The Alps 2: Controls on crustal subduction and (ultra)high‐pressure rock exhumation in Alpine‐type orogens

Butler, J. P.; Beaumont, Christopher; Jamieson, Rebecca Anne

doi:10.1002/2013jb010799

Cited by 36 publications

(51 citation statements)

References 69 publications

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“…A5) are derived from a small set of reliable laboratory flow laws scaled by the factor f to represent materials that are somewhat more or less viscous than the refwww.gsapubs.org | Volume 7 | Number 4 | LITHOSPHERE erence flow law (Butler et al, 2014;Appendix A2). The effective viscosities (Eq.…”

Section: Methodsmentioning

confidence: 99%

“…The effective viscosities (Eq. A5) are also linearly scaled between 1 and 1/W s over the strain range ε = 5-10 (Appendix A3; see also Butler et al, 2014) to represent strain weakening. For the sediments, we use scaled wet quartzite (WQ; Gleason and Tullis, 1995), WQ × f, where f = 1 and W s = 10.…”

Section: Methodsmentioning

confidence: 99%

“…The paradigm can be "regained" by recognizing that exhumation is controlled by the exhumation number, which takes both buoyancy and other factors into account. Following Raimbourg et al (2007), Warren et al (2008b), andButler et al (2014), for example, the exhumation number, E x , is defined by the competition between the buoyant up-channel Poiseuille flow of the low-density crust and the down-channel Couette flow resulting from the downward traction exerted on the crust by underlying subducting lithosphere, the numerator and denominator in the following force balance, respectively:…”

Section: Paradigm Regained: Buoyancy Vs the Exhumation Numbermentioning

confidence: 99%

“…The methodology is similar to that of Butler et al (2011Butler et al ( , 2014. The models are computed by solving the equations for incompressible creeping (Stokes) flows (Eq.…”

Section: A1 Sopale Nestedmentioning

confidence: 99%

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Paradigm lost: Buoyancy thwarted by the strength of the Western Gneiss Region (ultra)high-pressure terrane, Norway

2015

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Subduction and exhumation of ultrahigh-pressure (UHP) metamorphic terranes are typically envisaged as short-lived processes associated with the transition from oceanic subduction to continent-continent collision. Norway's Western Gneiss Region, by comparison, is a giant, late-orogenic UHP terrane that underwent protracted residence at UHP conditions during the Scandian phase of the Caledonian orogeny followed by relatively slow exhumation. Here, we use two-dimensional numerical thermal-mechanical models to explore the tectonics of orogens of this type and the associated controls on the size of their UHP terranes and the duration of UHP metamorphism.The models have four tectonic phases designed to capture the main stages of the Caledonian evolution: oceanic subduction and microcontinent accretion; continental margin subduction; plate quiescence; and postorogenic extension during plate divergence. Contrasting styles of exhumation are explored by varying the strength of the margin crust and investigating melt-induced weakening. The tectonic and metamorphic evolution of the Western Gneiss Region is consistent with a model in which continental margin crust was subducted beneath a thick orogenic wedge where it underwent metamorphism at (U)HP conditions for at least 15 million years (Myr) as subduction ended. The buoyant Baltican crust must have been especially strong in order to have stayed coupled to the underlying lithosphere during this phase, perhaps reflecting its refractory composition and/or a lack of fluids. Subsequent exhumation of the Western Gneiss Region can be explained by orogen-scale extension resulting from minor (~100 km) plate divergence, with removal of the orogenic wedge by combined top-to-thehinterland transport, normal faulting, and erosion. We conclude that large, long-duration UHP terranes are fundamentally different from transient smaller ones. The latter are often explained by the paradigm of buoyant exhumation. This paradigm is incomplete, but both types can be explained by control of the system by the exhumation number (ratio of buoyancy force to basal traction). By implication, the existence of this type of large UHP terrane is a consequence of the high strength of the subducted crust.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Paradigm Regained: Buoyancy Vs the Exhumation Numbermentioning

confidence: 99%

“…The methodology is similar to that of Butler et al (2011Butler et al ( , 2014. The models are computed by solving the equations for incompressible creeping (Stokes) flows (Eq.…”

Section: A1 Sopale Nestedmentioning

confidence: 99%

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Paradigm lost: Buoyancy thwarted by the strength of the Western Gneiss Region (ultra)high-pressure terrane, Norway

2015

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“…However, the hydrothermal circulation does not have a significant impact on the depth of dehydration reactions at shallow depths (Rosas et al 2016). Because the lithostatic pressure is much greater than the dynamic pressure (Babeyko & Sobolev 2008;Burov & Yamato 2008;Butler et al 2014;Gerya 2015), it has been neglected; thus, the depth scaled by the density is used here to define the progressive hydration of the mantle wedge. Then, the stability field of serpentine is calculated for each element by using the following two equations (Roda et al 2010 and references therein): .…”

Section: A2 Hydration and Serpentinization Within The Wedge Areamentioning

confidence: 99%

2-D numerical study of hydrated wedge dynamics from subduction to post-collisional phases

Regorda¹,

Roda²,

Marotta³

et al. 2017

Geophysical Journal International

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S U M M A R YWe developed a 2-D finite element model to investigate the effect of shear heating and mantle hydration on the dynamics of the mantle wedge area. The model considers an initial phase of active oceanic subduction, which is followed by a post-collisional phase characterized by pure gravitational evolution. To investigate the impact of the subduction velocity on the thermomechanics of the system, three models with different velocities prescribed during the initial subduction phase were implemented. Shear heating and mantle hydration were then systematically added into the models. We then analysed the evolution of the hydrated area during both the subduction and post-collisional phases, and examined the difference in P max -T (maximum pressure-temperature) and P-T max (pressure-maximum temperature) conditions for the models with mantle hydration. The dynamics that allow for the recycling and exhumation of subducted material in the wedge area are strictly correlated with the thermal state at the external boundaries of the mantle wedge, and the size of the hydrated area depends on the subduction velocity when mantle hydration and shear heating are considered simultaneously. During the post-collisional phase, the hydrated portion of the mantle wedge increases in models with high subduction velocities. The predicted P-T configuration indicates that contrasting P-T conditions, such as Barrovian-to Franciscan-type metamorphic gradients, can contemporaneously characterize different portions of the subduction system during both the active oceanic subduction and post-collisional phases and are not indicative of collisional or subduction phases.

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Contrasting styles of (U)HP rock exhumation along the Cenozoic Adria‐Europe plate boundary (Western Alps, Calabria, Corsica)

Malusà

Faccenna

Baldwin

et al. 2015

Geochem Geophys Geosyst

118

145

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Since the first discovery of ultrahigh pressure (UHP) rocks 30 years ago in the Western Alps, the mechanisms for exhumation of (U)HP terranes worldwide are still debated. In the western Mediterranean, the presently accepted model of synconvergent exhumation (e.g., the channel-flow model) is in conflict with parts of the geologic record. We synthesize regional geologic data and present alternative exhumation mechanisms that consider the role of divergence within subduction zones. These mechanisms, i.e., (i) the motion of the upper plate away from the trench and (ii) the rollback of the lower plate, are discussed in detail with particular reference to the Cenozoic Adria-Europe plate boundary, and along three different transects (Western Alps, Calabria-Sardinia, and Corsica-Northern Apennines). In the Western Alps, (U)HP rocks were exhumed from the greatest depth at the rear of the accretionary wedge during motion of the upper plate away from the trench. Exhumation was extremely fast, and associated with very low geothermal gradients. In Calabria, HP rocks were exhumed from shallower depths and at lower rates during rollback of the Adriatic plate, with repeated exhumation pulses progressively younging toward the foreland. Both mechanisms were active to create boundary divergence along the Corsica-Northern Apennines transect, where European southeastward subduction was progressively replaced along strike by Adriatic northwestward subduction. The tectonic scenario depicted for the Western Alps trench during Eocene exhumation of (U)HP rocks correlates well with present-day eastern Papua New Guinea, which is presented as a modern analog of the Paleogene Adria-Europe plate boundary.

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The Alps 2: Controls on crustal subduction and (ultra)high‐pressure rock exhumation in Alpine‐type orogens

Cited by 36 publications

References 69 publications

Paradigm lost: Buoyancy thwarted by the strength of the Western Gneiss Region (ultra)high-pressure terrane, Norway

Paradigm lost: Buoyancy thwarted by the strength of the Western Gneiss Region (ultra)high-pressure terrane, Norway

2-D numerical study of hydrated wedge dynamics from subduction to post-collisional phases

Contrasting styles of (U)HP rock exhumation along the Cenozoic Adria‐Europe plate boundary (Western Alps, Calabria, Corsica)

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