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Chemistry and Sr-Nd isotope signature of amphiboles of the magnesio-hastingsite–pargasite–kaersutite series in Cenozoic volcanic rocks: Insight into lithospheric mantle beneath the Bohemian Massif
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SYSNO ASEP 0490486 Document Type J - Journal Article R&D Document Type Journal Article Subsidiary J Článek ve WOS Title Chemistry and Sr-Nd isotope signature of amphiboles of the magnesio-hastingsite–pargasite–kaersutite series in Cenozoic volcanic rocks: Insight into lithospheric mantle beneath the Bohemian Massif Author(s) Ulrych, Jaromír (GLU-S) RID, SAI
Krmíček, Lukáš (GLU-S) RID, ORCID, SAI
Teschner, C. (DE)
Skála, Roman (GLU-S) RID, SAI, ORCID
Adamovič, Jiří (GLU-S) RID, SAI, ORCID
Ďurišová, Jana (GLU-S) RID, SAI
Křížová, Šárka (GLU-S) RID, SAI, ORCID
Kuboušková, S. (CZ)
Radoň, M. (CZ)Source Title Lithos. - : Elsevier - ISSN 0024-4937
Roč. 312, July 2018 (2018), s. 308-321Number of pages 14 s. Publication form Print - P Language eng - English Country NL - Netherlands Keywords Bohemian Massif ; Cenozoic volcanic rocks ; mantle metasomatism ; Sr–Nd isotopes ; Ti-amphibole Subject RIV DB - Geology ; Mineralogy OECD category Geology Institutional support GLU-S - RVO:67985831 UT WOS 000437064600018 EID SCOPUS 85047641827 DOI 10.1016/j.lithos.2018.05.017 Annotation Amphibole phenocrysts, xenocrysts and cumulate xenoliths from Cenozoic volcanic rocks of the Bohemian Massif (BM) belong to the magnesio-hastingsite–pargasite–kaersutite series. Their host rocks are mostly basaltic lavas, stocks, dykes and breccia pipe fills, less commonly also felsic rocks. Felsic rocks with amphibole cumulate xenoliths represent differentiated magmas which have undergone polybaric fractionation of the mafic minerals. The calculated p–T conditions suggest that almost all amphiboles crystallized in a relatively narrow temperature range (1020–1100 °C) at depths of ~20–45 km (0.7–1.2 GPa) during the magma ascent. These p–T estimates are compatible with the published experimental data on the stability of kaersutite. We therefore suggest the presence of a deep magma chamber situated close to the crust–mantle boundary where amphibole xenoliths to megacrysts could have formed. Nevertheless, crystallization of rare amphibole rims during the magma ascent was observed in a hornblendite cumulate in sodalite syenite from “Giegelberg”. The lowest concentration of incompatible elements in the amphiboles was found in xenocrysts in alkaline basaltic rocks and mantle xenoliths and megacrysts, followed by phenocrysts/xenocrysts in lamprophyric rocks, xenocrysts of cumulates in felsic rocks, and phenocrysts in subvolcanic rocks. Amphibole compositional and Sr–Nd isotope characteristics resemble those of amphiboles from metasomatic clinopyroxene/amphibole veins in mantle peridotites. The initial 143Nd/144Nd and 87Sr/86Sr ratios of amphiboles (0.51266–0.51281 and 0.70328–0.70407, respectively) are similar to those of their whole rocks (0.51266–0.51288 and 0.70341–0.70462, respectively). Amphiboles of the magnesio-hastingsite–pargasite–kaersutite series of the BM are mostly chemically homogeneous, with no pronounced Mg–Fe fractionation and zoning. The amphiboles are characterized by relatively homogeneous epsilon Nd = +1.4 to +3.8 values: only a single sample from the České Středohoří Volcanic Complex (CSVC) yielded a negative epsilon Nd (–0.6). This testifies to locally elevated proportions of recycled Variscan crustal material during melting of mantle peridotites rich in clinopyroxene–amphibole veins. These veins were formed by metasomatic fluids enriched in High Field Strength Elements (HFSE) and are isotopically similar to Enriched Mantle1 (EM1)-type mantle. Amphibole host rocks occur in areas with a significant concentration of basaltic magmas in rift zones along lithospheric block boundaries of the BM. Lithospheric mantle beneath such zones was probably strongly influenced by metasomatic fluids during the formation of clinopyroxene–amphibole veins in mantle peridotite that facilitated the generation of basaltic magma with amphibole. Workplace Institute of Geology Contact Jana Popelková, popelkova@gli.cas.cz, Sabina Janíčková, Tel.: 233 087 272 Year of Publishing 2019
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