Detrital zircon U-Pb dating of Heilongjiang complex and its tectonic implications.

Heilongjiang complex, along the Mudanjiang fault in the western part of the Jiamusi massif, was the high-pressure metamorphic belt due to the collision between the Jiamusi and Songnen massifs. According the tectonic-rock assemblages, metamorphism and deformation characteristics, the Heilongjiang complex are the similar to the residual parts of the huge accretionary wedge, which was overthrusted above the Jiamusi massif during the late stage of the collision between the two massifs. SHRIMP U-Pb dating from 88 zircon analyses give the three age populations; 170～220Ma with peak age at 183Ma, 240～338Ma with the peak age at 256Ma and 450～520Ma with peak age at 470Ma. The 28 zircon spots with the concordant ages give the two age populating; 240～ 338Ma with peak age at 256Ma and 450～500Ma with peak age at 470Ma. The age populations of the 240～338Ma with peak age at 256Ma is the ages for limited the deposition age of the Heilongjiang complex. Oldest age populations of the 450～520Ma with peak age at 470Ma are similar to the Mashan complex, and suggests that the Mashan complex was the marital source. The youngest age populations of the 170～220Ma with peak age at 183Ma, is the disconcordant ages but is similar to the Ar-Ar ages from muscovite in the Heilongjiang complex, which indicate that the ages of the thermal perturbation due to the collision between the Jiamusi and Songnen massifs. We suggests that the protolith age of the Heilongjing complex are at Early Triassic, the timing for collision between the two massifs and the overtrusting of Heilongjiang HP rocks on to the Jiamusi massif was Late Triassic to Early Jurassic, therefore the subduction between the two massifs should be during the Triassic. Those SHRIMP U-Pb dating not only show the geochronology framework in the NE China, but also give an important evidence for the transformation between the Paleozoic Central Asian Orogenic Belt (CAOB) and the Paleo-Pacific Accretion Belt (PPAB) during the Triassic.