Tectonic nature of the NE Asian continental margin during the Late Jurassic–Early Cretaceous: constraints from the geochronology and geochemistry of igneous rocks in the NE North China Craton

ABSTRACT This paper presents geochronological, geochemical, and zircon Hf–O isotope data for late Mesozoic intrusive rocks from the northeastern North China Craton (NCC), with the aim of constraining the late Mesozoic tectonic nature of the NE Asian continental margin. U–Pb zircon data indicate that the Late Mesozoic magmatism in the northeastern NCC can be subdivided into two stages: Late Jurassic (161 − 156 Ma) and Early Cretaceous (125 − 120 Ma). Late Jurassic magmatism consists mainly of monzogranites. These monzogranites display high Sr/Y ratios and the tetrad effect in their REE, respectively, and have negative εHf(t) values (−22.6 to −15.8). The former indicates that the primary magma was generated by partial melting of thickened NCC lower crust, the latter suggests that the monzogranites were crystallized from highly fractionated magma, with the primary magma derived from partial melting of lower continental crust. Combined with the spatial distribution and rock associations of the Late Jurassic granitoids, we conclude that the Late Jurassic magmatism in the eastern NCC formed in a compressional environment related to oblique subduction of the Paleo-Pacific Plate beneath the Eurasia. The Early Cretaceous magmatism consists mainly of granitoids and quartz diorites. The quartz diorites formed by mixing of melts derived from the mantle and lower crust. The coeval granitoids are classified as high-K calc-alkaline and metaluminous to weakly peraluminous series. Some of the granitoids are similar to A-type granites. The granitoid εHf(t) values and TDM2 range from −14.3 to −1.4 and 2089 to 1274 Ma, respectively. These values indicate that their primary magma was derived from partial melting of lower crustal material of the NCC, but with a contribution of mantle-derived material. We therefore conclude that Early Cretaceous magmatism in the northeastern NCC occurred in an extensional environment related to westward subduction of the Paleo-Pacific Plate beneath Eurasia. Graphical abstract


Introduction
The continental margin of northeast (NE) Asia includes the Xing-Meng Orogenic Belt (XMOB), the eastern North China Craton (NCC), eastern South China Block (SCB), the Sikhote-Alin Orogenic Belt (SAOB), the islands of Japan, and Korean Peninsula.The area has a complex tectonic history (Li et al. 1999;Wu et al. 2011;Tang et al. 2018).During the Palaeozoic, the tectonic evolution of the continental margin of NE Asia was characterized by the collision and amalgamation of microcontinents and the final closure of the Paleo-Asian Ocean (Sengör and Natal'in 1996;Li 2006;Zhang et al. 2018;Tang et al. 2019).During the Mesozoic the region was influenced by the circum-Pacific tectonic regime (Xu et al. 2013;Guo et al. 2015).Recently, the intensive studies on the Mesozoic tectonic evolution of the NE Asian continental margin have been carried out and focus mainly on two items, i.e., the timing of the onset of subduction of the Paleo-Pacific Plate beneath Eurasia (Ernst et al. 2007;Wu et al. 2007;Xu et al. 2009Xu et al. , 2013;;Zhou et al. 2009;Sun et al. 2015;Wilde and Zhou 2015;Yang et al. 2015;Bi et al. 2016;Tang et al. 2018) and the relationship between the subduction of the Paleo-Pacific Plate and Yanshanian Movement (Dong et al. 2015;Zhu et al. 2017;Wu et al. 2018;Zhu and Xu 2019).For the timing of the onset of subduction of the Paleo-Pacific Plate beneath Eurasia, four main hypotheses have been proposed: early Permian (Ernst et al. 2007;Yang et al. 2015;Bi et al. 2016), Late Triassic (Wu et al. 2011;Wilde and Zhou 2015), Late Triassic to Early Jurassic (Zhou and Li 2017), and Early Jurassic (Xu et al. 2013(Xu et al. , 2019;;Guo 2016;Wang et al. 2017aWang et al. , 2017b;;Tang et al. 2018;Zhang et al. 2019).At present, the favoured hypothesis is that subduction began in the Early Jurassic, as evidenced by the spatio-temporal distribution of Mesozoic igneous rocks on the continental margin of NE Asia (Yu et al. 2012;Xu et al. 2013Xu et al. , 2019;;Guo et al. 2015;Li et al. 2018;Tang et al. 2018;Zhang et al. 2019).Additionally, the late Early Cretaceous-Palaeogene tectonic evolutionary history of NE Asian continental margin have been well constrained based on spatio-temporal variations of late Mesozoic -Cenozoic igneous rocks (Xu et al. 2013;Tang et al. 2018;and references therein;Zhu and Xu 2019).However, compared with the Early Mesozoic and late Early Cretaceous-Palaeogene tectonic natures in NE Asian continental margin, the Late Jurassic to early Early Cretaceous tectonic nature remains controversial.Some authors have suggested that the Paleo-Pacific Plate had been continuously subducting beneath Eurasia since the Early Jurassic, forming the active continental margin of NE Asia during the Jurassic−Cretaceous (Zhou and Li 2000;Wu et al. 2005), whereas others hypothesized that flat subduction of the Paleo-Pacific Plate occurred during this period (Zheng et al. 2018).These varied hypotheses exist due to the lack of the Late Jurassic-early Early Cretaceous magmatisms along the continental margin of NE Asia and the limited number of studies on the Late Jurassic−early Early Cretaceous igneous rocks in the eastern NCC (Wu et al. 2005(Wu et al. , 2007;;Xu et al. 2013;Tang et al. 2018).As an important part of the continental margin and the largest ancient craton in China, the NCC is an ideal study area for constraining the tectonic conditions of the NE Asian continental margin during the late Mesozoic.To establish these conditions, we present here new zircon U-Pb ages, Hf-O isotope data, and major and trace element compositions of the Late Jurassic and Early Cretaceous intrusive rocks from the northeastern NCC.

Geological background
The continental margin of NE Asia consists of NE China, eastern North China, Russian Far East, Japan, and South and North Korea, tectonically corresponding to the Xing-Meng (Xing'an-Mongolian) Orogenic Belt (XMOB), the eastern NCC, the Sikhote-Alin Orogrnic Belt (SAOB), Japanese islands and Korean Peninsula.The eastern NCC is an important part of the continental margin of NE Asia and bounded by the Dabie-Sulu orogenic belts to the south and southwest, the Korean Peninsula to the northeast, and the XMOB to the north (Figure 1(a,b); Lu et al. 2003).The study area is located in the northeastern segment of the NCC.The Dunhua-Mishan Fault, as a branch of the Tan-Lu Fault, cuts the northwestern part of the area, and the Yalujiang Fault cuts across the southern area (Figure 1(b)).
The study area consists mainly of Late Archaean-Paleoproterozoic basement rocks, and can be subdivided into three tectonic units: the Longgang Block (LGB) in the north, the Liaonan-Nangrim Block in the south and the intervening Paleoproterozoic Liao-Ji Orogenic Belt (PLJB) (Figure 1(a,b); Bai 1993;Zhao et al. 2001, Zhao et al. 2005).Paleoproterozoic rocks unconformably overlie the Neoarchean rocks and metamorphosed during a 1.9-1.85Ga orogenic event (Lu et al. 2004;2006).Subsequently, the southern Liaoningsouthern Jilin area was covered by thick sequences of Meso-to Neoproterozoic and Palaeozoic sediments.Before the Mesozoic, igneous activity was weak, indicating that the study area was tectonically stable.Small amounts of Late Triassic and Jurassic volcanic and intrusive rocks occur in southern Jilin-south Liaoning provinces (Lu et al. 2003;Sun et al. 2005;Wu et al. 2005;Yang et al. 2007a;Pei et al. 2008;Yu et al. 2009).In contrast, the Early Cretaceous igneous rocks are widely distributed, and occupy an area of about 20,000 km 2 in southern Jilin-south Liaoning provinces (BGMRJ (Bureau of Geology and Mineral Resources of Jilin Province) 1988; Fang 1992;Wu et al. 2005;Yang et al. 2005;Pei et al. 2006, Pei et al. 2008, Pei et al. 2009, Pei et al. 2011;Yu et al. 2009).

Sample descriptions
A number of granitoid plutons are distributed along the Yalujiang Fault in southern Jilin Province, between the cities of Ji'an and Linjiang.Representative samples were selected from seven plutons for geochronological, geochemical, and isotope analyses (Figure 1(b)).From northeast to southwest, these are the Yaolin, Lishugou, Shengping, Shihu, Laoling, Ji'an, and Yushulinzi plutons (see Sections 2.1-2.7 for descriptions).The petrographic characteristics of the studied samples and details of the plutons are listed in Supplementary Table 1.
The classification and nomenclature of these igneous rocks are shown in Figure 3.

Analytical methods
Zircons were separated from samples using conventional heavy liquid and magnetic techniques and purified by handpicking under a binocular microscope at the Langfang Regional Geological Survey, Hebei Province, China.The zircon U-Pb dating and in situ Hf isotopic analyses were undertaken at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, China.In situ O isotopic analysis was undertaken at the State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Guangzhou, China.Details of the analytical methods used are given in the Appendix.

Zircon U-Pb dating
For this study, eight samples collected from seven plutons were obtained for LA-ICP-MS zircon U-Pb dating.CL images of representative zircons are shown in Figure 4.The zircon U-Pb analytical results are listed in Supplementary Table 2, and concordia diagrams are presented in Figure 5. Zircons from the eight samples are euhedral, 100 − 200 μm in size, exhibit typical oscillatory zoning (Figure 4), and have Th/U ratios of 0.21-2.52(Supplementary Table 2), consistent with a magmatic origin.The zircon U-Pb ages represent the crystallization ages of these intrusive rocks.

Lishugou pluton
Twenty four analyses on zircons from a biotite monzogranite sample (16XJ4-1) from the Lishugou pluton define a tight cluster on a concordia and yield a weighted mean 206 Pb/ 238 U age of 161 ± 1 Ma (Figure 5(a)), interpreted as the emplacement age of the Lishugou Pluton.

Yaolin pluton
Twenty one analyses on zircons from a muscovite monzogranite sample (16XJ1-1) from the Yaolin pluton gave 206 Pb/ 238 U ages that fall into two groups with weighted mean ages of 156 ± 1 Ma and 176 ± 1 Ma (Figure 5(b)).The former is interpreted to represent the crystallization age of the monzogranite, whereas the latter represents the crystallization ages of captured zircons entrained by the monzogranite magma.

Shengping pluton
Twenty two analyses on zircons from an alkali feldspar granite sample (16XJ8-1) from the Shengping pluton define a tight cluster on a concordia and yield a weightedmean 206 Pb/ 238 U age of 125 ± 1 Ma (Figure 5(c)), interpreted as the crystallization age of the alkali feldspar granite.

Ji'an pluton
Zircons from alkali feldspar granite sample (16XJ14-1, 21 analysis points) and granophyre sample (16XJ15-1, 23 analysis points) from the Ji'an pluton were analysed.These analyses form a tight cluster on a concordia and yield weighted-mean 206 Pb/ 238 U ages of 125 ± 1 (Figure 5(d)) and 121 ± 1 Ma (Figure 5(e)), respectively.They are interpreted as the crystallization ages of the alkali feldspar granite and granophyre, respectively.

Shihu pluton
Twenty analyses on zircons from a syenogranite sample (16XJ6-1) from the Shihu pluton define a tight cluster on a concordia and yield a weighted-mean 206 Pb/ 238 U age of 121 ± 1 Ma (Figure 5(f)), interpreted as the crystallization age of the syenogranite. .Classification of the Late Jurassic-Early Cretaceous igneous rocks in this study according to modal mineral contents (Streckeisen 1978).A, alkali feldspar; P, plagioclase; Q, quartz.

Yulin pluton
Twenty two analyses on zircons from a syenogranite sample (16XJ17-1) from the Yulin pluton define a tight cluster on a concordia and yield a weighted-mean 206 Pb/ 238 U age of 121 ± 1 Ma (Figure 5(g)), interpreted as the crystallization age of the syenogranite.

Laoling pluton
Twenty eight analyses on zircons from a quartz diorite sample (16XJ7-1) from the Laoling pluton define a tight cluster on a concordia and yield a weighted-mean 206 Pb/ 238 U age of 120 ± 1 Ma (Figure 5(h)), interpreted as the crystallization age of the quartz diorite.

Major and trace elements
The late Mesozoic intrusive rocks in the study area comprise a suite of monzogranites, syenogranites, granophyre, alkali feldspar granites, and quartz diorites.
Major and trace element data for these intrusive rocks are presented in Supplementary Table 3.

Late jurassic intrusive rocks
The

Emplacement age of late Mesozoic granitoids in the northeastern NCC
The late Mesozoic magmatic events in the northeastern NCC can be subdivided into at least two stages based on our zircon U− Pb ages: Late Jurassic (161-156 Ma) and Early Cretaceous (125 − 120 Ma).The Late Jurassic igneous rocks in the NCC are located mainly in northern Hebei and western Liaoning provinces, with further rocks occurring on Liaodong and Jiaodong peninsulas, as well as southern Jilin Province (Figure 9(a); Supplementary Table 5).Intermediate−acidic volcanic rocks of the Lanqi and Tiaojishan formations formed between 160 and 152 Ma, and occur in northern Hebei and western Liaoning provinces (Ma et al. 2015)

Petrogenesis of late Mesozoic intrusive rocks in the northeastern NCC
As stated above, late Mesozoic magmatism in the studied area can be subdivided into at least two stages (i.e., 161 − 156 Ma and 125 − 120 Ma), and these intrusive rocks are mainly quartz diorite and more evolved granitoids.The latter are characterized by high SiO 2 and Al 2 O 3 contents, with low concentrations of TiO 2 , total Fe 2 O 3 , and MgO, indicating that their primary magmas were derived from partial melting of crustal material (Zen 1986;Barbarin 1999;Nabelek et al. 2001;Koepke et al. 2007;Xu et al. 2009).However, these granitoids are geochemically varied, implying a number of different origins or heterogeneous magma sources.

Late Jurassic intrusive rocks
The Late Jurassic (161 − 156 Ma) granitoids are mainly monzogranites located in the Tonghua area, including the Lishugou and Yaolin plutons.Although these granitoids have similar major element compositions, their trace element compositions differ (Figure 7(a,b); Supplementary Tables 3).
The Lishugou biotite monzogranites contain high SiO 2 (71.14 − 72.54 wt.%) and high Sr/Y ratios, as well as low HREE abundances (Supplementary Table 3), making them geochemically similar to adakites (Defant and Drummond 1990).Such magma can be produced by various processes, including partial melting of hot subducted oceanic slab material (Defant and Drummond 1990;Martin, 1999;Martin et al. 2005), fractional crystallization of a parental basaltic magma (Macpherson et al. 2006), partial melting of a delaminated lower continental crust that subsequently reacted with mantle peridotite (Defant and Drummond 1990;Martin et al. 2005), mixing of mafic and felsic magmas (Martin et al. 2005;Guo et al. 2007), and partial melting of a thickened, hydrous, mafic lower crust (Smithies 2000).Firstly, the low zircon ε Hf (t) values (−19.7 to −17.2) for the Lishugou biotite monzogranites do not favour a slab melting model (Defant and Drummond 1990).Secondly, the lack of Eu anomalies of the monzogranites also excludes the possibility that the monzogranites formed by fractional crystallization of mafic melt.Thirdly, the low MgO, Cr, and Ni contents of the monzogranites are inconsistent with a melt derived from partial melting of delaminated lower crust or magma mixing (Martin, 1999).Considering these results, we conclude that the melt that formed the monzogranites was generated by partial melting of thickened lower crust (Smithies 2000).Combined with the zircon ε Hf (t) values (−19.7 to −17.2), T DM2 ages (2459 to 2299 Ma), δ 18 O values (5.12−6.96‰)(Figure 10), and relatively low saturation temperature (735 − 745°C) (Figure 11), we conclude that the primary magma for the Lishugou biotite monzogranites was derived from partial melting of thickened NCC mafic lower crust.
Compared with the Lishugou biotite monzogranites, the Yaolin muscovite monzogranites have relatively high HREE abundances, low LREE/HREE ratios, and negative Eu anomalies (Figure 7(a)), and they display a tetrad effect in their REE pattern (Jahn et al. 2001;Wu et al. 2004).Generally, the granitoids with this type of REE pattern are highly fractionated (Jahn et al. 2001;Wu et al. 2004) with low saturation temperatures of zircon (655°C − 662°C ) (Figure 11).Bau (1996) showed that the trace element distribution in common magmatic systems is largely charge-and-radius-controlled (CHARAC).However, the REE tetrad effect is often accompanied by non-CHARAC behaviour of other trace elements (Bau 1996;Irber 1999).This is clearly demonstrated in the Yaolin, Jingshan and woduhe granites (Figure 12).The K/Rb ratios are slightly higher than, or within the normal range of magmatic rocks in the granite samples where no tetrad pattern (non-tetrad granites) is seen, but the K/Rb ratios in the tetrad granites are unusually low (Figure 12(a)).In contrast, K/Ba ratios are strikingly high for the tetrad group and are only slightly higher than, or within the common range of, continental rocks for the non-tetrad group (Figure 12(b)).Investigating the Yaolin and Woduhe granites showed that the La/Nb and La/Ta ratios in the tetrad granites are an order of magnitude lower than in the nontetrad magmatic rocks.The Jingshan granites do not show such low ratios, but the distinction between the two groups is clear (Figure 12(c,d)).Zr and Hf are known to have closest geochemical behaviours and their ratio (Zr/Hf) in most terrestrial and extraterrestrial rocks are highly constant at about 38 ± 2 (Jahn et al. 2001).Deviation from this range is rare and is usually attributed to metasomatism or intense fractionation of accessory minerals (Dostal and Chatterjee 2000).In the Lishugou and Linglong plutons, the Zr/Hf ratios (32-39) of the nontetrad granites are quite normal, but the Zr/Hf ratios are reduced to ≈ 12 for the tetrad granites.In addition, the Zr/ Hf ratios show a negative correlation with the tetrad effect (TE 1, 3 ) (Figure 12(f)).The Y/Ho ratios in the Yaolin and Jianshan granites appear to be obvious deviated from the common range of magmatic rocks (Figure 12(g)), and . ε Hf (t) vs δ 18 O diagrams for zircon grains from Late Jurassic-Early Cretaceous intrusive rocks of the NCC (modified after Yang et al., 2012).Age (Ma) T( )   (Jahn et al. 2001;Yang et al. 2010;Jiang et al. 2012).Note that all of the Yaolin granite samples have ratios (K/Rb, K/Ba, Zr/Hf, La/Nb, La/Ta, Eu/Eu*) that differ from those of the non-tetrad granitic rocks.a negative correlation is showed between the Eu/Eu* value and the tetrad effect (Figure 12(h)).Such a strong negative Eu anomaly (Figures 7(a) and 12(h)) cannot be solely interpreted as due to feldspar separation although it is known to have a large positive Eu anomaly in its REE distribution coefficients (Bau 1996;Irber 1999;Jahn et al. 2001).These geochemical features of the Yaolin granites can be attributed to the effect of magma-fluid interaction (Irber 1999;Jahn et al. 2001Jahn et al. , 2004;;Monecke et al. 2002), between the residual melt and a coexisting aqueous hightemperature fluid.This interaction resulted in the formation of the non-CHARAC elemental features during the late stages of magmatic crystallization.

Early Cretaceous intrusive rocks
The Early Cretaceous intrusive rocks in the studied area comprise granitoids and quartz diorite.The quartz diorites were formed via fractional crystallization of mafic melt (Wilson 1989) or the mixing of mantle-derived mafic melt with crust-derived felsic melt.Firstly, based on the REE distribution coefficients of mafic minerals such as olivine, orthopyroxene, and clinopyroxene (Boynton 1984), the diorites formed via fractional crystallization of mafic melt should have higher LREE abundances and lower HREE abundances than their primary mafic melt.However, the quartz diorites have similar REE patterns to gabbros that show features attributed to a primary magma.This excludes the possibility that the dioritic rocks formed via fractional crystallization of mafic minerals.Secondly, the REE contents of the quartz diorites are between those of coeval granitoids and gabbros in the study area, and the diorites exhibit similar REE patterns (Figure 7(e)).This suggests that a mixing of mantle-derived mafic melt and crust-derived felsic melt could explain the formation of the quartz diorites.We therefore conclude that the quartz diorites were formed via the mixing of mantle-and crust-derived melts, as also indicated by mafic enclaves in the quartz diorites.
The Early Cretaceous granitoids consist of syenogranite, alkali feldspar granite, and granophyre.They have high SiO 2 (72.99 − 76.34 wt.%) and Al 2 O 3 (11.58− 14.17 wt.%) contents, and low MgO (0.01 − 0.42 wt.%), Cr (0.13 − 1.14 ppm), Co (0.05 − 1.72 ppm), and Ni (0.22 − 1.47 ppm) contents.This implies that the Early Cretaceous granitoids have a crustal origin (Xu et al. 2009), meaning that they were formed from a primary magma generated by partial melting of lower continental crust.However, these granitoids exhibit different geochemical features to other rocks in this study.Firstly, compared with the coeval granitoids in the study area, the Shengping alkali feldspar granites have high crystallization temperatures (923 − 955 ℃; Figure 11), suggesting that it is unlikely that the Shengping alkali feldspar granites formed by evolution of the coeval granitic magma.Secondly, the Shengping alkali feldspar granites have the highest REE abundances and the largest negative Eu anomalies within the Early Cretaceous granitoids (Figure 7(c)), implying that plagioclase is a residual phase and there was no garnet in the magma source (Boynton 1984).Thirdly, the zircons from the Shengping alkali feldspar granite have relatively high ε Hf (t) values (-1.4 to -4.6) and low δ 18 O values (5.32−5.84‰)similar to the mantle (Eiler 2001), indicating that the primary magma was derived from partial melting of mafic lower crust accreted during the Mesoproterozoic.These values also suggest that the mantle contribution (especially a thermal contribution) was more important in the petrogenesis of the Shengping alkali feldspar granites (Figure 10) than in the coeval granitoids.
Other Early Cretaceous granitoids in the study area display similar geochemical features, such as relatively high HREE contents and minor negative Eu anomalies compared with the coeval adakitic rocks (Xu et al. 2006), implying that the granitoids were derived from partial melting of lower crust of normal thickness.Their zircon ε Hf (t) values (−14.3 to −3.9), δ 18 O values (4.49−8.74‰),and saturation temperatures (755 − 807°C) indicate that the granitoids were derived from partial melting of Paleoproterozoic−Mesoproterozoic NCC lower crustal material.In addition, the variation in zircon ε Hf (t) values between different Early Cretaceous plutons could be related to magma source heterogeneity.For example, the zircons in the Early Cretaceous granitoids in the northern part of the study area have higher ε Hf (t) values than those in the southern part.

Late Jurassic compression related to oblique subduction of the Paleo-Pacific Plate beneath Eurasia
Late Jurassic magmatism in the northeastern NCC consists mainly of granitoids.Most of the Late Jurassic granitoids are similar to adakitic rocks of Liaodong and Jiaodong peninsulas and southern Jilin area (Wu et al. 2005;Yang et al. 2010;Ma et al. 2013).Geochemical analyses of these Late Jurassic granitoids indicate that they were derived from partial melting of thickened lower crust, implying a compressional environment (Wu et al. 2005).
During the Mesozoic, the tectonic evolution of the NE Asian continental margin was controlled mainly by the Mongol-Okhotsk and Paleo-Pacific tectonic regimes.Therefore, it is important to consider which tectonic regime was responsible for the formation of Late Jurassic magmatism in the northeastern NCC.The answer can be found from spatio-temporal variations in Late Jurassic igneous rocks within the continental margin.Compared with the Late Jurassic igneous rocks with an affinity to adakitic rocks in the northeastern NCC, the coeval magmatism in the Erguna-Xing'an massifs and the northern margin of the NCC is composed mainly of a suite of alkaline series igneous rocks, including A-type granites, monzonites, quartz monzonites, trachyandesite, and trachyte, indicating an extensional environment (Wang et al. 2006;Ying et al. 2010;Meng et al. 2011;Xu et al. 2013;Tang et al. 2015Tang et al. , 2018;;Shi et al. 2015;Dong et al. 2016).Combined with the absence of Late Jurassic magmatism at the continental margin (e.g., eastern NE China, Russian Far East, Japan, and the Korea Peninsula) (Figure 9(a); Tang et al. 2018), we can conclude that the Late Jurassic magmatism occurred to the west of the Songliao Basin (including the Erguna-Xing'an massifs and northern Hebei and western Liaoning provinces), forming in an extensional environment related to the collapse or delamination of thickened crust after closure of the Mongol-Okhotsk Ocean (Xu et al. 2013;Tang et al. 2015;Yu et al. 2016;Li et al. 2018).The Late Jurassic granitoid magmatism in the northeastern NCC, however, formed under a compressional environment related to oblique subduction of the Paleo-Pacific Plate beneath Eurasia (Figure 13(a,b)).
This conclusion is further supported by researches on a Jurassic accretionary complex within the NE Asian continental margin.First, zircon U-Pb dating of cumulate gabbros and plagioclase granites within the Raohe accretionary complex indicates that the complex originated as seamounts and was still located within the Paleo-Pacific Plate from 169 to 167 Ma (Zhou et al. 2014;Wang et al. 2015).Second, the Jurassic accretionary complex collided with Eurasia at ca. 160 Ma, as recorded by regional lowgrade high-P/T metamorphism (~160 Ma) of a Jurassic accretionary complex in Japan (Isozaki 1997).Third, provenance analysis of the terrigenous clasts within the Jurassic accretionary complex, together with palaeontological evidence, indicates that the original position of these Jurassic accretionary complexes (i.e., the location of the primary collision of the seamount with Eurasia) was in the eastern margin of the South China Block, at a low latitude (Shao and Tang 1995;Tang et al. 2018).However the complexes reached the eastern margin of the CAOB (i.e., a high latitude) when terrigenous clasts were deposited from the beginning of the Early Cretaceous (e.g., the Yongfuqiao Formation within the Raohe complex), overlying the Jurassic accretionary complex (Sun et al. 2015;Zhou et al. 2015;Tang et al. 2018).We therefore conclude that strike-slip deformation occurred in the region between the Jurassic accretionary complex and Eurasia during the Late Jurassic (~160 Ma) to early Early Cretaceous (~140 Ma).This is also supported by research on structural deformation events in NE China (Zhu et al. 2018).
In summary, we propose that the Late Jurassic granitoids in the northeastern NCC formed in a compressional environment related to low-angle oblique subduction of the Paleo-Pacific Plate beneath Eurasia, whereas the coeval magmatism that occurred in the Great Xing'an Range and northern margin of the NCC formed in an extensional environment related to the collapse or delamination of thickened lithosphere.The latter resulted from closure of the Mongol-Okhotsk Ocean during the Middle Jurassic (Li et al. 2015).In addition, a strike-slip tectonic event occurred in the region between the Jurassic accretionary complex and the Eurasian Plate during the Late Jurassic to the start of the Early Cretaceous (Xu et al. 2013;Tang et al. 2018).

Early Cretaceous extensional environment related to westward subduction of the Paleo-Pacific Plate beneath the Eurasian plate
The Early Cretaceous intrusive rocks in the northeastern NCC consist of a suite of bimodal igneous rocks.These Early Cretaceous granitoids belong to a high-K, calcalkaline, metaluminous to weakly peraluminous series.Some of the granitoids are similar to A-type granites such as the Shengping and Ji'an intrusions, indicating an extensional environment (Xu et al. 2013).Moreover, numerous Early Cretaceous calc-alkaline igneous rocks are found along the continental margin of NE Asia (Figure 9(b); Tang et al. 2018), including (from north to south) basaltic andesite-andesites of the Pekeshan Formation in the eastern Jiamusi Massif (Xu et al. 2013), the Quanshuicun Formation in the Yanbian area (Xu et al. 2013), and the Ergulazi Formation in the northeastern NCC (Yu et al. 2009).The coeval intracontinental igneous rocks (such as those in the Zhangguangcai Range, Songliao Basin, and Great Xing'an Range) consist of a suite of bimodal rocks (Xu et al. 2013).From the continental margin to the intracontinental area, the Early Cretaceous igneous rocks exhibit variations in composition related to subduction polarity; i.e., an increase in K 2 O, revealing westward subduction of the Paleo-Pacific Plate beneath Eurasia.Thus, we conclude that the Early Cretaceous igneous rocks in the northeastern NCC formed in an extensional environment related to westward subduction of the Paleo-Pacific Plate (Xu et al. 2013;Tang et al. 2018) (Figure 13(c,d)).The existence of an Early Cretaceous intracontinental extensional environment is also supported by the formation of coeval metamorphic core complexes in the NCC (Davis et al. 2001;Zhang et al. 2002;Yang et al. 2007a) and the formation of Early Cretaceous fault-bound basins parallel to the Eurasian continental margin (Li et al. 1997).

Conclusions
Based on zircon U-Pb ages, zircon Hf isotopic data, and geochemical data, we draw the following conclusions.

Figure 1 .
Figure 1.Geological sketch map of southern Jilin Province.(a) Simplified geological map of eastern China, showing the main tectonic units (modified after Yang et al. 2007b).(b) Geological map of southern Jilin Province showing the distribution of Mesozoic granitoids (modified after BGMRJ (Bureau of Geology and Mineral Resources of Jilin Province) 1988; BGMRL (Bureau of Geology and Mineral Resources of Liaoning Province) 1989).Abbreviations are as follows: JJOB -Jing-ji Orogenic Belt; LGB -Longgang Block; PLJB -Paleoproterozoic Liao-Ji Orogenic Belt.(c) Distribution of Mesozoic instrusions in the Liaodong Peninsula (modified after Yang et al. 2007b).
Figure3.Classification of the Late Jurassic-Early Cretaceous igneous rocks in this study according to modal mineral contents(Streckeisen 1978).A, alkali feldspar; P, plagioclase; Q, quartz.

Figure 4 .
Figure 4. Cathodoluminescence (CL) images of selected zircons from Late Jurassic-Early Cretaceous intrusive rocks of the NCC.Circled numbers indicate analysis spots, and ages, ε Hf (t) values, and δ 18 O values are provided below each image.

Figure 5 .
Figure 5. (a-h) LA-ICP-MS zircon U-Pb concordia diagrams for Late Jurassic to Early Cretaceous intrusive rocks of the NCC.

Figure 8 .
Figure 8. Co-variations between zircon ε Hf (t) values and zircon ages for Late Jurassic-Early Cretaceous intrusive rocks of the NCC.

(
161 Ma)  and Yaolin muscovite monzogranite (156 Ma) occur in southern Jilin area.Early Cretaceous igneous rocks in the NCC chiefly occur in its eastern-central part (Figure9(b); Supplementary Table5) and consist mainly of granitoids and volcanic rocks.Most of the granites in the studied region are A-type(Wu et al. 2005; Sun and Yang 2009), and coeval syenites, monzonites and trachytes belong to the alkaline series.In addition, many coeval metamorphic core complexes are found in the eastern part of the NCC (Yang et al. 2007a), including the Yunmengshan, Miyun, and Chengde complexes in the north of Hebei Province (Davis et al. 2001), the Louzidian-Dachengzi complex in the west of Liaoning Province (118 − 133 Ma; Zhang et al. 2002), and the Xiaoqinling complex at the southern margin of the NCC (127 − 107 Ma; Zhang and Zheng 1999).

Figure 9 .
Figure 9. (a) Distribution of Late Jurassic igneous rocks along the continental margin of NE Asia.(b) Distribution of Early Cretaceous igneous rocks along the continental margin of NE Asia (modified after Yang et al. 2007b).

Figure 12 .
Figure12.Variations in key elemental ratios as a function of the tetrad effect (TE1,3 of Irber 1999).Other reference values are shown for comparison(Jahn et al. 2001;Yang et al. 2010;Jiang et al. 2012).Note that all of the Yaolin granite samples have ratios (K/Rb, K/Ba, Zr/Hf, La/Nb, La/Ta, Eu/Eu*) that differ from those of the non-tetrad granitic rocks.

Figure 13 .
Figure 13.Simplified tectonic model of the Late Jurassic-Early Cretaceous tectonic evolution of the NCC.

( 1 )
Late Mesozoic magmatic events within the northeastern NCC can be subdivided into at least two stages: Late Jurassic (161 − 156 Ma) and Early Cretaceous (125 − 120 Ma).(2) The Late Jurassic magmatism in the northeastern NCC consists mainly of granitoids similar to adakitic rocks, which formed in a compressional environment related to low-angle oblique subduction of the Paleo-Pacific Plate beneath the Eurasian Plate.(3) Magmatism towards the end of the Early Cretaceous in the northeastern NCC is composed mainly of a suite of bimodal igneous rocks that formed in an extensional environment related to westward subduction of the Paleo-Pacific Plate beneath the Eurasian Plate.(4) A strike-slip tectonic event occurred in the region between Eurasia and the Paleo-Pacific Plate during the Late Jurassic and the beginning of the Early Cretaceous, likely related to low-angle oblique subduction of the Paleo-Pacific Plate beneath the Eurasian Plate.