical Pressure heterogeneities were proposed specifically to explain extreme Pressures of c. 5.5 GPa obtained in enstatite eclogite veins in the archetypal subducted continental terrane, the Western Gneiss Complex (WGC) in Norway. In this study, we use Lu–Hf garnet geochronology to test when, and thus, in what part of the burial cycle of the WGC the enstatite eclogite assemblages actually equilibrated. The results show that equilibration occurred at c. 393 Ma, which is much later than the typical ages obtained from ‘normal’ eclogites in the WGC and represents a time when the terrane was already at crustal depths (< 2.5 GPa). Finite element modeling of mechanical Pressure distribution demonstrates that late extreme Pressure excursions are feasible for the given rock system and could explain the seemingly spurious conditions recorded in these unusual rocks. The recognition of non-Lithostatic ultrahigh-Pressure in deeply buried continental crust allows crucial simplification of models for continental subduction and validates the importance of rock thermo-mechanics in interpreting observations from collision zones.
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Evidence for non-Lithostatic Pressure in subducted continental crust
Contributions to Mineralogy and Petrology, 2019Co-Authors: Jamie Cutts, Matthijs A. Smit, Johannes C. VrijmoedAbstract:Continental crust buried during collisional orogeny typically records Pressures of 3 GPa or lower; however, Pressures much higher than this are recorded locally, which would suggest burial to mantle depths. Deep continental subduction is not observed in active orogens and should be hindered by the positive buoyancy of sialic crust relative to the mantle. Non-Lithostatic Pressure caused by mechanical contrasts between rock types provides an alternative explanation for extreme Pressures recorded in buried continental crust; however, its occurrence and significance in natural systems is debated. Mechanical Pressure heterogeneities were proposed specifically to explain extreme Pressures of c. 5.5 GPa obtained in enstatite eclogite veins in the archetypal subducted continental terrane, the Western Gneiss Complex (WGC) in Norway. In this study, we use Lu–Hf garnet geochronology to test when, and thus, in what part of the burial cycle of the WGC the enstatite eclogite assemblages actually equilibrated. The results show that equilibration occurred at c. 393 Ma, which is much later than the typical ages obtained from ‘normal’ eclogites in the WGC and represents a time when the terrane was already at crustal depths (
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Current challenges for explaining (ultra)high‐Pressure tectonism in the Pennine domain of the Central and Western Alps
Journal of Metamorphic Geology, 2015Co-Authors: Filippo Schenker, Stefan M. Schmalholz, Evangelos Moulas, Jean Pleuger, Lukas P. Baumgartner, Yuri Y. Podladchikov, Johannes C. Vrijmoed, N. Buchs, Othmar MüntenerAbstract:The Pennine domain of the Central and Western (PCW) Alps, including the Dora-Maira, Monte Rosa, Gran Paradiso, Adula/Cima Lunga nappes and the Zermatt-Saas zone underwent ultrahigh- or high-Pressure [(U)HP >1.5 GPa] metamorphism during the Alpine orogeny. We review structural, petrological and geochronological data for the (U)HP units in the PCW Alps (i) to clarify the relationship between (U)HP metamorphism and deformation, (ii) to confront published exhumation models for the (U)HP units with the reviewed data and (iii) to evaluate consequences of different pre-Alpine paleogeographic settings (Penrose-type ocean v. hyperextended margins) on the Alpine orogeny. The review indicates that (i) peak Pressures are recorded only in minor volumes of the corresponding tectonic nappes; (ii) (U)HP rocks occur within coherent and imbricate thrust sheets which show substantial Pressure jumps; (iii) peak Pressures are mostly associated with a top-to-the-foreland kinematics; (iv) decompression from (U)HP (4 to >1.5 GPa) to greenschist or amphibolite facies (~1 GPa) metamorphic conditions was fast ( ~3180 kg m3) rocks is questionable, because there is no evidence of such rocks around the (U)HP units. An alternative model, which could explain the main characteristics of the (U)HP units in the PCW Alps, is an orogenic wedge model that (i) involves dynamic stresses deviating from Lithostatic Pressure and (ii) is formed during the convergence of hyperextended margins. Deviations of dynamic stresses from the Lithostatic Pressure and local Pressure variations cannot be excluded during the Alpine orogeny, but these deviations and variations have not been clearly identified until now.
Gaku Kimura - One of the best experts on this subject based on the ideXlab platform.
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Non-LithostaticPressure in subductionzones
2012Co-Authors: Hugues Raimbourg, Gaku KimuraAbstract:The Pressure at depth is not directly observable and no one knows precisely to which extent the Pressure conditions in subduction zones, recorded by high-Pressure metamorphic rocks, deviate from mantle Lithostatic Pressure. As an alternative to large-scale complex numerical models of subduction zones, the analytical subduction channel model can give us some insight on the physical processes that control the development of non-Lithostatic Pressure, as well as some estimation of its amplitude. We propose a new approach coupling the flow of crust within the channel to the deformation of the mantle bounding the channel, occurring as the Pressure within the channel deviates from mantle Lithostatic values. While for very weak crust within the subduction channel, the channel walls are rigid and channel geometry does not vary, for stronger crust, our coupled approach unravels a new domain of behaviour where the mantle is no longer completely rigid and the deformation of the channel walls prevents arbitrarily large non-Lithostatic Pressure to develop. This new regime poses an upper bound on the amplitude of non-Lithostatic Pressure within the channel that depends only on the mantle viscosity. The transition from one regime to another is dependent on an adimensional parameter 3 0 3 m c h L , incorporating not only mantle and crust viscosity but also the geometry of the channel. The development of larger non-Lithostatic Pressure in thinner channels than in larger ones, predicted in the rigid channel model, is partly inhibited in the fully coupled model as thinner channels more easily induce channel wall deformation. The lengthscale of the channel width perturbations influences the amplitude of non-Lithostatic Pressure, as small-scale ones, inducing a more rigid response of the mantle, potentially trigger larger non-Lithostatic Pressure.
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Non-Lithostatic Pressure in subduction zones
Earth and Planetary Science Letters, 2008Co-Authors: Hugues Raimbourg, Gaku KimuraAbstract:Abstract The Pressure at depth is not directly observable and no one knows precisely to which extent the Pressure conditions in subduction zones, recorded by high-Pressure metamorphic rocks, deviate from mantle Lithostatic Pressure. As an alternative to large-scale complex numerical models of subduction zones, the analytical subduction channel model can give us some insight on the physical processes that control the development of non-Lithostatic Pressure, as well as some estimation of its amplitude. We propose a new approach coupling the flow of crust within the channel to the deformation of the mantle bounding the channel, occurring as the Pressure within the channel deviates from mantle Lithostatic values. While for very weak crust within the subduction channel, the channel walls are rigid and channel geometry does not vary, for stronger crust, our coupled approach unravels a new domain of behaviour where the mantle is no longer completely rigid and the deformation of the channel walls prevents arbitrarily large non-Lithostatic Pressure to develop. This new regime poses an upper bound on the amplitude of non-Lithostatic Pressure within the channel that depends only on the mantle viscosity. The transition from one regime to another is dependent on an adimensional parameter α = μ m μ c h 0 3 L 3 , incorporating not only mantle and crust viscosity but also the geometry of the channel. The development of larger non-Lithostatic Pressure in thinner channels than in larger ones, predicted in the rigid channel model, is partly inhibited in the fully coupled model as thinner channels more easily induce channel wall deformation. The lengthscale of the channel width perturbations influences the amplitude of non-Lithostatic Pressure, as small-scale ones, inducing a more rigid response of the mantle, potentially trigger larger non-Lithostatic Pressure.
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In situ Pressure–temperature conditions of a tectonic mélange: Constraints from fluid inclusion analysis of syn-mélange veins
Island Arc, 2003Co-Authors: Yoshitaka Hashimoto, M. Enjoji, Arito Sakaguchi, Gaku KimuraAbstract:Pressure and temperature (P–T) conditions of melange formation are estimated from fluid inclusions within “syn-melange” veins developed in the necks of boudins of sandstone blocks in the melange of the Shimanto accretionary complex, south-west Japan. The melange records decollement-zone processes. P–T conditions are in the range of 81 (+15) to 235 (±18) MPa and 150 (±25) to 220 (±31)°C. Assuming a constant fluid-Pressure to Lithostatic-Pressure ratio for each data set, we estimate a P–T gradient of between 10.0°C/km (+0.2/−1.5) (Lithostatic Pressure) and 4.2°C/km (+0.1/−0.9) (hydrostatic Pressure) from these results. The estimated Lithostatic P–T gradient is much lower than that calculated from the age of the subducting oceanic plate. The estimated P–T conditions suggest that the melange was formed within the seismogenic zone (hypothesized from thermal modeling), although the deformation mechanism of melange (i.e. dominant diffusive mass transfer mainly in shale matrix with minor brittle breakage mainly in sandstone blocks) does not show evidence of seismic deformation. In addition, at the time of syn-melange vein formation, a shale matrix of melange has injected into the vein, which indicates a ductile deformation of shale. A possible explanation for this discrepancy is that the melange was formed during the interseismic period.
Jamie Cutts - One of the best experts on this subject based on the ideXlab platform.
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evidence for non Lithostatic Pressure in subducted continental crust
Contributions to Mineralogy and Petrology, 2020Co-Authors: Jamie Cutts, Matthijs A. Smit, Johannes C. VrijmoedAbstract:Continental crust buried during collisional orogeny typically records Pressures of 3 GPa or lower; however, Pressures much higher than this are recorded locally, which would suggest burial to mantle depths. Deep continental subduction is not observed in active orogens and should be hindered by the positive buoyancy of sialic crust relative to the mantle. Non-Lithostatic Pressure caused by mechanical contrasts between rock types provides an alternative explanation for extreme Pressures recorded in buried continental crust; however, its occurrence and significance in natural systems is debated. Mechanical Pressure heterogeneities were proposed specifically to explain extreme Pressures of c. 5.5 GPa obtained in enstatite eclogite veins in the archetypal subducted continental terrane, the Western Gneiss Complex (WGC) in Norway. In this study, we use Lu–Hf garnet geochronology to test when, and thus, in what part of the burial cycle of the WGC the enstatite eclogite assemblages actually equilibrated. The results show that equilibration occurred at c. 393 Ma, which is much later than the typical ages obtained from ‘normal’ eclogites in the WGC and represents a time when the terrane was already at crustal depths (< 2.5 GPa). Finite element modeling of mechanical Pressure distribution demonstrates that late extreme Pressure excursions are feasible for the given rock system and could explain the seemingly spurious conditions recorded in these unusual rocks. The recognition of non-Lithostatic ultrahigh-Pressure in deeply buried continental crust allows crucial simplification of models for continental subduction and validates the importance of rock thermo-mechanics in interpreting observations from collision zones.
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Evidence for non-Lithostatic Pressure in subducted continental crust
Contributions to Mineralogy and Petrology, 2019Co-Authors: Jamie Cutts, Matthijs A. Smit, Johannes C. VrijmoedAbstract:Continental crust buried during collisional orogeny typically records Pressures of 3 GPa or lower; however, Pressures much higher than this are recorded locally, which would suggest burial to mantle depths. Deep continental subduction is not observed in active orogens and should be hindered by the positive buoyancy of sialic crust relative to the mantle. Non-Lithostatic Pressure caused by mechanical contrasts between rock types provides an alternative explanation for extreme Pressures recorded in buried continental crust; however, its occurrence and significance in natural systems is debated. Mechanical Pressure heterogeneities were proposed specifically to explain extreme Pressures of c. 5.5 GPa obtained in enstatite eclogite veins in the archetypal subducted continental terrane, the Western Gneiss Complex (WGC) in Norway. In this study, we use Lu–Hf garnet geochronology to test when, and thus, in what part of the burial cycle of the WGC the enstatite eclogite assemblages actually equilibrated. The results show that equilibration occurred at c. 393 Ma, which is much later than the typical ages obtained from ‘normal’ eclogites in the WGC and represents a time when the terrane was already at crustal depths (
Nick Varley - One of the best experts on this subject based on the ideXlab platform.
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Pore Pressure embrittlement in a volcanic edifice
Bulletin of Volcanology, 2016Co-Authors: Jamie Farquharson, Michael J. Heap, Patrick Baud, Thierry Reuschlé, Nick VarleyAbstract:The failure mode of porous rock in compression—dilatant or compactant—is largely governed by the overlying Lithostatic Pressure and the Pressure of pore fluids within the rock (Wong, Solid Earth 102:3009–3025, 1997), both of which are subject to change in space and time within a volcanic edifice. While Lithostatic Pressure will tend to increase monotonously with depth due to the progressive accumulation of erupted products, pore Pressures are prone to fluctuations (during periods of volcanic unrest, for example). An increase in pore fluid Pressure can result in rock fracture, even at depths where the Lithostatic Pressure would otherwise preclude such dilatant behaviour—a process termed pore fluid-induced embrittlement. We explore this phenomenon through a series of targeted triaxial experiments on typical edifice-forming andesites (from Volcan de Colima, Mexico). We first show that increasing pore Pressure over a range of timescales (on the order of 1 min to 1 day) can culminate in brittle failure of otherwise intact rock. Irrespective of the pore Pressure increase rate, we record comparable accelerations in acoustic emission and strain prior to macroscopic failure. We further show that oscillating pore fluid Pressures can cause iterative and cumulative damage, ultimately resulting in brittle failure under relatively low effective mean stress conditions. We find that macroscopic failure occurs once a critical threshold of damage is surpassed, suggesting that only small increases in pore Pressure may be necessary to trigger failure in previously damaged rocks. Finally, we observe that inelastic compaction of volcanic rock (as we may expect in much of the deep edifice) can be overprinted by shear fractures due to this mechanism of embrittlement. Pore fluid-induced embrittlement of edifice rock during volcanic unrest is anticipated to be highest closer to the conduit and, as a result, may assist in the development of a fractured halo zone surrounding the conduit, potentially explaining commonly observed near-conduit outgassing at many active volcanoes. Further, rock embrittlement at depth may create transient outgassing pathways by linking fracture networks near the edifice to larger-scale regional fault systems. Our experimental results affirm that pore Pressure fluctuations associated with volcanic unrest may play a crucial role in dictating the evolution of a volcanic system.
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Pore Pressure embrittlement in a volcanic edifice
Bulletin of Volcanology, 2016Co-Authors: Jamie Farquharson, Patrick Baud, Thierry Reuschlé, Michael Heap, Nick VarleyAbstract:The failure mode of porous rock in compression—dilatant or compactant—is largely governed by the overlying Lithostatic Pressure and the Pressure of pore fluids within the rock, both of which are subject to change in space and time within a volcanic edifice. While Lithostatic Pressure will tend to increase monotonously with depth due to the progressive accumulation of erupted products, pore Pressures are prone to fluctuations (during periods of volcanic unrest, for example). An increase in pore fluid Pressure can result in rock fracture, even at depths where the Lithostatic Pressure would otherwise preclude such dilatant behaviour—a process termed pore fluid-induced embrittlement. We explore this phenomenon through a series of targeted triaxial experiments on typical edifice-forming andesites (from Volcán de Colima, Mexico). We first show that increasing pore Pressure over a range of timescales (on the order of 1 min to 1 day) can culminate in brittle failure of otherwise intact rock. Irrespective of the pore Pressure increase rate, we record comparable accelerations in acoustic emission and strain prior to macroscopic failure. We further show that oscillating pore fluid Pressures can cause iterative and cumulative damage, ultimately resulting in brittle failure under relatively low effective mean stress conditions. We find that macroscopic failure occurs once a critical threshold of damage is surpassed, suggesting that only small increases in pore Pressure may be necessary to trigger failure in previously damaged rocks. Finally, we observe that inelastic compaction of volcanic rock (as we may expect in much of the deep edifice) can be overprinted by shear fractures due to this mechanism of embrittlement. Pore fluid-induced embrittlement of edifice rock during volcanic unrest is anticipated to be highest closer to the conduit and, as a result, may assist in the development of a fractured halo zone surrounding the conduit, potentially explaining commonly observed near-conduit outgassing at many active volcanoes. Further, rock embrittlement at depth may create transient outgassing pathways by linking fracture networks near the edifice to larger-scale regional fault systems. Our experimental results affirm that pore Pressure fluctuations associated with volcanic unrest may play a crucial role in dictating the evolution of a volcanic system.
Matthijs A. Smit - One of the best experts on this subject based on the ideXlab platform.
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evidence for non Lithostatic Pressure in subducted continental crust
Contributions to Mineralogy and Petrology, 2020Co-Authors: Jamie Cutts, Matthijs A. Smit, Johannes C. VrijmoedAbstract:Continental crust buried during collisional orogeny typically records Pressures of 3 GPa or lower; however, Pressures much higher than this are recorded locally, which would suggest burial to mantle depths. Deep continental subduction is not observed in active orogens and should be hindered by the positive buoyancy of sialic crust relative to the mantle. Non-Lithostatic Pressure caused by mechanical contrasts between rock types provides an alternative explanation for extreme Pressures recorded in buried continental crust; however, its occurrence and significance in natural systems is debated. Mechanical Pressure heterogeneities were proposed specifically to explain extreme Pressures of c. 5.5 GPa obtained in enstatite eclogite veins in the archetypal subducted continental terrane, the Western Gneiss Complex (WGC) in Norway. In this study, we use Lu–Hf garnet geochronology to test when, and thus, in what part of the burial cycle of the WGC the enstatite eclogite assemblages actually equilibrated. The results show that equilibration occurred at c. 393 Ma, which is much later than the typical ages obtained from ‘normal’ eclogites in the WGC and represents a time when the terrane was already at crustal depths (< 2.5 GPa). Finite element modeling of mechanical Pressure distribution demonstrates that late extreme Pressure excursions are feasible for the given rock system and could explain the seemingly spurious conditions recorded in these unusual rocks. The recognition of non-Lithostatic ultrahigh-Pressure in deeply buried continental crust allows crucial simplification of models for continental subduction and validates the importance of rock thermo-mechanics in interpreting observations from collision zones.
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Evidence for non-Lithostatic Pressure in subducted continental crust
Contributions to Mineralogy and Petrology, 2019Co-Authors: Jamie Cutts, Matthijs A. Smit, Johannes C. VrijmoedAbstract:Continental crust buried during collisional orogeny typically records Pressures of 3 GPa or lower; however, Pressures much higher than this are recorded locally, which would suggest burial to mantle depths. Deep continental subduction is not observed in active orogens and should be hindered by the positive buoyancy of sialic crust relative to the mantle. Non-Lithostatic Pressure caused by mechanical contrasts between rock types provides an alternative explanation for extreme Pressures recorded in buried continental crust; however, its occurrence and significance in natural systems is debated. Mechanical Pressure heterogeneities were proposed specifically to explain extreme Pressures of c. 5.5 GPa obtained in enstatite eclogite veins in the archetypal subducted continental terrane, the Western Gneiss Complex (WGC) in Norway. In this study, we use Lu–Hf garnet geochronology to test when, and thus, in what part of the burial cycle of the WGC the enstatite eclogite assemblages actually equilibrated. The results show that equilibration occurred at c. 393 Ma, which is much later than the typical ages obtained from ‘normal’ eclogites in the WGC and represents a time when the terrane was already at crustal depths (