The underground gas storage near Příbram - a source of new information about granitoids of the Central Bohemian Pluton


Authors: Sokol A, Domečka K, Breiter K, Janoušek V

Published in: Bulletin of Geosciences, volume 75, issue 2; pages: 89 - 104;

Keywords: Bohemian Massif, Central Bohemian Pluton, granitoids, enclaves, geochemistry, petrology,

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The article presents petrologic and geochemical data obtained in the course of salvage investigation of unique three dimensional outcrop within artificial caverns of the underground gas storage (UGS) near town of Příbram in years 1996-98. The UGS is situated near the NW contact of the Central Bohemian Pluton. Within the UGS, three major rock complexes have been distinguished: a. granite complex (granite to granodiorite), b. tonalite complex (tonalite to granodiorite), c. basic complex (quartz diorite to quartz gabbro). Basic rocks occur in three forms: i. large irregular bodies, ii. breccias of angular blocks cemented by tonalite, iii. mafic microgranular enclaves (MME). Chemically, all rock types are slightly metaluminous, calc-alkaline granitoids. Evolutionary trends of most chemical elements in tonalites and granites are nearly linear supporting origin of granite by fractionation of tonalitic magma. The relatively variegated group of basic rocks shows trend different from that of tonalites and granites, and this fact supports its origin by independent fractionation of basic melt. The MME have the same chemical signature as basic rocks from large bodies, but modified by reactions with enclosing more acid rocks. The Sr-Nd isotopic data indicate that all acid and basic complexes shared a source with broadly similar geochemical and isotopic signature (CHUR-like mantle or metabasic rocks of deeper crust).