Abstract:

It remains a topic of debate that the tectonic evolution between the Songnen-Zhangguangcai Range and Jiamusi massifs and the timing of transformation from the Paleo-Asian Ocean to the circum-Pacific tectonic systems in the eastern Heilongjiang Province. In the present study, the geochronology and rock association of the Paleozoic-Early Mesozoic igneous rocks in the study area, combined with geochronological data of detrital zircons, provide strong constraints in this regard. LA-ICP-MS zircon U-Pb dating results indicate that the Paleozoic-Early Mesozoic magmatism in the eastern Heilongjiang Province can be divided into eight stages, i.e., the Early Ordovician(485 Ma), Late Ordovician(450 Ma), Middle Silurian (425 Ma), Middle Devonian (386 Ma), Early Permian (291 Ma), Middle Permian (268 Ma), Late Triassic (201-228 Ma), and Early Jurassic (184 Ma). The Early Ordovician-Middle Silurian magmatism, occurred in eastern margin of the Songnen-Zhangguangcai Range Massif with the obvious south-north-trend, is composed mainly of diorite, tonalite, and monzogranite, which formed in the subduction-collision tectonic setting, implying that the amalgamation between the Songnen-Zhangguangcai Range and Jiamusi massifs finished in the Middle Silurian (425 Ma). It is also supported by the geochronological data for detrital zircons from Early Devonian sedimentary rocks in study area. Middle Devonian volcanism is composed mainly of a series of bimodal volcanic rocks in eastern margin of the Jiamusi massif and the A-type rhyolite in the Songnen-Zhangguangcai Range massif, suggesting a post-collisional extensional environment. Early Permian calc-alkaline volcanic rocks, occurred in eastern margin of the Jiamusi massif, imply that the subduction of the Paleo-Asian Oceanic plate happened beneath the Jiamusi massif, whereas the coeval bimodal igneous rocks, occurred in the Songnen-Zhangguangcai Range massif, suggest an extensional environment similar to back-arc setting. The formation of Middle Permian syn-collisional volcanic rocks in southern-southeastern margin of the Jiamusi massif could be related to the collision between the Jiamusi and Khanka massifs. The Late Triassic bimodal volcanic rocks in the Zhangguangcai Range and the A-type rhyolite in the region to southeast of the Dunmi fault imply an extensional environment related to the final closure of Paleo-Asian Ocean. Additionally, the occurrence of Middle-Late Permian granites in the Songnen-Zhangguangcai Range and Jiamusi massifs, combined with the lack of Late Triassic to Early-Middle Jurassic magmatisms in the Jiamusi massif, imply that the breakup of the Songnen-Zhangguangcai Range and Jiamusi massifs could happen again along the Mudanjiang fault during Early Triassic. The occurrence of Early-Middle Jurassic calcalkaline volcanic rocks in the Dongning-Wangqing-Hunchun region and coeval bimodal igneous rocks in the Lesser Xing’an-Zhangguangcai Range, combined with the formation of the “Zhangguangcailing Group” and “Heilongjiang Group” tectonic melange, implies that the amalgamation between the Songnen-Zhangguangcai Range and Jiamusi massifs could take place again during Early-Middle Jurassic, also marking the beginning of the circum-Pacific tectonic system.

Key words: eastern Heilongjiang Province, Paleozoic, Early Mesozoic, igneous rocks, geochronology of detrital zircons, tectonic evolution