Geophysical Journal | 2016 volume 38 6

Evolution of melts and fluids during the crust and mantle formation in Neo-Archean-Paleo-Proterozoic. Stratigraphic effects

© O.V. Usenko, 2016

Evolution of composition of Precambrian magmatic and metamorphic rocks is related to directional change of deep fluids. It makes possible to use material composition of rocks as a sign for correlation. The paper presents a comparison of material composition of metamorphic complexes of the Ukrainian shield formed in Neo-Archean-Paleo-Proterozoic (after 2.8 and before 2.2 Ga ago). They were formed in the process of activation which consisted of two tectonic-magmatic cycles. The first one occurred in the central and western parts of the shield.
  Formation of magmatic and exhalation-sedimentary strata on the blocks took place with participation of deep chlorine-agueous fluids with potassium and alumina. On the surface the rocks are widely presented, which were formed of melts and fluids differentiated at a depth ~100 km. During the second tectonic-magmatic cycle (on the border of Neo-Archean and Paleo-Proterozoic) separation of the Ukrainian shield into blocks and suture zones took place, which differ by composition of accumulated strata and positions of material sources. On the blocks the composition of fluids and the course of geodynamic process did not change.
  Within suture zones, formed during the second tectonomagmatic cycle unloading of deep melts and fluids happened. In the layer of melting with its upper border situated under the crust oxidation- reduction reactions occurred with participation of at low figure fluoride-carbonate-sodium fluids. It brought about the separation of more oxidized aqueous-chloride fluid enriched by iron, into self- contained phase, and to formation of productive ferruginous layers on the surface.

Key words: the Ukrainian shield, Paleo-Proterozoic, fluid, evolution, magmatism, stratigraphy, asthenosphere, lithosphere.