minerals Article The Late Triassic Molasse Deposits in Central Jilin Province, NE China: Constraints on the Paleo-Asian Ocean Closure Zuozhen Han 1,2, Jingjing Li 1, Chenlin Zhu 1, Wenjian Zhong 1 and Zhigang Song 1,3,* 1 Key Laboratory of Depositional Mineralization & Sedimentary Mineral of Shandong Province, College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China; [email protected] (Z.H.); [email protected] (J.L.); [email protected] (C.Z.); [email protected] (W.Z.) 2 Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China 3 Research Center of Continental Dynamics, Shandong University of Science and Technology, Qingdao 266590, China * Correspondence: [email protected] 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 conglom- erate, and presence of the overlying Upper Triassic Sihetun Formation suggests that the molasse deposits on the Jin0gui 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, Citation: Han, Z.; Li, J.; Zhu, C.; together with depleted Hf and Nd isotopic values ("Hf(t) = +1.61 to +11.62; "Nd(t) = +3.3 to +4.2; Zhong, W.; Song, Z. The Late Triassic (87Sr/86Sr)i = 0.706458–0.706842) and juvenile second-stage Hf model ages (1148–512 Ma), suggest- Molasse Deposits in Central Jilin ing that they were probably generated by the partial melting of a Meso-Neoproterozoic juvenile Province, NE China: Constraints on metabasaltic lower crust. They are characterized by enrichments in large ion lithophile elements the Paleo-Asian Ocean Closure. (LILEs) and depletions in high field strength elements (HFSEs), with affinities to igneous rocks Minerals 2021, 11, 223. https:// forming in a subduction-related setting. This, combined with regional coeval subduction-related doi.org/10.3390/min11020223 magmatic rocks, indicates that the PAO still existed along the CYS. In addition, the identification of 0 Academic Editor: Clemente Recio 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 Received: 16 December 2020 took place prior to the Late Triassic. Accepted: 19 February 2021 Published: 22 February 2021 Keywords: molasse deposit; zircon U-Pb-Hf isotopes; geochemistry; NE China; Paleo-Asian Ocean Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- 1. Introduction iations. Northeast (NE) China, also called the Xing0an-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; Figure1a) [ 1–8]. It formed as a result of multiple subduction- and collision-related processes during the closure of the Copyright: © 2021 by the authors. Paleo-Asian Ocean (PAO) and the amalgamation of micro-continental blocks with different Licensee MDPI, Basel, Switzerland. origins and geological histories (Figure1b) [4–15]. It is widely accepted that the Solonker- This article is an open access article Xra Moron-Changchun-Yanji suture belt tectonically separates the NCC in the south from distributed under the terms and the micro-continental blocks in the north, and it marks the final closure of the Paleo-Asian conditions of the Creative Commons Ocean [4–6,16–20]. Therefore, the timing of collision and formation of the Solonker-Xar Attribution (CC BY) license (https:// Moron-Changchun-Yanji suture plays a significant role for us to understand the evolution creativecommons.org/licenses/by/ of the PAO. 4.0/). Minerals 2021, 11, 223. https://doi.org/10.3390/min11020223 https://www.mdpi.com/journal/minerals Minerals 2021, 11, x FOR PEER REVIEW 2 of 19 Minerals 2021, 11, 223 2 of 20 collision and formation of the Solonker-Xar Moron-Changchun-Yanji suture plays a significant role for us to understand the evolution of the PAO. SoSo far, althoughalthough aa largelarge number number of of studies studies have have investigated investigated the the sedimentology, sedimentology, pa- paleobiogeography,leobiogeography, magmatism, magmatism, metamorphism, metamorphism, paleomagnetism, paleomagnetism, structural structural deformation, defor- mation,and tectonic and tectonic evolution evolution in the regions in the regions around around the Changchun-Yanji the Changchun-Yanji suture (CYS)suture [21 (CYS–53],) [21–53],some important some important aspects of aspects the geology of the ofgeology this region, of this especially region, especially the precise the time precise of the time final ofclosure the final of the closure PAO, stillof the remain PAO, controversial. still remain controversial. In one school of In thought, one school the finalof thought, closure theoccurred final closure prior to theoccurred Permian, prior mainly to the including Permian, before mainly the Lateincluding Devonian before and the between Late De- the vonianLate Devonian and between [54–56 ]the and Late Early Devonian Carboniferous [54–56] [57 and–59 Early]. In an Carboniferous alternative view, [57–59] the closing. In an alternativeof the PAO view, occurred the duringclosing the of Permian–Triassic,the PAO occurred which during can the be Permian reclassified–Triassic, as during which the canlate be Early reclassified Permian [as60 ,duri61], duringng the thelate Middle–Late Early Permian Permian [60,61] [62, during–65], during the Middle the Late–Late Per- mian [4,34,48,66], during the Late Permian–Early Triassic [3,10,11,21,33,35,40,41,50,67–70], Permian [62–65], during the Late Permian [4,34,48,66], during the Late Permian–Early during the Late Permian–Middle Triassic [5,22,25,26,28,32,42,71,72], and during the Middle– Triassic [3,10,11,21,33,35,40,41,50,67–70], during the Late Permian–Middle Triassic Late Triassic [20,24,37,49,73]. Therefore, substantial controversy remains regarding the [5,22,25,26,28,32,42,71,72], and during the – [20,24,37,49,73] There- closure time of the PAO along the CYS. Middle Late Triassic . fore, substantial controversy remains regarding the closure time of the PAO along the CYS. Figure 1. (a) Tectonic outline of the Central Asian Orogenic Belt (CAOB) and surrounding regions (modified from [74]); Figure 1. (a) Tectonic outline of the Central Asian Orogenic Belt (CAOB) and surrounding regions (modified from [74]); (b) (b) Tectonic sketch map of NE China (modified from [5]). Tectonic sketch map of NE China (modified from [5]). MolasseMolasse generally generally provides provides ample ample evidence, evidence, present present a a record record of regional tectonic evolutions,evolutions, and and have have been been widely widely applied applied to to constrain constrain the the collision collision timing timing in inthe the study study of orogenicof orogenic belt belt [46,75–77]. [46,75–77 In]. this In this contribution, contribution, we wefocus focus on onthe the Yangjiagou Yangjiagou Formation Formation in centralin central Jilin Jilin Province, Province, since since this thisstratum stratum tectonically tectonically experienced experienced the evolution the evolution of the of CYS the andCYS has and the has nature the nature of molasse of molasse and carbonate and carbonate deposits deposits [78,79]. [78 ,Here,79]. Here, we present we present novel novel zir- conzircon U-Pb U-Pb dating, dating, zircon zircon Lu-Hf Lu-Hf isotopic isotopic data data,, and andwhole-rock whole-rock geochemical geochemical and andSr-Nd Sr-Nd iso- topicisotopic data data for forconglomerate conglomerate and and granitic granitic pebbles pebbles within, within, from from the themolasse molasse deposits deposits of the of Yangjiagouthe Yangjiagou Formation Formation in order in order to provide to provide constraints constraints on the on theTriassic Triassic tectonic tectonic evolution evolution of theof the CYS CYS and and the the timing timing of the of the final final closure closure of the of the PAO. PAO. 2. Geological Setting and Sample Descriptions 2.1. Geological Setting Minerals 2021, 11, x FOR PEER REVIEW 3 of 19 Minerals 2021, 11, 223 3 of 20 The central Jilin Province in NE China is located in the western part of the CYS at the junction of the Songnen Block and the NCC (Figure 1b). This region is adjacent to the 2.Dunhua–Mishan Geological Setting and Fault Sample and Descriptions the Songliao Basin to the east and west, respectively (Figure 2.1.1b). Geological The CYS Setting is composed mainly of Phanerozoic granitoids with a series of subduction- The central Jilin Province in NE China is located in the western part of the CYS at therelated junction tectonic of the Songnen mélanges, Block and including the NCC (Figure the Kaiyuan,1b). This region Xia′ertai, is adjacent Hulan, to the Seluohe, Qinglongcun, Dunhua–Mishanand Kaishantun Fault andtectonic the Songliao mélanges Basin to [12,15,2 the east and1–23,25–28,31,35,47]. west, respectively (Figure In1b). addition, minor Paleo- Thezoic CYS and is composed Mesozoic mainly sediments of Phanerozoic are granitoidsalso distribu with ated series in of the subduction-related “granite ocean” [39,43–46,48–50]. tectonic mélanges, including the Kaiyuan, Xia0ertai, Hulan, Seluohe, Qinglongcun, and KaishantunThe tectonic study m areaélanges is [12to, 15the,21 –southeast23,25–28,31,35 of,47 Jilin].