关键词: 华北克拉通北缘东段及邻区, 古亚洲洋, 三叠纪, 地壳厚度, 中亚造山带, 机器学习

Abstract: The tectonic evolution of the Paleo-Asian Ocean exerted a decisive control on the formation and evolution of the East Asian continent, profoundly influenced magmatic activity, stratigraphic development, and tectonic frameworks within the Central Asian orogenic belt. However, the final closure timing of its eastern segment remains controversial. This study applies machine learning techniques to reconstruct Triassic crustal thickness variations along the eastern segment of the northern margin of the North China craton and adjacent regions, thereby providing new constraints on the mechanism and timing of the final closure of the Paleo-Asian Ocean. During the Early-Middle Triassic, average crustal thickness reached its maximum of approximately 66 km in the Siping area of Jilin Province, a region concurrent with adakitic magmatism. Crustal thickness generally decreased eastward, where the lithological assemblage is dominated by calc-alkaline intermediate-acidic intrusive rocks. These findings suggest that the Paleo-Asian Ocean underwent closed first in the Siping area of Jilin Province in the Early-Middle Triassic, triggering pronounced crustal thickening. In contrast, the easternmost Yanbian area remained an active tectonic seaway, evidenced by crustal thickness comparable to that of normal continental crust. During the Late Triassic, the eastern segment of the northern margin of the North China craton and adjacent regions exhibited an eastward-increasing crustal thickening trend, reaching a maximum thickness of 66 km in the Yanbian area of Jilin Province, again accompanied by synchronous adakitic rocks. Meanwhile, regions like western Liaoning Province and central Jilin Province, which had thickened earlier, now experienced significant crustal thinning accompanied by the emplacement of Late Triassic bimodal igneous rocks. These observations indicate that final closure of the Paleo-Asian Ocean occurred in the Yanbian area during the Late Triassic, while the previously closed western segments transitioned from a collisional-compressional to a post-collisional extensional environment. The systematic spatial-temporal variations in Triassic crustal thickness, integrated with contemporaneous igneous rock assemblages, further confirm a scissor-like west-to-east diachronous closure model for the eastern segment of the Paleo-Asian Ocean, culminating in the Late Triassic.

Key words: eastern segment of the northern margin of the North China craton and adjacent regions, Paleo-Asian Ocean, Triassic, crustal thickness, Central Asian orogenic belt, machine learning