Tectonic evolution and crustal nature of the eastern Central Asian Orogenic Belt: Evidence from geochronology and geochemistry of early Paleozoic igneous rocks of the Lesser Xing'an Range, NE China

The Central Asian Orogenic Belt (CAOB) has become a hotspot of geological research, and was thought to record the most widespread event of Phanerozoic juvenile crust formation. NE China is located within the eastern CAOB, and is characterized by the Paleozoic amalgamation of micro-continental massifs, such as the Songnen-Zhangguangcai Range Massif (SZM) and Jiamusi Massif (JM). This paper presents new zircon U-Pb, Hf isotope, and whole-rock major and trace element data for early Paleozoic igneous rocks of the northern SZM, in order to constrain the early Paleozoic tectonic evolution and crustal nature of the eastern CAOB. Zircon U-Pb dating indicates that early Paleozoic magmatic events within the northern SZM can be subdivided into four stages: Middle Cambrian (~505 Ma), Late Cambrian (~490 Ma), Early-Middle Ordovician (~470 Ma), and Late Ordovician (460-450 Ma). Middle Cambrian monzogranites recorded the latest stage of continent (SZM)-continent (JM) collision, whereas Late Cambrian A-type granitoids suggest a post-collisional extension. Ordovician calc-alkaline igneous rocks recorded an active continental margin setting. Additionally, the large variations of zircon ɛHf(t) values for early Paleozoic igneous rocks from the northern SZM indicate heterogeneity of the deep crust beneath the study area. Furthermore, zircon Hf two-stage model ages for early Paleozoic igneous rocks from the northern SZM (prominent peaks around 1.9-1.8 and 1.5-1.4 Ga and secondary peaks between 1.3-1.2 Ga) and the JM (1.7-1.2 Ga), suggest significant reworking of the ancient crust rather than extensive juvenile crust formation during early Paleozoic and imply that these two massifs have similar histories of Mesoproterozoic and early Paleozoic crustal accretion and reworking, although the northern SZM contains much older crustal material than the JM. This work was supported by the National Basic Research Program of China (grant: 2013CB429802) and National Natural Science Foundation of China (grant: 41330206).