Problems and challenges in detection of pre-Mesozoic maar volcanoes: example from the Principálek Volcano in the Permian Krkonoše Piedmont Basin

Abstract

The Permian pyroclastic deposits on the Principálek Hill SW of Vrchlabí (Czech Republic) were investigated by means of geological mapping and geophysics. The pyroclastic rocks are exposed in several small coherent outcrops, yet many interpretations are based on debris. The preserved textures enable reconstruction of eruptive styles. The volcanism started with phreatomagmatic eruptions documented by the fine-grained tuff with accretionary lapilli at the base. Subsequently, the activity changed to phreato-Strombolian/Surtseyan producing lapilli-tuffs and lapillistones. These events were followed by a Strombolian phase as evidenced by ill-sorted scoriaceous tuff-breccias with volcanic bombs. The uppermost unit consists of welded lava agglutinates and basaltic lavas suggesting a Hawaiian style of eruption. One of the basaltic feeder necks is exposed in a small abandoned quarry. Geophysical surveys were carried out over the extent of pyroclastic deposits. These included gravimetry, magnetometry, and DC resistivity tomography. The magnetic data indicate the occurrence of basaltic dykes in the central part of the pyroclastic deposits. The DC tomography confirms the presence of dykes, enables estimation of the pyroclastic deposits thickness, and provides evidence for the size and position of the maar-diatreme. Gravity data yield an insignificant low associated with the diatreme, which is likely a product of low rock-density contrast between the diatreme and country rocks. We argue that this is due to short time gap between sedimentation and volcanic activity and also related to conjoint burial and diagenetic history of the diatreme and the surrounding country rocks.

Types of soft-sediment deformation structures in a lacustrine Ploužnice member (Stephanian, Gzhelian, Pennsylvanian, Bohemian Massif), their timing, and possible trigger mechanism

“…Moreover, major tectonic activity in halfgrabens precedes sedimentation (i.e., tectonic reactivation is interpreted to have occurred before Stephanian C time). The main volcanic activity occurred during the Lower Permian (Vrchlabí and Prosečné Formation; Stárková et al 2011;Valenta et al 2014). Accordingly, it is likely that the subsidence mechanism during deposition of the Semily Formation (and Ploužnice member) was dominantly thermal and compactional.…”

Emplacement History of the Miocene Zebín Tuff Cone (Czech Republic) Revealed From Ground Geophysics, Anisotropy of Magnetic Susceptibility, Paleomagnetic, and 40Ar/39Ar Geochronology Data

“…Ground geophysical methods provide a useful tool for imaging the internal structure of volcanoes and are frequently used in studies of maar‐diatreme volcanoes (e.g., Blaikie et al, , ; Bolós et al, ; Flechsig et al, ; Marshall et al, ; Schmidt et al, ; Skácelová et al, ; Valenta, Rapprich, Skácelová, Gaždová, & Fojtíková, ; Valenta, Rapprich, Skácelová, Skácelová, et al, ). Geophysical tomography studies of monogenetic pyroclastic cones are rather scarce and focus mostly on Quaternary volcanoes (e.g., Barde‐Cabusson et al, ; Bolós et al, ; Finizola et al, ; Peccerillo et al, ), which contrasts to the weathered and partly eroded Miocene Zebín Volcano.…”

A Permian andesitic tuff ring at Rožmitál (the Intra-Sudetic Basin, Czech Republic) – evolution from explosive to effusive and high-level intrusive activity

“…Phreatomagmatic erup tive cen tres, es pe cially maar-diatreme sys tems, have been iden ti fied in sev eral Permo-Carbonifeorous post-Variscan bas ins in Cen tral and West ern Eu rope (e.g., Nemec, 1981;Lorenz and Haneke, 2004;Valenta et al, 2014). Com pared to tuff rings and cones, the maar-diatreme sys tems must have rel a tively large pres erva tion po ten tial in an cient suc ces sions, as the diatremes extend well be low the palaeosurface and thus are not eas ily destroyed by ero sion.…”

“…1). In the same ba sin, Valenta et al (2014) dis cov ered the Principálek vol ca nic struc ture us ing a geo phys i cal sur vey. The Principálek vol cano started its ac tiv ity as a maar pen e trat ing poorly con sol i dated con ti nen tal de pos its.…”