Abstract. The origin of large miarolitic (also known as
“chamber”) pegmatites is not fully understood although they may have great
economic value. The formation of cavities in magmatic bodies is related to
melt degassing and gas or fluid flow through partially solidified magma. In
this paper, the origin of the Volyn pegmatite field, located in the
Palaeoproterozoic Korosten anorthosite–mangerite–charnockite–granite (AMCG) complex, North-Western region of the Ukrainian Shield, is discussed. Pegmatites of
the field host deposits of piezoelectric quartz that is accompanied by gem-quality beryl and topaz. The Volyn pegmatite field is confined to granites
located in the south-western part of the Korosten complex and extends for 22 km along the contact with the anorthosite massif within the Korosten
plutonic complex. Geological data indicate hybridization of basic melts and
partly crystallized granites, as well as direct impact of fluids derived from basic
melts on the chamber pegmatites. The new U–Pb zircon ages obtained for granites and pegmatites of the
Korosten complex confirm that the rock assemblage in the northern part of
the complex crystallized between 1800 and 1780 Ma, whereas rocks in the
southern part intruded mainly between 1768 and 1755 Ma. U–Pb zircon ages for
granites from the south-western part of the Korosten complex indicate that
granites were emplaced at 1770–1765 Ma, a few million years prior to the intrusion of
the gabbro–anorthosite massif (1762–1758 Ma), while chamber pegmatites in
these granites crystallized at 1760 ± 3 Ma, coevally with the basic
rocks. Ultimately, the formation of the chamber pegmatites was related to
the reheating of the semi-crystallized granitic intrusion and to fluids
migrating from the underlying gabbro–anorthosite massif.
Geochronology of granites of the western Korosten AMCG complex (Ukrainian Shield): implications for the emplacement history and origin of miarolitic pegmatites
