The Xing' an Block is located in the transitional area between the Eerguna and Songliao blocks in the CAOB, with a controversial tectonic affinity of micro-continent vs. orogenic belt. In this paper, we focused on the Zhalantun Metamorphic Complex from the Zhalantun area in the Xing' an Block. The Zhalantun Metamorphic Complex was named 'Xinghuadukou Group' according 1 : 200000 geological map, which consists of metasandstone, slate, phyllite, mica-schist, meta-acidic volcanics and meta-volcanic tuff. Mica-schist of analyzed sample was collected from south of the Xiangyangyu Reservoir, which consists of quartz (35% similar to 40%), chlorite (20% similar to 25%), muscovite (20% similar to 25%) and feldspar (8%). Sample D09-02A yielded abundant zircon grains, most of which are rounded to subhedral and range from 50 to 180 mu m in size. CL imaging reveals that most grains are oscillatory zoned and of magmatic origin, although some portions are darker with less distinct zoning. A total of 55 analyses were made on 55 grains. The data show a spread along concordia, with variable discordance. The detrital zircon components show great variation in U and Th contents and Th/U ratios, ranging respectively from 196 x 10(-6) similar to 2106 x 10(-6), 75 x 10(-6) similar to 2455 x 10(-6) and 0.2 similar to 1.8. The 55 zircons from D09-02A yield apparent ages ranging from 2952 +/- 32 to 481 +/- 12Ma. These results not only give information for the formation ages and detrital zircon age distributions of the Zhailantun Metamorphic Complex in this area, but also show the evidence to confirm the tectonic affinity of the Xing' an Block. (1) The Zhalantun Metamorphic Complex mainly occurs as a sequence of meta-clastic and meta-volcaniclastic rocks and shows greenschist to low-amphibolite facies metamorphism. Its formation age is younger than 481 Ma and different from that of the 'Xinghuadukou Group in the north of the Great Xing' an. (2) Detrital zircon U-Pb dating of the Zhalantun Metamorphic Complex yields three age groups at: 481 similar to 580Ma with a peak age of 529Ma, 699 similar to 998Ma with a peak age of 833Ma and 1213 similar to 2952Ma with a peak age of 2000Ma. These age groups correspond to two key tectonic events of the Gondwana and Rodinia episodes and the Archean basement, respectively. (3) With the revelation of the Neoproterozoic and Archean basement in the Xing' an block, we suggest that the block may belong to a micro-continent but not an orogenic belt.
