Clinopyroxene from an alkali pyroxenite xenolith, Louèná-Oberwiesenthal Volcanic Centre, Bohemian Massif: crystal chemistry and structure
- Author(s)
- Jaromír Ulrych, Daniel Niznansky, Franz Pertlik, Gerald Giester, Andreas Ertl, Franz Brandstätter
- Abstract
Alkali pyroxenite (and ijolite) xenoliths occur in the Tertiary Louc?naŽ-Oberwiesenthal Volcanic Centre associated with the Ohr?e/Eger Rift. The alkali pyroxenite xenoliths represent fragments of an intracrustal complex with Sr-Nd isotope ratios consistent with mantle sources of HIMU-affinity. The crystal structure of diopside from an alkali pyroxenite xenolith with the formula (Ca0.95Na0.04) (Mg0.65 Fe0.133+Fe0.102+ Ti0.104+Al0.01) (Si1.69 Al0.31) O6 and the lattice parameters a = 9.773(2), b = 8.886(2), c = 5.308(1) [A°] and ß = 105.89(3) [°] was refined to an R-value of 0.025 for 1174 reflections. The mean interatomic distances are: within the Me1-O6 octahedron A°, within the Me2-O8 polyhedron A°. The last value reflects the occupation of this atomic position by significant amounts of Fe2+ and Ti4+. The enlargement determined for the bond length to 1.657 A° is in accordance with the site population for this position: (Si1.69Al0.31). The molar ratio Fe2+/Fe3+ determined by Mošssbauer spectroscopy is equal to 0.786. The AlIV deficiency in T-sites of clinopyroxene of rims is negligible (up to 0.019 a.p.f.u.) restricted to sporadic local electron microprobe analyses. The presence of Fe3+ in the T-position of Si- and Al-poor clinopyroxenes was not confirmed by X-ray structural analyses because of its low quantity. Nevertheless, the Mošssbauer spectroscopy measurements (isomer shift of 0.36 mm/s) imply that Fe3+ is present only in the Me1-O6 positions.
- Organisation(s)
- Department of Mineralogy and Crystallography
- External organisation(s)
- Czech Academy of Sciences, Charles University Prague, Geologisk Museum
- Journal
- Geological Quarterly
- Volume
- 50
- Pages
- 257-264
- No. of pages
- 8
- ISSN
- 1641-7291
- Publication date
- 2006
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 1051 Geology, Mineralogy
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/1c48ee7c-1237-412b-96e1-5e52a4246eef