Roque Haute (volcano)
Coordinates: 43 ° 18 ′ 16 ″ N , 3 ° 22 ′ 5 ″ E The basaltic volcano of Roque Haute is the youngest volcanic phenomenon in the Languedoc in southern France . It originated in the Middle Pleistocene around 640,000 years ago.
Occurrence
The rather small, roughly rectangular volcanic deposit of Roque Haute, named after the hamlet of the same name and manor Domaine de Roque-Haute , measures 1250 meters in east-west and 1000 meters in north-south direction. Its surface area is around one square kilometer. It is located between Vias and Portiragnes , just under 5 kilometers west-southwest of Vias on a gravel terrace of the Old Pleistocene , about 3 kilometers north of the coast of the Golfe du Lion . The RN 112 runs one kilometer to the north and the Canal du Midi passes one kilometer further south .
The occurrence consists of the Grand Bost (also Grand Bosc ), a small basalt plateau at 27 to 23 meters above sea level and the Terres Nègres , which culminate in a 41 meter high ash cone.
stratigraphy
The Grand Bost plateau usually shows the following stratigraphic structure (from hanging wall to lying ):
- overlying tuffs
- coherent basalt
- underlying tuffs
The basis of the sequence is nowhere to be seen. The underlying tuffs are up to 3 meters thick. They consist of ash and glassy lapilli, as well as the occasional weathered blocks of basalt. Allochthonous inclusions are quite common, including red, hardened clays in layers (decimeter range), broken quartz pebbles , white marl blocks , yellow sand , Miocene? Lamellibranch limestone and sandstone from the Astium of Montblanc . The basalt thicknesses vary between 0.5 and 3 meters. The overlying tuffs also contain a lot of foreign material. They emerged from the central ash cone, whose funding center must have been in the northwest sector, recognizable by the increasing basalt lenses.
Petrology
In contrast to the basanite of Saint-Thibéry, the Roque Haute is a real coherent basalt with normal polarity, which builds up the plateau of the Grand Bost in the form of lava flows , but can also be present in vent facies . Basaltic tuffs with an accumulation of volcanic bombs raised the ash cone of the Terres Nègres. In contrast to the volcanic complex of Agde , which it otherwise looks astonishingly similar, the basalt does not contain any nodules of mantle rock. It consists of phenocrystals of augite and olivine , which float in a crystalline matrix of augite, plagioclase and magnetite . The plagioclase occurs in two generations with 200 and 10 μ. The volcanic heavy mineral fraction is dominated by various augites and olive green augite with clear fissile properties according to (110). Orthopyroxes are also less common in the lower tuff . Other heavy minerals are (with decreasing frequency) staurolite , tourmaline , epidote , zircon , garnet , rutile , andalusite and sillimanite .
Basalt mining and nature reserve
Roque Haute basalt has been mined since prehistoric times , with the main focus of mining activities in the Middle Ages . Because of its hardness, the stone was in demand for the manufacture of tools such as grinding stones and stone axes and as a building block. The churches of Portiragnes and Vias, several townhouses and the Domaine de Roque-Haute were built with the basalt. In the 16th century the stone was used to build the Canal du Midi. For the construction of the RN 112, Grand Bosc was broken at the edge of the basalt plateau and demolition walls up to 5 meters high were built.
After the end of the dismantling, small lakes and ponds were created , which now form the basis of the nature reserve that has existed since 1975 .
Individual evidence
- ↑ Frechen, J. von and Lippolt, HJ: Potassium-argon data on the age of Laacher volcanism, the Rhine terraces and the ice ages . In: Ice Age and the Present . tape 16 , 1965, pp. 5-30 .
- ^ Kloosterman, JB: Le volcanisme de la région d'Agde, Hérault, France (doctoral thesis) . In: Geologica Ultraiectina . No. 6. Mededelingen van het Mineralogical-Geological Institute of the Rijksuniversiteit te Utrecht, 1960.