Estivaux granite

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The Estivaux granite is a synkinematic, calcareous granite intrusion in the basement of the north-western French Massif Central . It forms part of the Thiviers-Payzac unit and was deformed in the lower carbon .

etymology

The Estivaux granite is named after its type locality , the municipality of Estivaux in the Corrèze department .

introduction

Geological overview map for the location of the Thiviers-Payzac unit (in green). The Estivaux granite is in the middle right (in red).

The Estivaux granite is about 8 kilometers long in the northwest-southeast direction and only 3 kilometers wide in the northeast-southwest direction. By means of the Estivaux Fault - a steep, sinistral lateral shift - it is demarcated in the northeast from the rocks of the lower gneiss cover . The southwest side of the intrusion is framed by the Thiviers sandstone . The clan flows along its frayed southeast side, near which several smaller apophyses have emerged. On its northwest side, the granite is split into several elongated, tentacle-shaped projections. The north-east side of the intrusion is gneis adhesive formed and of Mylonitzonen traversed.

Petrology

The Vézère at the Pont de Comborn, looking northeast. The dense forests here cover the Estivaux granite.

Four different facies areas can be distinguished in granite :

  • melanocratic facies along the southwest side
  • leucocratic facies along the northeast side
  • white facies in the center
  • pink facies on the southeastern margin

mineralogy

The mineral inventory of the Estivaux granite in the melanocratic facies is composed as follows:

The melanocratic facies contain many mafic inclusions and streaks . The white and pink facies are a fine-grained modification of the melanocratic facies, but hornblende and titanite no longer occur in either facies. The color contrast is due to the different coloring of the feldspars, so the pink facies are likely to have a lot more hematite . The leucocrate facies are to be regarded as very heavily sheared leucogranite , which is very rich in muscovite.

Chemical composition

Oxide
wt.%		 Estivaux granite
SiO 2 71.00
TiO 2 0.25
Al 2 O 3 15.30
Fe 2 O 3 0.55
FeO 1.20
MnO 0.03
MgO 0.85
CaO 1.40
Na 2 O 4.70
K 2 O 4.20
P 2 O 5 0.09
H 2 O - 0.10
H 2 O + 0.65

deformation

The Estivaux granite was deformed heterogeneously in its entirety. In the granite there is a strong gradient in the degree of deformation and in the mineral regulation from southwest to northeast; Thus, as the SC-mylonitic , left-shifting Estivaux fault gradually approaches, the little stressed melanocratic facies merge into the strongly deformed leucocratic facies; at the same time the content of microaplite (residual melt) sinks from 20 to only 5%.

The sense of shear in Estivaux granite is uniformly sinistral.

Age

Using the argon method, Roig and colleagues (1996) found an age from the Tournaisian of 346 ± 3.5 million years for the Estivaux granite . However, since this is a cooling age of the intrusion to 350/300 ° C, the actual intrusion age is likely to be much higher, possibly 360 to 355 million years. The formation of the granite is therefore related to the calcareous and sub-alkaline Limousin tonalite line , the maximum activity of which falls in the period 358 to 350 million years.

See also

swell

  • Jacques Grolier and others: Feuille Tulle . In: Carte géologique de la France à 1/50000 . BRGM.
  • Roig, JY: Evolution tectono-métamorphique d'un segment de la chaîne hercynienne. Rôle du plutonisme dans la caractérisation des tectoniques du Sud-Limousin (Massif Central français) - Doctoral thesis . Univ. Orléans, 1997, p. 287 .

Individual evidence

  1. ↑ Hibbard, MJ: Deformation of incompletely crystallized systems: granitic gneisses and their tectonic implications . In: J. Geol. Volume 95 , 1986, pp. 543-561 .
  2. ↑ a b Roig, JY, Faure, M. and Ledru, P .: polyphase wrench tectonics in the southern French Massif Central: kinematic inferences from pre- and syntectonic granitoid . In: Geologische Rundschau . tape 85 , 1996, pp. 138-153 .
  3. ^ Patrick Rolin and Michel Colchen: Les cisaillements hercyniens de la Vendée au Limousin . In: Géologie de la France . n ° 1-2, 2001, p. 87-116 .