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 represent (1) subduction under and (2) accretion to Asia of Kolyma-Omolon followed by local extension, (3) subduction along the northern edge of this superterrane, and (4) regional extension following closure of the South Anyui suture and/or the start of subduction associated with the Okhotsk-Chukotka volcanic belt.

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