Тезисы международной конференции

Рудный потенциал щелочного, кимберлитового

 и карбонатитового магматизма

Abstracts of International conference

Ore potential of alkaline, kimberlite

and carbonatite magmatism

Some features of alkaline magmatism of the East Antarctic (Jetty Oasis)

Sushchevskaya N.M.*, Belyatsky B.V.**, Kuzmin D.V.***, Krymsky R.Sh.****

^*Vernadsky Institute of Geochemistry (GEOKHI RAS), Moscow, Russia,

^**VNIIOkeangeologia, S.Petersburg, Russia,

^***М.Planck Institut fur Chemistry (MPI), Mainz, Germany,

^****CIR VSEGEI, S.Petersburg, Russia

nadsus@geokhi.ru

High-K picrites, connected with Kerguelen plume, have been discovered within the East Antarctic Shield. At the starting stage of Kerguelen plume functioning and its further evolution at about 130 Ma there could take place the intrusion of alkaline-ultrabasic dykes and sills in the area of Jetty oasis located in front of Kerguelen Islands [Foley et al., 2001; 2006]. Intermittent chain of six stock bodies of Jurassic-Cretaceous ages stretched for about 30 km along the eastern coast of Beaver Lake showing their connection with the sub-meridian zone of deep fracture system which mark the eastern margin of Beaver Lake graben.

Studying alkaline-ultrabasic magmatism of Jetty Oasis we have examined about 700 olivines extracted from both alkaline picrite basalts and mantle inclusions in them. The analysed olivines from South and North bodies, lamprophyre dykes close to Beaver Lake and also biotite picrite from Meredith Massif located in 100 km to the south from Jetty Oasis demonstrate very complicated character of variation in olivine composition with wide dispersion in magnesium number (Fo from 75 to 91). There is very wide dispersion of Ni and Mn concentrations in olivines with similar magnesium number which evidence to considerable heterogeneity of the melting source. The share of pyroxenite component in the melting source, calculated by Ni and Mn concentrations [Sobolev et al. 2007] in liquidus olivines, makes in average 60–80%. Preliminary analysis of Pb, Sr and Nd isotope compositions in alkaline picrites has demonstrated that in general these rocks by their isotope characteristics are close to isotope composition of Mesozoic basalts from Shirmacher Oasis and Queen Maud Land, basalts from Kerguelen plateau yielding the age of 110 Ma and also to the basalts of plagioclase-porphyry series of the old Afanasii Nikitin Rise in the Indian Ocean. Similar to the basalts of Queen Maud Land they are characterized by radiogenic lead composition (for example, ²⁰⁸Pb/²⁰⁴Pb ratio reaches 39.5). Continental origin of alkaline-ultrabasic complex of Jetty Oasis is also observed on the diagram of initial isotope composition ε¹⁴³Nd/¹⁴⁴Nd – ⁸⁷Sr/⁸⁶Sr where is traced the trend from weakly depleted to enriched types within which the alkaline magmas and mantle xenoliths are plotted.

So, it is possible to make a preliminary conclusion that alkaline-ultrabasic magmatism of Jetty Oasis is connected geochemically with the enriched component developed in the basalts of Karoo–Maud plume and Kerguelen Archipelago. This could reflect the long life of Karoo–Maud plume which had started at about 180 Ma and also its further expansion to the East along the collision zones of the Eastern Antarctic towards Jetty Oasis (130–110 Ma) and further into the Indian Ocean where it started functioning as Kerguelen plume (110 Ma till nowadays). Spreading of plume substance along the weakened zones reflects the possibility of deep flows – plume motions, which take place at different lithosphere layers and under-lithospheric mantle. The possibility of global plume existence and their ability to horizontal motion is proved by digital modeling [Burov et al., 2007].

The study is carried out under financial support of RFBR grant N 12-05-258

Fig.1. Variation of isotope ratios in lamproites and mantle inclusions from them (Jetty region), alkaline basalts of Shirmacher Oasis [Sushchevskaya et al. 2011]. The results are recalculated to the age of their intrusion.

Refernces:

Burov E., Guillou-Frottier L.,. d'Acremont E. et al. Plume head – lithosphere interactions near intra-continental plate bounadries. Tectonophysics. 2007. V.434. No.1-4. P. 15-38.

Foley S.F., Andronikov A.V., Melzer S. Petrology of ultramafic lamprophyres from the Beaver Lake area of Eastern Antarctica and their relation to the breakup of Gondwanaland. Mineralogy and Petrology. 2001. V.74. P. 361-384.

Foley S.F., Andronikov A.V., Jacob D.E., Melzer S. Evidence from Antarctic mantle peridotite xenoliths for changes in mineralogy, geochemistry and geothermal gradients beneath a developing rift. Geochemical et Cosmochemical Acta. 2006. V.70. P. 3096-3120.

Sobolev A.V., Hofmann A.W., Kuzmin D.V. et al. The amount of recycled crust in sources of mantle-derived melts. Science. 2007. V.316. P. 412-417.

Sushchevskaya N.M., Belyatsky B.V., Laiba A.V. Origin, distribubution and evolution of plume magmatism in East Antarctica. In: Volcanology (ed. F.Stoppa). INTECH, Rijeka, Croatia. 2011. P. 3-29. ISBN: 978-953-307-434-4.