Exhumation of high‐pressure rocks: a review of concepts and processes

Platt, J. P.

doi:10.1111/j.1365-3121.1993.tb00237.x

Cited by 463 publications

(292 citation statements)

References 95 publications

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“…This process would have increased the syn-orogenic surface slope, and it could also have reduced the dip of the sole thrust in the eastern parts of the orogen. Both geometrical adjustments, combined with reduced rate of convergence, would favour gravitational spreading of the mountain belt (England and Houseman, 1988;Platt, 1993). After initial extension possibly related to gravitational spreading, belt-wide reversal in the polarity of deformation, from top-east to top-west, occurred in the Scandinavian Caledonides with exception of the thin-skinned foreland fold and thrust belt.…”

Section: Discussionmentioning

confidence: 99%

Extensional tectonics in the Caledonides of southern Norway, an overview

1998

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The extensional collapse of the Scandinavian Caledonides resulted in rapid tectonic denudation of the orogen, exhumation of high-and ultra-high-pressure metamorphic rocks and provided a structural template for the formation of Devonian supra-detachment sedimentary basins. The geometry and intensity of the extensional deformation show considerable variation vertically in the crustal section as well as horizontally from east to west across the orogen. The most prominent structural feature related to the extension in central-south Norway is the change in the direction of tectonic transport, from the easterly directed nappe translation during the Silurian Scandian Orogeny, to top-westerly directed sense of shear during the extension. The Fennoscandian basement was little affected by extension in the eastern Caledonides. In the west, however, top-to-the-west shear zones are commonly observed in basement windows. Deformation affecting the Cambrian to Late Silurian rocks in the Caledonian foreland developed a typical of foreland fold and thrust belt geometry. Deformation in the foreland was apparently contemporaneous with the extension-related decompression of the high-pressure rocks in the hinterland. Thrusting in the foreland may thus have been driven by gravitational collapse, and as such have important similarities to the foreland-hinterland relationships of the Himalayan-Tibetan region. The basal contacts of the Jotun and other major nappes constitute prominent shear zones in which fabrics related to thrusting have been mostly destroyed by extensional shearing. The high structural levels of the Western Gneiss Region, adjacent to the western margin of the Jotun Nappe, were only moderately affected by the extensional deformation. Consequently, the Proterozoic orthogneiss complexes are generally well preserved in this area. The westernmost and structurally lowermost parts of the Western Gneiss Region have, however, been subjected to extreme overburden during the Caledonian continental collision. Initial, near-isothermal decompression of the high-pressure rocks occurred by non-rotational vertical shortening-horizontal stretching at eclogite-to amphibolite-facies conditions; at a later stage, decompression and cooling from amphibolite to greenschist facies occurred by rotational deformation associated with the large-scale extensional detachments. The initial extensional deformation in the hanging wall of the detachments in western Norway commenced at greenschist-facies conditions, and became progressively more brittle and localised as the complexes were exhumed in the Late Silurian to Middle Devonian. Major syn-depositional normal faults in the hanging wall of the extensional detachments eventually controlled sedimentation in the Devonian supra-detachment basins.

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Section: Discussionmentioning

confidence: 99%

Extensional tectonics in the Caledonides of southern Norway, an overview

1998

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“…Late-orogenic extensional denudation can explain rapid exhumation of deeper crustal rocks (e.g. Platt, 1993). Decompression driven by surficial or tectonic processes may also trigger partial melting by crossing phase boundaries during uplift (Teyssier & Whitney, 2002).…”

Section: Introductionmentioning

confidence: 99%

Pan-African extension and near-isothermal exhumation of a granulite facies terrain, Dronning Maud Land, Antarctica

Engvik

Elvevold

2004

Geol. Mag.

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-The Mühlig-Hofmann-and Filchnerfjella in central Dronning Maud Land, Antarctica, consist of series of granitoid igneous rocks emplaced in granulite and upper amphibolite facies metamorphic rocks. The area has experienced high-temperature metamorphism followed by near-isothermal decompression, partial crustal melting, voluminous magmatism and extensional exhumation during the later phase of the late Neoproterozoic to Cambrian Pan-African event. Remnants of kyanitegarnet-ferritschermakite-rutile assemblages indicate an early higher-pressure metamorphism and crustal overthickening. The gneisses experienced peak granulite facies temperatures of 800-900 • C at intermediate pressures. Breakdown of garnet + sillimanite + spinel-bearing assemblages to cordierite shows subsequent re-equilibration to lower pressures. An E-W foliation dominating the gneisses illustrates transposition of migmatites and leucocratic melts which evolved during the near-isothermal decompression. Occurrence of extensional shear bands and shear zones evolving from the ductile partial melting stage through semiductile towards brittle conditions, shows that the uplift persisted towards brittle crustal conditions under tectonic W/SW-vergent extension. Late-orogenic Pan-African quartz syenites intruded after formation of the main gneiss fabric contain narrow semiductile to brittle shear zones, illustrating that the extensional exhumation continued also after their emplacement. The latest record of the Pan-African event is late-magmatic fluid infiltration around 350-400 • C and 2 kbar. At this stage the Pan-African crust had undergone 15-20 km exhumation from the peak granulite facies conditions. We conclude that the later phase of the Pan-African event in central Dronning Maud Land is characterized by a near-isothermal decompression P-T path and extensional structures indicating tectonic exhumation, which is most likely related to a late-orogenic collapsing phase of the Pan-African orogen.

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“…Extensional shear zones are a common structural feature in modern and ancient convergent zones (Coward et al 1987, Malavieille 1993, Platt 1993. Such features have been described in the Caledonides (Marten and Dewey 1998, Fossen 2000, Stra-374 NOLAN M. DEHLER et al chan et al 2001, in the Himalaya (Herren 1987, Pêcher 1991, in the Andes (Dalmayrac and Molnar 1981), in the western Cordillera (Crittenden et al 1980, Wernicke 1981, Davis 1983, Spencer 1984, in the Alps (Selverstone 1988, Ratschbacher et al 1989, and elsewhere.…”

Section: Introductionmentioning

confidence: 99%

Kinematics and geometry of structures in the southern limb of the Paraíba do Sul divergent structural fan, SE Brazil: a true transtensional shear

Dehler

Machado

Dehler

et al. 2006

An. Acad. Bras. Ciênc.

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Shear zones geometry in the Paraíba do Sul belt, southeastern Brazil, delineates a NE-trending fan-like structure. Shear zones dip towards SE in the northern limb, and towards NW in the southern one. This geometry has been interpreted either due to transpression or to late folding of flat-lying thrust surfaces. Stretching lineation plunges to ENE-ESE in the northern limb and towards NNE-NE in the southern one. Structural data in the southern limb of the divergent fan suggest a two stage kinematic evolution in high-temperature conditions: an earlier stage with top-to-SSW/SW sinistral thrusting and orogenic-parallel tangential motion, and a later stage with top-down to NNE/NE transtensional deformation. We propose a heterogeneous deformation model to explain the observed shear reversal, and suggest that the imposed transpressional displacement gradient may change during progressive deformation due to transient rheological inhomogeneities in bulk pure shear strain. In the earlier stage, the partially molten material could easily accommodate the imposed strain rates, giving rise fi rstly to the SW-directed shearing. As the thermal disturbance tended to vanish and the convergence increased, the NNE-directed transtensional shearing developed. We propose that the transtensional deformation characterized in this paper could be related to extrusion processes during regional transpressional strain.

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Exhumation of high‐pressure rocks: a review of concepts and processes

Cited by 463 publications

References 95 publications

Extensional tectonics in the Caledonides of southern Norway, an overview

Extensional tectonics in the Caledonides of southern Norway, an overview

Pan-African extension and near-isothermal exhumation of a granulite facies terrain, Dronning Maud Land, Antarctica

Kinematics and geometry of structures in the southern limb of the Paraíba do Sul divergent structural fan, SE Brazil: a true transtensional shear

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