International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

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

Published: Aug 2020

Pages: 382 - 387

DOI: https://doi.org/10.31577/GeolCarp.71.4.6

Authors: LUKÁŠ KRMÍČEK, MARTIN J. TIMMERMAN, MARTIN A. ZIEMANN, MASAFUMI SUDO, JAROMÍR ULRYCH

Abstract: 40Ar/39Ar 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.

Keywords: Bohemian Massif, Železná hůrka, Eisenbühl, argon dating, mica, amphibole, melilitite

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Volume 71 no. 4 / August 2020

Volume 71 no. 4