Tectonic setting of the plutonic belts of Yakutia, northeast Russia, basedon Ar-40/Ar-39 geochronology and trace element geochemistry

Samples from plutonic belts and individual intrusions in the Sakha Republic (Yakutia), northeastern Russia, were analyzed using Ar-40/Ar-39 geochronol ogy and trace element geochemistry. Four phases of activity were identified : a subduction event along the southwest margin of the Kolyma-Omolon supert errane 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 s uperterrane dated at 130-123 Ma with a slightly older to contemporaneous ex tensional event to the west; and intrusions associated with east-west exten sion between 106 and 92 Ma. These phases are interpreted to represent (1) s ubduction under and (2) accretion to Asia of Kolyma-Omolon followed by loca l extension, (3) subduction along the northern edge of this superterrane, a nd (4) regional extension following closure of the South Anyui suture and/o r the start of subduction associated with the Okhotsk-Chukotka volcanic bel t.