Original paper
Isolated alkaline basalt occurrences in the northern Spessart, Germany: Outposts of the Early Miocene Vogelsberg shield volcano?
Okrusch, Martin; Schüssler, Ulrich; van den Bogaard, Paul; Koglin, Nikola; Brätz, Helene; Lorenz, Joachim; Karbusicka, Cliff; Spiegl, Tobias
Neues Jahrbuch für Mineralogie - Abhandlungen Band 196 Heft 3 (2020), p. 199 - 219
58 references
published: Jul 24, 2020
published online: Feb 11, 2020
manuscript accepted: Dec 13, 2019
manuscript revision received: Dec 10, 2019
manuscript revision requested: Dec 5, 2019
manuscript received: Aug 12, 2019
ArtNo. ESP154019603002, Price: 29.00 €
Abstract
Four isolated occurrences of Tertiary volcanic rocks in the northern Spessart at Beilstein, Hoher Berg, Madstein and Kasselgrund are relics of volcanic vents or dikes. They display alkaline basalts (s.l.) with mainly trachybasaltic composition, which, from normative mineral contents, may be designated as nepheline-bearing alkali-olivine basalts and basanites. In part, centimetre-sized xenoliths of spinel lherzolite occur. According to Ar-Ar dating, the alkaline basalts (s.l.) from Kasselgrund have erupted at 18.1 ± 0.3 or 19.3 ± 0.4 Ma, those of Hoher Berg between c. 18 and c. 21 Ma. These ages correspond to the Vogelsberg eruption stage I. A slightly younger Ar-Ar age of 16.8 ± 0.3 Ma was recorded for the Beilstein basalt, which is in chronological accordance to the turn of Vogelsberg eruption stages II and III. Samples of all four occurrences reveal major and trace element compositions, which are different from those of the Vogelsberg basalts. Compositions of basalts of the stage III from Vogelsberg coincide most with the Spessart basalts. This signals a special position of the northern Spessart volcanic rocks either as a discrete spatial part of the Vogelsberg volcanic suite or as smaller, independent eruption centres.
Keywords
Tertiary • Early Miocene • volcanism • Ar-Ar dating • geochemistry • Germany • Vogelsberg • Spessart