Late Archean Initial Potassic Magmatism of the Aldan Shield (Ukduska Massif): Evidence from U-Pb Single Zircon Dating

摘要

The alkaline rocks of the Ukduska layered massif are products of potassic-ultrahigh-potassic magmatism, which is very rare in the Precambrian. The massif is located in the southeastern part of the Olekma granite-greenstone terrain (Chara-Olekma geoblock) of the Aldan Shield near its junction with the Dzhugdzhur-Stanovik fold system. The massif intrudes tonalite-trondhjemite orthogneisses of the Olekma Complex with an age of 3.0-3.2 Ga. The predominant part of the massif—1.3 x 2 km in area—is composed of a layered series represented by biotite pyroxenites, shonkinites, and alkali feldspar syenites. They contain calciphyre lenses and carbonate-bearing syenite dikes.