ČOPJAKOVÁ, Renata, Radek ŠKODA and Jaroslava PERTOLDOVÁ. CR-BOHATÉ SPINELY Z ULTRAMAFICKÝCH HORNIN MOLDANUBIKA (CR-RICH SPINELS FROM MOLDANUBIAN ULTRAMAFIC ROCKS). Acta Mus. Moraviae, Sci. geol. Brno, LXXX, No 3, p. 87-96. ISSN 1211-8796. 2005.
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Basic information
Original name CR-BOHATÉ SPINELY Z ULTRAMAFICKÝCH HORNIN MOLDANUBIKA
Name in Czech CR-BOHATÉ SPINELY Z ULTRAMAFICKÝCH HORNIN MOLDANUBIKA
Name (in English) CR-RICH SPINELS FROM MOLDANUBIAN ULTRAMAFIC ROCKS
Authors ČOPJAKOVÁ, Renata (203 Czech Republic, guarantor), Radek ŠKODA (203 Czech Republic) and Jaroslava PERTOLDOVÁ (203 Czech Republic).
Edition Acta Mus. Moraviae, Sci. geol. Brno, 2005, 1211-8796.
Other information
Original language Czech
Type of outcome Article in a journal
Field of Study 10500 1.5. Earth and related environmental sciences
Country of publisher Czech Republic
Confidentiality degree is not subject to a state or trade secret
Organization unit Faculty of Science
Keywords in English Cr-spinels; peridotites; Moldanubian Zone; Bohemian Massif; Czech Republic
Tags Bohemian massif, Cr-spinels, Czech Republic, Moldanubian Zone, peridotites
Changed by Changed by: doc. Mgr. Radek Škoda, Ph.D., učo 21802. Changed: 26/6/2007 11:40.
Abstract
Cr-rich spinel is a common minor to accessory mineral in the Moldanubian spinel and garnet peridotites. Recently, Cr-rich spinels were found in the ultramafic tremolite rock near Nová Pec. Primary minerals of spinel group (MSG minerals of spinel group) from Moldanubian ultramafic rocks form grains disseminated in the rock, banded segregations or massive layers. Two principal compositional types of MSG from spinel peridotites have been identified: i) primary and ii) secondary. In general, the primary MSG exhibit a wide range of Cr# (0.15-0.87) and Mg# (0.35-0.79) with negative correlation between these parameters. They have characteristically low Fe2O3, TiO2, ZnO and MnO contents. MSG from dunites have higher Cr# than those from harzburgites and lherzolithes. The chemistry of primary MSG is controlled by the bulk rock composition and modal ratio of MSG and silicates in the rock. Primary Cr- spinels remain unaltered, occasionally with magnetite coatings formed during the serpentinization. Al-rich spinels are partly replaced by Cr-rich chlorite and mica. Secondary MSG were formed from primary ones by substitution Fe3+ (Cr3+, Al3+)-1 and (Fe2+, Zn2+,Ni2+,Mn2+)Mg2+-1 in peridotites during variscan metamorphism. Secondary MSG correspond to Fe3+-rich chromite and Cr-rich magnetite, usually with Cr-low magnetite rim. MSG from garnet peridotites have similar chemistry to primary MSG from spinel peridotites. Locally, Cr-poor spinels (Cr#<0.1) are found in kelyphites after garnet. MSG from tremolite rock exhibit the features of chromites metamorphosed under relatively low fO2. They are Cr-rich, Mg-low, with low Fe2O3, and elevated ZnO and MnO contents.
Abstract (in English)
Cr-rich spinel is a common minor to accessory mineral in the Moldanubian spinel and garnet peridotites. Recently, Cr-rich spinels were found in the ultramafic tremolite rock near Nová Pec. Primary minerals of spinel group (MSG minerals of spinel group) from Moldanubian ultramafic rocks form grains disseminated in the rock, banded segregations or massive layers. Two principal compositional types of MSG from spinel peridotites have been identified: i) primary and ii) secondary. In general, the primary MSG exhibit a wide range of Cr# (0.15-0.87) and Mg# (0.35-0.79) with negative correlation between these parameters. They have characteristically low Fe2O3, TiO2, ZnO and MnO contents. MSG from dunites have higher Cr# than those from harzburgites and lherzolithes. The chemistry of primary MSG is controlled by the bulk rock composition and modal ratio of MSG and silicates in the rock. Primary Cr- spinels remain unaltered, occasionally with magnetite coatings formed during the serpentinization. Al-rich spinels are partly replaced by Cr-rich chlorite and mica. Secondary MSG were formed from primary ones by substitution Fe3+ (Cr3+, Al3+)-1 and (Fe2+, Zn2+,Ni2+,Mn2+)Mg2+-1 in peridotites during variscan metamorphism. Secondary MSG correspond to Fe3+-rich chromite and Cr-rich magnetite, usually with Cr-low magnetite rim. MSG from garnet peridotites have similar chemistry to primary MSG from spinel peridotites. Locally, Cr-poor spinels (Cr#<0.1) are found in kelyphites after garnet. MSG from tremolite rock exhibit the features of chromites metamorphosed under relatively low fO2. They are Cr-rich, Mg-low, with low Fe2O3, and elevated ZnO and MnO contents.
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