Reconstruction of eroded monogenic Strombolian cones of Miocene age: A case study on character of volcanic activity of the Jičín Volcanic Field (NE Bohemia) and subsequent erosional rates estimation

Abstract

Relics of solitary volcanic edifices in NE Bohemia were newly interpreted as remnants of scoria cones and their conduits. Volcanic activity in this area occurred in a form of scattered Strombolian eruptions of basanitic magmas mostly ascending along E-W trending faults. Nearly all studied volcanoes erupted in similar style, Strombolian, mostly not producing larger lava flows. This volcanic activity took place mainly during Miocene (24.6-16.5 Ma). The lavas known on the Kozákov Hill were produced by much younger volcanic activity (6.7-3.5 Ma) and one of the studied locations is supposed to represent their feeder. The older Strombolian cones are relatively weakly affected by weathering processes. The erosional level at individual sites depends on geomorphology. On some of the edifices non-welded, poorly stratified scoriae are well preserved, at other sites a basal facies or upper vent facies were exposed by selective erosion. Interpretation of the exposed facies with the use of radiometric data brought new insight in relief evolution of this area. Erosion of Cretaceous marine deposits was very intensive during Oligocene, whereas during the last 17 M.y. only some 70 m of weak sediments were eroded.

Fingerprints of magma mingling processes within the Miocene Zebín tuff cone feeding system (Jičín Volcanic Field, Czech Republic)

“…3). The pyroclastic deposits are well-sorted and clast supported with indistinctive outward dipping bedding suggesting the Zebín Hill represents a remnant of pyroclastic cone with preserved wall facies (Rapprich et al 2007). The pyroclastic deposits consist of angular non-vesiculated fragments of basanite with predominating size around 1 cm and with numerous xenoliths of underlying Cretaceous sediments (Fig.…”

“…The distribution of the Cenozoic volcanoes follows the above-mentioned dominant fault systems as they controlled the magma ascent (Vaněčková et al 1993). The E-W trending tectonic grain, however, was the leading factor that influenced the geometry of the dikes and magma feeder conduits at shallow crustal depths (Rapprich et al 2007;Petronis et al 2015). Volcanic activity in the Jičín Volcanic Field occurred during two separate episodes: (1) Early Miocene (19-16 Ma) and (2) Early Pliocene (5-4 Ma).…”

“…Apart from the main volcanic complexes (see e.g., Ulrych et al 2002;Rapprich and Holub 2008;Cajz et al 2009;Holub et al 2010;Skála et al 2014;Ackerman et al 2015), several volcanic fields were formed also on the shoulders of the rift (Awdankiewicz 2005;Rapprich et al 2007;Büchner and Tietz 2012;Valenta et al 2014;Büchner et al 2015;Petronis et al 2015;Tietz and Büchner 2015;Awdankiewicz et al 2016;Ulrych et al 2016;Haase et al 2017). Our study focused on the Zebín Volcano, located in the Jičín Volcanic Field (Rapprich et al, 2007;Petronis et al 2015; Fig. 1) on the southeastern shoulder of the Eger Rift, where Miocene volcanic rocks were emplaced into, or erupted onto, Upper Cretaceous marine sediments of the Bohemian Cretaceous Basin and continental Permo-Carboniferous strata of the Krkonoše Piedmont Basin.…”

“…Eruptions occurred from scattered vents in the form of lava flows, lava lakes, phreatomagmatic craters, and scoria cones and tuff cones. Compositionally the rocks are intra-plate alkaline basalts sensu lato, including picrobasalt, basanite, and olivine nephelinite (Rapprich et al 2007). …”

“…2), about 2 km to the northeast from the historical center of Jičín Town. The volcanic activity of Zebín was dated by the K-Ar bulk rock method at 17.51 ± 0.74 Ma (Rapprich et al 2007). The volcano was constructed upon marine marlstones and claystones of Late Turonian to Early Coniacian age (e.g., Čech 2013).…”