Lower crustal rejuvenation and growth during post-thickening collapse: Insights from a crustal cross section through a Variscan metamorphic core complex

Costa, Sylvie; Rey, Patrice

doi:10.1130/0091-7613(1995)023<0905:lcragd>2.3.co;2

Cited by 124 publications

(73 citation statements)

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“…This age corroborates petrographical similarity with granulites of the European lower crust (e.g. Downes et al 1990;Costa and Rey 1995) related to postVariscan extension and also matches other granulite ages from the Southern Alps (see Discussion below). Nevertheless, the Gruf granulites have suffered multiple stages of equilibration (Galli et al 2011) and zircon zones and monazite ages cannot be unambiguously related to distinct metamorphic or magmatic events.…”

Section: Introductionsupporting

confidence: 62%

“…In Europe, the Permian magmatism is coeval with mafic underplating and lower crustal granitic intrusions that may partly derive from the granulitic lower crust; this event is associated with lithospheric thinning and transtensional collapse of the Variscan collisional orogen (Downes et al 1990;Burg et al 1994;Costa and Rey 1995;Schuster and Stüwe 2008). In the Alps, late CarboniferousPermian intrusions are recognised in several places from the Ivrea Zone (Peressini et al 2007) to the Eastern Alps (Eichhorn et al 2000).…”

Section: Permian Magmatic Coresmentioning

confidence: 99%

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U–Pb zircon dating of the Gruf Complex: disclosing the late Variscan granulitic lower crust of Europe stranded in the Central Alps

Galli

Bayon

Schmidt

et al. 2011

Contrib Mineral Petrol

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Permian granulites associated with noritic intrusions and websterites are a common feature of the post-Variscan European crust. Such granulites are common in the Southern Alps (e.g. Ivrea Zone), but occur only in the Gruf Complex in the Central Alps. To understand the geotectonic significance of these granulites, in particular in the context of Alpine migmatisation, zircons from 15 highgrade samples have been U-Pb dated by SHRIMP II analysis. Oscillatory zoned zircons from charnockite sheets, interpreted as melts generated through granulite facies fluid-absent biotite melting at 920-940°C, yield ages of 282-260 Ma. Some of these zircons contain inclusions of opx, unequivocally attributable to the granulite facies, thus confirming a Permian age for the charnockites and associated granulites. Two samples from an enclave-rich orthogneiss sheet yield Cambrian and Ordovician zircon cores. Two deformed leucogranites and six ortho-and augengneisses, which compose two-thirds of the Gruf Complex, give zircon ages of 290-260 Ma. Most zircons have milky rims with ages of 34-29 Ma. These rims date the Alpine amphibolite facies migmatisation, an interpretation confirmed by directly dating a leucosome pocket from upper amphibolite facies metapelites. The Gruf charnockites associated with metre-scale schlieren and boudins of opx-sapphirine-garnet-granulites, websterites and gabbronorites can thus be identified as part of the postVariscan European lower crust. A geotectonic reconstruction reveals that this piece of lower crust stranded in the (European) North upon rifting of the Neotethys, such contrasting the widespread granulite units in the Southern Alps. Emplacement of the Gruf lower crust into its presentday position occurred during migmatisation and formation of the Bergell Pluton in the aftermath of the breakoff of the European slab.

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Section: Introductionsupporting

confidence: 62%

Section: Permian Magmatic Coresmentioning

confidence: 99%

U–Pb zircon dating of the Gruf Complex: disclosing the late Variscan granulitic lower crust of Europe stranded in the Central Alps

Galli

Bayon

Schmidt

et al. 2011

Contrib Mineral Petrol

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“…Celles-ci seraient le résultat d'une faille de détachement de faible pendage qui a accommodé le régime extensionnel (NW-SE) et la mise en place du complexe métamorphique d' Aït Makhlouf à l'image des « metamorphic core complexes » ou (MCCs). Le synchronisme des bassins avec le soulèvement et l'exhumation des dômes métamorphiques durant l'extension tardi-et postorogénique a été également observé dans la chaîne varisque Costa et Rey 1995). A titre comparatif, une évolution semblable à été décrite dans le panafricain d'Egypte durant la pério-de (560-580 Ma) dans laquelle l'évolution tectonothermale du Néoprotérozoïque est contrôlée par l'extension et l'exhumation des MCCs (Fritz et al, 2002).…”

Section: Discussionunclassified

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Oudra¹,

Beraaouz²,

Ikenne³

et al. 2005

Estud. geol.

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“…Schematic tectonic evolution of the eastern edge of the French Massif Central during Carboniferous. Costa and Rey, 1995). The existence of mantle-derived and granulitic components in the lower crust is indicated by the aluminous and basic enclaves brought up in recent volcanoes (Leyreloup, 1973;Downes et al, 1990).…”

Section: Discussion: the Significance Of Crustal Anatexis In The Velamentioning

confidence: 99%

The Velay dome (French Massif Central): melt generation and granite emplacement during orogenic evolution

Ledru

Courrioux

Dallain³

et al. 2001

Tectonophysics

162

101

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This paper is a synthesis of available data on the Velay dome that include both small-and large-scale lithologic and structural mapping, strain analysis, isotope geochemistry, geochronology and pressure -temperature estimates. The Velay dome, one of the largest granite -migmatite domes of the Variscan Belt, formed during orogenic collapse at around 300 Ma. Its study allows an assessment of the thermal and geodynamic context leading to voluminous crustal anatexis of the Variscan orogenic crust. A first melting stage developed in connection with south-verging thrust zones during the Early Carboniferous, leading to a crustal thickening estimated at 20 km minimum. The involvement of fertile lithologies and the intrusion of plutons of deep origin contributed to the development of water-saturated melts. The volume of biotite granite extracted from melt during this period was limited. The second phase of melting, corresponded to generalized melting of gneiss achieved by biotite-dehydration melting reactions and accompanied by the generation of cordierite-bearing granites. At this stage, crustal-scale detachment faults were active and partially obliterated the earlier structures. The new structures were progressively tilted to the vertical at the margin of the Velay dome due to the southward and lateral ballooning of the granitic dome. The reconstructed P, T path indicate that the large volume of melt produced was a consequence of a significant increase in temperature at the onset of biotite dehydration melting. At the base of the crust, this melting event is coeval with granulite facies metamorphism associated to underplating of mantle-derived magmas as suggested by the geochemical signature of Late Paleozoic lower crustal xenoliths sampled by Cenozoic volcanoes and with the isotopic signature of the late granitic intrusions. Accordingly, it is proposed that asthenospheric upwelling was responsible for the temperature increase favoring melting of hydrous minerals.

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Lower crustal rejuvenation and growth during post-thickening collapse: Insights from a crustal cross section through a Variscan metamorphic core complex

Cited by 124 publications

References 0 publications

U–Pb zircon dating of the Gruf Complex: disclosing the late Variscan granulitic lower crust of Europe stranded in the Central Alps

U–Pb zircon dating of the Gruf Complex: disclosing the late Variscan granulitic lower crust of Europe stranded in the Central Alps

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The Velay dome (French Massif Central): melt generation and granite emplacement during orogenic evolution

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