Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)

Petrology of mantle xenoliths in alkaline neovolcanics from Northern Bohemia


Jana Brandová, František Holub

Geoscience Research Reports 36, 2003 (GRR for 2002), pages 162–163

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Our research has been focused on peridotite xenoliths entrained by nepheline basanites at six still poorly known localities (Provodínské kameny - Michlův vrch and Lysá skála, Hlupice, Býňov, Dobkovičky and Medvědický Hill in the České středohoří Mts.). The peridotite xenoliths exhibit protogranular textures and this implies none or weak deformation. Xenoliths are characterized by an anhydrous four-phase mineralogy consisting of olivine, orthopyroxene, clinopyroxene and spinel. Their contacts with the host basanite are always sharp, only where orthopyroxene came into contact with the alkaline melt a narrow reaction rim may occur. The xenoliths exhibit protogranular textures and this implies only a weak deformation. Modal compositions correspond to clinopyroxene-poor spinel Iherzolite and harzburgite. Equilibrium temperatures obtained by the two-pyroxene thermometer (WELLS 1977) range between 1060 and 1140 °C. Ten whole-rock analyses display refractory compositions characterized by low A12O3 (0.4-1.6 wt per cent) and CaO. However, xenoliths have high LREE/HREE ratios and are enriched in highly incompatible trace elements due to the mantle metasomatism.