Abstract
This paper presents a new detailed study including zircon U-Pb-Hf isotopic, whole-rock geochemical and Sr-Nd isotopic analyses of conglomerate and granitic pebbles from the molasse deposits in central Jilin Province, NE China. These data are used to better constrain the Late Permian–Triassic tectonic evolution regarding particularly the final closure of the Paleo-Asian Ocean (PAO) along the Changhun-Yanji suture (CYS). Zircon U-Pb data indicate that the granitic pebbles formed in the end-Permian (254–253 Ma). The youngest detrital zircon age of 231 Ma from the conglomerate, and presence of the overlying Upper Triassic Sihetun Formation suggests that the molasse deposits on the Jin′gui Island formed during the Late Triassic. The end-Permian granitic rocks display high SiO2 (66.07–74.77 wt %), with low MgO (0.55–2.05 wt %) and Mg# (31.61–43.64) values, together with depleted Hf and Nd isotopic values (εHf(t) = +1.61 to +11.62; εNd(t) = +3.3 to +4.2; (87Sr/86Sr)i = 0.706458–0.706842) and juvenile second-stage Hf model ages (1148–512 Ma), suggesting that they were probably generated by the partial melting of a Meso-Neoproterozoic juvenile metabasaltic lower crust. They are characterized by enrichments in large ion lithophile elements (LILEs) and depletions in high field strength elements (HFSEs), with affinities to igneous rocks forming in a subduction-related setting. This, combined with regional coeval subduction-related magmatic rocks, indicates that the PAO still existed along the CYS. In addition, the identification of Late Triassic molasse deposits on the Jin′gui Island in this study, coupled with occurrences of many Early Triassic syn-collisional granitoids along the CYS, indicates that the final closure of the PAO took place prior to the Late Triassic.
Highlights
Introduction iationsNortheast (NE) China, called the Xing0 an-Mongolian Orogenic Belt (XMOB), is located between the North China Craton (NCC) and Siberia Craton (SC) and is an important component of the Central Asian Orogenic Belt (CAOB; Figure 1a) [1,2,3,4,5,6,7,8]
It is widely accepted that the SolonkerXra Moron-Changchun-Yanji suture belt tectonically separates the NCC in the south from the micro-continental blocks in the north, and it marks the final closure of the Paleo-Asian
Considering the above, we suggest that final suturing of the eastern segment of the Paleo-Asian Ocean (PAO) took place during the Early–Middle Triassic in central Jilin Province
Summary
The central Jilin Province in NE China is located in the western part o junction of the Songnen Block and the NCC (Figure 1b) The central Jilin Province in NE China is located in the western part of the CYS at related mélanges, including the Kaiyuan, Xia′ertai, Hulan, the junctiontectonic of the Songnen. The Upper Permian Fanjiatun and Yangjiagou, (Figure and the According to the 1:200,000 geological map, this area mainly contains the Lower Permian dingzi formations [80] (Figure 2). Foramtion is dominated by gray to greenish slate, siltstone, sandstone, conglomerate and glomerate and tuffaceous breccia. This formation has a thickness of 500–120 tuffaceous breccia.
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