He thermochrology

Tectonophysics 672–673 (2016) 1–15

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Cenozoic exhumation history of Sulu terrane: Implications from (U–Th)/He thermochrology Lin Wu a,b,⁎, Patrick Monié b, Fei Wang a, Wei Lin a, Wenbin Ji a, Michael Bonno b, Philippe Münch b, Qingchen Wang a a b

State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 10029, China Géosciences Montpellier, UMR-CNRS 5243, Université de Montpellier 2, Pl. E.—Bataillon, F-34095, Montpellier Cedex, France

a r t i c l e

i n f o

Article history: Received 30 June 2015 Received in revised form 17 November 2015 Accepted 14 January 2016 Available online 18 February 2016 Keywords: Sulu belt (U–Th)/He thermochronology He partial retention zone Eocene enhanced cooling

a b s t r a c t The Qinling–Dabie–Sulu orogen is the most prominent Phanerozoic orogenic belt in China. The discovery of ultrahigh pressure (UHP) minerals in zircon inclusions suggests that the crust was subducted to deeper than 120 km into the mantle and then exhumed to shallow crustal. Recently, low temperature thermochronology has been applied to constrain the final exhumation of Dabie Shan, while there are few studies describing the Cenozoic exhumation history of the Sulu belt. Here we report some (U–Th)/He ages for various lithologies from Sulu Orogenic belt and its northern part-Jiaobei terrane. The single grain He ages range between 18 and 154 Ma, and most of the samples having large intra-sample age scattering. Several reasons such as invisible U/Th-rich inclusions, grain size effect, slow cooling rate, and zonation of parent nuclide or radiation damage effect may account for this dispersion. For all samples, the pattern of the single grain age data exhibits a peak at ~45 Ma which is consistent with the borehole fissiontrack age pattern in adjacent Hefei Basin. Both (U–Th)/He and fission track ages of the Sulu area suggest an enhanced exhumation/cooling in Early-Middle Eocene in the southern part of Tan-Lu fault zone. This enhanced cooling event coincides with rapid subsidence of North China Basin and rapid uplift of its surrounding reliefs, which indicates basin-mountain coupling. This Eocene event is widespread in central China and could be far-field consequence of India–Asia collision. The convergence rate between Pacific Plate and Eurasia decreased substantially during early Tertiary and reached a minimum in Eocene (~30–40 mm/yr) while at the same time the collision between India and Asia was completed. Therefore, the Cenozoic exhumation history of the Sulu Orogenic Belt was a combined result of far-field effect of India–Asia collision and declined subduction rate of the Pacific Plate under Eurasia. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Sulu is the eastern extension of Qinling–Dabie Orogenic belt, which is considered to result from continental collision between the North China Craton (NCC) and Yangtze Craton (YC) in Early Triassic (Fig. 1; Mattauer et al., 1985; Xu, 1987; Li et al., 1993; Ames et al., 1993; Hacker et al., 2006). The discovery of ultra-high pressure (UHP) minerals throughout the belt suggests that the crust was subducted to deeper than 120 km into the mantle and then exhumed to shallow crustal levels through a succession of tectonic processes constrained by low temperature thermochronology mainly in Qinling and Dabie areas (Reiners et al., 2003; Grimmer et al., 2002; Wang et al., 2004; Xu et al., 2005; Hu et al., 2005, 2006a, 2006b). In Sulu, the Mesozoic history has been well studied from the Early Triassic UHP metamorphism (Xu et al., 1992; Ye et al., 2000a, 2000b) to the Late Jurassic to Early Cretaceous magmatism (Fig. 2; Zhang et al., 2003a; Yang et al., 2003; Zhou et al., 2003a; Liu et al., 2004a, 2004b, 2008a, 2008b, 2009a, 2010; Liu ⁎ Corresponding author. Tel no.: +86 10 82998560, fax: +86 10 62010846. E-mail address: [email protected] (L. Wu).

http://dx.doi.org/10.1016/j.tecto.2016.01.035 0040-1951/© 2016 Elsevier B.V. All rights reserved.

and Liou, 2011; Hacker et al., 2006, 2009; Xu et al., 2006; Yang et al., 2005a, 2005b; Guo et al., 2005; Zhang et al., 2010, 2011; Lan et al., 2011) but its Cenozoic evolution remains poorly known, due to the scarcity of thermochronological data (Hu et al., 2006a; Liu et al., 2009b; Siebel et al., 2009). In this study, we reported new (U–Th)/He ages for the main rock types in Sulu UHP belt and the northwest part of the belt. Combined with published apatite fission-track dating both from the Chinese Continental Scientific Drilling program (Liu et al., 2009b) and surface samples (Hu et al., 2005), we may be able to answer the following questions: (1) Is there an exhumed apatite fission-track partial annealing zone (PAZ) and helium partial retention zone (PRZ) (Fitzgerald et al., 1995) in Sulu belt? (2) Was the Late Cretaceous to Cenozoic exhumation of the Sulu belt homogeneous or temporally variable? (3) What is the geodynamic background of this exhumation? 2. Geological setting The Sulu UHP orogenic belt, that is bounded by the Tan-Lu fault to the west, Yantai–Qingdao–Wulian fault (YQWF) to the north and Jiashan–Xiangshui fault to the southeast, is the eastern extension of

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L. Wu et al. / Tectonophysics 672–673 (2016) 1–15

Fig. 1. Geological map of eastern Shandong, with the sample locations for Helium ages and published FT ages by Hu et al., 2005.

giant Qinling–Dabie–Sulu orogen belt which resulted from continental collision between the North China and Yangtze cratons in Early Triassic (Figs. 1, 2; Chavagnac and Jahn, 1996; Hacker et al., 1998, 2006). This region has drawn much attention since the discovery of index ultra-high pressure minerals, such as coesite and micro-diamond in eclogites and the adjacent gneisses (Ye et al., 2000a; Xu et al., 1992). The metamorphic rocks of the Sulu ultra-high belt mainly consist of granitic gneisses and quartzofeldspathic schists, and minor kyanite-bearing quartzites, marbles, amphibolites and ultramafic rocks. The preservation of coesite both as inclusions in minerals and matrix minerals (Wallis et al., 2005; Yang et al., 2003; Liu et al., 2004a, 2004b, 2010; Liu and Liou, 2011) provide the evidence that the ultramafic rocks and country rocks were subjected to subduction to depth 100–200 km (Ye et al., 2000a, 2000b).

The Shandong peninsula (eastern part of Shandong Province separated by Tan-Lu Fault zone) is divided into three units: the Jiaobei Terrane, the Jiaolai Basin and the Sulu UHP orogenic belt (further called Sulu belt) (Fig 1). The YQWF is commonly regarded as the boundary between the NCC and YC (Zhai et al., 2000). The pre-Mesozoic rocks on both sides of YQWF are intruded by numerous igneous bodies of Triassic to Cretaceous age (Qiu et al., 2001; Yang et al., 2005a, 2005b; Guo et al., 2005; Meng et al., 2006; Lan et al., 2011; Liu et al., 2008a, 2008b; Zhang et al., 2010) and unconformably overlain by dominantly volcaniclastic Mesozoic to Cenozoic sedimentary rocks. The Jiaobei terrane was considered to belong to the southern periphery of NCC because of the existence of Archean gneisses, Proterozoic metasedimentary rocks (Fenzishan Group, Jingshan Group and Penglai

L. Wu et al. / Tectonophysics 672–673 (2016) 1–15

Fig. 2. Published geochronology data for including Mesozoic intrusive rocks from both Jiaobei terrane and Sulu Orogenic belt and ultra-high pressure rocks from Sulu ultrahigh pressure belt. Data source: Ames et al., 1996; Faure et al., 2003; Gao et al., 2004; Gong et al., 2007; Guo et al., 2004, 2005; Hacker et al., 2006, 2009; Huang et al., 2006; Lan et al., 2011; Leech et al., 2006; Li et al., 1993, 1994, 1999; Lin et al., 2005; Liu et al., 2004a, 2004b, 2008a, 2008b, 2009a, 2010; Meng et al., 2006; Miao et al., 1998; Rumble et al., 2002; Schmidt et al., 2008, 2011; Tang et al., 2008, 2009; Wallis et al., 2005; Wang et al., 2011; Yu et al., 2011; Zheng et al., 2004, 2009; Xu et al., 2006; Yang et al., 2003, 2005a ,2005b; Zhang and Zhang, 2007; Zhang et al., 2005, 2010, 2011; Zhao et al., 2006a, 2006b; Zhou et al., 2003a; Zong et al., 2010.

Group) and Paleozoic sedimentary sequences (Tang et al., 2006, 2007). In contrast, the basement of Sulu UHP belt (Jiaonan uplift) mainly consists of Neoproterozoic metavolcanic rocks which have Yangtze affinity (Zhou et al., 2008; Hacker et al., 2009). The Cretaceous sedimentary rocks are mainly distributed in the Cretaceous Jiaolai basin (Ren et al., 2007) and northwestern boundary of the Jiaonan uplifted area (Fig. 1). The Cretaceous Jiaolai basin is a terrestrial basin filled with volcaniclastic rocks interlayered with sandstones (Li et al., 2007a). The stratigraphical sequence consists of Early Cretaceous Laiyang Group and Qingshan Group, and Late Cretaceous Wangshi Group from bottom to top (Fig. 3). The Laiyang Group consists of fluvial-lacustrine deposits and conglomerates (Fig. 3) with a few interlayers of volcanoclastic deposits. Zhang and Zhang (2007) obtained zircon U–Pb and hornblende 40 Ar/39Ar ages of ~ 130 Ma from volcanic interlayer of Laiyang Group. The Qingshan Group is mainly composed with several eruptive cycles of volcanic rocks and minor clastic rocks. Whole rock 40Ar/39Ar ages of 108–109 Ma were yielded from early cycles of rhyolitic rocks and potassium-rich alkalic volcanic rocks (Qiu et al., 2001), while the later cycle of basaltic rocks got 40Ar/39Ar age of 96 ± 3 Ma (Kuang et al., 2012). The Wangshi Group consists of a suit of fluvial red clastic rocks with some basaltic lava. The Daxingzhuang alkali basalt in Wangshi Group yielded a whole rock 40Ar/39Ar age of 73.2 ± 0.3 Ma (Yan et al., 2003) which defines this group to Late Cretaceous. Numerous geochronologic data (Fig. 2) support a Triassic age for peak metamorphism (240–220 Ma) during the continental collision, rapid exhumation under eclogite facies and amphibolite facies (Zhang

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et al., 2003a; Yang et al., 2003; Liu et al., 2004a, 2004b, 2009a, 2010; Liu and Liou, 2011; Hacker et al., 2006; Xu et al., 2006), and late metamorphic overprint in the Jurassic (Hacker et al., 2006). This is followed in early to middle Cretaceous by large scale of extension (Ni et al., 2013; Lin et al., 2015) and widespread magmatism (Qiu et al., 2001; Yang et al., 2005a, 2005b; Guo et al., 2005; Meng et al., 2006; Lin et al., 2005; Zhou et al., 2003a; Liu et al., 2008a, 2008b; Zhang and Zhang, 2007; Zhang et al., 2010; Lan et al., 2011). In particular, a bimodal magmatism provides evidence for the early Cretaceous extensional regime in the Sulu belt (Fan et al., 2001). It is coeval with the a large scale extension that occurred all along the southeastern margin of Eurasia from Late Jurassic to Early Cretaceous (Northrup et al., 1995; Rastchbacher et al., 2000; Ren et al., 2002; Meng, 2003; Zhang et al., 2003b, 2007; Zhu et al., 2012; Lin et al., 2013). This Early Cretaceous extension is revealed by a regional unconformity in basins along the eastern margin of Chinese continent (Ren et al., 2002; Wei et al., 2011). Since Tertiary, the whole Shandong peninsula experienced uplift and especially in the North part of Shandong Peninsula and Sulu belt. Two regional uplift events are recognized (RGSS, 1991; Ren et al., 2002). The first uplift event, called “Jiyang movement”, occurred during Middle Eocene (fourth member of Shahejie Formation) and the second one (called “Dongying movement”) occurred during the end of Oligocene (the end of sedimentation of Dongying Formation). The timing of these two tectonic episodes are consistent with the stratigraphic record of nearby basins (Ren et al., 2002; Wei et al., 2011) and stress field analysis, which indicates that the Cenozoic deformation of Sulu belt and Jiaobei terrane is closely related to the activity of Tan-Lu fault zone (Mercier et al., 2013). The Tan-Lu fault is a lithospheric stike–slip fault that runs on the continental margin of eastern China over more than 5000 km and experienced a complex evolution since its formation in the Triassic (Xu et al., 1987; Lin et al., 1998; Wang, 2006; Wang and Zhou, 2009; Zhu et al., 2001, 2004, 2005; Zhang et al., 2003b).

3. Samples and previous low temperature thermochronological data 3.1. Sample description Sixteen samples including Mesozoic granites, mylonites, and migmatites of the Sulu UHP belt and Jiaobei Terrane were selected for (U–Th)/He dating in Géosciences Montpellier, Université de Montpellier 2 (UM2) and some samples are selected for intra-laboratory comparison in Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS, see Appendix A for details of the analytical procedure). The samples are located on Fig. 1 and the lithology and GPS coordinates of each sample is given in the Table 1. Six samples are from the Jiaobei terrane, i.e. the southern extension of the North China block. 12SL12 and 12SL13 are granites taken from a private mine field in Jiuqu gold mine. U–Pb chronology showed that this granite emplaced during the Jurassic (152–160 Ma, Miao et al., 1998). Other samples (SL19, 23, 24 and 45) are from the undeformed Early Cretaceous granites (U–Pb ages from 113 to 122 Ma, Meng et al., 2006; Zhang and Zhang, 2007; Zhang et al., 2010; Lan et al., 2011) widely developed in both Jiaobei Terrane and Sulu orogenic belt. Among these samples, 12SL24 and 12SL45 are from the same pluton dislocated by a N30°E striking fault called Taocun–Dongdoushan fault, which is branching to the SW to the Muping–Jimo fault zone. Ten samples are from the Sulu belt, to the East of the Tan-Lu and Taocun–Dongdoushan faults. Samples 12SL41 and 12SL99 are foliated migmatites respectively from the northern part (Weihai) and southern part (Rizhao) of the Sulu belt. Samples 12SL39, 12SL103 and 12SL104 are mylonitic gneiss with NW–SE lineation and nearly horizontal foliation. The last samples are again from undeformed Early Cretaceous plutons present all along the Sulu belt (12SL44, 57, 83, 84, 94). All these samples were collected at low elevation between the sea level and a maximum value of 306 m for 12SL13.

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L. Wu et al. / Tectonophysics 672–673 (2016) 1–15

Fig. 3. Stratigraphic sequence in Jiaolai Basin with a field photograph showing the conglomerate at the base of Early Cretaceous Laiyang Group.

3.2. Available AFT and (U–Th)/He thermochronological data

4.1. Jiaobei terrane

Apatite fission-tack (AFT) ages from the Chinese Continental Scientific Drilling (CCSD, location in Fig. 1) project borehole range between 87 Ma (surface) and 3.2 Ma (3899 m depth) and define a present-day partial annealing zone at 1810–4150 m beneath the earth surface (Fig. 4, data from Liu et al., 2009b). An anomalously old age of 98.6 ± 17.0 Ma was also reported from this borehole. The AFT ages for surface samples range from 58 to 106 Ma throughout the Sulu area (Hu et al., 2005; Liu et al., 2009b; Siebel et al., 2009) and are consistent with those from Dabie Shan bracketed between 42 and 86 Ma (Grimmer et al., 2002; Reiners et al., 2003; Zhou et al., 2003b; Hu et al., 2006b). In Sulu, Siebel et al. (2009) used multiple thermochronometers on a Late Triassic post-orogenic alkali-gabbro and got the apatite fissiontrack and He ages of 106 ± 6 Ma (mean confined track length of 13.1 ± 1.3 μm) and 39 ± 5 Ma, respectively. In Dabie Shan, the apatite He ages range between 23 and 66 Ma in (Reiners et al., 2003) and from 26 to 76 Ma in Qinling (Hu et al., 2006b). Hu et al. (2006a) obtained a He age of 44.3 ± 2.2 Ma (weighted mean age for 2 single apatite grains) from a granodiorite sample (AFT central age 70 ± 4 Ma) in Tongbai Shan.

12SL12 is Jurassic (Miao et al., 1998) granite taken from a mine field to the northeast of Zhaoyuan city. 10 single grain Helium ages have a large variation far beyond their analytical error with the youngest age 45 Ma (Table 1). All ten grains have a narrow range of Th/U ratio of 0.63–1.54. 12SL13 is the same granite as 12SL12, but taken from an elevation of 306 m. Three crystals got Helium ages of 79.1, 111.9 and 57.2 Ma respectively, with Th/U ratio similar to 12SL12. 12SL19 is sampled from Early Cretaceous Guojialing pluton. Three grains have Helium ages of 45.7, 57.6 and 43.2 Ma respectively with consistent Th/U ratio. In order to make an inter-laboratory comparison, four additional grains of 12SL19 were selected and analyzed in new (U–Th)/He laboratory of IGGCAS (Table 1). Two grains yielded ages of ~ 47.7 Ma and the other two got older ages. 12SL23 and 12SL24 are taken from two different locations of the same pluton, which was named Yashan pluton. Zhang and Zhang (2007) yielded similar zircon and biotite 40Ar/39Ar ages (118 and 116 Ma respectively) for this pluton, which indicates this pluton cooled rapidly soon after its emplacement. Three crystals of 12SL23 got dispersed ages from 28.4 to 38.1 Ma and uniform Th/U ratios about 7, while four grains of 12SL24 got ages between 35.0 and 51.9 Ma with lower Th/U ratios (~3). Three grains were analyzed in IGGCAS, two of which got consistent ages of 42 Ma except one abnormally old age of 149 Ma (lower Th/U ratio than other grains). 12SL39 is a mylonite to the northeast margin of Jiaolai Basin with NW–SE stretching lineation. Four grains got Helium ages between 53.8 and 154.4 Ma. The two older grains (G1 and G3) are problematic due to the fact this sample got a biotite 40Ar/39Ar age of 120.3 ± 0.3 Ma (Wu, 2014). 12SL45 is a Cretaceous granite to the northeast of Jiaolai basin and has a similar emplacement age (113.4 ± 2.5 Ma, Zhang and Zhang, 2007) as 12SL23. Seven single crystals obtained in Geoscience Montpellier range from

4. Results The single grain Helium ages range from 18 Ma to 154 Ma and some of the samples have large intra-sample age variation for different crystals (Table 1, Figs. 4, 5). One foliated migmatite (12SL41) and three granites (12SL44, 45, 83) obtained consistent single grain ages (Table 1), which probably due to the relative large grain size and clear appearance indicating free of inclusions.

L. Wu et al. / Tectonophysics 672–673 (2016) 1–15

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Table 1 He age results for Shandong samples. Sample

Mol 238U

12SL12 12SL12G1 4.50E−13 12SL12G2 4.90E−13 12SL12G5 2.76E−13 12SL12G6 ‡ 6.92E−13 12SL12G7 7.94E−13 12SL12G8 1.89E−13 12SL12G9 1.13E−13 12SL12G10 ‡ 6.10E−14 12SL12G11 8.77E−14 12SL12G12 6.55E−14 12SL13 12SL13G1 5.25E−13 12SL13G2 6.68E−13 12SL13G4 1.60E−13 12SL19 12SL19G1 7.55E−13 12SL19G5 1.14E−12 12SL19G6 3.72E−13 12SL19-a* 1.06E−12 12SL19-b* 3.13E−13 12SL19-c* 7.74E−13 12SL19-d* 5.34E−13 12SL23 12SL23G1 8.31E−14 1.43E−13 12SL23G3 12SL23G4 8.79E−14 12SL23-b* 1.38E−13 12SL23-c* ‡ 2.40E−13 12SL23-d* 9.45E−14 12SL24 12SL24G3 7.38E−13 12SL24G4 6.77E−13 12SL24G8 7.64E−13 12SL24G9 1.14E−12 12SL39 12SL39G1 ‡ 2.53E−13 12SL39G3 ‡ 8.39E−14 12SL39G4 2.83E−13 12SL39G5 1.08E−13 12SL41 12SL41G1 1.05E−12 12SL41G2 8.23E−13 12SL41G5 1.23E−12 12SL41G6 1.15E−12 12SL41G7 1.96E−12 12SL44 12SL44G1 4.29E−13 12SL44G2 3.88E−13 12SL44G5 1.58E−12 12SL44G6 1.42E−12 12SL44-01* 7.23E−13 12SL44-02* 7.78E−13 12SL44-03* 2.77E−13 12SL44-04* 1.35E−12 12SL44-a* 1.14E−12 12SL44-b* 2.44E−12 12SL44-c* 1.32E−12 12SL44-d* 3.42E−12 12SL44-e* 7.93E−13 12SL44-f* 8.65E−13 12SL44-g* 8.58E−13 12SL44-h* 2.02E−12 12SL45 12SL45G1 6.57E−13 12SL45G2 7.73E−13 12SL45G6 2.11E−13 12SL45G7 3.58E−13 12SL45G8 4.87E−13 12SL45G12 1.51E−13 12SL45G13 9.00E−14 12SL45-01* 1.14E−13 12SL45-02* 3.28E−13 12SL45-03* 1.75E−13

Std. 238U

Mol 232Th

Std. 232Th Mol 4He

37°27.667′ 3.05E−15 5.24E−15 3.44E−15 6.01E−15 1.29E−14 3.33E−15 1.54E−15 4.82E−15 3.01E−15 2.16E−15 37°27.966′ 5.60E−15 5.41E−15 2.95E−15 37°32.535′ 7.37E−15 8.19E−15 7.02E−15 2.49E−14 8.74E−15 1.78E−14 1.39E−14 37°13.057′ 1.05E−15 2.58E−15 1.49E−15 2.99E−15 5.82E−15 2.13E−15 37°11.101′ 6.76E−15 7.81E−15 1.24E−14 7.94E−15 37°07.624′ 4.26E−15 2.01E−15 3.87E−15 1.77E−15 37°24.84′ 3.99E−15 1.20E−14 1.56E−14 9.72E−15 3.92E−14 37°19.224′ 8.59E−15 7.76E−15 3.17E−14 2.85E−14 1.45E−14 1.56E−14 5.55E−15 2.70E−14 2.29E−14 4.88E−14 2.64E−14 6.84E−14 1.59E−14 1.73E−14 1.72E−14 4.03E−14 37°19.278′ 8.32E−15 6.18E−15 4.99E−15 6.71E−15 3.90E−15 3.98E−15 1.15E−15 2.28E−15 6.57E−15 3.50E−15

120°32.595′ 4.86E−13 4.13E−13 3.97E−13 6.83E−13 4.96E−13 1.59E−13 1.13E−13 9.39E−14 1.23E−13 9.34E−14 120°32.287′ 3.54E−13 2.83E−13 1.36E−13 120°53.857′ 3.42E−12 4.10E−12 1.47E−12 2.20E−12 1.26E−12 3.14E−12 1.57E−12 121°00.19′ 5.36E−13 9.38E−13 6.87E−13 7.82E−13 6.39E−13 5.48E−13 121°06.256′ 2.40E−12 2.46E−12 2.55E−12 4.10E−12 121°14.392′ 5.31E−13 1.68E−13 4.15E−13 1.65E−13 122°11.76′ 4.54E−13 3.30E−13 2.08E−12 5.31E−13 7.70E−13 122°25.236′ 2.37E−12 2.15E−12 9.79E−12 7.92E−12 3.87E−12 4.09E−12 1.42E−12 7.13E−12 5.66E−12 4.66E−12 7.36E−12 4.83E−12 4.22E−12 4.81E−12 3.31E−12 9.42E−12 121°22.884′ 3.04E−12 1.72E−12 4.88E−13 1.38E−12 1.74E−12 6.37E−13 4.23E−13 3.05E−13 8.77E−13 6.67E−13

Granite 2.01E−14 3.31E−14 1.51E−14 4.17E−14 2.48E−14 1.72E−14 2.26E−14 1.22E−13 4.64E−15 5.73E−14 2.53E−15 1.08E−14 1.80E−15 1.10E−14 1.11E−15 9.99E−15 1.54E−15 9.88E−15 1.72E−15 5.56E−15 Granite 1.17E−14 5.48E−14 2.14E−15 9.52E-14 2.18E−15 1.17E−14 Granite 2.74E−14 8.25E−14 2.48E−14 1.46E−13 1.32E−14 3.35E−14 4.59E−14 7.93E−14 2.78E−14 2.69E−14 6.16E−14 9.06E−14 3.08E−14 4.82E−14 Granite 6.43E−15 5.30E−15 1.11E−14 1.30E−14 7.72E−15 7.64E−15 1.78E−14 1.20E−14 1.42E−14 5.54E−14 1.07E−14 7.77E−15 Granite 3.03E−14 4.68E−14 1.65E−14 4.49E−14 2.18E−14 5.74E−14 3.52E−14 1.11E−13 Myonlite 4.72E−15 5.39E−14 2.48E−15 1.84E−14 4.55E−15 3.50E−14 3.33E−15 8.40E−15 Deformed migmatite 3.00E−15 6.10E−14 2.80E−15 4.73E−14 1.78E−14 7.57E−14 7.09E−15 6.75E−14 1.54E−14 1.14E−13 Granite 4.73E−14 3.44E−14 4.30E−14 4.40E−14 1.96E−13 1.90E−13 1.58E−13 1.42E−13 7.74E−14 6.89E-14 8.18E−14 6.13E−14 2.84E−14 1.91E−14 1.43E−13 1.27E−13 1.13E−13 1.04E−13 9.31E−14 1.73E−13 1.47E−13 1.44E−13 9.66E−14 1.74E−13 8.44E−14 6.76E−14 9.63E−14 7.78E−14 6.62E−14 6.21E−14 1.88E−13 1.80E−13 Granite 2.44E−14 7.76E−14 1.37E−14 8.53E−14 5.95E−15 2.47E−14 8.43E−15 2.85E−14 1.59E−14 3.92E−14 5.06E−15 1.11E−14 3.99E−15 6.31E−15 6.10E−15 6.47E−15 1.75E−14 2.25E−14 1.33E−14 1.11E−14

Std. 4He

Age (Ma) ±1σ (Ma) FT

Cor Age (Ma) ±1σ (Ma) Th/U

[eU] (μg/g)

8.78E−17 45.72 8.31E−17 55.30 5.32E−17 36.34 3.35E−16 110.89 1.59E−16 48.97 4.00E−17 37.32 4.36E−17 57.71 4.40E−17 87.93 3.72E−17 62.07 2.99E−17 46.65

0.47 0.61 0.67 1.09 0.71 0.58 0.75 5.51 1.75 1.28

0.838 54.56 0.845 65.44 0.806 45.09 0.855 129.70 0.876 55.90 0.827 45.13 0.724 79.71 0.645 136.32 0.708 86.57 0.699 66.74

3.29 3.99 3.09 7.76 3.61 2.96 5.02 15.36 6.77 5.17

1.08 6.8 0.84 7.8 1.44 8.9 0.99 7.7 0.63 6.2 0.84 4.6 1.00 9.5 1.54 13.1 1.40 10.1 1.43 7.4

1.50E−16 69.97 2.45E−16 100.38 4.11E−17 47.37

0.75 0.79 0.76

0.884 79.09 0.896 111.92 0.828 57.16

4.80 6.48 3.78

0.67 0.42 0.85

5.4 4.8 5.5

2.46E−16 3.82E−16 8.58E−17 1.22E−15 4.22E−16 1.26E−15 7.39E−16

41.52 54.38 36.59 39.28 34.69 46.94 41.81

0.29 0.3 0.4 0.91 0.83 0.97 0.97

0.823 0.855 0.766 0.824 0.728 0.824 0.81

45.71 57.55 43.18 47.67 47.65 56.97 51.62

2.60 3.19 2.63 3.49 3.52 4.03 3.78

4.53 3.61 3.96 2.08 4.02 4.06 2.93

23.6 19.0 27.8 21.4 30.7 20.5 18.0

3.03E−17 18.72 4.12E−17 26.44 3.02E−17 22.65 1.84E−16 29.29 7.65E−16 110.52 1.27E−16 27.31

0.21 0.3 0.25 0.65 2.46 0.60

0.658 28.44 0.692 38.21 0.674 33.61 0.688 42.57 0.742 148.95 0.657 41.57

1.74 2.34 2.05 3.07 10.76 2.99

6.45 6.56 7.82 5.65 2.66 5.80

22.4 28.0 21.3 26.7 22.3 23.6

1.34E−16 1.37E−16 1.59E−16 3.43E−16

28.17 28.06 33.00 41.40

0.23 0.21 0.34 0.26

0.804 0.77 0.814 0.797

35.04 36.44 40.54 51.94

2.04 2.09 2.44 2.92

3.25 3.63 3.34 3.58

23.8 35.1 23.8 43.2

1.44E−16 111.08 5.94E−17 116.25 9.98E−17 71.59 3.49E−17 44.82

1.34 2.03 0.79 0.62

0.789 140.79 0.753 154.38 0.836 85.54 0.833 53.77

8.74 10.42 5.22 3.43

2.10 11.7 2.00 6.6 1.47 5.4 1.53 3.7

1.57E−16 1.27E−16 2.12E−16 1.76E−16 1.44E−15

41.04 40.91 34.41 41.18 41.40

0.18 0.56 0.34 0.34 0.93

0.875 0.859 0.875 0.873 0.869

46.88 47.59 39.31 47.14 47.64

2.55 3.03 2.35 2.75 3.45

0.43 7.5 0.40 8.0 1.70 10.6 0.46 8.4 0.39 14.3

5.15E−16 6.60E−16 2.85E−15 2.13E−15 8.62E−16 7.91E−16 2.46E−16 1.58E−15 1.28E−15 2.12E−15 1.70E−15 2.23E−15 8.57E−16 1.08E−15 8.10E−16 2.45E−15

25.74 36.35 36.11 31.98 33.13 27.68 24.60 32.99 32.82 38.34 37.20 29.85 29.72 30.63 29.78 33.37

0.17 0.32 0.23 0.23 0.63 0.53 0.47 0.62 0.62 0.75 0.69 0.61 0.57 0.61 0.57 0.66

0.727 0.666 0.813 0.811 0.761 0.755 0.685 0.803 0.795 0.843 0.813 0.812 0.755 0.792 0.782 0.832

35.40 54.58 44.41 39.43 43.53 36.66 35.91 41.08 41.28 45.48 45.76 36.76 39.36 38.67 38.08 40.11

2.00 3.21 2.50 2.26 3.00 2.54 2.48 2.83 2.84 3.16 3.14 2.59 2.72 2.70 2.63 2.80

5.51 5.55 6.18 5.57 5.35 5.26 5.12 5.28 4.95 1.91 5.58 1.41 5.32 5.57 3.86 4.67

48.6 69.0 52.0 53.2 53.8 59.7 46.0 57.2 54.5 44.8 69.7 85.0 61.2 43.2 42.3 47.3

1.94E−16 2.31E−16 7.42E−17 8.16E−17 1.17E−16 5.01E−17 3.28E−17 1.03E−16 2.99E−16 1.74E−16

44.32 56.56 59.28 32.75 32.20 27.23 24.58 27.29 32.88 26.21

0.35 0.37 0.97 0.35 0.23 0.42 0.25 0.59 0.65 0.55

0.817 0.771 0.778 0.747 0.784 0.671 0.606 0.654 0.734 0.67

54.25 73.36 76.20 43.84 41.07 40.58 40.56 41.73 44.80 39.12

3.14 4.15 5.06 2.66 2.35 2.66 2.44 2.99 3.13 2.78

4.63 2.23 2.31 3.87 3.58 4.22 4.70 2.68 2.67 3.81

22.3 34.9 11.6 24.5 20.4 30.6 31.1 20.7 22.5 28.2

(continued on next page)

6

L. Wu et al. / Tectonophysics 672–673 (2016) 1–15

Table 1 (continued) Sample

Mol 238U

Std. 238U

Mol 232Th

Std. 232Th Mol 4He

12SL45-04* 12SL45-a* 12SL45-c* 12SL45-d* ‡ 12SL45-e* ‡ 12SL45-f* 12SL45-g* 12SL45-h*

1.37E−13 2.86E−13 4.33E−13 4.14E−13 9.31E−14 1.14E−13 2.65E−13 6.09E−14 12SL57 3.54E−13 1.03E−13 9.44E−14 1.60E−14 2.47E−14 4.82E−14 9.54E−14 4.14E−14 12SL83 2.30E−13 6.86E−13 2.84E−13 3.37E−13 1.97E−13 2.25E−13 12SL84 2.65E−−13 1.76E−13 1.40E−13 8.92E−14 4.94E−14 4.68E−14 8.11E−14 6.17E−14 4.96E−14 12SL94 2.36E−13 5.41E−13 1.23E−13 4.95E−13 1.59E−13 1.55E−13 1.41E−13 1.67E−13 12SL99 5.56E−13 5.50E−13 7.37E−13 4.31E−13 12SL103 7.46E−14 7.02E−14 9.40E−14 12SL104 1.23E−13 1.90E−13 1.41E−13 1.51E−13

2.74E−15 5.73E−15 8.66E−15 8.28E−15 1.86E−15 2.28E−15 5.29E−15 1.22E−15 35°38.586′ 6.32E−15 2.58E−15 2.64E−15 1.31E−15 6.67E−16 9.64E−16 1.91E−15 1.24E−15 34°59.658′ 4.06E−15 6.69E−15 3.26E−15 3.87E−15 3.43E−15 4.51E−15 34°59.658′ 3.92E−15 3.37E−15 3.52E−15 1.98E−15 1.31E−15 1.21E−15 2.02E−15 1.36E−15 1.67E−15 34°45.726′ 4.92E−15 9.63E−15 2.21E−15 6.52E−15 4.58E−15 5.22E−15 4.02E−15 4.57E−15 35°20.02′ 6.29E−15 5.08E−15 7.03E−15 5.54E−15 35°23.89′ 1.72E−15 1.44E−15 1.37E−15 35°22.5′ 8.55E−16 2.61E−15 2.76E−15 2.22E−15

4.22E−13 8.29E−13 9.87E−13 1.48E−12 2.13E−13 4.01E−13 8.47E−13 1.47E−13 119°55.074′ 2.73E−12 9.25E−13 9.82E−13 5.65E−13 2.58E−13 1.29E−13 1.99E−13 4.27E−13 118°45.54′ 9.58E−13 1.41E−12 7.68E−13 1.09E−12 6.66E−13 5.04E−13 118°45.54′ 8.82E−13 8.46E−13 4.94E−13 3.92E−13 5.20E−13 1.02E−13 1.64E−13 1.76E−13 1.86E−13 118°35.25′ 1.24E−12 3.04E−12 7.63E−13 2.15E−12 6.02E−13 7.20E−13 8.86E−13 7.82E−13 119°17.12′ 1.42E−12 5.84E−13 1.91E−12 9.36E−13 119°09.02′ 3.66E−13 7.75E−13 4.42E−13 119°09.01′ 4.91E−13 6.04E−13 3.45E−13 5.22E−13

8.44E−15 8.24E−15 1.14E−16 27.35 1.66E−14 1.91E−14 3.18E−16 31.04 1.97E−14 2.62E−14 3.45E−16 30.88 2.95E−14 5.72E−15 9.45E−17 5.90 4.26E−15 3.39E−14 4.42E−16 183.68 8.03E−15 7.59E−15 1.57E−16 28.57 29.93 1.69E−14 1.77E−14 2.57E−16 2.94E−15 2.66E−15 5.74E−17 21.83 Granite 3.00E−14 3.88E−14 1.14E−16 30.65 1.11E-14 7.83E−15 3.83E−17 19.20 2.50E−14 1.29E−14 4.55E−17 31.15 3.43E−14 2.62E−15 2.40E−17 13.93 7.03E−15 2.98E−15 5.48E−17 27.48 2.58E−15 5.51E−15 8.03E−17 54.84 3.98E−15 3.29E−14 4.52E−16 179.32 1.56E−14 6.52E-15 1.11E−16 36.17 Granitic gabbro 7.04E−15 2.91E−14 9.84E−17 50.13 1.60E−14 5.72E−14 1.79E−16 43.93 1.32E−14 2.23E−14 7.64E−17 37.58 1.46E−14 2.87E−14 9.56E−17 37.92 6.62E−15 1.73E−14 5.54E−17 38.46 34.16 7.57E−15 1.50E−14 5.10E−17 Syntetonic gabbro 9.88E−15 2.58E−14 8.60E−17 42.73 1.07E−14 1.74E−14 6.33E−17 36.46 8.09E−15 9.17E−15 3.81E−17 28.06 5.97E−15 9.86E−15 4.17E−17 42.60 6.63E−15 9.65E−15 3.53E−17 44.21 4.80E−15 1.74E−15 2.07E−17 19.22 4.59E−15 3.69E−15 8.14E−17 24.18 5.84E−15 3.33E−15 6.93E−17 25.28 5.08E−15 3.53E−15 5.52E−17 29.66 Granite 1.44E−14 3.47E−14 1.00E−16 51.59 1.85E−14 6.83E−14 2.15E−16 42.72 5.54E−15 1.77E−14 6.00E−17 46.10 1.73E−14 7.10E−14 2.12E−16 55.65 1.29E-14 1.79E−14 2.47E−16 46.53 1.49E−14 1.87E−14 2.56E−16 45.27 2.90E−14 1.33E−14 2.17E−16 29.94 1.62E−14 1.88E−14 3.08E−16 42.03 Strongly deformed migmatite 1.36E−14 7.69E−14 2.15E−16 67.42 6.10E−15 4.07E−14 1.19E−16 46.19 1.31E−14 1.23E−13 3.51E−16 80.84 9.47E−15 3.69E−14 1.09E−16 44.24 Myonlite 3.69E−15 1.10E−14 3.71E−17 53.80 8.62E−15 1.30E−14 4.52E−17 40.62 5.26E−15 1.19E−14 4.52E−17 46.99 Myonlite 4.53E−15 2.10E−14 6.63E−17 69.04 6.55E−15 3.85E−14 1.08E−16 90.49 6.62E−15 1.58E−14 5.13E−17 55.50 6.56E−15 2.51E−14 7.33E−17 71.82

12SL57G1 12SL57G2 12SL57G5 12SL57G6 12SL57-a* 12SL57-b* 12SL57-c* ‡ 12SL57-d* 12SL83G1 12SL83G2 12SL83G3 12SL83G5 12SL83G4 12SL83G9 12SL84G1 12SL84G2 12SL84G3 12SL84G4 12SL84G6 12SL84G8 12SL84-a* 12SL84-b* 12SL84-c* 12SL94G1 12SL94G2 12SL94G3 12SL94G5 12SL94-a* 12SL94−b* 12SL94-c* 12SL94-d* 12SL99G2 12SL99G3 12SL99G4 12SL99G5 12SL103G1 12SL103G2 12SL103G3 12SL104G1 12SL104G2 12SL104G3 12SL104G5

Std. 4He

Age (Ma) ±1σ (Ma) FT

Cor Age (Ma) ±1σ (Ma) Th/U 3.08 2.89 2.28 3.56 2.29 3.53 3.20 2.41

[eU] (μg/g)

0.55 0.69 0.61 0.13 3.67 0.72 0.61 0.57

0.679 40.28 0.755 41.11 0.769 40.16 0.661 8.93 0.753 243.93 0.649 44.02 0.711 42.10 0.638 34.22

2.82 2.97 2.80 0.64 17.07 3.31 2.96 2.60

19.5 18.2 23.0 99.4 5.7 27.2 23.5 14.9

0.31 0.24 0.63 0.77 0.77 1.13 3.69 1.16

0.805 34.25 0.696 24.82 0.704 39.80 0.702 17.86 0.729 37.70 0.707 77.57 0.829 216.31 0.755 47.91

2.06 1.55 2.79 1.88 2.94 5.48 15.27 3.93

7.71 19.9 8.94 25.9 10.40 18.4 35.28 8.4 10.44 4.12 2.67 5.6 2.09 1.9 10.32 4.3

0.52 0.36 0.39 0.35 0.43 0.5

0.79 0.847 0.779 0.779 0.808 0.798

57.06 46.66 43.39 43.78 47.57 42.78

3.44 2.72 2.62 2.59 2.91 2.77

4.17 9.3 2.06 9.5 2.71 12.9 3.25 17.8 3.39 6.7 2.24 8.9

0.44 0.43 0.46 0.6 0.55 0.5 0.71 0.71 0.80

0.796 0.792 0.774 0.752 0.75 0.738 0.726 0.742 0.757

48.29 41.41 32.62 50.95 58.91 26.04 33.31 34.07 39.18

2.91 2.56 2.17 3.27 3.68 1.98 2.64 2.66 3.02

3.33 10.0 4.80 9.3 3.52 7.7 4.40 7.0 10.53 6.7 2.18 3.9 2.02 7.1 2.86 5.5 3.76 4.1

0.61 0.39 0.42 0.46 1.07 1.08 0.84 0.99

0.705 0.788 0.688 0.765 0.733 0.679 0.731 0.699

65.78 48.76 60.24 65.41 63.48 66.67 40.96 60.13

4.07 2.88 3.56 3.81 4.63 4.92 3.20 4.42

5.25 5.61 6.22 4.34 3.78 4.65 6.28 4.68

0.57 0.38 0.58 0.43

0.849 0.873 0.876 0.853

79.34 52.88 92.21 51.84

4.64 3.08 5.27 3.10

2.56 15.7 1.06 7.5 2.60 11.4 2.17 10.5

0.67 0.43 0.48

0.737 0.689 0.74

72.92 58.90 63.44

4.55 3.57 3.82

4.90 8.9 11.03 22.2 4.71 9.2

0.45 0.87 0.81 0.74

0.774 89.10 0.791 114.40 0.821 67.55 0.835 85.94

5.04 6.82 4.36 5.18

4.00 13.3 3.18 8.9 2.44 6.5 3.46 6.0

36.4 32.7 40.0 33.4 17.8 29.5 18.4 23.6

* apatite grains analyzed in IGGCAS, ‡ single grain ages have been rejected.

40.6 to 76.2 Ma and Th/U ratio between 2.2 and 4.7. Except the first three grains (G1, G2 and G6) got dispersed old ages, the rest four grains yielded consistent ages of ~40 Ma (average 41.5 ± 1.6 Ma). Eight grains in IGGCAS got similar ages (39.1 to 44.0 Ma, with average 41.7 ± 2.0 Ma) and Th/U ratio (2.3–3.6) as in laboratory in Montpellier. One crystal (12SL45−e) got anomalously old age of 243.9 ± 5.1 Ma, while 12SL45-d got very young age of 8.9 ± 0.2 Ma. 4.2. Jiaonan uplift (Sulu ultra-high pressure belt) To the east of Yantai–Qingdao–Wulian fault, nine samples of Sulu uplift (ultra-high pressure metamorphic belt) were analyzed. 12SL41 is a mylonitic migmatite with NW–SE stretching lineation. Five grains

got homogeneous age (except one younger grain with age of 39.3 Ma and higher Th/U ratio than the other three), four of which got an average age of 47.3 ± 0.4 Ma. 12SL44 was taken from an Early Cretaceous granite called Rongcheng pluton, whose zircon U–Pb age was 108 Ma (Guo et al., 2005). Four grains analyzed in Geoscience Montpellier gave ages between 35.4 and 54.6 Ma (average 43.5 ± 8.3 Ma) with homogeneous Th/U ratio around 5. Twelve additional grains were analyzed in laboratory of IGGCAS got ages from 35.9 to 45.7 Ma (average 40.2 ± 3.3 Ma, which is indistinguishable with the average age in Montpellier) with Th/U ratio about 5 (except two grains, e.g. 12SL44-b and 12SL44-d). 12SL57, which was porphyritic granite collected from the coast, got dispersed ages (17.9 Ma to 77.6 Ma) and Th/U ratios (2.09 to 35.3) in both laboratories. 12SL83 and 12SL84 are granodiorites

L. Wu et al. / Tectonophysics 672–673 (2016) 1–15

7

from the same pluton. Five of six single grain ages (except 12SL83G1 got older age and higher Th/U ratio than the others) of 12SL83 were consistent, which gave an average age of 44.8 ± 2.1 Ma. Results of six grains in UM2 and three from IGGCAS of 12SL84, however, got scattered ages range from 26.0 to 59.9 Ma. 12SL94 is a granite close to Tan-Lu fault. Four grains in UM2 yielded an average age of 60.1 ± 7.9 Ma and four grains in IGGCAS got consistent average age of 57.8 ± 11.6 Ma within error. 12SL99 is a deformed granite with NW–SE stretching lineation. Two of four selected grains got ages of 52 Ma and the other two were older. 12SL103 and 12SL104 are mylonites with N–S stretching lineation. Both samples got dispersed single grain ages with the youngest ages 59 and 68 Ma respectively. 5. Discussions 5.1. Possible reasons for intra-sample variation in single grain (U–Th)/He ages

Fig. 4. (a) Single grain helium age distribution pattern in Shandong Peninsula. (b) Apatite patterns in CCSD bore hole (data source: Liu et al., 2009b). Geothermal gradient is quoted form (He et al., 2006). The data suggest that there exist an exhumed partial annealing zone and thus an exhumed partial retention zone for 4He, while the onset of denudation was at ca. 45 Ma.

Fig. 5. Age-[eU] relation for single grain He ages. It is obvious that two populations showed on the correlation diagram. The first population which has higher [eU] (N15 μg/g) has smaller age dispersion, while the second population which has lower [eU] (b15 μg/g) has relatively large age dispersion.

For most samples, the intra-sample variations in apatite single grain ages are much larger than the age errors. Several possible reasons could account for this feature: grain size effect, chemical heterogeneities and contribution of radiogenic 4He from 147Sm (Fitzgerald et al., 2006 and references therein), slow cooling through the 4He partial retention zone (Wolf et al., 1998), radiation damage (Shuster et al., 2006), 4He implantation from U/Th-rich minerals (Spiegel et al., 2009), undetectable U/Th-rich inclusions, chemical variation between grains and contribution of radiogenic 4He from 147Sm (Fitzgerald et al., 2006 and references therein). It has been shown that the U content of apatite can significantly influence the age distribution within a single apatite population (Shuster et al., 2006), because of the variable density of radiation damages due to U decay. Reported on an age-[eU] correlation diagram (Fig. 5), our data can be divided into two groups according to the [eU] concentration: [eU] N 15 μg/g (group 1) and [eU] b 15 μg/g (group 2). Grains of group 2 have lower [eU] and larger intra-sample variation, which indicates these grains are more susceptible to different effects that contribute to the 4He budget, such as cooling rate, the presence of inclusions or implantation from adjacent U–Th rich reservoirs such as zircons and/or bulk matrix components (i.e. samples 12SL12, 12SL13, 12SL39, 12SL84). Spiegel et al. (2009) noticed that even for rapid cooling rates, the effect of 4He implantation is only significant in crystals with [eU] b 5 μg/g and could cause large intra-sample age dispersion. However, two samples are less affected by the [eU] concentration (12SL41 and 12SL83) probably because large grain size and clean appearance (free of fractures and inclusions) for apatite crystals in these two samples. For group 2 grains, they have smaller dispersion but still larger than the errors, which might attribute to undetectable U/Thrich inclusions. 147 Sm-derived 4He can contribute to the total amount of 4He released from an apatite grain and cause overestimated ages (Fitzgerald et al., 2006). Major and trace element analyses show that Sm concentration in the Mesozoic granites ranges from 0.96 to 10.7 μg/g, mostly less than 3 μg/g (Zhang et al., 2011) and 6.3 to 13.5 μg/g in orthogneisses (Liu et al., 2004a). Higher Sm in the gneisses might be one reason for the larger age dispersion in mylonites than the granites. For slowly cooled samples, there is a general correlation between cooling rate and variation of single grain (U–Th)/He ages (Fitzgerald et al., 2006). When the rate of cooling is faster than 4 °C/Myr, the variation in single grain helium ages is much smaller than that of cooling rate slower than 4 °C/Myr (Fitzgerald et al., 2006). In Shandong Peninsula, the general cooling trend after Late Cretaceous (ca. 100 Ma) was very slow (on average ~ 1 °C/Myr Hu et al., 2006a), which means the slow cooling rate is probably a dominant factor for large intra-sample variation of the studied apatite ages. There is no obvious correlation (except 12SL23) between helium ages and grain radius on the age-radius diagram (not shown). However,

8

L. Wu et al. / Tectonophysics 672–673 (2016) 1–15

Brown et al. (2013) concluded that the age dispersion arising from difference in absolute grain size (56–164 μm) could be as much as 7% to 60%, which is of a similar magnitude to that caused by analyzing crystal fragments (grains with 0 or 1 termination) of whole grains. Especially the combined effect of crystal size, fragments with missing terminations, different eU content and long time residence in helium partial retention zone (hence more daughter loss by diffusion) will lead to more complex grain age dispersion pattern (Brown et al., 2013). Except the above-mentioned factors, natural radiation damage is another possible reason for the age dispersion. Diffusion experiments on apatite grains suggest that no correlation exists between helium diffusion and apatite chemistry including F/Cl ratio, but the closure temperature (therefore the age) is positively correlated with the radiogenic 4He concentration in these samples (Shuster et al., 2006). This means radiation-induced damages in apatite crystals could increase 4He retentivity by creating an internal pathway network acting as a trap for helium, thus resulting in higher activation energy for 4He diffusion in apatite. To summarize, slow cooling rate, undetectable U/Th-rich inclusions (for grains with [eU] N 15 μg/g), 4He implantation from U/Th-rich neighboring phases (especially for grains with [eU] b15 μg/g), grain size variation, and radiation damage are most probable factors inducing large intra-sample age dispersion. Relative high 147Sm in the mylonite samples can provide certain amount of 4He. However, the amount of 4 He contributed by 147Sm could not lead to the large variation in the dated grains.

5.2. Cenozoic exhumation of Sulu Orogenic Belt Several studies suggest that very slow cooling occurred in Dabie–Sulu Orogenic belt during the Cenozoic (Hu et al., 2005, 2006a). In Sulu UHP belt and Jiaobei terrane, apatite fission track ages for surface samples (small topographic relief in the Shandong Peninsula) range from 52 to 106 Ma (Hu et al., 2005; Liu et al., 2009b; Siebel et al., 2009) which also indicates a very slow cooling rate. Apatite fission track data in CCSD (Fig. 4) and Hefei basin (Chen et al., 2005) clearly support the existence of an exhumed paleo partial annealing zone (PAZ) at ~400–500 m beneath the earth surface and hence a paleo Helium partial retention zone (PRZ). The large AFT age range of surface samples taken at low elevation (b 300 m) also supports the idea that these samples resided in the paleoPAZ for a long time period. The general distribution of the single grain age population exhibits a peak at ~45 ± 5 Ma, which indicates that the onset of denudation occurred at about 45 Ma. The presence at 400–500 m depth of a paleo AFT PAZ (Fig. 4) and the average elevation of 100– 200 m suggest that a minimum crustal column of ~3.8 km has been eroded since 50 Ma, which corresponds to a denudation rate of ~0.1 km/myr. K-feldspar multi-domain diffusion (MDD) modeling suggests that rocks from Sulu crosscut the 150 °C isotherm at ~95 Ma (Wu, 2014). Both the AFT and Ar–Ar data indicate that nearly no exhumation occurred in the 95–45 Ma period. This result is consistent with the exhumation history of the Dabie Orogen since 90 Ma for which two main periods of exhumation are identified (Zhou et al., 2003b).

Fig. 6. Contemporaneous enhanced cooling/uplifting occurred in large area of China (from Central Tibet to the west to Sulu orogen to the east, revised from Zhang et al., 2003b) is at about 50–45 Ma and areas with Eocene unconformity. Stratigraphies of two basins with this Eocene unconformity are shown in Fig. 7. All the enhanced cooling phases are close to the major strike–slip faults which were supposed to accommodate the large gravitational potential difference between the western China and Eastern China produced by the India–Asia collision.

L. Wu et al. / Tectonophysics 672–673 (2016) 1–15

5.3. Early Tertiary enhanced cooling event in Shandong Peninsula The present data suggest that the post-magmatic (~120 Ma) cooling of Shandong Peninsula was modest and relatively steady compared to the fast cooling that prevailed during the early exhumation of the UHP rocks, in agreement with the observations made in the Tongbai–Dabie belt (Hu et al., 2006a, 2006b). However, according to the surface (U–Th)/He age distribution and apatite fission track age pattern in the CCSD (Fig. 4; Liu et al., 2009b), thermochronological data argue for an Eocene enhanced cooling event (~45 Ma) in Shandong Peninsula. In addition, the sedimentary record in neighboring basin and tectonothermal evolution of the Tan-Lu fault zone could provide further evidences for this enhanced cooling event. Since Early Eocene, the eastern China continental margin and marginal seas experienced widespread rifting (Fig. 6) characterized by alkaline basalt eruptions and development of syn-rifting basins including the Lower Liao River Basin, North China Basin, Southeast China Basin Group (Hellinger et al., 1985; Ma and Wu, 1987; Ye et al., 1987; Allen et al., 1997; Ren et al., 2002; Yin, 2010). The Shandong Peninsula is located to the southeast of North China Basin, one of the largest Cenozoic rifting systems in China (Figs. 6, 7, 8). Three major boundary faults (Wulian fault, Tan-Lu fault and Lan-Liao fault) divide the Shandong Province into four fault-bounded blocks, namely North China Basin, Luxi Block (western Shandong), Jiaobei terrane and Sulu ultra-high pressure belt (Fig. 8). Lower Tertiary terrestrial clastic sediments mainly

9

distribute in North China Basin and Luxi Block, whereas a very limited area to the north of Shandong Peninsula preserved Early Tertiary sediments (~500 m thick, RGSS, 1991). It is likely that the different lithologies of the Jiaobei terrane, Jiaolai basin and Sulu UHP belt represent the source material for Tertiary sediments of Eastern Shandong. Allen et al. (1997) proposed that the North China Basin experienced two phases of extension during Cenozoic (Fig. 7). The first phase initiated between the deposition of the Kongdian Formation and the fourth member of Shahejie Formation (~50 Ma) and the subsidence rate reached its maximum during this rifting stage (Fig. 7; Li et al., 2007b; Ren et al., 2002), which is temporally consistent with the enhanced cooling event revealed by (U–Th)/He ages. The Mesozoic to Cenozoic evolution of eastern China continental margin was closely related to the tectonothermal history of Tan-Lu fault zone, which is considered as a very crucial boundary fault (Xu et al., 1987). This fault zone experienced a very complex evolution history since its formation during the Triassic collision of North China and Yangtze cratons (Gilder et al., 1999; Zhang et al., 2003b, 2007; Zhu et al., 2001, 2004, 2005; Grimmer et al., 2002; Mercier et al., 2007, 2013). Xu et al. (1987) recognized three phases of evolution for Tan-Lu fault zone: left-lateral strike–slip motion from Triassic to Early Cretaceous, extension from Early Cretaceous to Early Eocene, and E–W compression that began in Early Eocene. The Early Cretaceous extension of Middle part of this fault zone controlled the formation of Jiaolai basin, which is located between Jiaodong terrane and Sulu UHP belt (Fig. 8;

Fig. 7. Filling sequences in Subei (North Jiangsu) Basin (left, Wei et al., 2011) and Bohai Basin (right, Ren et al., 2002). The Eocene unconformity corresponds to the rapid exhumation event revealed by apatite Helium and fission track data.

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L. Wu et al. / Tectonophysics 672–673 (2016) 1–15

Fig. 8. (a) Major tectonic division of Shandong Province. (b) Crustal section across Shandong Province, with coupling between Eocene subsidence of North China Basin and uplift of surrounding blocks. Rapid uplift of Taihangshan Mountain from Qing et al. (2008), rapid cooling of Taihangshan detachment fault from Zhang et al. (2002), Luxi Block from Li and Zhong (2006), Jiaodong terrane and Sulu UHP belt from this study.

Zhang et al., 2003b). 40Ar/39Ar geochronological data (110–143 Ma) from the southern part of this fault provide compelling evidence for its Early Cretaceous reactivation (Zhu et al., 2001, 2004, 2005). During Late Cretaceous to Early Eocene, the same segment was reactivated as a normal fault (Zhu et al., 2004; Liu et al., 2006; Wang and Zhou, 2009), which lead to uplift of the footwall (i.e., Shandong Peninsula and Zhangbaling massif) and subsidence of hanging-wall (Luxi Block, North China Basin and Hefei Basin). Liu et al. (2006) argued for Early Tertiary uplift of Zhangbaling massif, which provided sedimentary material for more than 3 km thick of Early Tertiary clastic sediments in Hefei Basin. Grimmer et al. (2002) also correlated the 45–58 Ma apatite fission track ages very close to the Tan-Lu fault zone to rapid cooling during its Paleocene–Eocene normal motion. Moreover, to the west of North China Basin, Zhang et al. (2002) recognized two phases of relatively rapid cooling at 68–52 Ma and 23–18 Ma respectively based on apatite and zircon fission track ages from detachment fault zone between Taihangshan Mountain and North China Basin, which indicates

Paleocene–Eocene reactivation of Taihangshan fault. The first phase of reactivation coincides with the first rifting phase of North China Basin (Fig. 7). Rapid cooling phase of Early Eocene in Wutai Mountain area was suggested by Qing et al. (2008) using apatite fission track thermochronology. All the above-mentioned evidences support the fact that subsidence of North China Basin is coupled with the uplift of its surrounding mountains (Fig. 8). 5.4. Synchronous Early Tertiary enhanced cooling in central China and its geodynamic background Low-temperature thermochronology of central Tibet provides apatite He ages around 49 ± 6 Ma (Rohrmann et al., 2012), which indicates that the under-thrusting of Indian lithosphere is recorded as far north as the northern Qiangtang terrane by 45 Ma, and the plateau-like conditions were regionally broad by then. An enhanced cooling at 45 ± 10 Ma in the Dabie Shan (Grimmer et al., 2002), in the hanging-wall

L. Wu et al. / Tectonophysics 672–673 (2016) 1–15

of the West Qinling thrust (~ 45–50 Ma) and South Qaidam thrust (~35 Ma, Clark et al., 2010), in the south-wall of Altyn Tagh and Kunlun strike–slip fault zones (40 ± 10 Ma, Jolivet et al., 2001), in the Northern Qinling Shan and in the footwall of the faults bordering the Weihe graben to the south (Hu et al., 2006b; Liu et al., 2013) has been related to reactivation of faults of various age. The Taishan Mountain in the Western Shandong (Luxi) uplift also experienced a rapid uplift at 48 Ma (Li and Zhong, 2006). While further east in the southeast part of Sulu uplift, the Subei basin (North part of Jiangsu Province) was subjected to an uplift which resulted in a low-angle unconformity between Eocene Sanduo and Dainan formations, with a significant decrease of subsidence rate from 30–50 m/Ma to 8–15 m/Ma (Shu et al., 2006). AFT age pattern in the Hefei basin borehole (Chen et al., 2005) indicates that an exhumed apatite partial annealing zone existed at about 450 m depth, which is similar to the situation in Sulu (Fig. 4b; Liu et al., 2009b). The contemporaneous enhanced cooling/uplifting and compressional deformation in a large area of China is probably the result of a far-field effect of India–Eurasia collision, which occurred at about 52–50 Ma (Rowley, 1996). The areas affected by enhanced cooling events are regionally associated to the major strike–slip faults (Fig. 6) which are supposed to accommodate the large gravitational potential difference between the western China and Eastern China produced by the India– Asia collision. These observations and our new He ages support the assertion that very early in the India–Asia collision, deformation occurred far to the north and east along major mechanical boundaries in the Asian lithosphere (Jolivet et al., 2001). This large distance of far-field effect to the eastern free boundary of Eurasia continent was verified by Jolivet et al. (1990), who argued that right-lateral shear along the eastern margin of Asia which led to the opening of pull-apart basins such as Bohai basin and Japan Sea was a consequence of indentation of Asia by India. Molnar and Tapponnier (1975) also considered that the opening of Shanxi graben and Baikal rift is also a consequence of India collision with Asia. Liu et al. (2004c) noticed that a continuous low-velocity asthenospheric mantle structure extends from the Tibet plateau to eastern China, which could be the result of lateral mantle extrusion accounting for the widespread Cenozoic rifting and basaltic volcanism in eastern China. Structural mapping of western Sea of Okhotsk based on grids of multichannel seismic data led Worrall et al. (1996) to conclude that the tertiary Sakhalin–Hokkaido dextral fault system developed in Okhotsk Sea and related faults can be viewed as a far-away effect of India–Asia collision. All these evidences thus reinforce the view that strike-slip extrusion of Asian block is an important process that accommodates ~ 2000 km of crustal shortening induced by India–Asia collision besides the crustal thickening of Himalayan–Tibetan Plateau (Tapponnier et al., 1990, 2001; Wang and Burchfiel, 1997; Kirby et al., 2007). In our area, the rapid exhumation of Shandong Peninsula might be partly caused by the strike–slip motion of Tan-Lu fault, coevally with other fast cooling/exhumation events of central China. However, the effect of Pacific subduction beneath the Eurasia Plate could not be ignored. The subduction direction changed from N-NNW to NW about 50 Ma ago with a significant decrease of the convergence rate from 80 cm/year to 40 cm/year (Northrup et al., 1995). So the eastern margin of Eurasia became an orthogonal subduction boundary and trench-arc-basin system formed along the continental margin (Xu and Ma, 1992). From Late Cretaceous to Eocene, the continental margin and marginal sea of Eastern China were subjected to intensive rifting (Ye et al., 1987; Ma and Wu, 1987; Ren et al., 2002; Yin, 2010) in conjunction with sporadic basaltic volcanism along the Tan-Lu fault zone (Liu et al., 1983, 2001). This extensive event led to two rifting zones along continental margin of Eastern and Southeastern China. The first zone developed mainly along the Tan-Lu fault zone involving the formation of North China Plain Basin and new subsidence of previous Mesozoic basins (Hefei Basin, North Jiangsu Basin). The second zone of rifting includes several back-arc basins (Sea of Okhotsk, Japan Sea and South China Sea) in the Western Pacific and highly extended continental

11

margin (Bohai Bay, North Yellow Sea, East China Sea, Yin, 2010 and references therein). We suggest that the Cenozoic exhumation of Shandong Peninsula was partly affected by this rifting regime. Not only the convergence angle changed, but also the convergence rate between Pacific Plate and Eurasia decreased substantially during early Tertiary time and reached a minimum in Eocene time of ~30–40 mm/yr (Northrup et al., 1995) while at the same time the collision between India and Asia was completed and the two continents assembled. The reduction in horizontal compressional stress along with the increasing extensional stress induced by decrease of convergence rate favored the rifting along the eastern Asian continental margin and exhumation of Shandong Peninsula. So the Cenozoic rapid exhumation of Shandong Peninsula was a combined result of slowing down of Pacific subduction beneath the Eurasia continent and India-Asia continental collision. 6. Conclusions In this study, we obtained the first batch of regional-scale helium ages for different tectonic units in both Sulu region and Jiaobei terrane. Detailed analysis of the helium age pattern in the studied area and of Cenozoic subsidence history of North China basins allows us to draw the following concluding remarks: 1. There is a paleo AFT-PAZ and HePRZ in Sulu area, which is ~ 400– 500 m below the earth surface. 2. Large intra-sample (U–Th)/He age variations most probably result from very slow cooling during the Cenozoic, grain size variation, radiation damage, and some undetectable U/Th-rich inclusions and 4 He implantation from U/Th rich minerals. 3. An enhanced cooling occurred at about 45 Ma in Shandong Peninsula, which is coupled with the rapid subsidence of nearby North China riftbasins and the uplift of Taihangshan Mountain to the east of North China Basin. 4. The enhanced cooling in Sulu area, which is a widespread event from Tibet to Eastern Asia continental margin and mostly concentrated along the major strike–slip faults, indicates the possible relationship of this cooling to India–Asia continental collision. Close relationship between Cenozoic rifting along both the eastern China continental margin and marginal seas and the subduction direction and rate of the Pacific Plate implies possible combined effect of Pacific back-arc extension and far-field effect of India–Asia collision to the enhanced cooling event in Shandong Peninsula. Acknowledgments Lin Wu was funded by a Joint PHD student Project by the Chinese Academy of Sciences (CAS) and Le Centre National de la recherché scientifique (CNRS). This study is jointly funded by the China Natural Science Foundation (41503055, 41025010, 41221002 and 41302114) and the “Strategic Priority Research Program” of the Chinese Academy of Sciences (XDB03020203). Jacques L. Mercier and two anonymous reviewers are appreciated for their helpful and critical reviews. Des Patterson provided tremendous help during the establishment of the (U–Th)/He laboratory of IGGCAS. Noreen J. Evans from Curtin University was sincerely thanked for valuable suggestions to improve the standard procedure of helium dating. Appendix A. (U–Th)/He measurement procedure A.1. (U–Th)/He measurement procedure in University Montpellier 2 (UM 2) The whole (U–Th)/He dating procedure was achieved in Geosciences Montpellier, using the noble gas mass spectrometers and ICP-MS facilities. After the standard rock crushing and heavy liquid separation procedures, 4–6 relatively euhedral apatite grains free of visible inclusions and internal fractures were selected and measured under a macroscope. In

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L. Wu et al. / Tectonophysics 672–673 (2016) 1–15

Table 2 ICP-MS parameters. RF Generator power (W)

1220

Plasma Argon flow (L/min) Plasma gas Auxiliary Nebuliser Standard resolution Data acquisition mode Dwell time (ms) Sweeps Number of replicates Channels Seperation AMU Analysis time per sample (min) Mass Mnoitored

13.0 0.8 1.05 125 Peak jump 10 100 7 3 0.02 1.5 230, 232, 234, 235, 238

the mylonite and migmatite samples, we only got rounded grains. Each grain was then wrapped in 1 mm × 1 mm platinum capsule and loaded on a drilled oxygen-free copper disk. The samples were heated at about 900 °C for 12 min with a 1090 nm fiber laser operating at 20 W which is enough to extract N 99.9% of the total amount of 4He in the grains as shown by replicate heating. Gas purification was achieved with a cryogenic trap and two SAES AP-10-N getters and helium was measured with a Quadrupole PrismaPLus QMG 220. The helium content was measured by the peak height method using a 3He spike and are 10–100 times higher the typical blank levels. After helium extraction, aliquotes were retrieved for U and Th measurements. Apatite grains were dissolved in 220 ml of doubly spiked (230Th, 233U) HNO3 13 N at 120 °C for 2 h. 238U

and 232Th were measured by using isotope dilution ICP-MS. Errors reported for each age determination represent one standard deviations of replicate analyses (Table 1) and exceed analytical precision determined at ~5%. Thus, quoted errors reflect both sample heterogeneity and analytical procedure. Apatite helium ages were calculated and corrected for α emission following the procedure of Gautheron et al. (2009). Durango apatite replicates were analyzed each 3 analyzed samples. During the course of this study, we obtained an age of 31.49 ± 0.81 Ma (2σ) for the Durango apatite standard. This is in good agreement with the Durango AHe age of 31.13 ± 1.01 Ma reported by McDowell et al. (2005). A.2. (U–Th)/He measurement procedure in Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS) In order to compare the results of different laboratories, more grains of seven samples (Table 1) were analyzed in Helium laboratory of IGGCAS, which was established in 2013. Grain selection and measuring were similar to that in Geosciences Montpellier. However, for helium analysis, we use a full-automatic He extraction system called Alphachron MK II produced by Australian Scientific Instrument Pty Limited (ASI). The system consists of a 970 nm diode laser, full-automatic gas purification line and a Quadruple Mass spectrometer. Multiple analysis suggests that 10 A (heating to a temperature of 850–900 °C) laser heating for 5 min was enough to extract N99% of 4He in the heated crystal. Replicate heating released gas amount roughly the same as hot blank assured total extraction. Gas purification was achieved with two SAES AP-10-N getters and helium was measured with a Quadrupole PrismaPLus QMG 220. 4He/3He ratio of Q standard (known amount of 4 He) mixed with pure 3He which we called spiked standard was

Table 3 Durango (U–Th)/He age results. Sample

238

U (mol)

University Montpellier 2 DUR 116 6.52E−13 DUR 117 5.32E−13 DUR 118 1.14E−12 DUR 119 9.39E−13 DUR 120 4.95E−13 DUR 121 9.38E−13 DUR 122 4.40E−13 DUR 123 1.08E−12 DUR 124 7.75E−13 DUR 125 6.92E−13 DUR126 1.05E−12 DUR127 9.21E−13 DUR128 6.46E−13 DUR129 5.03E−13 DUR130 6.22E−13 DUR131 5.52E−13 DUR133 4.85E−13 DUR134 5.25E−13 DUR135 7.63E−13 DUR 144 4.91E−13 DUR 145 7.26E−13 DUR 146 1.04E−12 DUR 147 4.42E−13 DUR 148 4.07E−13

± std. (mol)

232

4.48E−15 3.99E−15 1.05E−14 3.92E−15 6.61E−15 6.57E−15 5.16E−15 3.59E−15 2.68E−15 6.96E−15 4.60E−15 1.73E−14 6.25E−15 7.97E−15 7.51E−15 6.65E−15 6.70E−15 4.78E−15 5.26E−15 8.66E−15 6.49E−15 6.53E−15 6.88E−15 5.22E−15

1.52E−11 1.21E−11 2.42E−11 2.17E−11 1.34E−11 2.03E−11 1.17E−11 2.36E−11 1.74E−11 1.66E−11 2.20E−11 2.03E−11 1.44E−11 1.14E−11 1.49E−11 1.31E−11 1.29E−11 1.41E−11 1.86E−11 1.16E−11 1.72E−11 2.48E−11 9.86E−12 9.60E−12

Th (mol)

Institute of Geology and Geophysics, Chinese Academy of Sciences Dur 04 1.10E−12 2.20E−14 2.09E−11 Dur 05 6.41E−13 1.28E−14 1.32E−11 Dur 06 1.41E−12 2.83E−14 2.32E−11 Dur 59 4.35E−13 8.71E−15 7.99E−12 Dur 60 4.83E−13 9.66E−15 8.75E−12 Dur 61 6.64E−13 1.33E−14 1.21E−11 Dur 141 3.95E−13 1.09E−14 7.94E−12 Dur 142 3.91E−13 8.22E−15 7.42E−12 Dur 143 3.16E−13 8.00E−15 6.47E−12 Dur 144 2.64E−13 7.20E−15 4.82E−−12

± std. (mol)

4

± std. (mol)

Age (Ma)

±1σ (Ma)

8.33E−14 5.77E−14 1.18E−13 1.38E−13 1.27E−13 1.79E−13 7.24E−14 1.13E−13 9.63E−14 6.48E−14 1.66E−13 1.44E−13 5.23E−14 1.03E−13 1.09E−13 1.33E−13 1.02E−13 1.63E−13 1.04E−13 9.21E−14 9.17E−14 1.84E−13 4.28E−14 9.08E−14

1.72E−13 1.36E−13 2.66E−13 2.39E−13 1.43E−13 2.24E−13 1.25E−13 2.66E−13 1.98E−13 1.92E−13 2.49E−13 2.15E−13 1.66E−13 1.27E−13 1.66E−13 1.47E−13 1.43E−13 1.57E−13 1.92E−13 1.30E−13 1.91E−13 2.79E−13 1.08E−13 1.07E−13

5.33E−16 4.16E−16 8.84E−16 7.94E−16 4.36E−16 8.34E−16 3.51E−16 7.99E−16 5.86E−16 5.24E−16 7.15E−16 6.67E−16 4.76E−16 3.50E−16 4.64E−16 4.39E−16 4.13E−16 4.20E−16 5.52E−16 4.14E−16 6.01E−16 9.72E−16 2.68E−16 3.06E−16 Mean age

32.10 31.67 30.66 31.18 30.94 31.00 30.83 31.58 32.10 32.98 31.46 29.78 32.55 31.48 31.75 31.92 31.99 32.38 29.49 31.84 31.54 31.95 30.81 31.7 31.49

0.18 0.16 0.17 0.2 0.28 0.26 0.19 0.16 0.18 0.15 0.22 0.22 0.15 0.27 0.22 0.3 0.25 0.34 0.17 0.25 0.18 0.23 0.16 0.28 0.81

4.18E−13 2.63E−13 4.64E−13 1.60E−13 1.75E−13 2.41E−13 1.61E−13 1.49E−13 1.57E−13 1.02E−13

2.43E−13 1.41E−13 2.70E−13 9.48E−14 9.74E−14 1.35E−13 9.81E−14 9.13E−14 8.05E−14 6.09E−14

2.98E−15 1.74E−15 3.32E−15 1.20E−15 1.21E−15 1.66E−15 1.40E−15 1.32E−15 1.29E−15 8.16E−16 Mean age

31.93 29.71 30.95 32.3 30.24 30.45 34.22 33.70 34.56 34.34 32.24

0.66 0.62 0.63 0.68 0.63 0.63 0.77 0.75 0.9 0.77 1.01

He (mol)

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measured. For the apatite sample, extracted 4He mixed with the same amount of 3He and 4He/3He ratio (spiked sample) was measured. 4He content (in nano cc) in the sample was calculated using the following equation (Des Patterson, personal communication): 4


He sample ¼

4

 
He standard  4 He=3 He

spiked sample

  = 4 He=3 He

spiked standard

After helium extraction, Pt wrapped grains were transferred to PFA vials for dissolution following the procedure of Evans et al. (2005). 25 μL spike solution (stored in 7 Mol/L HNO3) containing about 15 ng/mL U and 5 ng/mL Th (235U/238U = 838 ± 7, 230Th/232Th = 10.45 ± 0.05) was added into each vial. In order to completely dissolve U and Th, the PFA vials were ultrasonic washed for 15 min. After left at least 4 h at room temperature for fully dissolution, 325 μL reagent grade Milli-Q water was added to the vials and diluting them to a total volume of 350 μL. All the spiked samples are measured on a Thermal Fisher X-Series II ICP-MS with suitable parameters are chosen (Table 2). The same acid as used in the spike solution was used as reagent blank. Durango apatite was used as standard to verify analytical procedure. An average age of 32.24 ± 1.01 Ma (Table 3) was obtained for the Durango apatite, which is in consistent with ages yielded by other laboratories (McDowell et al., 2005; Reiners and Nicolescu, 2006). References Allen, M.B., Macdonald, D.I.M., Xun, Z., Vincent, S.J., Brouet-Menzies, C., 1997. Early Cenozoic two-phase extension and late Cenozoic thermal subsidence and inversion of the Bohai Basin, northern China. Mar. Pet. Geol. 14 (7/8), 951–972. Ames, L., Tilton, G.R., Zhou, G., 1993. Timing of collision of the Sino-Korean and Yangtze cratons: U–Pb zircon dating of coesite-bearing eclogites. Geology 21, 339–342. Ames, L., Zhou, G., Xiong, B., 1996. Geochronology and geochemistry of ultrahigh-pressure metamorphism with implications for collision of the Sino-Korean and Yangtze cratons, central China. Tectonics 15, 472–489. Brown, R.W., Beucher, R., Roper, S., Persano, C., Stuart, F., Fitzgerald, P., 2013. Natural age dispersion arising from the analysis of broken crystals. Part I: Theroretical basis and implications for the apatite (U–Th)/He thermochronometer. Geochim. Cosmochim. Acta 122, 478–497. Chavagnac, V., Jahn, B.M., 1996. Coesite-bearing eclogites from the Bixiling complex, Dabie Mountains, China: Sm–Nd ages, geochemical characteristics and tectonic implications. Chem. Geol. 133, 29–51. Chen, G., Zhao, Z.Y., Li, P.L., Ren, Z.L., Chen, J.P., Tan, M.Y., Li, X.P., 2005. Fission Track evidence for the tectonic–thermal history of the Hefei Basin. Chin. J. Geophys. 48 (6), 1433–1442. Clark, Martin K., Farley, Kenneth A., Zheng, D.W., Wang, Z.C., Duvall, A.R., 2010. Early Cenozoic faulting of the northern Tibetan Plateau margin from apatite (U–Th)/He ages. Earth Planet. Sci. Lett. 296, 78–88. Evans, N.J., Byrne, J.P., Keegan, J.T., Dotter, L.E., 2005. Determination of Uranium and Thorium in zircon, apatite, and fluorite: application to laser (U–Th)/He thermochronology. J. Anal. Chem. 60 (12), 1159–1165. Fan, W.M., Guo, F., Wang, Y.J., Lin, G., Zhang, M., 2001. Post-orogenic bimodal volcanism along the Sulu Orogenic Belt in Eastern China. Phys. Chem. Earth A 26 (9–10), 733–746. Faure, M., Lin, W., Scharer, U., Shu, L.S., Sun, Y., Arnaud, N., 2003. Continental subduction and exhumation of UHP rocks: structural and geochronological insights from the Dabieshan (East China). Lithos 70 (3-4), 213–241. Fitzgerald, P.G., Sorkhabi, R.B., Redfield, T.F., Stump, E., 1995. Uplift and denudation of the central Alaska Range: a case study in the use of apatite fission track thermochronology to determine absolute uplift parameters. J. Geophys. Res. 100 (B10), 20175–20191. Fitzgerald, P.G., Baldwin, S.L., Webb, L.E., O’Sullivan, P.B., 2006. Interpretation of (U–Th)/ He single grain ages from slowly cooled crustal terranes: a case study from the Transantarctic Mountains of southern Victoria Land. Chem. Geol. 225, 91–120. Gao, T.S., Chen, J.F., Xie, Z., Yang, S.H., Yu, G., 2004. Zircon SHRIMP U–Pb age of garnet olivine pyroxenite at Hujialin in the Sulu terrane and its geological significance. Chin. Sci. Bull. 49 (20), 2198–2204. Gautheron, C., Tassan-Got, L., Barbarand, J., Pagel, M., 2009. Effect of alpha-damage annealing on apatite (U–Th)/He thermochronology. Chem. Geol. 266, 157–170. Gilder, S.A., Leloup, H., Courtillot, V., Chen, Y., Coe, R.S., Zhao, X.X., Xiao, W.J., Halim, N., Cogné, J.P., Zhu, R.X., 1999. Tectonic evolution of the Tancheng–Lujiang (Tan-Lu) fault via Middle Triassic to Early Cenozoic paleomagnetic data. J. Geophys. Res. 104 (B7), 15365–15390. Gong, B., Zheng, Y.F., Wu, Y.B., Zhao, Z.F., Gao, T.S., Tang, J., Chen, R.Y., Fu, B., 2007. Geochronology and stable isotope geochemistry of UHP metamorphic rocks at Taohang in the Sulu orogen, east-central China. Int. Geol. Rev. 49, 259–286. Grimmer, J.C., Jonckheere, R., Enkelmann, E., Ratschbacher, L., Hacker, B.R., Blythe, A.E., Wanger, G.A., Wu, Q., Liu, S., Dong, S., 2002. Cretaceous–Cenozoic history of the southern Tan-Lu fault zone: apatite fission-track and structural constraints from the Dabie Shan (eastern China). Tectonophysics 359, 225–253.

13

Guo, F., Fan, W.M., Wang, Y.J., Zhang, M., 2004. Origin of early Cretaceous calc-alkaline lamprophyres from the Sulu orogen in eastern China: implications for enrichment processes beneath continental collisional belt. Lithos 78, 291–305. Guo, J.H., Chen, F.K., Zhang, X.M., Siebel, W., Zhai, M.G., 2005. Evolution of syn- to postcollisional magmatism from north Sulu UHP belt, eastern China: zircon U–Pb geochronology. Acta Petrol. Sin. 21 (4), 1281–1301 (in Chinese with English abstract). Hacker, B.R., Ratschbacher, L., Webb, L.E., Ireland, T.R., Walker, D., Dong, S., 1998. U/Pb zircon ages constrain the architecture of the ultrahigh-pressure Qinling–Dabie Orogen, China. Earth Planet. Sci. Lett. 161, 215–230. Hacker, B.R., Wallis, S.R., Ratschbacher, L., Grove, M., Gehrels, G., 2006. High-temperature geochronology constraints on the tectonic history and architecture of the ultra-highpressure Dabie–Sulu orogen. Tectonics 25, TC5006. http://dx.doi.org/10.1029/ 2005TC001937. Hacker, B.R., Wallis, S.R., McWilliams, M.O., Gans, P.B., 2009. 40Ar/39Ar constraints on the tectonic history and architecture of the ultrahigh-pressure Sulu orogen. J. Metamorph. Geol. http://dx.doi.org/10.1111/j.1525-1314.2009.00840.x. He, L.J., Hu, S.B., Yang, W.C., Wang, J.Y., Yang, S.C., Yuan, Y.S., Cheng, Z.Y., 2006. Temperature measurement in the main hole of the Chinese continental scientific drilling. Chin. J. Geophys. 49 (3), 745–752 (in Chinese with English abstract). Hellinger, S.J., Shedlock, K.M., Sclater, J.G., Ye, H., 1985. The Cenozoic evolution of the North China Basin. Tectonics 4 (4), 343–358. Hu, S.B., Hao, J., Fu, M.X., Wang, J.Y., 2005. Cenozoic denudation and cooling history of Qinling–Dabie-Sulu orogens: apatite fission track thermochronology constraints. Acta Petrol. Sin. 21 (4), 1167–1173 (in Chinese with English abstract). Hu, S.B., Kohn, B.P., Raza, A., Wang, J.Y., Gleadow, A.J.W., 2006a. Cretaceous and Cenozoic cooling history across ultrahigh pressure Tongbai–Dabie belt, central China, from apatite fission-track thermochronology. Tectonophysics 420, 409–429. Hu, S.B., Raza, A., Min, K., Kohn, B.P., Reiners, P.W., Ketcham, R.A., Wang, J.Y., Gleadow, A.J.W., 2006b. Late Mesozoic and Cenozoic thermotectonic evolution along a transect from the north China craton through the Qinling orogen in to Yangtze craton, central China. Tectonics 25, TC6009. http://dx.doi.org/10.1029/2006TC001985. Huang, J., Zheng, Y.F., Zhao, Z.F., Wu, Y.B., Zhou, J.B., Liu, X.M., 2006. Melting of subducted continent: element and isotopic evidence for a genetic relationship between Neoproterozoic and Mesozoic granitoids in the Sulu orogen. Chem. Geol. 229, 227–256. Jolivet, L., Davy, P., Cobbold, P., 1990. Right-lateral shear along the northwest pacific margin and the India–Eurasia collision. Tectonics 9 (6), 1409–1419. Jolivet, M., Brunel, M., Seward, D., Xu, Z., Yang, J., Roger, F., Tapponnier, P., Malavieille, J., Arnaud, N., Wu, C., 2001. Mesozoic and Cenozoic tectonics of the northern edge of the Tibetan plateau: fission-track constraints. Tectonophysics 343, 111–134. Kirby, E., Harkins, N., Wang, E.Q., Shi, X.H., Fan, C., Burbank, D., 2007. Slip rate gradients along the eastern Kunlun fault. Tectonics 26, TC2010. http://dx.doi.org/10.1029/ 2006TC002033. Kuang, Y.S., Pang, C.J., Luo, Z.Y., Hong, L.B., Zhong, Y.T., Qiu, H.N., Xu, Y.G., 2012. 40Ar–39Ar geochronology and geochemistry of mafic rocks from Qingshan Group, Jiaodong area: implications for the destruction of the North China Craton. Acta Petrol. Sin. 28 (4), 1073–1091 (in Chinese with English abstract). Lan, T.G., Fan, H.R., Santosh, M., Hu, F.F., Yang, K.F., Yang, Y.H., Liu, Y.S., 2011. Geochemistry and Sr–Nd–Pb–Hf isotopes of the Mesozoic Dadian alkaline intrusive complex in the Sulu orogenic belt, eastern China: implications for crust–mantle interaction. Chem. Geol. 285, 97–114. Leech, M.L., Webb, L.E., Yang, T.N., 2006. Diachronous histories for the Dabie–Sulu orogen from high-temperature geochronology. In: Hacker, B.R., McClellad, W.C., Liou, J.G. (Eds.), Ultrahigh-Pressure Metamorphism: Deep Continental Subduction. Geological Society of America Special Paper 403, pp. 1–22. http://dx.doi.org/10.1130/2006. 2403(01). Li, L., Zhong, D.L., 2006. Fission track evidence of Cenozoic uplifting events of Taishan Mountain, China. Acta Petrol. Sin. 22 (2), 457–464 (in Chinese with English abstract). Li, S.G., Xiao, Y.L., Liu, D.L., Chen, Y.Z., Ge, N.J., Zhang, Z.Q., Sun, S.S., Cong, B.L., Zhang, R.Y., Hart, S.R., Wang, S.S., 1993. Collision of the North China and Yangtze Blocks and formation of coesite-bearing eclogites: timing and processes. Chem. Geol. 109, 89–111. Li, S.G., Wang, S.S., Chen, Y.Z., Liu, D.L., Qiu, J., Zhou, H.X., Zhang, Z.M., 1994. Excess argon in phengite from eclogite: evidence from dating of eclogite minerals by Sm/Nd, Rb/Sr and 40Ar/39Ar methods. Chem. Geol. 112 (3-4), 343–350. Li, S.G., Jagoutz, E., Lo, C.H., Chen, Y.Z., Li, Q.L., Xiao, Y.L., 1999. Sm/Nd, Rb/Sr and 40Ar/39Ar isotopic systematics of the ultrahigh-pressure metamorphic rocks in the Dabie–Sulu belt Central China: a retrospective view. Int. Geol. Rev. 41, 1114–1124. Li, J.L., Zhang, Y.Q., Liu, Z.Q., Ren, F.L., Yuan, J.Y., 2007a. Sedimentary-subsidence history and tectonic evolution of the Jiaolai basin, eastern China. Geol. China 34 (2), 240–250 (in Chinese with English abstract). Li, L., Zhong, D.L., Shi, X.P., 2007b. Cenozoic uplifting/subsidence coupling between the West Shandong Rise and the Jiyang Depression, Northern China. Acta Geol. Sin. 81 (9), 1215–1229 (in Chinese with English abstract). Lin, A.M., Miyata, T., Wan, T.F., 1998. Tectonic characteristics of the central segment of the Tancheng–Lujiang fault zone, Shandong Peninsula, eastern China. Tectonophysics 293, 85–104. Lin, L.H., Wang, P.L., Lo, C.H., Tsas, C.H., Jahn, B.M., 2005. 40Ar/39Ar thermochronological constraints on the exhumation of ultrahigh-pressure metamorphic rocks in the Sulu terrane of Eastern China. Int. Geol. Rev. 47, 872–886. Lin, W., Faure, M., Chen, Y., Ji, W.B., Wang, F., Wu, L., Charles, N., Wang, J., Wang, Q.C., 2013. Late Mesozoic compressional to extensional tectonics in the Yiwulvshan massif, NE China and its bearing on the evolution of the Yinshan–Yanshan orogenic belt (Part I: Structural analyses and geochronological constraints). Gondwana Res. 23, 54–77. Lin, W., Ji, W.B., Faure, M., Wu, L., Li, Q.L., Shi, Y.H., Scharer, U., Wang, F., Wang, Q.C., 2015. Early Cretaceous extension reworking of the Triassic HP-UHP metamorphic orogen in Eastern China. Tectonophysics 662, 256–270.

14

L. Wu et al. / Tectonophysics 672–673 (2016) 1–15

Liu, F.L., Liou, J.G., 2011. Zircon as the best mineral for P–T-time history of UHP metamorphism: a review on mineral inclusions and U–Pb SHRIMP ages of zircons from the Dabie–Sulu UHP rocks. J. Asian Earth Sci. 40, 1–39. Liu, R.X., Sun, J.Z., Chen, W.J., 1983. Cenozoic basalts in North China—their distribution, geochemical characteristics and tectonic implications. Geochemistry 2 (1), 17–33. Liu, J., Han, J., Fyfe, W., 2001. Cenozoic episodic volcanism and continental rifting in northeast China and possible link to Japan Sea development as revealed by K–Ar geochronology. Tectonophysics 399, 385–401. Liu, F.L., Xu, Z.Q., Xue, H.M., 2004a. Tracing the protholith, UHP metamorphic, and exhumation ages of orthogneiss from the SW Sulu terrane (eastern China): SHRIMP U–Pb dating of mineral inclusion-bearing zircon. Lithos 78, 411–429. Liu, F.L., Xu, Z.Q., Liou, J.G., Song, B., 2004b. SHRIMP U–Pb ages of ultrahigh-pressure and retrograde metamorphism of gneisses, south-western Sulu terrane, eastern China. J. Metamorph. Geol. 22, 315–326. Liu, M., Cui, X.J., Liu, F.T., 2004c. Cenozoic rifting and volcanism in eastern China: a mantle dynamic link to the Indo-Asian collision? Tectonophysics 393, 29–42. Liu, G.S., Zhu, G., Niu, M.L., Song, C.G., Wang, D.X., 2006. Meso-Cenozoic evolution of the Hefei Basin (eastern part) and it's response to activities of the Tan-Lu Fault Zone. Chin. J. Geol. 41 (2), 256–269 (in Chinese with English abstract). Liu, F.L., Gerdes, A., Zeng, L.S., Xue, H.M., 2008a. SHRIMP U–Pb dating, trace elements and the Lu–Hf isotope system of coesite-bearing zircon from amphibolite in the SW Sulu UHP terrane, eastern China. Geochim. Cosmochim. Acta 72, 2973–3000. Liu, S., Hu, R.Z., Gao, S., Feng, C.X., Qi, Y.Q., Wang, T., Feng, G.Y., Coulson, I.M., 2008b. U–Pb zircon age, geochemical and Sr–Nd–Pb–Hf isotopic constraints on age and origin of alkaline intrusions and associated mafic dikes from Sulu orogenic belt, Eastern China. Lithos 106, 365–379. Liu, F.L., Gerdes, A., Xue, M., 2009a. Differential subduction and exhumation of crustal slices in the Sulu HP-UHP metamorphic terrane: insights from mineral inclusions, trace elements, U–Pb and Lu–Hf isotope analyses of zircon in orthogneiss. J. Metamorph. Geol. 27, 805–825. Liu, S.S., Weber, U., Glasmacher, U.A., Xu, Z.Q., Wanger, G.A., 2009b. Fission track analysis and thermotectonic history of the main borehole of the Chinese Continental Scientific Drilling project. Tectonophysics 475, 318–326. Liu, F.L., Robinson, P.T., Gerdes, A., Xue, H.M., Liu, P.H., Liou, J.G., 2010. Zircon U–Pb ages, REE concentrations and Hf isotope compositions of granitic leucosome and pegmatite from the north Sulu UHP terrane in China: constraints on the timing and nature of partial melting. Lithos 117, 247–268. Liu, J.H., Zhang, P.Z., Lease, R.O., Zheng, D.W., Wan, J.L., Wang, W.T., Zhang, H.P., 2013. Eocene onset and late Miocene acceleration of Cenozoic intracontinental extension in the North Qinling range-Weihe graben: insights from apatite fission track thermochronology. Tectonophysics 584, 281–296. Ma, X.H., Wu, D.N., 1987. Cenozoic extensional tectonics in China. Tectonophysics 133, 243–255. Mattauer, M., Matte, P., Malavieille, J., Tapponnier, P., Maluski, H., Xu, Z., Lu, Y., Tang, Y., 1985. Tectonics of the Qinling Belt: build-up and evolution of Eastern Asia. Nature 317, 496–500. McDowell, F.W., McIntosh, W.C., Farley, K.A., 2005. A precise 40Ar–39Ar reference age for the Durango apatite (U–Th)/He and fission-track dating standard. Chem. Geol. 214, 249–263. Meng, Q.R., 2003. What drove late Mesozoic extension of the northern China–Mongolia tract? Tectonophysics 369 (3–4), 155–174. Meng, F.C., Shi, R.D., Li, T.F., Liu, F.L., Xu, Z.Q., 2006. The ages and sources of Late Mesozoic granites in southern Sulu region. Acta Geol. Sin. 80 (12), 1867–1876 (in Chinese with English abstract). Mercier, J.L., Hou, M.J., Vergély, P., Wang, Y.M., 2007. Structural and stratigraphical constraints on the kinematics history of the Southern Tan-Lu Zone during the Mesozoic Anhui Province, China. Tectonophysics 439, 33–66. Mercier, J.L., Vergely, P., Zhang, Y.Q., Hou, M.J., Bellier, O., Wang, Y.M., 2013. Structural records of the Late Cretaceous–Cenozoic extension in Eastern China and the kinematics of the Southern Tan-Lu and Qinling fault zone (Anhui and Shan'xi province, PR China). Tectonophysics 582, 50–72. Miao, L.C., Luo, Z.K., Guan, K., Huang, J.Z., 1998. The implication of the SHRIMP U–Pb age in zircon to the petrogenesis of the Linglong granite, East Shandong Province. Acta Petrol. Sin. 14 (2), 198–206 (in Chinese with English abstract). Molnar, P., Tapponnier, P., 1975. Cenozoic tectonics of Asia: effects of a continental collision. Science 189, 419–426. Ni, J.L., Liu, J.L., Tang, X.L., Yang, H.B., Xia, Z.M., Guo, Q.J., 2013. The Wulian metamorphic core complex: a newly discovered metamorphic core complex along the Sulu Orogenic Belt, Eastern China. J. Earth Sci. 24 (3), 297–313. Northrup, C.J., Royden, L.H., Burchfiel, B.C., 1995. Motion of the Pacific plate relative to Eurasia and its potential relation to Cenozoic extension along the eastern margin of Eurasia. Geology 23, 719–722. Qing, J.C., Ji, J.Q., Wang, J.D., Peng, Q.L., Niu, X.L., Ge, Z.H., 2008. Apatite fission track study of Cenozoic uplift and exhumation of Wutai Mountain, China. Chin. J. Geophys. 51 (2), 384–392 (in Chinese with English abstract). Qiu, J.S., Xu, X.S., Lo, C.H., 2001. 40Ar/39Ar dating and source tracing of K-rich volcanic rocks and lamprophyres in Western Shandong Province. Chin. Sci. Bull. 46 (18), 1500–1508 (in Chinese with English abstract). Rastchbacher, L., Hacker, B.R., Webb, L.E., Mc Williams, M., Ireland, T., Dong, S., Calvert, A., Chateigner, D., Wenk, H.R., 2000. Exhumation of the ultra-high pressure crust in eastern China: Cretaceous to Cenozoic unroofing and the Tan-Lu fault. J. Geophys. Res. 105, 13303–13338. Regional Geological Survey of Shandong, 1991. Regional Geology of Shandong Province. Geological Publishing House, Beijing, p. 595.

Reiners, P.W., Nicolescu, S., 2006. Measurement of parent nuclides for (U–Th)/He chronometry by solution sector ICP-MS. ARHDL Rep. 1 (http://www.geo.arizona.edu/ ~reiners/arhdl/arhdl.htm). Reiners, P.W., Zhou, Z.Y., Ehlers, T.A., Xu, C.H., Brandon, M.T., Donelick, R.A., Nicolescu, S., 2003. Post-orogenic evolution of the Dabie Shan, Eastern China, From (U–Th)/He and fission-track thermochronology. Am. J. Sci. 303, 489–518. Ren, J.Y., Tamaki, K., Li, S.T., Zhang, J.X., 2002. Late Mesozoic and Cenozoic rifting and its dynamic setting in Eastern China and adjacent areas. Tectonophysics 344, 175–205. Ren, F.L., Zhang, Y.Q., Qiu, L.G., Liu, Z.Q., Wang, D.H., 2007. Evolution of the structural stress field in Jiaolai basin in Cretaceous. Geotecton. Metallog. 31 (2), 157–167 (in Chinese with English abstract). Rohrmann, A., Kapp, P., Carrapa, B., Reiners, P.W., Guynn, J., Ding, L., Heizler, M., 2012. Thermochronologic evidence for plateau formation in central Tibet by 45 Ma. Geology 40 (2), 187–190. Rowley, D.B., 1996. Age of initiation of collision between India and Asia: a review of stratigraphic data. Earth Planet. Sci. Lett. 145, 1–13. Rumble, D., Giorgis, D., Ireland, T., Zhang, X.M., Xu, H.F., Yi, T.F., Yang, J.S., Xu, Z.Q., Liou, J.G., 2002. Low δ18O zircons, U–Pb dating, and the age of the Qinglongshan oxygen and hydrogen isotope anomaly near Donghai in Jiangsu Province. Geochim. Cosmochim. Acta 66, 2299–2306. Schmidt, A., Weyer, S., Mezger, K., Scherer, E.E., Xiao, Y.L., Hoefs, J., Brey, G., 2008. Rapid eclogitisation of the Dabie–Sulu UHP terrane: constraints from Lu–Hf garnet geochronology. Earth Planet. Sci. Lett. 273 (1–2), 203–213. Schmidt, A., Mezger, K., O’Brien, P.J., 2011. The time of eclogite formation in the ultrahigh pressure rocks of the Sulu terrane: constraints from Lu–Hf garnet geochronology. Lithos 125 (1–2), 743–756. Shu, L.S., Wang, B., Wang, L.S., He, G.Y., 2006. Analysis of Northern Jiangsu Prototype Basin from Late Cretaceous to Neogene. Geol. J. China Univ. 11 (4), 534–543 (in Chinese with English abstract). Shuster, D.L., Flowers, R.M., Farley, K.A., 2006. The influence of natural radiation damage on helium diffusion kinetics in apatite. Earth Planet. Sci. Lett. 249, 148–161. Siebel, W., Danišík, M., Chen, F.K., 2009. From emplacement to unroofing: thermal history of the Jiazishan gabbro, Sulu UHP terrane, China. Mineral. Petrol. 96, 163–175. Spiegel, C., Kohn, B., Belton, D., Berner, Z., Gleadow, A., 2009. Apatite (U–Th–Sm)/He thermochronology of rapidly cooled samples: The effect of He implantation. Earth Planet. Sci. Lett. 285, 105–114. Tang, J., Zheng, Y.F., Wu, Y.B., Gong, B., 2006. Zircon SHRIMP U–Pb dating, C and O isotopes for impure marbles from the Jiaobei terrane in the Sulu orogen: implication for the tectonic affinity. Precambrian Res. 144, 1–18. Tang, J., Zheng, Y.F., Wu, Y.B., Gong, B., Liu, X.M., 2007. Geochronology and geochemistry of metamorphic rocks in the Jiaobei terrane: constraints on its tectonic affinity in the Sulu orogen. Precambrian Res. 152, 48–82. Tang, J., Zheng, Y.F., Wu, Y.B., Gong, B., Zha, X.P., Liu, X.M., 2008. Zircon U–Pb age and geochemical constraints on the tectonic affinity of the Jiaodong terrane in the Sulu orogen, China. Precambrian Res. 161, 389–418. Tang, H.Y., Zheng, J.P., Yu, C.M., 2009. Age and composition of the Rushan intrusive complex in the northern Sulu orogen, eastern China: petrogenesis and lithospheric mantle evolution. Geol. Mag. 146 (2), 199–215. Tapponnier, P., Lacassin, R., Leloup, P.H., Schärer, U., Zhong, D.L., Hu, H.W., Liu, X.H., Ji, S.C., Zhang, L.S., Zhong, J.Y., 1990. The Ailao Shan/Red River metamorphic belt: Tertiary left-lateral shear between Indochina and South China. Nature 343 (1), 431–438. Tapponnier, P., Xu, Z.Q., Roger, F., Meyer, B., Arnaud, N., Wittlinger, G., Yang, J.S., 2001. Oblique stepwise rise and growth of the Tibet Plateau. Science 294 (23), 1671–1677. Wallis, S., Tsuboi, M., Suzuki, K., Fangning, M., Jiang, L.L., Tanaka, T., 2005. Role of partial melting in the evolution of the Sulu (eastern China) ultrahigh-pressure terrane. Geology 33 (2), 129–132. Wang, Y., 2006. The onset of the Tan-Lu fault movement in eastern China: constraints from zircon (SHRIMP) and 40Ar/39Ar dating. Terra Nova 18, 423–431. Wang, E.C., Burchfiel, B.C., 1997. Interpretation of Cenozoic tectonics in the right-lateral accommodation zone between the Ailao Shan shear zone and the eastern Himalayan syntaxis. Int. Geol. Rev. 39, 191–219. Wang, Y., Zhou, S., 2009. 40Ar/39Ar dating constraints on the high-angle normal faulting along the southern segment of the Tan-Lu fault system: an implication for the onset of eastern China rift-systems. J. Asian Earth Sci. 34, 51–60. Wang, R.C., Xu, S.Q., Fang, Z., Shieh, Y.N., Li, H.M., Li, D.M., Wan, J.L., Wu, W.P., 2004. Protolith age and exhumation history of metagranites from the Dabie UHP metamorphic belt in east-central China: a multi-chronological study. Geochem. J. 38, 345–362. Wang, W., Zhang, Z.M., Yu, F., Liu, F., Dong, X., Liou, J.G., 2011. Petrological and geochronological constraints on the origin of HP and UHP kyanite–quartzites from the Sulu orogen, Eastern China. J. Asian Earth Sci. 42 (4), 618–632. Wei, X.F., Zhang, T.S., Huang, J., Liang, X., Yao, Q.C., Tang, X.Y., 2011. Sequence stratigraphy characteristics and filling evolution models of Paleogene in Baiju sag, Subei Basin. Acta Geosci. Sin. 32 (4), 427–437 (in Chinese with English abstract). Wolf, R.A., Farley, K.A., Kass, S.M., 1998. Modeling of the temperature sensitivity of the apatite (U–Th)/He thermochronometer. Chem. Geol. 148, 105–114. Worrall, D.M., Kruglyak, V., Kunst, F., Kuznetsov, V., 1996. Tertiary tectonics of the Sea of Okhotsk, Russia: far-field effects of the India–Eurasia collision. Tectonics 15 (4), 813–826. Wu, L., 2014. Thermal evolution of the Sulu Orogenic Belt—constraints from medium-low temperature thermochronology. University of Chinese Academy of Sciences (Thesis of doctoral degree (in Chinese with English abstract)). Xu, Z.Q., 1987. Etude tectonique et microtectonique de la Chaine paleozoique et Triasique des Qinlings (Chine) Thése de dotorat Uni. Sci. Tch., Langedoc, Montpellier.

L. Wu et al. / Tectonophysics 672–673 (2016) 1–15 Xu, J.W., Ma, G.F., 1992. Review of ten years (1981–1991) of research on the Tancheng– Lujiang fault zone. Geol. Rev. 38 (4), 316–324 (in Chinese with English abstract). Xu, J.W., Zhu, G., Tong, W., Cui, K., Liu, Q., 1987. Formation and evolution of the Tancheng– Lujiang wrench fault system: a major shear system to the northwest of the Pacific Ocean. Tectonophysics 134, 273–310. Xu, S.T., Okay, A.I., Ji, S.Y., Sengor, A.M.C., Su, W., Liu, Y.C., Jiang, L.L., 1992. Diamond from the Dabie Shan metamorphic rocks and its implication for tectonic setting. Science 256, 80–82. Xu, C.H., Zhou, Z.Y., Haute, P.V.D., Donelick, R.A., Grave, J.D., Ma, C.Q., Reiners, P.W., 2005. Apatite-fission-track geochronology and its tectonic correlation in the Dabieshan orogen, central China. Sci. China Ser. D Earth Sci. 48 (4), 506–520 (in Chinese with English abstract). Xu Z., Zeng L., Liu F., Yang J., Zhang Z., McWilliams M., Liou J.G., 2006, Polyphase subduction and exhumation of the Sulu high-pressure–ultrahigh-pressure metamorphic terrane, in Hacker B.R., McClelland W.C.Liou J.G.Ultrahigh-Pressure Metamorphism: Deep Continental Subduction: Geol. Soc. Am. Spec. Pap., 403, 93–113, doi: http://dx.doi. org/10.1130/2006.2403(05). Yan, J., Chen, J.F., Xie, Z., Zhou, T.X., 2003. Mantle xenolith in Late Cretaceous basalt of eastern Shandong Province: new evidence constraining the timing of lithospheric thinning of eastern China. Chin. Sci. Bull. 48 (14), 1570–1574 (in Chinese with English abstract). Yang, J.S., Wooden, J.L., Wu, C.L., Liu, F.L., Xu, Z.Q., Shi, R.D., Katayama, I., Liou, J.G., Maruyama, S., 2003. SHRIMP U–Pb dating of coesite-bearing zircon from the ultrahigh-pressure metamorphic rocks, Sulu terrane, east China. J. Metamorph. Geol. 21, 551–560. Yang, J.H., Wu, F.Y., Chung, S.L., Wilde, S.A., Chu, M.F., Lo, C.H., Song, B., 2005a. Petrogenesis of Early Cretaceous intrusions in the Sulu ultrahigh-pressure orogenic belt, east China and their relationship to lithospheric thinning. Chem. Geol. 222, 200–231. Yang, J.H., Chung, S.L., Wilde, S.A., Wu, F.Y., Chu, M.F., Lo, C.H., Fan, H.R., 2005b. Petrogenesis of post-orogenic syenites in the Sulu Orogenic Belt, East China: geochronological, geochemical and Nd–Sr isotopic evidence. Chem. Geol. 214, 99–125. Ye, H., Zhang, B.T., Mao, F.Y., 1987. The Cenozoic tectonic evolution of the Great North China: two types of rifting and crustal necking in the Great North China and their tectonic implications. Tectonophysics 133, 217–227. Ye, K., Cong, B.L., Ye, D.N., 2000a. The possible subduction of continental material to depth greater than 200 km. Nature 407, 734–736. Ye, K., Yao, Y.P., Katayama, I., Cong, B.L., Wang, Q.C., Maruyama, S., 2000b. Large areal extent of ultrahigh-pressure metamorphism in the Sulu ultrahigh-pressure terrane of East China: new implications from coesite and omphacite inclusions in zircon of granitic gneiss. Lithos 52, 157–164. Yin, A., 2010. Cenozoic tectonic evolution of Asia: a preliminary synthesis. Tectonophysics 488, 293–325. Yu, F., Zhang, Z.M., Wang, W., Liu, F., Dong, X., Liou, J.G., 2011. Zircon U–Pb constraints on the origin of UHP meta-supracrustal rocks in the Southern Sulu orogen, eastern China. J. Asian Earth Sci. 42 (4), 740–751. Zhai, M.G., Cong, B.L., Guo, J.H., Liu, W.J., Li, Y.G., Wang, Q.C., 2000. Sm–Nd geochronology and petrography of garnet pyroxene granulites in the northern Sulu region of China and their geotectonic implications. Lithos 52, 23–33. Zhang, T., Zhang, Y.Q., 2007. Geochronological sequence of Mesozoic intrusive magmatism in Jiaodong Peninsula and its tectonic constraints. Geol. J. China Univ. 13 (2), 323–336 (in Chinese with English abstract). Zhang, J.S., Xu, J., Wang, J.L., Guo, Z.W., 2002. Meso-Cenozoic detachment zones in the front of Taihang Mountains and their FT ages. Geol. Bull. China 21 (4–5), 207–210 (in Chinese with English abstract). Zhang, R.Y., Liou, J.G., Yang, J.S., Ye, K., 2003a. Ultrahigh-pressure metamorphism in the forbidden zone: the Xugou garnet peridotite, Sulu terrane, eastern China. J. Metamorph. Geol. 21, 539–550.

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Zhang, Y.Q., Dong, S.W., Shi, W., 2003b. Cretaceous deformation of the middle Tan-Lu fault zone in Shandong Province, eastern China. Tectonophysics 363, 243–258. Zhang, R.Y., Yang, J.S., Wooden, J.L., Liou, J.G., Li, T.F., 2005. U–Pb SHRIMP geochronology of zircon in garnet peridotite from the Sulu UHP terrane, China: implications for mantle metasomatism and subduction-zone UHP metamorphism. Earth Planet. Sci. Lett. 237, 729–743. Zhang, Y.Q., Li, J.L., Zhang, T., Yuan, J.Y., 2007. Late Mesozoic kinematic history of the Muping–Jimo fault zone in Jiaodong Peninsula, Shandong Province, East China. Geol. Rev. 53 (3), 289–301 (in Chinese with English abstract). Zhang, J., Zhao, Z.F., Zheng, Y.F., Dai, M.N., 2010. Postcollisional magmatism: geochemical constraints on the petrogenesis of Mesozoic granitoids in the Sulu orogen, China. Lithos 119, 512–536. Zhang, J., Zhao, Z.F., Zheng, Y.F., Liu, X.M., Xie, L.W., 2011. Zircon Hf–O isotope and wholerock geochemical constraints on origin of postcollisional mafic to felsic dykes in the Sulu Orogen. Lithos 136–139, 225–245. Zhao, R.X., Liou, J.G., Li, T.F., 2006a. SHRIMP U–Pb zircon of the Rongcheng eclogite and associated peridotite: new constraints for ultrahigh-pressure metamorphism of mantle-derived mafic–ultramafic bodies from the Sulu terrane. In: Hacker, B.R., McClellad, W.C., Liou, J.G. (Eds.), Ultrahigh-Pressure Metamorphism: Deep Continental Subduction. Geological Society of America Special Paper 403, pp. 115–125. http://dx. doi.org/10.1130/2006.2403(06). Zhao, Z.F., Zheng, Y.F., Gao, T.S., Wu, Y.B., Chen, B., Chen, F.K., Wu, F.Y., 2006b. Isotopic constraints on age and duration of fluid-assisted high-pressure eclogite-facies recrystallization during exhumation of deeply subducted continental crust in the Sulu orogen. J. Metamorph. Geol. 24, 687–702. Zheng, Y.F., Wu, Y.B., Chen, F.K., Gong, B., Li, L., Zhao, Z.F., 2004. Zircon U–Pb and oxygen isotope evidence for a large-scale 18O depletion event in igneous rocks during the Neoproterozoic. Geochim. Cosmochim. Acta 68, 4145–4165. Zheng, Y.F., Chen, R.X., Zhao, Z.F., 2009. Chemical geodynamics of continental subductionzone metamorphism: insights from studies of the Chinese Continental Scientific Drilling (CCSD) core samples. Tectonophysics 475, 325–356. Zhou, J.B., Zheng, Y.F., Zhao, Z.F., 2003a. Zircon U–Pb dating on Mesozoic granitoids at Wulian, Shandong Province. Geol. J. China Univ. 9 (2), 185–194 (in Chinese with English abstract). Zhou, Z.Y., Xu, C.H., Reiners, P.W., Yang, F.L., Donelick, R.A., 2003b. Exhumation history of Tiantangzhai of Dabieshan region since Late Cretaceous—evidence from (U–Th)/He and fission track analysis. 2003. Chin. Sci. Bull. 48 (6), 598–602 (in Chinese with English abstract). Zhou, J.B., Wilde, S.A., Zhao, G.C., Zhang, X.Z., Zheng, C.Q., Jin, W., Cheng, H., 2008. SHRIMP U–Pb zircon dating of the Wulian complex: defining the boundary between the North and South China Cratons in the Sulu Orogenic Belt, China. Precambrian Res. 162, 559–576. Zhu, G., Song, C.Z., Wang, D.X., Liu, G.S., Xu, J.W., 2001. Studies on 40Ar/39Ar thermochronology of strike–slip time of the Tan-Lu fault zone and their tectonic implications. Sci. China. Ser. D Earth Sci. 44 (11), 1002–1009. Zhu, G., Hou, M.J., Wang, Y.S., Liu, G.S., Niu, M.L., 2004. Thermal evolution of the Tanlu fault zone on the eastern margin of the Dabie Mountains and its tectonic implications. Acta Geol. Sin. 78 (4), 940–953. Zhu, G., Wang, Y.S., Liu, G.S., Niu, M.L., Xie, C.L., Li, C.C., 2005. 40Ar/39Ar dating of strike–slip motion on the Tan-Lu fault zone, East China. J. Struct. Geol. 27, 1379–1398. Zhu, G., Jiang, D.Z., Zhang, B.L., Chen, Y., 2012. Destruction of the eastern North China Craton in a back arc setting: evidence from crustal deformation kinematics. Gondwana Res. 22, 86–103. Zong, K.Q., Liu, Y.S., Gao, C.G., Hu, Z.H., Gao, S., Gong, H.J., 2010. In situ U–Pb dating and trace element analysis of zircons in thin sections of eclogite: refining constraints on the UHP metamorphism of the Sulu terrane, China. Chem. Geol. 269 (3-4), 237–251.