2013

Abstracts Travel
Program Organizing committee

 Mafic-ultramafic and syenite-carbonatite association of the Ilmeny Mountains, South Urals: Geochemical peculiarities and age

 E.V. Medvedeva1, P.M. Valizer1, A.A. Krasnobaev2, A.I. Rusin2, N.N. Baneva2

 1 Ilmensky State reserve of UB RAS Miass, Russia

2 Zavaritsky Institute of geology and geochemistry UB RAS Ekateriburg, Russia

 

The Ilmeny-Vishnevorogsk complex, South Urals, is one of the largest alkaline complexes. The Ilmeny (southern) and Vishnevogorsk (northern) segments are shifted for more than 100 km along the longitudinal shear zone, which is marked by the narrow milonitized miaskites and pyroxene syenites. The mafic-ultramafic and syenite-carbonatite rocks are major associations of the complex.

The mafic-ultramafic association (Nb/Ta = 16, Zr/Hf = 43, U/Th = 16, Sm/Nd = 0.09970.2071) is characterized by increased Rb, Ba, K, Nb, La and Ce and decreased Ti, V, Ni and Cr contents relative to the primitive mantle. The Nd and Sr isotopic compositions relate these rocks to the EM1 and EM2 mantle types (Rusin et al., 2010).

The REE contents in syenite-carbonatite association increase from syenites to carbonatites. The ratios of indicative elements widely vary in these rocks: from 4.6 (pyroxene syenite), 8.41 (miaskite) to 12.31310 (carbonatite) for Nb/Ta and from 0.068780.09232 (miaskite) to 0.061860.09476 (carbonatite) for Sm/Nd. The Nd and Sr isotopic components indicate EM1 mantle reservoir (Nedosekova et al., 2009).

The U/Pb SHRIMP age of zircons was identified for the reviewed rocks. Three clusters are characteristic of mafic rocks: 5278.5 to 52619 Ma, 4358.5 to 4447.3 Ma, and 30110 to 2795.0 Ma. The following ages are typical of the rocks of the syenite-carbonatite association: (i) 4197 Ma and 2785 Ma for malignite, (ii) 4175.2, 38314, and 27910 Ma for amphibole miaskite, and (iii) 41920, 33615, and 2827.4 Ma for carbonatite.

The continental rifting (Late CambrianEarly Ordovician) was characterized by origination of the magmatic reservoir, following melt differentiation, and separation of syenite-carbonatite melt from the alkaline-ultramafic association and further (in Middle Silurian) of the miaskite melt. The Carboniferous and Permian ages are related to the collision events and postcollision shear deformations.

 

Nedosekova I.L., Vladykin N.V., Pribavkin S.V., Bayanova T.B. The IlmenskyVishnevogorsky MiaskiteCarbonatite Complex, the Urals, Russia: Origin, Ore Resource Potential, and Sources. Geol Ore Dep 51(2): 139161 (2009).

Rusin A.I., Krasnobaev A.A., Medvedeva E.V., Baneva N.N., Valizer P.M. Grospydite level of the parental melts of the Ilmeny alkaline-ultramafic association, South Urals. In: Geochemistry of Alkaline rocks. Abstracts of XXVII International conference Moscow-Koktebel, p. 150-152 (2010).