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@article{1641678,
author = {Janousek, V. and Holub, F.V. and Verner, K. and Čopjaková, Renata and Gerdes, A. and Hora, J.M. and Kosler, J. and Tyrrell, S.},
article_location = {Amsterdam},
article_number = {OCT 2019},
doi = {http://dx.doi.org/10.1016/j.lithos.2019.05.028},
keywords = {(Ultra-)potassic magmatism; Durbachites; Geothermobarometry; Geochemistry; Variscan Orogeny; Bohemian Massif},
language = {eng},
issn = {0024-4937},
journal = {Lithos},
title = {Two-pyroxene syenitoids from the Moldanubian Zone of the Bohemian Massif: Peculiar magmas derived from a strongly enriched lithospheric mantle source},
url = {https://www.sciencedirect.com/science/article/pii/S002449371930218X},
volume = {342},
year = {2019}
}
TY - JOUR
ID - 1641678
AU - Janousek, V. - Holub, F.V. - Verner, K. - Čopjaková, Renata - Gerdes, A. - Hora, J.M. - Kosler, J. - Tyrrell, S.
PY - 2019
TI - Two-pyroxene syenitoids from the Moldanubian Zone of the Bohemian Massif: Peculiar magmas derived from a strongly enriched lithospheric mantle source
JF - Lithos
VL - 342
IS - OCT 2019
SP - 239-262
EP - 239-262
PB - Elsevier
SN - 00244937
KW - (Ultra-)potassic magmatism
KW - Durbachites
KW - Geothermobarometry
KW - Geochemistry
KW - Variscan Orogeny
KW - Bohemian Massif
UR - https://www.sciencedirect.com/science/article/pii/S002449371930218X
L2 - https://www.sciencedirect.com/science/article/pii/S002449371930218X
N2 - In the Variscan Bohemian Massif, (ultra-)potassic plutons are conspicuously associated with the high-grade, lower crustal/upper mantle Gfohl Unit (Moldanubian Zone). They can be subdivided into two contrasting groups: (1) coarse amphibole-biotite melagranite to quartz syenite with conspicuous K-feldspar phenocrysts (the 'durbachite suite'), and (2) essentially equigranular biotite-two-pyroxene quartz syenites to melagranites (the 'syenitoid suite'). The latter suite, represented by the Tabor and Jihlava plutons, is characterized by an originally 'drier' mineral assemblage orthopyroxene + clinopyroxene + Mg-biotite + plagioclase + K-feldspar + quartz, with accessory zircon, apatite, ilmenite, monazite and/or rutile + chromite. The rich assemblage of both rock-forming and accessory minerals allows testing of numerous geothermobarometers. The resulting P-T data are mutually consistent; they document emplacement of the parental magmas at mid-crustal levels (similar to 5 kbar/19 km for Tabor and 7-8 kbar/26-30 km for Jihlava) and record near-isobaric crystallization from at least 1170 degrees C to the solidus. New Isotope-Dilution Thermal Ionization Mass-Spectrometry (ID-TIMS) U-Pb ages for zircon (336.9 + 0.6 Ma) and rutile (336.8 + 0.8 Ma) from the Tabor Pluton, together with previously published ages from the Jihlava Pluton, provide temporal constraints for the emplacement and rapid cooling of the syenitoids below c. 600 degrees C. This supports the hypothesis of post-tectonic emplacement of a hot and dry melt (>1200 degrees C?) into an essentially consolidated orogenic crust. The two syenitoid plutons have comparable, crust-like radiogenic isotope signatures (Sr-87/Sr-86(337) = 0.7114-0.7133, epsilon(337)(Nd) = -6.8 to -8.0). This, in context of whole-rock geochemical variation and K-feldspar Pb isotopic compositions, is consistent with generation from a strongly enriched lithospheric mantle source. Shortly before melting, the local orogenic mantle was most likely modified by deep subduction and relamination of felsic crustal material of the Saxothuringian provenance, transformed to the felsic high-pressure granulites common in the Moldanubian Zone. In the subsequent evolution of the two-pyroxene syenitoid plutons, crystal fractionation and accumulation played a key role, unlike in the durbachite suite itself, where magma mixing with leucogranitic melts was much more important. Structural relations inside and around the (ultra-)potassic plutons (similar to 343-335 Ma) suggest that - besides different depths and specific processes of magma emplacement - these plutons track different kinematic histories and evolutions of regional strain fields in their high-grade country rocks in this crucial period of the Variscan Orogeny.
ER -
JANOUSEK, V., F.V. HOLUB, K. VERNER, Renata ČOPJAKOVÁ, A. GERDES, J.M. HORA, J. KOSLER a S. TYRRELL. Two-pyroxene syenitoids from the Moldanubian Zone of the Bohemian Massif: Peculiar magmas derived from a strongly enriched lithospheric mantle source. \textit{Lithos}. Amsterdam: Elsevier, 2019, roč.~342, OCT 2019, s.~239-262. ISSN~0024-4937. Dostupné z: https://dx.doi.org/10.1016/j.lithos.2019.05.028.
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