Isotope- geochemical systematics (Sm-Nd, Lu-Hf) of Neoarchean subalkaline and alkaline rocks of the Keivy structure (Kala Peninsula): their age and genetic relations

Vetrin V. R.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2018. V. 147. N 4. P. 1-13

https://doi.org/10.30695/zrmo/2018.1474.00

Full text is available on eLIBRARY.RU

Language: Russian

Abstract

The Neoarchaean subalkaline magmatism of Keivy structure is expressed in formation of volkano-plutonic association of latite-monzonite-granite (ALMG).The formation of ALMG magmas is assumed to appear due to the melting of metasomatically altered rocks of the basic composition during intrusion of basaltic melts initial for the rocks of the dike complex and the gabbro-labradorite massifs into the lower crust. The alkaline granites associating with ALMG have a close U-Pb age, but the later formation time according to geological data. Relative to ALMG, alkali granites have increased concentrations of SiO₂, alkalis (K₂O/Na₂O = 1.1—1.4), iron (F = 84—98 %), high agpaitic index (K_agp = 0.86—1.2) and the lower quantities of TiO₂, MgO, Fe_tot, Al₂O₃, which was conditioned probably by the higher degree of differentiation of their initial melts, as compared to ALMG.

Key words: latite-monzonite-granite association, subalkaline magmatism, isotope age data, melting, degree of differentiation, Keivy structure.