The Jiamusi Block involved in the East Gondwana's interior orogeny: Constrained by geochronology of paragneiss from the Mashan Complex

Tectonic evolution from the breakup of the Rodinia supercontinent to the assembly of the Gondwana megacontinent has been well investigated on major continents/cratons. However, the role of microcontinents during the evolution from Rodinia to Gondwana has been poorly discussed. The Jiamusi Block, an important Precambrian microcontinent in the easternmost Central Asian Orogenic Belt (CAOB), is characterized by Pan-African metamorphic records and can be a suitable research objective for reconstructing Gondwana. Here we present a field-based zircon geochronological and Hf isotopic study for the paragneiss of the Mashan Complex in the Jiamusi Block. Four paragneiss samples yielded detrital zircon ages ranging from 2712 to 714 Ma, with the youngest age group of 787, 852, 812, and 915 Ma, respectively. Considering the Neoproterozoic orthogneisses (757, 725, and 898 Ma) intruding the studied paragneisses, we propose that the Mashan Complex contains two sets of supracrustal rocks, with their protoliths deposited at 915-898 Ma and 812-725 Ma, respectively. The metamorphic zircons from the paragneisses yield concordant ages of 566-484 Ma. Considering zircon morphology, internal structures, U-Pb ages, trace elements, and Hf isotopes, we figure out that the metamorphic zircons with ages of 566-560 Ma record granulite-facies metamorphism, which are characterized by high initial Hf isotopic ratios (0.282212-0.282359) and steep chondrite-normalized REE patterns. The 546-484 Ma metamorphic zircons record retrograde metamorphism and exhibit lower initial Hf isotopic ratios (0.281999-0.282204) and relatively flat chondrite-normalized heavy REE patterns. Based on new data and geological comparison, a unified Bureya-Jiamusi-Khanka Block in the Neoproterozoic is proposed, which was initially originated as part of Northeast India. It was collided with Australia-East Antarctica resulting in the Kuunga-Pinjarra Orogen in the late Pan-African (570-550 Ma). Subsequently, at sometime after 470 Ma, the Jiamusi Block was detached from the Kuunga-Pinjarra Orogen and drifted northward to collide with the Songnen Block of the CAOB in the Middle Jurassic.