AGE OF LAMPROITES OF THE ALDAN PROVINCE

Abstract

The first occurrences of lamproites in Soviet Union were identified on the Aldan Shield, in the region of the Murun Pluton and in the Central Aldan block. By the geological position of the lamproite bodies and the geological history of the region, it was assumed that the lamproites are of Mesozoic age. However, until now there were no geochronological data on these rocks. The authors have obtained the first isotopic data on the age of lamproites in the Aldan province, specifically those in central, western and eastern parts of the Aldan Shield. All the analyses were done at the laboratory of isotope geochronology of IGEM by the method of isotope dilution with 38Ar, using an improved MI-1201 mass spectrometer and an IGEM argon apparatus. By the results the lamproite of the Aldan province are from two stages, the Upper Jurassic and the Lower Cretaceous. The Upper Jurassic (Kimmeridgian to Volgian) lamproite is found only locally, in a small zone of the Central Aldan Shield. Lower Cretaceous lamproite is found throughout Aldan province.