DETRITAL-ZIRCON GEOCHRONOLOGY OF THE HANGAY-HENTEY BASIN: IMPLICATIONS FOR THE TECTONICS OF THE MONGOL-OKHOTSK OCEAN, MONGOLIA

The Hangay-Hentey basin is filled with Cambrian to Carboniferous sediments and is located along the Mongol-Okhotsk suture. This suture is a remnant of the late Paleozoic to mid-Mesozoic ocean that occupied the area between the Siberian and Mongol/North China cratons. The tectonic history of the Mongol-Okhotsk ocean is not conclusive. Authors have proposed the closure of this ocean at various times from the Permian to Jurassic. Furthermore, there is substantial disagreement on the tectonic setting in which the sediments of the Hangay-Hentey basin are deposited. These include a trench-slope, forearc, interarc, intra-arc, backarc, remnant ocean, and intermontane tectonic settings. Detrital-zircon grains collected from the Cambrian to Carboniferous sediments within the Hangay-Hentey basin are dated and constrain the tectonic history of the Mongol-Okhotsk ocean. U-Pb geochronologic analyses are conducted on 497 detrital-zircon grains from five sample localities. The zircon grains from Cambrian feldspathic arenites mainly yield ca. 490-640 Ma and 810-950 Ma ages. These sediments also include grains from Paleoproterozoic and Archean sources, which are likely located in the Siberian craton. The zircon grains from Silurian to Carboniferous feldspathic arenites mainly yield ca. 330-390 Ma ages. These sediments also include grains from Ordovician and Cambrian sources, which probably are from early Paleozoic magmatic arcs. The Cambrian sediments are interpreted to have formed in a backarc setting that, in part, drained from the Siberian craton. The Silurian to Carboniferous sediments may have been deposited in an intra-arc or forearc setting that was isolated from the Siberian craton. The spatial distribution of the samples from which detrital-zircon ages are obtained also give clues to the disputed location of the Mongol-Okhotsk suture.