Volcanism in the northern Upper Rhine Rift

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The volcanic relics and phenomena of the Cretaceous-Palaeogenous age in the Upper Rhine Plain and the bordering areas of the Palatinate Forest , Odenwald , Taunus and Spessart , which can be found in the section north of Karlsruhe, are summarized as volcanism in the northern Upper Rhine Rift . The literature also speaks of a volcanic area Odenwald, Spessart and Taunus .

The volcanic formations that can be recognized today are usually not very extensive and are often geographically isolated. The volcanic activity that led to the formation of these rocks is associated with the early phase of the formation of the Upper Rhine Rift Valley.

Appearances in the terrain

In the area of ​​the low mountain range surrounding the Upper Rhine Graben, eroded chimneys are common, which sometimes protrude as hard parts from the softer adjacent rock, e.g. B. on the Otzberg (volcano) or on the Katzenbuckel , but are often topographically completely inconspicuous. Volcanic passages are less common. In the actual Upper Rhine Rift itself, occurrences of volcanic rocks are hidden under younger sediment deposits and have so far only been discovered by chance (during drilling). Exceptions are the occurrences on the Niersteiner and Sprendlinger Horst, where clods of the subsoil have been lifted out and reach the surface. On the Sprendlinger Horst there is, for example, the Maar of Messel , which is famous for its sedimentary filling and the fossils it contains, but which is not immediately recognizable as a volcanic formation.

Rocks from a "forerunner" of the Vogelsberg with a chimney near the town of Bellmuth and crevices in the Ranstadt area in the Wetterau, which was subsequently eroded down to the sub-volcanic level, are only detectable through drilling or as xenolites .

Age of volcanism

The available dating of the individual occurrences shows that volcanic activity began early in this area, long before the actual rift valley actually formed. The oldest dating of 83 million years ago refers to a small occurrence of basalt in the Spessart. The oldest volcanic rocks of the Katzenbuckels in the southern Odenwald are dated to around 70 million years. A comparable age between 70 and 65 million years was determined for some occurrences of trachyte on the Sprendlinger Horst. The rocks of the "Vogelsberg precursor" are also of a corresponding age. All of these occurrences are still of the Upper Cretaceous Age. In the Paleogene there is then a certain accumulation of rock ages for the Paleocene or Eocene ; in addition, there are more recent occurrences up to the large-scale onset of younger volcanism in the Vogelsberg and the Rhön , which essentially took place in the Neogene .

Petrography

The most common rocks in these deposits are basalt , basanite and foidite . The latter includes the well-known sanidine nephelinite of the Katzenbuckels. Some of these rocks are also limburgite . In addition, there are isolated trachytes and, with a single occurrence (the Rückersbach Gorge in the Spessart), phonolite . Pyroclastics (tuffs) of basaltic, basanitic or foiditic composition are also found only in a few places .

Economical meaning

Volcanic rocks were broken in many places, but the small size of the deposits usually did not allow for large-scale extraction.

On the Main, in the area from Aschaffenburg to Obernburg, mineralization with iron ore occurs in connection with the volcanic formations, which was bound to the contact zone of the volcanic rocks with the host rock and was mined in small pits and mines. However, the production of these ores came largely to a standstill in the nineteenth century; Basalt was sometimes mined in the old pits afterwards.

Differentiation from Permian volcanism

In the northern section of the described area there are also some from the Permian in close proximity to the Cretaceous-Paleogene volcanic rocks. These are mostly altered basalts ("Melaphyre", for example on the Kaiserlei rock near Frankfurt am Main) or rhyolites ("Porphyry", for example near Groß-Umstadt or Sailauf in the Spessart). These rocks - although of volcanic origin - are not included under the generic term "volcanism in the northern Upper Rhine Rift", but are products of a much older volcanic activity after the end of the Variscan mountain formation on the edge of the Saar-Saale valley.

literature

  • Hofbauer, Gottfried: Volcanoes in Germany. , Wissenschaftliche Buchgesellschaft, Darmstadt 2016, pp. 209–211.
  • Meschede, Martin: Geology of Germany. A process-oriented approach. Springer Spektrum, Berlin, 2015, pp. 193–206.
  • Lotz, Kurt: Introduction to the geology of the state of Hesse. Hitzeroth, Marburg, 1995, pp. 92-96, 118-122.
  • Koritnig, Hans; Baranyi, István; Todt, Wolfgang: The potassium-argon ages of the post-Permian volcanic rocks of the north-eastern Upper Rhine Rift. In: The opening . Special volume 27, Heidelberg 1975, pp. 205-211.

Individual evidence

  1. ^ Gottfried Hofbauer: Volcanoes in Germany. Scientific Book Society, Darmstadt, 2016, pp. 209–211
  2. ↑ Maurice Krafft: Guide to the volcanoes of Europe. Volume 2: Germany - France. Ferdinand Enke Verlag, Stuttgart, 1984, pp. 1-2
  3. ^ Gerhard Eisbacher, Werner Fielitz: Collection of geological guides. Volume 103: Karlsruhe and the surrounding area. Borntraeger Verlag, Stuttgart, 2010, pp. 72-73
  4. ↑ a b Heinz-Dieter Nesbor: The Vogelsberg volcanic area . In: Geological Yearbook Hessen . tape 139 . Wiesbaden 2018, p. 5-41 .
  5. ^ Martin Okrusch, Gerd Geyer, Joachim Lorenz: Collection of geological guides. Volume 106: Spessart. Borntraeger Verlag, Stuttgart, 2011, pp. 211-212
  6. ^ Otto Mäussnest: Mining and volcanoes on sheet 6120 Obernburg a. Main . In: Bayerisches Geologisches Landesamt (Ed.): Geologica Bavarica . tape 87 . Bavarian Geological State Office, Munich 1985, p. 97-117 .
  7. ^ Gustav Klemm: About the basalts and the iron ore deposits of the eastern Odenwald . In: Notes of the Geography Association and the Hessian Geological State Institute in Darmstadt . V episode, 14th issue. Hessischer Staatsverlag, Darmstadt 1933, p. 8-19 .
  8. ^ Martin Meschede: Geology of Germany. A process-oriented approach. Springer Spectrum, Berlin, 2015, pp. 104–107