U-Pb zircon dating of the Heilongjiang complex at Huanan, Heilongjiang Province.

The Heilongjian complex is consist of greeschist rocks and tectonic mylonites, and has been believed making up of Precambrian basement with the Mashan complex together in northeastern China. This conclusion, however, lacks of evidences of isotopic age and paleontology. LA-ICP-MS zircon U-Pb dating of the greeschist from the Hunanying Formation of the Heilongjian complex is carried out in order to determine the age and to discuss geotectonic background and metamorphic events the Heilongjian complex has experienced. Results show that zircons from analyzed sample present available Th/U ratio between 0.27～1.27 , and show well defined two group ages, i. e. weighted average ~(206)Pb/ ~(238)U ages are 511±10Ma ( n = 13 , MSWD = 1.6) and 274.7±3.6Ma (n =9, MSWD =0.91 ). The oldest ages from 969～747Ma imply the origination of Mesoproterozoic to Neoproterozoic. These ages along with metamorphic age of ～511 Ma display that the Heilongjian complex, contains detrital zircons, which are possibly derived from the spatially intimately associated Mashan complex. The group age ～275Ma obtained subsequently suggest another orogenic event, probably representing the closure of the Paleo-Asia oceanic plate during the Late Paleozoic.