Carboniferous magmatism related to progressive pull-apart opening in the western French Massif Central

2014 ◽  
Vol 185 (3) ◽  
pp. 171-189 ◽  
Author(s):  
Patrick Rolin ◽  
Didier Marquer ◽  
Charles Cartannaz ◽  
Philippe Rossi
Keyword(s):  
Shear Zones ◽  
Strike Slip ◽  
Fault System ◽  
Normal Faults ◽  
Variscan Belt ◽  
French Massif Central ◽  
Massif Central ◽  
Granite Emplacement ◽  
Regional Deformation ◽  
Northern Border

AbstractThe Variscan continental collision induced the development of large crustal melting in the western French Massif Central, accompanied by emplacement and deformation of syn- to post-tectonic granites spatially related to normal and strike slip faulting. Our study focuses on the regional deformation and shear zone patterns in the Millevaches massif, one of the largest magmatic area of the French Massif Central. In this massif, the syn-tectonic intrusions are related i) to the dextral wrenching along the Treignac-Pradines shear zones and the Creuse faults system, and ii) to the coeval extension along the N000°–N020° normal faults on the western edge of the Millevaches massif (Bourganeuf and Argentat faults). The analysis of deformation and kinematics correlated to new datations of granites allow us to propose a pull-apart model to explain the tectono-magmatic evolution of this part of the Variscan belt from 350 Ma to 325 Ma. At that time, these granites intruded a “pull-apart” system bounded by two major N140°–160° dextral strike-slip zones operating in the middle continental crust during a bulk N020° regional shortening.From 325 Ma to 320 Ma, a clockwise rotation of the regional shortening axis was responsible for the late reactivation of the N020° eastern Millevaches tectonic border as a dextral fault system (Felletin-Ambrugeat fault system). This NE-SW shortening displaced the N140°–160° Creuse fault system and induced a reverse motion along the northern border of the Millevaches massif (St-Michel-de-Veisse fault). This Visean tectono-magmatic event induced the late exhumation of the Millevaches massif with respect to surrounding units and favoured the widespread granite emplacement in this part of the Variscan belt.

Famenno-Carboniferous (370-320 Ma) strike slip tectonics monitored by syn-kinematic plutons in the French Variscan belt (Massif Armoricain and French Massif Central)

2009 ◽  
Vol 180 (3) ◽  
pp. 231-246 ◽  
Author(s):  
Patrick Rolin ◽  
Didier Marquer ◽  
Michel Colchen ◽  
Charles Cartannaz ◽  
Alain Cocherie ◽  
...  
Keyword(s):  
Large Scale ◽  
Western Europe ◽  
Shear Zones ◽  
Strike Slip ◽  
Variscan Belt ◽  
French Massif Central ◽  
Massif Central ◽  
Granite Emplacement ◽  
Regional Deformation ◽  
Dextral Shear

AbstractThe Variscan continental collision has led to the development of large strike-slip shear zones in western Europe. Our study focuses on the regional deformation and shear zone patterns in the Massif Armoricain and the French Massif Central. The synthesis of granite emplacement ages associated to granite deformation fields, allow us to propose a geodynamic model for the tectonic evolution of this part of the Variscan belt between 370 Ma – 320 Ma (Late Devonian – Namurian).After the first steps of the continental subduction-collision, leading to high temperature and anatexis associated with N-S shortening at 380-370 Ma (Frasnian to Famennian), the southern part of the Massif Armoricain and western part of French Massif Central underwent large dextral shearing along N100-N130 trending shear zones up to early Visean time. These large-scale displacements progressively decreased at around 350-340 Ma, during the first emplacements of biotite bearing granites (Moulins-les Aubiers-Gourgé massif and Guéret massif intrusions).During middle Visean times, the shortening axis direction rotated towards a NNE-SSW direction implying changes in the regional deformation field. The occurrence of N070-N100 sinistral and N110-N130 dextral conjugate shear zones within leucogranites are related to that time. Finally, new N150-N160 dextral shear zones appeared in middle to late Visean times: as for examples, the Parthenay and the Pradines shear zones in the SE Massif Armoricain and the Millevaches massif, respectively. These shear zones were conjugated to the sinistral N020 Sillon Houiller in the French Massif Central. They reflect large scale brittle continental indentation in the French Variscan belt during the middle to late Visean.

scholarly journals Is the Eastern Denali fault still active?

Geology ◽  
2021 ◽  
Author(s):  
Minhee Choi ◽  
David W. Eaton ◽  
Eva Enkelmann
Keyword(s):  
Bering Sea ◽  
Active Fault ◽  
Strike Slip ◽  
Historical Seismicity ◽  
Fault System ◽  
Denali Fault ◽  
Regional Deformation ◽  
Source Mechanisms ◽  
Structural Boundary ◽  
The Bering Sea

The Denali fault, a transcurrent fault system that extends from northwestern Canada across Alaska toward the Bering Sea, is partitioned into segments that exhibit variable levels of historical seismicity. A pair of earthquakes (M 6.2 and 6.3) on 1 May 2017, in proximity to the Eastern Denali fault (EDF), exhibited source mechanisms and stress conditions inconsistent with expectations for strike-slip fault activation. Precise relocation of ~1500 aftershocks revealed distinct fault strands that are oblique to the EDF. Calculated patterns of Coulomb stress show that the first earthquake likely triggered the second one. The EDF parallels the Fairweather transform, which separates the obliquely colliding Yakutat microplate from North America. In our model, inboard transfer of stress is deforming and shortening the mountainous region between the EDF and the Fairweather transform. This is supported by historical seismicity concentrated southwest of the EDF, suggesting that it now represents a structural boundary that controls regional deformation but is no longer an active fault.

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>

French and Belgian Uplands

2005 ◽  
Author(s):  
Bernard Etlicher
Keyword(s):  
Continental Crust ◽  
Rift Valley ◽  
Sedimentary Basins ◽  
Shear Zones ◽  
Metamorphic Complex ◽  
French Massif Central ◽  
Massif Central ◽  
Montagne Noire ◽  
Oceanic And Continental Crust ◽  
Moderate Elevation

The French Uplands were built by the Hercynian orogenesis. The French Massif Central occupies one-sixth of the area of France and shows various landscapes. It is the highest upland, 1,886 m at the Sancy, and the most complex. The Vosges massif is a small massif, quite similar to the Schwarzwald in Germany, from which it is separated by the Rhine Rift Valley. Near the border of France, Belgium, and Germany, the Ardennes upland has a very moderate elevation. The largest part of this massif lies in Belgium. Though Brittany is partly made up of igneous and metamorphic rocks, it cannot be truly considered as an upland; in the main parts of Brittany, altitudes are lower than in the Parisian basin. Similarities of the landscape in the French and Belgian Uplands derive from two major events: the Oligocene rifting event and the Alpine tectonic phase. The Vosges and the Massif Central are located on the collision zone of the Variscan orogen. In contrast, the Ardennes is in a marginal position where primary sediments cover the igneous basement. Four main periods are defined during the Hercynian orogenesis (Bard et al. 1980; Autran 1984; Ledru et al. 1989; Faure et al. 1997). The early Variscan period corresponds to a subduction of oceanic and continental crust and a highpressure metamorphism (450–400 Ma) The medio- Variscan period corresponds to a continent–continent collision of the chain (400–340 Ma). Metamorphism under middle pressure conditions took place and controlled the formation of many granite plutons: e.g. red granites (granites rouges), porphyroid granite, and granodiorite incorporated in a metamorphic complex basement of various rocks. The neo-Variscan period (340–320 Ma) is characterized by a strong folding event: transcurrent shear zones affected the units of the previous periods and the first sedimentary basins appeared. At the end of this period, late-Variscan (330–280 Ma), autochthonous granites crystallized under low-pressure conditions related to a post-collision thinning of the crust. Velay and Montagne Noire granites are the main massifs generated by this event. Sediment deposition in tectonic basins during Carboniferous and Permian times occurred in the Massif Central and the Vosges: facies are sandstone (Vosges), shale, coal, and sandstone in several Stephanian basins of the Massif Central, with red shale and clay ‘Rougier’ in the south-western part of the Massif Central.

scholarly journals The Velay dome (French Massif Central): melt generation and granite emplacement during orogenic evolution

2001 ◽  
Vol 342 (3-4) ◽  
pp. 207-237 ◽  
Author(s):  
P. Ledru ◽  
G. Courrioux ◽  
C. Dallain ◽  
J.M. Lardeaux ◽  
J.M. Montel ◽  
...  
Keyword(s):  
French Massif Central ◽  
Massif Central ◽  
Granite Emplacement ◽  
Melt Generation

Quantifying fault reactivation risk in the western Gippsland Basin using geomechanical modelling

2013 ◽  
Vol 53 (1) ◽  
pp. 255 ◽  
Author(s):  
Ernest Swierczek ◽  
Cui Zhen-dong ◽  
Simon Holford ◽  
Guillaume Backe ◽  
Rosalind King ◽  
...  
Keyword(s):  
Structural Model ◽  
Strike Slip ◽  
Fault Reactivation ◽  
Fault System ◽  
Co2 Injection ◽  
Normal Faults ◽  
Surface Geometry ◽  
Northern Margin ◽  
Fault Surface ◽  
Gippsland Basin

The Rosedale Fault System (RFS) bounds the northern margin of the Gippsland Basin on the Southern Australian Margin. It comprises an anastomosing system of large, Cretaceous-age normal faults that have been variably reactivated during mid Eocene-Recent inversion. A number of large oil and gas fields are located in anticlinal traps associated with the RFS, and in the future these fields may be considered as potential storage sites for captured CO2. Given the evidence for geologically recent fault reactivation along the RFS, it is thus necessary to evaluate the potential impacts of CO2 injection on fault stability. The analysis and interpretation of 3D seismic data allowed the authors to create a detailed structural model of the western section of the RFS. Petroleum geomechanical data indicates that the in-situ stress in this region is characterised by hybrid strike-slip to reverse faulting conditions where SHmax (40.5 MPa/km) > SV (21 MPa/km) ~ Shmin (20 MPa/km). The authors performed geomechanical modelling to assess the likelihood of fault reactivation assuming that both strike-slip and reverse-stress faulting regimes exist in the study area. The authors’ results indicate that the northwest to southeast and east-northeast to west-southwest trending segments of the RFS are presently at moderate and high risks of reactivation. The authors’ results highlight the importance of fault surface geometry in influencing fault reactivation potential, and show that detailed structural models of potential storage sites must be developed to aid risk assessments before injection of CO2.

Strike-Slip Earthquakes at the Northern Edge of the Calabrian Arc Subduction Zone

2020 ◽  
Author(s):  
Giovanna Calderoni ◽  
Anna Gervasi ◽  
Mario La Rocca ◽  
Guido Ventura
Keyword(s):  
Subduction Zone ◽  
Shear Zones ◽  
Strike Slip ◽  
Corner Frequency ◽  
Tyrrhenian Sea ◽  
Northern Border ◽  
Source Directivity ◽  
Northern Edge ◽  
East West ◽  
Good Agreement

Abstract We analyzed earthquakes of a swarm started in October 2019 in the Tyrrhenian Sea, at the northern border of the Calabrian arc subduction zone. The swarm is located in the same area where a subduction-transform edge propagator (STEP) shear- zone -oriented east–west is recognized from ocean floor morphology and submarine volcanoes. We computed focal mechanism, relative location, stress drop, corner frequency, and source directivity of the mainshock Mw 4.4 and of some aftershocks in the local magnitude range 2.3–3.7. Results indicate clearly that the mainshock occurred on a northwest–southeast-oriented fault, with right-lateral strike-slip motion, and it was characterized by a strong directivity of the rupture propagation from northwest to southeast. On the contrary, most of aftershocks were located on another strike-slip fault oriented northeast–southwest and had left-lateral kinematics. The kinematic features of these earthquakes indicate a strain field with the P-axis oriented north–south and the T-axis oriented east–west. Fault directions and stress field are in good agreement with the theoretical fracture model of shear zones associated with a STEP.

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.

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