Mineralogy, petrology, age, and origin of the teschenite association rocks of Žermanice sill, Czech Republic

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Marco E. Ciriotti
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Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Mineralogy, petrology, age, and origin of the teschenite association rocks of Žermanice sill, Czech Republic

Messaggio da Marco E. Ciriotti » mar 25 set, 2018 10:13

Referenza:
▪ Matýsek, D., Jirásek, J., Skupien, P., Thomson, S.N. (2018): The Žermanice sill: new insights into the mineralogy, petrology, age, and origin of the teschenite association rocks in the Western Carpathians, Czech Republic. International Journal of Earth Sciences, 107, 2553–2574.

Abstract:
The Žermanice locality represents the best-exposed example of the meta-basaltoid/meta-gabbroic rock type of the teschenite association. It forms a subhorizontal volcanic body (sill) 27–30 m thick. The subvolcanic rock is inhomogeneous and slightly differentiated. The predominant rock type is a basaltoid (diabase-dolerite), medium-grained, speckled, mesocratic rock exhibiting an evident subophitic texture. Miarolitic cavities are abundant in some places. The major rock constituents are albite, microcline, chlorite, and pyroxene, as well as analcime and plagioclase in places. The accessory magmatic phases are "biotite", ilmenite, fluorapatite, sulphides, Ti-rich magnetite, Nb-rich baddeleyite, and chevkinite–(Ce) or perrierite–(Ce). A large extent of alteration is evident from the presence of chloritization, albitization of plagioclases, and zeolitization (analcimization). Geochemical analyses reveal an affinity for metaluminous igneous rocks. The best fit is with the within-plate basalts or the within-plate volcanic zones. The classification of this rock is problematic because of the mixed intrusive and extrusive features; the choice is between meta-alkali basalt and metadolerite (meta-microgabbro). 207Pb common lead-corrected U–Pb apatite dating yields a weighted mean age of 120.4 ± 9.6 Ma, which corresponds to the middle Aptian. The igneous body is at most ca. 10 Ma younger than the surrounding late Hauterivian sediments and might have been emplaced into unconsolidated or partly consolidated sediments. According to our research, it is evident that at least some teschenite association rocks are in fact low-grade metamorphic rocks.
Marco E. Ciriotti

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