Permo-Triassic granitoids of the Xing'an-Mongolia segment of the Central Asian Orogenic Belt, Northeast China: age, composition, and tectonic implications

摘要

The Xing'an-Mongolia orogenic belt is located in the southeastern segment of the Central Asian Orogenic Belt. Its tectonic evolution, especially during the Late Palaeozoic to Early Mesozoic, remains controversial. Here, we report new zircon U-Pb dates, whole-rock geochemistry, and Hf isotopes of representative samples from four plutons in the Linxi area of Northeast China to provide new constraints on this issue. Zircon U-Pb dating indicates that the intrusions were emplaced in two stages: (1) Late Permian to Early Triassic (the Banshifangzi and Xinangou plutons (252 +/- 3)-(246.3 +/- 3.3)Ma); and (2) Late Triassic (the Baoshan and Hada plutons (220.8 +/- 2.7)-(211.4 +/- 2.6)Ma). Their positive epsilon Hf(t) values (6.6-14.1), coupled with their geochemical characteristics, suggest that the provenance of investigated granitoids were most likely to be dominated by juvenile crustal materials. Based on these new data and previous studies, we propose three stages of tectonic evolution during the Late Palaeozoic-Early Mesozoic in the XMOB: (1) Late Carboniferous-Early Permian (330-270Ma): double-sided subduction of the Palaeo-Asian Ocean; (2) Middle Permian-Middle Triassic (270-237Ma): the closure of the Palaeo-Asian Ocean and subsequent continent-continent collision between the North China Craton and the South Mongolia Terrane; and (3) Late Triassic (237-211Ma): post-collisional extension.