Saint Mathieu Cathedral
The Saint-Mathieu-Dom is a dome-like bulge in the basement of the north-western Massif Central in France . It enables an insight into structurally deeper, parautochthonous units.
designation
The cathedral structure was named after the small town of Saint-Mathieu in the Haute-Vienne department .
Geography and geology
The Saint-Mathieu-Dom is located directly on the north-western edge of the Massif Central. In the southwest it is bounded by the Mesozoic sediments of the northern Aquitaine Basin , which are often separated from the basement by a marginal fault . The eastern boundary is the thrust of the lower gneiss cover (units LGU and A on the geological map), which crosses the mica schist of the parautochonous mica slate unit (unit PMU ) between Saint-Jean-de-Côle in the south and Peyrassoulat (municipality of Chéronnac ) in the north . The northern boundary is formed by paragneiss of the lower gneiss cover. The north-west corner is cut off by the Le Lindois fault , which separates the Mazerolles unit in the northern section and Lias in the southern section from the interior of the cathedral. The dome structure measures around 35 kilometers in its maximum longitudinal extent (in north-south direction), and around 25 kilometers at its widest point in east-west direction.
Inside the Saint-Mathieu-Dom are the following geological units:
- Parautochthonous mica slate unit (unit PMU ) bounded by the Saint-Mathieu leukogranite in the west (unit SML ) and by the Chéronnac leukogranite on the northern edge (unit CL ) and at the same time intruded by the former.
- Paragneiss ( P units ) into which the Piégut-Pluviers granodiorite ( PPG unit ) has penetrated.
The west side of the cathedral structure is traversed by a roughly north-south trending fault zone, which separates the western edge of the Piégut-Pluviers-Granodiorite from the paragneiss. This disruption relay runs from Lacrète (municipality of Étouars ) in the south to north of Massignac .
Emergence
What is striking about the interior of the dome structure is the predominance of intrusive rocks, especially in the east of the north-south fault zone. Overall, the intrusive rocks are likely to occupy around 80% of the total surface of the structure. It can therefore be assumed that the dome structure was caused by the inflation of the neovarizean intrusive bodies. A tectonic cause in connection with the older, mediovariszischen collapse of the nappes in the Limousin (period 400 to 360 million years) can be ruled out, since the Saint-Mathieu-Leukogranit breaks the thrust orbit of the lower gneiss cover and further sends apophyses into the gneiss.
Age
The Neo-Varisian Intrusiva penetrated in the Pennsylvania , for example the Piégut-Pluviers-Granodiorite has a (Namurian / West Phalanx) age of 315 to 314 million years BP . The Saint-Mathieu leukogranite is younger, its coarse-grained facies are 304 million years old. This end-carbonic age is very likely the time for the final bulging of the Saint-Mathieu-Dom.
Regional geological overview
The high structure of the Saint-Mathieu-Dom is located in the western extension of a large-scale syncline ( Saint-Germain-les-Belles-Synform ) in the Variscan ceiling stack, the south of Limoges from the parautochthonous mica slate unit, the lower gneiss cover and the upper gneiss cover pushed over it is constructed. Due to the bending open of the stack of ceilings on the eastern edge of the Saint-Mathieu-Dom, the otherwise hidden parautochthonous mica slate unit under the lower gneiss ceiling comes to light.
Very similar tectonic conditions also prevail in the Millesvaches massif in the east of the central syncline. Like the Saint-Mathieu-Dom, the Millesvaches massif, which is also oriented north-south, consists largely of intrusive rocks and is largely framed by mica slates from the parautochthonous mica slate unit. The Millesvaches massif is much longer at 160 kilometers. The length of 35 kilometers in the Saint-Mathieu-Dom are a minimum, however, as the cathedral may continue further south under the sediments of the Aquitaine Basin.
swell
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