We report new occurrences of ca. 1460 Ma magmatism in western Lithuania, where large volumes of granitoid melts were intruded into host supracrustal and charnockitoid rocks, and formed the Zemaiciu Naumiestis pluton. Numerous granitoids of that age have previously been described from southern Sweden and from the Danish island of Bornholm, but none have been reported from the eastern side of the Baltic Sea, where the crystalline basement is covered by Phanerozoic sediments. Petrological studies demonstrate that the Zemaiciu Naumiestis intrusion consists of quartz monzodiorites, monzogranites and syenogranites. The dominant ferromagnesian mineral is biotite. Rare clinopyroxene grains occur in the quartz monzodiorites. The rocks are fine to coarse-grained, often porphyritic. Chemically, the studied granitoids are dominantly alkali-calcic and shoshonitic, metaluminous to peraluminous, and ferroan to magnesian. The geochemical data indicate that the pluton consists of two rock suites, one representing monzodiorites and monzogranites, and other mostly syenogranites. The suites originated from slightly different sources. The rocks within the Zemaiciu Naumiestis pluton are variably deformed and locally cataclased. Some are, however, rather massive. Two samples of monzogranite yielded ID-TIMS U-Pb zircon ages of 1462 +/- 8 (MSWD = 1.09) and 1459 +/- 3 Ma (MSWD = 0.28).
|Status||Published - 2006|