scholarly journals Precambrian protoliths and Early Paleozoic magmatism in the French Massif Central: U–Pb data and the North Gondwana connection in the west European Variscan belt

2010 ◽  
Vol 17 (1) ◽  
pp. 13-25 ◽  
Author(s):  
Jérémie Melleton ◽  
Alain Cocherie ◽  
Michel Faure ◽  
Philippe Rossi
Keyword(s):  
Variscan Belt ◽  
French Massif Central ◽  
Early Paleozoic ◽  
The West ◽  
Massif Central ◽  
The North ◽  
North Gondwana ◽  
West European

scholarly journals Cadomian S-type granites as basement rocks of the Variscan belt (Massif Central, France): Implications for the crustal evolution of the north Gondwana margin

Lithos ◽  
2017 ◽  
Vol 286-287 ◽  
pp. 16-34 ◽  
Author(s):  
Simon Couzinié ◽  
Oscar Laurent ◽  
Marc Poujol ◽  
Michaël Mintrone ◽  
Cyril Chelle-Michou ◽  
...  
Keyword(s):  
Crustal Evolution ◽  
Variscan Belt ◽  
Massif Central ◽  
The North ◽  
Basement Rocks ◽  
Gondwana Margin ◽  
North Gondwana

scholarly journals The formation of the West European Rift; a new model as exemplified by the Massif Central area

2001 ◽  
Vol 172 (2) ◽  
pp. 213-221 ◽  
Author(s):  
Olivier Merle ◽  
Laurent Michon
Keyword(s):  
Sea Level ◽  
Central Area ◽  
Rift System ◽  
The South ◽  
The West ◽  
Massif Central ◽  
New Model ◽  
The North ◽  
Crustal Thinning ◽  
West European

Abstract In this paper, we use mainly field data from the Massif Central area, which have been presented in a companion paper [Michon and Merle, 2001], to discuss the origin and the evolution of the West European Rift system. It is shown that the tectonic event in the Tertiary is two-stage. The overall geological evolution reveal a tectonic paradox as the first stage strongly suggests passive rifting, whereas the second stage displays the first stage of active rifting. In the north, crustal thinning, graben formation and sedimentation at sea level without volcanism during the Lower Oligocene, followed by scattered volcanism in a thinned area during Upper Oligocene and Lower Miocene, represent the classical evolution of a rift resulting from extensional stresses within the lithosphere (i.e. passive rifting). In the south, thinning of the lithospheric mantle associated with doming and volcanism in the Upper Miocene, together with the lack of crustal thinning, may be easily interpreted in terms of the first stage of active rifting due to the ascent of a mantle plume. This active rifting process would have been inhibited before stretching of the crust, as asthenospheric rise associated with uplift and volcanism are the only tectonic events observed. The diachronism of these two events is emphasized by two clearly distinct orientations of crustal thinning in the north and mantle lithospheric thinning in the south. To understand this tectonic paradox, a new model is discussed taking into account the Tertiary evolution of the Alpine chain. It is shown that the formation of a deep lithospheric root may have important mechanical consequences on the adjacent lithosphere. The downward gravitational force acting on the descending slab may induce coeval extension in the surrounding lithosphere. This could trigger graben formation and laguno-marine sedimentation at sea level followed by volcanism as expected for passive rifting. Concurrently, the descending lithospheric flow induces a flow pattern in the asthenosphere which can bring up hot mantle to the base of the adjacent lithosphere. Slow thermal erosion of the base of the lithosphere may lead to a late-stage volcanism and uplift as expected for active rifting.

scholarly journals Detrital zircon U–Pb–Hf systematics of Ediacaran metasediments from the French Massif Central: Consequences for the crustal evolution of the north Gondwana margin

2019 ◽  
Vol 324 ◽  
pp. 269-284 ◽  
Author(s):  
Simon Couzinié ◽  
Oscar Laurent ◽  
Cyril Chelle-Michou ◽  
Pierre Bouilhol ◽  
Jean-Louis Paquette ◽  
...  
Keyword(s):  
Detrital Zircon ◽  
Crustal Evolution ◽  
French Massif Central ◽  
Massif Central ◽  
The North ◽  
Gondwana Margin ◽  
North Gondwana

scholarly journals Coupling RSCM paleothermometry with 40Ar/39Ar analysis in the south Variscan belt (Cévennes, France): new constraints on the late-orogenic metamorphic gradient in an orogen outer domain.

2020 ◽  
Author(s):  
Clément Montmartin ◽  
Michel Faure ◽  
Stéphane Scaillet ◽  
Hugues Raimbourg
Keyword(s):  
Cross Sections ◽  
Crustal Thickening ◽  
Early Event ◽  
Variscan Belt ◽  
French Massif Central ◽  
Raman Spectrometry ◽  
Massif Central ◽  
Temperature Jumps ◽  
Outer Domain ◽  
The One

<p>In the SE part of the Variscan French Massif Central, the Cévennes area belongs to the para-autochthonous unit of the southern Variscan belt. This area underwent three metamorphic events (Faure et al., 2001).  I) A green schist to low amphibolite facies one (500°C, 4.5Kb Arnaud, 1997) developed in micaschists and quartzites. These rocks were stacked as south-directed nappes during the final stage of the Variscan crustal thickening dated at ca 340 Ma by <sup>40</sup>Ar/<sup>39</sup>Ar on biotite (Caron, 1994). This early event was responsible for the flat-lying foliation, the N-S striking stretching lineation, and intrafolial foliation. II) A high temperature event (680°C, 4.5kb Rakib, 1996) dated at ca 325 Ma (<sup>40</sup>Ar/<sup>39</sup>Ar on two biotites, Najoui et al, 2000) overprinted the early one. On the basis of the mineral assemblages of this event, a NE-ward increase of the T conditions was interpreted as a remote effect of the Velay Dome (Rakib, 1996). III) Finally, the M<sup>t</sup>-Lozère and Aigoual-S<sup>t</sup>-Guiral-Liron monzogranitic plutons intruded the Cévennes para-autochthonous unit. Monazite and biotite yield U-Pb, and <sup>40</sup>Ar/<sup>39</sup>Ar ages at 315-303Ma and 306 Ma , respectively (Brichaud et al. 2008). The pluton emplacement conditions are determined at 695°C, 1.5Kb (Najoui et al, 2000).</p><p>We report Raman Spectrometry of Carbonaceous Matter (RSCM) paleotemperature data acquired on more than 100 samples throughout the entire Cévennes area. These show a regional homogeneous thermal distribution with a 535 ± 50 °C mean temperature without any geometric correlation with the nappes structure, nor the granitic intrusions. Moreover, no thermal increase towards the NE can be documented. SW of the Aigoual-S<sup>t</sup>-Guiral-Liron massif, our RSCM data document a temperature jumps between the overlying Cévennes micaschists and the underlying epimetamorphic rocks belonging the the Fold-and-Thust belt unit of the French Massif Central.</p><p>In order to constrain the age of this regional thermal event, we <sup>40</sup>Ar/<sup>39</sup>Ar dated 25 new regionally-distributed syn- and post-folial muscovites by step heating along two N-S cross sections within the Cévennes micaschists series. In areas distant from the plutons, the muscovite yields a ca 325 Ma age interpreted as the one of the HT event recorded by the RSCM measurements. However, young muscovite ages at ca 305Ma are observed around the plutons. We assume that the heat supplied by the plutons reset these muscovites at around 400°C while the organic matter cannot record the contact metamorphic peak lower than the regional one. Moreover, <sup>40</sup>Ar/<sup>39</sup>Ar in-situ analyses carried out on 5 mm-sized post folial (but deformed) biotites in the central part of the micaschist series provide ages around 320Ma. The presence of a hidden dome, underneath the Cévennes micaschists, similar to the pre-Velay migmatites exposed in the northern part of the Cévennes area (Faure et al., 2001, Be et al., 2006) is discussed.</p>

Monazite U-Th/Pb chemical dating of the Early Carboniferous syn-kinematic MP/MT metamorphism in the Variscan French Massif Central

2009 ◽  
Vol 180 (3) ◽  
pp. 283-292 ◽  
Author(s):  
Jérémie Melleton ◽  
Michel Faure ◽  
Alain Cocherie
Keyword(s):  
Electron Probe ◽  
Early Carboniferous ◽  
Variscan Belt ◽  
French Massif Central ◽  
Massif Central ◽  
Close Range ◽  
Chemical Dating

AbstractIn situ U-Th-Pb geochronology on monazite using Electron Probe Micro Analyser, constrained by structural and textural observations, has been performed on four samples from the Limousin area (northwest part of the French Massif Central) in order to date the syn-kinematic MP/MT metamorphism related to the top-to-the-NW shearing that deformed the stack of nappes in this zone of the Variscan belt. All the analyzed samples lead to a mean age at 360 ± 4 Ma. The close range of ages obtained during this study (360 Ma) and with the previous 40Ar-39Ar ones (360–350 Ma) suggests fast processes of cooling and exhumation during the Early Carboniferous in internal zones of the Variscan belt. The geodynamic significance of this Early Carboniferous event is discussed at the scale of the Ibero-Armorican orocline.

scholarly journals Origin and age of the Shenshan tectonic mélange in the Jiangshan-Shaoxing-Pingxiang Fault and late Early Paleozoic juxtaposition of the Yangtze Block and the West Cathaysia terrane, South China

2021 ◽  
Author(s):  
Lijun Wang ◽  
Kexin Zhang ◽  
Shoufa Lin ◽  
Weihong He ◽  
Leiming Yin
Keyword(s):  
South China ◽  
Strike Slip ◽  
Carbonaceous Shale ◽  
Early Paleozoic ◽  
Yangtze Block ◽  
The West ◽  
Northern Margin ◽  
The North ◽  
Tectonic Mélange ◽  
Different Parts

When and how the Yangtze Block (Yangtze) and the West Cathaysia terrane (West Cathaysia) in South China were amalgamated are critical to a better understanding of the Neoproterozoic to early Paleozoic tectonic evolution of South China and remain highly debatable. A key to this debate is the tectonic significance of the Jiangshan-Shaoxing-Pingxiang (JSP) Fault, the boundary between Yangtze and West Cathaysia. The Shenshan mélange along the JSP Fault has the typical block-in-matrix structure and is composed of numerous shear zone-bounded slivers/lenses of rocks of different types and ages that formed in different tectonic environments, including middle to late Tonian volcanic and volcanogenic sedimentary rocks (turbidite) of arc/back-arc affinity, a series of middle Tonian ultramafic to mafic plutonic rocks of oceanic island basalt affinity, a carbonaceous shale that was deposited in a deep marine environment, and a red mudstone. U-Pb zircon ages and acritarch assemblages (Leiosphaeridia-Brocholaminaria association) found in the turbidite confirm its Tonian age, and fossils from the carbonaceous shale (Asteridium-Comasphaeridium and Skiagia-Celtiberium-Leiofusa) constrains its age to the Early to Middle Cambrian. Field relationships and available age data leave no doubt that the ultramafic-mafic rocks are exotic blocks (rather than intrusions) in the younger metasedimentary rocks. We conclude that the Shenshan mélange is not an ophiolitic mélange, but rather a tectonic mélange that formed as a result of movement along the JSP Fault in the early Paleozoic. We suggest that Yangtze and West Cathaysia were two separate microcontinents, were accreted to two different parts of the northern margin of Gondwana in the early Early Paleozoic, and juxtaposed in the late Early Paleozoic through strike-slip movement along the JSP Fault. We further suggest that the ca. 820 Ma collision in the Jiangnan Orogen took place between Yangtze and a (micro)continent that is now partly preserved as the Huaiyu terrane and was not related to West Cathaysia. We compare our model for South China with the accretion of terranes in the North American Cordillera and propose a similar model for the relationship between the Avalon and Meguma terranes in the Canadian Appalachians, i.e., the two terranes were accreted to two different parts of the Laurentian margin and were later juxtaposed through margin-parallel strike slip faulting.

scholarly journals Determining the Plio-Quaternary uplift of the southern French massif-Central; a new insights for intraplate orogen dynamics

2019 ◽  
Author(s):  
Oswald Malcles ◽  
Philippe Vernant ◽  
Jean Chéry ◽  
Pierre Camps ◽  
Gaël Cazes ◽  
...  
Keyword(s):  
Numerical Models ◽  
Morphological Evolution ◽  
Vertical Motion ◽  
French Massif Central ◽  
Dynamic Topography ◽  
Active Deformation ◽  
Massif Central ◽  
The North ◽  
Cave System ◽  
Clay Deposits

Abstract. The evolution of intra-plate orogens is still poorly understood. Yet, this is of major importance for understanding the Earth and plate dynamic, as well as the link between surface and deep geodynamic processes. The French Massif Central is an intraplate orogen with a mean elevation of 1000 m, with the highest peak elevations ranging from 1500 m to 1885 m. However, active deformation of the region is still debated due to scarce evidence either from geomorphological or geophysical (i.e. geodesy and seismology) data. Because the Cévennes margin allows the use of karst sediments geochronology and morphometrical analysis, we study the vertical displacements of that region: the southern part of the French Massif-Central. Geochronology and morphometrical results, helped with lithospheric-scale numerical modelling, allow, then, a better understanding of this intraplate-orogen evolution and dynamic. Using the ability of the karst to durably record morphological evolution, we first quantify the incision rates. We then investigate tilting of geomorphological benchmarks by means of a high-resolution DEM. We finally use the newly quantified incision rates to constrain numerical models and compare the results with the geomorphometric study. We show that absolute burial age (10Be/26Al on quartz cobbles) and the paleomagnetic analysis of karstic clay deposits for multiple cave system over a large elevation range correlate consistently. This correlation indicates a regional incision rate of 83.4 +17.3/−5.4 m Ma−1 during the last ca 4 Myrs (Plio-Quaternary). Moreover, we point out through the analysis of 55 morphological benchmarks that the studied region has undergone a regional southward tilting. This tilting is expected as being due to a differential vertical motion between the north and southern part of the studied area. Numerical models show that erosion-induced isostatic rebound can explain up to two-thirds of the regional uplift deduced from dating technics and are consistent with the southward tilting obtain from morphological analysis. We presume that the remaining part is related to dynamic topography or thermal isostasy due to the Massif Central plio-quaternary magmatism.

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