Metasomatic effects in the lithospheric mantle beneath the NE Bohemian Massif: A case study of Lutynia (SW Poland) peridotite xenoliths

Spinel Iherzolite and spinel harzburgite mantle xenoliths occur in the 4.56 +/- 0.2 Ma Lutynia basanite in SW Poland. Only one studied xenolith contains minor pargasitic amphibole. Minerals forming the xenoliths are chemically unzoned. Olivine (Fo [(Mg/(Mg + Fe(tot)))*100] (89 8-92 4)) contains 034-0.45 wt % NiO and <780 ppm Ca, orthopyroxene is Al enstatite (#mg [(Mg/(Mg + Fe(tot))* 100] 090-0 92. Al 0 06-0.17 a.pfu), chnopyroxene is Al-Cr diopside (#mg 0.91-0.93. Al 0 104-0 197 a.pfu). Exsolved orthopyroxene occurs in the chnopyroxene and vice versa. Al-Mg spinel occurs in symplectites with chnopyroxene. Second generation crystals of olivine (Fo (88 0-91 7). Ca up to 1800 ppm), clinopyroxene and spinel occur in small interstitial patches containing feldspar Clinopyroxene II is Al-poor (0 018-0 070 a pfu, #mg 0 921-0 932) when coexisting with alkali feldspar, but Al-rich (0 046-0 261 a pfu, #mg 0907-0.925) when found with plagioclase. Four types of REE (rare earth elements) patterns are found in the chnopyroxene. (group A) flat HREE (heavy REE) with LREE (light REE) content increasing smoothly: (group B) flat HREE with an abrupt increase of MREE (medium REE) and LREE; (group C) LREE-enriched, flat HREE with negative inflection at MREE, (group D) smoothly LREE-enriched with no flat HREE pattern. The exception is chnopyroxene from xenolith MM30 which is extremely depleted in LREE. Chnopyroxene I from all the xenoliths (excluding MM30) contains high amounts of Th and U Chnopyroxene trace element compositions record 8-15% of partial melting Major and trace element compositions of minerals record later cryptic metasomatism induced by a CO(2)-bearing alkaline melt. Variable REE patterns for chnopyroxene I from groups A, 13 and C are due to chromatographic enrichment, with group A peridotites located close to the metasomatic source and group C being the furthest The pargasite-bearing MM04 was probably the closest to the metasomatic source and thus recorded incipient modal metasomatism. Chnopyroxene-spinel symplectites and ortho-/chnopyroxene exsolutions suggest that the peridotites were transported from the garnet-lherzolite facies into the spinel one where they cooled and equilibrated at 960-1000 degrees C The patches formed by the second generation of minerals are the effect of pre-eruption infiltration by the basanitic melt. (C) 2010 Elsevier B V All rights reserved