Very low-grade metamorphism of Rheno-Hercynian allochthons (Variscides, Germany): facts and tectonic consequences

Doublier, Michael P.; Potel, Sébastien; Franke, Wolfgang; Roache, Tony

doi:10.1007/s00531-011-0718-3

Cited by 26 publications

(6 citation statements)

References 55 publications

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“…KI values were calibrated using a correlation with the ‘CIS’ standard (Warr & Rice, ) (KI CIS = 1.1943 × IC measured + 0.0141), and adjusted to the Kübler scale following the procedure outlined in Doublier et al . ().…”

Section: Methodsmentioning

confidence: 97%

The tectono‐metamorphic evolution of the very low‐grade hangingwall constrains two‐stage gneiss dome formation in the Montagne Noire (Southern France)

Doublier

Potel

Wemmer

2014

Journal Metamorphic Geology

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The Montagne Noire in the southernmost French Massif Central is made of an ENE-elongated gneiss dome flanked by Palaeozoic sedimentary rocks. The tectonic evolution of the gneiss dome has generated controversy for more than half a century. As a result, a multitude of models have been proposed that invoke various tectonic regimes and exhumation mechanisms. Most of these models are based on data from the gneiss dome itself. Here, new constraints on the dome evolution are provided based on a combination of very low-grade petrology, K-Ar geochronology, field mapping and structural analysis of the Palaeozoic western Mont Peyroux and Faug eres units, which constitute part of the southern hangingwall of the dome. It is shown that southward-directed Variscan nappethrusting (D 1 ) and a related medium-P metamorphism (M 1 ) are only preserved in the area furthest away from the gneiss dome. The regionally dominant pervasive tectono-metamorphic event D 2 /M 2 largely transposes D 1 structures, comprises a higher metamorphic thermal gradient than M 1 (transition low-P and medium-P metamorphic facies series) and affected the rocks between c. 309 and 300 Ma, post-dating D 1 /M 1 by more than 20 Ma. D 2 -related fabrics are refolded by D 3 , which in its turn, is followed by dextral-normal shearing along the basal shear zone of both units at c. 297 Ma. In the western Mont Peyroux and Faug eres units, D 2 /M 2 is largely synchronous with shearing along the southern dome margin between c. 311 and 303 Ma, facilitating the emplacement of the gneiss dome into the upper crust. D 2 /M 2 also overlaps in time with granitic magmatism and migmatization in the Zone Axiale between c. 314 and 306 Ma, and a related low-P/high-T metamorphism at c. 308 Ma. The shearing that accompanied the exhumation of the dome therefore was synchronous with a peak in temperature expressed by migmatization and intrusion of melts within the dome, and also with the peak of metamorphism in the hangingwall. Both, the intensity of D 2 fabrics and the M 2 metamorphic grade within the hangingwall, decrease away from the gneiss dome, with grades ranging from the anchizone-epizone boundary to the diagenetic zone. The related zonation of the pre-D 3 metamorphic field gradients paralleled the dome. These observations indicate that D 2 / M 2 is controlled by the exhumation of the Zone Axiale, and suggest a coherent kinematic between the different crustal levels at some time during D 2 /M 2 . Based on integration of these findings with regional geological constraints, a two-stage exhumation of the gneiss dome is proposed: during a first stage between c. 316 and 300 Ma dome emplacement into the upper crust was controlled by dextral shear zones arranged in a pull-apart-like geometry. The second stage from 300 Ma onwards was characterized by northeast to northward extension, with exhumation accommodated by northdipping detachments and hangingwall basin formation along the northeastern dome margin.

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Section: Methodsmentioning

confidence: 97%

The tectono‐metamorphic evolution of the very low‐grade hangingwall constrains two‐stage gneiss dome formation in the Montagne Noire (Southern France)

Doublier

Potel

Wemmer

2014

Journal Metamorphic Geology

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“…As already been investigated in the Rheno-Hercynian zone in the northern Variscan branch (e.g. Fielitz and Mansy, 1999;Doublier et al, 2012), the study of thermicity in foreland basins can be extended to other areas within the Variscan belt. For instance, Mouthoumet massif (Kretschmer et al, 2015), Balearic or southern Sardinia areas are suitable places to get a general picture of the Variscan thermicity.…”

Section: Resultsmentioning

confidence: 99%

Paleotemperature investigation of the Variscan southern external domain: the case of the Montagne Noire (France)

Montmartin¹,

Faure²,

Raimbourg³

2021

BSGF - Earth Sci. Bull.

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The Montagne Noire located in the southern part of the French Massif Central represents the northern part of the South-Variscan Foreland. It is subdivided into three parts. The granite-migmatite Axial Zone dome is surrounded by non- or weakly metamorphosed Paleozoic sedimentary series. Both northern and southern flanks of the Montagne Noire dome are deformed by km-scale, south to southeast facing recumbent folds and thrusts sheets. The Raman Spectroscopy of Carbonaceous Material (RSCM) method, carried out in the low-grade metamorphic rocks of the southern flank of the Montagne Noire, yielded temperatures comprised between 400°C near the dome, and 230°C in the southern domain. Three Raman geothermometers were used to cover this temperature range. RSCM temperatures comply qualitatively with previous estimates based on illite crystallinity, conodont colour alteration, and fluid inclusions carried out in the same area, which document a metamorphic temperature increase towards the dome. The isotherms cut across the different nappe contacts and are oriented parallel to the southern margin of the Axial Zone. This temperature distribution supports the idea that the thermal structure was acquired during the Axial Zone dome emplacement. The thermal structure acquired during the recumbent folds emplacement and burial of the sedimentary series is totally overprinted by the doming. In addition, in a domain relatively remote from the Axial Zone dome, the RSCM measurements yielded significantly higher temperatures than illite crystallinity. This discrepancy points to a higher sensitivity of RSCM to short-lived thermal events than illite crystallinity, possibly because of more efficient kinetics of the carbonization reaction. On the other hand, high RSCM temperatures analysed far from the Axial Zone, between 300°C and 360°C, could be explained by the presence of granitic plutons under the foreland basin.

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“…In order to further characterize the samples and improve interpretation of geochronological results, the Kübler index (KI), K‐white mica (KWM) b cell dimension, and the mineral content of respective samples were determined using techniques described by Doublier et al (, ).…”

Section: Methodsmentioning

confidence: 99%

Evidence for Deformation in the Cambrian‐Ordovician Warburton Basin and Implications for the Evolution of the Tasmanides (Eastern Australia)

et al. 2019

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The Paleozoic tectonic history of the Tasmanides in eastern Australia was dominated by subduction‐related processes along the margin of eastern Gondwana. The earliest deformation event, Delamerian Orogeny, took place in the middle‐late Cambrian and is recorded in rocks within the Delamerian and Thomson orogens. The Cambrian‐Ordovician Warburton Basin covers the boundary between the Delamerian and Thomson Orogens, but very little is known about its origin and deformation history. Here we interpret geophysical data, including 2‐D seismic reflection transects, Bouguer gravity, and aeromagnetic data that provide new insights into the deformation in the eastern Warburton Basin and the kinematics of major faults. Our results show that curvilinear NE‐trending faults in the eastern Warburton Basin are basement reverse faults that experienced multiple phases of contractional deformation. Evidence for a syn‐kinematic Cambrian package (Kalladeina Formation) suggests that faulting commenced in response to the Delamerian Orogeny. A subsequent Early Devonian deformation in the eastern Warburton Basin is evident from K‐Ar geochronology of low‐grade (subgreenschist) metasedimentary rocks. We suggest that the NE‐trending Cambrian fold‐thrust belt within the eastern Warburton Basin marks the continuation of the curved Delamerian Orogen into the Thomson Orogen. This oroclinal structure may have developed in the Early Devonian in response to dextral transpression along the northern boundary of the Delamerian Orogen. Our results provide a demonstration for the complex interactions that can take place during the evolution of convergent plate boundaries, involving deformation in the fold‐thrust belt, development of sedimentary basins, and oroclinal bending.

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Very low-grade metamorphism of Rheno-Hercynian allochthons (Variscides, Germany): facts and tectonic consequences

Cited by 26 publications

References 55 publications

The tectono‐metamorphic evolution of the very low‐grade hangingwall constrains two‐stage gneiss dome formation in the Montagne Noire (Southern France)

The tectono‐metamorphic evolution of the very low‐grade hangingwall constrains two‐stage gneiss dome formation in the Montagne Noire (Southern France)

Paleotemperature investigation of the Variscan southern external domain: the case of the Montagne Noire (France)

Evidence for Deformation in the Cambrian‐Ordovician Warburton Basin and Implications for the Evolution of the Tasmanides (Eastern Australia)

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