The Inhul megablock is one of the largest struc­tur­al ele­ments of the Ukrain­ian Shield, occu­py­ing a sig­nif­i­cant part of cen­tral Ukraine. Its geo­log­i­cal struc­ture reflects a com­plex his­to­ry of crustal for­ma­tion span­ning more than 3 bil­lion years.

With­in this megablock, numer­ous fold­ed and meta­mor­phic com­plex­es, intru­sive mas­sifs, deep fault sys­tems, and ore-bear­ing struc­tures are con­cen­trat­ed. Its study is of key impor­tance for under­stand­ing the tec­ton­ic evo­lu­tion of the Ukrain­ian Shield, as well as for assess­ing the min­er­al resource poten­tial of the region.

The Inhul megablock is locat­ed in the cen­tral part of the Ukrain­ian Shield. To the west, it bor­ders the Holo­vanivsk suture zone, while to the east it adjoins the Mid­dle Dnipro megablock. Its bound­aries are defined by the Yadlovo–Trakhtemyriv, Per­vo­maisk, and West Inhulets fault sys­tems, as well as by mar­gin­al fault zones. The Earth’s crust here is 35–40 km thick and belongs to the sial­ic type. The struc­tur­al fea­tures of the megablock are com­mon­ly explained by the mod­el of the Kirovohrad man­tle diapir.

The cen­tral part of the megablock is occu­pied by the Korsun–Novomyrhorod plu­ton. The east­ern part is rep­re­sent­ed by the Inhulo–Inhulets Syn­cli­no­ri­um, while the south­west­ern part is occu­pied by the Bratske syn­cli­no­ri­um. Archean for­ma­tions occur main­ly as dome-shaped struc­tures, where­as Pale­o­pro­tero­zoic rocks form lin­ear gneis­sic folds.

The south­ern part of the megablock includes the Dniester–Bug series, com­posed of pyrox­ene and amphibole–pyroxene schists and gneiss­es enclosed with­in pla­giogran­ites. Rocks of the Kon­ka series, relat­ed to deposits of fer­rug­i­nous quartzites, belong to the Mesoarchean.

The Inhulo–Inhulets series com­pris­es supracrustal for­ma­tions of Neoarchean and Pale­o­pro­tero­zoic age. It is best stud­ied in the west­ern part of the megablock and includes:

• Zelenorichyn for­ma­tion — amphi­bo­lites, biotite gneiss­es, and quartzites (up to 200 m thick);
• Artemiv­ka for­ma­tion — silicate–magnetite quartzites and gneiss­es con­tain­ing gar­net and sil­li­man­ite (50–200 m);
• Rodi­on­iv­ka for­ma­tion — quartzites, mar­bles, and graphite–mica schists (550‑1300 m);
• Spa­siv­ka for­ma­tion — gneiss­es con­tain­ing hyper­s­thene, biotite, and amphi­bole (up to 3000 m);
• Cheche­li­iv­ka for­ma­tion — a thick suc­ces­sion of biotite and garnet–biotite gneiss­es exceed­ing 2 km in thick­ness.

With­in the Bratske syn­cli­no­ri­um, the fol­low­ing for­ma­tions are dis­tin­guished:

• Kami­an­no-Kos­to­vats­ka for­ma­tion — gneiss­es and crys­talline schists con­tain­ing pyrox­ene, cordierite, and mag­netite (up to 2 km thick);
• Roshchakhiv­ka for­ma­tion — biotite, garnet–biotite, and lep­titic gneiss­es.

These rock units are fold­ed into iso­cli­nal folds trend­ing north­west. Their geochronol­o­gy is com­plex: the Cheche­li­iv­ka For­ma­tion has an upper age lim­it of ~2100 Ma, while zir­con data indi­cate sig­nif­i­cant­ly old­er source mate­r­i­al. Age deter­mi­na­tions for oth­er for­ma­tions remain con­tro­ver­sial.

The Dnipropetro­vsk com­plex dom­i­nates the struc­ture of the megablock. It con­sists main­ly of pla­giogran­ites, migmatites, and dior­ites with an age of ~3075 Ma. It is accom­pa­nied by less wide­spread rocks of the Tash­lyk com­plex, includ­ing gran­ites and Archean ender­bites.

The Inhulets com­plex is rep­re­sent­ed by pla­giogran­ites, trond­hjemites, and tonalites dat­ed at 3140–2850 Ma. Pale­o­pro­tero­zoic rocks form the Kirovohrad com­plex, which includes the Kirovohrad, Dolyn­s­ka, and Chy­hyryn mas­sifs. Two stages of gran­i­ti­za­tion are rec­og­nized (2100–2020 Ma and 2020–1980 Ma). These process­es are asso­ci­at­ed with min­er­al­iza­tion, includ­ing gold, rare met­als, and ura­ni­um.

The Novoukrain­ka com­plex includes the Novoukrain­ka and Bobrynets mas­sifs. Its rocks are biotite gran­ites, gra­n­odi­or­ites, mon­zonites, and gab­bros, with an age of approx­i­mate­ly ~2020 Ma.

Lat­er evo­lu­tion­ary stages include the for­ma­tion of sod­ic meta­so­matites, the Korsun–Novomyrhorod plu­ton, and dyke swarms. The meta­so­matites formed in fault-relat­ed zones and are asso­ci­at­ed with ura­ni­um and gold min­er­al­iza­tion (1800–1720 Ma).

The Korsun–Novomyrhorod plu­ton is a mul­ti-phase intru­sive body com­posed of rapakivi-type gran­ites, anorthosites, gab­bros, and syen­ites (1750–1720 Ma). It is also asso­ci­at­ed with apatite–titanium ore occur­rences.

Dyke com­plex­es are rep­re­sent­ed by three gen­er­a­tions (1700 Ma, 1445–1260 Ma, and 1215–1125 Ma), con­sist­ing of dia­bas­es, ortho­phyres, and lam­pro­phyres that form region­al dyke swarms.