Geophysical Journal | 2014 volume 36 2

On the age of white anorthosite of the Novomirgorod massif of the Korsun-Novomirgorod pluton (the Ukrainian Shield)

© E.E. Shestopalova, L.M. Stepanyuk, T.I. Dovbush, A.V. Kovtun, 2014

Xenolites of white anorthosites have been found in anorthosites of the main phase of the Novomirgorod massif of the Korsun-Novomirgorod pluton (the Ukrainian Shield, the Ingul megablock). The age of white anorthosite has been determined by classical uranium-lead method by zircon. Isotopic study of zircon showed considerable dispersion of values that is possibly caused by heterogeneous internal structure zircon crystals and different combination of generations of different ages. The most ancient, practically concordant age has been obtained for two fractions of light rosy zircon (1796-1806 b. y). that is considerably older than the age of zircon from enclosing anorthosites (1750,2 b. y.) and in our opinion characterizes the age of anorthosite. There are several assumptions as to the origin of xenolites of white anorthosites. They can be the earlier phase of basic rocks of the pluton; a fragment of substance of the lower crust transported from the depth and changed by superposed metasomatic and hydrothermal processes, leucocrate variety of "ancient" anorthosite of AMCHG association, represented by white bronsite anorthosites in the Korosten pluton.

Key words: anorthosite, xenolith, zircon, isotopic dating, uranium-lead geochronology method.

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