Lithos 175–176 (2013) 1–15

Contents lists available at SciVerse ScienceDirect

Lithos

j ourna l homepage: www.e lsev ie r .com/ locate / l i thos

A two-stage exhumation in Western French Massif Central: Newgeochronological evidences of syn-collisional extension

Christian Le Carlier de Veslud a,⁎, Paul Alexandre b, Gilles Ruffet a, Michel Cuney c, Alain Cheilletz d,e

a Géosciences Rennes, UMR CNRS 6118, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, Franceb Queen's University, Kingston, Ontario, Canadac UMR GEORESOURCES 7539 CNRS-UL, BP 239, 54506 Vandoeuvre-lès-Nancy, Franced Université de Lorraine, ENSG, INP, Rue Doyen Marcel Roubault, Vandoeuvre-les-Nancy, Francee CRPG UMR 7358 CNRS-UL, 15 Rue Notre Dame des Pauvres, Vandoeuvre les Nancy, France

⁎ Corresponding author. Tel.: +33 2 23 23 33 41; faxE-mail address: christian.le-carlier@univ-rennes1.fr

0024-4937/$ – see front matter © 2013 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.lithos.2013.04.013

a b s t r a c t

a r t i c l e i n f o

Article history:Received 19 July 2012Accepted 9 April 2013Available online 24 April 2013

Keywords:Hercynian orogenFrench Massif Central40Ar/39Ar datingSyn-orogenic extension

Systematic 40Ar/39Ar dating of granitoids and surrounding metamorphic rocks has been performed in theLimousin area (W of French Massif Central) in order to provide new constrains concerning itslate-orogenic thermal and tectonic evolution. The same 40Ar/39Ar age of ca. 335–338 Ma is found on thepresent-day outcrop surface for most of the Limousin metamorphic rocks, hence indicating that the entiremassif was uniformly cooled down at this period. These ages are very close to the 40Ar/39Ar ages proposedin the Sioule and Brevenne areas in the literature, but also to the coupled tectonic and magmatic activityin the south Limousin. These results help to document the existence of two exhumation stages, each oneassociated with an extensional stage. A first exhumation stage, has been active at ca. 335–340 Ma. Avail-able data indicate that this extension and associated exhumation and cooling occurred over a distance ofmore than 200 km in the internal zones of the belt, whereas compression was still active in the northernand southern parts of the belt. A second exhumation stage may be related to the late-orogenic extensionand collapse of the belt, at ca. 310–305 Ma, and is characterized by the uplift of the St. Sylvestre complexby unroofing of the overlying metamorphic and granitoidic formations.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

The European Variscan belt is one of the major segments inthe periatlantic Paleozoic orogeny. In Europe, the Variscan beltresults from the convergence and subsequent collision betweenthe Baltica (northern Europe) and Gondwana (southern Europeand Africa) continents (Matte, 1986; Nance et al., 2010; vonRaumer and Stampfli, 2008). The orogenic evolution of the FrenchMassif Central mostly occurred during Paleozoic as in the wholeWest European Variscan belt. The following major phases havebeen distinguished:

(i) early orogenic closure of the Ordovician oceanic domains dur-ing Silurian (Ducrot et al., 1983; Nance et al., 2010; Peucat etal., 1982; Pin and Peucat, 1986).

(ii) mid-orogenic continental collision with thrust tectonics andintra-continental evolution from Devonian to Middle Carbonif-erous (Burg, 1983; Burg and Matte, 1978; Matte, 1986).

: +33 223236100.(C. Le Carlier de Veslud).

rights reserved.

(iii) late-orogenic general collapse of the belt, during the Late Carbon-iferous (Faure, 1995; Faure andPons, 1991;Quenardel et al., 1991).

The mid-orogenic stage appears to be the most complex one, par-ticularly in the French Massif Central, where it is characterized by vo-luminous magmatism and volcanism, contemporaneous with wrenchand extensional tectonics along crustal scale faults with basin opening(Bruguier et al., 1998; Burg et al., 1994; Faure, 1995; Gébelin et al.,2007). If most of the available geochronological data concerning this pe-riod are focused on intrusions and faults (e.g. Alexandrov et al., 2002;Gébelin, 2004; Scaillet et al., 1996a), only few geochronological data areavailable on themetamorphic rocks hosting the intrusions. Thus, system-atic 40Ar/39Ar single-grain dating on micas of both granitoids and sur-rounding metamorphic rocks has been performed at a regional scale inthe Limousin (NW part of the French Massif Central, Figs. 1 and 2). Theaims of the present study are: (1) to supplement already available geochro-nological data on the Limousin area (U/Pb ages: Holliger et al., 1986; Rb/Srages:Duthouet al., 1984 and 40Ar/39Ar ages: Alexandrov, 2000; Alexandrovet al., 2000, 2002; Cuney et al., 2002; Scaillet et al., 1996a) withnew 40Ar/39Ar ages and (2) to propose a consistent tectono-thermalmodel for the evolution of the Limousin crustal block, the inner orogenicdomain of the mid-European Variscan belt, from the end of the thrusttectonics to the onset of the late-orogenic general extension.

Vosges

Ardennes

Massif Armoricain

Massif Central

Brevenne

Sioule

Montagne Noire

Argentat fault

Sillon Houiller fault

Limousin

100 km

Southern foreland

Northern foreland

Cévennes

Bray fault

Silurian suture (Eo-Variscan)

Rheic suture

Lahaye-Lubine fault

BlackForrest

Variscan front

0° 4°E 8°E

0° 4°E4°W

44°N

46°N

48°N

50°N

44°N

46°N

48°N

50°N

52°N

Saxo-thuringian suture

Variscan belt outcrop

Late Viseanexternal basin

Fig. 1. Simplified structural map of the central Variscan belt and position of the French Massif Central within the European Variscides.After Matte (1986) and Faure et al. (2002).

2 C. Le Carlier de Veslud et al. / Lithos 175–176 (2013) 1–15

2. Geological background

2.1. Nappe pile of the Limousin region

According to their lithology and metamorphic evolution, fourmajor Units separated by low dip thrust contacts have been definedin the Limousin (Ledru et al., 1989; Santallier et al., 1994, Fig. 2).From top to bottom these Units are:

(a) The Upper Allochthon Unit (UAU), consisting of low grade(greenschists to lower amphibolite facies) Paleozoic units.

(b) The Upper Gneiss Unit (UGU), representing an Early Paleozoicoceanic or marginal domain with basic–ultrabasic complexes,overlain by ortho- or para-derived rocks. Numerous eclogiticrelics are witnesses of a lithospheric subduction stage. This

unit overlies a stack of (c) and (d) units, representing the northGondwana continental margin.

(c) The Lower Gneiss Unit (LGU), composed of medium-grade(amphibolite facies) frequently anatectic, para- to ortho-derivedrocks.

(d) The Para-Autochthon Unit (PAU), made of micaschists with rareorthogneisses, is interpreted as the relative autochthon forthe other units. This unit is weakly metamorphosed (garnet tobiotite–staurolite) compared to the overlying units.

The Hercynian magmatism in Limousin is represented by twomajor episodes:

(i) A Late Devonian–Early Carboniferous episode (ca. 355 Ma),which follows the major thrust tectonic stage. It consists ina medium- to high-K calc-alkaline gabbro-dioritic to granitic

1c

0 10 20 30 kmUpper Gneiss Unit

Lower Gneis Unit

Upper Allochthon Unit

Upper-Carboniferous granitoids

N

Late Devonian granitoids

Mesozoic sediments

Paris

Para-Autochthon Unit

Blond

St Sylvestre-Thaurion

Bourneix

1a

4

2

5

6

3

7

8

FaultThrust

1b

Vienne

Fig. 3

Fig. 5

Fig. 7

AF

OF

MF

RN

20F

NF

MF

OzF

ArF

Fig. 2. Simplified geological map of the Limousin. The localization of the three areas of interest and the figure number that provide a zoom of each area, are indicated. The locali-zation of Vienne plutonic complex, hidden under a Jurassic sedimentary cover, is also shown. Key for themain granitic massifs: Limousin-type: (1) St. Sylvestre complex: 1a— Brâmeunit, 1b— St. Sylvestre unit, 1c—WesternMarche, (2) Blond, (3)Millevaches complex; Guéret-type: (4) Guéret, (5) Vaulry, (6) Glane, (7)Auriat, (8)Aureil. Key for the faults: NF = Nantiatfault, MF = Marche fault, OzF = Ouzilly fault, ArF = Arrênes fault, NeF = Noémie fault, OF = Oradour fault, AF = Argentat fault.

3C. Le Carlier de Veslud et al. / Lithos 175–176 (2013) 1–15

magmatism (Bertrand et al., 2001; Cuney et al., 2001a, 2001b;Peiffer, 1985), synchronouswith a peraluminous biotite ± cordi-erite granodioritic to granitic magmatism (Guéret-type, Berthieret al., 1979).

(ii) A Namurian–Westphalian (325 ± 15 Ma, Alexandrov et al., 2002;Holliger et al., 1986; Monier, 1980), widespread peraluminoustwo mica granite and leucogranite (Limousin-type) magmatism.They are spatially associated with very small bodies of high-Pperaluminous Rare Metal Granites (rich in Ta, Nb, Sn, W and U),emplaced at 310 ± 3 Ma (Alexandrov et al., 2002; Cheilletz etal., 1992; Cuney et al., 2002; Raimbault, 1999).

According to Turpin et al. (1990), the isotopic data suggest amixed origin for Guéret-type granites, involving partial melting ofperaluminous metasedimentary rocks and basic metaigneous rocks.In contrast, the Limousin-type granites would have been generatedby pure crustal partial melting.

2.2. Tectonic evolution of the Limousin area

Although controversial, the polyphased Variscan deformation inthe Limousin area can be further subdivided into the following maintectonic stages (Bellot and Roig, 2007; Faure and Pons, 1991; Faure

0 5 km

BLOND

VAULRY

ORADOUR

UGU

Limousin-type leucogranite

UGU

Guéret-type granite

LGU (anatectic gneiss)

UGU (paragneiss)

Oradour fault

Nan

tiat f

ault

LGU

Fault

99 Bl 12

99 Bl 7

99 Bl 8

LGU

N

Fig. 3. Geological map and sample location of the Blond–Vaulry area.

4 C. Le Carlier de Veslud et al. / Lithos 175–176 (2013) 1–15

et al., 1997; Ledru et al., 1989; Matte, 1986; Quenardel et al., 1991;Rolin and Colchen, 2001):

(i) 430–400 Ma (Silurian): closure of oceanic domains (Nance etal., 2010), which leads to the formation of high pressure meta-morphism recorded by eclogites in the UGU.

(ii) 400–370 Ma (Devonian to Early Carboniferous, D1 stage): begin-ning of continental collision. During this period first thrustingevents (380–370 Ma, Duthou, 1978; Lafon, 1986; Roig and Faure,2000), having a south to southwest vergence, thrusted the UGUover the LGU during Middle Devonian (at about 380 Ma), underupper amphibolite metamorphic condition (700 °C/7 kbar).

(iii) 370–345 Ma (Late Devonian to Early Visean, D2 stage): the colli-sion becomes oblique in the Limousin, whereas the collision frontmigrates towards the south (Burg et al., 1987). Subsequently, thenappes are remobilized, and a second event, having a northwestvergence, thrusted the UGU and the LGU onto the PAU, and theUAU onto the gneissic units (UGU and LGU) with P–T conditionsat about 600 °C/5 kbar (Roig and Faure, 2000).

(iv) 345–310 Ma (Middle and Late Visean, D3 stage): extensional tec-tonics started towards the end of the continental convergence. Itis diachronous, and concerns mainly the inner and thickest partsof the belt, whereas the collision front migrates southward.

(v) 310–280 Ma (Late Carboniferous to Early Permian, D4 stage): gen-eral extension corresponding to a return to thermo-mechanicalequilibrium of the thickened crust by normal faulting and erosion,together with the development of coal basins (Burg et al., 1994).

2.3. Sampling

Samples were taken from intrusive and metamorphic ortho- andpara-derived rocks, in the host rocks of the Middle Carboniferousleucogranites, and at several kilometers from of them these granites,to avoid the thermal effects of their emplacement limiting the numberof possible sampling sites. The samples were selected to be representa-tive of the corresponding lithologies. Muscovite and/or biotite are com-mon primary minerals in these lithologies. However, most of theserocks show local evidence of a late-stage hydrothermal activity charac-terized by the development of chlorite after biotite or fine-grainedwhitemicas after feldspar. Thus, only the freshest sampleswere consid-ered. Three particular areas were selected for their geological interestand to complement already available data (Fig. 2 and Table 1).

∙ Blond–Vaulry area (Figs. 2 and 3, Table 2). The samples werecollected from the host rocks of the Blond granite, two in thecoarse-grained and locally porphyroïd biotite granite of Vaulry(Guéret-type) and one in the LGU to the north. In these two lithol-ogies, muscovite is rare (mainly incipient sericitization of feld-spars, Chèvremont et al., 1992), and only biotites were analyzed.

Table 1Schematic chart of tectonic and magmatic events occurred during Variscan orogeny in the

Area Location Event dated M

Blond area Blond Limousin-type graniteemplacement and cooling

U(

Thaurion area Guéret granite Guéret-type graniteemplacement

R(

Guéret granite Guéret-type graniteemplacement

U(

Saint Sylvestre complex Limousin-type graniteemplacement

U(

Saint Sylvestre complex Granite cooling

Auriat granite Guéret-type graniteemplacement

Aureil granite Guéret-type graniteemplacement

∙ Bourneix area, an EW oriented antiform (Figs. 2 and 5, Table 3) be-longing to the LGU, is intruded by several types of granitoids(leucogranites or pegmatites). In these lithologies, muscovite iscommon. Muscovites were collected from one gneiss sample fromthe LGU, three granitoid types (two-mica granite, leucogranite, andpegmatite). One sample of muscovite was collected in a vein in theLGU, and is in this case considered as hydrothermal.

∙ Thaurion area, located at the SE extremity of the St. Sylvestreleucogranitic complex (Figs. 2 and 7, Table 4). Samples were locat-ed: (i) along an 8-km long transect, roughly perpendicular to thecontact with the St. Sylvestre leucogranitic complex, in fine- tomedium-grained, biotite + silimanite + muscovite gneisses andmicaschists of the LGU (Arène et al., 1972), and (ii) 25 km southof the leucogranite, close to Puy-les-Vignes, in a silimanite +orthoclase + biotite gneiss of the LGU (Chenevoy et al., 1984).

2.4. Available data about the St. Sylvestre–Western Marche leucogranitecomplex

The St. Sylvestre–Western Marche leucogranitic complex (Fig. 2)has been extensively studied because it hosts one of the largest Udeposits of economic importance in Western Europe (Cuney et al.,1990). For this reason, many data are available, and particularly

Limousin area, and more specific dating available on each area of interest.

ethod (mineral) Age ± 1σ (Ma) References

/Pbzircon)40Ar/39Ar (muscovite)

319 ± 7 Alexandrov et al.(2000, 2002)315 − 305

b/Srwhole rock)

356 ± 10 Berthier et al. (1979)

/Pbzircon and monazite)

352 ± 5 Cartannaz et al. (2007)351 ± 5353 ± 6

/Pbzircon and monazite)

324 ± 4 Holliger et al. (1986)

40Ar/39Ar(muscovite and biotite)

From 315 (top)to 300 (bottom)

Scaillet et al.(1996a and b)

U/Pb(zircon and monazite)

324 ± 1 Gebauer et al. (1981)

Rb/Sr(whole rock)

346 ± 14 Duthou (1978)

Table 2Summary of all 40Ar/39Ar dating, including additional technical data performed in thisstudy on the Blond–Vaulry area. See Fig. 3 for sample location.

Sample ID Lithology Mineral Plateau age % 39ArK

99 Bl 07 Vaulry granite Biotite 335.9 ± 0.8 7899 Bl 08 Vaulry granite Biotite 310.7 ± 0.5 7599 Bl 12 Gneiss LGU Biotite 330.9 ± 1.1 58a

a Pseudo-plateau.

Table 4Summary of all 40Ar/39Ar dating, including additional technical data performed in thisstudy on the Thaurion area. See Fig. 7 for sample location.

Sample ID Lithology Mineral Plateau age % 39ArK

96 Li 02 St Sylvestre granite Muscovite 308.3 ± 0.3 7196 Li 03 Gneiss (LGU) Muscovite 307.7 ± 0.3 94CT 1 Paragneiss (LGU) Muscovite 309.2 ± 0.6 97CT 6 Paragneiss (LGU) Muscovite 325.8 ± 0.7 9298 Lim 9 Gneiss (LGU) Muscovite 321.1 ± 0.7 10098 Lim 8 Gneiss (LGU) Muscovite 330.6 ± 0.7 9598 Lim 6 Gneiss (LGU) Muscovite 336.1 ± 0.5 8498 Lim 14 Gneiss (LGU) Muscovite 335.7 ± 0.6 8799 PV 06a Paragneiss Biotite 335.1 ± 0.5 9999 PV 11 Paragneiss Biotite 334.7 ± 0.5 94

335.9 ± 0.8 Ma

330.9 ± 1.1 Ma

5C. Le Carlier de Veslud et al. / Lithos 175–176 (2013) 1–15

geochronological data including 40Ar/39Ar ages (see Scaillet et al.,1996a, 1996b).

A synthesis of geophysical and structural data (Scaillet et al.,1996a) indicates that the St. Sylvestre–Western Marche complex isa 2–3 km thick laccolith, with a series of roots down to 6 km, partic-ularly along the RN20 shear zone.

In most of the St. Sylvestre complex, the magmatic foliation(Mollier and Lespinasse, 1985) is weakly dipping with a lineation ori-ented N120. In the vicinity of the RN20 magmatic shear zone (Fig. 2),the magmatic foliation becomes strongly dipping and parallel withthe shear zone direction (N20 direction). The main magmaticstretching lineations are oriented N110 and parallel to that of theenclosing rocks (Mollier and Bouchez, 1982). The Western Marchecomplex includes both Guéret- and Limousin-type granites. TheLimousin-type granites show dominantly nearly vertical WNW–ESEtrending magmatic or ductile foliations. The magmatic structures be-come parallel to the main structures limiting the complex, the Marcheshear zone to the N and the Ouzilly shear zone to the south. Thestretching lineations are gently dipping to the WNW orientation(Guineberteau et al., 1989).

The St. Sylvestre–WesternMarche complex, emplaced at 324 ± 4 Ma(Holliger et al., 1986) at a depth of 10.5 ± 1.5 km, 40Ar/39Ar ages rangefrom 315 Ma at the roof of the complex, to 300 Ma towards the base ofthe complex (Scaillet et al., 1996a). Thermal modeling has shown thatsuch age variation resulted from a first episode with slow exhumationfollowed by a fast exhumation episode (with exhumation rate of ca.1.5 mm/yr, Scaillet et al., 1996b), which started at about 305 Ma duringthe generalized late Variscan extension stage.

3. Analytical methods and results

3.1. Analytical methods

The argon isotope analyses were performed at Nice (UMR-Géosciences Azur) on single grains of muscovite and biotite. Aftercrushing and sieving, grains without visible signs of alterations havebeen selected under a binocular microscope. Gas was extractedfrom the single-grains of biotite or muscovite by laser step-heatingand analyzed on a VG 3600® mass spectrometer according to theprocedure described in Ruffet et al. (1997). The isotopic ratios werecorrected for background noise, blank value, Ca, K and Cl interfer-ences, instrumental mass discrimination and atmospheric argon con-tamination. A plateau age is obtained when apparent ages of at leastthree consecutive steps, representing a minimum of 70% of the 39Arreleased, agree within 2σ error bars with the integrated age of the

Table 3Summary of all 40Ar/39Ar dating, including additional technical data performed in thisstudy on the Bourneix area. See Fig. 5 for sample location.

Sample ID Lithology Mineral Plateau age % 39ArK

97 CFM 41a Gneiss (LGU) Muscovite 337.0 ± 0.4 9597 Lim 06 Vein in gneiss (LGU) Muscovite 334.6 ± 0.4 9997 CFM 38 Granite Muscovite 338.1 ± 0.2 9797 CFM 30 Leucogranite Muscovite 338.3 ± 0.5 9297 CFM 45 Pegmatite Muscovite 337.8 ± 0.3 92

plateau segment (Castonguay et al., 2001). Pseudo-plateau ages canbe calculated with less than 70% of the 39Ar released. All age errorsare displayed at the 1σ level.

3.2. Closure temperature

Isotopic mineral ages are commonly interpreted to record coolingbelow a critical temperature, known as the closure temperature (Tc),or the age of mineral (re)crystallization, if this occurred at tempera-tures lower than Tc. 40Ar/39Ar isotopic closure temperatures ofmuscovite were first estimated at ca. 350 °C by the calibration of iso-topic ages versus metamorphic grade (Purdy and Jager, 1976). Thisestimate is currently debated and higher values of ca. 500 °C are pro-posed (e.g. Villa, 1998). Frommuscovite diffusion coefficient data andbased on Harrison et al.'s (2009) model, Pitra et al. (2010) calculatedclosure temperatures for diffusion radii (500 and 1000 μm) over acomplete range of cooling rates, from 1 to 1000 °C·My−1. If oneconsiders an effective diffusion radius of few hundreds of μm and acooling rate of 10–200 °C·My−1, that are relevant values for thisstudy, Tc will vary in the 450–500 °C range, in the absence of recrys-tallization. Therefore, this range will be used for muscovite. Similarly,a 400–450 °C range will be used for the biotite closure temperature(Grove and Harrison, 1996; Villa, 1998; Villa and Puxeddu, 1994).

3.3. Results

3.3.1. Blond–Vaulry area (Figs. 3, 4 and Table 2)Biotite 99Bl08 yields a plateau age at 310.7 ± 0.5 Ma,whereas biotite

99Bl12 displays a staircase-shaped age spectrum with a pseudo-plateauage at 330.9 ± 1.1 Ma (58% of 39ArK). Age spectra of biotites 99Bl08and 99Bl12, from the UGU and Vaulry granite, have been both disturbed

310.7 ± 0.5 Ma

99BL08 (300m to contact)99BL12 (1250m to contact)99BL07 (1400m to contact)

Biotites

Fig. 4. 40Ar/39Ar spectra and ages of the Blond–Vaulry area. See Fig. 3 for sample loca-tion and text for discussion.

6 C. Le Carlier de Veslud et al. / Lithos 175–176 (2013) 1–15

by the intrusion of the Blond granite at ca. 313 Ma (Alexandrov et al.,2002). The first one, closest to the contact with the granite (0.5 km inmap view, but less if the 3D shape of the granite is considered, Améglioet al., 1997; Le Carlier de Veslud et al., 2000), is totally reset during the in-trusion of the Blond granite, whereas the second one, located at 1.5 kmfrom the granite, is less disturbed with a lower radiogenic argon loss.Biotite 99Bl07 from the Vaulry granite yields an older plateau age at335.9 ±0.8 Ma.

3.3.2. Bourneix area (Figs. 5, 6 and Table 3)Five muscovite-rich samples from the Bourneix area were

analyzed. All muscovites from the Bourneix area yield plateau agesfrom 337.0 ± 0.4 to 338.3 ± 0.5 Ma (92 to 97% released gas), exceptmuscovite 97Lim06 from a vein which gives a slightly youngerage at 334.6 ± 0.4 Ma. This sample presents a slight saddle shapesuggesting a disturbance after its crystallization (Alexandrov et al.,2002; Tartèse et al., 2011). This may explain its slightly younger pla-teau age. The mean age calculated from the remaining four plateauages (97CFM30, 38, 41a and 45) is 337.8 ± 0.35 Ma.

3.3.3. Thaurion area (Figs. 7, 8, 9 and Table 4)Ten samples (muscovites and biotites) were collected at increas-

ing distances from the contact with the St. Sylvestre leucogranite.All results give well defined plateau ages.

∙ Muscovite samples collected at the contact with the St. Sylvestreleucogranite (CT1, 96Li02 and 96Li03) give ages from 307.7 ± 0.3

N

97 CFM 45 (pegmatite)

97 CFM 41a (gneiss)

97 CFM 30 (leucogranite) 97 CFM 38 (granite)

Jumilhac

Ladignac

Fig. 5. Geological map and sample

to 309.2 ± 0.6 Ma comparable to those obtained by Scaillet et al.(1996a) in the eastern part of the leucogranite.

∙ With an increasing distance to the leucogranite contact (Fig. 9), threesamples (CT6, 98Lim9 and 98Lim8) give ages at 325.8 ± 0.7 Ma,321.1 ± 0.7 Ma and 330.6 ± 0.7 Ma, respectively. At about 5 kmfrom the contact, concordant muscovite ages of 336.1 ± 0.5 Maand 335.7 ± 0.6 Ma are obtained respectively for samples 98Lim6and 98lim14.

∙ Two biotites 99PV06a and 99PV11, from rocks belonging to the LGU,sampled as far as possible (about 20 km) from the St. Sylvestreleucogranite, yield ages of 335.1 ± 0.5 Ma and 334.7 ± 0.5 Ma, re-spectively, slightly younger than the previous ages of muscovites98Lim 6 and 98Lim14.

4. Discussion

The results of this study, compared with those from the literature,will be discussed in terms of: (1) the significance of argon ages, and(2) their implications concerning the regional or local evolution ofthe Limousin area.

4.1. Late Visean exhumation phase

4.1.1. Interpretation of argon closureExcept for one “pseudo-plateau” age, all 40Ar/39Ar data obtained in

the present study are well defined plateau ages which allow dating of

1 2 3 4 50 km

Paragneiss and micaschist

Orthogneiss

Calc-alkaline leucogranite

Alkaline leucogranite

Fault

97 Lim 06 (vein)

LGU

location of the Bourneix area.

0 5 10 km

ST SYLVESTREST GOUSSAUD

AURIAT

GUERET

UIG

CT 1

CT 698 Lim 9

98 Lim 8

98 Lim 14

96 Li 296 Li 3

Paragneiss and micaschist

Paragneiss-orthogneiss

Guéret-type granite

Limousin-type granite

N

98 Lim 6

AUREIL

Arène-Ouzilly

99 PV 06a

99 PV 11

Fault

LGU

Fig. 7. Geological map and sample location of the Thaurion area.

338.1 ± 0.2 Ma

337.0 ± 0.4 Ma

334.6 ± 0.4 Ma

337.8 ± 0.3 Ma

338.3 ± 0.5 Ma

97CFM38

97CFM45Muscovites

97CFM41a97Lim06

97CFM30

Muscovites

300

320

340

360

380

400 300

320

340

360

380

400

300 320 340 360 380 4000

2

4

6

8

10

337-338Ma

Age(Ma)

Freq

uenc

y

Fig. 6. 40Ar/39Ar spectra and ages of the Bourneix area. See Fig. 5 for sample locationand text for discussion. The inset shows the frequency diagram for all the spectra.

7C. Le Carlier de Veslud et al. / Lithos 175–176 (2013) 1–15

the isotopic closure of analyzed minerals. Three scenarios of argonclosure in micas can be considered:

(1) closure at or after initial crystallization of the micas dependingon whether the crystallization temperature of the analyzedmineral was below or above its isotopic closure temperature.In this case, the 40Ar/39Ar ages are respectively crystallizationages or cooling ages.

(2) closure after a complete loss of argon from the analyzedminer-al, during a thermal event at a temperature significantly higherthan the isotopic closure temperature of the mineral. In thiscase, the mineral allows dating of the thermal event.

(3) closure after a complete recrystallization of the analyzed miner-al, during a fluid circulation and/or a deformation event(s). Themineral allows the dating of this(ese) event(s) (e.g. Alexandrovet al., 2002; Boulvais et al., 2007; Tartèse et al., 2011).

No noticeable geographic variation of 40Ar/39Ar ages is observedover a verywide area in Limousinmetamorphic rocks,with concordant40Ar/39Ar muscovite ages (336–338 Ma) and slightly younger biotiteages (335–336 Ma). Close to the late-Carboniferous leucogranites,the40Ar/39Ar mica ages (Figs. 9 and 10) are older or similar tothe 40Ar/39Ar mica ages of these intrusions (e.g. Alexandrov etal., 2002). Far away from late-Carboniferous intrusions (e.g. 5 km,Fig. 9), micas display ages increasing up to the 335–338 Ma agerange observed regionally. This pattern means that host-rocks were al-ready cooled below the closure temperature of the micas when theywere intruded by Late Carboniferous leucogranites.

At a regional scale, P–T paths (Bellot and Roig, 2007; Quenardel etal., 1991) suggest a continuous cooling of the Limousin area after theend of the nappe stacking at ca. 350 Ma. Therefore, scenarios (2) or(3) would require an exceptional thermal event (increased heat orfluid flow) producing a complete resetting of the argon isotopic systemof the minerals at the scale of the whole area. The large late-Carboniferous leucogranitic intrusions are posterior to the 40Ar/39Arages obtained in this study, and their emplacement is characterized bya limited thermal resetting of argon ages (Figs. 9 and 10). Similarly, itis difficult to imagine a widespread fluid circulation able to produce ahomogeneous resetting of the isotopic system of the micas at the scaleof the whole Limousin area. Such an extensive fluid circulation has not

been observed during this period and would produce variable degreesof resetting (e.g. Alexandrov et al., 2002). Therefore, we proposethat concordant 40Ar/39Ar muscovite and biotite ages of ca. 335–338 Ma over a distance of more than 80 km correspond to a regionalcooling episode experienced by all the rocks from the metamorphicpile (scenario 1).

4.1.2. P–T–t path in the Bourneix areaDue to the presence of economic gold deposits, the Bourneix area

has been extensively studied. Therefore, and contrary to the Thaurionand Blond–Vaulry areas, it is possible to build a P–T–t path from 355to 300 Ma combining the results of this study with petrographic(Bellot and Roig, 2007), metallogenic (Bouchot et al., 1989, 1999,2005) and fluid inclusion studies (Boiron et al., 2003; Essaraj et al.,2001; Vallance et al., 2004), and direct or indirect ages, when avail-able (Fig. 11). It should be noted that P–T conditions on the LGU atca. 345 Ma (Bellot and Roig, 2007) provide an average thermal gradi-ent relatively high of ca. 35 °C·km−1 for a depth of ca. 15–20 km.Thus, the muscovite Tc of 450–500 °C corresponds to 12.5 to 14 km

308.3 ± 0.3 Ma

309.2 ± 0.6 Ma307.7 ± 0.3 Ma

96Li02

CT1Muscovites96Li03

300

320

340

360

380

400

325.8 ± 0.7 Ma330.6 ± 0.7 Ma

321.1 ± 0.7 Ma

CT6

98Lim8Muscovites98Lim9

320

340

360

380

400

336.1 ± 0.5 Ma

98Lim6

99PV06aMuscovites98Lim14

300

320

340

360

380

400

335.1 ± 0.5 Ma

99PV11

334.7 ± 0.5 Ma

335.7 ± 0.6 Ma

Frequency

335-336Ma

1 2 43 5 6

(a)

(b)

(c)

Age (M

a)

Age

(M

a)A

ge (

Ma)

0 20 40 60 80 100

% 39Ar

Fig. 8. 40Ar/39Ar spectra and ages of the Thaurion area. See Fig. 7 for sample location and text for discussion. (a) Samples at the contact with the St. Sylvestre leucogranitic complex,(b) Samples located at less than 5 km from the complex, (c) Samples located at more than 5 km from the complex, considered as representing the regional cooling age, and asso-ciated frequency diagram.

310

320

1 2 3 4 5 6 7 80Distance from the Saint Sylvestre complex (km)

Age

, Ma

CT 1

CT 6

330

340

98 Lim 8

98 Lim 9

98 Lim 6

98 Lim 14336 ± 1 MaRegional age:

Fig. 9. Evolution of the 40Ar/39Ar with distance from the St. Sylvestre complex. SeeFig. 7 for sample location.

8 C. Le Carlier de Veslud et al. / Lithos 175–176 (2013) 1–15

or 0.35 to 0.4 GPa assuming a density of 2.7. The following evolutionmay be proposed:

(i) during the late D2 stage (Bellot and Roig, 2007), a significantexhumation of 15–20 km is associated with a moderate tem-perature decrease. Although not accurately dated, these resultssuggest that at ca. 345 Ma, P–T conditions of 0.4–0.5 GPa and500–550 °C could be reached.

(ii) from 345 to 335 Ma period, i.e., early D3 phase, the exhumationrate decreaseswith timewhereas the cooling rate increases to ca.10–20 °C·My−1. The pre-ore stage fluid inclusion P–T values,interpreted as occurring during a retrograde exhumation stage(Essaraj et al., 2001, Fig. 11), coincide partly with those ofargon data. This suggests firstly that the P–T values of the circu-lating fluids correspond to those of their host rocks, and second-ly, that the pre-ore stage could have occurred in the 335–345 Maperiod.

(iii) fluid inclusions record a pressure drop of about 0.25 GPMa witha continuous decrease of temperature. According to Essaraj et al.(2001), this pressure drop cannot be interpreted simply in termsof variations between lithostatic and hydrostatic conditions at aconstant depth, but requires an exhumation of about 5 km. Theore stage I, characterized by quartz vein formation and As–S–Feparagenesis (Bouchot et al., 2005) may be related to fluid

0 10 20 30 km

Upper-Carboniferous granitoids

N

Late Devonian granitoids Metamorphic rocks

Fault

324 ± 4

319 ± 7

324 ± 1

~314

~314

~300

~300

~305 ~308309-311

~325

~336

~331~331

~335

~338 ~338

~336

Figs. 3 and 4

Figs. 5 and 6

Figs. 7 and 8

Blond

Thaurion

Bourneix

356 ± 10

346 ± 14

~325

Granitoid emplacement age 346 ± 14 Whole rock Rb/Sr324 ± 1 U/Pb

Ar/ Ar cooling age40 39

352 ± 17

~314

352 ± 5351 ± 5

353 ± 6

AF

OF

MF

RN

20F

NF

MF

OzF

ArF

Fig. 10. Synthesis of all the ages obtained in this study, compared with literature geochronological data (see Table 1). The key for the fault is the same as in Fig. 2.

9C. Le Carlier de Veslud et al. / Lithos 175–176 (2013) 1–15

inclusions with P–T conditions of 0.15–0.25 GPa (interpreted aslithostatic) and 350–450 °C. In addition, the quartz veins formedin a brittle–ductile regime, suggesting a temperature of ca.350 °C. This again indicates that fluid temperatures could be

close, at least in part, to those of their host rocks. This stagecan only be indirectly dated between 335 (this study) and310 Ma (see iv directly below). However, the sudden P dropwith an almost continuous temperature decrease suggests that

1.0

0.5

0.0

300 400 500 600 700

Ky

Sil

And

T(°C)

P(G

Pa)

Lower Gneiss Unit: Bourneix area

Syn-D2 P-T path (355-345 Ma)(Bellot and Roig, 2007).

Muscovite Tc

355-345 Ma

335-340 Ma

Early D3 P-T path (340-335 Ma)(this study).

200

300-310 Ma

D3 and D4 P-T path (335-300 Ma)

Fluid inclusion studiesa: pre-ore stageb: As-S ore stage Ic: Au ore stage II(Essaraj et al., 2001;Boiron et al., 2003)

a

b

c

Ductile_brittle quartz veinformation (Bouchot et al., 1989)

Tc range inmuscovite 300-310 Ma Available direct or indirect ages

Fig. 11. P–T–t path for the Bourneix area from a synthesis of metamorphic (Bellot andRoig, 2007), fluid inclusion (Boiron et al., 2003; Essaraj et al., 2001; Vallance et al.,2004), structural and metallogenic (Bouchot et al., 1989; Marignac et al., 2003).Geothermobarometry errors were assumed by Bellot and Roig (2007) to be of theorder of ±0.1 GPa and 50 °C. See text for more explanations.

10 C. Le Carlier de Veslud et al. / Lithos 175–176 (2013) 1–15

this drop occurred just after 335 Ma, and not at 305–310 Ma assuggested by Essaraj et al. (2001).

(iv) finally, the main Au ore stage II occurred at 300–310 Ma, in P–Tconditions of 0.01–0.08 GPa (about 2 km) and 200–250 °C(Bouchot et al., 1999, 2005; Essaraj et al., 2001).

In summary, the P–T–t path obtained in the Bourneix area sug-gests a significant change of P–T conditions close to 335 Ma. As thisage was also obtained in the other studied areas, it is interesting to in-vestigate its significance at the regional scale.

4.1.3. Significance of 320–340 agesIn the northern part of the French Massif Central, the 320–340 Ma

period is characterized by intense, and spatially linked tectonic,magmat-ic and volcanic activities (Faure and Pons, 1991; Faure et al., 2002;Gébelin, 2004; Rolin and Colchen, 2001). The magmatic activity corre-sponds to the emplacement of large volumes of leucogranitic magmas(Alexandre et al., 2002; Holliger et al., 1986; Monier, 1980; Roig et al.,2002). These plutons and their metamorphic aureoles exhibit NW–SEtrending stretching lineations (Fig. 12). Ductile normal fault activityis also widespread (Figs. 2 and 12), with for instance the Argentatfault (with a throw of ca. 10 km and 40Ar/39Ar ages of 337 ± 4 and335 ± 4 Ma, Bellot, 2007; Bitri et al., 1999; Roig et al., 2002), theNantiatfault and theArrênes fault (Faure, 1995; Lespinasse et al., 1986; Rolin andColchen, 2001). Shear zonesmay be reactivated to accommodate lateral-ly themotion induced by the normal faults (e.g. around the Guéret gran-ite, Lespinasse et al., 1986). This tectonic activity is also associated withthe opening of small-sedimentary basins (Bruguier et al., 1998). It isworth noting that in the Sioule area (100 km east of the Limousin area,Fig. 1) a similar pattern of constant 40Ar/39Ar ages at ca. 331–335 Maon both biotites and muscovites has been related by Faure et al. (2002)to a regional cooling of the metamorphic pile by exhumation.

Two main models have been proposed to explain this Late Viseantectono-magmatic evolution. For Burg et al. (1994) and Faure (1995),

this episode may correspond to a syn-collision extensional stage(mainly Visean) which occurred in the inner zones, in the thickenedcrust. The cooling would be related to rock exhumation afterthe main stages of deformation and metamorphism. By contrast,Gébelin et al. (2007, 2009) suggest that the transpressive tectonicat ca. 350 Ma led to the development of ductile shear zones constitut-ing branches of a large and single wrenching lithospheric systemextending from the south Armorican Massif to the Limousin, andcomparable to a pop-up structure. This large system would havebeen active from 350 to 300 Ma and would have promoted rapid ex-humation and cooling of metamorphic rocks and ascent of magma.Although our data do not allow to confirm this model, it should benoted that our data in the Limousin area and those of Faure et al.(2002) in the Sioule area, indicate a relatively synchronous anduniform cooling episode at ca. 335–330 Ma whereas the model ofGébelin et al. (2007) is based on ages ranging from 350 to 300 Ma.Therefore, we suggest that this cooling reflects the onset of syn-collisional extension, associated with widespread crustal melting, de-veloped during Late Visean times at the scale of the internal parts ofthe Variscan belt: in the Limousin area (Faure and Pons, 1991, andthis study), the Sioule and Brevenne areas (Faure et al., 2002), andthe Vosges area (Rey et al., 1991–1992). At the same time, the exter-nal zones are still in compression, such as the Montagne Noire on thesouthern foreland (Maluski et al., 1991) and the Ardennes on thenorthern foreland (Raoult and Meilliez, 1987).

It is worth noting that wrench and normal fault tectonics are notincompatible in the inner zone of an orogen. Thermo-mechanical nu-merical simulations of a real 3D collision (i.e. of finite axial extent,Seyferth and Henk, 2004) have shown that if the initial stage of a con-vergence (frontal collision) is accommodated by an important thicken-ing, further convergence is mainly accommodated by lateral extrusionand widening of the orogenic belt. In that case, the compressive areasmigrate towards the external zones whereas the internal thickenedparts of the orogen are characterized by strike-slip and normal faultingin the upper level, as observed in the 370–310 Ma period in the FrenchMassif Central. At depth, a contrasted tectonic regime is obtained, withthe upper crustal levels being in extension, whereas the deeper levelsare still in compression, favoring synconvergent exhumation of the in-ternal zone of the orogen. Finally, the 15–20 My time period recordedbetween the maximum thickening (ca. 350 Ma) and the onset ofleucogranitic magmatism (ca. 335 Ma) is sufficient to allow a radiogen-ic heating and amelting of lower crust (Thompson et al., 1997). To sum-marize, the models of Seyferth and Henk (2004), although simplisticcompared to the geometrical complexity of the Variscan belt, providesimple explanations of the tectonic–thermal events observed in theLimousin area. They further suggest that the conjunction of a heatedand less dense lower crust and tectonic denudation and topography-induced erosion in the upper crust may promote syn-collisional exhu-mation of internal zones and associated cooling that could explain therather uniform 40Ar/39Ar ages obtained in this study. The fact that sed-imentation in the foreland basins, which was marine until the MiddleVisean, became continental thereafter further confirms that a signifi-cant uplift and erosion of the Variscan belt occurred as soon as theLate Visean. In parallel, the radiogenic heating of the thickened crust(Thompson et al., 1997) may have promoted the melting of lowercrust metasedimentary rocks, which are a probable source of theLimousin-type leucogranites according to Downes and Duthou (1988)and Williamson et al. (1996).

4.2. Pennsylvanian exhumation: an example of a tectonic denudationaround the St. Sylvestre complex

A synthesis of the 40Ar/39Ar ages (present study and Scaillet et al.,1996a, 1996b) in and around the St. Sylvestre–Western Marcheleucogranitic complex (Fig. 2) presents a blockwise symmetric distri-bution (Fig. 10). The 40Ar/39Ar ages increase from ca. 300 Ma in the

GuéretSt Sylvestre

Sillo

n ho

uille

r

1c

AF

MF

NF

MF

OzF ArF

Millevaches

Aigurande

Streching lineation in host rocks

Streching lineation in plutons

Limousin-type granites

Ductile normalfault

0 25 50 km

N

Fig. 12. Main Limousin-type granites and active normal faults, with coeval stretching lineations related to the Late Visean–Namurian (340–320 Ma) NW–SE extensional tectonics.The key for the faults is the same as in Fig. 2. Modified from Rolin and Colchen (2001) and Faure et al. (2009).

11C. Le Carlier de Veslud et al. / Lithos 175–176 (2013) 1–15

central part of the complex, up to 314 Ma to the NW (WesternMarche unit) and 308 Ma to the SE (Saint Goussaud unit). In themetamorphic host rocks, to the SE, close to the contact with theleucogranite, intermediate ages at ca. 325 Ma are observed betweenthe “regional” ages at ca. 336–338 Ma and those obtained on theleucogranite or just at contact (CT1 at ca.309 Ma). Symmetrically aregional age of ca. 336 Ma (99BL07) is observed in the metamorphicblock to the west of the Nantiat fault (Fig. 10).

If one considers that the intrusion age at 324 ± 4 Ma proposedby Holliger et al. (1986) is valid and does not reflect inheritance asfrequently observed on leucogranites, the numerical simulation(Scaillet et al., 1996b) indicates that after its intrusion the complexthermally equilibrated with its country rocks by conduction in ca.4 My. This time duration is not sufficient to explain the 10–14 My re-quired for the closure of the argon ages observed within theleucogranitic complex (Scaillet et al., 1996a).

In order to explain the age distribution of Fig. 10, one could invokethe role of fluids. By combining accurate mineralogical, petrologicaland geochemical studies, Tartèse et al. (2011) have shown that recrys-tallization and/or reequilibration of muscovite by fluid circulationscould reset argon geochronometer, although well-defined plateauswere obtained. A similar process was invoked by Alexandrov et al.(2002) for the nearby Blond leucogranite, (Fig. 2) to explain the differ-ence betweenU/Pb age (319 ± 7 Ma) and variable 40Ar/39Ar age (from305 to 312 Ma). The St. Sylvestre–Western Marche complex is knownto have been affected by significant fluid circulations progressively in-volving meteoric fluids at ca. 305 Ma (Lespinasse and Cathelineau,

1990; Lespinasse and Pêcher, 1986). These circulations, strongly fo-cused on intragranitic shear zones, led to a quartz leaching and alkalimetasomatism of granite (“episyenites”, Cathelineau, 1986; Leroy,1984). However, several lines of evidence suggest that this hypothesisshould be discarded. Firstly, Scaillet et al. (1996a, 1996b) indicate thattheir samples do not present any visible form of alteration whereasthe episyenite alteration is known to have substantially affected theoriginal composition of the granite. Secondly, the regional age trend(Fig. 10) clearly extends far beyond the hydrothermal effects of theepisyenite alteration. Finally, a perturbation of the argon systemwould likely produce a variable resetting of the argon ages as observedfor the nearby Blond granite (Alexandrov et al., 2002).

Therefore, the age pattern most probably reflects true differences inoriginal cooling ages throughout the St Sylvestre complex and surround-ing rocks. These results are consistent with the model of Scaillet et al.(1996a, 1996b), and allow us to extend it by proposing that the increaseof argon ages around the St. Sylvestre complex could be mainly con-trolled by the vertical component of displacement of tectonic structures(Fig. 13), activated or reactivated during the gravitational collapse of thewhole thickened domain that occurred from 300 to 280 Ma (Burg et al.,1994). This pattern would correspond to a downwarping of the meta-morphic and granitoidic covers, initially situated at a higher structurallevel and thus having cooled down earlier. For instance (Figs. 10 and13), the Nantiat fault would be responsible for the jump from ca.336 Ma in themetamorphites to 300 Ma in the Brâme block, itself sepa-rated by the RN20 magmatic shear zones from the 303 to 308 Ma agesmeasured in the St. Sylvestre block. To the S, along the Thaurion

Nantiat RN20

Blond

SSC

Blond

SSC

~ 3 km ~ 1 km ~ 1 km total ~ 3 km

Nantiat RN20

Blond

300 Ma

315 Ma325 Ma

335 Ma335 Ma

300 Ma 310 Ma325 Ma

335 Ma335 Ma

340-310 Ma

310-300 MaBelt collapse, exhumationof the SSC by downwarpingof its cover

335 Ma 335 Ma

325 Ma

Present time

Auriat

Auriat

Auriat8 km

11 km

vertical offset

Emplaced at 324 +/- 4 Ma, in surrounding rocks whosetemperature is > closure temperature of muscovite and biotite Ar system

Emplaced at 315-305 Ma

324 Ma

Variable closure of muscovite-biotite Ar system according to the depth, from 315 Ma (top) to 300 Ma (base)

7 km

~ 5 km

WNW ESE

~310 Ma

Horst structure of the SSCand surrounding rocks andassociated argon ages

Depth

Depth

Thermal contact aureole of the Saint Sylvestre Complex

Emplaced at 324 +/- 1 Ma

closure of biotitemuscovite Ar system

Regional syn-collision exhumationand granite emplacement

~ 3 km

(a)

(b)

(c)

Fig. 13. Schematic cartoon of the thermo-chronological evolution of the Limousin area from 350 Ma to 300 Ma. (a) The 340–310 Ma period, with the syn-collision extension,followed by the emplacement of the large St. Sylvestre leucogranitic Complex (SSC) associated with a ca. 5 km thermal aureole (Scaillet et al., 1996b), (b) The 310–300 Ma periodcorresponds to the tectonic collapse of the belt, which is characterized in Limousin by tectonic denudation of the St. Sylvestre complex by downwarping of its metamorphic or gra-nitic cover. (c) The present time state points out the horst configuration of the St. Sylvestre complex, surrounded by down-faulted blocks and corresponding argon ages.

12 C. Le Carlier de Veslud et al. / Lithos 175–176 (2013) 1–15

cross-section perpendicular to the main lithological interfaces (Figs. 7and 9), a transition zone of ca. 5 km is observed, within which theargon ages increase progressively from ca. 308 Ma in the St. Sylvestrecomplex to the regional age of 335 Ma (Fig. 9). No large structureis known in this area, but many small-scale faults parallel to theleucogranite contact are observed or inferred (Arène et al., 1972). Thus,it is suggested that these faults and/or the reactivation of lithological

boundaries (Fig. 7) may be responsible for this transition zone. Globally,this fault pattern is in agreement with the E–W extension direction thatoccurred during Late Stephanian to Early Permian in theWof the FrenchMassif Central (Burg et al., 1994). Finally, this unroofing could be anexplanation for the transient episode of faster denudation rate of1.5 mm · y−1 related to the late-orogenic extension and collapse ofthe belt, at ca. 305 Ma proposed by Scaillet et al. (1996a, 1996b).

13C. Le Carlier de Veslud et al. / Lithos 175–176 (2013) 1–15

4.3. Estimation of exhumation rates

A question may arise from the previous results: is the exhumationin the Limousin in the 340–300 Ma period to be regarded as severaldistinct pulses, or as a continuous process. An estimation of the exhu-mation rates could provide information on that subject. However, anddespite the relatively large amount of data available on this area, onlyfirst order averaged values can be obtained.

If one considers globally the present level of exposure in theLimousin area, at the end of the nappe stacking, at ca. 350 Ma, a pres-sure of ca. 0.5 GPa, i.e. a depth of 15–20 km, is observed in the LGU(Bellot and Roig, 2007). On the other hand, at ca. 300 Ma, its depthis about 4 km (Bouchot et al., 2005; Scaillet et al., 1996b). Thus,a very rough average exhumation rate of 0.3 mm · y−1 may beobtained. The main issue is to determine how this exhumation ratehas varied through time?

For the St. Sylvestre complex, Scaillet et al. (1996b) proposed atwo-stage model, with an exhumation rate of 0.3 mm · y−1 duringthe 320–306 Ma period, followed by a faster rate of 1.5 mm · y−1

during the 306–305 Ma period. However, this higher rate was notbased directly on P–t values, but is the result of a transient thermalmodel best fitting argon thermochronological and fluid inclusiondata.

In the better constrained Bourneix area, the exhumation rates canbe deduced from P–T–t path based on various data (see Section 4.1and Fig. 11). The results (Table 5a) indicate a rate of 0.6 mm · y−1

for the 345–335 Ma period and a rate of 0.4 mm · y−1 for the 335–310 Ma period. It should be noted that the pressure drop and relatedenhanced exhumation rate highlighted by the fluid inclusion studiesafter 335 Ma cannot be identified due to a lack of direct dating. Iffor instance, one considers this pressure drop to have occurred withina 5 My period, from 335 to 330 Ma (Table 5b), then the exhumationrate has to be in the order of 1 mm · y−1 for that this period.

Therefore, available dating does not allow a direct identification ofexhumation pulses, typically with a rate ≥ 1 mm · y−1, that is equiva-lent to 1 km · My−1. However, it should be noted that:

• The structural study of the Argentat fault suggests 2 main deforma-tion stages (Roig et al., 2002). The first one at 340–330 Ma, with theformation of a ductile normal listric fault, and the second one at ca.305 Ma with a reactivation of the ductile structure zone leading tothe formation of a highly dipping brittle normal fault.

• The fluid inclusion studies in the Bourneix area similarly suggest 2 orestages (Essaraj et al., 2001, see also Section 4.1 and Fig. 11). In agree-ment with Marignac et al. (2003), we suggest to relate the ore stage I(As–S–Fe) to the ca. 335 Ma exhumation episode and the ore stage IIto the ca. 305 Ma exhumation episode. At a more regional scale, the305 Ma exhumation episode is also related to the creation episyenitewithin the St. Sylvestre–Western Marche complex.

Table 5Estimation of average exhumation rates in the Bourneix area, from P–T–t data synthe-sized in Fig. 11. (a) Raw estimation from available P–T–t data. (b) Estimation assumingthat the 5 km exhumation suggested by fluid inclusions, took place within the 335–330 Ma period.

Time (Ma) P (GPa) Depth (km) Exhumation rate (mm·y−1)

a345 0.5 19 0.6335 0.35 13 0.4310 0.1 4

b345 0.5 19 0.6335 0.35 13 1330a 0.2 7 0.2310 0.1 4

a Hypothetical age added for discussion purpose.

Thus, these lines of evidences further support the existence of twoexhumation pulses in the Limousin area, at ca. 335 Ma and 305 Ma. Itis interesting to note that a similar scenario, involving linked exhu-mation and fluid circulation episodes, was proposed for theVariscangold metallogenesis in northern Portugal by Noronha et al. (2000).

5. Conclusions

Systematic 40Ar/39Ar dating of metamorphic rocks performed inthe western part of the French Massif Central (Limousin area) helpsto document the existence of two exhumation stages, each one asso-ciated with an extensional stage.

(1) A first exhumation stage occurred at ca. 335 Ma (Late Visean).This age is very close to exhumation ages proposed in theSioule and Brevenne areas by Faure et al. (2002). This stage isalso synchronous to the coupled tectonic and magmatic activi-ty along the Argentat structure (Roig et al., 2002). This stagemay be related to the onset of syn-convergent extension(Burg et al., 1994; Faure, 1995; Faure and Pons, 1991) that oc-curred in the French Massif Central, roughly 15–20 My afterthe end of the nappe stacking (ca. 350–360 Ma). Availabledata indicate that this extension and associated exhumationand cooling, occurred over a distance of more than 200 km inthe internal zones of the belt, whereas compression was stillactive in the northern and southern parts of the belt.

(2) A second exhumation stage may be related to the late-orogenicextension and collapse of the belt, at ca. 310–305 Ma(Westphalian–Stephanian). This last stage is characterizedby an exhumation of the St. Sylvestre complex by thedownwarping of metamorphic and granitoidic formations.

Acknowledgment

This work was supported by the GéoFrance 3D program “3-DMapping and Metallogeny of the French Massif Central”. Many thanksto the Editor (M. Scambelluri) and the two reviewers (L. Gaggero andan anonymous reviewer) for their careful and constructive reviews.

References

Alexandre, P., Le Carlier de Veslud, C., Cuney, M., Ruffet, G., Virlogeux, D., Cheilletz, A.,2002. Datation 40Ar/39Ar des leucogranites sous couverture du complexeplutonique de Charroux-Civray (Vienne). Comptes Rendus Geosciences, Paris334 (16), 1141–1148.

Alexandrov, P., 2000. Géochronologie U–Pb et 40Ar/39Ar de deux segments de la chaîneVarisque: le Haut Limousin et les Pyrénées Orientales. INPL, Nancy, France(Unpublished PhD thesis, 186 pp.).

Alexandrov, P., Cheilletz, A., Deloule, E., Cuney, M., 2000. 319 ± 7 Ma age for the Blondgranite (northwest Limousin, French Massif Central) obtained by U/Pb ion-probedating of zircons. Comptes Rendus de l'Académie des Sciences, Paris 330, 1–7.

Alexandrov, P., Ruffet, G., Cheilletz, A., 2002. Muscovite recrystallization and saddle-shaped 40Ar/39Ar age spectra: example from the Blond granite (Massif Central,France). Geochimica et Cosmochimica Acta 66 (10), 1793–1807.

Améglio, L., Vigneresse, J.L., Bouchez, J.L., 1997. Granite pluton geometry and emplace-ment mode inferred from combined fabric and gravity data. In: Bouchez, J.L.,Hutton, D.H.W., Stephens, W.E. (Eds.), Granite: From Segregation of Melt to Em-placement Fabrics. Kluwer Academic Publishers, Dordrecht, Boston, London, pp.199–214.

Arène, J., Autran, A., Coffrant, D., Labernardière, H., Burnol, J., 1972. 1/50000th geolog-ical map of Bourganeuf. BRGM, France.

Bellot, J.P., 2007. Pre- to syn-extension melt-assisted nucleation and growth of exten-sional gneiss domes: the western French Massif Central (Variscan belt). Journalof Structural Geology 29, 863–880.

Bellot, J.P., Roig, J.Y., 2007. Episodic exhumation of HP rocks inferred from structuraland P–T paths from the southwestern Massif Central (Variscan belt, France). Jour-nal of Structural Geology 29, 1538–1557.

Berthier, F., Duthou, J.L., Roques, M., 1979. Datations géochronologiques Rb/Sr surroches totales du granite de Guéret (Massif Central). Age fini-dévonien de miseen place de l'un de ses faciès type. Bulletin du B.R.G.M, série II 2, 59–72 (section II).

Bertrand, J.M., Leterrier, J., Delapierre, E., Brouand, M., Cuney, M., Stussi, J.M., Virlogeux,D., 2001. Géochronologie U–Pb sur zircons de granitoïdes du Confolentais, du mas-sif de Charoux-Civray (seuil de Poitou) et de Vendée. Géologie de la France 1–2,167–181.

14 C. Le Carlier de Veslud et al. / Lithos 175–176 (2013) 1–15

Bitri, A., Truffert, C., Bellot, J.P., Bouchot, V., Ledru, P., Milési, J.P., Roig, J.Y., 1999.Imagerie des paléochamps hydrothermaux As–Au–Sb d'échelle crustale et despièges associés dans la chaîne varisque: sismique réflexion verticale (GéoFrance3D:Massif central français). Comptes Rendus de l'Académie des Sciences 329 (11),771–777.

Boiron, M.-C., Cathelineau, M., Banks, D.A., Fourcade, S., Vallance, J., 2003. Mixing ofmetamorphic and surficial fluids during the uplift of the Hercynian upper crust:consequences for gold deposition. Chemical Geology 194, 119–141.

Bouchot, V., Gros, Y., Bonnemaison, M., 1989. Structural controls of the auriferous shearzones of the Saint-Yrieix district, Massif central, France; evidences from the LeBourneix and Lauriéras gold deposits. Economic Geology 84, 1315–1327.

Bouchot, V., Alexandrov, P., Monie, P., Morillon, A., Cheilletz, A., Ruffet, G., Roig, J.,Charonnat, X., Chauvet, A., Faure, M., Le Carlier, C., Cuney, M., Gama, S., Ramboz,C., Becq Giraudon, J., Truffert, C., Ledru, P., Milesi, J., 1999. The W–As–Au–Sb metal-liferous peak: an “instantaneous” marker of the late orogenic evolution of theVariscan belt at 310–305 Ma, 293. BRGM 32–36.

Bouchot, V., Ledru, P., Lerouge, C., Lescuyer, J.L., Milesi, J.P., 2005. Late Variscan miner-alizing systems related to orogenic processes: the French Massif Central. Ore Geol-ogy Reviews 27 (1–4), 169–197.

Boulvais, P., Ruffet, G., Cornichet, J., Mermet, M., 2007. Cretaceous albitization anddequartzification of Hercynian peraluminous granite in the Salvezines massif(French Pyrénées). Lithos 93 (1–2), 89–106.

Bruguier, O., Becq-Giraudon, J.F., Bosch, D., Lancelot, J., 1998. Late Visean (UpperMississipian) hidden basin in the internal zones of the Variscan Belt: U–Pb zirconevidence from the French Massif Central. Geology 26 (7), 627–630.

Burg, J.P., 1983. Tectogénèse comparée de deux segments de chaîne de collision: le suddu Tibet (suture de Tsangpo), la chaîne hercynienne d'Europe (suture du Massifcentral). Univ. Montpellier (Unpublished PhD thesis, 361 pp.).

Burg, J.P., Matte, P., 1978. A cross section through the FrenchMassif Central and the scopeof its Variscan geodynamic evolution. Zeitschrift der Deutschen Geologischen Gesell-schaft 129, 429–460.

Burg, J.P., Balé, P., Brun, J.P., Girardeau, J., 1987. Stretching lineation and transport direc-tion in the Ibero-Armorican arc during Siluro-Devonien collision. GeodynamicaActa 1 (1), 71–87.

Burg, J.P., Van Den Driessche, J., Brun, J.P., 1994. Syn- to post-thickening extension:mode and consequences. Comptes Rendus de l'Académie des Sciences, Paris 319,1019–1032.

Cartannaz, C., Rolin, P., Cocherie, A., Marquer, D., Legendre, O., Fanning, C.M., Rossi, P.,2007. Characterization of wrench tectonics from dating of syn- to post-magmatismin the north-western French Massif Central. International Journal of Earth Sciences96, 271–287.

Castonguay, S., Ruffet, G., Tremblay, A., Féraud, G., 2001. Tectonometamorphic evolu-tion of southern Québec Appalachians: 40Ar/39Ar evidences for Ordovician crustalthickening and Silurian exhumation of the internal Humber zone. Geological Soci-ety of America Bulletin 113, 144–160.

Cathelineau, M., 1986. The hydrothermal alkali metasomatism effects on granitic rocks:quartz dissolution and related subsolidus changes. Journal of Petrology 27,945–965.

Cheilletz, A., Archibald, D., Cuney, M., Charoy, B., 1992. Ages 40Ar/39Ar du leucogranite àtopaze-lépidolite de Beauvoir et des pegmatites sodolithiques de Chédeville (NordMassif Central, France). Signification pétrologique et géodynamique. ComptesRendus de l'Académie des Sciences, Paris 315, 329–336.

Chenevoy, M., Constans, J., Recoing, M., 1984. 1/50 000th Geological Map of Saint Léonardde Noblat. BRGM, France.

Chèvremont, P., Constans, J., Ledru, P., Ménillet, F., 1992. 1/50 000th Geological Map ofOradour sur Glane. BRGM, France.

Cuney, M., Friedrich, M., Blumenfeld, P., Bourguignon, A., Boiron, M.C., Vigneresse, J.L.,Poty, B., 1990. Metallogenesis in the French part of the Variscan orogen. Part I: Upreconcentration in pre-Variscan and Variscan formations — a comparison withSn, W and Au. Tectonophysics 177, 39–57.

Cuney, M., Brouand, M., Stussi, J.M., 2001a. Le magmatisme hercynien en Vendée. Cor-rélations avec la Vienne et le Confolentais. Géologie de la France 1–2, 117–142.

Cuney, M., Brouand, M., Stussi, J.M., Virlojeux, D., 2001b. Le complexe plutonique deCharroux-Civray (Vienne): témoin du magmatisme infra-carbonifère dans le segmentoccidental de la chaîne varisque européenne. Géologie de la France 1–2, 143–166.

Cuney, M., Alexandrov, P., Le Carlier de Veslud, C., Cheilletz, A., Raimbault, L., Ruffet, G.,Scaillet, S., 2002. The timing of W–Sn-rare metals mineral deposit formation in thewestern Variscan Chain in their orogenic setting; the case of the Limousin area(Massif Central, France). In: Blundell, D., Neubauer, F., von Quadt, A. (Eds.), TheTiming and Location of Major Ore Deposits in an Evolving Orogen Geological Soci-ety Special Publication, 204, pp. 213–228.

Downes, H., Duthou, J.L., 1988. Isotopic and trace-element arguments for the lower-crustal origin of Hercynian granitoids and pre-Hercynian orthogneisses, MassifCentral (France). Chemical Geology 68 (3–4), 291–308.

Ducrot, J., Lancelot, J.R., Marchand, J., 1983. Datation U–Pb sur zircons de l'éclogite de laBorie (Haut Allier, France) et conséquences sur l'évolution anté-hercynienne del'Europe occidentale. Earth and Planetary Science Letters 18, 97–113.

Duthou, J., 1978. Les granitoïdes du Haut Limousin (Massif central français) chronologieRb/Sr de leur mise en place; le thermo-métamorphisme carbonifère. Bulletin de laSociété Géologique de France (7), 229–235 (XX, n°3).

Duthou, J., Cantagrel, J.M., Didier, J., Vialette, Y., 1984. Paleozoic granitoids from theFrench Massif Central: age and origin studied by the 87Rb–87Sr system. Physics ofthe Earth and Planetary Interiors 35, 131–144.

Essaraj, S., Boiron,M.-C., Cathelineau, M., Fourcade, S., 2001. Multistage deformation of Au-quartz veins (Lauriéras, French Massif Central): evidence for late gold introductionfrommicrostructural, isotopic and fluid inclusion studies. Tectonophysics 336, 79–99.

Faure, M., 1995. Late orogenic Carboniferous extensions in the Variscan French MassifCentral. Tectonics 14 (1), 132–153.

Faure, M., Pons, J., 1991. Crustal thinning recorded by the shape of Namurian–Westphalianleucogranite in the Variscan belt of the northern Massif Central, France. Geology 19,730–733.

Faure, M., Leloix, C., Roig, J.-Y., 1997. L'évolution polycyclique de la Chaîne hercynienne.Bulletin de la Société Géologique de France 168, 695–705.

Faure, M., Monié, P., Pin, C., Maluski, H., Leloix, C., 2002. Late Visean thermal event inthe northern part of the French Massif central: new 40Ar/39Ar and Rb–Sr isotopicconstraints on the Hercynian syn-orogenic extension. International Journal ofEarth Sciences 91, 53–75.

Faure, M., Lardeaux, J.M., Ledru, P., 2009. A review of the pre-Permian geology of theVariscan French Massif Central. Comptes Rendus Geosciences 341, 202–213.

Gebauer, H., Bernard-Griffiths, J., Grünenfelder, M., 1981. U/Pb zircon and monazitedating of mafic–ultramafic complex and its country rocks. Example: Sauviat-sur-Vige, French Massif Central. Contributions to Mineralogy and Petrology 76,292–300.

Gébelin, A., 2004. Déformation et mise en place des granites (360–300 Ma) dans unsegment de la Chaîne Varisque (Plateau de Millevaches, Massif Central). Univ.Montpellier, Montpellier, France (Unpub PhD thesis, 324 pp.).

Gébelin, A., Brunel, M., Monié, P., Faure, M., Arnanud, N., 2007. Transpressional tec-tonics and Carboniferous magmatism in the Limousin, Massif Central, France:structural and 40Ar/39Ar investigations. Tectonics. http://dx.doi.org/10.1029/2005TC001822.

Gébelin, A., Roger, F., Brunel, M., 2009. Syntectonic crustal melting and high-grademetamorphism in a transpressional regime, Variscan Massif Central, France.Tectonophysics 477, 229–243.

Grove, M., Harrison, T.M., 1996. 40Ar⁎ diffusion in Fe-rich biotite. American Mineralo-gist 81, 940–951.

Guineberteau, B., Cuney, M., Carré, J.L., 1989. Structure magmatique et plastique deMarche Occidentale: un couloir transformant hercynien dans le NW duMassif Cen-tral français. Comptes Rendus de l'Académie des Sciences, Paris 309, 1695–1702.

Harrison, T.M., Celerier, J., Aikman, A.B., Hermann, J., Heizler, M.T., 2009. Diffusion of40Ar in muscovite. Geochimica et Cosmochimica Acta 73, 1039–1051.

Holliger, P., Cuney, M., Friedrich, M., Turpin, L., 1986. Ages carbonifères de l'unité deBrâme du complexe granitique peralumineux de Saint-Sylvestre (NO Massif Central)défini par les données isotopiques sur zircon et monazite. Comptes Rendus del'Académie des Sciences, Paris 303, 1309–1314.

Lafon, J.M., 1986. Géochronologie U–Pb appliquée à deux segments du Massif Centralfrancais: le Rouergue oriental et le Limousin central. Univ. Montpellier (Unpub.PhD thesis, 152 pp.).

Le Carlier de Veslud, C., Cuney, M., Royer, J.J., Floc'h, J.P., Améglio, L., Alexandrov, P.,Vigneresse, J.L., Chèvremont, P., Itard, Y., 2000. Relationships between granitoidsand mineral deposits: 3-D modelling of the Variscan Limousin province (NWFrench Massif Central). Transactions of the Royal Society of Edinburgh: Earth Sci-ences 91, 283–301.

Ledru, P., Lardeaux, J.-M., Santallier, D., Autran, A., Quenardel, J.-M., Floc'h, J.-P.,Lerouge, G., Maillet, N., Marchand, J., Ploquin, A., 1989. Où sont les nappes dansle Massif Central Français ? Bulletin de la Société Géologique de France 5 (3),605–618.

Leroy, J., 1984. Episyénitisation dans le gisement d'uranium du Bernardan (Marche):comparation avec les gisements similaires du nord-ouest du Massif CentralFrançais. Mineralium Deposita 19, 26–35.

Lespinasse, M., Cathelineau, M., 1990. Fluid percolation in a fault zone: a study of fluidinclusion planes in the St. Sylvestre granite, North West Massif Central, France.Tectonophysics 184, 173–187.

Lespinasse, M., Pêcher, A., 1986. Microfracturing and regional stress field: a study of thepreferred orientations of fluid inclusion planes in a granite from the Massif Central,France. Journal of Structural Geology 8, 169–180.

Lespinasse, M., Mollier, B., Delair, J., Bladier, Y., 1986. Structuration tangentielle etchevauchements carbonifères dans les leucogranites du NW du Massif Centralfrançais: l'exemple des failles de Bussières-Madeleine et d'Arrènes-Ouzilly.Comptes Rendus de l'Académie des Sciences, Paris 303, 1575–1580.

Maluski, H., Costa, S., Etchler, H., 1991. Late Variscan tectonic evolution by thinning ofearlier thickened crust. An 40Ar/39Ar study on the Montagne Noire, southern MassifCentral, France. Lithos 26, 287–304.

Marignac, C., Boiron, M.C., Cathelineau, M., Fourcade, S., 2003. Variscan lode gold de-posits: the case for a crustal-scale hydrothermal system rooted in the middlecrust (Saint-Yrieix district, Limousin, French Massif Central). In: Eliopoulos, D.G.,et al. (Ed.), Mineral Exploration and Sustainable Development, vol. 2. Millpress,Rotterdam, pp. 783–786.

Matte, P., 1986. Tectonics and plate tectonics model for the Variscan belt of Europe.Tectonophysics 126, 329–374.

Mollier, B., Bouchez, J.L., 1982. Structuration magmatique du complexe granitique deBrâime-St. Sylvestre-St. Goussaud (Limousin, Massif Central françals). ComptesRendus de l'Académie des Sciences, Paris 294, 1329–1334.

Mollier, B., Lespinasse, M., 1985. Déformation magmatique et plastique en limitenord du granite de Saint-Sylvestre (Nord-Ouest du Massif Central français): lafaille d'Arrênes-Ouzilly. Comptes Rendus de l'Académie des Sciences, Paris 300,681–686.

Monier, G., 1980. Pétrologie des granitoïdes du Sud-Millevaches (Massif Central français).Minéralogie, Géochimie, Géochronologie. Univ. Clermont-Ferrand (Unpub. PhD Thesis,288 pp.).

Nance, R., Gutiérrez-Alonso, G., Keppie, J., Linnemann, U., Murphy, J., Quesada, C.,Strachan, R., Woodcock, N., 2010. Evolution of the Rheic Ocean. Gondwana Re-search 17, 194–222.

15C. Le Carlier de Veslud et al. / Lithos 175–176 (2013) 1–15

Noronha, F., Cathelineau, M., Boiron, M.-C., Banks, D.A., Doria, A., Ribeiro, M., Nogueira, P.,Guedes, A., 2000. A three stage fluid flow model for Variscan gold metallogenesis innorthern Portugal. Journal of Geochemical Exploration 71, 209–224.

Peiffer, M.T., 1985. Données nouvelles sur la ligne tonalitique du Limousin et les “dioritesquartziques” qui la composent. Comptes Rendus de l'Académie des Sciences, Paris300, 345–348.

Peucat, J.J., Vidal, P., Godard, G., Postaire, B., 1982. Precambrian U–Pb zircon ages ineclogites and garnet pyroxenites from South Brittany (France); an old oceaniccrust in the West European Hercynian Belt? Earth and Planetary Science Letters60 (1), 70–78.

Pin, C., Peucat, J.J., 1986. Ages des épisodes de métamorphisme paléozoiques dans leMassif central et le Massif armoricain. Bulletin de la Société Géologique de FranceVIII 2 (3), 461–469.

Pitra, P., Ballèvre, M., Ruffet, G., 2010. Inverted metamorphic field gradient towards aVariscan suture zone (Champtoceaux Complex, Armorican Massif, France). Journalof Metamorphic Geology 28, 183–208.

Purdy, J.W., Jager, E., 1976. K–Ar Ages on Rock FormingMinerals from the Central Alps, 30.Memorie degli Istituti di Geologia e Mineralogia dell'Università di Padova, pp. 1–32.

Quenardel, J.M., Santallier, D., Burg, J.P., Bril, H., Cathelineau, M., Marignac, C., 1991. LeMassif Central. Sciences Géologiques Bulletin 44 (1–2), 105–206.

Raimbault, L., 1999. Tin–tungsten vein mineralisation at Moulin-Barret, France. In:Stanley, et al. (Ed.), Mineral Deposits: Processes to Processing. Balkema, Rotter-dam, pp. 417–420.

Raoult, J.F., Meilliez, F., 1987. The Variscan front and the Midi fault between the channeland the Meuse river. Journal of Structural Geology 9, 437–479.

Rey, P., Burg, J.P., Caron, J.M., 1991–1992. Middle and Late Carboniferous extension inthe Variscan belt: structural and petrological evidences from the Vosges massif(Eastern France). Geodynamica Acta 8 (1-2), 17–36.

Roig, J.Y., Faure, M., 2000. La tectonique cisaillante polyphasée du Sud Limousin (Massifcentral français) et son interprétation dans un modèle d'évolution polycycliquede la chaîne hercynienne. Bulletin de la Société Géologique de France 171 (3),295–307.

Roig, J.Y., Faure, M., Maluski, H., 2002. Superimposed tectonic and hydrothermal eventsduring the late-orogenic extension in the Western French Massif Central: a struc-tural and 40Ar/39Ar study. Terra Nova 14, 25–32.

Rolin, P., Colchen, M., 2001. Les cisaillements hercyniens de la Vendée au Limousin.Géologie de la France 1–2, 87–116.

Ruffet, G., Gruau, G., Ballèvre, M., Féraud, G., Philippot, P., 1997. Rb–Sr and 40Ar/39Arlaser probe dating of high-pressure phengites from the Sesia Zone (Western

Alps); underscoring of excess argon and new age constraints on the high-pressure metamorphism. Chemical Geology 141 (1–2), 1–18.

Santallier, D., Lardeaux, J.M., Marchand, D., Marignac, C., 1994. Metamorphism. In:Keppie, J.D. (Ed.), Pre-Mesozoic Geology in France and Related Areas. Springer-Verlag, pp. 324–334.

Scaillet, S., Cheilletz, A., Cuney, M., Farrar, E., Archibald, A.D., 1996a. Cooling pattern andmineralisation history of the Saint Sylvestre and Western Marche leucogranitepluton, French Massif Central: I.40Ar/39Ar isotopic constraints. Geochimica etCosmochimica Acta 60 (23), 4653–4671.

Scaillet, S., Cuney,M., Le Carlier de Veslud, C., Cheilletz, A., Royer, J.J., 1996b. Cooling patternand mineralisation history of the Saint Sylvestre and Western Marche leucogranitepluton, French Massif Central: II. Thermal modelling and implications for the mecha-nisms of U-mineralization. Geochimica et Cosmochimica Acta 60 (23), 4673–4688.

Seyferth, M., Henk, A., 2004. Syn-convergent exhumation and lateral extrusion incontinental collision zones — insights from three-dimensional numerical models.Tectonophysics 382 (1–2), 1–29.

Tartèse, R., Ruffet, G., Poujol, M., Boulvais, P., Ireland, 2011. Simultaneous resetting ofthe muscovite K–Ar and monazite U–Pb geochronometers: a story of fluids. TerraNova 23, 390–398. http://dx.doi.org/10.1111/j.1365-3121.2011.01024.x).

Thompson, A.B., Schulmann, K., Jezek, J., 1997. Thermal evolution and exhumation inobliquely convergent (transpressive) orogens. Tectonophysics 208, 171–184.

Turpin, L., Cuney, M., Friedrich, M., Bouchez, J.L., Aubertin, M., 1990. Meta-igneous or-igin of Hercynian peraluminous granites in N.W. French Massif Central: implicationfor crustal history reconstitutions. Contributions to Mineralogy and Petrology 104,163–172.

Vallance, J., Boiron, M.C., Cathelineau, M., Fourcade, S., Marignac, C., 2004. The granitehosted gold deposit of Moulin de Cheni (St Yrieix District, Massif Central, France):petrographic, structural, fluid inclusion and oxygen isotope constraints. MineraliumDeposita 39, 265–281.

Villa, I.M., 1998. Isotopic closure. Terra Nova 10, 42–47.Villa, I.M., Puxeddu, M., 1994. Geochronology of the Larderello geothermal field: new

data and the closure temperature issue. Contributions to Mineralogy and Petrology115, 415–426.

von Raumer, J., Stampfli, G., 2008. Early Paleozoic subsidence patterns and subsequenttectonic plate scenarios. Tectonophysics 461, 9–20.

Williamson, B.J., Shaw, A., Downes, H., Thirlwall, M.F., 1996. Geochemical constraintson the genesis of Hercynian two-mica leucogranites from the Massif Central,France. Chemical Geology 127, 25–42.