Garnet Sm-Nd and U-Pb systems: A case study of a granulite from the European Variscan belt

2002 ◽  
Vol 47 (15) ◽  
pp. 1284 ◽  
Author(s):  
Fukun CHEN
Keyword(s):  
Variscan Belt

Fold interference pattern in thick-skinned tectonics; a case study from the external Variscan belt of Eastern Anti-Atlas, Morocco

2016 ◽  
Vol 119 ◽  
pp. 204-225 ◽  
Author(s):  
L. Baidder ◽  
A. Michard ◽  
A. Soulaimani ◽  
A. Fekkak ◽  
A. Eddebbi ◽  
...  
Keyword(s):  
Interference Pattern ◽  
Variscan Belt

The role of regional-scale shear zones in paleogeographic reconstructions: the case study of the Variscan belt in the Mediterranean area

2021 ◽  
Author(s):  
Matteo Simonetti ◽  
Rodolfo Carosi ◽  
Chiara Montomoli ◽  
Salvatore Iaccarino
Keyword(s):  
Earth Sciences ◽  
Shear Zone ◽  
Regional Scale ◽  
Shear Zones ◽  
Mediterranean Area ◽  
Variscan Belt ◽  
Metamorphic Evolution ◽  
The Mediterranean ◽  
Scale Shear

<p>Paleogeographic reconstruction and recognition of the tectono-metamorphic evolution of ancient orogenic belt is often complex. The combination of an adequate amount of paleomagnetic, metamorphic, structural and geochronological data is necessary. Fundamental data derive from the study of regional-scale shear zones, that can be directly observed, by combining detailed field work with structural analysis, microstructural analysis and petrochronology. The Southern European Variscan Belt in the Mediterranean area was partially overprinted by the Alpine cycle (Stampfli and Kozur, 2006) and correlations are mainly based on lithological similarities. Little attention has been paid to the compatibility of structures in the dispersed fragments. A main debate is the connection among the Corsica-Sardinia Block (CSB), the Maures-Tanneron Massif (MTM) and the future Alpine External Crystalline Massifs (ECM) (Stampfli et al., 2002; Advokaat et al., 2014) and if these sectors were connected by a network of shear zones of regional extent, known as the East Variscan Shear Zone (EVSZ).</p><p>We present a multidisciplinary study of shear zones cropping out in the CSB (the Posada-Asinara shear zone; Carosi et al., 2020), in the MTM (the Cavalaire Fault; Simonetti et al., 2020a) and in the ECM (the Ferriere-Mollières and the Emosson-Berard shear zones; Simonetti et al., 2018; 2020b).</p><p>Kinematic and finite strain analysis allowed to recognize a transpressional deformation, with a major component of pure shear and a variable component of simple shear, coupled with general flattening deformation. Syn-kinematic paragenesis, microstructures and quartz c-axis fabrics revealed that shear deformation, in all the studied sectors, occurred under decreasing temperature starting from amphibolite-facies up to greenschist-facies. A systematic petrochronological study (U-Th-Pb on monazite collected in the sheared rocks) was conducted in order to constrain the timing of deformation. We obtained ages ranging between ~340 Ma and ~320 Ma. Ages of ~340-330 Ma can be interpreted as the beginning of the activity of the EVSZ along its older branches while ages of ~320 Ma, obtained in all the shear zones, demonstrate that they were all active in the same time span.</p><p>The multidisciplinary approach revealed a similar kinematics and tectono-metamorphic evolution of the studied shear zones contributing to better constrain the extension and timing the EVSZ and to strength the paleogeographic reconstructions of the Southern Variscan belt during Late Carboniferous time, with important implications on the evolution of the Mediterranean area after the Late Paleozoic. This case study demonstrates how paleogeographic reconstructions could benefit from datasets obtained from large-scale structures (i.e., shear zones) that can be directly investigated.</p><p> </p><p>Advokaat et al. (2014). Earth and Planetary Science Letters 401, 183–195</p><p> </p><p>Carosi et al. (2012). Terra Nova 24, 42–51</p><p> </p><p>Carosi and Palmeri (2002). Geological Magazine 139.</p><p> </p><p>Carosi et al. (2020). Geosciences 10, 288.</p><p> </p><p>Simonetti et al (2020a). International Journal of Earth Sciences 109, 2261–2285</p><p> </p><p>Simonetti et al. (2020b). Tectonics 39</p><p> </p><p>Simonetti et al. (2018). International Journal of Earth Sciences. 107, 2163–2189</p><p> </p><p>Stampfli and Kozur (2006). Geological Society, London, Memoirs 32, 57–82</p><p> </p><p>Stampfli et al. (2002). Journal of the Virtual Explorer 8, 77</p>

Applicability of the RSCM geothermometry approach in a complex tectono-metamorphic context: The Jebilet massif case study (Variscan Belt, Morocco)

Lithos ◽  
2016 ◽  
Vol 256-257 ◽  
pp. 1-12 ◽  
Author(s):  
Sylvain Delchini ◽  
Abdeltif Lahfid ◽  
Alexis Plunder ◽  
André Michard
Keyword(s):  
Variscan Belt

Folding in orogens: a case study in the northern Iberian Variscan Belt

2010 ◽  
Vol 45 (5-6) ◽  
pp. 597-622 ◽  
Author(s):  
F. Bastida ◽  
J. Aller ◽  
J. A. Pulgar ◽  
N. C. Toimil ◽  
F. J. Fernández ◽  
...  
Keyword(s):  
Variscan Belt

scholarly journals On the development of kink-bands: A case study in the Westasturian-Leonese Zone (Variscan belt, NW Spain)

2020 ◽  
Vol 191 ◽  
pp. 6 ◽  
Author(s):  
Jesús Aller ◽  
Fernando Bastida ◽  
Nilo C. Bobillo-Ares
Keyword(s):  
Kink Band ◽  
Field Analysis ◽  
Variscan Belt ◽  
Geometrical Analysis ◽  
Nw Spain ◽  
Dominant Mechanism ◽  
Kink Bands

A field analysis of kink bands developed in slates from three areas (Grandas, Boal and Luarca areas) of the Westasturian-Leonese Zone (Iberian Variscan belt) is presented. The analysis of the main parameters that characterize the geometry of the studied kink bands shows that those of the Grandas and Luarca areas exhibit a different evolution than those of the Boal area. In this latter area, the interlimb angle of the kink bands has lower values than those developed in the former areas and it involves rotation of the foliation inside and outside the band. In the areas with higher bulk shortening associated with the development of kink bands, chevron folds formed by juxtaposition of kink bands. Slip between folia and their rotation was probably the dominant mechanism in the formation of the kink bands, as deduced from the different values of the angle between the kink plane and the foliation inside (φK) and outside (φ) the band, and the occurrence of fractures along the kink planes and small steps between folia cross-cutting these fractures planes. The fractures along the kink planes prevented subsequent hinge migration. Geometrical analysis of kink bands formed by slip between folia and their rotation provides an estimation of the changes in area and thickness, and the strain inside the kink band. For angles of folia rotation ψ < 50°, the ratio between the strain ellipse axes is < 3 inside the band; this ratio is almost independent of the orientation of the kink planes with respect to the foliation outside the band (angle φ).

scholarly journals Mafic magma as metal source for Sb-W-Hg mineralisation? A case study of the early Carboniferous mafic magmatic event from the French Armorican Variscan belt

2021 ◽  
Author(s):  
Anthony Pochon ◽  
Giada Iacono-Marziano ◽  
Saskia Erdmann ◽  
Eric Gloaguen ◽  
Johann Tuduri
Keyword(s):  
Fluid Inclusions ◽  
Mafic Magma ◽  
Early Carboniferous ◽  
Magmatic Fluid ◽  
Variscan Belt ◽  
Metal Enrichment ◽  
Metal Source ◽  
Mafic Magmatism ◽  
Magmatic Fluids

&lt;p&gt;A possible genetic link between Sb-W-Hg mineralisation (vein-type and stratabound) and mafic magmatism has been proposed for the Variscan belt during the early Carboniferous, but this hypothesis remains to be rigorously assessed. The metal enrichment of the fluids producing Variscan Sb-W-Hg deposits may be ascribed to (i) crystallization of metal-rich primary mafic magma, and/or (ii) exsolution of metal-rich magmatic fluids and their local concentration, and/or (iii) an efficient hydrothermal leaching of surroundings sedimentary rocks by fluid release due to contact metamorphism. The aim of this project is thus to estimate the contribution of mafic magmas as the metal source of Sb-W-Hg deposits. Our case study focuses on the Saint-Jean-du-Doigt gabbro from the Variscan Armorican belt, Brittany, France. We have characterized the Sb-, W-, and Hg-carrier minerals (&lt;em&gt;e.g. &lt;/em&gt;Fe-Ti oxides) and volatile-bearing minerals (&lt;em&gt;e.g.&lt;/em&gt; apatite) to quantify the metal content and volatile inventory during purely magmatic and magmatic-hydrothermal processes. Abundant primary amphibole and biotite, and the presence of pegmatoids indicate that the melt was likely to be enriched in volatile. An alteration gradient is observed from the base of the intrusion towards its roof. Moreover, high temperature replacement mineral reactions (&lt;em&gt;e.g. &lt;/em&gt;saussuritization) mainly occur in the upper part of the intrusion, suggesting that magmatic fluids were accumulated toward the top of the intrusion. Cathodoluminescence and apatite compositions are taken to record the magmatic-hydrothermal transition and hydrothermal alteration. Apatite ranges in composition between fluorapatite and fluor-hydroxyapatite, but the latter is largely more frequent. A high volatile content of the silicate melt is suggested by the high proportion of negative-shaped fluid inclusions into ilmenite (up to 15 % crystal volume), which hint at a primary magmatic origin. SEM, EPMA and LA-ICP-MS investigations show that magmatic fluid inclusions contain significant amounts of Sb and W. Our results highlight that metals (&lt;em&gt;i.e.&lt;/em&gt; Sb, W) were partly partitioned into the fluid phase during magma crystallization and degassing. In addition, trace element content of ilmenite also records metal enrichment from the base to the intrusion roof, probably due to magma degassing and deuteric/metasomatic processes. We therefore propose that mafic magmatism is a potential metal source of the early Carboniferous Sb-W-Hg mineralization event and should be considered as possible sources for other Sb-W-Hg province worldwide. This work was funded by the ANR (ANR-19-MIN2-0002) and author&amp;#8217;s institutions in the framework of the ERA-MIN2 AUREOLE project (https://aureole.brgm.fr).&lt;/p&gt;

The Genesis and Internal Dynamics of El Salvador's People's Revolutionary Army, 1970–1976

2014 ◽  
Vol 38 (01) ◽  
pp. 102-129
Author(s):  
ALBERTO MARTÍN ÁLVAREZ ◽  
EUDALD CORTINA ORERO
Keyword(s):  
Latin America ◽  
El Salvador ◽  
Early Years ◽  
Left Wing ◽  
Internal Dynamics ◽  
Internal Coherence ◽  
The 1960S

AbstractUsing interviews with former militants and previously unpublished documents, this article traces the genesis and internal dynamics of the Ejército Revolucionario del Pueblo (People's Revolutionary Army, ERP) in El Salvador during the early years of its existence (1970–6). This period was marked by the inability of the ERP to maintain internal coherence or any consensus on revolutionary strategy, which led to a series of splits and internal fights over control of the organisation. The evidence marshalled in this case study sheds new light on the origins of the armed Salvadorean Left and thus contributes to a wider understanding of the processes of formation and internal dynamics of armed left-wing groups that emerged from the 1960s onwards in Latin America.

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