Evolving magma sources during continental lithospheric extension: Insights from the Liaonan metamorphic core complex, eastern North China craton

TECTO-126545; No of Pages 15 Tectonophysics xxx (2015) xxx–xxx

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Evolving magma sources during continental lithospheric extension: Insights from the Liaonan metamorphic core complex, eastern North China craton Mo Ji a,1, Junlai Liu a,⁎, Ling Hu a, Liang Shen a, Huimei Guan b a b

State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 10083, China Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China

a r t i c l e

i n f o

Article history: Received 25 August 2014 Received in revised form 31 December 2014 Accepted 25 January 2015 Available online xxxx Keywords: Continental lithospheric extension Evolving magma sources Coupled crust–mantle detachment Parallel Extension Tectonics Liaonan metamorphic core complex, North China craton

a b s t r a c t The relation between magmatic activity and detachment faulting during continental lithospheric extension remains a persistent question. This paper takes the Liaonan metamorphic core complex (mcc) in the eastern North China craton as an example to explore how magma generation relates to detachment faulting in response to continental lithospheric extension due to the subduction of the Paleopacific plate beneath the Eurasian continent in the Early Cretaceous. Dating of lower plate granitic intrusions and trachy-dacitic volcanic rocks in the supradetachment basin constrains a progressive exhumation of the mcc between ca. 134 Ma and 113 Ma. Syn-tectonic magmatism is grouped into three types, i.e., early syn-kinematic, late syn-kinematic, and postkinematic magmatism, in reference to detachment faulting. The magmatic rocks exhibit obvious differences in whole-rock Sr–Nd isotopes, implying varying sources, e.g., lithospheric mantle, juvenile and ancient lower crusts. Evolving magma sources during the progressive exhumation of the mcc are shown from one with a lithospheric mantle signature for the early syn-kinematic intrusions to one with mixed derivations from both juvenile and ancient lower crust for the late syn-kinematic plutons and volcanics and, finally, to a juvenile lower crust source for the post-kinematic intrusions. The source evolution of magmatism during the continental lithospheric extension implies that both crustal and mantle processes may have been involved in the magma generation. The Parallel Extension Tectonics model is applied to explain both the tectonic faulting and magmatic activities. In the model, the evolving magma sources accompanying the mcc exhumation were attributed to thinning of the cratonic lithosphere as a consequence of coupled crust–mantle detachment faulting during tectonic extension. The model can be applied to the variably extended provinces in the North China craton, but integrated structural, geochronological and geochemical studies are needed to present a comprehensive tectono-thermal (magmatic) history of these provinces. © 2015 Elsevier B.V. All rights reserved.

1. Introduction Exhumation of mcc's and magmatism are broadly contemporaneous in many extensional settings (e.g., Baldwin et al., 1993; Coney, 1980; Coney and Harms, 1984; Crittenden et al., 1980; Fornash et al., 2013; Foster and Fanning, 1997; Gans et al., 1989; Haxel et al., 1984; Jolivet et al., 1998; Lister and Davis, 1989; Spencer and Reynolds, 1990). The detachment faults of core complexes generally root into the middle crust, while plutonic or volcanic magmas associated with faulting may be derived either from the lower crust or from the mantle. The former characterizes the extension of the middle and

⁎ Corresponding author. E-mail address: [email protected] (J. Liu). 1 Now at China National Offshore Oil Corporation Research Institute, Beijing 100027, China.

upper crust (Amstrong, 1982; Coney, 1980; Coney and Harms, 1984, Crittenden et al., 1980; Davis et al., 2002; Lin et al., 2013a,b; Lister and Davis, 1989; Liu et al., 2005; Wang et al., 2011), while the latter provides information on the genesis of magmas from deep crustal/ mantle processes or crust–mantle interactions (Menzies and Xu, 1998; Wu et al., 2005; Xu, 1999; Yang et al., 2005). The relationships between continental lithospheric deformation and magmatism are still controversial. In many cases it is not clear whether magmatism promoted or was the product of extension (Axen et al., 1993; Foster and Fanning, 1997). In one interpretation, mantle-driven magmatism has been suggested to lead to deep crustal melting and facilitate deep crustal flow (Konstantinou et al., 2013). Short-lived thermal events (caused by igneous intrusions) may trigger transient metamorphism and ductile deformation in shear zones during episodes of continental extension (Lister and Baldwin, 1993). Meanwhile, intrusion of individual magma chambers may provide the buoyancy force for core complex uplift (Lister and Baldwin, 1993).

http://dx.doi.org/10.1016/j.tecto.2015.01.023 0040-1951/© 2015 Elsevier B.V. All rights reserved.

Please cite this article as: Ji, M., et al., Evolving magma sources during continental lithospheric extension: Insights from the Liaonan metamorphic core complex, eastern North China craton, Tectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.01.023

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However, numerical experiments confirm that the buoyancy force is secondary to strain rate during the exhumation of the mcc's (Gessner et al., 2007; Rey et al., 2009; Wijns et al., 2005). Furthermore, some highly extended areas in the Basin and Range Province are devoid of significant synextensional plutons (e.g.,Wernicke, 1985), suggesting that relatively little melt was generated in the underlying asthenosphere (Hawkesworth et al., 1995). In other examples, tectonic extension predated plutonism or volcanism (Liu et al., 2013). In such cases, tectonic lithosphere extension may dominate over magmatism. The two processes are mutually enhancing and are suggested to be the parallel-products of continental lithospheric extension (e.g., Konstantinou et al., 2013; Liu et al., 2013). The relation (if any) between magmatic activity and detachment faulting thus remains a persistent question (Fornash et al., 2013). Studies on this relation may thus help to establish a potential link between shallow and deep processes under the framework of continental lithospheric extension. Late Mesozoic metamorphic core complexes, mostly with volcanics in their supradetachment basins and synkinematic granitic plutons in their lower plates, are widespread in the eastern North China craton (Lin et al., 2008; Liu et al., 2006, 2011, 2013; Wang et al., 2011). They provide a basis for understanding of the essential relationships between continental lithospheric extension, mcc exhumation and magmatism, and the major causes of thinning of the cratonic lithosphere. Previous studies on the mcc's reveal that they were exhumed due to regional WNW–ESE extension broadly from ca. 134 Ma to 113 Ma (Liu et al., 2011; Wang et al., 2011). In the regional context, the extension responsible for the exhumation of the mcc's was probably due to the retreat of the subducting Paleo-pacific plate beneath the Eurasian plate in the Early Cretaceous (Liu et al., 2011, 2013; Zhu et al., 2012a). Petrological and geochemical studies on the mcc-related magmatic rocks suggest that the magmas were derived from ancient crust, juvenile crust, or the upper mantle (Yang et al., 2005). Two prevailing categories of models, i.e., the top–down and the bottom–up tectonics models, have been applied to interpret the magmatism and thinning of the cratonic lithosphere during continental lithospheric extension (Menzies et al., 2007). The top–down tectonics model suggests that the subcontinental lithospheric mantle (SCLM) was delaminated together with or without part of the lower crust (Deng et al., 1996, 2006, 2007; Gao et al., 2004; Wu and Sun, 1999; Wu et al., 2000, 2003, 2006). On the other hand, the bottom–up tectonics model posits that thermo-mechanical and chemical erosion starting from the base of the lithospheric mantle (Griffin et al., 1998; Zheng et al., 2006a; Zheng et al., 2006b; Xu, 2001; Xu, 2004; Xu et al., 2004; Zheng, 1999; Zheng et al., 2007) dominated the thinning of the lithosphere. Both models address the major roles of deep magmatism for the Mesozoic tectonic evolution and thinning of the lithosphere of the North China craton (Wu et al., 2005; Xu, 2001). In the models, the crustal extension was considered to be the consequence of either of the above deep processes. Recent studies, however, highlighted the role of detachment faulting on triggering magmatism in the Liaonan mcc in the eastern North China craton. A new model, i.e., the Parallel Extension Tectonics model, proposes that magmatism related to the exhumation of the mcc's was the consequence of detachment faulting in the crust and mantle and stressed on the coeval extension of both the crust and the upper mantle that resulted in the detachment faulting and magmatism (Liu et al., 2013). This paper summarizes integrated geological studies of the structural geology, geochronological dating, geochemical and Sr–Nd isotopic analyses of both plutonic and volcanic rocks from the Liaonan mcc. We address the tectonic implications of changing magma sources as detachment faulting proceeded during the exhumation of the mcc. Our results indicate that continental lithospheric extension led to detachment faulting in the shallow crust and induced magmatism at depth. On such a basis, the Parallel Extension Tectonics model is applied and revised, in detail, to relate lithospheric extension to magmatism.

2. Geology and characteristics of igneous rocks of the Liaonan mcc 2.1. Geology of the Liaonan mcc Early Cretaceous extensional structures, e.g., the Liaonan and Wanfu mcc's, the Dayingzi detachment fault, and the Tongyuanpu and Benxi fault-bounded extensional basins cover an area of ca. 40,000 km2 (Liu et al., 2011) in the Liaodong Peninsula Early Cretaceous Extensional Province (LEP) in the eastern NCC (Liu et al., 2013). Co-existing with these extensional structures are the widely distributed Cretaceous igneous rocks that resulted from an Early Cretaceous giant magmatism (Wu et al., 2005). They occur as plutonic intrusions in the lower plates of the mcc's and detachment faults or as volcanic eruptions in faultbounded extensional basins and supradetachment basins of the mcc's. The Liaonan mcc, which is a typical example of the Cretaceous extensional structures, is a Cordilleran type mcc constituted by five structural elements (Fig. 1), i.e., the Jinzhou master detachment fault and lower plate tectonites beneath the fault, Archean metamorphic rocks and Early Cretaceous syn-kinematic intrusions in the lower plate, and weakly deformed Neoproterozoic-lower Paleozoic sedimentary rocks and supradetachment basin of Early Cretaceous volcanic rocks and lacustrine sedimentary rocks in the upper plate (Liu et al., 2005, 2006). The Jinzhou master detachment fault (200 km in length) strikes NNE and dips WNW in the western part, and strikes ENE and dips south in the southern segment. A sequence of fault-related rocks underlies the master detachment fault. They preserve cataclastic to mylonitic structures, and vary from fault gouges, pseudotachylite, chloritic breccias, brecciated mylonites, mylonites to gneissic mylonites. Within the fault gouges and chloritic breccias are often phacoids of mylonites or gneissic mylonites. The lowermost part of the fault-rock sequence is the mylonitic gneisses formed by ductile shearing and dynamic recrystallization under upper greenschist to amphibolite facies (Liu et al., 2005). As a typical corrugation structure, the initiation of the master detachment fault was controlled by extensional faulting, but the geometry of the fault was finally shaped by late syn-kinematic emplacement of some granitic plutons (Ji et al., 2008a). The lower plate gneisses were derived from the Archean trondhjemite, tonalite and granodiorite (TTG) sequence (Gang et al., 1999). Pb–Pb ages of single grain zircons from gneisses are 2467 ± 18 Ma and 2773 ± 50 Ma (LBGMR, 1994), and the zircon U–Pb LA– ICPMS ages are 2501 ± 17 Ma and 2436 ± 17 Ma (Lu et al., 2004). The upper plate is composed of a supradetachment basin (i.e., the Wafangdian basin) and weakly deformed sedimentary rocks (Neoproterozoic to lower Paleozoic) as the basement of the basin. The Wafangdian basin covers an area of more than 200 km2, and is filled with fluvial conglomerates, lacustrine sedimentary rocks and sedimentary–volcanic sequences (LBGMR, 2001). Cretaceous igneous masses are widespread as granitic– granodioritic intrusions in the lower plate and as the Yuhuangding trachy-dacite within the sedimentary–volcanic sequences. 2.2. Lower plate intrusions The granitic intrusions in the lower plate of the Liaonan mcc include the Gudaoling complex, the Yinmawanshan batholiths, the Zhaofang granodioritic porphyry, the Qixingtai monzogranite, the Wazidian monzogranite and the Zhaotun monzogranite. The zircon U–Pb (SHRIMP and LA–ICPMS) ages of the plutonic rocks range from 130 ± 5 Ma to 113 ± 2 Ma (Ji et al., 2009; Wu et al., 2005). However, the Zhaofang granodioritic porphyry, was suggested to be a typical postkinematic intrusion (Ji et al., 2009), but the others were suggested to be syn-kinematic intrusions during regional extension (Ji, et al., 2009; Liu et al., 2011, 2013; Wu et al., 2005). In addition, the trachy-dacite at Yuhuangding in the supradetachment basin was also related to the formation of the basin during extension. The Zhaotun (SL0570, SL06205, 130 ± 5 Ma; Wu et al., 2005) monzogranite, distributed dominantly in the central-southern part of

Please cite this article as: Ji, M., et al., Evolving magma sources during continental lithospheric extension: Insights from the Liaonan metamorphic core complex, eastern North China craton, Tectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.01.023

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Fig. 1. a. Geological map of Liaonan mcc. b. Geological framework of the North China craton. SHRIMP, LA–ICPMS and TIMS zircon ages are from Wu et al. (2005), Ji et al. (2009) and Liu et al. (2011, 2013). 40Ar/39Ar ages of hornblende, muscovite, biotite and K-feldspar are from Yang et al. (2007a),Yang et al. (2007b) and Lin et al. (2011). Details are shown in Supplementary Table 1.

the lower plate, is composed of K-feldspar, plagioclase, quartz, biotite and minor amphibole. At some localities, the granite contains mafic enclaves composed mostly of biotite aggregates. There is an obvious L fabric, which characterizes a typical L-type tectonite (Fig. 2a). Due to intensive ductile shearing, the mafic enclaves were transformed into folded dark bands. Microscopically, weakly deformed sub-euhedral feldspar, quartz aggregates by subgrain rotation recrystallization, and biotite aggregates (Fig. 3a) suggest that not only flow of melt and crystals but also crystal plastic deformation contributed to the formation of the fabrics. Such fabrics were defined as submagmatic flow fabrics at a relatively deep level (Vernon, 2000). It is significant that submagmatic lineations in the intrusions have consistent WNW–ESE orientations

that are parallel to the stretching lineations in the overlying detachment fault rocks. In combination with the crystallization ages, we may group the Zhaotun granite as an early syn-kinematic intrusion formed early during shearing along the detachment fault zone at depth. In addition, crystallization temperatures of the Zhaotun monzogranite range from ca. 700 °C to 800 °C (average of 766.2 °C), estimated by hornblendeplagioclase geothermometry. The emplacement depth is therefore estimated as ca. 25.50 km, given a geothermal gradient of ca. 30 °C/km (Ji et al., 2008b). Combining structural and microstructural analysis and geothermobarometry data, it is suggested that the Zhaotun monzogranite emplaced and deformed at a relatively deep crustal level during detachment faulting.

Please cite this article as: Ji, M., et al., Evolving magma sources during continental lithospheric extension: Insights from the Liaonan metamorphic core complex, eastern North China craton, Tectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.01.023

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Fig. 2. The macro-structures of Cretaceous igneous rocks. a. The Zhaotun monzogranite; b. the outcrop of the Wazidian monzogranite; c. the Qixingtai fine-grained monzogranite; d. oriented xenoliths in Yinmawanshan batholiths; e. the chilled margin along the margin of the Zhaofang granodioritic porphyry; f. columnar joints in Yuhuangding trachy-dacite.

The Wazidian monzogranite (SL0615, 120 ± 4 Ma, Figs. 2b, 3b), Qixingtai monzogranite (SL0693, SL0694, 116 ± 5 Ma, Figs. 2c, 3c) and Yinmawanshan batholiths (SL0543, 129–120 Ma, Figs. 2d, 3d) are distributed in the lower plate (Fig. 2; Wu et al., 2005; Guo et al., 2004; Ji et al., 2009; Liu et al., 2013). The Yinmawanshan batholith is composed of mylonitic, gneissic, porphyritic and fine/medium grained granites from the margin to the center (Charles et al., 2012). Two zones are recognized in the batholiths, an early marginal zone of granodiorite and porphyritic monzogranite, and a late inner zone of finer grained granodiorite. Biotite grains define a weak high dip angle (60°–80°) magmatic foliation in the inner zone, suggesting that a vertical emplacement process dominated intrusion of the pluton core. The marginal zone is composed of medium-coarse grained granodiorite and porphyritic monzogranite. Amphibole grains and grain aggregates in coarsegrained granodiorite are oriented, with increasing fabric strengths approaching to the detachment fault. The mylonitic foliation along the western margin of the batholith is composed of elongated and plastically deformed grains and aggregates. These mylonitic foliations, dipping WNW, show identical shear sense to those within the Jinzhou

detachment fault zone. Moreover, the Wazidian and Qixingtai monzogranites have similar characteristics to the rocks in the inner zone of Yinmawanshan batholiths. Microscopically, there is no obvious deformation of minerals in the rocks (Fig. 3). The three major intrusions (i.e., the inner zone of the Yinmawanshan batholiths, the Wazidian and the Qixingtai monzogranites) are, on the other hand, distributed in the antiform cores of the corrugated detachment fault zone, which implies that the corrugation of the fault zone was partly affected by synkinematic emplacement of these plutons. Taking the relative younger age population approximately 120-116 Ma into consideration, we therefore suggest that these plutons are late syn-kinematic intrusions. The Zhaofang granodioritic porphyry (SL0536, 113 ± 2 Ma; Ji et al., 2009, Figs. 2e, 3e) is a typical post-kinematic granodioritic porphyry, which possesses chilled margins and cuts across the master detachment fault. The intrusion intrudes both the lower and upper plates. Porphyritic crystal comprises plagioclase, quartz and biotite. There are also some mylonite enclaves in the porphyry (Fig. 3e). These characteristics clearly indicate that the Zhaofang granodioritic porphyry emplaced after the termination of detachment faulting.

Please cite this article as: Ji, M., et al., Evolving magma sources during continental lithospheric extension: Insights from the Liaonan metamorphic core complex, eastern North China craton, Tectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.01.023

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Fig. 3. Microstructures of Cretaceous igneous rocks. a. Rectangular band of quartz and the subhedral plagioclase in Zhaotun monzogranite; b. the Wazidian monzogranite with magmatic quartz and feldspar; c. the Qixingtai monzogranite with feldspar phenocryst and quartz-feldspar-biotite matrix; d. magmatic structure in Yinmawanshan batholiths; e. the mylonitic inclusions in Zhaofang granodioritic porphyry; f. k-feldspar phenocryst and the pilotaxitic textures of matrix in Yuhuangding trachy-dacite.

Most of the lower plate intrusions are syn-kinematic in relation to the Jinzhou detachment shearing. They can be grouped into early synkinematic and late syn-kinematic intrusions, which were emplaced early (e.g., the Zhaotun monzogranite and the marginal phase of Yinmawanshan batholiths) and late (e.g., the inner phase of Yinmawanshan batholiths, the Wazidian monzogranite, the Qixingtai monzogranite) during shearing, respectively. Furthermore, the Zhaofang granodioritic porphyry exemplifies one post-kinematic intrusion.

joints commonly occur in the outcrops (Fig. 2f). The rocks contain plagioclase, hornblende, pyroxene, and biotite as phenocrysts (Fig. 3f). Polysynthetic twins are common in euhedral plagioclase phenocrysts. The matrix, which is composed of fine-grained plagioclase and glassy matter, has a pilotaxitic texture. There is local alteration, e.g., sericitization, chloritization and carbonatation (Fig. 3f). The volcanics are distributed locally in the supradetachment basin, implying the controlling role of basin formation on the volcanism. 3. Techniques

2.3. Upper plate volcanics A thick layer of trachy-dacites crop-outs in the central part of the Cretaceous Wafangdian supradetachment basin, i.e., the Yuhuangding trachy-dacite (SL0577, SL0581, SL0583, SL0585, 126 ± 6 Ma; Liu et al., 2011). The volcanics are embedded in lacustrine sediments in the middle section of the basin fill. They show parallel unconformity with lacustrine sediments both above and below the volcanic sequence. Columnar

After petrographic examination, fresh samples were selected for geochemical analysis and crushed in a hardened jaw crusher and then powdered in an agate mill to b 200 mesh (75 μm). Chemical analyses were carried out at the Institute of Geology and Geophysics, China Academy of Sciences. Major element oxides were analyzed on fused glass disks employing a Phillips PW 1500 X-ray fluorescence spectrometer. The precision and accuracy of the major-element data as determined

Please cite this article as: Ji, M., et al., Evolving magma sources during continental lithospheric extension: Insights from the Liaonan metamorphic core complex, eastern North China craton, Tectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.01.023

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by the Chinese whole-rock basalt standard GSR-3 (Xie et al., 1989) are ≤3% and ca. 5% (2σ), respectively. The FeO concentration was determined using a conventional titration procedure. Trace elements were measured by inductively coupled plasma mass spectrometry with a Finnigan MAT Element II mass spectrometer. Samples were dissolved in distilled HF + HNO3 in 15 ml Savillex Teflon screw-cap breakers and high-pressure Teflon bombs at 120 °C for 6 days, dried and then diluted to 50 ml for analysis. A blank solution was prepared, and the total procedural blank was b 50 mg for all trace elements. Indium was used as an internal standard to correct for matrix effects and instrument drift. The internal standard was used for monitoring the signal shift during ICP-MS measurement; this showed good stability, with ~5% variation. Samples for isotopic analysis were dissolved in Teflon bombs after being spiked with 84Sr, 87Sr, 150Nd and 147Sm tracers before HF + HNO3 (with a ratio of 2:1) dissolution. Rb, Sr, Sm and Nd were separated using conventional ion exchange procedures as described by Yang et al. (2004b). Sr–Nd isotopic data were measured on a MAT 262 mass spectrometer. The Sr and Nd isotope ratios were respectively normalized to 86 Sr/88Sr = 0.1194 and 146Nd/144Nd = 0.7219. Typical within-run precision (2σ) for Sr and Nd was estimated to be ±0.000015. The BCR-2 Nd standard and NBS-987 Sr standard were 143Nd/144Nd = 0.512630 ± 12 (2σ, n = 2) and 87Sr/86Sr = 0.710252 ± 11 (2σ, n = 1), respectively. The initial 87Sr/86Sr and 143Nd/144Nd ratios were calculated using their Zircon U–Pb SHRIMP ages.

4. Results 4.1. Major and trace elements Samples of trachy-dacite (SL0577, SL0581, SL0583, SL0585) show a narrow range in SiO2 values from 66.90 to 67.66 wt.%. Major element oxides of trachy-dacite are characterized by Al2O3 (15.04–15.44 wt.%), FeOT (2.95–3.08 wt.%), MgO (0.98–1.21 wt.%), CaO (1.28–2.03 wt.%), TiO2 (0.49–0.52 wt.%), Na2O/K2O (1.127–1.394), K2O + Na2O (7.7–8.88) and Mg# (0.41–0.44) contents (Fig. 5, Table 1). Samples of granitic intrusions (SL06205, SL0570, SL0694, SL0693, SL0615, SL0536) form part of a calc-alkaline suite, with SiO2 content ranging from 66.85 to 73.09 wt.% (Figs. 4 & 5, Table 1). They are peraluminous, with A/CNK (molar ratios Al2O3/(CaO + Na2O + K2O)) of 1.01–1.02 (Fig. 4, Table 1). Values of oxide (TiO2, FeOT and CaO) typically ranged from high to low as samples varied among the Zhaotun monzogranite (the early syn-kinematic intrusions), the Qixingtai and Wazidian monzogranites (the late syn-kinematic intrusions) and the Zhaofang granodioritic porphyry (the post-kinematic intrusions) (Fig. 5, Table 1). The Zhaotun monzogranite (the early syn-kinematic intrusions) has the highest Mg# (molar 100 ∗ MgO / (MgO + FeOT) = 43.98), and the Zhaofang granodioritic porphyry (the post-kinematic intrusions) has the lowest Mg# (molar 100 ∗ MgO / (MgO + FeOT) = 6.57) (Table 1). In chondrite-normalized rare earth element (REE) patterns (Fig. 6), the trachy-dacite (samples SL0577, SL0581, SL0583 and SL0585) has high total REE contents and is enriched in light REE and depleted in heavy REE, with La (45.58–56.74 ppm), Yb (0.65–0.72 ppm), (La/Yb)N ratios of 43.68–58.34, as well as insignificant positive Eu anomalies (Eu/Eu⁎ = 1.23–1.32) (Table 1). However, the granites have complicated REE patterns (Fig. 6, Table 1) and can be subdivided into 2 groups: the early granites (i.e., Zhaotun monzogranite, SL06205) have low total REE contents, with La (2.41–2.42 ppm), Yb = 0.08–0.09 ppm, (La/Yb)N ratios of 18.65–19.73, and positive Eu anomalies (Eu/Eu* = 1.71–5.61); the late granites (Qixingtai monzogranite, SL0694; Wazidian monzogranite, SL0615; Zhaofang granodioritic porphyry, SL0536), however, have high total REE contents, with La (60.44– 80.75 ppm), Yb (0.59–1.56 ppm), (La/Yb)N ratios of 26.24–92.79 and weak negative Eu anomalies (Eu/Eu* = 0.83–0.89).

In primitive mantle (PM)-normalized trace element patterns (Fig. 6, Table 1), the trachy-dacite (SL0577, SL0581, SL0583, SL0585) is enriched in large ion lithosphere elements (LILEs, such as Rb, Sr, Ba, K, Eu), with Rb = 69.946–73.101 ppm, Sr = 471.91–549.34 ppm, Ba = 1633–1887.4 ppm, Eu = 1.945–2.110 ppm, as well as depleted in high field strength elements (HFSEs, such as Nb and Ti). The late synkinematic granites (Qixingtai monzogranite, SL0694; Wazidian monzogranite, SL0615) and post-kinematic Zhaofang granodioritic porphyry (SL0536) are enriched in large ion lithophile elements (LILEs, e.g., Rb, Ba, K, Eu), with Rb = 94.872–140.59 ppm, Sr = 121.96– 450.38 ppm, Ba = 477.6–592.1 ppm and Rb = 97.833–124.79 ppm, Sr = 324.21–604.93 ppm, Ba = 1481.4–2167.7 ppm, Eu = 1.547– 1.712 ppm respectively (Table 1) but depleted in high field strength elements (HFSEs). However, the early granites (the Zhaotun monzogranite, SL06205) have moderate negative Ba, Th, Nb, Zr, Sr, P, Eu and Ti anomalies (Table 1), which are ten times less than that of the late-kinematic granites (the Qixingtai monzogranite, SL0694; the Wazidian monzogranite, SL0615), and the post-kinematic (Zhaofang granodioritic porphyry, SL0536) (Fig. 6). 4.2. Sr–Nd isotopes The initial 87Sr/ 86 Sr ratios and ε Nd (t) values (Table 2) of the samples have been calculated by their zircon SHRIMP U–Pb ages (Supplement data). The depleted mantle model ages (T DM) were obtained using the model of DePaolo (1981). The data are shown in a plot of εNd (t) versus (87 Sr/86 Sr) i diagram (Fig. 7) following Yang et al. (2004a). The trachy-dacite (SL0577, SL0581, SL0583, SL0585) has strong negative εNd (t) values, with (87 Sr/ 86 Sr) i ratio (0.7086–0.7090) and ε Nd (123 Ma) = − 18.4 to − 18.6. The early syn-kinematic granites (Zhaotun monzogranite, SL06205) show (87Sr/86Sr)i ratio (0.7072) and εNd (130 Ma) = − 0.3. The late synkinematic granites (Qixingtai monzogranite, SL0694; Wazidian monzogranite, SL0615) have characteristics that are similar to the Yinmawanshan batholiths (strong negative ε Nd (t) values), with (87Sr/ 86 Sr) i ratio (0.7112–0.7122) and ε Nd (120 Ma) = − 19.0 to − 19.6. Post-kinematic Zhaofang granodioritic porphyry (SL0536) shows (87Sr/86Sr)i ratio (0.7062) and εNd(113 Ma) = − 19.4. 5. Discussion The exhumation of the Liaonan mcc was dominantly due to extensional faulting along the west-rooting Jinzhou master detachment fault. A thick sequence of fault-related cataclastic, mylonitic and gneissic rocks beneath the master detachment fault, Early Cretaceous synkinematic igneous mass in the lower plate, and Early Cretaceous sedimentary and volcanic rocks in the supradetachment basin were formed (Liu et al., 2005) as the consequences of continental lithospheric extension. In particular, magmatic records both in the lower and upper plates provide a general temporal framework of the regional extension and particularly offer constraints on magma genesis and deep processes during detachment faulting and exhumation of the mcc under the tectonic extension. 5.1. Relative timing of tectonic and magmatic events during exhumation of the Liaonan mcc Several thermo-chronological studies have recently been conducted on magmatic zircons (U–Pb dating) from the igneous rocks and metamorphic minerals (Ar–Ar dating) from mylonitic rocks along the detachment fault zone and from metamorphic rocks in the lower plate of the Liaonan mcc (Fig. 8). SHRIMP U–Pb and LA–ICP-MS dating of zircons from the granitic intrusions and the Yuhuangding trachy-dacite give the following age sequence: 130 ± 5 Ma and 129 ± 2 Ma for the early syn-kinematic Zhaotun monzogranite (FW01-57, Wu et al., 2005) and the early

Please cite this article as: Ji, M., et al., Evolving magma sources during continental lithospheric extension: Insights from the Liaonan metamorphic core complex, eastern North China craton, Tectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.01.023

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Table 1 Major and trace element analyses of magmatic rocks in Liaonan mcc. Pluton rock type

SL06205

SL0577

Zhaotun monzogranite

Yuhuangding trachy-dacite

Major elements (wt.%, by XRF) 73.09 SiO2 TiO2 0.08 Al2O3 15.19 FeOT 0.53 MnO 0.02 MgO 0.21 CaO 1.38 Na2O 5.21 3.66 K2O P2O5 0.02 LOI 0.28 Total 99.67 Mg# 43.98 A/NK 1.21 A/CNK 1.01 Trace elements (ppm, by ICP-MS) Sc 1.2530 Cr 43.1390 Co 1.1209 Ni 1.4430 Cu 2.3422 Zn 49.3420 Ga 25.0190 Rb 94.8720 Sr 440.0200 Y 0.7828 Zr 55.0890 Nb 3.3791 Cs 1.3507 Ba 477.62 Hf 3.0946 Ta 0.2901 Pb 50.3880 Th 1.2399 U 0.5350 Rare earth elements (ppm, by ICP-MS) La 2.4170 Ce 4.9909 Pr 0.6098 Nd 2.3857 Sm 0.4402 Eu 0.3033 Gd 0.4248 Tb 0.0465 Dy 0.1903 Ho 0.0392 Er 0.0950 Tm 0.0165 Yb 0.0828 Lu 0.0151 (La/Yb)N 19.7304 δEu 2.1432

SL0581

SL0583

SL0585

SL0694

SL0615

SL0536

Qixingtai monzogranite

Wazidian monzogranite

Zhaofang granitic porphyry

66.90 0.49 15.44 2.95 0.03 1.02 2.03 4.08 3.62 0.20 3.18 99.94 40.66 1.45 1.08

67.40 0.52 15.43 2.97 0.02 1.06 1.52 5.05 3.73 0.20 1.62 99.52 41.42 1.25 1.02

67.24 0.49 15.04 3.08 0.04 1.21 1.95 4.75 3.62 0.19 2.05 99.66 43.77 1.28 0.98

67.66 0.51 15.36 2.97 0.03 0.98 1.28 5.17 3.71 0.19 1.90 99.76 39.53 1.23 1.03

71.54 0.37 14.35 2.23 0.03 0.44 1.74 3.63 4.57 0.08 0.60 99.57 28.11 1.31 1.02

69.88 0.40 15.17 2.29 0.03 0.65 2.05 3.80 4.55 0.12 0.60 99.53 35.99 1.36 1.02

66.85 0.46 15.06 3.38 0.04 0.12 2.07 3.77 4.64 0.21 3.13 99.73 6.57 1.34 1.01

5.9200 18.3630 5.0977 4.9814 7.3142 62.4020 19.9550 69.9640 479.9100 8.0455 122.7900 9.4537 1.7932 1633.00 3.8577 0.8121 13.8390 7.4900 1.0371

5.1900 17.5050 4.9425 5.0893 7.1071 61.2200 20.0690 70.7020 517.2900 8.4158 132.3800 10.3550 0.7742 1887.40 4.3333 0.6522 17.2070 7.8500 1.2481

5.8900 18.1290 5.2658 4.7840 7.9264 63.6850 22.1890 72.0080 549.3400 9.6923 140.5800 10.2200 0.6898 1644.50 4.2495 0.6424 14.5140 7.5400 1.1472

7.0500 19.6910 4.9819 4.7780 6.5397 59.8390 18.5430 73.1010 471.9100 9.6059 190.5000 11.4540 0.9108 1684.50 4.6208 0.5922 13.4190 7.8300 1.2094

3.8825 18.3040 2.3517 1.9718 1.6569 37.4230 20.8650 97.8330 398.6200 7.1203 341.9700 7.7695 0.3157 1836.00 8.5960 0.3210 16.3260 12.2270 0.4846

5.7828 16.5750 3.1768 3.4062 2.5922 39.0570 20.2930 98.8930 604.9300 14.9020 300.2100 13.5260 0.3421 2167.70 6.6472 0.6720 11.8810 9.9688 1.8375

6.7834 9.5342 5.8897 5.4403 7.3560 38.4300 18.9330 124.7900 324.2100 17.9360 288.4400 13.8280 1.0590 1481.40 6.8372 0.6128 12.3030 9.1457 1.3163

51.4860 97.6740 10.6120 39.5330 5.3202 1.9455 4.1217 0.5366 1.9877 0.3218 0.8765 0.1208 0.7210 0.1002 48.2574 1.2696

56.7420 107.7400 11.3030 44.7410 6.1403 2.1099 3.8571 0.6091 2.3256 0.3567 1.0391 0.1355 0.6573 0.1131 58.3382 1.3249

51.1420 98.3710 10.4010 39.6980 6.0968 2.0310 4.2041 0.5642 2.1662 0.3824 0.8619 0.1136 0.6519 0.0972 53.0146 1.2260

45.5790 87.9400 9.3278 36.9580 5.3918 1.9666 4.2025 0.5200 2.1620 0.3764 0.9284 0.1279 0.7052 0.1062 43.6774 1.2625

80.7510 154.2100 15.4790 51.7000 6.6782 1.5469 4.8976 0.5294 1.7120 0.2785 0.8497 0.1011 0.5881 0.1010 92.7907 0.8266

64.5040 116.3600 11.9810 42.1760 6.4281 1.7121 5.4429 0.7167 3.2903 0.5300 1.4746 0.1989 1.1374 0.1649 38.3230 0.8846

60.4370 117.8600 11.9690 40.2520 5.7497 1.5770 5.0844 0.6667 3.0876 0.5867 1.7331 0.2285 1.5564 0.2160 26.2402 0.8913

phase of the Yinmawanshan batholiths, respectively, 120 ± 4 Ma (SK14-1, Wu et al., 2005), 116 ± 5 Ma (SL0694, Liu et al., 2013) and 120 ± 4 Ma for the late syn-kinematic Wazidian monzogranite, Qixingtai monzogranite, and late (or inner) phase of the Yinmawanshan batholiths (SK11-1, SK11-4, FW02-39, FW02-41, Wu et al., 2005), respectively, 123 ± 7 Ma for the late syn-kinematic Yuhuangding trachy-dacite (SL0585, Liu et al., 2011), and 113 ± 2 Ma for the postkinematic Zhaofang granodioritic porphyry (SL0536, Ji et al., 2009). Yang et al. (2007a), Yang et al. (2007b) reported 11 Ar–Ar dating results of muscovite, hornblende, biotite and K-feldspar from the mylonitic rocks, suggesting that the lower plate of the core complex cooled between ca. 120 Ma and 107 Ma. Lin et al. (2011) reported 7 more Ar–Ar dating results of biotite and amphibole from the orthogneiss, gneissic migmatite, mylonitic granodiorite and gneissic granodiorite from the lower plate, which revealed a two-cooling regime of the lower plate of

the Liaonan mcc, i.e., a slow cooling of 3–10 °C/my before 122 Ma and a rapid cooling of 40–55 °C/my after that time. Ji et al. (2009) suggested that the post-extensional Zhaofang granodioritic porphyry emplaced at 113 ± 2 Ma marks the termination of a series of tectono-magmatic activities. Liu et al. (2011) presented 4 zircon U–Pb dating results of volcanic rocks, collected from supradetachment basins of the Liaodong peninsula, of which the Yuhuangding trachy-dacite has an age of 126 ± 6 Ma. Liu et al. (2013) reported the existence of some tectonically controlled leucocratic dykes along the Jinzhou detachment fault zone and therefore proposed that the extensional shearing may be dated back to ca. 134 Ma. The tectono-magmatic evolution of the Liaonan mcc is subdivided into three stages, when the above dating results are applied to establish a temporal framework of the detachment faulting and exhumation of the mcc. The early syn-kinematic dykes place the lower limit of timing

Please cite this article as: Ji, M., et al., Evolving magma sources during continental lithospheric extension: Insights from the Liaonan metamorphic core complex, eastern North China craton, Tectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.01.023

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Fig. 4. Plots of Na2O + K2O vs. SiO2 and A/NK vs. A/CNK for the Zhaotun monzogranite (SL0570, SL06205), the Wazidian monzogranite (SL0615), the Qixingtai monzogranite (SL0693, SL0694), the Zhaofang (SL0536) granitic porphyry and the Yuhuangding trachy-dacite (SL0577, SL0581, SL0583, SL0585).

of extensional ductile shearing at middle crust at ca. 134 Ma (Liu et al., 2013). A first stage ductile detachment faulting in the middle to lower crust and possibly also brittle detachment faulting in the upper crust was initiated prior to ca. 134 Ma and lasted to 130 Ma due to regional extension of the cratonic lithosphere. During the second stage from ca. 130 Ma, the tectono-magmatic activity reached its peak at 120 ± 5 Ma, with rapid exhumation of the lower plate (Liu et al., 2013) accompanied by a giant magmatism (Wu et al., 2005). The active emplacement of syn-kinematic (either early syn-kinematic, e.g., the Yinmawanshan batholiths, or late syn-kinematic, e.g., the Qixingtai granite and the Wazidian granite) granitic plutons was triggered by detachment faulting. The emplacement of the intrusions subsequently contributed to the corrugation of the master detachment fault during progressive extension (at ca. 120 to 116 Ma). Contemporaneously, volcanic eruptions (at ca. 126 Ma) were active in the supradetachment basin (i.e., the Yuhuangding trachy-dacite). The third or postkinematic stage (113 Ma~) magmatism is evidenced by the emplacement of the Zhaofang granodioritic porphyry. The porphyry intruded the master detachment fault and its lower plate mylonite zone, and remained undeformed by detachment faulting. Such characteristics

also imply that the detachment faulting ceased to be active at least from ca. 113 Ma.

5.2. Magma sources: constraints from Sr–Nd isotopes A general conclusion from the studies of Sr–Nd isotopes of the granitic rocks from the Liaodong peninsula is that the Early Cretaceous granitic magmas in the peninsula were derived from multiple sources, but various contributions of three end members (Yang et al., 2004a), i.e., the juvenile lower crust with low initial 87Sr/86Sr ratios and highly negative εNd(t), the ancient lower crust with high initial 87Sr/86Sr ratios and highly negative εNd(t), and lithosphere mantle with the low initial 87Sr/86Sr ratios and positive εNd(t). Similar studies by Guo et al. (2004) on the Yinmawanshan batholiths with ages of 130 Ma to 120 Ma revealed that the magma was mainly derived from ancient lower crust. From the high Mg# characteristics of the intrusions, they (Guo et al., 2004) deduced that other sources (e.g., lithosphere mantle and juvenile crust) possibly also contributed to the formation of the magmas of the Yinmawanshan batholiths.

Fig. 5. Various oxide plots [TiO2, Al2O3, FeOT, MgO, CaO and K2O + Na2O vs. SiO2 (all expressed in wt.%)] for the Zhaotun monzogranite (SL0570, SL06205), the Wazidian monzogranite (SL0615), the Qixingtai monzogranite (SL0693, SL0694), the Zhaofang (SL0536) granitic porphyry and the Yuhuangding trachy-dacite (SL0577, SL0581, SL0583, SL0585).

Please cite this article as: Ji, M., et al., Evolving magma sources during continental lithospheric extension: Insights from the Liaonan metamorphic core complex, eastern North China craton, Tectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.01.023

M. Ji et al. / Tectonophysics xxx (2015) xxx–xxx

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Fig. 6. Chondrite-normalized REE patterns and primitive mantle normalized element patterns for the Zhaotun monzogranite (SL06205), the Wazidian monzogranite (SL0615), the Qixingtai monzogranite (SL0694), the Zhaofang (SL0536) granitic porphyry and the Yuhuangding trachy-dacite (SL0577, SL0581, SL0583, SL0585).

Our present study demonstrates obvious variations of the Sr–Nd isotopic characteristics of the igneous rocks in relation to the kinematic history of the detachment faulting at various stages. Firstly, the emplacement of the post-kinematic Zhaofang granodioritic porphyry, the youngest intrusion in the Liaonan area, marked the cessation of detachment faulting. The porphyry has a relatively low (87Sr/86Sr)i ratio (0.7062) and low εNd(113 Ma) (−19.4), which implies a magma derivation from juvenile crust. Secondly, the late syn-kinematic intrusions (e.g., the Qixingtai monzogranite, the Wazidian monzogranite, and the inner zone of Yinmawanshan batholiths), which also contributed to corrugation of the master detachment fault (Ji et al., 2009), and the volcanic rocks from the supradetachment basin, were emplaced or erupted during detachment faulting. Such rocks show strong negative εNd(t) values (εNd(120 Ma) = −19.0 to −19.6), with varying (87Sr/86Sr)i ratio from 0.7112 to 0.7123, and the volcanic rocks have (87Sr/86Sr)i ratios between 0.7086 and 0.7090, and εNd(123 Ma) between −18.4 and −18.6. These values may imply a combined contribution of magma sources from early (ca. 123 Ma) dominant juvenile crust to late (ca. 116 Ma) dominant ancient crust. The mantle contribution to the magmatism at this stage was rather small, as shown by the strong negative εNd(t) values of the rocks. In addition, the Zhaotun monzogranite possesses structural, microstructural and geochronological characteristics of early syn-kinematic intrusions. The monzogranite is characterized by a low (87Sr/86Sr)i ratio of 0.7072 and high εNd(130 Ma) of −0.3. The geochemical features suggest that the parent magma of the monzogranite has a very strong mantle signature. However, the occurrence of some relic zircon grains with Archean ages has also been reported (Liu et al., 2013) from the monzogranite, which may imply the importance of ancient crust for the generation of the magma. One of the most probable explanations is that the Zhaotun monzogranitic magma was derived from melts

originated from Archean ancient crust mixed with melts from underplated lithospheric mantle magma. The conclusion is also supported by the low total REE contents of the monzogranite, similar to that of lithospheric mantle (Fig. 6). The high Cr and low Nb, U and 87 Sr/86Sr b 0.705 of the monzogranite would otherwise suggest that the monzogranite is similar to the M-type granite. On the other hand, the Zhaotun monzogranite has (87Sr/86Sr)i values (≈0.707) similar to those of the high-Mg basalts from the lower Yixian Formation that was suggested to be dominantly derived from the mantle with a complex magma source (Zhang and Zhang, 2005). 5.3. Evolving magma sources during crust/mantle detachment faulting due to subduction-induced continental lithospheric extension The North China craton best exemplifies inhomogeneous destruction of an old and thick Precambrian craton and local loss of its continental lithospheric root that occurred mainly in the Early Cretaceous (e.g., Liu et al., 2011; Wu et al., 2005; Yang et al., 2010; Zhu et al., 2011). Major consequences of the destruction of the craton and loss of the lithosphere root (Zhu et al., 2012a; He, 2015; Kusky et al., 2014; Liu et al., 2011, 2013; Wu et al., 2005, 2008; Xu, 2001, 2004; Xu et al., 2004; Zhu et al., 2011; Zhu et al., 2012b, 2012c) are the distributed and localized occurrences of mcc's, extensional basins and magmatic provinces in the crustal level (Liu et al., 2006, 2011; Wu et al., 2005). Various conceptual models have been applied to interpret the tectonic and magmatic processes (e.g., Top–Down Tectonics model, Deng et al., 1994; 2004, 2007; Gao et al., 2002, 2004; Wu et al., 2005; Menzies et al., 2007; Bottom–Up Tectonics model, Menzies and Xu, 1998; Xu, 1999, 2001; Parallel-Extension Tectonics, Liu et al., 2013). Diverse interpretations were offered previously, including the effects of India– Eurasia collision that nevertheless occurred since only ca. 50 Ma

Table 2 Rb–Sr and Sm–Nd isotopic results of magmatic rocks in Liaonan mcc.

Rb (ppm) Sr (ppm) Rb/86Sr 87 Sr/86Sr (87Sr/86Sr)i Sm (ppm) Nd (ppm) 147 Sm/144Nd 143 Nd/144Nd TDM εNd (t) fSm/Nd 87

SL06205

SL0577

SL0581

SL0583

SL0585

SL06094

SL06015

SL0536

88.4805 433.7405 0.5902 0.7083 0.7072 0.403 2.1138 0.1153 0.5126 922.4937 −0.2502 −0.414

77.1867 536.5714 0.4163 0.7094 0.7086 5.2439 36.7169 0.0863 0.5116 1845.3061 −18.4058 −0.561

75.047 556.3526 0.3903 0.7094 0.7087 5.2961 37.3308 0.0858 0.5116 1851.7374 −18.6392 −0.564

71.007 538.1776 0.3818 0.7097 0.709 4.9209 33.6028 0.0885 0.5116 1882.3592 −18.5199 −0.5499

73.1748 477.3287 0.4436 0.7095 0.7087 4.5906 31.6233 0.0878 0.5116 1872.3501 −18.532 −0.5538

88.038 391.8265 0.6504 0.7134 0.7122 3.912 26.7018 0.0886 0.5115 1945.8807 −19.524 −0.5497

86.7463 533.2893 0.4708 0.712 0.7112 5.2867 33.2326 0.0962 0.5116 2026.5809 −19.0207 −0.5111

104.4724 277.5954 1.0889 0.708 0.7062 5.0336 34.3438 0.0886 0.5116 1928.1754 −19.3809 −0.5495

Please cite this article as: Ji, M., et al., Evolving magma sources during continental lithospheric extension: Insights from the Liaonan metamorphic core complex, eastern North China craton, Tectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.01.023

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Fig. 7. εNd(t) vs. (87Sr/86Sr)i plots for the Zhaotun monzogranite (SL0570, SL06205), the Wazidian monzogranite (SL0615), the Qixingtai monzogranite (SL0693, SL0694), the Zhaofang (SL0536) granitic porphyry and he Yuhuangding trachy-dacite (SL0577, SL0581, SL0583, SL0585).

(Liu et al., 2006), Triassic North–South China plate collision (Gao et al., 2002; Menzies et al., 1993) that happened much earlier and localized along the southern margin of the North China craton (Liu et al., 2006), and Paleopacific or Izanagi plate subduction that was dominantly prevailing in the Mesozoic (Liu et al., 2011, 2013; He, 2015). Most recent studies agree that these processes were dominantly linked to the subduction of Paleopacific plate, as determined from structural analysis of extensional structures (e.g., Ren et al., 2002;Liu et al., 2006, 2008, 2009, 2011, 2013; Zhu et al., 2010, 2011, 2012b), geochemical analysis of magmatic rocks (e.g., Sun et al., 2007; Wu et al., 2006; Zhao and Ohtani, 2009; Zhao et al., 2007; Zhu et al., 2011, 2012c), or geothermal studies (He, 2015). Arc/back-arc settings (Zhu et al., 2012a; Zhu et al., 2012b, 2012c) due to subduction or subduction roll-back (Kusky et al., 2014; Liu et al., 2011) or the existence of convection cells (Ren et al., 2002) or huge mantle wedge (He, 2015) related to the Paleopacific plate subduction may be responsible for the generation of the tectonic deformation and magmatism. These models, however, differ from each other with regard to the relative importance of mantle-derived magmatism and tectonic deformation. Top–Down and Bottom–Up tectonics models predict that detachment faulting for the exhumation of the mcc's occurred as a consequence of deep processes, such as delamination (Deng et al., 2004, 2007; Wu et al., 2005) or thermal/chemical– mechanical erosion (Menzies and Xu, 1998; Xu, 2001). The Parallel Extension Tectonics model suggests that detachment faulting in the crust and/or in the mantle, the breakup of lithosphere, and magmatism are parallel processes due to lithosphere scale extension related to the interaction of the Paleopacific and Eurasian plates (Liu et al., 2011, 2013). Our combined structural geology and geochemical results outline a general scenario of magmatic source variations with preceding detachment faulting. Early syn-kinematic magmatism for the Zhaotun monzogranite involves melting of the ancient (Paleoproterozoic) lower crust, but with extensive contributions from the enriched mantle lithosphere. During the late syn-kinematic stage when the Qixingtai monzogranite, Wazidian monzogranite, inner zone of Yinmawanshan batholiths and the Yuhuangding volcanic were emplaced, the magmatic sources evolved from an early dominant juvenile crust contribution to

late dominant ancient crustal contribution. Furthermore, the postkinematic intrusions (e.g., the Zhaofang porphyry) were derived from magma of a dominant juvenile crustal source. A reasonable explanation of the variation of magma sources would favor the Parallel Extension Tectonics model (Liu et al., 2013), which involves inhomogeneous detachment faulting in the crust and mantle of the cratonic lithosphere during tectonic extension (Fig. 9). In such a case, the cratonic lithosphere was extended by a stress field owing to subduction roll-back of the subducting Paleopacific plate (Chen et al., 2004; Liu et al., 2011, 2013; Zhu et al., 2012a; Zhu et al., 2012b, 2012c; Kusky et al., 2014), hydrated and weakened by water dehydrated from the subducting slab (Kusky et al., 2014; Windley et al., 2010; Xia et al., 2010, 2013), and heated due to an influx of mantle materials (magma or volatile, Kusky et al., 2014; He, 2015). In the highly extended and hydrated regions, the crust and the lithospheric mantle are decoupled along the Moho due to tectonic extension resulted from Paleopacific subduction (Liu et al., 2013) and detachment faulting occurred contemporaneously at both the middle–upper crust and upper mantle levels. As a result, detachment faulting in the upper mantle may have enhanced partial melting or metasomatization of the lithospheric mantle and provided channels for the upwelling and underplating of magma along the decoupled crust/mantle boundary. Detachment faulting from ca. 134 Ma in the crust may have induced partial melting both in the lower crust and contributed to melting in the upper mantle, which may have further led to the emplacement of magma derived from the ancient lower crust (e.g., the early phase of the Yinmawanshan granite) or magma with significant mantle contribution (e.g., the Zhaotun granite at ca. 130–129 Ma, Fig. 9). Similarly, pressure decreases due to detachment faulting in the upper mantle and temperature increase due to upwelling of the asthenosphere probably also enhanced further partial melting of both the lower crust and the upper mantle predominantly from 130 to 120 Ma (Fig. 9). Meanwhile, increasing temperature due to underplating along the decoupled crust/mantle boundary and reduced pressure by detachment faulting in the middle–upper crust triggered intense partial melting of the lower crust, either ancient or juvenile, and resulted in the Early

Please cite this article as: Ji, M., et al., Evolving magma sources during continental lithospheric extension: Insights from the Liaonan metamorphic core complex, eastern North China craton, Tectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.01.023

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Fig. 8. Geochronology of magmatism and deformation in the Liaonan mcc. SHRIMP, LA–ICPMS and TIMS zircon ages are from Wu et al. (2005), Ji et al. (2009) and Liu et al. (2011). 40Ar/39Ar ages of hornblende, muscovite, biotite and K-feldspar are from Yang et al. (2007a), Yang et al. (2007b) and Lin et al. (2011). Details are shown in Supplementary Table 1.

Cretaceous giant magmatism (Wu et al., 2005), i.e., the emplacement of magma in the basins (e.g., the Yuhuangding trachy-dacite at 123 Ma) or in the lower plate (e.g., the Wazidian monzogranite Ma and the inner phase of the Yinmawanshan batholiths at ca. 120 Ma). The magmatism lasted to a later stage but was relatively weak (e.g., the Qixingtai monzogranite at ca. 116 Ma) in comparison with the peak stage. Continued emplacement of magma from juvenile crust resulted in the local occurrence of the post-extensional Zhaofang granodioritic porphyry after the cessation of the detachment faulting along the Jinzhou detachment fault at ca. 113 Ma (Fig. 9). For the three stages of magmatic evolution, the following processes can be constructed. The early syn-kinematic intrusions (i.e., Zhaotun granites) may imply important contributions from upwelling mantlederived materials only along local channels, although mantleoriginated magmatism may have been prevailed at the decoupled crust/mantle boundary via underplating (Zheng et al., 2006a; Zheng et al., 2006b; Zhai et al., 2007). Many late syn-kinematic and postkinematic intrusions or volcanic rocks that show affinities with juvenile crust may provide further arguments for an early stage of large scale underplating beneath the lower crust. The giant magmatism between 130 Ma and 116 Ma, however, accompanied large-scale detachment faulting both in the mantle and in the crust. Due to the lack of large scale mantle derived magmatism (e.g., mafic magmatism), early underplating of mantle magma may have only provided a heat source which first heated the juvenile and then the ancient lower crusts to generate late syn-kinematic granitic magma. During this processes, detachment faulting in the middle to upper crust may have also contributed to the generation of the late syn-kinematic magma by providing magma channels and by decreasing the pressure conditions for the heated lower

crust. The local occurrence of the post-kinematic magma was possibly related to local detachment faulting in the middle–upper crust. Mantle detachment faulting may have ceased to be active at the time that the magma generation was only locally active. Mostly due to widespread distribution of underplated mafic magma, the juvenile crust became the only magma source during post-extensional evolution. In such a tectono-magmatic scenario, the regional tectonic extension related to plate interactions is the primary driving force for the various processes in the lithosphere (e.g., detachment faulting, partial melting and upwelling of the magmas). In contrast to the traditional Top– Down tectonics (e.g., delamination model, Wu et al., 2005) and Bottom–Up tectonics (e.g., thermal–mechanical erosion model, Xu, 2001) models which have been applied to interpret the Early Cretaceous tectonic evolution and lithosphere thinning of the eastern North China craton, the Parallel Extension Tectonics model predicts that 1) the tectonic extension triggered detachment faulting in both the mantle and the crust inhomogeneously, either temporally or spatially. It is the primary cause of any other process from the deep crust or mantle to the uppermost part of the crust. 2) The magma sources evolved as the detachment faulting, underplating and partial melting of the lower crust and upper mantle progressed. The model also shows that the upwelling of mantle-derived magma occurred where detachment faults were formed and connected to the magma sources. Meanwhile, delamination (Wu et al., 2005), thermal, chemical and mechanical erosion (Xu, 2001), and replacement of the mantle lithosphere (Zheng et al., 2006a; Zheng et al., 2006b) were the local consequences of the detachment faulting. They were localized only at or near high strain zones, which may well explain the rare occurrence of mafic magmatic rocks, either intrusive or volcanic, in the highly extended and thinned areas. On the other

Please cite this article as: Ji, M., et al., Evolving magma sources during continental lithospheric extension: Insights from the Liaonan metamorphic core complex, eastern North China craton, Tectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.01.023

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Fig. 9. Coupled crust–mantle detachment in Parallel Extension Tectonics for the exhumation of mcc's and magmatism. a. Early-kinematic Zhaotun monzogranite (130 ± 5 Ma and 129 ± 2 Ma); b. late-kinematic Wazidian monzogranite, Qixingtai monzogranite, and late (or inner) phase of the Yinmawanshan batholiths (120 ± 4 Ma, 116 ± 5 Ma and 120 ± 4 Ma), syn-kinematic Yuhuangding trachy-dacite (123 ± 7 Ma); c. post-kinematic Zhaofang granodioritic porphyry (113 ± 2 Ma).

hand, involvement of fluid phases (Niu, 2005; Windley, et al., 2007) may have enhanced the localization and progressive development of the detachment faulting, predominantly via hydrolytic weakening

(Yang et al., 2007a; Yang et al., 2007b). Fluid involvement probably also contributed to partial melting of the lithosphere mantle and the lower crust and generation of the various magmas.

Please cite this article as: Ji, M., et al., Evolving magma sources during continental lithospheric extension: Insights from the Liaonan metamorphic core complex, eastern North China craton, Tectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.01.023

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Geological and petrological data indicate that the Archaean lithospheric mantle beneath the eastern North China craton has been significantly but not completely removed since the Mesozoic (Chen et al., 2003; Liu et al., 2009, 2013). The thinning of the lithosphere and destruction of the North China craton is therefore a spatially inhomogeneous process. The involvement of ancient crust, juvenile crust and lithospheric mantle in the generation of magmas may vary from place to place as a result of different degrees of lithospheric extension and development of crust/mantle detachment related to Paleopacific plate subduction. The following are some examples. Chen et al. (2008, 2009) stressed the importance of magma mixing for the origin of a syenite–gabbroic diorite–monzonite complex, and of mafic enclaves in an intermediate and felsic granitic complex from the western part of eastern North China craton. For the former, they suggested that lithospheric extension caused partial fusion of the enriched portions of subcontinental lithospheric mantle generating voluminous mafic magmas. Subsequently, underplating of the mafic magmas in the lower crust resulted in partial melting of the ancient basement rocks to produce granitic melts, which was followed by mixing between the mafic and granitic magmas. For the latter, they proposed that an evolved basaltic magma first mixed with a granitic magma of crustal origin at depth and that subsequently the mixed magma broke up into discrete globules upon entering the felsic magma chamber, forming enclaves by convective motion or forceful injection in the host felsic magma. Recently, Chen et al. (2013) reported the existence of high-Mg dioritic rocks from the eastern part of North China craton, the origin of which had been attributed to equilibration of partial melts from delaminated mafic crust (eclogite) with mantle peridotite. From both petrological and Os isotope analysis, they argued for a process of magma mixing between siliceous crustal melts and basaltic magma from metasomatized mantle. From the same area, Wang et al. (2006) reported the emplacement of a ca. 125 Ma gabbro with EMI-like isotopic signatures from the Great Xing'an Range, northeast China, which is believed to have resulted from lithospheric extension. The extension might have induced the melting of a metasomatised lithospheric mantle in response to the upwelling of the asthenosphere to generate the gabbroic rocks in the area. Although the above studies have not documented in detail the tectonic aspects for the magma evolution, they have reached an agreement that tectonic lithospheric extension related to Paleopacific plate subduction has predominated over the entire process from generation, mixing and emplacement of magmas. The Parallel Extension Tectonics model describes the tectono-magmatic processes during the exhumation of the Liaonan mcc (Liu et al., 2013). The model is expected to fully or partly apply to other highly extended provinces in or beyond the eastern North China craton. Integrated structural, geochronological and geochemical studies, however, are needed to present a comprehensive tectono-thermal (magmatic) history of these areas. 6. Conclusions (1) The intensive magmatic activities (either volcanic or plutonic) associated with the detachment faulting and exhumation of mcc during regional tectonic extension can be grouped into three different types, i.e., the early syn-kinematic, the late synkinematic, and the post-kinematic intrusions. (2) The extension-related magmas were variably derived from juvenile lower crust, ancient lower crust or lithospheric mantle. During progressive regional extension, there was a change in sources from a strong lithospheric mantle signature for early syn-kinematic intrusions, mixed derivations from both juvenile and ancient lower crust for late syn-kinematic pluton and volcanics, to a juvenile lower crust source for post-kinematic intrusion.

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(3) The complicated source evolution of magmatism is best interpreted by the Parallel Extension Tectonics model. In the model, the magma sources evolved as detachment faulting, decoupling along the crust/mantle boundary, underplating of mantle magmas, and partial melting of the lower crust and upper mantle were in progress. The evolving sources of the magmas accompanying the mcc exhumation and destruction of the craton are therefore the consequences of decoupling along the crust/mantle boundary and coupled crust–mantle detachment faulting during continental lithospheric extension related to Paleopacific plate subduction.

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Please cite this article as: Ji, M., et al., Evolving magma sources during continental lithospheric extension: Insights from the Liaonan metamorphic core complex, eastern North China craton, Tectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.01.023