Deciphering orogeny: a metamorphic perspective Examples from European Alpine and Variscan belts

2014 ◽  
Vol 185 (5) ◽  
pp. 281-310 ◽  
Author(s):  
Jean-Marc Lardeaux
Keyword(s):  
Regional Development ◽  
Western Alps ◽  
Temporal Data ◽  
French Massif Central ◽  
Massif Central ◽  
Metamorphic History ◽  
Variscan Metamorphism ◽  
Geochemical Constraints ◽  
Metamorphic Series

AbstractIn this paper we review and discuss, in a synthetic historical way, the main results obtained on Variscan metamorphism in the French Massif Central. First, we describe the pre-orogenic architecture of the French Massif Central on the base of available lithostratigraphic and geochemical constraints. Second, we portray the progressive metamorphic evolution through time and space with the presentation of 6 metamorphic maps corresponding to critical orogenic periods, namely 430–400 Ma, 400–370 Ma, 370–360 Ma, 360–345 Ma, 340–325 Ma and 320–290 Ma. We discuss the role of multiple subductions in orogeny, the metamorphic effects of continental collision (i.e. regional development of intermediate-pressure metamorphic series) as well as the links between post-thickening tectonics and the regional development of low-pressure metamorphic series coeval with crustal partial melting. As it was the case for the western Alps, we emphasize the lack of temporal data on high-pressure/low-temperature metamorphic rocks as well as the uncertainties on the sizes of rock units that have recorded the same metamorphic history (i.e. coherent P-T-t/deformation trajectories). Finally, we underline the main differences and similarities between the metamorphic evolutions of the western Alps and the French Massif Central.

Deciphering orogeny: a metamorphic perspective. Examples from European Alpine and Variscan belts

2014 ◽  
Vol 185 (2) ◽  
pp. 93-114 ◽  
Author(s):  
Jean-Marc Lardeaux
Keyword(s):  
High Pressure ◽  
Low Temperature ◽  
Western Alps ◽  
Metamorphic Rocks ◽  
Temporal Data ◽  
Metamorphic Evolution ◽  
Metamorphic History ◽  
Alpine Metamorphism ◽  
Collision Processes

AbstractIn this paper we review and discuss, in a synthetic historical way, the main results obtained on Alpine metamorphism in the western Alps. First, we describe the finite metamorphic architecture of the western Alps and discuss its relationships with subduction and collision processes. Second, we portray the progressive metamorphic evolution through time and space with the presentation of 5 metamorphic maps corresponding to critical orogenic periods, namely 85-65 Ma, 60-50 Ma, 48-40 Ma, 38-33 Ma and 30-20 Ma. We underline the lack of temporal data on high-pressure/low-temperature metamorphic rocks as well as the severe uncertainties on the sizes of rock units that have recorded the same metamorphic history (i.e. coherent P-T-t/deformation trajectories). We discuss the role of subduction-driven metamorphism in ocean-derived protoliths and the conflicting models that account for the diachrony of continental subductions in the western Alps.

scholarly journals Pressure-temperature conditions and significance of Upper Devonian eclogite and amphibolite facies metamorphisms in southern French Massif central

2020 ◽  
Vol 191 ◽  
pp. 28
Author(s):  
Anissa Benmammar ◽  
Julien Berger ◽  
Antoine Triantafyllou ◽  
Stéphanie Duchene ◽  
Abderrahmane Bendaoud ◽  
...  
Keyword(s):  
Upper Devonian ◽  
Amphibolite Facies ◽  
Garnet Growth ◽  
French Massif Central ◽  
Massif Central ◽  
Metamorphic History ◽  
Zircon Crystallization ◽  
Intermediate Unit ◽  
Armorican Massif ◽  
Subduction System

The southwestern French Massif central in western Rouergue displays an inverted metamorphic sequence with eclogite and amphibolite facies units forming the top of the nappe stack. They are often grouped into the leptyno-amphibolite complex included, in this area, at the base of the Upper Gneiss Unit. We sampled garnet micaschists and amphibolites to investigate their metamorphic history with isochemical phase diagrams, thermobarometry and U-Pb zircon dating. Our results demonstrate that two different tectono-metamorphic units can be distinguished. The Najac unit consists of biotite-poor phengite-garnet micaschists, a basic-ultrabasic intrusion containing retrogressed eclogites and phengite orthogneisses. Pressure and temperature estimates on micaschists with syn-kinematic garnets yield a prograde with garnet growth starting at 380 °C/6–7 kbar, peak pressure at 16 kbar for 570 °C, followed by retrogression in the greenschist facies. The age of high pressure metamorphism has been constrained in a recent publication between ca. 383 and 369 Ma. The Laguépie unit comprises garnet-free and garnet-bearing amphibolites with isolated lenses, veins or dykes of leucotonalitic gneiss. Thermobarometry and phase diagram calculation on a garnet amphibolite yield suprasolidus peak P-T conditions at 710 °C, 10 kbar followed by retrogression and deformation under greenschist and amphibolite facies conditions. New U-Pb analyses obtained on igneous zircon rims from a leucotonalitic gneiss yield an age of 363 ± 3 Ma, interpreted as the timing of zircon crystallization after incipient partial melting of the host amphibolite. The eclogitic Najac unit records the subduction of a continental margin during Upper Devonian. It is tentatively correlated to a Middle Allochthon, sandwiched between the Lower Gneiss Unit and the Upper Gneiss Unit. Such an intermediate unit is still poorly defined in the French Massif central but it can be a lateral equivalent of the Groix blueschists in the south Armorican massif. The Uppermost Devonian, amphibolite facies Laguépie unit correlates in terms of P-T-t evolution to the Upper Gneiss Unit in the Western French Massif central. This Late Devonian metamorphism is contemporaneous with active margin magmatism and confirms that the French Massif central belonged to the continental upper plate of an ocean-continent subduction system just before the stacking of Mississippian nappes.

Thermal maturation and exhumation of a middle orogenic crust in the Livradois area (French Massif Central)

2011 ◽  
Vol 182 (1) ◽  
pp. 5-24 ◽  
Author(s):  
Véronique Gardien ◽  
Olivier Vanderhaeghe ◽  
Nicolas Arnaud ◽  
Alain Cocherie ◽  
Marion Grange ◽  
...  
Keyword(s):  
Final Stage ◽  
Crustal Melting ◽  
Early Permian ◽  
French Massif Central ◽  
Rapid Cooling ◽  
Massif Central ◽  
Upper Carboniferous ◽  
Peak Metamorphism ◽  
Metamorphic Series ◽  
Granitic Dome

AbstractUpper Carboniferous heating and melting of the middle orogenic crust associated with the emplacement of syntectonic granitoids are documented in the Upper Gneissic Unit of the Livradois area (central part of the French Massif Central). Crustal melting post-dates peak metamorphism conditions (800-625°C, 10-8 kb) dated at 360 ± 4 Ma (U-Th-Pb on monazite). The P-T evolution of the metamorphic series indicates that Barrovian metamorphism was followed by a decompression (from 10 ± 1 kbar to 6 ± 1 kbar) associated with either a decrease in temperature in the southern part of the series or with an increase in temperature (of about 150°C) in the northern part of the series. This evolution records the first step of the exhumation of the series coeval with granitoids intrusion, of which the emplacements were dated at 315 ± 4 and 311 ± 18 Ma (U-Pb on zircon). The final stage of the exhumation is associated with an isobaric cooling of the whole series. Similarity of 40Ar/39Ar ages for biotite in the paragneisses (307-300 Ma) and K-feldspar in the granitoids (306-300 Ma) document rapid cooling for this stage. Moreover dextral reverse mylonites, at the border and the northern part of the metamorphic series indicate north-south compression coeval with the unroofing of the series. Youngest 40Ar-39Ar ages on K-feldspar (274.6 ± 5 Ma) combined with normal shearing in mylonites limiting the Carboniferous Brassac-les-Mines basin document the late Carboniferous-early Permian stage of extension coeval with the upwelling of the Velay granitic dome.

Geochemical constraints on restite composition and unmixing in the Velay anatectic granite, French Massif Central

Lithos ◽  
1997 ◽  
Vol 40 (2-4) ◽  
pp. 295-319 ◽  
Author(s):  
B.J. Williamson ◽  
H. Downes ◽  
M.F. Thirlwall ◽  
A. Beard
Keyword(s):  
French Massif Central ◽  
Massif Central ◽  
Anatectic Granite ◽  
Geochemical Constraints

THE ROLE OF CRUSTAL ANATEXIS AND MANTLE-DERIVED MAGMAS IN THE GENESIS OF SYNOROGENIC HERCYNIAN GRANITES OF THE LIVRADOIS AREA, FRENCH MASSIF CENTRAL

2007 ◽  
Vol 45 (3) ◽  
pp. 581-606 ◽  
Author(s):  
F. Solgadi ◽  
J.-F. Moyen ◽  
O. Vanderhaeghe ◽  
E. W. Sawyer ◽  
L. Reisberg
Keyword(s):  
French Massif Central ◽  
Crustal Anatexis ◽  
Massif Central

Extensional ductile tectonics of the Sioule metamorphic series (Variscan French Massif Central)

1993 ◽  
Vol 82 (3) ◽  
pp. 461-474 ◽  
Author(s):  
M. Faure ◽  
J. Grolier ◽  
J. Pons
Keyword(s):  
French Massif Central ◽  
Massif Central ◽  
Metamorphic Series

Giscience in the Mountain Geography

2010 ◽  
Vol 27 (1-2) ◽  
pp. 81-90
Author(s):  
Krishna Poudel
Keyword(s):  
Spatial Data ◽  
Environmental Data ◽  
Temporal Data ◽  
Observation Systems ◽  
Research Findings ◽  
Temporal And Spatial ◽  
Temporal And Spatial Characteristics ◽  
Mountain Geography ◽  
Different Sources

Mountains have distinct geography and are dynamic in nature compared to the plains. 'Verticality' and 'variation' are two fundamental specificities of the mountain geography. They possess distinct temporal and spatial characteristics in a unique socio-cultural setting. There is an ever increasing need for spatial and temporal data for planning and management activities; and Geo Information (GI) Science (including Geographic Information and Earth Observation Systems). This is being recognized more and more as a common platform for integrating spatial data with social, economic and environmental data and information from different sources. This paper investigates the applicability and challenges of GISscience in the context of mountain geography with ample evidences and observations from the mountain specific publications, empirical research findings and reports. The contextual explanation of mountain geography, mountain specific problems, scientific concerns about the mountain geography, advances in GIScience, the role of GIScience for sustainable development, challenges on application of GIScience in the contexts of mountains are the points of discussion. Finally, conclusion has been made with some specific action oriented recommendations.

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