GEOCHRONOLOGICAL CONSTRAINTS ON THE EMPLACEMENT HISTORY OF AN ANORTHOSITE - RAPAKIVI GRANITE SUITE - U-PB ZIRCON AND BADDELEYITE STUDY OF THE KOROSTEN COMPLEX, UKRAINE
Yv. Amelin et al., GEOCHRONOLOGICAL CONSTRAINTS ON THE EMPLACEMENT HISTORY OF AN ANORTHOSITE - RAPAKIVI GRANITE SUITE - U-PB ZIRCON AND BADDELEYITE STUDY OF THE KOROSTEN COMPLEX, UKRAINE, Contributions to Mineralogy and Petrology, 116(4), 1994, pp. 411-419
U-Pb zircon/baddeleyite ages obtained for the Korosten anorthosite-rap
akivi granite complex, Ukrainian shield, suggest that different magmat
ic phases were emplaced during a period of ca. 30 million years as a s
eries of distinct igneous episodes. The earliest 1789.1 +/- 2.0 Ma ano
rthosites were followed by 1781.3 +/- 3.2 Ma dykes of plagiogranite po
rphyries. The emplacement of a major rapakivi granite phase took place
at 1767.4 +/- 2.2 Ma, and was followed by emplacement of layered intr
usions of anorthosites, gabbronorites, diabases and ultrabasic rocks b
etween 1761 and 1758 Ma. The minimum duration of magmatism of about 30
million years, the 6-15 million years interval between igneous pulses
, and alternation of discrete episodes of basic and felsic magmatism a
re common features of major anorthosite-mangerite-charnockite-rapakivi
granite complexes. Temporal distribution of igneous activity in the K
orosten complex shows that the gabbro-anorthosites and the granites ar
e not comagmatic, although they are possibly cogenetic, and that at le
ast four portions of granitic and basic magmas were generated during a
relatively long period of at least 30 million years. The time gap of
about 20-25 million years between early basic and later and more volum
inous granitic magmatism, characteristic of the Korosten pluton, Wibor
g and Salmi batholiths, probably reflects the duration of extensional
processes before the generation of large volumes of magma in the lower
crust.