Ukrainian Crystalline Shield
Ukrainian Crystalline Shield (aka the Ukrainian Massif or Azov-Podolian Shield). An uplifted block of outcropping crystalline rocks of the Precambrian age running through the central reaches of Ukraine mainly on the right bank of the Dnipro River. It originally made up the southwestern portion of the Fennosarmatian paleocontinent and is now tilted toward the west. It extends in the form of a boomerang for some 1,000 km from the Horyn River in the northwest to the Sea of Azov in the southeast and covers an area of about 200,000 sq km. Within the shield area the crystalline rocks outcrop in deeply incised river valleys (such as the Dnipro Valley between Dnipro and Zaporizhia) in the form of picturesque cliffs and rapids. To the northwest the Ukrainian Crystalline Shield dips under the Hercynian structures of the Dnipro-Donets Trough (including the Donets Basin), without apparently being involved in their late Paleozoic structural deformation, and connects in the subsurface to the Voronezh Massif north of Vovcha and the iron-ore district of Belgorod. Elsewhere it dips under Alpine folded structures of late Mesozoic and early Cenozoic, in the Caucasus Mountains to the east, the Crimean Mountains to the south, and the Carpathian Mountains to the west.
The Ukrainian Crystalline Shield is made up of a folded basement broken up by deep meridional faults into a series of blocks: Volhynia-Podilia, Bila Tserkva–Odesa, Kropyvnytskyi, and Dnipro-Azov. The shield is divided into an older Archean and a younger Proterozoic series of igneous and metamorphic rocks.
The Archean is represented predominantly by gneisses, granites, and green schists that are 3,500 to 1,900 million years old. A lower suite, the Dnipro River series, 3,500 to 2,700 million years old, contains various gneisses (see Gneiss) and amphibolites and is intruded by pegmatites and aplites associated with migmatites. An upper suite, 2,700 to 1,900 million years old, consists of paragneisses, biotite, sillimanite and graphite schists, quartzites, marbles, and amphibolites intruded by monzonites, diorites, and either charnockitic or microcline-bearing granites. The degree of deformation increases to the southwest. Both the lithologic composition and the grade of metamorphism are distinctly different from rocks of the Lower Proterozoic and their precise subdivision is not generally accepted.
Wedged into the Archean and separated from it by angular unconformity are tight, long, narrow folds of Lower Proterozoic rocks (1,900–1,600 million years old) of a lower grade of metamorphism. Basal arkosic and conglomeratic sandstones are overlain first by phyllites and quartzose schists, then by talcose and actinolitic schists, and finally by ferruginous hornstones and jaspilites. The jaspilitic iron ores (banded iron formation) of the Kryvyi Rih series, composed of alternating laminae of chert and hematite, extend north to include the iron ores of Kremenchuk. Owing to intensive folding the ore-bearing sequence is never less than 50 m thick, and often exceeds 1,000 m.
The sequence is surrounded by Middle Proterozoic (1,600–1,300 million years ago) metamorphosed sediments and volcanics and is cut by postorogenic Rapakivi granites in plutons at Korosten, Korsun, and Novomyrhorod as well as an Sea of Azov complex of alkaline gabbros. They are covered by chloritic, carbonaceous, and quartz-mica schists with intercalations of dolomitic marble. The highest beds are quartzose schists.
The Upper Proterozoic (1,100–570 million years ago) is represented by the Ovruch series of quartzites, schists, and quartz porphyries as well as by muddy sandstones and volcanics. A sharp unconformity separates it from a thin covering of younger sedimentary rocks (Paleogene, Neogene, and Quaternary) that include the Dnipro Lignite Coal Basin and the Nikopol Manganese Basin.
BIBLIOGRAPHY
Bezborod'ko, M. Ukraïns'ka krystalichna smuha (Kyiv 1935)
Luchyts'kyi, V.; et al. Ukraïns'kyi krystalichnyi masyv (Kyiv 1947)
Platformennye struktury obramleniia Ukrainskogo shchita i ikh metallonosnost' (Kyiv 1972)
Peter Sonnenfeld
[This article originally appeared in the Encyclopedia of Ukraine, vol. 5 (1993).]