40Ar/39Ar step-heating dating of phlogopite and kaersutite megacrysts from the Železná hůrka (Eisenbühl) Pleistocene scoria cone, Czech Republic

Abstract

40 Ar/ 39 Ar step-heating of mica and amphibole megacrysts from hauyne-bearing olivine melilitite scoria/tephra from the Železná hůrka yielded a 435±108 ka isotope correlation age for phlogopite and a more imprecise 1.55 Ma total gas age of the kaersutite megacryst. The amphibole megacrysts may constitute the first, and the younger phlogopite megacrysts the later phase of mafic, hydrous melilitic magma crystallization. It cannot be ruled out that the amphibole megacrysts are petrogenetically unrelated to tephra and phlogopite megacrysts and were derived from mantle xenoliths or disaggregated older, deep crustal pegmatites. This is in line both with the rarity of amphibole at Železná hůrka and with the observed signs of magmatic resorption at the edges of amphibole crystals.

Microbial Signatures in Deep CO2-Saturated Miocene Sediments of the Active Hartoušov Mofette System (NW Czech Republic)

“…The PPZ started to develop at the boundary from Mid to Late Pleistocene (Bankwitz et al, 2003a , b ). CO 2 -rich nephelinitic magma (Seifert and Kämpf, 1994 ; Geissler et al, 2007 ; Brandl et al, 2015 ) erupted in the Mid Pleistocene (Mrlina et al, 2007 ; Rohrmüller et al, 2018 ; Krmíček et al, 2020 ; Lied et al, 2020 ). Age determinations of the hydrothermal activity of Karlovy Vary spa with travertine deposits go back to 0.23 Ma (Vylita et al, 2007 ).…”