TECTONIC SETTING OF THE PLUTONIC BELTS OF YAKUTIA, NORTHEAST RUSSIA, BASED ON 40AR/39AR GEOCHRONOLOGY AND TRACE ELEMENT GEOCHEMISTRY

Abstract

Samples from plutonic belts and individual intrusions in the Sakha Republic (Yakutia), northeastern Russia, were analyzed using 40Ar/39Ar geochronology and trace element geochemistry. Four phases of activity were identified: a subduction event along the southwest margin of the Kolyma-Omolon superterrane with apparent ages of ca. 160-140 Ma, a superposed collisional event dated at 143-138 Ma, a subduction event along the northern margin of the superterrane dated at 130-123 Ma with a slightly older to contemporaneous extensional event to the west; and intrusions associated with east-west extension between 106 and 92 Ma. These phases are interpreted to represents (1) subduction under and (2) accretion to Asia of Kolyma-Omolon followed by local extension, (3) subduction along the South Anyui suture and/or the start of subduction with the Okhotsk-Chekotka volcanic belt.