关键词: 佳木斯-兴凯地块, 中亚造山带东段, 古亚洲洋, 古太平洋, 构造体制转换

Abstract: Since the Paleozoic, Northeast China has experienced the superimposition of multiple paleo-ocean tectonic regimes, including the Panthalassa, Mongol-Okhotsk Ocean, Paleo-Asian Ocean, and Paleo-Pacific Ocean. However, the processes of their superimposition and transition remain poorly understood. The Jiamusi-Khanka block, located at the easternmost end of the microcontinental blocks in Northeast China, represents a key a key tectonic nexus: It marks the final closure of the eastern segment of the Central Asian orogenic belt (Paleo-Asian Ocean tectonic domain), connects to the Mongol-Okhotsk tectonic domain in the northeast, and lies at the core of the superimposed influence of the circum-Pacific (Panthalassa) tectonic domain along the eastern margin of Eurasia. Consequently, it serves as a critical bridge for understanding the superimposition and transition processes among these paleo-ocean tectonic regimes. This study comprehensively analyzes the lithology, geochronology, and geochemical characteristics of the metamorphic basement, sedimentary cover, and peripheral tectonic mélanges of the Jiamusi-Khanka block, reconstructing its tectonic evolution from the Paleozoic to the Mesozoic. The findings provide key constraints on the tectonic regime superimposition and transition processes along the eastern margin of Eurasia. The Paleozoic-Mesozoic tectonic evolution of the Jiamusi-Khanka block can be divided into four stages: (1) Prior to the Early Paleozoic, the Jiamusi-Khanka block, together with other microcontinental blocks in Northeast China, formed a large composite block that originated in the Sayan-Baikal orogenic belt within the Siberian craton and collectively underwent Pan-African metamorphism (~500 Ma). (2) During the tectonic evolution of the Central Asian orogenic belt, these blocks drifted southward to the eastern segment of the orogen around 500 Ma. (3) In the Late Paleozoic, subduction of the Mongol-Okhotsk Ocean or Panthalassa induced a back-arc extension, leading to the opening of the Heilongjiang Ocean. This rifted the Jiamusi block from the composite block and caused its eastward drift, separating it from the eastern segment of the Central Asian orogenic belt. (4) From the Late Triassic to the Early Jurassic, the closure of the Heilongjiang Ocean and the subduction of the Paleo-Pacific Ocean in the east drove the re-amalgamation of Jiamusi block with the adjacent Central Asian orogenic belt. This event marked the final formation of the Central Asian orogenic belt and the regional transition to a new stage dominated by the Paleo-Pacific tectonic regime.

Key words: Jiamusi-Khanka block, eastern Central Asian orogenic belt, Paleo-Asian Ocean, Paleo-Pacific Ocean, tectonic transition