The Jiamusi Block: A hinge of the tectonic transition from the Paleo-Asian Ocean to the Paleo-Pacific Ocean regimes

Abstract

The time frame and detailed tectonic processes during the transition from the Paleo-Asian Ocean to the Paleo-Pacific Ocean regimes have long been controversial. The Jiamusi Block, which is located in the eastern margin of the Eurasia, is a transitional zone between the Paleo-Asian Ocean and the Paleo-Pacific Ocean regimes. The Jiamusi Block has been considered to be the last unit collaged to the Central Asian Orogenic Belt (CAOB) but also influenced by subsequent westward subduction and accretion of the Paleo-Pacific plate. Abundant geological units in the Jiamusi Block provide key insights into the final amalgamation of the CAOB and the onset of the Paleo-Pacific Ocean regime. This paper presents a review on the tectonic affinity and origin linkage of the Jiamusi Block based on detailed characterization of both the granulite facies basement and the Phanerozoic sedimentary cover, as well as the surrounding Mesozoic accretionary complexes. From these analyses, we develop an integral tectonic model for the Jiamusi Block aiming to better constraining the evolution history from the final amalgamation of the eastern CAOB to the onset of the Paleo-Pacific Ocean regime. We found that the tectonic history of the Jiamusi Block can be divided into at least four stages: (1) prior to the Early Paleozoic, the Jiamusi Block was conterminous with the other mirco-continents in NE China as a large combined block, which originated from the Sayang–Baikal orogenic belt within the Siberia Craton and experienced the Pan-African metamorphism (ca. 500 Ma); (2) along the tectonic evolution of the CAOB, those blocks in NE China drifted south to the eastern CAOB in some time after ca. 500 Ma; (3) during the Late Paleozoic, the subduction of the Mongol-Okhotsk Ocean or the Panthalassa induced back-arc extension and eventually the opening of the Heilongjiang Ocean, which ripped off the Jiamusi Block and drove it eastward away from the CAOB; (4) during the period from the Late Triassic to the Early Jurassic, following the closure of the Heilongjiang Ocean and the subduction of the Paleo-Pacific Ocean in the east, the Jiamusi Block was reunited with the contiguous CAOB, marking the final amalgamation of the CAOB and tectonic shift to a dominance by the Paleo-Pacific Ocean tectonic regime in the region.