High-Al amphibolites of the Bohemian-Moravian HeightsArticle PDF
High-Al amphibolites of the Bohemian-Moravian Heights
In the Bohemian-Moravian Heights high-Al amphibolites having 21-22 wt % Alp, were observed in four amphibolite complexes (at Kozlov, Račice and Rožná in the Strážek subdivision of the Moldanubian Complex, and at Kasany in the southernmost part of the Svratka Complex). Their occurrences evidently are only solitary and of small extension. Their high Alp, level is either due to their elevated content of basic plagioclase, whose share in the rock exceeds 50 %, or due to the extremely high basicity of the constituting plagioc1ase (anorthite) in rocks with otherwise current petrography. Before regional metamorphism the rocks were leucogabbros and high-Ca gabbros. This view is also supported by the fact that similar basic types rich in basic plagioclase are common within the family of plutonic rocks, but exceptional within the family of volcanie rocks, and by the geochemical signature of the rocks. The metaleucogabbros represent an additional type among the pre-metamorphic gabbroic protoliths which in the Moldanubian Complex of the Bohemian-Moravian Heights, also include Mg and Fe metagabbros.
Dušan Němec, Institute of Mineralogy, Petrography and Geochemistry, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic