DETRITAL ZIRCON CHRONOLOGY OF CONGLOMERATE IN YUEJINSHAN COMPLEX, HEILONGJIANG PROVINCE: Geotectonic Implications

The Yuejinshan Complex developed in Shichang area of Raohe County, Heilongjiang Province, is a set of marine-terrigenous sedimentary strata with rich Late Triassic fossils. The LA-ICP-MS zircon U-Pb dating results of conglomerate samples yield four groups of age, namely, above 800 Ma, 500 Ma, 251-284 Ma and 219-222 Ma respectively. The former three are completely in accordance with the ages of thermal events in Jiamusi massif, reflecting the sediment source mainly from Jiamusi massif. The latter, the youngest age group, can be roughly regarded as the latest sedimentary age of conglomerate. It is basically consistent with the early Late Triassic granite (210-228 Ma) widely distributed in Zhangguangcailing area of the east margin of Songliao massif, which indicates that the youngest detrital zircons are probably from the eastern Songliao massif. The characteristics of detrital zircon ages and source area reveal that the Yuejinshan accretionary complex has been located on and become a part of the east continental margin of Jiamusi massif before Late Triassic.