Major role of shear heating in intracontinental inverted metamorphism: Inference from a thermo-kinematic parametric study

Duprat-Oualid, Sylvia; Yamato, Philippe; Pitra, Pavel

doi:10.1016/j.tecto.2013.07.037

Cited by 17 publications

(21 citation statements)

References 91 publications

(153 reference statements)

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“…Burg et al, 1984;Duprat-Oualid et al, 2013;Harrison et al, 1998;Hubbard, 1996;Johnson and Strachan, 2006;Le Fort, 1975;Molnar and England, 1990;Pitra et al, 2010;Searle et al, 1999;Vannay and Grasemann, 2001). Although the dataset presented here from does not uniquely identify the heat sources for the inverted metamorphism, our data does provide some new insight into likely contributing sources.…”

Section: Model For Inverted Metamorphism Development In the Sikkim Himentioning

confidence: 83%

“…It is therefore possible to suggest that heat advected from depth with the exhuming GHS was augmented by unusually high radiogenic heat flux generated from the K, U, Th-rich pelitic lithologies (England and Molnar, 1993;Inger and Harris, 1992;Johnson and Strachan, 2006;Ruppel and Hodges, 1994). Furthermore, the prolonged deformation and shearing that occurred during the down-cutting of the active thrust plane and the progressive accretion of the upper footwall to the hanging wall provides an additional possible heat source from shear heating (Arita, 1983;Bird, 1978;Duprat-Oualid et al, 2013;Kidder et al, 2013;Le Fort, 1975).…”

Section: Model For Inverted Metamorphism Development In the Sikkim Himentioning

confidence: 99%

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Developing an inverted Barrovian sequence; insights from monazite petrochronology

Mottram

Warren

Regis

et al. 2014

Earth and Planetary Science Letters

145

139

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Editor: T.M. Harrison Keywords: inverted metamorphism ductile thrusting petrochronology monazite geochronologyIn the Himalayan region of Sikkim, the well-developed inverted metamorphic sequence of the Main Central Thrust (MCT) zone is folded, thus exposing several transects through the structure that reached similar metamorphic grades at different times. In-situ LA-ICP-MS U-Th-Pb monazite ages, linked to pressure-temperature conditions via trace-element reaction fingerprints, allow key aspects of the evolution of the thrust zone to be understood for the first time. The ages show that peak metamorphic conditions were reached earliest in the structurally highest part of the inverted metamorphic sequence, in the Greater Himalayan Sequence (GHS) in the hanging wall of the MCT. Monazite in this unit grew over a prolonged period between ∼37 and 16 Ma in the southerly leading-edge of the thrust zone and between ∼37 and 14.5 Ma in the northern rear-edge of the thrust zone, at peak metamorphic conditions of ∼790 • C and 10 kbar. Monazite ages in Lesser Himalayan Sequence (LHS) footwall rocks show that identical metamorphic conditions were reached ∼4-6 Ma apart along the ∼60 km separating samples along the MCT transport direction. Upper LHS footwall rocks reached peak metamorphic conditions of ∼655 • C and 9 kbar between ∼21 and 16 Ma in the more southerly-exposed transect and ∼14.5-12 Ma in the northern transect. Similarly, lower LHS footwall rocks reached peak metamorphic conditions of ∼580 • C and 8.5 kbar at ∼16 Ma in the south, and 9-10 Ma in the north. In the southern transect, the timing of partial melting in the GHS hanging wall (∼23-19.5 Ma) overlaps with the timing of prograde metamorphism (∼21 Ma) in the LHS footwall, confirming that the hanging wall may have provided the heat necessary for the metamorphism of the footwall. Overall, the data provide robust evidence for progressively downwards-penetrating deformation and accretion of original LHS footwall material to the GHS hanging wall over a period of ∼5 Ma. These processes appear to have occurred several times during the prolonged ductile evolution of the thrust. The preserved inverted metamorphic sequence therefore documents the formation of sequential 'paleothrusts' through time, cutting down from the original locus of MCT movement at the LHS-GHS protolith boundary and forming at successively lower pressure and temperature conditions. The petrochronologic methods applied here constrain a complex temporal and thermal deformation history, and demonstrate that inverted metamorphic sequences can preserve a rich record of the duration of progressive ductile thrusting.

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Section: Model For Inverted Metamorphism Development In the Sikkim Himentioning

confidence: 83%

Section: Model For Inverted Metamorphism Development In the Sikkim Himentioning

confidence: 99%

Developing an inverted Barrovian sequence; insights from monazite petrochronology

Mottram

Warren

Regis

et al. 2014

Earth and Planetary Science Letters

145

139

View full text Add to dashboard Cite

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“…Indeed tectonic structures can often be put into relation with temperature increases, e.g. in thrust zones [49,50], strike-slip zones [20,51,52], or extensional detachments [53]. Although it is clear that strain heating is not the only mechanism involved in strain localization [11], it should however be considered as a first-order mechanism which converts external mechanical work into internal energy.…”

Section: Discussionmentioning

confidence: 99%

Shear heating-induced strain localization across the scales

Duretz

Schmalholz

Podladchikov

2015

Philosophical Magazine

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We investigate the dynamics of thermally activated shear localization in power law viscoelastic materials. A two-dimensional (2D) thermomechanical numerical model is applied that uses experimentally derived flow laws for rock. We consider viscous and viscoelastic rheologies and show that the numerical solutions for shear bands are mesh insensitive and energetically conservative. Deformation under long-term tectonic strain rates (10 −14 s −1 ) yields to shear localization on the scale of kilometres. Although viscous and viscoelastic models exhibit comparable shear zone thickness, the timing of shear localization and stress magnitudes are affected by viscoelasticity. Large values of shear modulus (10 11 Pa) promotes fast stress loading (within 1% strain) and localization (<10% strain), whereas lower values (5 × 10 9 Pa) delays localization (∼15% strain) and reduces the maximum effective stress by a factor two. High stress exponents (up to n = 10) focuses the deformation into narrow shear zones (∼1000 m) while maintaining a relatively high average stress level in the material outside the shear zone (stress drop of ∼60%). Conversely, Newtonian materials produce broad shear zones (∼6× larger than for n = 10) and exhibit a stronger thermal weakening (stress drops of ∼85%). Finally, we evaluate the thickness of shear zones for a wide range of strain rates (from 10 −14 s −1 to 10 10 s −1 ) using both numerical models and an analytical scaling law. Our results suggest that thermally activated shear localization may occur from the scale of kilometre down to the nanometre.

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“…Two main processes, not mutually exclusive, may account for the presence of this narrow strip of migmatites along the roof of the UPU. The strip may reflect the "hot iron" effect produced by carrying a higher-grade hangingwall (the SU) onto its footwall (the UPU) (e.g., Le Fort, 1996), a process possibly assisted by shear heating along the main fault contact (e.g., Duprat-Oualid et al, 2013). Alternatively, because the second anatectic event involved water-assisted melting, the strip may represent the width of the zone in which fluids were abundant enough to produce large amounts of melt.…”

Section: A Major Thrusting Event During Eocene Anatexismentioning

confidence: 99%

Polycyclic alpine orogeny in the Rhodope metamorphic complex: the record in migmatites from the Nestos shear zone (N. Greece)

Gautier

Bosse

Cherneva

et al. 2017

Bull. Soc. géol. Fr.

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-The Rhodope Metamorphic Complex (RMC) is a high-grade crystalline massif located at the northern margin of the Aegean region. Numerous scenarios have been proposed for the evolution of the RMC during Alpine times. A debated issue is whether there has been a single protracted orogenic cycle since around the mid-Mesozoic or whether Alpine orogeny involved distinct episodes of subduction and crustal accretion. We describe a key outcrop located on the Nestos Shear Zone (NSZ), a major NNE-dipping top-to-SW shear zone characterized by an inverted metamorphic sequence. Structural and petrological data document the existence of two anatectic events. The first event, best preserved in decametric structural lenses, is pre-kinematic with respect to top-to-SW shearing and involved high-temperature "dry" melting. Zircon and monazite LA-ICPMS U-Th-Pb data indicate that this event occurred at ∼140 Ma. The second event is syn-kinematic with respect to top-to-SW shearing and involved lower-temperature water-assisted melting. Zircon and rutile LA-ICPMS U-Pb data indicate that this second event occurred at ∼40 Ma. During ongoing top-to-SW shearing and as late as ∼36 Ma, the rocks from the outcrop were at higher temperatures than the peak temperatures experienced by lower levels of the NSZ. This confirms the existence of the inverted metamorphic sequence and demonstrates that the NSZ was a major thrust at 36-40 Ma. The ∼100 Myr time laps between the two anatectic events encompasses the period from ∼115 to ∼70 Ma characterized by a gap in the geochronological record on the scale of the RMC (the Eastern Rhodope excluded). This ∼45 Myr gap likely reflects a period of tectonic quiescence between the mid-Mesozoic orogen and the Cenozoic one, attesting for polycyclic Alpine orogeny in the RMC. Unlike assumed in several geodynamic scenarios, the Alpine evolution of the RMC did not consist of a single orogenic cycle of Mesozoic age followed by Cenozoic crustal-scale extension triggered by mantle delamination. Polycyclic orogeny has resulted in a two-loop P-T-t path for the hangingwall unit of the NSZ. The Cenozoic P-T paths of this unit and the footwall unit merged while both units were being exhumed, a feature attributed to synthrusting extensional spreading of the main mass of the hangingwall unit above the NSZ.Keywords: Aegean / syn-deformation migmatization / U-Pb dating / LA-ICPMS / inverted metamorphism / synmetamorphic thrusting Résumé -Orogenèse alpine polycyclique dans le complexe métamorphique du Rhodope : enregistrement dans les migmatites de la zone de cisaillement du Nestos (Grèce). Le Rhodope est un complexe métamorphique de haut grade situé à la frange Nord de la région égéenne. De nombreux scénarios ont été proposés pour son évolution durant la période alpine. Une question débattue est de déterminer s'il n'y a eu qu'un seul cycle orogénique de longue durée depuis le milieu du Mésozoïque ou bien si l'orogenèse alpine a impliqué des épisodes distincts de subduction-accrétion crustale. Nous décrivons un affleurement-...

show abstract

Major role of shear heating in intracontinental inverted metamorphism: Inference from a thermo-kinematic parametric study

Cited by 17 publications

References 91 publications

Developing an inverted Barrovian sequence; insights from monazite petrochronology

Developing an inverted Barrovian sequence; insights from monazite petrochronology

Shear heating-induced strain localization across the scales

Polycyclic alpine orogeny in the Rhodope metamorphic complex: the record in migmatites from the Nestos shear zone (N. Greece)

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