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| Titel |
Alkaline and carbonatite metasomatism of lithospheric mantle beneath SW Poland- Pilchowice case |
| VerfasserIn |
Mateusz Ćwiek, Magdalena Matusiak-Małek, Jacek Puziewicz, Theodoros Ntaflos |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250086772
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| Publikation (Nr.) |
 EGU/EGU2014-697.pdf |
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| Zusammenfassung |
| The Cenozoic basanites from Pilchowice (SW Poland) form volcanic plug located exactly at Intra- Sudetic Fault. These basanites belong to the Polish part of the Central European Volcanic Province and contain numerous, usually small (<10 cm) peridotitic mantle xenoliths.
Their protogranular texture (olivine up to 8 mm, common kink bands) is obliterated by
intense fissuring and fragmentation of the grains. The peridotites have harzburgitic composition (Ol 87- 86%, Opx 13- 9%, Cpx 3-0%, Spl 8-0%). Fragmentated and sometimes serpentinized olivines (Fo 90.2- 91.5) contains 0.35- 0.45 wt. % NiO. The orthopyroxene Al content varies from 0.02 to 0.12 atoms pfu and mg# from 0.915- 0.920 . One xenolith contains clinopyroxene with abundant spongy rims. Primary clinopyroxene is very rare and Al-enriched (mg# 0.92, 0.17 atoms of Al pfu). The spinel is Cr enriched (cr# 0.46-0.68) and is usually associated with clinopyroxene.
Orthopyroxene is depleted in REE compared to primitive mantle. Orthopyroxene from majority of xenoliths are strongly LREE depleted ((La/Lu)N = 0.03-0.21).
All studied peridotites contain clinopyroxene which is enriched (2 to 70 times) in REE compared to primitive mantle. Clinopyroxene patterns show relative low HREE concentration ((La/Lu)N = 4.75- 19.99), moreover patterns from three samples are convex- upward shaped with inflection point on Nd ((La/Nd)N = 0.36-0.96).
Clinopyroxene- poor lithology, high cr# in spinel and LREE- depleted nature of orthopyroxene suggest that upper mantle sampled by Pilchowice basanite is a restite after partial melting. The LREE enriched composition of clinopyroxene suggest that peridotites were metasomatised. Clinopyroxene convex- upward shaped REE plots with inflection point on Nd is typical for metasomatism related with alkaline melt. On the other hand very low ratios of Ti/ Eu (24.8- 738.9) and high (La/ Yb)N (3.5- 17) ratio (Coltorti, 1999) suggest that the metasomatic agent was either a mixture of alkaline silicate melt with carbonatite or peridotite reaction with two independent agents is recorded.
This study is a part of MSc thesis of the first author and was possible thanks to the project NCN 2011/03/B/ST10/06248 of Polish National Centre for Science.
Coltorti, M., Bonadiman, C., Hinton, R. W., Siena, F. & Upton, B. G. J. (1999). Carbonatite metasomatism of the oceanic upper mantle: Evidence from clinopyroxenes and glasses in ultramafic xenoliths of Grande Comore, Indian Ocean. Journal of Petrology 40, 133-165. |
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