Situated between the Tarim Block, Siberian Block (SB), and North China Craton (NCC), the Central Asian Orogenic Belt (CAOB) (Figure 1a) is the world’s largest and youngest segment of Phanerozoic crust, formed through complex accretionary processes [1,2]. Its evolution is dominated by the bidirectional subduction of the Paleo-Asian Ocean (PAO): northward beneath the SB during the Ordovician-Silurian, and southward beneath the NCC from the Devonian to Triassic [3,4]. The CAOB represents the most significant region documenting Phanerozoic crustal growth, with subduction and accretion processes initiating as early as the Ordovician along the southern Siberian margin. While these early stages were dominated by progressive accretionary tectonics, our study focuses specifically on the terminal closure of the PAO during the late Permian to Triassic along the northern NCC margin. The CAOB represents the most significant region documenting Phanerozoic crustal growth [1,2], with subduction and accretion processes initiating as early as the Ordovician along the southern Siberian margin. While these early stages were dominated by progressive accretionary tectonics, our study focuses specifically on the terminal closure of the PAO during the late Permian to Triassic along the northern NCC margin. Since the Neoproterozoic, the CAOB has undergone complex subduction–accretion processes, closely linked to the double-sided subduction of the PAO plate during the Paleozoic–Mesozoic. Its unique geographical position and geological history make it a focus of geological research [5,6]. The northeastern segment of the CAOB, located within Northeastern China, is traditionally referred to as the Xingmeng Orogenic Belt (XOR). This belt comprises a series of crustal fragments (microcontinental blocks, island arcs, accretionary wedges, and ophiolites that underwent progressive amalgamation [7,8,9]. Recent studies [4] suggest many of these fragments may have shared a common tectonic history since ~500 Ma, though their final amalgamation records the PAO’s subduction and subsequent Siberian-NCC collision [3,10,11]. During the Mesozoic, the XOR was further modified by the superposition of the circum-Pacific and Mongolia–Okhotsk tectonic domains [10], which resulted in an extremely complex tectonic evolution [3,12,13,14,15,16]. Therefore, a better understanding of the geological evolution of the XOR is essential to reconstruct the tectonic history of the CAOB. Current data indicate several issues and controversies regarding the Late Paleozoic to Early Mesozoic evolution of the XOR, particularly concerning the timing and location of the closure of the PAO and the collision processes along the northern margin of the NCC. Two competing viewpoints exist regarding the timing of the closure of the PAO: one hypothesis suggests that the collision between the NCC and northern blocks occurred between the Middle to Late Devonian and Early Carboniferous [10,17], while the other suggests that the collision occurred during the Late Permian–Early Middle Triassic [3,18]. One view places the collision between the NCC and northern blocks along the Solonker–Hegen–Heihe zone [7,19,20], whereas another locates it along the Solonker–Xar Moron–Changchun–Yanji zone [9,13,15,18,21]. Another major debate centers on whether the eastern margin of the NCC was in a collisional or post-collisional stage during the Triassic. Different interpretations include the following: (1) an extensional environment due to post-collisional gravitational collapse triggered by isostatic rebound following slab breakoff [22]; (2) extension-induced decompression melting within the mantle wedge above the subducted slab [19]; (3) possible continuation of the NCC–northern blocks collision into the Middle Triassic [23]. These interpretations reflect two fundamental debates about Triassic tectonics: (1) The tectonic state—whether the region was in post-collisional extension or still experiencing terminal collision; (2) the driving mechanisms of extension, where some models emphasize (a) slab breakoff-induced collapse [22]; (b) mantle wedge decompression [19]; (c) detachment of PAO fragments [14,16,24,25].

The northern Liaoning region is located south of the Solonker–Xar Moron–Changchun–Yanji suture zone and spans two major tectonic units: the NCC and XOR (Figure 1b). During the Paleozoic, this region recorded the responses to the retreating subduction zone of the PAO, characterized by back-arc basin extension and fragmentation of the continental margin, culminating in the final closure of the PAO. This complex evolution involved intense magmatic activity and diverse geological processes [26,28,29,30,31,32,33,34,35,36,37]. To address stratigraphic uncertainties in northern Liaoning, our geological fieldwork employed detailed structural–lithological mapping, with particular attention to tectonic mélange zones as key markers of paleo-subduction and collision boundaries [38]. This approach follows established methodologies for resolving complex orogenic belts, where mélange zones—despite their complexity—provide critical evidence for reconstructing tectonic interfaces between distinct crustal blocks [38]. This approach enabled us to redefine and formally separate the previously ambiguous “Fangjiatun Formation” and “Tongjiatun Formation”. These two formations were distinguished by contrasting matrix compositions and rock fragment assemblages. Both formations contain a series of Permian–Triassic intermediate metavolcanic rocks. The Fangjiatun–Tongjiatun contact zone, a suture-parallel melange, preserves relics of the PAO subduction. Volcanic clasts in Fangjiatun directly correlate with our dated magmatic suite, while Tongjiatun’s Proterozoic clasts indicate crustal recycling during the NCC–Songliao collision [18,38]. This study investigates the geochronology and geochemistry of these magmatic rocks and explores the nature of the magma source and tectonic evolution in the area covered by the Songliao Basin along the eastern margin of the NCC, providing essential data for understanding the tectonic history of the southern margin of the XOR.

The study area is tectonically complex and bordered by the Solonker–Xar Moron– Changchun–Yanji suture zone, with the eastern segment of the CAOB to the north and the NCC to the south (Figure 1c,d). The research area lies within the PAO domain, encompassing distinct near-EW-trending active continental margin belts of both Early and Late Paleozoic age, primarily developed along the northern margin of the NCC since the Ordovician. Since the Mesozoic, the study area has been within the circum-Pacific tectonic domain, with extensive superposition of rift basins and the development of NE- and NNE-oriented structures. The study area preserves a pre-Mesozoic basement composed primarily of highly metamorphosed and deformed intrusive-volcanic complexes, now partially overlain by Mesozoic sedimentary cover. After the Mesozoic, the area became covered by the sedimentary strata of the Songliao Basin and intermediate basic to acidic volcanic rocks. The exposed strata mainly include Early Cretaceous Yixian Formation volcanic rocks, Early Cretaceous Shahuizhen Formation sedimentary strata, and mid-Cretaceous Quantou Formation sedimentary strata. The study area predominantly comprises Silurian, Permian, Triassic, and Jurassic granitic intrusions (Figure 1d).

For this study, Mesozoic–Triassic magmatic rocks were chosen for geochronological and geochemical analyses. Representative sample collection locations are shown in Figure 1c. The samples include the Gongzhuling rhyolite and dacite, Wangjiadian dacite, Wafangxi rhyolite, Haoguantun rhyolite, and Sheshangou pluton.

The Gongzhuling rhyolite (PM107-9, 123°16′32″ E, 42°30′55″ N) and Gongzhuling dacite (PM107-8, 123°16′32″ E, 42°30′54″ N) are located in the eastern part of the study area, covering a small area, in contact with Early to Middle Permian volcanic rock structures. The Gongzhuling rhyolite has a foliated granoblastic texture with foliate and massive structures. The rock consists of quartz (±60%), muscovite (±35%), and hornblende (±5%), with quartz being the predominant felsic mineral (Figure 2a and Figure 3a). The Gongzhuling dacite has a similar foliated granoblastic texture with a mylonitic structure. It is composed of felsic minerals (±55%), biotite (±20%), muscovite (±10%), and hornblende (±15%). The felsic minerals are mainly quartz, which is elongated and oriented, with some parts showing banded quartz (Figure 2b and Figure 3b).

The Wangjiadian dacite (LWY, 123°15′30″ E, 42°33′12″ N) is exposed in the northeastern part of the study area, covering approximately 0.51 km². The Gongzhuling dacite is tectonically juxtaposed with Early–Middle Permian volcanic rocks within the NNE-trending shear zone, as evidenced by its foliated granoblastic texture and mylonitic structure. This contact represents a tectonic boundary rather than a magmatic inclusion, confirming its emplacement during post-collisional deformation. The rock is composed of felsic minerals (±57%), muscovite (±25%), biotite (±15%), and hornblende (3%). The felsic minerals include feldspar and quartz, with some feldspar exhibiting a ball structure, indicating a mylonitic structure. Biotite and muscovite are arranged in a continuously oriented manner, forming a foliated structure (Figure 2c and Figure 3c).

The Wafangxi (PM201-5, 123°33′16″ E, 42°39′12″ N) and Haoguantun rhyolites (PM202-6, 123°34′21″ E, 42°37′57″ N) are exposed in the northwestern part of the study area and are in contact with Early to Middle Permian volcanic rocks. The Wafangxi rhyolite covers an area of approximately 1.1 km². The rock appears grayish-white, with a mylonitic structure, and the matrix has a foliated granoblastic texture containing phenocrysts of plagioclase and quartz. Plagioclase (±7%) develops polysynthetic twinning, with weak clay and carbonate alteration. Quartz (±5%) forms several lens-shaped and short-banded aggregates that are oriented. The matrix is mainly composed of small felsic minerals and muscovite, with felsic minerals (±48%) being granular and embedded with muscovite (±40%), showing an oriented distribution (Figure 2d and Figure 3d).

The Haoguantun rhyolite (PM202-6, 123°34′21″ E, 42°37′57″ N) is exposed in the northwestern part of the study area, covering an area of approximately 1.2 km². The rock appears grayish-white, with a weak mylonitic structure, predominantly composed of felsic components. The rock consists of muscovite (±5%), feldspar (±15%), alkaline feldspar (±45%), and quartz (±35%). The feldspar and quartz appear elongated or lens-shaped, with muscovite appearing as fibrous sheets, constituting a weak mylonitic structure. Plagioclase exhibits polysynthetic twinning. Alkaline feldspar is composed of microcline and exhibits grid-like twinning (Figure 2e and Figure 3e).

The Sheshangou pluton (SSGC, 123°29′47″ E, 42°30′34″ N) is exposed in the central part of the study area, covering 12.95 km². It intrudes Middle Triassic granite and Middle Permian quartz diorite bodies. The lithologies include monzogranite and muscovite-bearing monzogranite. The rock appears gray with a faint pink hue, exhibiting a medium-to-coarse-grained granite structure and massive texture. The mineral composition includes muscovite (±5%), plagioclase (±30%), alkaline feldspar (±40%), and quartz (±30%). Plagioclase exhibits polysynthetic twinning, while alkaline feldspar appears as striped feldspar, with some developing Carlsbad twinning (Figure 2f and Figure 3f).

Major elements were analyzed by XRF (1–5% precision) and trace elements by ICP-MS (>10% precision), using contamination-free equipment. Zircon U-Pb dating employed a 193 nm laser ablation system (32 μm spot) coupled with ICP-MS, with data processed using ICPMSDATACAL and Isoplot, following Andersen’s Pb-correction method [39] and Yuan et al.’s protocol [40]. Zircon Lu-Hf isotopes were analyzed via laser ablation MC-ICP-MS (60 μm spot), yielding ¹⁷⁶Hf/¹⁷⁷Hf values of 0.282316 ± 30 (91500) and 0.282507 ± 50 (MT), with methods detailed in Geng et al. [41].