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| Titel |
Petrology and Geochemistry of mantle xenoliths from Margasan, Baikal Lake region (Russia) Preliminary results |
| VerfasserIn |
Elijah Dippenaar, Theodoros Ntaflos, Igor Ashchepkov |
| 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 |
250096274
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| Publikation (Nr.) |
 EGU/EGU2014-11770.pdf |
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| Zusammenfassung |
| Off-cratonic mantle xenoliths collected from the Margasan volcanic field in eastern Siberia (Russia) were analysed to characterize their mineralogical composition, their petrological and geochemical properties. The xenoliths are spinel bearing lherzolithe and have been transported to the surface by alkali basalts.
The studied samples are fertile lherzolithes with modal compositions as follows: Forsterite 56% - 78%, orthopyroxene 35% - 16%, clinopyroxene 6% - 20% and spinel 0% - 4.5%. The majority of the samples have textures ranging from protogranular to equigranular. Some of the samples with equigranular texture show characteristic foliation suggesting deformation in the depths. Frequently, olivine grains show kink-bands. The clinopyroxenes show characteristic spongy rims with variable width as a consequence of interaction with interganulate circulating melts/fluids. Alternatively they could be formed en route to the surface due to pressure decrease. Microprobe analyses have shown that Forstertite (Fo) contents in olivine vary from 89 to 90. The mg#*100 in orthopyroxene and clinopyroxene ranges from 90 to 90.5 and 89 to 91 respectively. Spinels are Al2O3-rich with 100*cr# ranging from 9 to 17. The TiO2, Cr2O3 and Na2O contents in clinopyroxene vary from 0.4% to 0.7%, 0.6% to 1.1% and 0.6 to 2.1 respectively. The clinopyroxene spongy rims consist of glass and second generation clinopyroxene, which differs from the primary clinopyroxenes in that the TiO2, Al2O3 and Na2O contents are lower than in the primary clinopyroxenes. According to the model of batch melting the studied xenoliths indicate that they are the residues after 1.5% to 7% partial melting. The calculated equilibrium temperature at a pressure of 15kbar ranges from 940°C to 1120°C, indicating that xenoliths have been sampled from different depths. |
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