THE U-PB ZIRCON AGE OF PLAGIOGRANITE FROM THE PLAGIOGRANITE-AMPHIBOLITE COMPLEX OF THE GANYCHALAN BLOCK, THE WESTERN KORYAK HIGHLAND

Abstract

The Ganychalan block is a fragment of the Early-Middle Paleozoic Talovka-Main-Vaega oceanic plateau expressed in the present-day structure of the western Koryak Highland as a series of blocks extending along the Verkhoyansk-Chukotka continental margin from the eastern coast of the Taigonos Peninsula to the left bank of middle reaches of the Anadyr River [4]. Three (Il'pinei, Kalisimitkin, and El'giminai) nappe complexes make up the block. The lower (Il'pinei) nappe is composed of basalts, cherts, and seamount carbonate rocks metamorphosed under conditions of the glaucophane-greenschist facies [1, 4]. The two other nappes consist of basement ultramafics and gabbroids overlapped by basalt-carbonate-terrigeneous cover of the Lower-Middle Paleozoic oceanic plateau. At the base of nappe sheets, the cover units tectonically alternate with metamorphic rocks of the gneissic and plagiogranite-amphibolite complexes.