Čertova zeď u Suletic („Hibschův monchiquit“) – žíla kenozoického alkalického lamprofyru v Českém středohoří

0524637 - GLÚ 2021 RIV CZ cze J - Článek v odborném periodiku
Krmíčková, Simona - Krmíček, Lukáš
Čertova zeď u Suletic („Hibschův monchiquit“) – žíla kenozoického alkalického lamprofyru v Českém středohoří.
[Devil’s Wall near Suletice („Hibsch’s monchiquite“) - a dyke of Cenozoic alkaline lamprophyre in the České Středohoří Mts.]
Zprávy o geologických výzkumech = Geoscience Research Reports. Roč. 53, č. 1 (2020), s. 35-45. ISSN 0514-8057
Institucionální podpora: RVO:67985831
Klíčová slova: České Středohoří Volcanic Complex * camptonite * monchiquite * wesselite * petrography * geochemistry * Sr–Nd isotopes
Obor OECD: Geology
Způsob publikování: Open access
http://www.geology.cz/img/zpravyvyzkum/fulltext/05_Krmickova_200525.pdf

Článek přináší první podrobnou petrografickou a geochemickou charakteristiku (včetně izotopů Sr–Nd) kenozoického alkalického lamprofyru monchiquitového až camptonitového složení, který tvoří žilné těleso vypreparované do podoby morfologicky výrazné skalní zdi se zřetelnou horizontální sloupcovitou odlučností. Žíla leží u obce Suletice v Českém středohoří a díky její morfologické podobnosti s žilným systémem Čertových zdí v Ralské pahorkatině je označována jako Čertova zeď u Suletic, či lokálně jako „Hibschův monchiquit“, podle geologa J. E. Hibsche, který žílu poprvé popsal.

A spectacular NE–SW-trending dyke of Cenozoic alkaline lamprofyre is located near Suletice in the České Středohoří Volcanic Complex (CSVC) and is spatially associated with a large magmatic centre of the Roztoky Intrusive Complex (Fig. 1). The dyke was exposed by denudation from surrounding less resistant basaltic rocks into the striking shape of the rock wall with distinct horizontal columnar jointing, which is ca. 1m thick, 10m long and 5m high. A supposed continuation of the dyke was tracked SW from the rock wall in the distance of ca. 400m (Figs 2 and 3). Due to its similarity with famous olivine nephelinite to melilitite dyke of the Great Devil’s Wall near Osečná in Northern Bohemia, it is called simply „Devil’s Wall“ or „Hibsch’s monchiquite“ according to J. E. Hibsch, the geologist who first documented the dyke. The mineral composition of the alkaline lamprophyre includes large phenocrysts of clinopyroxene, minor Ti-rich amphibole and accessory minerals such as magnetite and apatite, which are present in the form of inclusions in clinopyroxene. The fine-grained groundmass is formed by thin plagioclase laths and/or by basaltic volcanic glass. The proportion of plagioclase and glass in the groundmass varies within the intrusive body. Plagioclase-dominated groundmass is typical rather for the samples from the core represented by the rock wall, whereas hyaline groundmass of the rock forming the dyke continuation is exclusively composed of glass. Vesicular fillings or tiny veinlets of zeolite mineralisation also occur within the groundmass (Fig. 4). Alkaline lamprophyre of the Devil’s Wall is ultrabasic (SiO₂ content ~40 wt. %) and is enriched in TiO₂, Al₂O₃, Fe₂O₃^tot and K₂O. In contrast, it is relatively poor in MgO with Mg-number varying from 44 to 58 (Table 3). The investigated samples display positive anomalies of Ti and Ta along with negative anomaly of Pb and show an enrichment of LREE over HREE (Fig. 5). Initial Sr–Nd isotope composition of the Devil’s Wall dyke yielded the least radiogenic ⁸⁷Sr/⁸⁶Sr ratios from the CSVC alkaline lamprophyres along with relatively high ¹⁴³Nd/¹⁴⁴Nd values (Fig. 6). Observed isotope signature in combination with the LILE/HFSE ratios similar to those of MORB indicates a more substantial contribution of the asthenospheric mantle component to the metasomatised lithospheric mantle source of the Devil’s Wall alkaline lamprophyre. Regarding the variable mineralogical and geochemical features of the studied dyke, the composition of the alkaline lamprophyre varies from camptonite to monchiquite, resembling a special variety of alkaline lamprophyre called „wesselite“. Considering the fact that an occurrence of such a spectacular rock wall formed by alkaline lamprophyre has not yet been documented in the Bohemian Massif and, moreover, any „wesselite“-like dyke has not yet been described in the CSVC, it makes the dyke of Devil’s Wall near Suletice a unique geoheritage not only in the České Středohoří Mts., but in the whole Bohemian Massif.
Trvalý link: http://hdl.handle.net/11104/0309162