Final closure of the Paleo-Asian Ocean and initiation of the Paleo-Pacific subduction: Geophysical evidence from the Nadanhada Terrane

Located in Northeast Asia, the Nadanhada Terrane contains the Paleozoic and Mesozoic accretionary complex that is an ideal record for studying the closure of the Paleo-Asian Ocean and the evolution of the Paleo-Pacific Ocean. To reveal the process of the Nadanhada Terrane's composition and formation we use geophysical and geological data. The characteristics reveal that the Nadanhada Terrane is composed of three distinct tectonic units ordered from southwest to northeast: the Yuejinshan Complex Belt, the Raohe Basin, and the Raohe Complex Belt. The electrical characteristics indicate that the Yuejinshan Complex Belt and Jiamusi Block share a common basement, while the Raohe Complex Belt is a complete accretionary terrane. The order of gravity anomalies from high to low of the three tectonic units is the Yuejinshan Complex Belt, followed by Raohe Basin and then the Raohe Complex Belt. High magnetic volcanic rocks are developed in the Yuejinshan and Raohe complexes, and low magnetic granite is developed in the Raohe Basin. The Nadanhada Terrane was formed via continuous accretion during the multi-stage subduction of oceanic and continental plates. The main formation process was as follows: 1) From the Late Carboniferous to the Late Triassic, the Paleo-Asian Ocean continued to subduct below the Jiamusi Block, resulting in the formation of the main body of the Yuejinshan Complex Belt. 2) From the Late Triassic to the Early Cretaceous, the Paleo-Pacific (Izanagi) Plate was subducted toward Northeast Asia, and the Mesozoic parts of the Yuejinshan Complex and the Raohe Complex were formed via collage and accretion. 3) During the Early Cretaceous, an extensional tectonic background was generally formed in Northeast Asia and the Raohe Basin began to form. 4) During the Late Cretaceous, the Pacific Plate was subducted toward Northeast Asia, and the Nadanhada Terrane was continuously squeezed and formed.