HR: 1400h
AN: V53B-05    [Abstracts]
TI: Periodical and Spatial Compositional Variations for Flood-basalts of the Siberian Platform
AU: * Sharapov, V
EM: vik@uiggm.nsc.ru
AF: Novosibirsk State Univeristy, 2 Pyrogova Street, Novosibirsk, 630090, Russian Federation
AU: * Sharapov, V
EM: vik@uiggm.nsc.ru
AF: Institute of Geology and Mineralogy, 3 Koptyug Pr., Novosibirsk, 630090, Russian Federation
AU: Rakhmenkulova, I
EM: iraida0205@yahoo.com
AF: Novosibirsk State Univeristy, 2 Pyrogova Street, Novosibirsk, 630090, Russian Federation
AU: Rakhmenkulova, I
EM: iraida0205@yahoo.com
AF: Institute of Geology and Mineralogy, 3 Koptyug Pr., Novosibirsk, 630090, Russian Federation
AU: Perepechko, Y
AF: Institute of Geology and Mineralogy, 3 Koptyug Pr., Novosibirsk, 630090, Russian Federation
AB: Flood-basalts of the Siberian Platform (SP) have a typical spatial trend: the content of MgO decreases from north to south, while TiO₂ and K₂O contents increase. 'Explosivity' coefficient increases in the same direction (from ~ 11-14% to more then 50%). Volcanism of the northwestern and northern SP parts has two stages; the rest has only one stage. These stages of magma evolution can be distinguished based on lava content fluctuation, when geochemical melts changed from contaminated (at the beginning) to non-contaminated (in the end). The most complete effusive profile for the Norilsk region has the following quantitative rock content: picritoids - slightly more then 10%, trachybasalts - less then 10%, low-potassium tholeiites - more then 65%, tholeiites of high K₂O content - less then 15%. Spectral amplitude for content variations attenuates by the end of time series and functions look like 'white noise'. The 'total' linear trend for the following components is negative: SiO₂, Al₂O₃, MgO, Na₂O, K₂O, P₂O₅; TiO₂, FeO* have a positive trend. Flood-basalt profile for the Putorana Plateau (Lama Lake) is typically monotonous; most petrogenic components are characterized by 'white noise' functions; only TiO₂ and MgO have little correlation coefficients (0.29) for the first logs. Distribution functions are low-coherent for practically all the components. The local linear trend of distribution functions is close to ones of the Kharaelakhskaya syncline of the Norilsk region. Frequency spectra of 26 elements of the borehole profile SG-19 for the Kharaelakhskaya syncline (ARIMA method) for 4 main peaks show that both petrogenic and trace elements have both similar and greatly varying maximum content frequencies. It is important to note, that trace elements have maximums both for high-frequency and low frequency parts of time series spectra, while petrogenic components do not have these peaks. The 'extractants' of non-volatile components (boron and fluorine) have spectral frequency characteristics close to both petrogenic and ore elements. Most petrologists suggest that the above-mentioned lava profiles of both contaminated and non-contaminated melting of primary magmas resulted from two different mantle sources. Periodicity of local distribution functions of lava compositions shows that those different-level magma sources existed simultaneously. However, the composition of the lithospheric mantle substrates for different SP parts varied greatly (well-known data of lava geochemistry for the Norilsk, Maymecha-Kotuy and Putorana provinces). We constructed a numerical model for two-level melting zone above hotspots. Compositions for basic melts and the depth for the upper melt level in the lithosphere mantle above an 'asthenolens' depends on the thickness of the earth crust, the thinness of the lithosphere and the degree of its metasomatic change. This model allows us to explain evolutionary trends and variations for lava compositions of various petrochemical SP provinces, - the upper melting boundary can vary from about 70 to 120 km from the earth's surface (depending on the initial conditions); virtual dimensions of the melting zone are close to the lava shield size. However, there is no periodical eruption model for this magma system so far. This work was supported by the Russian Foundation for Basic Research (Grants: #04-05-64107; #040-05- 64322) and by the Russian Ministry for Science and Education (Grant #DSP.2.1.1.702).
DE: 1038 Mantle processes (3621)
DE: 8400 VOLCANOLOGY
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly