SEDIMENT PROVENANCE AND DRAINAGE EVOLUTION OF THE MAJOR TRIBUTARY (NEN RIVER) OF THE HEILONGJIANG-AMUR RIVER, NE ASIA BY DETRITAL ZIRCON U-PB GEOCHRONOLOGY

The Nen River drainage is located in NE China and is one of the superior tributaries of the Heilongjiang-Amur River. The Nen River originate from the Yilehuli Mountains of the Greater Khingan Mountains and flows through Songnen plain from north to south. The Nen River joins the second Songhua River to form the Songhua River. It is the longest tributary of the Heilongjiang-Amur drainage. Chinese scholars have conducted some studies on the Nen River drainage. Based on previous studies, 16 groups of detrital zircon samples were collected and added into the core samples of the Neogene Taikang Formation(1.79Ma) to construct a database of detrital zircon geochronology of major rivers in the Nen River. The Taikang Formation samples were collected from well SK-1, the International Continental Scientific Drilling Project of the Songliao basin. This study compared the detrital zircon geochronology data of surface river sands at adjacent sampling sites and/or river bed sand (The sample depth is about 70 cm.) as well as the detrital zircon geochronology data of river sand and/or sedimentary rocks in geological history. We conclude that the provenance of surface river sand is not different from that of river bed sand. The provenance of these two periods mainly came from the Greater Khingan Mountains. However, the detrital zircon geochronological data of surface river sand and Taikang Formation sample are very different. The Taikang Formation samples are very similar to the present Ussuri/Wusuli River samples, suggesting that the provenance of the ancient Nen River drainage may be from the southeastern part of the basin. Therefore, we infer that there was a river flowing from east to west and from south to north in the study area 10Ma ago, which is no longer present.

Key words: Detrital zircons geochronology; Nen River drainage; Source analysis; Drainage evolution