Variscan Granites from Brittany

Carron, Jean-Paul; Kerneizon, M. Le Guen de; Nachit, H.

doi:10.1007/978-3-642-84915-2_22

Cited by 12 publications

(5 citation statements)

References 9 publications

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“…The Central Vosges Mg-K association (180 km 2 ) is composed of several bodies corresponding to amphibole-biotite porphyritic Martínez et al 1990;Neubauer & von Raumer 1993;Carron et al 1994;Ledru et al 1994) monzonite or granite ('Crêtes' granite, or 'Kammgranit' of German researchers; Groth 1877). It can be subdivided into the following: (1) the most basic ('acid' and 'basic' are terms used to express silica contents), amphibole-biotite syenite ( Fig.…”

Section: Magmatic Suitesmentioning

confidence: 99%

Chronology, petrogenesis and heat sources for successive Carboniferous magmatic events in the Southern–Central Variscan Vosges Mts (NE France)

Tabaud

Janoušek

Skrzypek

et al. 2014

JGS

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Plutonic bodies of the Central and Southern Vosges Mts can be assigned to two major early Carboniferous magmatic events: a Visean Mg–K event ( c. 345 and 340–336 Ma) and a younger S-type event (329–322 Ma). New petrological, geochemical and Sr–Nd isotopic data highlight the existence of two groups of Mg–K intrusions that might be related to the nature of their primary magma sources; that is, CHUR-like and enriched mantle, which interacted with juvenile and mature crustal material, respectively. The differences between these two groups are explained by a geodynamic scenario involving deep subduction and relamination of the Saxothuringian continental crust under the Moldanubian continent. The relaminated radiogenic Saxothuringian material is thought to have been responsible for dehydration melting of both subducted crust and underlying metasomatized mantle, thereby generating the Mg–K magma subsequently emplaced at middle crustal depth. During their ascent, the mafic magmas interacted with crustally derived felsic melts. Significantly later ( c . 10–15 myr) a widespread mid-crustal anatexis occurred, generating voluminous granite intrusions from mixed crustal sources (paragneisses and/or immature felsic–intermediate metaigneous rocks mixed with Mg–K plutons). The principal heat source for such a major melting event is related to the presence of Mg–K plutons rich in heat-producing elements, which were responsible, after the time lag specified, for a temperature increase at mid-crustal levels by in situ radiogenic heat production. The current study underlines the importance of deep continental crust subduction and relamination for the magmatism and development of collisional orogens. Supplementary material: Analytical methods and data, and supplementary figures, are available at http://www.geolsoc.org.uk/SUP18795 .

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Section: Magmatic Suitesmentioning

confidence: 99%

Chronology, petrogenesis and heat sources for successive Carboniferous magmatic events in the Southern–Central Variscan Vosges Mts (NE France)

Tabaud

Janoušek

Skrzypek

et al. 2014

JGS

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“…Finally, the latest deformation (D4) is related to the activity of the dextral strike-slip South-Armorican Shear Zone, accompanied by the intrusion of Upper-Carboniferous two-mica leucogranites (e.g. Le Corre et al, 1991;Carron et al, 1994). An associated dextral strike-slip fault system affects the north-eastern part of the complex.…”

Section: Geological Settingmentioning

confidence: 99%

Inverted metamorphic field gradient towards a Variscan suture zone (Champtoceaux Complex, Armorican Massif, France)

Pitra

Ballèvre

Ruffet

2010

Journal Metamorphic Geology

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International audienceWe describe, date and constrain the PT conditions of a syntectonic inverted metamorphic sequence associated with continental collision and crustal-scale thrusting in one of the key regions of the late Palaeozoic Variscan belt of Western Europe the Champtoceaux Complex (Armorican Massif, France), interpreted as a trace of the Variscan suture zone between Laurussia and Gondwana. The Complex consists of several stacked units, some of them eclogite-bearing, that are sandwiched between two main pieces of continental crust the Parautochthon and the Upper Allochthon. Moderately to steeply dipping foliation parallels the main lithological boundaries. From the bottom to the top of the metamorphic rock pile, the following sequence testifies to the syntectonic temperature increase: chlorite biotite-bearing metagreywackes (Parautochthon); orthogneisses with eclogite lenses; micaschists with chloritoidchloritegarnet; orthogneisses; micaschists with staurolitebiotitegarnet with chloritoid inclusions (Lower Allochthon); and migmatites with boudins of eclogite and kyanitebiotitegarnetbearing metapelitic lenses (Upper Allochthon). Mylonitic amphibolites with lenses of serpentinized peridotite mark the boundary between the Lower Allochthon and the overlying Upper Allochthon, suggesting the presence of a major thrust. It is inferred that the latter is responsible for the development of the inverted metamorphic zoning. Multiequilibrium thermobarometry and pseudosections calculated with THERMOCALC indicate that equilibration temperatures of the syntectonic peak metamorphic assemblages increase upwards in the rock pile from <500 C in the Parautochthon to >650 C in the Upper Allochthon. All units equilibrated at similar pressures between 7 and 10 kbar. In the Upper Allochthon, chronological results on muscovite suggest initial cooling from c. 343 Ma (muscovite RbSr) to c. 337 Ma (muscovite 40Ar39Ar). A subsequent very rapid temperature decrease is suggested by the synchronous closure of the muscovite and biotite KAr and biotite RbSr isotopic systems (c. 337335 Ma). This cooling is also recorded in the Upper Micaschists of the Lower Allochthon and in the Parautochthon with muscovite 40Ar39Ar ages of c. 336334 and 332 Ma, respectively. Ages of c. 343 Ma inferred from disturbed muscovite spectra from the Parautochthon are possibly linked to a previous higher pressure metamorphic event in this unit. It is suggested that the development of the inverted metamorphic zoning in the Champtoceaux Complex is due to the emplacement of a hot nappe over colder units and is contemporaneous with major crustal thrusting and associated pervasive ductile deformation. The preservation of this inverted field gradient was possible because of fast cooling, tentatively associated with the syn-compressional denudation of the tectonic pile, expressed by the detachment at the top of the nappe pile. The efficiency of cooling is best shown by the near-coincidence of RbSr and 40Ar39Ar ages, obtained on both sides of the maj...

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“…lc). They are late-Hercynian in age (305 to 280 Ma, PI oumanach, Morlaix; Barriere 1980;Carron et al 1994) and have a similar chemical composition, although N d Pb isotope data is not currently available. A major difference is the presence of associated gabbros, which have promoted theories for these I-type granites being generated from a single basic to acid magma fraction ation (Barriere 1977) or through hybridization (Fourcade 1981).…”

Section: Geodynamic Frameworkmentioning

confidence: 99%

Multiple crustal sources for post-tectonic I-type granites in the Hercynian Iberian Belt

et al. 2009

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A post-tectonic plutonic array of felsic I-type granites crops out in the western Hercynian Iberian Belt. Isotope (Sr, N d, Pb) data favour the absence of an important input of juvenile magmas in late-to post-tectonic Hercynian felsic magmatism in western Iberia, but suggest a reworking of different crustal protoliths, including oceanic metabasic rocks accreted to mid-to-Iower crustal levels during the early stages of the collision. I-type granites were derived from different meta-igneous protoliths ranging from metabasic to felsic compositions depending on their geographical position from the external (e.g. Galicia-N Portugal, GNP) to the innermost continental areas (Spanish Central System and Los Pedroches Batholiths). The GNP 1-type pIu tons related to eo-Hercynian accretional terranes have lower initial 87 Sr/ 86 Sr ratios, lower negative ENd values, and higher 2 06 Pb P 04 Pb ratios than other I-type

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Variscan Granites from Brittany

Cited by 12 publications

References 9 publications

Chronology, petrogenesis and heat sources for successive Carboniferous magmatic events in the Southern–Central Variscan Vosges Mts (NE France)

Chronology, petrogenesis and heat sources for successive Carboniferous magmatic events in the Southern–Central Variscan Vosges Mts (NE France)

Inverted metamorphic field gradient towards a Variscan suture zone (Champtoceaux Complex, Armorican Massif, France)

Multiple crustal sources for post-tectonic I-type granites in the Hercynian Iberian Belt

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