Geochronology of granites of the western Korosten AMCG complex (Ukrainian Shield): implications for the emplacement history and origin of miarolitic pegmatites

Abstract

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.

U-Pb Age and Hf Isotope Systematics of Zircon from Eclogite Xenoliths in Devonian Kimberlites: Preliminary Data on the Archaean Roots in the Junction Zone between the Sarmatian and Fennoscandian Segments of the East European Platform

“…1.83-1.81 Ga [65][66][67] (and continued for the next ~100 Myr, causing the rotation of Sarmatia [68]). At the same time, the Prutivka-Novogol large igneous province formed, consisting of numerous mantle-derived mafic and ultramafic dykes and large anorthosite-mangerite-charnockite-granite complexes [69][70][71].…”

Fossilization of Precambrian microfossils in the Volyn pegmatite, Ukraine

“…Typical for kerite is the high N content, which goes up to 9 wt % (Luk'yanova et al, 1992;Franz et al, 2017). The maximum age of the fossils is restricted by the 1760 ± 3 Ma intrusion age of the pegmatites (Shumlyanskyy et al, 2021;Fig. 1).…”

<sup>40</sup>Ar/<sup>39</sup>Ar dating of a hydrothermal pegmatitic buddingtonite–muscovite assemblage from Volyn, Ukraine

“…1a), the formation of such a large volume of basalt over a distance from Poland and Belarus far into Ukraine must have been accompanied by an increased geothermal gradient effecting also the upper crust. A hydrothermal overprint at this time, at temperatures below the closure temperature of muscovite, is also seen in one of the zircon ages presented by Shumlyanskyy et al (2021), which shows a discordia with a lower intercept at 550 ± 55 Ma. The further Phanerozoic geological development of the area is poorly restricted, but during the Devonian the Prypyat branch of the Dnieper-Donets paleorift (Shumlyanskyy et al, 2016) developed towards the northeast of the Ukrainian Shield (Fig.…”

“…The large time difference between crystallization of the pegmatites (1760 ± 3 Ma; Shumlyanskyy et al, 2021) of approximately 270 Ma indicates a hydrothermal event independent of the cooling stage of the pegmatite. Cooling of the pegmatite down to temperatures suitable for microorganisms is also required by the fact that the kerite fossils grew inside the miarolitic cavities.…”

“…A summary of descriptions of these pegmatites is found in Lyckberg et al (2009, 2019, andreferences therein). Intrusion ages of the pluton range from 1.84 to 1.72 Ga (Shumlyankskyy et al, 2017), and the ages of the granite (1766 ± 3 Ma) and pegmatite (1760 ± 3 Ma) near to Volyn were determined on zircon by U-Pb dating with secondary ion mass spectrometry (SIMS; Shumlyanskyy et al, 2021).…”