Polyphase structural deformation of low- to medium-grade metamorphic rocks of the Liaohe Group in the Jiao-Liao-Ji Orogenic Belt, North China Craton: Correlations with tectonic evolution

Accepted Manuscript Polyphase structural deformation of low- to medium-grade metamorphic rocks of the Liaohe Group in the Jiao-Liao-Ji Orogenic Belt, North China Craton: correlations with tectonic evolution Zhonghua Tian, Fulai Liu, Brian F. Windley, Pinghua Liu, Fang Wang, Chaohui Liu, Wei Wang, Jia Cai, Wenjiao Xiao PII: DOI: Reference:

S0301-9268(16)30567-8 http://dx.doi.org/10.1016/j.precamres.2017.08.017 PRECAM 4864

To appear in:

Precambrian Research

Received Date: Revised Date: Accepted Date:

30 November 2016 26 July 2017 26 August 2017

Please cite this article as: Z. Tian, F. Liu, B.F. Windley, P. Liu, F. Wang, C. Liu, W. Wang, J. Cai, W. Xiao, Polyphase structural deformation of low- to medium-grade metamorphic rocks of the Liaohe Group in the Jiao-Liao-Ji Orogenic Belt, North China Craton: correlations with tectonic evolution, Precambrian Research (2017), doi: http://dx.doi.org/ 10.1016/j.precamres.2017.08.017

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Polyphase structural deformation of low- to medium-grade metamorphic rocks of the Liaohe Group in the Jiao-Liao-Ji Orogenic Belt, North China Craton: correlations with tectonic evolution

Zhonghua Tiana, FulaiLiua,Brian F. Windleyb,PinghuaLiua, Fang Wanga, ChaohuiLiua, Wei Wanga, JiaCaia, WenjiaoXiaoc

a

Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China

b

Department of Geology, The University of Leicester, Leicester LE1 7RH, UK.

c

State Key Laboratory of Lithospheric Evolution, Institute of Geology and

Geophysics, Chinese Academy of Sciences, Beijing 100029, China

* Corresponding author: Tel.: +86 15811130352; E-mail: [email protected]

Manuscript submitted to Precambrian Research 1st July 2017

Abstract The Paleoproterozoic Jiao-Liao-Ji Orogenic Belt in the eastern North China Craton provides evidence of the evolution from the early rifting and ocean opening to the final collision of the Longgang and Nangrim blocks. However, it is still open to debate, and thus controversial, as to whether the Jiao-Liao-Ji Orogenic Belt formed by closure of a rift without subduction or from an ocean with subduction. Based on detailed field mapping and structural analysis on a micro/meso-scale of the Liaohe Group in the center of the Orogenic Belt, we define at least four phases of deformation and metamorphism. S0 is bedding formed during deposition of the lower Liaohe sediments in the Liaohe back-arc basin. During D1 deformation an early greenschist facies event (M1) was associated with a bedding-parallel S1 metamorphic foliation, penetrative axial planar foliation, micro- to meso-scale folds (F1), and an L1 lineation, all formed during accretion, probably in a trench-subduction setting. An M2 metamorphism took place during medium-pressure Barrovian-type amphibolite facies conditions and associated D2 deformation that gave rise to major thrusts, open-isoclinal folds and a well-developed crenulation cleavage during exhumation of high-pressure and high-temperature rocks and collision of the Longgang and Nangrim blocks. M3 metamorphism at sillimanite (M31) and cordierite (M32) grade was associated with D3 deformation that produced regional gentle re-folds related to post-collisional exhumation of the Orogenic Belt. An M4 retrograde metamorphism and D4 deformation gave rise to a weak foliation that can be correlated with late Cretaceous extension that affected the whole eastern North China Craton. We present new isotopic

ages (LA-ICPMS U-Pb zircon ) of a granitic vein (2162Ma), a pegmatite (1840Ma), and a very late granite (114Ma) that are integrated with relevant published data. Accordingly, the formation age of deformation and metamorphism was set up, and at last, a modified tectonic model was presented.

Keywords: North China Craton, Jiao-Liao-Ji Orogenic Belt, Liaohe Group, Deformation and metamorphism

1. Introduction The North China Craton traditionally consists of three Paleoproterozoic tectonic belts (Fig. 1): the Khondalite Belt in the west, the Trans-North China Orogen in the center, and the Jiao-Liao-Ji orogenic belt (JLJOB) in the east (Zhao et al., 2012). The Paleoproterozoic JLJOB (or the Jiao-Liao-Ji or Liaoji Belt) is located in the NE corner of the North China Craton (Zhai and Santosh 2011; Zhao et al., 2012; Kusky et al. 2016) (Fig. 1). It divides the Eastern Block of the Craton into the Longgang Block to the north in China and the Nangrim Block to the south in Korea (e.g., Zhao et al, 2012, Fig. 1). Several geodynamic models have been proposed to explain the tectonic evolution of the JLJOB including: (1) arc-continent collision model (Hu, 1992; Bai,1993; Faure et al., 2004; Meng et al., 2014; Li et al., 2015), (2) continent-continent collision (He and Ye, 1998a), (3) the opening and closure of an intra-continental rift (Yang et al., 1988; Liu et al., 1997a,b; Luo et al., 2004 and 2008; Li et al., 2005), (4) a retro-arc basin accretion (Kusky et al. 2016).These models are predominantly based on

geochemical, metamorphic and geochronological data, combined with regional lithological studies, but few field-based structural studies have been carried out on this Paleoproterozoic Orogenic Belt, except for Li et al. (2005, 2012) and Peng, et al. (2016). In the middle segment of the JLJOB, three phases of deformation (D1 to D3) and four episodes of metamorphism (M1 to M4) were recognized in the Liaohe Group by Li et al. (2005), who suggested that it formed in a Paleoproterozoic rift; the D1 deformation was related to early extension of the rift, the D 2 and D3 deformations were associated with the final closure of the rift basin. In the southern segment of the JLJOB, most of the Fenzishan and Jingshan Groups (Fig. 1b) underwent three stages of deformation (D1 to D3) and two of ductile shearing (STZ1 and STZ2). However, Li et al. (2012) further concluded that the deformation and metamorphic history of the Fenzishan and Jinshan Groups were related to oblique southeastward subduction beneath the northwestern margin of the Nangrim block (Fig. 1). Stratigraphically, the Liaohe Group is divisible into the North and South Liaohe Groups (He and Ye, 1998; Cai et al., 2002) (Fig. 1b). The North Liaohe Group in eastern Liaoning is well correlated with the Fenzishan Group in eastern Shandong, and the South Liaohe Group in eastern Liaoning is correlatable with the Jingshan Group (Li et al., 2005; Luo et al., 2008; Tam et al., 2011;Li et al., 2012; Zhao et al., 2012) (Fig. 1b). One problem that arises with this correlation is that, according to their structural and metamorphic histories, the Fenzishan and Jinshan Groups in the southern segment of the JLJOB underwent subduction (Li et al., 2012), but the Liaohe Group in the central segment

apparently did not (Li et al., 2005). So, we may well ask: did the North and South Liaohe Groups in the Liaoning area undergo the same subduction/accrection processes as the Fenzishan and Jinshan Groups, as suggested by Li et al(2012)? Peng et al (2016) analyzed the most recent Bouguer gravity anomaly, gravity, magnetic, and electrical profile data, and suggested that a basin-controlling boundary fault (dip to the south) formed during the early stage of formation of the Jiao-Liao-Ji Belt. It represents the tectonic boundary between the Longgang Block and the rift zone, the rift zone was compressed, and thrust faults developed between 1920 and 1900 Ma, the Eastern Block closed by two-way (southward and northward) subduction and collision at ‫׽‬1900 Ma, and the Eastern Block can be regarded as a micro-block. A

mafic magmatic belt, recognized by Faure et al. (2004) between the Longgang and Nangrim blocks, was interpreted as an arc developed above a south-directed subduction zone, which was subsequently overthrust to the north upon the Longgang Block. From structural and metamorphic studies in the JLJOB (Li et al., 2003, 2005, 2012; Tam et al., 2011, 2012a,b,c), we can conclude that this Orogenic Belt underwent polyphase compressive deformation and clockwise P-T path metamorphism, not only in the Laoling Group, North Liaohe, and Fenzishan Groups located in the north, but also in the Ji¶an, Jinshan, and South Liaohe Groups in the south. The model for opening and closure of a rift, as proposed by Li et al. (2005), is difficult to explain with this multi-stage tectonic evolution (Zhao et al., 2012). The aim of this paper is to report new structural and geochronological data from the North and South Liaohe Groups in the central JLJOB, in order to decipher the

multiple structural and metamorphic events in the low- to medium-grade metamorphic Liaohe Group, in order to help resolve some of the problems alluded to above. Thus, combined with previous published geochemical and regional geological data-sets, we have modified the structural and metamorphic history of the Liaohe Group, and accordingly we present a modified tectonic model for the evolution of the JLJOB. 2. Geological setting Geographically, the current JLJOB, which extends for over 2000 km from south (eastern Shandong Province) to north (southern Jilin Province), is situated between NE China in the west and the Korean Peninsula in the east (Fig. 1). Due to its critical position, the JLJOB is not only significant for understanding the evolution of the Eastern Block of the North China Craton, but it is also a key area for study of the geological relationships between northern China and the Korean peninsula (Oh et a., 2015). Tectonically, the Paleoproterozoic JLJOB is situated in the east of the Eastern Block as the collisional Orogenic Belt between the Longgang and Nangrim blocks (Zhao et al., 2012). South of the Nangrim Block in the southern Korean peninsula, there are many small tectonic units, Orogenic belts and basins (Kim et al., 2014; Oh et a., 2015). The southern JLJOB is connected with the Mesozoic Su-Lu Orogenic Belt, which underwent ultrahigh-pressure metamorphism and exhumation tectonics. Recently, many studies have been carried out in the JLJOB on igneous and metamorphic petrology (Tam et al., 2012a, b; Zou et al., 2017), structure (Li et al., 2012), geochemistry (Li et al., 2015; Li and Chen, 2014) and geochronology (Liu et al.,

2014) in order to unravel its tectonic evolution, but nevertheless, the tectonic development of the Jiao-Liao-Ji Belt is still controversial.

2.1 Regional geology of the Jiao-Liao-Ji Orogenic Belt North of the JLOB, the oldest rocks in China are ~3.8 Ga trondhjemitic gneisses that form an Early-Middle Archean basement in the Anshan area in the northern JLJOB (Liu et al., 1997a, b). Also a Late Archean (2.8±2.5 Ga) basement mainly consists of widespread 2.6±2.5 Ga tonalitic±trondhjemitic±granodioritic (TTG) gneisses with minor supracrustal rocks (Zhao et al., 1998). The northern JLJOB includes the Macheonayeong Group in North Korea (Fig. 1b)WKH/DROLQJDQG-L¶DQ Groups in southern Jilin, and the Liaohe Groups in the eastern Liaoning Peninsula. The southern JLJOB contains the Fenzishan and Jingshan Groups in the Jiaobei Terrane, and the Wuhe Group in Anhui Province (Fig. 1b). Stratigraphically, the Fenzishan Group is often correlated with the North Liaohe and Laoling Groups in the north, and the Jingshan Group is comparable with the South /LDRKHDQG-L¶DQ Groups in the south (Luo et al., 2004;Li et al., 2005; Zhao et al., 2005;Lu et al., 2006; Tam et al., 2011). Therefore, the JLJOB can be subdivided into two tectonic belts: the northern belt includes the North Laiohe, Laoling, and Fenzishan Groups, and the southern belt the South Liaohe, -L¶DQDQG-LQJVKDQ Groups. The Qinglongshan-Zaoerling ductile shear zone (Fig. 1b) is in the centre of these two belts (Fig. 1; Li et al., 2005; Zhao et al., 2005, 2012). Generally, the northern belt contains medium-pressure meta-pelitic rocks that

record clockwise P±T paths, whereas the southern belt has low-pressure meta-pelitic rocks and meta-volcanic rocks that have counterclockwise P-T paths (Lu, 1996; He and Ye, 1998). However, from their study of the mineral assemblages of high-pressure mafic granulites in the Jiaobei massif (the Jingshan Group), Tam et al. (2012) recorded a clockwise P-T path, and suggested that the southern segment of the JLJOB underwent subduction/collision-related tectonic processes at 1.93-1.90 Ga.

2.2 Stratigraphy and lithologies of the Liaohe Group The Liaohe Group is probably the most significant lithostratigraphic unit in the JLJOB. It is further divisible into five formations. From the lowermost Langzishan Formation to the uppermost Gaixian Formation (Fig.2), there is an upwards transition from arkoses and volcanic rocks to carbonates and at the top argillites (Li et al., 2005). According to the 1:200, 000 geological map (LBG, 1975) (Fig. 2) and our own field mapping at a scale of 1:50,000 (Fig. 3), the lowermost Langzishan Formation in the northern area (Fig. 2) is transected by many NW/SE-striking faults, and consists of conglomerates, quartzites, garnet-bearing schists and Phyllite (Fig. 2). This Formation contacted with the late Archean Anshan Complex by a normal fault. Based on field observations and U-Pb data, Li et al. (2014a) proposed that the Langzishan Formation is very similar to the Gaixian Formation (upper layer of the Liaohe Group), and suggested that the Langzishan Formation should be grouped with the upper clastic sediments of the Liaohe Group, but not at the bottom, as previously considered. The Gaojiayu and Li'eryu Formations rest conformably on the Langzishan

Formation. They consist of meta-volcanic rocks, gneiss, garnet- and magnetite-bearing schist, amphibolite, and locally marble (Fig. 2). However, in the north (Fig. 2), these two Formations are associated with marble (the Dashiqiao Formation), pegmatite and mafic intrusions. The deformation and metamorphism of these two Formations in the north are much less than in the south. For example, in the north the Gaojiayu Formation consists of slate, and meta-siltstone (greenschist facies metamorphism) that are interbedded with limestone or marble (the Dashiqiao Formation), and the original S0 bedding is well preserved, which indicates that the deformation is weak. In contrast, in the south where deformation and metamorphism are higher, crenulation cleavage and amphibolite facies metamorphic rocks are prominent. These north-south differences enable the Liaohe Group to be subdivided into North and South Groups along the Liudaohe bridge (Fig. 2). Some layers of these two Formations contain iron and phosphate mineral deposits. According to Peng and Palmer (1995) the metamorphosed basal magnetite-microcline beds with their high K content and high Fe2O3/FeO ratio represent original basal red beds of the Liaohe Group, which makes sense and which has never been challenged in later publications. Resting conformably on the Li'eryu and Gaojiayu Formations, the Dashiqiao Formation is composed of marbles, tremolitites, diopsidites, boron-bearin gevaporites, a large magnesite deposit, and occasionally pelitic schists (Fig. 2). The extent of the marbles is considerable, occupying 600 km2 of our study area (Fig. 2). The metamorphic grade of the Dashiqiao Formation in the south is much higher than in the north. Conformably above the Dashiqiao Formation, the Gaixian Formation contains

meta-sandstone and meta-siltstone with a very low grade metamorphism (Fig. 2). 3. Structural analysis of polyphaser deformation history of the Liaohe Group The JLJOB is a structurally complex belt that underwent polyphase deformation. Our new geological map of the Sanjiazi area is shown in Fig. 3. Generally, most of the rocks in this area have undergone moderate to intense deformation, except for the Triassic and Jurassic granites in the southeast and the low-grade metamorphic siltstone (Gaixian Formation) in the northwest. We recognize four phases of deformation (D1 to D4) in the Liaohe Group based on overprinting and refolding relationships.

3.1 Foliation S1 related to D1 deformation Although the Liaohe Group (see section 2.2 and Fig. 2) has undergone multi-phase deformation, the primary bedding is well preserved and easily recognizable. For example, in the Dashiqiao Formation, the original well-preserved bedding (Fig. 4a) can be defined as S0 sedimentary compositional layering, which changes from meta-siltstone interbedded with schist to tremolite-bearing marble; these variations no doubt indicate different sedimentary environments. Fig. 4b shows very thin, compositional sandstone layers (1-10 cm) in marble, and some relict S0 bedding can be recognized in this photograph. Bedding-parallel foliation can commonly be observed in the Dashiqiao and Gaixian Formation (Fig. 4b). In this paper we define this foliation as S1 that formed parallel to bedding, possibly in a water-saturated setting in a trench, which is different from penetrative foliation S1 (cross-cut bedding, Fi.g 4c) that formed from regional

tectonic stresses. We note that Kusky et al. (2016) concluded that the Liaohe Group was deposited in a retro-arc foreland basin and was metamorphosed during Andean-type subduction tectonics. In addition, the main macroscopic surface of the Liaohe Group also contains a metamorphic foliation (penetrative axial planar foliation, S1). Penetrative axial planar foliation (S1) (Fig. 4d) and micro- to macroscopic folds (F1) deformed the original S0 bedding. More than the well-defined S1 metamorphic foliation, small-scale asymmetric, isoclinal, rootless intrafolial and recumbent folds are typically D1 structures, which deformed the original bedding S0 (Fig. 5). For example, recumbent folds in marble, the axial planes of which are sub-parallel to the S1 metamorphic foliation, which dips to the NNE (Fig. 5). A sheath fold in the centre (Fig. 5a) demonstrates extreme shear along hinge (NW to SE) during the first thrust deformation. A ductile shear zone has folded the S1 foliation into tight isoclinal folds with minor folds in the hinge (Fig. 5b), where a competent sandstone layer has been boudined and deformed by axial plane cleavage, which is sub-parallel to the S1 metamorphic foliation (Fig. 5d). Microscopically, the S1 foliation is defined by parallel crystals of feldspar, biotite, muscovite and quartz in a shcist (meta-pelitic) from the Li'eryu Formation (Figs. 6a, 6b). The early mineral assemblage developed at this stage was quartz + albite + muscovite + biotite + chlorite ± garnet (Figs. 6a, 6b). This assemblage and corresponding mineral compositions typically develop at a very low temperature (~400-500ć) and pressure (~2-8Kba) (Proyer, 2003). However, the early metamorphic mineral such as chlorite was difficult to preserve because of the later

metamorphic event. Quartz shows bulging (BLG) and sub-grain rotation (SGR) recrystallization (Figs. 6c-d),which indicates that the deformation temperature was up to 400-500 ć (Passchier and Trouw, 2005, p57). The S1 foliation has a moderate to steep dip and has variable orientation due to later deformation (Fig. 6d). On some schistosity (S1) surfaces of schists in the Li¶eryu Formation there are mineral lineations and aggregate stretching lineations. Aggregate stretching lineations are typically marked by the preferred orientation of quartz rods, biotite, muscovite, and fibrous sillimanite (Figs.4e-f). The L1 lineation has a variable orientation because of the variable orientation of the S1 foliation.

3.2 D2 deformation with crenulation cleavage S2 crenulation cleavage has folded the S1 schistosity (Figs. 6d and 7a-c) in schist (15Tzh40) from the LL¶eryu Formations, Fig. 7a show well-preserved S2 crenulation cleavages in an outcrop and its interpretation map (Upper left corner). The S2 crenulation cleavages have folded the S1 foliations (Fig. 7b) , and a quartz vein originally parallel to S1 was deformed by minor folds, which show S and Z parasitic folds on the limbs of major folds, whereas the hinge region contains M-type folds (Fig. 7b). The axial plane of these parasitic folds has the same orientation as that of the S2 crenulation cleavages. Crenulation cleavages on a macro- and microscopic scale (Figs. 7c-e) consist of microlithon domains, which have the following six characteristics (after Powell, 1979 and Borradaile et al., 1982): (1) the cleavage domain is mica-rich; (2) the microlithons consist of quartz, feldspar, muscovite, sillimanite and occasionally

garnet (Fig. 6d); (3) the spacings of cleavage domains are ~1mm to 3mm apart per centimeter; (4) the volume percentage of cleavage domains (width of the zones) in gneiss, which is almost 30%, shows zonal foliation; (5) the transition between cleavage domains and microlithons is gradational; (6) microfolds in crenulation cleavages have asymmetric shapes. The distribution of these fabric elements in the schist defines the foliation is spaced (crenulation cleavage), which indicate the temperature and deformation increasing. Generally, the S2 crenulation cleavages in this area dip to the WSW at high angles (Fig. 3). Samples 16KD63-2 and D2079 are schist and gneiss from the Li'eryu Formation (Fig. 3) respectively, the metamorphic mineral assemblage of quartz + plagioclase + muscovite + biotite + garnet +staurolite ± kyanite was preserved in this stage of deformation (Figs. 6e-g). Except for well-preserved crenulation cleavages (S2, axial plane foliation), structures designated as D2 also include a series of meter-scale to kilometer-scale tight to open asymmetric folds, and mineral stretching L2 lineations (Fig. 4h), such as meter-scale, tight to open, asymmetric folds in the marble of the Dashiqiao Formation (Fig. 8). The F2 axial planes have the same attitude as the S2 crenulation cleavages, which dips steeply to the WSW, but the L2 lineation is rare. In addition, there are several thrust faults (from WSW to ENE) might relate to D2 in the Dashiqiao Formation, which include imbricate fans and duplexes (Fig. 9) that have the same stress field orientations as the crenulation cleavages and F2 axial planes. The duplexes might result from successive and progressive F2 folding. All these structures such as crenulation cleavage, folds and related thrusts suggest that the D 2 deformation was the

consequence of a regional tectonic compression.

3.3 D3 deformation The D3 deformation produced regional superposed folds (Fig. 8), which deformed the earlier D1 to D2 fabrics. S3 kink bands preserved in a schists (15Tzh40) of the Li'eryu Formation that deform early S1 and S2 foliations (Figs. 7d and 7e). Similarly, in the Yingfengzhai and Tangchi areas three foliations (S1, S2, and S3) were recognized in a single outcrop by Li et al., (2005), the S3 kink bands deflecting S2 surfaces. Mineral assemblage in this stage consisted of sillimanite + garnet + staurolite + plagioclase + quartz + biotite ± cordierite in schist (Figs. 6g and 6h), the presence of sillimanite along S2 planes means that the M3 metamorphism occurred during the D3 deformation. At outcrop scale, typical pressure-decrease structures in garnets are present in plagioclase amphibolites (Fig. 4i). There are regional superposed folds in marbles of the Dashiqiao Formation; the axial plane surface of F2 folds strike NE-SW in the northern part of the cross-section of Fig. 8, and NW-SE in the southern part, and they are deformed by the axial plane surfaces of F3 folds that strike E-W (Fig. 2). The F3 superposed folds are upright and open, but they do not have any appreciable S3 axial plane cleavage. The resulting fold interference patterns include dome-and-basin, mushroom-shape (Ramsay, 1967) and Mode 3 types (Ghosh et al., 1992). In the hinge zones there are rare F3 brittle kink bands in low-grade meta-sedimentary rocks. The D3 phase of deformation formed during relatively lower temperature conditions compared to the D1 and D2 structures,

because S3 foliations are rare or occur as brittle kink bands. Many structures related to D3 include regional-scale thrust faults and shear zones.

3.4 D4 deformation related to Mesozoic extension D4 structures are recognizable in the western part of the study area (Fig. 3). An weakly deformed granitic vein and a pegmatite intruded the marble of the Dashiqiao Formation (Fig. 13). The granite has a Cretaceous LA-ICPMS U-Pb zircon age (see section 4). This Cretaceous intrusion age is probably related to the widespread Cretaceous extension in eastern Asia, as indicated by many metamorphic core complexes (Liu et al., 2005 and 2017). For example, the Liaonan metamorphic core complex formed in the period 120±107 Ma (Yang et al., 2007), a time which is consistent with the initial crystallization temperature of 700°C of zircons in syntectonic leucogranite dikes and granitic intrusions, and the 40Ar/39Ar data on hornblende, biotite, and K-feldspar confirm that these plutons had cooled to ~200°C by 107 Ma. The synkinematic intrusions of the Liaonan metamorphic core complex were emplaced at 128±118 Ma, close to the time of exhumation (Yang et al., 2007). Detachment fault was preserved between the Liaohe Group (hanging wall) and Achean Anshan Group (footwall) in the study area (Fig. 2, columnar picture). Along the fault zone, S-C fabric shows sinistral shearing which indicate the hanging wall was detached (Fig. 4j). Later retrograde metamorphic minerals including chlorite (Fig. 6i) and muscovite (Fig. 6j) might be related to the Mesozoic extension. However, this correlation needs more research.

4. Geochronology Determining the absolute age of deformation (D1 to D4) is difficult, especially for the Paleoproterozoic Jiao-Liao-Ji Orogenic Belt, which underwent many post-Paleoproterozoic tectonic events. Therefore, determination of the relative ages of deformation by means of discordant intrusive veins is important. Many granitic and pegmatitic veins and intrusions help to constrain the timing of D1 to D4. Three samples (15Tzh 36, 15Tzh 30 and 15Tzh 31) from different locations were collected for zircon U±Pb dating. Sample locations are marked in Fig. 3, and detailed experimental methods are given in the Appendix. Firstly, sample 15Tzh 36, which was collected from the southwest of the study area, is one of many granitic veins that intruded marbles of the Dashiqiao Formation (Figs. 10a and b). The granitic veins are ~10 meters long and 3 meters wide (Fig. 10a), have the same feature as the Liaoji granite (Fig. 11a). S1 foliations developed in the granitic veins are the same as in the marble, which indicate that the granitic veins can pre-date the D1. The granitic veins and marble deformed by a shear zone after D1 (age unknown), horizontal lineation was preserved on the fault surface in marble (Fig. 10c). Twenty-nine zircons were selected from sample 15Tzh 36, most of which have long columnar morphologies in cathodoluminescence (CL) images (Fig. 11b). Although the CL images of some zircons are not clear, oscillatory zoning can still be observed, which indicates relatively slow cooling during crystallization. Isotopic ages and data are shown in supplementary Table 1. 206Pb/207Pb ages range from 1676 Ma to 2183 Ma,

and concentrate in two small areas close to or on the Concordia line (Figs. 11c-d). Two age groups are shown in Figs. 11e-f; the older group (11 measurements) has a Paleoproterozoic age of 2162 ±26 Ma, while the second group (17 measurements) has an age of 1720 Ma (Late Paleoproterozoic).We interpret the older age to represent the magmatic crystallization age of the granitic vein, and the younger group a metamorphic age, or the time of later fluid activity (the content of U is much higher than the older age group, see supplementary data table 1). Secondly, samples 15Tzh 31 and 15Tzh 30 are from the same area near a large fault that strikes NNW-SSE (Fig. 3). 15Tzh31 was sampled from a pegmatite vein that intruded a marble of the Dashiqiao Formation (Figs. 10d and 10e). In another cross-section (Fig.10g) or outcrop (Fig. 10h), undeformed pegmatites (similar age, 1802Ma by Yang et al., 2017) intruded into a schist with S2 crenulation cleavage in the Li'eryu Formation. This relationship between pegmatite and schist indicates that the formation age of pegmatite can post-date the D2 &D3 (Fig. 7e). Fig. 12a shows 6 zircons from pegmatite sample 15 Tzh31, most of which have long columnar shapes. However, oscillatory zoning is hard to observe because of the dark color, which might be related to the high uranium content. Isotopic ages and data for this sample are shown in supplementary Table 2. 206Pb/207Pb ages range from 1614 Ma to 1953 Ma, but many ages do not concentrate well on the Concordia line (Fig. 12b), except for one group, which is concentrated in as mall area close to or on the Concordia line, that has an age of 1840Ma (Fig. 12c).We interpret the 1840Ma age to represent the time of formation of the pegmatite.

A younger granitic vein (15Tzh 30) that had intruded the marble and pegmatite has a weak foliation (Figs. 10d and 10f )ˈwhich might be related to the Cretacous extension. Fig. 12d shows 10 zircons from sample 15Tzh 30, almost all of which have long columnar morphologies. Half the zircons have well defined oscillatory zones, and the other half contain oscillatory zones. Isotopic ages and data for this sample are shown in supplementary data Table 3. The 206Pb/238U ages range from 110 Ma to 220 Ma, and concentrate in four small areas close to or on the Concordia line (Fig. 12e). The oldest group contains only one spot with a maximum age of 220.4 Ma, the second group contains 9 spots with an age of 164.4 Ma, the third group contains 10 spots with an age of 136.4 Ma, and the youngest group with 5 spots has a minimum age of 114 Ma (Fig. 12f). We interpret the 164 Ma to 136 Ma age to be the time of magmatic crystallization of the granitic vein.

5. Discussion The data presented above include geological maps, cross-sections, structural and geochronological data for the Liaohe Group, which enables us to decipher the many stages of deformation and related regional metamorphism. Combined with previous regional geological data, we will discuss the relationships between deformation and metamorphism, timing of the deformation and metamorphism stages, and their regional geological implications. Finally, we will present a modified tectonic model of the three tectonic models previously suggested.

5.1 Relationships between deformation and metamorphism Deformation process often associated with metamorphic event in an orogenesis cycle. Not only three stages of deformation were recognized by Li et al. (2005), but also four episodes of metamorphism were discriminated for the Liaohe Group in the Jiao-Liao-Ji orogenic belt. The M1 stage is represented by fine-grained metamorphic muscovite, chlorite, biotite, quartz and albite, which occur in

low-strain lenses

within the S1 schistosity. chlorites, biotites and muscovites grew parallel to original bedding during low-grade crystallization (Li et al., 2005). The authors therefore proposed that the M1 stage formed before the regional D1 deformation. He and Ye (1998) presented that the M1 metamorphism mineral assemblage includes quartz + plagioclase + muscovite + biotite + chlorite ± almandite. Inclusions in almandite are random, which indicate that almandite formed before S1 schistosity (D1). The M1 is represented by quartz + albite + muscovite + biotite ± chlorite ± garnet from meta-pelitic rocks (e.g. D2100, D2127 and 16KD63-2, Fig. 6) in this study. We suggestted that this early greenschist facies metamorphism correlates with formation of the bedding-parallel and metamorphic S1 foliation in D1 for the following two reasons: (1) some inclusions in garnet are random, some of them however show syn-tectonic feature along S1 foliation (Fig. 6b), which indicate that the formation age of M1 and D1 were very close or almost the same; (2) Pre-tectonic (before D1) porphyroblasts preserved in metamorphic minerals at early stage such as chlorite are rare and seem to be uncommon in our study area affected by regional middle-pressure/temperature metamorphism.

Previously, at the M2 metamorphism stage, the presence of low pressure andalusite-bearing rocks that are mainly exposed in the central and southern parts of our study area, whereas the northern part contains medium-pressure kyanite-bearing rocks (He and Ye, 1998). Accordingly, Li et al. (2005) described two representative mineral assemblages that formed during M2 from a schist sample in the Liaohe Group: (1) quartz + plagioclase + muscovite + biotite + garnet + staurolite + kyanite (medium-pressure type) and (2) quartz + plagioclase + muscovite + biotite + garnet +andalusite +staurolite (low-pressure type). This study we only observed the mineral assemblage of quartz + plagioclase + muscovite + biotite + garnet +staurolite ± kyanite without andalusite in M2 from schists and gnesses (e.g. 16KD63-2 and D2079, Fig. 6) in the Li'eryu Formation (Fig. 3). Inclusions in staurolite and garnet at M2 show syn-tectonic characteristic along S2 crenulation cleavage. Garnets formed in D1 from the sample 16KD63-2 are characterized from core to rim by a decrease in spessartine and a increase in pyrope, which indicate a progressive metamorphic process (Figs. 13a-c). We therefore conclude that the second amphibolite facies (M2) metamorphism correlates with the S2 crenulation cleavages in D2. We further proposed that this stage represented the peak-metamorphism and deformation phase resulting from crustal thickening in a compressional tectonic setting. The M3 metamorphic stage is more complicated (Fig. 14a): (1) formation of sillimanite indicates a process of temperature increase (M31); (2) formation of cordierite indicates pressure decrease (M32). Some muscovites and biotites that occur along S2 crenulation cleavages have been partially replaced by sillimanite (Figs. 7d

and 7e) (M31 metamorphism). The presence of sillimanite along S2 planes, deformed by S3 kink band means that the M3 metamorphism occurred a little older than or during the D3 deformation. Typical decompression structures in garnets are present in a gneiss, cordierite reaction rims around the garnet (Fig. 6h). At outcrop scale, typical pressure-decrease structures in garnets are present in plagioclase amphibolites (Fig. 4i) in the study area. We suggetted that the M3 (retrograde, pressure-decrease) correlates with D3 resulting from slab detachment (Wakabayashi, 2004) (M31) and post-collision exhumation (M32). Li et al., (2005) reported that the M3 mineral assemblage consisted of sillimanite + garnet + cordierite + staurolite + plagioclase + quartz + biotite in andalusite-bearing (low-pressure) rocks from the Liaohe Group. From correlation with microstructures, they concluded that the M3 metamorphic stage occurred after D2 before D3. The following two reactions occurred during this metamorphism (M3): (1) 2muscovite + 2H+ = 3sillimanite +3quartz+2K++3H2O and (2) 4biotite = 2sillimanite +10quartz +12 (Mg, Fe)O + 2K2O + 4H2O (Li et al., 2005). A very late retrograde metamorphism (M 4) was recognized in the Liaohe Group in our study area. Undeformed sericites (muscovite) and chlorites occur in retrograde rims, replacing staurolite, garnet, kyanite, andalusite and cordierite porphyroblasts (Li et al., 2005). We suggest that the M4 metamorphism and associated weak deformation (Figs. 10d-f) took place in the Cretaceous regional extension for the following two reasons: (1) after post-collisional (~1840 Ma) (exhumaton) retrograde in the M3 stage, from Meso-proterozoic to at least early Mesozoic the JLJOB was relatively stable, Cretaceous exhumation was the second huge extension event affected the Orogenic

belt; (2) Cretaceous metamorphic core complex developed in the Jiao-Liao-Ji Orogenic belt, caused the deep upper crust ductile shear zone (~15km) detaching to the earth surface, a retrograde metamorphism (M4) occurred in this stage seems reasonable. However, these evidences are lack of geochronology supporting although it is very hard, more age dating work should be down.

5.2 Deformation and metamorphic age Before discussing the timing of D1 to D4, we discuss the depositional age of the Liaohe Group. Previously, the Lower Liaohe Group, as in the Langzishan and Li¶eryu Formations, was recognized forming before 2.46 Ga, because Zhang and Yang (1988) reported U±Pb zircon ages of 2462 Ma from mafic dykes that intruded the Lower Liaohe Group. Plagioclase amphibolites from the Li'eryu and Gaojiayu Formations have Sm±Nd whole-rock isochron ages of 2214f56 Ma and 2063 f 38 Ma (Bai, 1993), respectively, suggesting that the younger 2063 f 38 Ma age was the time of emplacement of the mafic magmas. Paleoproterozoic meta-basalts and related rocks from the Liaohe Group were dated by LA-ICPMS on zircons by Li et al. (2014b), who suggested that the volcanic rocks formed at 2204±2158 Ma and were metamorphosed at 1895±1919 Ma. Tang et al. (2008) studying the į18O and į13C of marbles from the Dashiqiao Formation of Upper Liaohe Group suggested that the carbonates were deposited at 2.33-2.06 Ga, because the most positive į13C excursion appeared at this time during the worldwide Jatulian Event. However, Luo et al. (2004) analyzed detrital zircons from the Lower Liaohe Group (the Langzishan Formation) and found

concordant U±Pb ages ranging from 2.24 to 2.05 Ga, indicating that the Lower Liaohe Group was deposited at some time after 2.05 Ga. The relationship between the Liaoji granite (Figs. 2 and 11a) and the Liaohe Group is significant. A Liaoji fine-grained magnetite-bearing monzogranite has two populations of SHRIMP igneous zircon ages: 2168f13 Ma and 2447 f 28 Ma (weighted mean 207Pb/206Pb age) (Li et al., 2003; Wu et al., 2004). Li et al., (2005) interpreted the former age (2168f13 Ma) to be the time of crystallization of the monzogranite, and the later age (2447 f 28 Ma) to be inherited, because it is similar to the 2501±2466 Ma age of late Archean basement gneisses (Wu et al., 2004). Therefore, Li et al., (2005) considered that the Liaoji monzogranite was emplaced in the period 2168±2094 Ma. The Liaoji granite was considered to have intruded the Liaohe Group (Zhang and Yang, 1988), though no obvious intrusive relationships were recorded. This study, a granitic vein was found in the southwest of our mapping area (Fig. 3 and Fig. 10a), has the same petrologic feature as the Liaoji granite (Fig. 11a). The granitic vein (with S1) was intruded into a marble (also deformed with S1) of the Dashiqiao Formation in the upper part of Liaohe Group. Sample 10Tzh36 from the vein was dated having an age of 2162 Ma, which indicates that (1) the upper layer of the Liaohe Group must be older than 2162 Ma (S0>2162 Ma), and (2) the Deformation age of D1 is younger than 2162 Ma (2162 Ma̱D1). Fortunately, in north of our study area, a gabbro intrusion was found that intruded into the Langzishan Formation in the lower part of the Liaohe Group (Figs. 13d-e). SIMS Pb±Pb dating on baddeleyites from one ~1000 m thick sill nearby the gabbro

intrusion in the Xialiulinzi village yields an average 207Pb/206Pb age of 2115 ±3Ma (n=15,MSWD=2.3), representing the timing of crystallization of these mafic intrusion (Wang et al., 2016). The gabbro was deformed by the D1, foliations in gabbro and phylite of the Langzishan Fromation are the same, its age therefore can pre-date the first stage of deformation and metamorphism (2115 Ma̱D1). Many evidences indicate that a strong metamorphic event occurred at ~1900 Ma in our study area: (1) Lu±Hf isotopes combined with previous geological data indicated two crustal growth events at 2.50 and 2.15 Ga, after which the whole area was reworked by a metamorphic event at 1.90 Ga (Meng et al., 2014); (2) The metamorphic age of the Liaohe Group is constrained by a biotite 40Ar/39Ar age of 1896 f7 Ma from the main detachment shear zone in the Liaohe Group (Yin and Nie, 1996); (3) The volcanic rocks from the Li'eryu Formation in the lower layer of the Liaohe Group formed at 2204±2158 Ma and were metamorphosed at 1895±1919 Ma (Li et al. (2014b); (4) Using integrated petrography, mineral compositions, metamorphic reaction history, thermobarometry, and geochronology, Liu et al., (2013) defined a near-isothermal decompressional clockwise P-T-t path for the Jiaobei High pressure mafic granulites in the southern part of the JLJOB, and suggested that the Jiaobei terrane underwent initial crustal thickening during 1950-1860 Ma, followed by relatively rapid exhumation, cooling, and retrogression in the period 1860-1820 Ma. Accordingly, this study we suggested that the metamorphic event around 1900Ma was consistent with the peak-metamorphic event M2 associated with D2. The D1 accompanied by M1 formed from 2115Ma to ~1900Ma.

A post-tectonic rapakivi granite, which was intruded the Upper Liaohe Group, has a SHRIMP U±Pb zircon age of 1875f10 Ma, suggesting that the metamorphic event occurred before 1875 Ma (Li et al., 2003). Cai et al. (2002) and Wu et al. (2004) obtained U±Pb zircon ages of 1857f20 Ma and 1843f23 Ma respectively, from post-tectonic calc-alkaline syenites that intrude the Liaohe Group, further supporting the conclusion that the metamorphic event of the Jiao-Liao-Ji Belt occurred at ~1.9Ga Ma. This study, based on a field cross-section (Fig. 10g) and many undeformed pegmatite veins that intruded into schists of the Li'eryu Formation with S2&S3 crenulation cleavage, we proposed that the formation age of pegmatite (~1840Ma) can post-date the age of D2 or D3 (Fig. 7e). Accordingly, we posit that the D3 deformation associated with M3 was created at a time between ~1900Ma and ~1840Ma. Extensional deformation, metamorphism and magmatism in the Cretaceous were intense in our study area. Especially the Liaonan metamorphic core complex (Yang et al., 2007; Lin et al., 2011; Liu et al., 2005; Ji et al., 2015) illustrates how magma generation related to detachment faulting was induced by continental lithospheric extension, which resulted from sub-continental lithospheric delamination of the hydro-weakened Eastern Block of the North China Craton caused by multiple hydrous plate subduction (Windley et al., 2005, 2010; Zhai et al., 2007) including westward subduction of the Paleopacific plate in the Early Cretaceous (Ji et al., 2015). Dating granitic intrusions and trachy-dacitic volcanic rocks in a supra-detachment basin obtained a progressive exhumation of the metamorphic core complex between ca. 134 Ma and 113 Ma (Ji et al., 2015). Yang et al. (2007) also pointed out that the

Liaonan metamorphic core complex developed at 120±107 Ma, and that synkinematic intrusions were emplaced at 128-118Ma. Based on the correlation of deformation, metamorphism and their formation ages, the P-T-t-D circle could be set up (Fig. 14a). D1 associated with M1 occurred between 2115Ma to ~1900 Ma (greenschist facies), strongest D2 with peak-metamorphism M2 (clockwise, prograde metamorphism, amphibolite facies) affected the Liaohe Group at ~1900 Ma. From ~1900 Ma to ~1840 Ma,

D3 accompanied by M3 (temperature

increase M31, pressure decrease M32) affected the Jiao-Liao-Ji Orogenic belt. Previously, the metamorphic evolution of the Liaohe Group can be characterized by two different metamorphic pressure-temperature trajectories: a clockwise path for the North Liaohe Group (Fig. 14a) and an anticlockwise P-T path for the South Liaohe Group (Lu et al., 1996; He and Ye, 1998; Li et a., 2001). However, recent study by our group suggested that the South Liaohe Group also experienced a clockwise P-T path (Fig. 14b). Similarly, in the southern Jiao-Liao-Ji Orogenic Belt, four metamorphic stages including the pre-peak (M1), peak(M2), post-peak (M3), and retrograde (M4) were recognized by Tam et al., (2012) through study of microstructural relationships in high-pressure mafic granulites from the Jiaobei massif (Fig. 1b). M1 is represented by the mineral assemblage: garnet (core) + inclusion minerals in garnet (biotite + kyanite + muscovite + plagioclase + quartz + ilmenite). M2 is characterized by garnet (mantle) + K-feldspar + kyanite + plagioclase + biotite + rutile+ ilmenite + quartz. The metamorphic temperatures and pressures of M1 and M2 in the Jiaobei massif were higher than those of M1 and M2 in the Liaohe Group in our study area. Tam et al.

(2012) further demonstrated that the metamorphic evolution of the high-pressure mafic granulites is characterized by a clockwise P-T path, which is consistent with the idea that the high pressure southern segment of the Jiao-Liao-Ji Orogenic Belt formed by subduction, exhumation and collision, and not by the simple closure of a rift system.

5.3 Tectonic setting of Deformation and metamorphism to the Liaohe Group The nature of the D1 deformation of the Liaohe Group has caused considerable controversial view points: (1) D1 resulted from compressional deformation because of many recumbent folds and thrust fault related to D1 could be observed in the Liaohe Group; combined with regional data, the Liaohe Group formed in an N-S back-arc basin, the D1 and D2 deformations resulted from closure of the basin (Hu, 1992; Bai et al., 1993); (2) D1 formed in an extensional environment (Li et al., 1997, 2005; Liu et al., 1997a, b). The D1 deformation formed during regional extension for the following reasons: (1) no large-scale thrust folds and faults were associated with D1; (2) the stratigraphy of the Liaohe sub-groups indicates no stratigraphic repetitions or inversions; (3) the F1 fold axes of the Liaohe Group have variable orientations and plunge, many D1 structures including A-type folds, asymmetric folds, and shear-sense indicators show extensional movements, and L1 lineations and asymmetric pressure shadows of garnets indicate variable motion sense rather than single-direction compressive deformation; (4) the D1 deformational event was related to the emplacement of the Liaoji granitoids, which have a chemical affinity with A-type granites typical of an extensional environment (Zhang and Yang, 1988; Li et al., 1997,

2007; Liu et al., 1997a, b). The structures in our study area (Fig. 2) have not only been modified/replaced by Proterozoic tectonic events, but also by major Cenozoic extensional tectonics. For example, Cretaceous delamination and thinning of the whole Eastern Block of the North China Craton gave rise to major extensional structures such as metamorphic core complexes (Yang et al., 2007; Liu et al., 2005; Ji et al., 2015). Stratigraphic repetitions and inversions of the Liaohe Group associated with the D1 deformation are common in the Sanjiazi and Shangmatun areas (Cross-section in Fig. 2,

Figs. 13 f-g).

The D2 and D3 deformations produced outcrop-scale and regional-scale folds, respectively, which significantly reworked the early D1 fabrics. The variable orientations of F1 fold axes of the Liaohe Group cannot be used as evidence for extension, and similarly for the variable L1 lineations and symmetric pressure shadows of garnets. Small-scale A-type folds, asymmetric folds that are related to D1 are difficult to relate to regional extensional tectonics. The suggestion that the D1 deformation event was associated with the emplacement of most LiaoJi granitoids (monzogranites) is hard to accept for the following reasons: (1) there are no outcropping LiaoJi granitoids in the North Liaohe Group, and yet the rocks there clearly contain abundant D1 structures (Figs. 2 and Fig. 13d); (2) more and more evidences show the LiaoJi granite formed in a subduction-related setting (Yang et al., 2015; Li et al., 2017 ) (3) the LiaoJi granitoids were emplaced at 2168-2094 Ma (Li et al., 2005). This study also obtained a 2162Ma age for the LiaoJi granitoids, which intruded into the Dashiqiao Formation in the upper layer of the Liaohe Group, the

Liaohe Group therefore was a little older than the LiaoJi granitoids. Accordingly, this paper presented that the tectonic setting of D1 was related to the early subduction and accretion for the following reasons: firstly, from the lithologic associations, the Liaohe Group consist of (1) conglomerate, garnet-bearing schist, phyllite in the Langzishan Formation; (2) meta-volcanic rock including rhyolite and mafic rocks, schist, B/Fe2S/P-bearing rocks in the Li'eryu/Gaojiayu Formation; (3) marble and magnesite-bearing marble in the Dashiqiao Formation; (4) meta-sandstone and siltstones in the Gaixian Formation. This lithologic associations is very similar to the modern earth plate tectonic settings: (1) the East African rift valley full of clastic sediments (and in places plume-derived alkaline volcanoes) derived by erosion of the old continental blocks on either side, opens up with deposition of evaporites in Afar Depression with rift-type dykes and lavas, and (2) it opens further to become the Red Sea with carbonate banks/shelves on top of the evaporites, and then (3) the narrow ocean opens further to become the Atlantic Ocean when deeper water shales and pelites with pelagic organisms are deposited. Secondly, Li et al. (2014b) studied the meta-volcanic rocks of the Li¶eryu and Gaojiayu Formations in the Lower Liaohe Group, and concluded that the meta-basalts have a calc-alkaline affinity and an arc-like geochemical composition. These meta-volcanic rocks are enriched in LREEs and LILEs, depleted in HFSEs (Nb, Ta, Zr, +I7L DQGVKRZYDULDEOHKLJKİNd(t). They also suggested that the Paleoproterozoic meta-volcanic rocks formed in an active margin setting, and not in a continental rift setting, and they were subsequently deformed and metamorphosed to amphibolite

facies during arc-continental collision at 1.9 Ga. Trace element analyses of gabbros, pyroxenites and shales from a mafic-ultramafic magmatic belt with marine sedimentary rocks between the northern Archean Anshan Block and a southern Paleoproterozoic block demonstrate formation in a Paleoproterozoic active continental margin above a south-directed subduction zone (Faure et al., 2004). Meta-gabbros, meta-diabases, and amphibolites from the central Liaodong Peninsula (including our study area) were studied by Meng et al. (2014), who suggested they were emplaced at 2154 Ma and metamorphosed at 1897 Ma. Geochemical and isotopic data indicate that the mafic rocks originated from a depleted mantle source, and were metasomatized by subduction-derived fluids. These authors are all suggested that subduction in the eastern Longgang Block started by at least 2150 Ma, and that the rocks formed in a back-arc basin. Thirdly, we considered that the bedding-parallel foliation and penetrative axial planar foliation (S1) associated with the M1 metamorphism was related to early deposition and accretion. The sediments deposited in an ocean (Kusky et al., 2016), experienced M1 (greenschist facies) metamorphism and D1 deformation during accretion and such bedding-parallel primary deformation is characteristic of trench accretion in Japan. The D1 deformation including S1 penetrative axial planar foliation and F1 micro- to mesoscopic folds were superimposed by M2 amphibolite facies metamorphism and thrust deformation during compressional tectonics, probably when the basin or ocean closed by subduction and which led to crustal thickening. Based on former evidences and consider the following two reasons: (1) Large scale thrusting

and crustal thickening causes metamorphism is not always restricted to collisional orogens, they can also occur in the back-arc region of a continental margin arc-trench system, may not have been associated with a collision such as the Sevier and Laramide belts of North America (Dickinson and Snyder, 1978; Wakabayashi, 2004); (2) the size of JLJOB; We therefore suggest that the Liaohe Group deposited in a back-arc tectonic setting. The back-arc basin was closed by subduction at a trench. Similarly, the original ocean between the Eastern and Western blocks of the North China Craton was consumed by subduction, and continent-arc-continent collision, and gave rise to regional top-to-the-NW thrusting, small-scale tight isoclinal folds (F1) and penetrative foliation (S1) in the lithologies of the Hengshan Complex, accompanied by early prograde metamorphism (M1) (Zhang et al., 2007). Metamorphic P-T paths are commonly used as tools to interpret the tectonic history of orogenic belts (Wakabayashi, 2004). Wakabayashi (2004) suggested that clockwise P±T paths from continuous subduction have a high probability of preservation and exposure in young rocks (<~400Ma). Subduction zone metamorphism occurs at high P/T ratios (low geothermal gradients), and is accompanied by high exhumation rates, the chance of preservation of subduction P±T paths is low in old rocks (>~400Ma). Similarly in this study, although a clockwise P-T-t was set up for the Paleo-proterozoic Liaohe Group (Fig. 14a), the M1 stage which we suggested having a relationship with crustal thickening is hard to observe. The M2 metamorphic assemblage are quartz + plagioclase + muscovite +biotite + garnet + staurolite ± kyanite (Figs. 7e-f). The mineral assemblage indicates a

medium-pressure amphibolite facies, and diagnostic of Barrovian-type metamorphism, which was recognized as the thermal relaxation of thickened crust (England and Thompson, 1984). However, Barrovian-type metamorphism was associated with extension and exhumation consequent on thrust tectonics in the Swiss Alps, and the Caledonides of Scotland, which is the type locality for Barrovian isograds (Aoki et al. 2014). Recently, studying the P-T-t constraints of the Barrovian-type metamorphic series in the Khondalite belt of the North China Craton, Huang et al. (2016) suggested that the Daqingshan and Jining terranes in the Khondalite belt (Fig. 1a) belonged to a continental arc and an accretionary wedge, respectively. They further suggested that the P-T paths of the Barrovian metamorphic series in the Daqingshan terrane represent crustal over-thickening during the prograde stage, then an isobaric heating after the Pmax, followed by cooling with exhumation. Therefore, Barrovian metamorphism does not always result from crustal extension, but can also form in a subduction or collision tectonic environment (Dewey and Bird, 1970). Volcanic-sedimentary sequences, granitoids and mafic intrusions formed in the period 2.2-1.9Ga in the JLJOB, which formed as a result of subduction and collision at ~1.9 Ga (Zhao et al., 2012). According to our age dating, the age of D2/D3 was older than the age of pegmatite intrusions (1840 Ma). Combined with previous studies (Faure et al., 2004; Zhao et al., 2012; Meng et al., 2014), we suggest that the D2 deformation and associated metamorphism (M2) was the result of a collisional event at ~1900Ma between Longgang block and Nangrim block. After 1900Ma, the whole Jiao-Liao-Ji Orogenic Belt entered a post-collisional stage. Huge pegmatites that

formed at ~1840 Ma were deformed into lenses, which indicate considerable extension in the post-collisional stage. Structures resulting from the D3 deformation began at this time including regional-scale superposed folds and pegmatite boudinage. Metamorphic event associated with D3 is M3, M3 experienced temperature increase and pressure decrease processes, which correlate with formation of the kink bands and regional superposed folds in post-collisional conditions before the fourth regional extensional deformation (D4). Finally, post-tectonic rapakivi granites and alkaline syenites formed at this stage (Cai et al., 2002; Wu et al., 2004).

5.4 Evolution model of the JLJOB Many tectonic models have been proposed for the evolution of the Jiao-Liao-Ji Orogenic belt (Bai et al., 1993; He and Ye, 1998; Li et al., 2005). From our new data in combination with the efficacies of these models, we are now able to present a new model (Fig. 15), which better portrays the timing and tectonic evolution of the main terranes in the Paleo-proterozoic in the JLJOB. Our new tectonic evolutionary model illustrated in Fig. 15 is explicable as follows: (a) Before or at ~2199 Ma, the Liaohe back-arc basin (similar to the sea of Japan) was beginning to rift, separated the Achaean Anshan basement into the Longgang to the north and Nangrim block to the south. After 2199 Ma, the Liaohe Group including the Langzishan, Li'eryu/Gaojiayu, Dashiqiao Formation (Fig. 2) deposited in the Liaohe back-arc basin. Iron (Fe2S), phosphorus and boron mines deposited at this stage (2199-2162Ma) in the Li'eryu/Gaojiayu Formation. Around 2162Ma (this study),

the carbonate deposited, and provided the original resource of magnesite. Magmatism include Liaoji granite and mafic intrusions began activity at ~2162Ma. (b) Between 2162Ma and ~1900 Ma, the Liaohe back-arc basin was beginning to close, a north-dipping subduction zone formed and affected the Liaohe Group. D1 and M1 formed at the time (~2115Ma) resulting from crustal thickening by subduction. Around 1900Ma, progressive deformation and metamorphism (D2&M2) occurred, at the time, the JLJOB formed because of the collision between the south Nangrim Block and the north Longgang block. (c) From ~1900Ma to ~1840 Ma, the JLJOB underwent slab detachment (increase temperature) and exhumation (decrease pressure), D3 deformation associated with M3 occurred at the time. Pegmatites began to intrude into the Liaohe Group at ~1840Ma. The major Cretaceous extensional event that resulted from sub-continental lithospheric delamination affected the eastern North China Craton as indicated by the creation of many metamorphic core complexes (Davis et al., 2001; Davis et al., 2002; Windley et al., 2010; Lin et al., 2013; Ji et al., 2015). For example, the Liaonan metamorphic core complex formed at 120-107 Ma (Yang et al., 2007; Liu et al., 2017). Synkinematic intrusions were emplaced at 128±118 Ma, close to the time of exhumation of the metamorphic complex (Yang et al., 2007). These ages are close to that of our dated 114 Magranitic vein. Finally, we present a new stage of deformation (D4), which might be related to the Cretaceous exhumation and thinning extensional events. Associated with the new stage of deformation (D4) is a very late retrograde metamorphism (M4).

6. Conclusions The following conclusions can be drawn from our structural, petrological and geochronological investigations of the low-medium-grade metamorphic rocks from the Liaohe Group in the JLJOB: (1) Structural analysis indicates that (a) the D1 structures including a bedding-parallel S1 foliation, penetrative axial planar foliation (S1), and micro- to mesoscopic folds (F1); (b) the D2 structures including a crenulation cleavage and thrust fault, were the result of compressional deformation caused by accretion and thickening, and not by extension in a continental rift. (2) Four deformational events (D1 to D4) and four episodes of metamorphism (M 1 to M4) mutually correlate within the overall structure of the region and correlate with previous studies. The widespread Cretaceous extensional event affected the JLJOB as indicated by a weakly deformed granitic vein and many brittle detachment faults. (3) Our geochronology integrated with regional tectonic data indicates that the S 1 foliation in the D1 deformation took place between 2115 Ma and ~1900 Ma, the D2 deformation occurred at ~1900 Ma, the D3 deformation between 1900 Ma and 1840 Ma, and the last D4 deformation was related to the widespread Cretaceous extension that affected much of eastern China. (4) The D1 associated with M1 was related to subduction and accretion probably in a trench during closure of the back-arc basin between 2162-2115 Ma and 1900 Ma. The D2 associated with M2 was related to collision between the Longgang and Nangrim blocks giving rise to the JLJOB at ~1900Ma. The D3 deformation and

retrograde M3 metamorphism formed in post-collisional times or during exhumation of the JLJOB. Finally, the D4 deformation was related to the Cretaceous extension that affected much of the North China Craton.

Appendix Analytical methods: Zircon cathodoluminescence and geochronology Three samples, 15Tzh 36, 15Tzh 31 and 15Tzh 30, from the central Jiao-Liao-Ji Orogenic Belt, were selected for zircon U-Pb dating. After sample crushing, >100 zircon grains were sorted by standard heavy liquid and magnetic techniques. Representative zircons were selected and mounted on adhesive tape, then enclosed in epoxy resin and polished. CL images were made using a SX51 Electron Probe Micro-analyzer for high-resolution imaging and spectroscopy at the (Institute of Geology, Chinese Academy of Geological Science) IGCAGS. The acceleration voltage during the CL imaging was 15kV. For all the samples, isotopic measurements were made with an Agilent 7500a quadrupole (Q)-ICPMS at the LA-MC-ICPMS laboratory of Northwest University in ;L¶DQ7KHODVHUDEODWLRQVWrategy is a single spot in one zircon. The ICP-MS measurementswere carried out using time-resolved analysis operating in fast-peak-jumping mode (20 ms per peak) and DUAL detector modeusing a short integration time. 207Pb/206Pb, 206Pb/238U, 205Pb/235U and208Pb/232Th ratios were calculated with the GLITTER 4.0 program(Macquarie University), and then corrected using the Harvard zircon91500 as an external standard with a recommended

206Pb/238U age of1065.4±0.6 Ma (Wiedenbeck et al., 2004) to correct for bothinstrumental mass bias and depth-dependent elemental and isotopicfractionation. Concordia diagrams and weighted mean calculationswere made withIsoplot (version2.49)(Ludwig, 2001). U, Th and Pbconcentrations were calibrated using 29Si as an internal standard andNIST SRM610 as an external standard. Zircon standards 91500 and GJ-1were analyzed as unknowns. The two standard zircons \LHOGHGZHLJKWHGPHDQ3E8DJHVRI“0DQ ı  DQG“0DQ ı UHVSHFWLYHO\ZKLFKDUHLQJRRGDJUHHPHQWZLth the recommended ID-TIMS ages (Wiedenbeck et al., 1995). The age data are shown in Tables 1, 2 and 3.

Acknowledgements We thank Dr. Ji'en Zhang, Dr. Jianhui Liu, Prof. Yongsheng Dong, Prof. Jiejiang Yu and Phd students Lishuang Liu, Wang Xu and Fuqiang Li for their helpful discussions and assistance during joint field work. This project was financially supported by the National Natural Science Foundation of China

(Grant no.

41430210) and the Chinese Geological Survey Bureau projects (Grant nos. DD20160121 and 12120114061901), and the Basic Scientific Research Foundations of the Institute of Geology, Chinese Academy of Geological Sciences (grant no. J1613).

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complete P-T path and its tectonic implications. Journal of Asian Earth Sciences 134, 103-121. Figure captions Fig. 1. (a) Tectonic subdivision of the North China Craton and Korea, Modified after Zhao et al. (1998), Zhao et al. (2005) and Oh et al. (2015); (b) Map of the Paleoproterozoic Jiao-Liao-Ji Orogenic Belt in the Eastern Block of the North China Craton, showing the distribution of the Macheonayeong Group in North Korea, the Ji'an and Laoling groups in southern Jilin, the North and South Liaohe Groups in eastern Liaoning Peninsula, the Fenzishan and Jingshan groups in the Jiaobei terrane, and the Jiaobei massif in the Shandong Province, Modified after Zhao et al. (2005). Abbreviations: TB, Taebaeksan Basin, QZSZ, Qinglongshan-Zaoerling Shear zone. Our study area (Fig. 2) is between the Longgang and Nangrim blocks.

Fig. 2. Geological map of the Sanjiazi and Shangmatun area in the central Jiao-Liao-Ji Orogenic Belt (Modified after 1: 200 000 geological maps and combined with our own data) (LBG, 1975). The black dotted line separates the Liaohe Group into the North Liaohe and South Liaohe Groups. Lithostratigraphic units of the Liaohe Group is on the right side. Below the geological map, a detail cross-section is shown from A to A'. The areas of Fig. 3 and Fig. 5 are marked. Locations of three cross-sections of Fig. 8, 9 and 10g are shown. Topographic contour lines are from 90 DEM database (USGS).

Fig. 3. Geological map (Upper) of the Sanjiazi area in the central Jiao-Liao-Ji

Orogenic Belt at a scale of 1:50,000. The lower section crosses most of the strata with a W/E-strike. The sampling points for geochronology dating and thin sections (in Fig. 4 and Fig. 6) are marked. Location of Fig. 10a is shown, topographic contour lines are from 90 DEM database (USGS).

Fig. 4. Photographs showing (a) original bedding S0 between meta-siltstone and marble; (b) original bedding S0 between marble and sandstone and S1 bedding-parallel foliation; (c) S1 foliation cross-cutting the original bedding S0 in a schist of the Li'eryu Formation, which indicate the strata was overturned; (d) well-developed penetrative axial planar foliation (S1) in the Li'eryu Formation; (e) stretching lineation (L1) on the S1 surface; (f) Photomicrographs (cross-polarized light) showing stretching lineation (L1); (g) field characteristic of the schist (15Tzh40) studied in this paper; (h) stretching lineation (L2) on the S2 surface; (i) typical pressure-decrease structures of garnet in plagioclase amphibolite; (j) S-C fabrics developed in a schist of the Li'eryu Group, indicated detachment fault feature.

Fig. 5. An outcrop structural sketch map showing (a) complicated folding in marble of the Dashiqiao Formation, include sheath fold, shear zone-related folds, asymmetry folds and parasitic folds. Photographs showing (b) shear zone-related folds, (c) asymmetry folds. The axial planes of the parasitic folds and sheath folds are parallel to the S1 foliation. Relict S0 bedding can be seen in the hinge zone of the fold (d), a competent cleaved sandstone bed; the cleavage has the same attitude as the S 1

foliation.(e) local development of very small parasitic folds; (f) S1 foliation; insert projections on stereonets are axial planes of asymmetric fold measured in the study area, lower hemisphere equal-area projections.

Fig. 6. Photomicrographs (cross-polarized light) showing (a) S1 foliation marked in a schist (D2100); (b) garnet with inclusions developed in schist (D2127); (c) S1 foliation marked in a schist (D6002), quartz showing bulging recrystallization; (d) S2 crenulation cleavage crossing folded S1 foliation in a schist (15Tzh40);

(e)

cross-polarized light (e) and single-polarized light (f) showing straurolite formed in M2 metamorphic stage; (g) pseudomorphic crystal of kyanite in a gneiss; (h) cordierite formed in the decompression process of M 3 around garnet; (i) chlorite and (j) muscovite retrograde minerals developed in very late metamorphism.

Fig. 7. Photographs showing (a) outcrop-scale of crenulation cleavage S2 from a schist in the Li'eryu Formation (15Tzh 40), and its interpreted map in the top left corner; (b) crenulation cleavage S2 in schist (15Tzh 40) and its interpreted map in the top left corner, which shows the quartz vein intruded into schist and folded; (c) crenulation cleavage S2 in this sample with folded S1, Coin for scale; (d) three generations of foliation are shown, an early S1 foliation is folded with an S2 axial planar crenulation cleavage. S3 kink bands and opened fractures have deformed the S1 foliation (cross-polarized light); (e) local image of (d), single-polarized light.

Fig. 8. Cross-section showing two stages of deformation in marble (location is marked in Fig. 2). In the south of the section, the axial planes of F2 folds strike NW-SE, whereas in the north F2 folds strike NE-SW, which indicates that the F2 has been deformed by E-W striking F3 folds. Insert model shows the F3 folded F2.

Fig. 9. Photographs showing (a) a thrust duplex in marble of the Dashiqiao Formation caused by D2 deformation; (b) and (c) show small parts of the structure; (d) west-plunging phlogopites lineation developed on S1 surfaces, which indicates eastward movement. The yellow lines in (a), (b) and (c) indicate many imbricate thrust faults between horses.

Fig. 10. Photographs showing (a) a granitic vein intruded into marble of the Dashiqiao Formation, and (b) its interpretation map; (c) mineral stretching lineation (L1) defined by sub-horizontal oriented phlogopites in marble; (d) pegmatite veins intruded into marble of the Dashiqiao Formation; (e) the pegmatite has been deformed and extended to form boudins; (f) an intrusive, deformed granitic vein contains fracture cleavages; (g) a cross-section showing the pegmatite can post-date the second/third stage of deformation (D2&D3); (h) pegmatite intruded into a schist, see (g) for location.

Fig. 11. (a) outcrop showing the characteristic of Liaoji granite; (b) Cathodoluminescence (CL) images of zircons from sample 15Tzh 36, on which analytical spots with a diameter of 32 µm are marked with yellow circles. The CL

images were made with a SX51 Electron Probe Micro analyzer for high-resolution and spectroscopy at the IGCAGS in Beijing; (c) and (d) U±Pb Concordia age diagrams for zircons from the granitic vein 15Tzh 36, marked in Fig. 2 in the Sanjiazi area. Data-SRLQWHUURUHOOLSVHVDUHıe) and (f) show the weighted average 207Pb-206Pb ages for the younger and older Groups, respectively. All the data are listed in supplementary data Table 1. Fig. 12. Cathodoluminescence (CL) images of zircons from sample 15Tzh 31 (a) and sample 15Tzh 30 (d).(b) and (e) are U±Pb Concordia age diagrams for zircons from pegmatite vein 15Tzh 31 and the granitic vein 15Tzh 30, respectively, which are all marked in Fig. 2. Data-SRLQWHUURUHOOLSVHVDUHıF DQGI VKRZWKHZHLJKWHG average 207Pb-206Pb and 238U-206Pb ages for these two samples. All the data are listed in supplementary data Tables 2 and 3.

Fig. 13. (1) A Garnet from sample 16KD63-2 (location see Fig. 3) in the Li'eryu Formation of the Liaohe Group (b) spessartine decrease and (c) pyrope increase, SEM in the IGCAGS. (d) Field picture showing a gabbro intruded into a phyllite of the Langzishan Formation, the S1 foliation developed in the gabbro is the same as in phyllite (e), which indicate that the gabbro can pre-date the D1; (f) Field picture showing the relationship between original bedding S0 and cleavage S1 in the Li'eryu Formation of the Liaohe Gorup, (g) Local picture showing the bedding/cleavage relationship from (f), the dip angle of S0 is much higher than cleavage S1, which indicate that bedding is overturned; sketch map showing the reason of S0 overturned.

Fig. 14. (a) Metamorphic P-T path (black solid line) of the North Liaohe Goup (He and Ye, 1998); Red solid line represents a metamorphic P-T path of the South Liaohe Group, 16KD63-2, D2079, 15Tzh40 and D2077 (Fig. 3) are referenced, combined with data from Li et al. (2005); (b) Metamorphic P-T paths of midium-pressure pelitic granulite in the South Liaohe Group (Liu et al., 2015).

Fig. 15. Tectonic evolution of the Jiao-Liao-Ji Orogenic belt; (a) the Liaohe back-arc basin began to rift before or at 2199Ma, then the Liaohe Group deposited in the basin; (b) subduction to collision stage at 2162 Ma (this study)-2115Ma (Wang et al., 2016) to ~1900 Ma; (c) collision to exhumation stage at ~1900 to ~1840 Ma (this study), detail explanation see the chapter 5.4.

Tables Table 1 U-Pb isotope dates of magmatic zircons from the granitic vein (15Tzh 36) that intruded marble of the Dashiqiao Formation in the Sanjiazi area. See Fig. 3 for sample location. Table 2 U-Pb isotope dates of magmatic zircons in the pegmatite (15Tzh 31) from the Sanjiazi area. See Fig. 3 for the sample location. Table 3 U-Pb isotope dates of magmatic zircons in the granitic vein (15Tzh 30) that intruded the marble and pegmatite in the Sanjiazi area. See Fig. 3 for the sample location.

Highlights 1. The D1 structures were the result of compressional deformation caused by crustal thickening 2. (D1 to D4) and (M1 to M4) mutually correlate within the overall structure of the region and correlate with previous studies 3. The D1 &M1 , D2&M2 , D3 &M3 and D4&M4 were related to subduction and accretion (2162-1900 Ma), collision (forming the Jiao-Liao-Ji Orogenic Belt, ~1900 Ma), post-collisional (1900-1840Ma) and the Cretaceous extension events, respectively.

Graphical abstract