Pages: 383 - 397
Abstract: The Roztoky Intrusive Centre (RIC) is formed by a trachytic crater vent, hypabyssal intrusions, together with more than 1000 almost radially arranged dykes and more rare cone sheets. Hypabyssal Weakly Alkaline Series of essexite (33–31 Ma)-monzodiorite (33–30 Ma)-sodalite syenite (30–28 Ma) and two coexisting weakly [camptonite (31 Ma)/gauteite I?-sodalite syenite porphyry-gauteite II? (24 Ma)/trachyte?] and strongly alkaline dyke series [camptonite (28 Ma)/monchiquite (26 Ma)-phonolite/tinguaite (26 Ma)/nepheline syenite porphyry cone sheet (30 Ma)] were recognized. Four principal dyke groups were distinguished: I — lamprophyres (58 %) dominated over II — semilamprophyres (28 %), minor III — basaltic rocks (6 %) and IV — felsic derivatives (9 %). Both radial steeply dipping dykes of lamprophyres, semilamprophyres, basaltic and rare phonolitic rocks and flat dipping cone sheets of trachyte and phonolite/nepheline syenite porphyry are present. Dykes of (semi)lamprophyres, and basaltic rocks show similar preferred strikes of 90° and 0°; felsic derivatives of 330° and 0°. Majority (91–98 %) of dykes (100 % of felsic dykes) are present within a distance of 7 km from the Roztoky main centre. Joint and dyke patterns are controlled by the regional paleostress field existing in the upper crust during magma ascent, by orientations of pre-existing fracture sets in the region and by the superimposed local stress field exerted by the rising intrusion. For the interval of 31–26 Ma in the RIC, the analysis of dyke geometries indicates the dominance of regional stress characterized by N-S tension (lamprophyres ≈ semilamprophyres > basaltic rocks > felsic derivatives).
Keywords: N Bohemia, Ceske stredohori Mts., Cenozoic Roztoky Intrusive Centre, dyke rocks, differentiation, orientations, age relationsDownload PDF document Show Text Version