Back to contents
GEOCHRONOLOGY OF THE PRECAMBRIAN OF THE UKRAINIAN SHIELD ON DATA OF THE REFERENCE ISOTOPE DATING
N.P. Shcherbak1, G.V. Artemenko1, A.N. Ponomarenko1, V.M. Skobelev1 and L.M. Stepanyuk2
1. Institute of Geochemistry, Mineralogy and Ore-formation National Academy of Science of Ukraine, Palladin prospect 34, 03680 Kiev, Ukraine
e-mail: igmof@mail.kar.net
2. Ukrainian State Geological Research Institute, Autozavodska Str., 78, 04114, Kyiv, Ukraine
e-mail: ukrdgri@geologiya.com.ua

 There are five main geocronological units in the Precambrian history of the Ukrainian Shield: the Paleoarchean, the Mesoarchean, the Neoarchean, and the Paleoproterozoic (the last unit is subdivided into two sub-units: the Paleoproterozoic-I, and the Paleoproterozoic-II). These units were determined on the base of the reference isotope data determined on zircon in volcanic rocks, granitoids, and metasedimentary rocks.

The Paleoarchean (3.65-3.2 Ga) is represented by rocks of the Western-Azov, the Auly, the Dniester-Bug groups (series) of metamorphic rocks; the Novopavlivka and Gayvorone granitoid complexes. The low age limit of the Paleoarchean was determined on the magmatic formations of ultramafic-mafic-thonalite rock association of the Novopavlivka complex, and the high one – on enderbites of the Gayvorone and Novopavlivka complexes. The poor iron-ore mineralization of vague genesis is correlated with the Paleoarchean formations. Thus, The Paleoarchean formation are identified and dated with certainty in the Dniester-Bug and Azov megablocks.

The Mesoarchean (3.2-2.8 Ga). The typical volcanic-plutonic rock assemblages of the greenstone belts are generated during the Mesoarchean. At least three volcanic-plutonic rock assemblages are characterized by isotope age data into the Middle Dnieper megablock, as follows: 1) metadacite of the Sura series (3.17 Ga) – thonalite of the Sura complex of the 1st phase (3.17 Ga); 2) metarhyolite of the Chartomlyk suite (3.14 Ga) – thonalite of the Sura complex of the 2nd phase (3.14 Ga); and 3) metarhyolite of the Solenivka suite (3.08 Ga) – thonalite of the Sura complex of the 3rd phase (3.05 Ga).

Into the basement of the greenstone structures the differentiated intrusions of the Sophyivka and Alexandrivka complexes were generated synchronously to the volcanic-plutonic rock assemblages.

The Neoarchean (2.8-2.6 Ga) is represented by rocks of the Ros’-Tickich and Bug series. The low age limit of the Bug series is determined on clastogene zircon, and the upper age limit of the Ros’-Tickich series – on zircon of granitoids. Maybe some craton-like structures of the Azov geoblock belong to the same age epoch (such as the Gulyay Pole structure). A lot of granitoid complexes are characteristic for the Neoarchean.

They are post-tectonic for the proto-platform geoblocks (the Dniester-Bug and Middle Dnieper), and syn-tectonic for the Ros’-Ticckich geoblock.

The formation of the large depressions crowded with metamorphosed volcanogenic-sedimentary rocks is characteristic to the Paleoproterozoic-I (2.6-2.0 Ga). It is the formations of the Kriviy Rig-Kremenchuk, Ingul-Ingulets and Teterev geostructures. The rock complexes are represented by clastogene sedimentary formations mainly (the Kriviy Rig, Teteriv and Ingul-Ingulets series); the role of volcanic rocks is moderate there.

The radioactive accessory minerals were found in clastogene rocks of the Skelevatka suite of the Kriviy Rig series. These rocks are products of denudation of the greenstone rock formation. Their ages are 2.8-3.0 Ga.

The age of felsic volcanic rocks of the Teterev series is 2.43 Ga. The beginning of forming of these depressions is estimated 2.4-2.6 Ga. The ages of syntectonic anatectic granits (the Zhitomir, Kirovograd and other complexes) are the high limit of evolution of these depression structures (2.08 Ga). Thus, their evolution was last during 500 Ma. Based on geophysical data, the large sinking of the Moho surface, and thickening of the Earth crust, are connected with formation of these structures.

The genesis of two volcanic-plutonic assemblages of the Volin’ geoblock (the Klesiv-Osnitsk (2.02-1.97 Ga) and Ovruch-Volcha-Korosten’(1.80-1.74 Ga)) correspond to the Paleoproterozoic-II (2.0-1.6 Ga). The sub-platform sedimentary rocks of the Tolckachy suite of the Ovruch series (1.74-1.6 Ga) are the latter Precambrian formation in the Ukrainian Shield.

Thus, subdivisions of the Archean of the Ukrainian Shield correspond to geochronological units of the International Scale of the Geological Time (the upper limits are for the Paleoarchean, 3.2 Ga; the Mesoarchean, 2.8 Ga and the Neoarchean, 2.5 Ga). The Meso- and Neoproterozoic formations are not discovered on the area of the Ukrainian Shield. Two sub-units (the Paleoproterozoic-I and the Paleoproterozoic-II) are distinguished in the Paleoproterozoic unit (2.5-2.0 Ga, and 2.0-1.6 Ga).
Metallogeny of Precambrian Shields. International Symposium. Kyiv, Ukraine, September 13-26, 2002. Abstracts.
© 2002 N.P. Shcherbak, G.V. Artemenko, A.N. Ponomarenko, V.M. Skobelev, L.M. Stepanyuk
© 2002 Ukrainian State Geological Survey
© 2002 Ukrainian State Geological Research Institute