Comparison of PTt paths in allochthonous high pressure metamorphic terrains from the Scandinavian Caledonides and the French Massif Central: Contrasted thermal structures during uplift

1991 ◽  
Vol 80 (2) ◽  
pp. 333-348 ◽  
Author(s):  
L. Mercier ◽  
H. L. M. van Roermund ◽  
J. M. Lardeaux
Keyword(s):  
High Pressure ◽  
French Massif Central ◽  
Massif Central ◽  
Scandinavian Caledonides ◽  
Thermal Structures

Timing and duration of Variscan high-pressure metamorphism in the French Massif Central: A multimethod geochronological study from the Najac Massif

Lithos ◽  
2018 ◽  
Vol 308-309 ◽  
pp. 381-394 ◽  
Author(s):  
Caroline Lotout ◽  
Pavel Pitra ◽  
Marc Poujol ◽  
Robert Anczkiewicz ◽  
Jean Van Den Driessche
Keyword(s):  
High Pressure ◽  
French Massif Central ◽  
Massif Central ◽  
High Pressure Metamorphism ◽  
Geochronological Study

Conditions et ages 40 Ar/ 39 Ar de mise en place des granitoides de la zone externe sud du Massif central francais; exemple des granodiorites de St-Guiral et du Liron (Cevennes, France)

2000 ◽  
Vol 171 (5) ◽  
pp. 495-510 ◽  
Author(s):  
Khalid Najoui ◽  
Andre Francois Leyreloup ◽  
Patrick Monie
Keyword(s):  
Gravitational Collapse ◽  
Regional Metamorphism ◽  
Low Grade ◽  
French Massif Central ◽  
The South ◽  
Massif Central ◽  
Laser Probe ◽  
Thermal Structures ◽  
Minimum Age ◽  
Contact Aureoles

Abstract The St-Guiral and the Liron laccolithic granodiorites outcropping in the southeastern area of the French Massif Central intrude the Cambro-Ordovician low grade series of the western Cevennes. The petrological study of their contact aureoles shows that these plutons emplaced at low depth (1-2 kb; 690-700 degrees C). The laser probe 40 Ar/ 39 Ar allows us to suggest a minimum age of 324 Ma for the emplacement of the St-Guiral granodiorite. This emplacement seems synchronous with the LP-HT regional metamorphism in the western Cevennes for which the cooling ages are identical. The Liron granodiorite (310 Ma) is younger and crosscuts the thermal structures of the LP-HT regional metamorphism. Accordingly these plutons emplaced at the Namurian-early Westphalian during the extensional phases related to the generalised gravitational collapse of the previously thickened Hercynian belt. The detachment of the subducted lithosphere (slab detachment) could be related to these phenomena and could explain the granitization of the south external area of the Hercynian belt as well as the migration of the magmatism towards the south of the belt.

scholarly journals From Burial to Exhumation: Emplacement and Metamorphism of Mafic Eclogitic Terranes Constrained Through Multimethod Petrochronology, Case Study from the Lévézou Massif (French Massif Central, Variscan Belt)

2020 ◽  
Vol 61 (4) ◽  
Author(s):  
C Lotout ◽  
M Poujol ◽  
P Pitra ◽  
R Anczkiewicz ◽  
J Van Den Driessche
Keyword(s):  
High Pressure ◽  
Trace Element ◽  
Metamorphic Rocks ◽  
Variscan Orogeny ◽  
Continental Margins ◽  
Variscan Belt ◽  
French Massif Central ◽  
Massif Central ◽  
Mineral Growth ◽  
Exhumation Rates

Abstract Linking mineral growth and time is required to unravel the evolution of metamorphic rocks. However, dating early metamorphic stages is a challenge due to subsequent retrograde overprinting. A fresh eclogite and a former eclogite retrogressed under amphibolite facies from the southern French Massif Central (Lévézou massif, Variscan belt) were investigated with a large panel of geochronometers (U–Pb in zircon, rutile and apatite, Lu–Hf and Sm–Nd in garnet) in a petrological context tightly constrained by petrographic observations, trace element analyses and phase equilibrium modelling. Both samples recorded similar HP conditions at 18–23 kbar and 680–800°C, whereas the retrogressed eclogite later equilibrated at 8–9·5 kbar and c.600°C. In the retrogressed sample, most of the zircon grains are characterized by negative Eu anomalies and HREE enrichment, and yield an Ordovician U–Pb date of 472·3 ± 1·7 Ma, interpreted as the emplacement age of the mafic protolith. In agreement with other data available for the Variscan belt, and based on zircon trace element record and whole-rock geochemistry, this age is considered to represent the magmatism associated with the extreme thinning of the continental margins during the Ordovician. In the same sample, a few zircon rims show a weaker HREE enrichment and yield a date of 378 ± 5·7 Ma, interpreted as a prograde pre-eclogitic age. Lu–Hf garnet dating from both samples yields identical dates of 357 ± 13 Ma and 358·0 ± 1·5 Ma inferred to approximate the age of the high-pressure metamorphic peak. Fresh and retrogressed samples yield respectively 350·4 ± 7·7 Ma and 352 ± 20 Ma dates for Sm–Nd garnet dating, and 367·8 ± 9·1 Ma and 354·9 ± 9·5 Ma for U–Pb rutile dating. Apatite grains from the retrogressed sample give a mean age of 351·8 ± 2·8 Ma. The similarity between all recorded ages from distinct chronometers and radiometric methods (U–Pb, rutile, apatite; Lu–Hf, garnet; Sm–Nd, garnet) combined with P–T estimations from high-pressure metamorphic rocks equilibrated under different conditions testifies to very fast processes that occurred during the Variscan orogeny, highlighting a major decompression of 15–8·5 kbar in less than 7 Myr, and suggesting mean exhumation rates in excess of 6·3 mm/yr.

scholarly journals Prograde and retrograde P–T evolution of a Variscan high-temperature eclogite, French Massif Central, Haut-Allier

2020 ◽  
Vol 191 ◽  
pp. 14
Author(s):  
Luc de Hoÿm de Marien ◽  
Pavel Pitra ◽  
Florence Cagnard ◽  
Benjamin Le Bayon
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Garnet Growth ◽  
French Massif Central ◽  
Temperature Peak ◽  
Massif Central ◽  
Slab Rollback ◽  
High Pressure Granulite ◽  
Garnet Growth Zoning ◽  
Growth Zoning

The P–T evolution of a mafic eclogite sample from the Haut-Allier was studied in order to constrain the dynamic of the Variscan subduction in the eastern French Massif Central. Three successive metamorphic stages M1, M2 and M3, are characterized by assemblages comprising garnet1-omphacite-kyanite, garnet2-plagioclase, and amphibole-plagioclase, respectively, and define a clockwise P–T path. These events occurred at the conditions of eclogite (M1; ∼ 20 kbar, 650 °C to ∼ 22.5 kbar, 850 °C), high-pressure granulite (M2; 19.5 kbar and 875 °C) and high-temperature amphibolite facies (M3; < 9 kbar, 750–850 °C), respectively. Pseudosection modelling of garnet growth zoning and mineralogy of the inclusions reveal a prograde M1 stage, first dominated by burial and then by near isobaric heating. Subsequent garnet1 resorption, prior to a renewed growth of garnet2 is interpreted in terms of a decompression during M2. High-pressure partial melting is predicted for both the M1 temperature peak and M2. M3 testifies to further strong decompression associated with limited cooling. The preservation of garnet growth zoning indicates the short-lived character of the temperature increase, decompression and cooling cycle. We argue that such P–T evolution is compatible with the juxtaposition of the asthenosphere against the subducted crust prior to exhumation driven by slab rollback.

Evaluating Holocene natural hazards in the French Massif Central from a regional lake sediment approach

2021 ◽  
Author(s):  
E. Chapron ◽  
A. Foucher ◽  
L. Chassiot ◽  
W. Fleurdeus ◽  
V. Arricau ◽  
...  
Keyword(s):  
Natural Hazards ◽  
Lake Sediment ◽  
French Massif Central ◽  
Massif Central

Sellaphora labernardierei (Sellaphoraceae, Bacillariophyta), a new epilithic species from French spring and four new combinations within the genus Sellaphora

Phytotaxa ◽  
2016 ◽  
Vol 260 (3) ◽  
pp. 235 ◽  
Author(s):  
AUDE BEAUGER ◽  
CARLOS E. WETZEL ◽  
OLIVIER VOLDOIRE ◽  
ALEXANDRE GARREAU ◽  
LUC ECTOR
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Central Area ◽  
Mineral Waters ◽  
New Combinations ◽  
French Massif Central ◽  
Small Species ◽  
Massif Central ◽  
Floristic Survey ◽  
Scanning Electron

During a floristic survey of freshwater springs in the French Massif Central region, a new Sellaphora species (Bacillariophyceae) was found and is hereby described: Sellaphora labernardierei sp. nov. This new small species, with linear to linear-elliptical valves, slightly inflated in the middle, is formally described using light and scanning electron microscopy. The species has a single H-shaped chloroplast and striae usually biseriate tending to be uniseriate near the centre of the valve. The valve dimensions, the valve, pole and central area shapes, and the striae density and pattern allow their separation from similar taxa belonging to the genera Eolimna, Naviculadicta and Sellaphora. The ecological preferences of Sellaphora labernardierei are mineral waters with high nitrate concentrations. The examination of similar taxa belonging to the genera Eolimna and Naviculadicta and their characteristics lead to propose four new combinations of Sellaphora species.

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