The Volyn megablock is a geo­log­i­cal struc­ture of the Ukrain­ian Shield. It is bound­ed to the west and north by mar­gin­al fault sys­tems, while its east­ern bound­ary fol­lows the Bru­syliv deep fault, which sep­a­rates it from the Rosyn–Tykych megablock. To the south, it is lim­it­ed by the Teteriv and Andrushiv­ka faults, beyond which lies the Dniester–Bug megablock. This region is char­ac­ter­ized by a rel­a­tive­ly thick crust reach­ing up to ~50 km, pre­dom­i­nant­ly of femic com­po­si­tion. An excep­tion is the Korosten mas­sif, where the crust is thin­ner (about 36 km) and has a more sial­ic char­ac­ter.

In the mod­ern geo­log­i­cal struc­ture of the Ukrain­ian Shield, the west­ern and north­ern bound­aries of the Volyn megablock coin­cide with mar­gin­al faults, while its east­ern bound­ary fol­lows the Bru­syliv deep fault, which sep­a­rates it from the Ros–Tykych megablock. The south­ern bound­ary is formed by the Teteriv and Andrushiv­ka faults, beyond which the Dniester–Bug megablock is locat­ed. The Volyn megablock is char­ac­ter­ized by a rel­a­tive­ly thick con­ti­nen­tal crust—up to 50 km—mainly of femic com­po­si­tion, except for the Korosten mas­sif, where the crust is thin­ner (about 36 km) and of sial­ic type.

The Volyn megablock is main­ly com­posed of Pale­o­pro­tero­zoic for­ma­tions. Archean rocks are rep­re­sent­ed by the Dniester–Bug series, which includes diaftor­ized schists, pyrox­ene and amphibole–pyroxene rocks, as well as pla­giogneiss­es. Archean units are rel­a­tive­ly rare and occur most­ly as xeno­liths with­in intru­sive and ultra­m­eta­mor­phic gran­i­toids. Most region­al­ly meta­mor­phosed rocks belong to the Teteriv and Kle­siv series of the Pale­o­pro­tero­zoic. Local­ly, old­er for­ma­tions such as the Vasylivs­ka suite and the Novohrad-Volyn­s­ka sequence are also present.

The Teteriv series is sub­di­vid­ed into three suites. The low­er (Vasylivs­ka) suite con­sists of biotite gneiss­es and schists con­tain­ing gar­net, sil­li­man­ite, cordierite, and graphite. Sm–Nd dat­ing indi­cates an age of about 2.4 bil­lion years. The mid­dle (Horod­s­ka) suite is com­posed of biotite gneiss­es with graphite inclu­sions (e.g., the Burtinske deposit) and reach­es a thick­ness of about 2000 m. The upper (Kocherivs­ka) suite has a car­bon­ate com­po­si­tion, includ­ing calc-sil­i­cate rocks, mar­bles, and amphibole–diopside gneiss­es, with thick­ness­es up to 6000 m. These rocks formed under amphi­bo­lite-facies region­al meta­mor­phism (560–660 °C, 3–5 kbar) between 2.08 and 1.95 Ga. The Teteriv series forms the Teteriv and Kocheriv syn­clines.

The Novohrad-Volyn­s­ka sequence forms the Novohrad-Volyn­s­ka syn­cline and is com­posed main­ly of vol­canic rocks, includ­ing meta­mor­phosed tuffs, tuffites, dia­bas­es, and andesitic por­phyrites. Zir­con dat­ing indi­cates an age of approx­i­mate­ly 2.43 bil­lion years.

The Kle­sivs­ka series, rep­re­sent­ing the upper part of the stratig­ra­phy, includes kleso­vites, lep­titic gneiss­es, and meta­mor­phosed dia­bas­es and andesites. It formed as a result of high-tem­per­a­ture amphi­bo­lite-facies meta­mor­phism, with an iso­topic age of 2.02–1.97 bil­lion years. It occurs as ero­sion­al rem­nants (inliers) with­in the Osyt­sky gran­i­toids dat­ed at about 1.99 bil­lion years. The thick­ness of the series ranges from 4000 to 5000 meters. The for­ma­tion of the Kle­sivs­ka series is believed to be asso­ci­at­ed with the Ovruch–Mikashevichi volcanic–plutonic belt (Volyno–Polissia belt).

The ultra­m­eta­mor­phic and mag­mat­ic for­ma­tions of the Volyn megablock include the Shereme­tiv, Berdy­chiv, Zhy­to­myr, Buky, Nar­cy­siv, and Pru­tiv com­plex­es of the Kryvyi Rih domain, as well as the Osnyt­sia, Horod­nyt­sia, Kyshyn, Kami­anyi, Korosten, and Perzhany com­plex­es of the Kle­siv domain. Dyke com­plex­es of both the Kle­siv and Ovruch domains are also wide­ly devel­oped.

The old­est for­ma­tions are the pla­giogran­i­toids of the Shereme­tiv com­plex. The Berdy­chiv com­plex formed as a result of gran­i­ti­za­tion of the Dniester–Bug series. Its gar­net-bear­ing rocks have a lim­it­ed spa­tial dis­tri­b­u­tion. The Zhy­to­myr com­plex, formed through ultra­m­eta­mor­phism of the Teteriv series, is typ­i­cal of the Volyn megablock and con­sists of medi­um-grained gran­ites and migmatites with mus­covite, known in the areas of Horod­nyt­sia, Myropil, and south of Zhy­to­myr. Peg­matites, aplite–pegmatites, and quartz veins are com­mon. The iso­topic age of the com­plex is 2.08–2.02 Ga. The Zhy­to­myr gran­ites are asso­ci­at­ed with ore occur­rences of pre­cious met­als, mica, and ceram­ic raw mate­ri­als.

Lat­er, the Buky and Pru­tiv intru­sive com­plex­es were formed. The Buky mas­sif (near the vil­lage of Buky) is a mul­ti­phase gabbro–monzonite com­plex with quartz dior­ites and gra­n­odi­or­ites, with an iso­topic age of about 1.99 Ga. The Pru­tiv com­plex is com­posed main­ly of gab­bros, gab­bro-norites, pyrox­en­ites, and peri­dotites. Togeth­er with coeval dike swarms, these com­plex­es form a Meso­pro­tero­zoic trap asso­ci­a­tion dat­ed at 1.99–1.98 Ga, indi­cat­ing the tec­ton­ic sta­bil­i­ty of the plat­form at that time.

The Osnyt­sia com­plex (1.99 Ga) is rep­re­sent­ed by dior­ites, gra­n­odi­or­ites, and gran­ites formed as a result of the gran­i­ti­za­tion of the Kle­siv series. Recent stud­ies sug­gest the syn­chronic­i­ty of the for­ma­tion of the Osnyt­sia and Zhy­to­myr gran­ites. The close­ly relat­ed Kysyn alkaline–ultrabasic com­plex (1.95 Ga) includes ultra­maf­ic rocks of the Zhdaniv­ka mas­sif, asso­ci­at­ed with meta­so­mat­ic alter­ations and ore occur­rences of pre­cious met­als, cop­per, and ura­ni­um. K–Ar iso­topic dat­ing indi­cates an age of about 1945 Ma for phl­o­go­pite and 1890 Ma for amphi­boles. The Mukhariv and Novohrad-Volyn­skyi mas­sifs are some­times dis­tin­guished as sep­a­rate com­plex­es.

The Kysyn com­plex (1.95 Ga) unites mas­sifs of sub­al­ka­line biotite and biotite–amphibole gran­ites. The Kami­an­ka com­plex con­sists of basic and ultra­ba­sic intru­sions host­ing cop­per, nick­el, and plat­inum min­er­al­iza­tion.

Sed­i­men­ta­ry-relat­ed intru­sive for­ma­tions of the Volyn megablock, belong­ing to the upper parts of the Kle­siv and Ovruch series, formed dur­ing a sub­plat­form stage. Dur­ing this time, an orthog­o­nal sys­tem of graben–syncline struc­tures devel­oped, accom­pa­nied by inten­si­fied mag­mat­ic activ­i­ty, the for­ma­tion of the Korosten plu­ton, the Perzhany meta­so­mat­ic zones, and dyke swarms. This mag­mat­ic activ­i­ty is asso­ci­at­ed with the col­li­sion between the Sar­ma­t­ian and Fennoscan­di­an pro­to-con­ti­nen­tal ter­ranes.

The Ovruch series fills the Ovruch and Vilcha rift-relat­ed depres­sions, over­ly­ing the gran­ites of the Korosten and Zhy­to­myr com­plex­es as well as the gneiss­es of the Teteriv series. Among its sub­di­vi­sions, the Zbrankiv­ka suite (effu­sive rocks, dia­bas­es, schists, and tra­chyan­desites) and the Tovkachiv­ka suite (red quartzites and pyro­phyl­lite schists) are dis­tin­guished, sep­a­rat­ed by a strati­graph­ic uncon­for­mi­ty. Their age ranges from 1770 to 1700 Ma.

The Korosten plu­ton — the cen­tral mas­sif of the Pre­cam­bri­an base­ment of the megablock — was formed in sev­er­al phas­es between 1800 and 1737 Ma and includes anorthosites, rapakivi gran­ites, labradorites, and gran­ite por­phyries. It is asso­ci­at­ed with deposits of piezo­elec­tric quartz, gem­stones, tita­ni­um ores, and apatite–titanium min­er­al­iza­tion. At the end of the Pale­o­pro­tero­zoic, sub­al­ka­line gran­ites and potas­si­um meta­so­matites of the Perzhany com­plex formed, con­tain­ing rare-met­al and poly­metal­lic min­er­al­iza­tion, includ­ing beryl­li­um and oth­er rare met­als.

Dyke com­plex­es are wide­spread through­out the shield. Two age gen­er­a­tions are dis­tin­guished: the Kle­siv gen­er­a­tion (basic dia­bas­es and pyrox­en­ites) and the Ovruch gen­er­a­tion (quartz por­phyries). They form a diag­o­nal belt sys­tem in the Novohrad-Volyn­skyi, Yemilchyne, Horodok, Tomash­horod, and Horyn regions.