2011

Тезисы международной конференции

Рудный потенциал щелочного, кимберлитового

 и карбонатитового магматизма

Abstracts of International conference

Ore potential of alkaline, kimberlite

and carbonatite magmatism

Geochemical peculiarities of alkaline rocks of the Ukrainian Shield as indicator of geodynamic conditions of its formation

Parfenova A.Y., Senkevich A.Y.

N.P. Semenenko Institute of geochemistry, mineralogy and ore formation NAS of Ukraine, Kyiv, Ukraine

Ukrainian State Geologycal Research Institute, Kyiv, Ukraine

parfenova_a@ukr.net

Two main province of alkaline magmatism (Azov Eastern and Western) are known within the Ukrainian Shield (USh). In Azov area the alkaline rocks are enough various in composition and age (2.1-2.0; 1.8 and 0.4 Ga)  whereas in Western are known only Proterozoic (2.0 and 1.8 Ga) ones. In last province among well-known massifs and small occurrences of alkaline rocks (Proskurovka, Antonovka, Gorodnica, Glumcha, Bol’arka and other) are prevail their alkaline-ultrabasic varieties with subordinate development of alkaline and nepheline syenites. At the same time in Azov province are known predominantly massifs with nepheline, alkaline and subalkaline syenites (Oktyabrsky, South-Kalchyk, Mala-Tersa and other) and only one alkaline ultrabasic with carbonatites complex (Chernigovka or Novo-Poltavka) is known, tough in this region were reveled another small occurrences of carbonatite comlex at the last time.

If alkaline rocks of Azov province have typical for these type such geochemical peculiarities as high or increased Nb, Zr, REE and Sr content whereas some named rocks of Western province are anomaly in this regard. Especially low Zr, Nb contents are in alkaline rocks of this province, and separately in Gorodnica, Glumcha and Bol’arka occurrences REE concentrations are low too. At the same time these rocks are characterized by high Cr content and presences of chrome spinelids (including  their deep-derived varieties with high Cr and Mg).

In previous papers (Tsymbal et al., 1997; Kryvdik et al., 2005) the assumption about generation of these rocks at low partial melting of mantle material with negligible mantle metasomatosis or  of its absence (low contents Nb, Zr, REE were explained by this factors).

As alternative explanations of such anomaly can be formation of the alkaline rocks in Western province at the pressing conditions of Earth’s crust. There are  three suture zones (KryvoyRog-Kremenchuk, Golovaniv, Kocherov-Nemirov) and Osnitsk-Mikashevichy volcanic-plutonic belt in this area. The rocks of the last (low-Ti gabbros, diorites, granodiorites) are very similar to basalts, andesites and dacites in modern arc islands. On the diagram Zr-Nb (Thompson, Fowler, 1986) the alkaline rocks of Western province lie in “subduction” field while the alkaline rocks of Azov area are in riftgene one.