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Long story encrypted in a small grain – zircon from meta-andesite in the Lower Köli Nappes reveals a complex history of the Virisen Arc Terrane, Scandinavian Caledonides, Sweden

Walczak Katarzyna A., Włodek Adam, Cuthbert Simon, Carter Isabel S. M., Ziemniak Grzegorz

Mineralogia

2025

Vol. 56, iss. 1

34--43

This short report presents the investigation results on the zircon from meta-andesitic rock from the Ankarede Volcanite Formation of the Lower Köli Nappe Complex in Scandinavian Caledonides. Previous U-Pb dating revealed a wide span of dates ranging from ca. 520 to ca. 480 Ma, with a mean age of 491 ± 3 Ma for the zircon cores. Using cathodoluminescence and back-scattered electron imaging, along with chemical mapping, we identified distinct zones within the zircon grains; 1) cores of clear magmatic provenance, 2) mantles also of magmatic origin but with a slightly different chemical composition and 3) zircon rims that suffered metamictisation and fluid-induced alterations. These findings highlight a complex growth history and alteration of studied zircon that affect the interpretation of zircon dating results. This research underscores the importance of detailed zircon studies for understanding the intricate processes involved in the magmatic and metamorphic evolution of Virisen terrain in Scandinavian Caledonides.

Titanite from the NYF-type pegmatites of Szklarska Poręba Huta quarry, Karkonosze granite massif, SW Poland

Mil Karolina, Gołębiowska Bożena, Pieczka Adam, Włodek Adam

Acta Geologica Polonica

2024

Vol. 74, no. 3

art. no. e20

Titanite, an accessory mineral of pegmatite related to aplogranite, was identified in the Szklarska Poręba Huta quarry within the Karkonosze granite massif in Lower Silesia, Poland. It formed during pegmatitic to hydrothermal stages. Besides the isovalent substitution Sn → Ti, the chemical composition of the mineral is characterized by three coupled substitutions: (1) (Al, Fe, Sc)3+ + (OH, F) - → Y Ti + ZO, (2) XREE3+ + Y (Al, Fe, Sc) 3+ → XCa2+ + Y Ti4+, and (3) (Al, Fe, Sc) 3+ + (Nb, Ta)5+ → 2 Y Ti. These substitutions are strongly dependent on the composition of the magma in terms of its Al2O3/TiO2 activity ratio, with the first one also influenced by the H2O/HF fugacity ratio. Fluorine, which induced the most common substitution (1), had its source in high-temperature F-bearing fluids released from rocks of the metamorphic envelope adjacent to the intruding granite. These fluids mobilized and transported various rock components (Sc, REE, Nb, Ta, etc.) among others in the form of fluoride complexes, enriching the aplogranite magma with some metallic elements. The substitution of Sn for Ti developed with decreasing temperature to the extent that in thin ore-mineralized quartz veins cutting aplogranite, titanite reaches Sn-bearing compositions up to the prevalence of Sn corresponding to malayaite.