Geophysical modelling of the Ebersbrunn diatreme, western Saxony, Germany

The Ebersbrunn diatreme near Ebersbrunn, western Saxony, Germany, causes an elliptical Bouguer anomaly of about –2.5 m Gal, which covers an area of approximately 2.2 km × 2 km and an elliptical magnetic anomaly with values between –250 nT and 1000 nT about half a kilometre smaller in diameter and situated within the southern part of the Bouguer anomaly. Considering magnetic susceptibility and density values determined from core samples of the diatreme, a symmetrical, cone-shaped body with an oval surface outcrop of 2 km × 1.5 km and a dip angle of the slopes of about 82° is modelled. It comprises a central structure with a diameter of 800–900 m and susceptibility values up to 9000*10-6 SI higher and densities up to 220 kg/m3 lower than the surrounding chimney. Additionally, susceptibility within the body increases with depth and decreases with the degree of weathering. The geometry can clearly be associated with the diatreme of a maar-diatreme-volcano. Regarding the petrographic information (the occurrence of pelletal lapilli as juvenile phase, the basaltoid character of the occurring ground mass of magmatic origin and 80% wall rock content) and the final geophysical model, the Ebersbrunn structure can definitely be regarded as the partially eroded remnant (diatreme and root zone) of a maar-diatreme-volcano. The association of earthquake swarms in intraplate regions of intersecting fractures and volcanism has led to renewed interest in the eroded maar-diatreme-volcano.

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