Zircon U-Pb ages and Lu-Hf isotope compositions from clastic rocks in the Hutuo Group: Further constraints on Paleoproterozoic tectonic evolution of the Trans-North China Orogen

Accepted Manuscript Zircon U-Pb ages and Lu-Hf isotope compositions from clastic rocks in the Hutuo Group: Further constraints on Paleoproterozoic tectonic evolution of the Trans-North China Orogen Lilin Du, Chonghui Yang, Derek A. Wyman, Allen P. Nutman, Lei Zhao, Zenglong Lu, Huixia Song, Yuansheng Geng, Liudong Ren PII: DOI: Reference:

S0301-9268(16)30571-X http://dx.doi.org/10.1016/j.precamres.2017.04.007 PRECAM 4724

To appear in:

Precambrian Research

Received Date: Revised Date: Accepted Date:

30 November 2016 21 March 2017 2 April 2017

Please cite this article as: L. Du, C. Yang, D.A. Wyman, A.P. Nutman, L. Zhao, Z. Lu, H. Song, Y. Geng, L. Ren, Zircon U-Pb ages and Lu-Hf isotope compositions from clastic rocks in the Hutuo Group: Further constraints on Paleoproterozoic tectonic evolution of the Trans-North China Orogen, Precambrian Research (2017), doi: http:// dx.doi.org/10.1016/j.precamres.2017.04.007

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Zircon U-Pb ages and Lu-Hf isotope compositions from clastic rocks in the Hutuo Group: Further constraints on Paleoproterozoic tectonic evolution of the Trans-North China Orogen

LilinDua,b* , Chonghui Yanga, Derek A. Wymanb, Allen P. Nutmanc, Lei Zhaod, ZenglongLu a, HuixiaSonga, YuanshengGenga, Liudong Rena

a

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

b

School of Geosciences, The University of Sydney, Sydney, NSW 2006, Australia

c

GeoQuEST Research Center, School of Earth & Environmental Sciences, University of Wollogong, Wollongong, NSW 2522, Australia

d

Institute of Geology and Geophysics, ChineseAcademy of Sciences, Beijing 100029, China

*

Corresponding author at: Baiwanzhuang Road 26, Xicheng District, Beijing 100037, China. Tel: 86 10 68999709; fax: 86 10 68997803. E-mail address: [email protected]

Abstract: The Hutuo Group, as one of the classic examples of Paleoproterozoic strata, plays an important role in establishing evolutionary processes in the Tran-North China Craton. In this contribution, we present petrologic, detrital zircon U-Pb ages and Lu-Hf isotopes from three subgroups of the Hutuo Group. Sandstones in the Doucun and Dongye Subgroups are dominated by Q (monocrystalline and polycrystalline quartz) and F (K-feldspar and plagioclase) with minor lithic fragments, suggesting that the detrital components were mainly derived from both the continental block and recycled orogen. In contrast, clastic components in the Guojiazhai Subgroup are mainly Q and lithic fragments, indicating they were derived predominantly from the recycled orogen. The ages of detrital zircons from sandstones in the Doucun and Dongye Subgroups are mainly concentrated at ca. 2.5 Ga and 2.2−2.1 Ga with minor 2.7 Ga zircons also present which indicates they were dominantly sourced from 2.5 Ga Wutai, Fuping and Zanhuang Complexes, and Paleoproterozoic intrusives. The Guojiazhai Subgroup displays a different zircon age population of ca.2.4 Ga, 2.2−2.1 Ga and 2.0−1.9 Ga, which indicates likely derivation from Paleoproterozoic intrusives in the Wutai, Lüliang and Hengshan areas. Based on the observation that sandstone clastic components in the Doucun and Dongye Subgroups are dominantly quartz, feldspar and sedimentary lithic fragments, but not volcanic lithics, we propose that they were deposited in a rift-related setting. Zircons from the lower sequence of the Hutuo Group yielded a young population of 2140 Ma. Considering the volcanic rocks of 2140±14 Ma at the base of the group and 2.2−2.0 Ga magmatism along the TNCO, we propose that Doucun and Dongye Subgroups formed at 2.2−2.0 Ga. The youngest,

ca. 1.9 Ga, zircons in the Guojiazhai Subgroup indicate this Group was deposited during closure of the rift at 1.9−1.8 Ga. The two stage model ages of the detrital zircons mainly range from 2.6 to 2.9 Ga with a minor ~2.5 Ga contribution. Therefore, we infer that 2.6−2.9 Ga represents a period of intensive crustal growth in the Trans-North China Orogen, but that some degree of crustal growth continued to ~2.5 Ga.

Keywords: The Hutuo Group, Clastic rock, Zircon U-Pb age, Lu-Hf isotope, rift-related environment

1.

Introduction As one of the oldest cratons in the world, the North China Craton (NCC) has

witnessed a long and complicated evolutionary history. There is a broad consensus that the NCC achieved final cratonization via welding of several micro-continental blocks during a late Paleoproterozoic orogenic process termed the Lüliang Movement in Chinese literature (Wu et al., 1998; Zhai and Santosh, 2011, 2013; Zhao et al., 2005, 2012; Zhao and Zhai, 2013). There are, however, three different models concerning evolutionary process in the NCC from the Neoarchean to the late Paleoproterozoic (Kusky and Li, 2003; Li and Kusky, 2007; Zhai and Santosh, 2011; Zhao et al., 2005, 2013). (1) Some researchers considered the NCC to contain seven micro-blocks that were amalgamated in late Archean to form a craton, which then evolved by 2.35−1.97

Ga rifting-accretion-collision processes along the Fengzhen, Liaoji and Jinyü orogenic belts/mobile beltswithin the craton. These events were followed by extension from 1.95 Ga to 1.82 Ga, which corresponds to finial crationization of the NCC in late Paleoproterozoic (Zhai and Santosh 2011). (2) Others have proposed that the NCC is divided into an Eastern Block (EB), a Western Block (WB) and a Central Orogenic Belt (COB). In this scenario, the EB subducted beneath the WB and the two blocks collided with each other at ca. 2.5 Ga, and that the “orogenic belt” actually relates to a series widely distributed rifts developed in the early Paleoproterozoic (2.5−2.4 Ga) (Kusky and Li, 2003; Li and Kusky, 2007). However, (3) a more popular model suggests that the NCC contains an Eastern Block (EB) and a Western Block (WB) along with an intervening Trans-North China Orogen (Zhao et al., 1999a, 1999b). Zhao et al. (2005) further divided the WB into the Ordos and Yinshan Blocks and the Paleoproterozoic Khondalite Belt, while also distinguishing the Jiao-Liao-Ji Belt in the EB. The WB formed by wielding the Yinshan and Orodos Blocks along the Khondalite Belt at 2.0−1.9 Ga, and the EB underwent rifting and rift closure to form the Jiao-Liao-Ji belt from 2.2 Ga to 1.9 Ga. Finally, the EB and WB collided along the TNCO and ultimately achieved cratonization at 1.85−1.8 Ga (Zhao et al., 2005, 2010, 2012). One of the most contentious topics of debate in these three models is the Paleoproterozoic evolution in the TNCO (COB or Jinyu mobile belt). Thus, further study of Paleoproterozoic magmatism and sedimentation in basin of the TNCO is vital for unravelling the geological evolution of the NCC. The TNCO is a nearly S-N striking zone up to 1200 km long and 300 km wide,

which is separated from the EB and WB by the Xinyang﹣Kaifeng﹣Shijiazhuang﹣ Jianping and Huashan﹣Lishi﹣Datong﹣Duolun faults, respectively (Fig. 1; Zhao et al., 1999a,1999b). As previously noted, this feature is most widely considered to be collisional orogen that formed after the long-lived eastward-directed subduction between the EB and WB from 2.5 Ga to 1.85 Ga (Zhao et al., 1999a, 1999b, 2005, 2008, 2010, 2012). Recent studies, however, have revealed a complex series of geological events in the TNCO during this extended interval in the Paleoproterozoic. Based on the tectonic deformation of the Wutai, Fuping and Zanhuang Complexes and the geochemical compositions of some intrusives in Wutai and Fuping areas, some geologists have proposed that ca. 2.1 Ga collisional events occurred prior to the 1.85−1.8 Ga orogen (Liu et al., 2005; Faure et al., 2007; Trap et al., 2009, 2012; Wang et al., 2010). Conversely, other researchers suggested that the 2.2−2.0 Ga magmatic events were related to rifting in the TNCO, mainly based on the geochemistry and the rock associations of the magmatic rocks in this belt (Du et al., 2009, 2010a; 2012a, 2013a, 2015b, 2016a; Peng et al., 2012; Yang et al., 2011; Zhang et al., 2011; Zhao et al., 2011; Xie et al., 2012; Wang et al., 2014; Zhou et al., 2014, 2015). Paleoproterozoic strata are distributed widely along the TNCO in the Taihua, Zhongtiao, Lüliang, Zanhuang and Wutai areas. The Group, located in Wutai Mountains, best presents the classic Paleoproterozoic stratigraphy in the belt, and the depositional environment of the Group therefore plays an important role on resolving the evolution of the TNCO. Previous studies have produced divergent interpretations on the sedimentary environment of the Hutuo Group. Based on detrital zircon U-Pb

ages and Lu-Hf isotopes in clastic rocks, Liu et al. (2011) propose that the Hutuo Group was deposited in a retro-arc foreland basin after 2.1 Ga. In contrast, Du et al. (2011, 2015b) argue for a rift-related setting based on the study of the clastic rocks and basalts in the Group. Additionally, other researchers consider the Hutuo Group to have formed in a foreland basin after 1880 Ma, mainly based on the deformation in the Wutai-Hengshan-Fuping and Zanhuang Complexes (Faure et al., 2007; Li et al., 2010; Trap et al., 2009, 2012). Previous researchers have provided the geochemical data and zircon U-Pb ages for the volcanic rocks (Sun et al., 1992; Du et al., 2009, 2010a, 2015b) and geochemical data plus the U-Pb ages and Lu-Hf isotopes of zircons from sandstones in the northern part of the Hutuo Group. The data have been interpreted in terms of a retro-arc foreland basin (Liu et al., 2011) or a rift-related basin setting for the Group (Du et al., 2011). The origin of clastic fragments in the sandstones and the depositional sequences/facies of the Hutuo Group have not been determined but are, however, vital for establishing the sedimentary environment of the clastic rocks (Dickinson et al., 1983; Dickinson, 1985). In addition, few studies have been undertaken of the Doucun and Guojiazhai Subgroups in the southern sector of the Hutuo Group. In this contribution, we evaluate these sedimentary sequences, their facies and the clastic components of the Hutuo Group. Based on the detailed investigation on different sections of the Hutuo Group, we present petrologic, detrital zircon U-Pb geochronological and Lu-Hf isotopic data for different subgroups of the Hutuo Group, and in order to constrain the Group’s depositional age and to deduce its

provenance and tectonic setting. The results provide new evidence on the tectonic setting of the Hutuo Group and crustal growth in the Central TNCO. 2.

Geological background

2.1. The Wutai Complex The Wutai Mountains area is situated in the central Trans-North China Orogen and is one of the classic regions for the exposures of the early Precambrian complex in the NCC. The early Precambrian components in this area are mainly the late Archean Wutai Group and TTG gneisses and the Paleoproterozoic Hutuo Group and granitoids. The Wutai Group and TTG gneisses are considered to be one of the best-preserved late Archean greenstone belts in the NCC (Fig. 2; Wu et al., 1998; Zhai and Santosh, 2011). The Wutai Group has conventionally been subdivided based on metamorphic grades, from the bottom up, into three units (Taihuai, Shizui and Gaofan Subgroups) which are considered to represent original stratigraphic sequences (Bai, 1986). The Shizhui Subgroup dominantly contains basic to intermediate-basic volcanic rocks, with intermediate to acidic lava, volcanoclastic rock, and banded iron formation (BIF) interlayered locally, and clastic sedimentary rocks and carbonate at the base, all of which underwent amphibolite facies metamorphism. The Taihuai Subgroup is mainly composed of tholeiite, and intermediate to acidic volcanic rocks with lesser sandstones and BIF assemblages in the lower part that were metamorphosed to greenschist facies (Bai, 1986). The Gaofan Subgroup dominantly comprises sandstone, siltstone and pelite with basic volcanic rocks at the top, and has undergone subgreenschist facies metamorphism (Bai, 1986; Tian, 1991). In view of

two unconformities between three units (Shizhui, Taihuai and Gaofan subgroups) in the Wutai Group, BGMRSP (1989) further promoted three subgroups to group status and reclassified the Wutai Group as the Wutai Supergroup. However, Wilde et al. (2004a) obtained identical SHRIMP zircon U-Pb ages of 2533−2513 Ma from the intermediate to felsic volcanic rocks in three subgroups of the Wutai sequences, which do not display correlation in age with metamorphic grade. They therefore concluded that there was no layer-cake stratigraphy preserved in the Wutai Complex and the rocks were tectonically juxtaposed with each other (Wilde et al., 2004a). More recently, Wan et al. (2010) obtained a youngest detrital zircon

207

Pb/206Pb age of

2.47±0.03 Ga from a quartzite in the Gaofan Subgroup and considered this unit to be one of the oldest Paleoproterozoic sediments in the NCC. Liu et al. (2016) further confine the Gaofan subgroup between 2.35 Ga and 2.18 Ga based on the youngest detrital zircons (2348 Ma) and 2176−2161 Ma felsic intrusions. The metamorphosed volcanic-sedimentary rocks in the Wutai Group are interpreted to have formed in an island arc to back arc basin (Wang et al., 2004), fore-arc or intra-arc basins etting (Liu et al., 2016). The late Archean granitoids in the Wutai Mountains are mainly TTG gneisses except for the Lanzhishan granite, which is dominated by a potassic to monzonitic component with an age of 2560−2537 Ma (Liu et al., 1985; Wilde et al., 1997). Based on the emplacement ages, these TTG gneisses are divided into two stages, in which the first pulse includes the Ekou and portions of the Chechang-Beitai granites with the age of 2560−2540 Ma, and the second contains the Shifo, Guangmingsi and grey

phase of the Wangjiahui granite emplaced between 2540 and 2513 Ma (Wilde et al., 2005). Geochemical features and Nd isotopic compositions of the granitoids indicate they were likely generated by partial melting of subducted slab or metasomatized mantle wedge (Sun et al., 1992; Liu et al., 2004). In addition to the widespread late Archean granites, Paleoproterozoic intrusives also sporadically occur in the Wutai Mountains, and include the Dawaliang granite (2176±12 Ma, Wilde et al., 1997), the pink phase of the Wangjiahui granite (2084−2117 Ma, Wilde et al., 2005), the Huangjinshan granite porphyry (2137±9 Ma Du et al., 2013a), and the Jiangcun quartz porphyry (2138−2166 Ma, Du et al., 2015b), which are coeval with mafic and felsic volcanics in the Hutuo Group (Wilde et al., 2004b; Du et al., 2010a). 2.2. The Hutuo Group The Hutuo Group is mainly distributed on the southern flank of the Wutai Mountains with a total area of 1700 km2, and occurs as a composite syncline uncomformably overlying the Wutai Group and late Archaean granitoids (Fig. 3; Bai, 1986; Miao et al., 1999; Guo et al., 2011). The Hutuo Group is divided upwards into the Doucun, Dongye, Guojiazhai Subgroups (Bai 1986; BGMRSP, 1989) in which the Doucun Subgroup mainly occurs at the northwest limb of the syncline with minor occurrence on the southeast limb, and the Dongye Subgroup dominantly takes up the southeast limb of the fold (Fig. 3), and is locally unconformable on the Doucun Subgroup (Bai, 1986). Based on the stratigraphic sequences and lithologic associations, the Hutuo Group is further divided into twelve (BGMRSP, 1989) or fourteen formations (Bai, 1986). After our own detailed field work, we have adopted

the Bai’s subdivision scheme in this paper (Fig. 4; Bai, 1986). The Doucun Subgroup is composed of conglomerate, sandstone, silt and carbonate with basalt at the top. Conglomerate at the base of the Doucun Subgroup, the Sijizhuang conglomerate, mainly contains granite, quartzite, BIF, and chlorite schist pebbles from late Archean Wutai Group and granitiods (Fig. 4; Bai, 1986; Zhang et al., 2006; Wu et al., 2008; Du et al., 2012a). Additionally, Paleoproterozoic (2138−2166 Ma) quartz porphyry pebbles locally occur in the Sijizhuang Formation of the Jiangcun area (Fig. 5a; Du et al., 2015a). The conglomerates at the bottom of the Hutuo Group have features of fluvial and littoral shoal facies deposit (Bai, 1986). Sandstones in the Sijizhuang and Nantai Formations usually retain the cross bedding with local ripple structures (Fig. 5b), and silt and slate are interlayered with carbonate in the Qingshicun Formation, suggesting littoral facies deposition (Bai, 1986).In the Dongye Subgroup, the lower sequences are dominated by the purple-red sandstone and slate/siltstone with local quartz sandstone layers, in which the cross-bedding is preserved (Fig.5c). On top of the slate, dolomites are the major lithology and stromatolites occurrences are widespread (Fig. 5d; Bai, 1986). In the Hebiancun Formation, sandstones retain ripple and flute marks structures (Fig. 5e, f), and dolomites locally become sedimentary breccia (Fig. 5g). Basalt with brown oxide crust occurs in the top layer of the Hebiancun Formation (Fig. 5h; Du et al., 2015b). Except for phyllite in the middle sequence of the Jianancun Formation, the upper stratigraphic sequences in the Dongye Subgroup are mainly composed of stromatolite-bearing dolomites (Fig.5i, j). The sedimentary associations and structures in the Dongye Subgroup denote littoral to

neritic facies with local marine-terrigenous facies (Bai, 1986). The Guojiazhai Subgroup unconformably overlies the folded Dongye Subgroup (Fig. 5k) and mainly comprises siltstone, sandstone and conglomerate from base to top (Fig. 4; Bai, 1986, BGMRSP, 1989; Miao et al., 1999; Du et al., 2011). The Xiheli Formation contains siltstone and greywacke with local conglomerate at the bottom. In the sandstone, cross bedding and ripple structures are preserved (Fig. 5l). The Heishanbei Formation mainly includes medium- to coarse-grained quartz arenite interlayered with conglomerate. The pebbles in the conglomerate are dominated by purple-red sandstone (Fig. 5m), which are identical with sandstone in the lower sequence of the Wenshan Formation. The upper sequence, or Diaowangshan Formation, is mainly composed of conglomerate (Fig. 5n), in which dolomite pebbles are the major components that locally retaining the stromatolite (Fig. 5p). The last feature further indicates that sediments in the upper sequence of the Guojiazhai Subgroup are derived from the lower Dongye Subgroup. The Guojiazhai Subgroup was deposited in a fluvial to alluvial facies environment (Bai, 1986). The Hutuo Group is conventionally considered as a suit of Paleoproterozoic strata in the NCC. However, the initial depositional age is still in debate. The TIMS zircon U-Pb age of 2366+103/-94 Ma from basalt in the Qingshicun Formation suggests that the maximal depositional age is as early as ca. 2.4−2.3 Ga (Wu et al., 1986). A large number of zircon U-Pb ages from volcanic and sedimentary rocks constrain deposition of the Hutuo Group deposit to after the 2.2 Ga (Wilde et al., 2004b; Du et al., 2010a, 2011, 2015a; Liu et al., 2011). Based on the unconformity between the Guojiazhai Subgroup and lower sequences

(the Doucun and Dongye Subgroups), Wu et al. (2008) and Du et al. (2011) separated the Guojiazhai from the Hutuo Group and considered it to represent the different process than the lower units. 3. Clastic composition in sandstones of the Hutuo Group 27 sandstone samples were collected from three subgroups in the Hutuo Group to count the grain mode (Table 1) as proposed by Dickinson (1970) and Ingersoll et al. (1984). Sandstones in the Doucun Subgroup are lithic greywacke, feldspathic greywacke, and feldspathic quartz sandstone, in which the clastic components include quartz (monocrystalline and polycrystalline quartz), feldspar (K-feldspar and plagioclase), and lithic fragments (Table 2; Fig.6a, b). Quartz and feldspar grains in the sandstones display subrounded to angular shapes, indicating short transport distance. Sandstone samples in the lower sequence of the Wenshan Formation dominantly include quartz, lithic fragments, and/or Fe-oxide matrix (Fig. 6c, d). In contrast, clastic rocks in the Hebiancun Formation of the Dongye Subgroup are composed only of quartz arenites (Table 2). In the Guojiazhai Subgroup, sandstone samples are mainly composed of lithic quartz greywacke in the Xiheli Formation and quartz arenites in the Heishanbei Formation (Table 2). The clastic compositions in the greywackes mainly contain quartz and lithic fragments (Fig. 6e, f). After recalculation of the mode components in the sandstones, all samples in the Hutuo Group are found to be dominated by quartz grains with minor feldspar and lithic fragments (Table 2). Thus, samples from the Doucun and Dongye subgroups are mainly situated in the craton region on provenance plots, with subordinate recycled orogen provenance,

whereas those from the Guojiazhai Subgroup are predominantly fall within the recycled orogen field (Fig.7). 4. Analytical methods 4.1. Zircon separation, mounting and imaging Zircons were concentrated by crushing, followed by panning for the heavy mineral fraction, and then passing through an isodynamic separator. Zircons were hand-picked under a binocular microscope, and then cast in a 1 inch expoxy resin disc. After grinding and polishing the disc to present mid-sections through the zircons, transmitted and reflected light and cathodoluminescence (CL) images were obtained. These images were used to choose sites within the zircons for analysis. 4.2. La-ICPMS zircon U-Pb dating Most of zircon U-Pb dating was performed at the State Key Laboratory of Continental Dynamics, Northwest University in Xi’an, China. The experimental procedures followed those of Diwu et al. (2011, 2014). Zircons was dated on an Agilent 7500a ICP-MS instrument equipped with a 193 nm (wave length) ArF excimer laser (MicroLasTM Beam Delivery Systems, Lambda Physik AG, Germany). A fixed beam diameter of 32 µm with a laser repetition rate of 6 Hz was adopted throughout the analyses. Helium was used as the carrier gas to ensure efficient aerosol delivery to the torch. The standard silicate glass NIST 610 was used to optimize the instrument to obtain the maximum signal intensity (238U signal intensity of >2000 cps/ppm) and low oxide production (ThO/Th<1%). The ion signal intensity ratio measured for both 238U and

232

Th (NIST SRM 610) (238U and 232Th≈1) was used as an

indicator of complete vaporization (Günther and Hattendorf, 2005). The laser ablation strategy used was a single laser spot on each zircon. Analyzed elements were collected in the time-resolved, single-point-per-peak mode. Dwell times were set to be 10 ms for Th; 15 ms for U, Pb and Ti; and 6 ms for other elements. The DUAL (pulse and analog counting) detector mode used in a short integration time. Here, the 207

Pb/206Pb,

206

Pb/238U,

207

Pb/235U, and

208

Pb/232Th ratios were calculated using the

GLITTER 4.0 program (Macquarie University), with the Harvard zircon 91500 being used as an external reference material with recommended

206

Pb/238U age of

1062.4±0.4 Ma (Wiedenbeck et al., 1995), to correct for both instrumental mass bias and depth-dependent elemental and isotopic fractionation. Pooled ages were plotted and calculated using ISOPLOT (Ludwig, 2001). Concentrations of U, Th, Pb and trace elements were calibrated by using

29

Si as an internal standard and NIST SRM

610 as an external standard. Zircon standards 91500 and GJ-1 were analyzed as unknown samples. The two standard zircons yielded weighted mean

206

Pb/238U ages

of 1062.4±1.6 Ma (n=115, 2σ) and 605.6±1.4 Ma (n=44, 2σ), respectively, which are in good agreement with the recommended ID-TIMS ages (Wiedenbeck et al., 1995; Jackson et al., 2004). Zircon U-Pb dating analyses for two samples (HT44-1 and HT45-1) were conducted at the Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing. Detailed operating conditions for the laser ablation system and MC-ICPMS instrument and data reduction are the same as given by Hou et al. (2007). Laser sampling was performed using a Newwave UP 213 laser ablation system. A

Thermo Finnigan Nepture MC-ICP-MS instrument was used to acquire ion-signal intensities. The carrier gas was helium. Argon was used as the make-up gas and mixed with the carrier gas via a T-connector before entering the ICP. Each analysis incorporated a background acquisition of approximately 20−30 s (gas blank) followed by 30 s data acquisition from the sample. Off line raw data selection and integration of background and analytic signals, and time-drift correction and quantitative calibration for U-Pb dating was performed by ICPMS DataCal (Liu et al., 2010). The zircon GJ1 was used as external standard for U-Pb dating, and was analyzed twice every 5−10 analyses. Time-dependent drifts of U-Th-Pb isotopic ratios were corrected using a linear interpolation (with time) for every 5−10 analyses according to the variations of GJ1 (i.e., 2 zircon GJ1 + 5−10 samples + 2 zircon GJ1; Liu et al., 2010). Preferred U-Th-Pb isotopic ratios used for GJ1 are from Jackson et al. (2004). Uncertainties of the preferred values for the external standard GJ1 were propagated to the ultimate results of the samples. In all analyzed zircon grains, the common Pb correction was not necessary due to the low signal of common 206

204

Pb and high

Pb/204Pb. U, Th, and Pb concentration was calibrated by zircon M127 ( with U=923

ppm; Th=439 ppm; Th/U: 0.475) (Nasdala et al., 2008). Concordia diagrams and histogram were made using ISOPLOT (Ludwig, 2001). 4.3. Zircon Lu-Hf isotopes In situ zircon Lu-Hf isotope analyses were carried out using a GeoLas 200M 193 nm laser-ablation microprobe, attached to a Bruker aurora M90 ICP-MS at Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing. The Lu-Hf

analyses were performed after the U-Pb dating, with Lu-Hf and U-Pb analysis sites coinciding as closely as possible in their location. Instrumental conditions and data acquisition were comprehensively described by Hou et al. (2007) and Wu et al. (2006). A stationary spot was used, with a beam diameter of 55−65 µm. Helium was used as carrier gas to transport the ablated sample from the laser-ablation cell to the ICP-MS torch via an argon mixing chamber. In order to correct the isobaric interferences of 176

Lu and

176

Yb on

176

Hf,

176

Lu/175Lu=0.02658 and

176

Yb/172Yb=0.5887 ratios were

determined (Chu et al., 2002). For instrumental mass bias correction Yb isotope ratios were normalized to 179

173

Yb/172Yb=1.35274 (Chu et al., 2002) and Hf isotope ratios to

Hf/177Hf=0.7325 using an exponential law. The mass bias behavior of Lu was

assumed to follow that of Yb. Mass bias correction protocol details were described by Wu et al. (2006) and Hou et al. (2007). Zircon GJ-1 was used as the reference standard, with a weighted mean

176

Hf/177Hf ratio of 0.282011±0.000002 (n=77, 2σ)

during our routine analyses. It is consistent with a weighted mean 176Hf/177Hf ratio of 0.282013±0.000019 (2σ) from in situ analysis by Elhlou et al. (2006). 5. Analytical results 5.1. The Doucun Subgroup 5.1.1. HT58-6 Sample HT58-6 is a coarse- to medium-grained feldspathic quartz greywacke collected from the upper section of the Sijizhuang Formation near the Jiangcun town, Dingxiang County (Fig. 3, 4; 38°32′05.00″N; 113°02′49.82″E). The greywacke mainly contains quartz (30%−40%), K-feldspar (10%−15%), plagioclase (5%−10%)

grains and matrix (20%−30%) with minor lithic fragments, and clastic grains often have a subround to angular appearance, suggesting short transport distances. Zircons from sample HT58-6 can be divided into two types where one group is subrounded with grain sizes of 200−400 µm, and the other group shows short to long columnar crystals of 200−300 µm. In CL images, some zircons show magmatic oscillatory zoning, whereas, others have blurred internal structure (Fig. 8a). Sixty-four grains in the greywacke were randomly chosen for zircon U-Pb analysis. Contents of U and Th are 11−572 ppm and 17−196 ppm with Th/U ratios of 0.35−3.41 (Supplementary table1). Except for seven spots with strong Pb loss (concordance less than 90%), the data yielded concordant

207

Pb/206Pb and

206

Pb/238U

ages (Supplementary table1; Fig. 9A). Fifty-seven analyses mainly concentrate at two groups 207Pb/206Pb ages ranging from 2046 Ma to 2212 Ma and 2506 Ma to 2596 Ma (Fig.9B). Additionally, nine spots have

207

Pb/206Pb ages of 2632−2767 Ma

(Supplementary table1; Fig.9B). For Paleoproterozoic zircons,

176

Lu/177Hf and

176

Hf/177Hf ratios range from

0.000496 to 0.001797, and 0.281377 to 0.281582, respectively.

176

Hf/177Hfi and εHf(t)

are 0.281318−0.281521 and -3.36−+3.66, and the model age TDM1 and TDMC are2368−2647 Ma and 2497−2931 Ma, respectively (Supplementary table2). 176

Lu/177Hf and

176

Hf/177Hf ratios of 2506−2596 Ma zircons have a range from

0.000312 to 0.001325, and 0.281224 to 0.281413.

176

Hf/177Hfi and εHf(t) vary from

0.281179 to 0.281317 and 0 to +5.69. TDM1 and TDMC are 2591−2821 Ma and 2628−3006 Ma (Supplementary table2). For zircons of 2632−2767 Ma,

176

Lu/177Hf

and

176

Hf/177Hf ratios are from 0.000524 to 0.001886, and 0.281119 to

0.281286.176Hf/177Hfi and εHf(t) are of 0.281088−0.281259, and +0.83−+7.38. TDM1 and TDM C have a range of 2707−2973 Ma and 2708−3076 Ma (Supplementary table2; Fig.10A). 5.1.2. HT18-1 The feldspathic quartz greywacke sample HT18-1 was collected from the middle to upper sequence of the Sijizhuang Formation (Fig. 3, 4; 38°47.656′N; 113°02.063′E). This greywacke is composed of quartz (45%−50%), feldspar (~10%) and matrix (30%−35%) (Du et al., 2011). Zircon U-Pb dating results from sample HT18-1 have been published by Du et al. (2011). In this paper, we only chose 50 grains with highly concordant ages (over 90%) for Lu-Hf isotopic analysis.

176

Lu/177Hf and

176

Hf/177Hf

ratios of three ca. 2.1 Ga zircons are 0.000700−0.001441 and 0.281469−0.281533, respectively.

176

Hf/177Hfi and εHf(t) values have a range of 0.281428−0.281475 and

+0.78−+1.32 with T DM1 and TDMCof 2432−2492 Ma and 2617−2688 Ma (Supplementary table2). Forty-seven ca. 2.5 Ga zircon grains have 176

176

Lu/177Hf and

Hf/177Hf ratios ranging from 0.000313 to 0.001265 and 0.281361 to

0.281403.176Hf/177Hfi and εHf(t) are from 0.281155 to 0.281378 and -1.63 to +7.25. TDM1 and TDMC values vary from 2554 Ma to 2848 Ma and 2578 Ma to 2964 Ma (Supplementary table2; Fig.10B). 5.1.3. HT19-1 Pebble bearing feldspathic quartz greywacke sample HT19-1 was collected from the upper section of the Sijizhuang Formation (Fig. 3, 4; 38°47.482′N; 113°01.273′E).

The greywacke contains quartz (~50%), feldspar (5%−8%), lithic fragment (15%−20%) and matrix (30%−35%) (Du et al., 2011). Du et al. (2011) published the zircon U-Pb dating result. Thus, we further report the Lu-Hf isotopic analysis in the paper. For fifteen ca. 2.1 Ga zircons,

176

Lu/177Hf and

176

Hf/177Hf ratios are from

0.000358 to 0.000861 and 0.281230 to 0.281452, and 176Hf/177Hfi and εHf(t) values are from 0.281212 to 0.281425 and -7.66 to -0.19 with TDM1 and TDMC of 2493−2605 Ma and 2718−3177 Ma (Supplementary table 2).

176

Lu/177Hf and

176

Hf/177Hf ratios in ca.

2.5 Ga zircon have a range of 0.000349−0.001870 and 0.281143−0.281407. 176

Hf/177Hfi and εHf(t) are from 0.281086 to 0.281351 and -1.04 to 6.85, and model

age TDM1 and TDM C show a range of 2587−2939 Ma and 2622−3069 Ma (Supplementary table 2; Fig.10C). 5.1.4. HT44-1 Sample HT44-1 isa lithic quartz greywacke collected from the middle sequence of the Nantai Formation (Fig. 3, 4; 38°49.670′N; 113°07.968′E). Lithic quartz greywacke mainly contains quartz grains (~30%), quartzite lithic fragments (10%−15%), and matrix (40%−50%) with minor plagioclase. Zircons in the greywacke are 200−300 µm in grain size and are granular and columnar with round to subround appearance. Some zircons have concentric magmatic zones, whereas some show no internal texture (Fig.8b). Sixty-nine grains were analyzed for U-Pb dating. U and Th concentrations are 6−566 ppm and 6−433 ppm with Th/U ratios of 0.55−8.36 (Supplementary table 1). Except for twelve spots that have strong lead loss, the analyses fall near or on the

concordia line (Fig.9C). For fifty-seven spots, the major

207

Pb/206Pb ages are from

2506 Ma to 2589 Ma, and subordinate ages have a range of 2110−2169 Ma, with a few grains giving ages of 2602−2880 Ma (Fig.9D). A zircon U-Pb age histogram from this sample is similar to those of sandstones HT18-1 and HT19-1 in the Sijizhuang Formation (Du et al., 2011). 176

Lu/177Hf and

176

Hf/177Hf ratios in fifty-seven grains are 0.000299−0.003098

and 0.281120−0.281680.

176

Hf/177Hfi and εHf(t) values in the 2506−2589 Ma grains

are 0.281146−0.281431 and -0.79−+9.18, and TDM1 and TDMC range from 2478 Ma to 2862 Ma and 2453 Ma to 3067 Ma (Supplementary table 2). For 2110−2169 Ma zircons,

176

Hf/177Hfi and εHf(t) values are 0.281365−0.281555 and -1.69−+4.71, and

TDM1 and TDMC range from 2331 Ma to 2575 Ma and 2442 Ma to 2832 Ma (Supplementary table 2; Fig.10D). 5.1.5. HT41-2 Sample HT41-2 is a magnetite bearing lithic quartz greywacke collected from the middle sequence of the Qingshicun Formation (Fig. 3, 4;38°51′02.12″N; 113°35′24.45″E). The sandstone contains quartz grains (30%−40%), quartzite fragments (~10%), magnetite (5%−8%) and matrix (35%~40%) with minor chlorite. Zircons are mainly granular to columnar with subhedral to anhedral crystals. Most of the zircons show oscillatory zoning and some have band zoning while a few show no internal texture in CL images (Fig.8c). The U and Th concentrations of sixty-seven grains are 13−192 ppm and 29−477 ppm with Th/U ratios of 0.29−0.93 (Supplementary table 1). On a concordia diagram,

seventeen grains display strong Pb loss, but other fifty spots yield concordant 207

Pb/206Pb and 206Pb/238U ages (Fig.9e). Except for three grains with ages over 2.2 Ga,

the 207Pb/206Pb ages span 2073−2197 Ma with a peak of ca. 2.1 Ga (Fig. 9f). 176

Lu/177Hf

and

176

Hf/177Hf

ratios

0.000630−0.002510and 0.281372−0.281704, and

from 176

forty-six

zircons

are

Hf/177Hfi and εHf(t) have a range

of 0.281324−0.281600 and -1.82− +7.27 with TDM1 and TDMC range from 2259 Ma to 2625 Ma and 2303 Ma to 2805 Ma (Supplementary table 2; Fig.10E). 5.2. The Dongye Subgroup 5.2.1. HT45-1 Sample HT45-1 is a fine-grained quartz greywacke collected from the bottom of the Wenshan Formation (Fig.3, 4; 38°35.863′N; 113°07.457′E). The sandstone mainly contains quartz grains (50%−60%) and matrix (30%−40%) with minor feldspars and lithic fragments. All clastic minerals show subround to subangular appearance, indicating a proximal provenance. Zircons are subhedral and anhedral columnar to granular with grains size of 100−200 µm. In CL images, some grains display band zoning and some show oscillatory zoning, whereas others have no internal structure (Fig.11a). Eighty spots were chosen for zircon U-Pb isotopic analysis. Contents of U and Th are 3−161 ppm and 3−369 ppm with Th/U ratio from 0.65 to 2.3 (Supplementary table 1). Only two spots among all of the analyses show strong lead loss; the others are distributed on or near the concordia line (Fig.12A). In seventy-eight analyses with high concordance, ten spots yielded ages of 2522−2673 Ma and the remainder have

207

Pb/206Pb ages from 2055 Ma to 2189 Ma with a strong peak ca. 2066 Ma (Fig.12B),

which is identical with the result from a lithic quartz sandstone at the base of the Wenshan Formation (Du et al., 2011). In sixty-nine zircon Lu-Hf analyses,

176

Lu/177Hf and

176

Hf/177Hf ratios range

from 0.000359 to 0.002677 and 0.280858 to 0.281633, respectively (Supplementary table 2). For the ca. 2.5 Ga zircons,

176

Hf/177Hfi and εHf(t) values are

0.280830−0.281393 and -11.89−+4.90 with ranges of 2537−3285 Ma and 2765−3743 176

Ma.

Hf/177Hfi

and

εHf(t)

values

in

the

Paleoproterozoic

zircons

are

0.281314−0.281585 and -5.55−+4.49, and TDM1 and TDMC are 2280−2662 Ma and 2397−2999 Ma (Supplementary table 2; Fig.10F). 5.2.2. HT62-1 Sample HT62-1 was collected from the bottom of the Hebiancun Formation (Fig.3, 4; 38°36′13.70″N; 113°07′43.18″E), and only contains quartz grains with round to subround shapes, indicating that they are well sorted following long-distance transport. Zircons in the quartz sandstone are 100 µm to 200 µm in size and chiefly show a granular form with a round appearance. Some grains display magmatic oscillatory zoning, and some have band zoning, whereas others do not show internal structure (Fig.11b ). In seventy-eight spots analyses, U and Th contents are 15−477 ppm and 7−1418 ppm with Th/U ratios from 0.36 to 6.77 (Supplementary table 2). All analyses yielded the

207

Pb/206Pb ages of 2407−2604Ma, in which seventeen spots have strong lead loss

(Supplementary table 2; Fig.12C). In

207

Pb/206Pb ages with concordance over 90%,

sixty-one spots form an obvious peak of ca. 2530 Ma (Fig.12D). 176

Lu/177Hf and

176

Hf/177Hf ratios in fifty-eight grains have a range of

0.000357−0.002643 and 0.281228−0.281533, respectively.

176

Hf/177Hfi and εHf(t)

values vary from 0.281177 to 0.281453 and from 1.84 to 8.93 with TDM1 and TDMC of 2448−2822 Ma and 2434−2957 Ma (Supplementary table 2; Fig.10G). 5.2.3. HT60-1 HT60-1 is a fine-grained lithic quartz greywacke collected from the middle sequence of the Jianancun Formation (Fig.3, 4; 38°36′42.06″N; 113°07′24.18″E). The sandstone is mainly composed of quartz grains (30%−50%), quartzite and metabasic volcanic lithic fragments (10%−15%) and a Fe-oxide matrix (20%−30%). Quartz grains and lithic fragments display subangular to angular shape indicating the poor sorting and short distance transport. Zircons are 100−150 µm and show long columnar to granular forms with subround to subangular appearance. In CL images, most zircons display oscillatory zoning, but a few show no internal structure (Fig.11c). Thirty-nine spots were analyzed. U and Th contents are 17−436 ppm and 11−332 ppm with Th/U of 0.20−1.34. Except two Paleoproterozoic grains of 2242±35 Ma and 2267±53 Ma, the

207

Pb/206Pb ages range from 2406 Ma to 2589 Ma, in which six

analyses display obvious lead loss (Supplementary table 1; Fig.12e). Thirty-two 207

Pb/206Pb ages form a strong peak of 2515 Ma (Fig.12f). In twenty-nine spots with highly concordant

176

207

Pb/206Pb ages,

176

Lu/177Hf and

Hf/177Hf ratios are 0.000465−0.002378 and 0.281214−0.281456, respectively

(Supplementary table 2). Except for two Paleoproterozoic zircons, results for

176

Hf/177Hfi and εHf(t) range between 0.281175−0.281426 and -0.58−+7.79 with TDM1

and TDMC of 2674 Ma to 2738 Ma and 2784 Ma to 2850 Ma, respectively (Supplementary table 2; Fig.10H). 5.3. The Guojiazhai Subgroup 5.3.1. HT51-3 Sample HT51-3 is a medium-grained lithic quartz greywacke collected from the lower to middle sequence of the Xiheli Formation (Fig.3, 4; 38°41′12.49″N; 113°06′24.25″E). The sandstone contains quartz grains (40%−50%), lithic fragments (~20%) and matrix (20%−30%) in which clastic components show angular shape. Zircons are 100−200 µm in grain size and exhibit subround to round granular and columnar shapes. Some grains show magmatic concentric zoning or banded zoning, whereas others do not have an internal structure (Fig.13a). U and Th contents from eighty spots are 28−299 ppm and 18−395 ppm with Th/U of 0.24−3.1 (Supplementary table 1). Fourteen spots have obvious lead loss but others provide the near concordant Sixty-six grains yield

207

207

Pb/206Pb and

206

Pb/238U ages (Fig.14A).

Pb/206Pb ages ranging from 1990 Ma to 2737 Ma, and form a

strong peak of ca. 2400 Ma with subordinate shoulders of 2196 Ma and 2030 Ma. Additionally, three spots return ages of 2658−2737 Ma (Fig.14B). In sixty-three spots examined for Lu-Hf isotopic analyses, 176

176

Lu/177Hf and

Hf/177Hf ratios have a range of 0.000607−0.003285 and 0.281048−0.281746,

respectively.

176

Hf/177Hfi and εHf(t) values are 0.281015−0.281702 and TDM1 and TDMC

range from 2120 Ma to 3039 Ma and 2177 Ma to 3341 Ma (Supplementary table 2;

Fig.10J). 5.3.3. HT53-1 Sample HT53-1 is a fine- to medium-grained lithic quartz arenite collected from the base of the Heishanbei Formation (Fig.3, 4; 38°41′38.61″N; 113°06′16.69″E). The sandstone is dominantly composed of quartz grains (75%−80%), lithic fragments (~10%) with subround to angular shapes. Zircons are anhedral granular to columnar with grain sizes of 100−200 µm. Most zircons show magmatic zoning but and a few have no internal structures (Fig.13b). Thirty-four grains were analyzed. Contents of U and Th are 38−1212 ppm and 17−359 ppm with Th/U of 0.06−2.81. On a zircon U-Pb concordia diagram, eleven spots show strong lead loss, whereas others provide the concordant and

207

Pb/206Pb ages

206

Pb/238U ages (Supplementary table 1; Fig.14C). Twenty-two analyses with

highly concordant ages are distributed between 1963±36 Ma and 2403±35 Ma, of which sixteen spots form a strong peak at ca. 1995 Ma, and five grains define ca. 2175 shoulder. Six younger zircons cluster at 1960−1980 Ma (Fig.14D). In

twenty-two

analyses,

176

Lu/177Hf

0.000507−0.003174 and 0.281470−0.281732, and

and 176

176

Hf/177Hf

ratios

are

Hf/177Hfi and εHf(t) values are

0.281365−0.281698 and +1.47−+6.30 with TDM1 and TDMC of 2126−2577 Ma and 2217−2670 Ma (Supplementary table 2; Fig.10K). 5.3.3. HT47-1 Sample HT47-1 is a coarse- to medium-grained quartz arenite collected from the lower section of the Heishanbei Formation (Fig.3, 4; 38°42′46.28″N; 113°13′36.01″E).

The sandstone mainly comprises quartz grains with subround to subangular shapes. Zircon grains are 200−400 µm and mainly show anhedral granular with a few euhedral to subhedral appearance. Most zircons display magmatic zoning, but a few grains exhibit blur structure (Fig.13c). Forty-five grains were analyzed. Concentrations of U and Th are 49−807 ppm and 24−224 ppm with Th/U ratios from 0.10 to 1.73 (Supplementary table 1). All the analyses yield nearly concordant 207

207

Pb/206Pb and

206

Pb/238U ages (Fig.14E). Zircon

Pb/206Pb ages define two strong peaks at ca. 1960 Ma and ca. 2375 Ma (Fig.14F). 176

Lu/177Hf and

176

Hf/177Hf ratios in forty-five analyses vary from 0.000516 to

0.002801 and from 0.281038 to 0.281860, respectively.

176

Hf/177Hfi and εHf(t) values

are 0.280962−0.281821 and -6.99−+10.27, and TDM1 and TDM C values are 1957−3115 Ma and 1953−3349 Ma (Supplementary table 2; Fig.10L). 5.3.4. HT48-2 Sample HT48-2 is a conglomerate collected from the middle to upper sequence of the Heishanbei Formation (Fig.3, 4; 38°42′49.63″N; 113°13′31.81″E), in which purple-red sandstone and quartzite pebbles are major components and show round to subround appearance. Zircons are 50−200 µm in grain size and most grains have anhedral granular form. Most zircons have oscillatory zoning and a few display banded zoning (Fig.13d). Fifty-eight spots were analyzed. U and Th contents are 19−283 ppm and 27−324 ppm, and Th/U ratios are 0.25−2.14 (Supplementary table 1). Except for six analyses with obvious lead loss, the data fall near or on the concordia line (Fig.14G).

207

Pb/206Pb ages in fifty-two spots span a wide range from 1974±37 Ma to 2683±33

Ma, in which the results form a strong peak of ca. 2175 Ma with a subordinate ca. 2510 Ma shoulder (Fig.14H). In the fifty-one analyses,

176

Lu/177Hf and

176

Hf/177Hf ratios have a range from

0.000592 to 0.002171 and from 0.281043 to 0.281749, respectively.

176

Hf/177Hfi and

εHf(t) values are 0.280962−0.281705 and -3.72−+8.21 and TDM1 and TDMC ages are 2115−3118 Ma and 2150−3364 Ma (Supplementary table 2; Fig.10M). 5.3.5. HT48-1 Sample HT48-1 is a coarse- to medium-grained quartz arenite collected about 30 m north of Sample HT48-2 (Fig. 3, 4). The sandstone mainly contains quartz grains with subround to round appearance. Zircons are 100−200 µm and mainly show anhedral granular form. In CL images, some grains have magmatic oscillatory zoning, and some show banded zoning, while a few have no internal structure (Fig.13e). Seventy-one grains were chosen for U-Pb analysis at random. Contents of U and Th are 37−649 ppm and 14−940 ppm with Th/U ratios of 0.20−4.07 (Supplementary table 1). Thirty-seven spots have low concordance and deviate from the concordia line (Fig.14L). The other thirty-four have

207

Pb/206Pb ages over a wide range of

1939−2893 Ma but with two obvious peaks of ca. 1980 Ma and ca. 2375 Ma (Fig.14K). 176

Lu/177Hf

and

176

Hf/177Hf

ratios

0.000384−0.002703 and 0.281023−0.281782.

from 176

thirty-three

zircons

are

Hf/177Hfi and εHf(t) values are

0.280974−0.281739 and -4.38−+7.89 with TDM1 and TDMC ages from 2072 Ma to 3089

Ma and from 2124 Ma to 3214 Ma, respectively (Supplementary table 2; Fig.10N). 6. Discussion 6.1.

Provenance of clastic rocks in the Hutuo Group The Hutuo Group unconformably overlies the late Archean Wutai Group and

granitic gneisses and pebbles in the Sijizhuang Formation conglomerate show strong affinity with the underlying Wutai Group and gneisses (Fig. 4; Bai, 1986; BGMRSP, 1989; Tian, 1991; Bai, 1986; Zhang et al., 2006; Wu et al., 2008; Du et al., 2012a). Sandstones from three units of the Hutuo Group, however, exhibit more complicated clastic compositions and zircon U-Pb age distributions (Fig.9, 12, 14; Du et al., 2011; Liu et al., 2011), indicating differences in transport, sorting and provenance for these clastic rocks. Three sandstone samples in the Doucun Subgroup are feldspathic quartz greywacke, lithic quartz greywacke and calcarenaceous quartz greywacke, and the clastic grains in these greywackes generally show subround to angular shape, indicating the poor sorting and short distance transport. Therefore, the sandstones should be located close to their source areas. Of 163 detrital zircons from the Doucun Subgroup, 56 percent of the grains have

207

Pb/206Pb ages ranging from 2073 Ma to

2212 Ma that form a strong peak at ca. 2135 Ma, and fifty-one zircons provided 207

Pb/206Pb ages of 2488−2596 Ma and formed an obvious peak at ca. 2520 Ma.

Additionally, eighteen spots yielded the

207

Pb/206Pb age from 2602 Ma to 2880 Ma

(Supplementary table 1; Fig.15A). The 2488−2596 Ma detrital zircon ages are identical with the ages of granitic gneisses (2560−2513 Ma) and supracrustal rocks

(2533−2513 Ma) in Wutai (Wilde et al., 1997, 2004a, 2005), and Fuping and Hengshan TTG gneisses (2.52−2.48 Ga; Guan et al., 2002; Zhao et al., 2002; Cheng et al., 2004; Kröner et al., 2005), suggesting the late Archean complexes are the most important provenances of clastic rocks in the Doucun Subgroup. In the Sijizhuang sandstone HT58-6, the Paleoproterozic detrital zircons are predominant (Fig.9a, b), which is distinct from other sandstones in the same formation that are dominated by ca. 2.5 Ga zircons (Du et al., 2011; Liu et al., 2011). These zircons form a strong peak at ca. 2140 Ma, which is identical to the age of quartz porphyry in the Jiangcun area (Du et al., 2015a). Conglomerate and gravel bearing sandstone in Jiangcun town also contain pebbles with the same ages as the 2138−2166 Ma quartz porphyry (Du et al., 2015a). Thus, it is reasonable to infer that the Paleoproterozoic detrital zircons in sandstone HT58-6 are derived from the local quartz porphyry. In the Nantai and Qingshicun Formations sandstones, the 2080−2190 Ma zircon fraction is an important population, which has ages identical to those of Paleoproterozoic intrusives in Wutai, Fuping and Hengshang areas (Wilde et al., 2005; Zhao et al., 2002; 2011; Wang et al., 2010; Du et al., 2010a, 2015a). In addition, some zircons in the Qingshicun sandstone show banding zoning similar to those in intermediate to basic rocks (Corfu et al., 2003). Therefore, we infer that Paleoproterozoic zircons in the Qinshicun sandstone were likely partly derived from intermediate-basic volcanic rocks in the lower sequence of the Hutuo Group (Du et al., 2010a; 2011). The minor 2.6−2.8 Ga detrital zircons were probably from ca. 2.7 Ga gneisses in the Fuping, Hengshan and Zanhuang Complexes (Guan et al., 2002; Kröner et al., 2005; Han et al., 2012; Lu et

al., 2014; Yang et al., 2013). Detrital zircons from the Dongye Subgroup show two peaks at ca. 2070 Ma and ca. 2530 Ma (Fig.15B). Late Archean detrital zircons are dominant in the Hebiancun and Jianancun sandstones and a minor component in the Wenshan sandstone, and are also identical to the ages of gneisses in the Wutai, Fuping and Hengshan areas (Wilde et al., 1997, 2004a, 2005; Guan et al., 2002; Zhao et al., 2002; Cheng et al., 2004; Kröner et al., 2005). However, sandstone at the base of the Wenshan Formation is mainly composed of 2050−2190 Ma zircons (Supplementary table 1; Fig.12A, B), and the sample mainly contains quartz grains with some volcanic and sedimentary lithics. Therefore, we propose that these zircons are mainly from the Paleoproterozoic granites in the Wutai, Fuping and Hengshan Complexes, and subordinately from the volcanic rocks in the lower sequences of the Doucun Subgroup (Wilde et al., 2004b; 2005; Zhao et al., 2002; 2011; Wang et al., 2010; Du et al., 2010a, 2011, 2015a). The detrital zircon population in the Guojiazhai Subgroup is distinct from with those in the Doucun and Dongye Subgroups in that the sandstones dominantly contain Paleoproterozoic zircons from 1910 Ma to 2450 Ma with minor contributions ranging from 2.5 Ga to 2.9 Ga (Fig.15C), suggesting the late Archean basements in the Wutai, Hengshan and Fuping complexes are not major sources. In all Paleoproterozoic populations overall, zircon grains concentrate at three peaks of ca. 2.38 Ga, ca. 2.18 Ga and ca. 1.98 Ga (Fig.15C). As previously discussed, 2.2−2.0 Ga magmatism is widespread in the Wutai, Fuping and Hengshan areas (Du et al., 2016a and references therein), and meanwhile, zircons with the same age frequencies also occur in

sandstones of the Doucun and Dongye Subgroups (Du et al., 2011; Liu et al., 2011; this paper). On the other hand, in the Guojiazhai Subgroup, gravel bearing sandstone and conglomerate contain some components that were derived from the Dongye Subgroup (Fig.5m-p). Therefore, we propose that some 2.2−2.0 Ga zircons came from the Paleoproterozoic magmatic rocks in the Wutai, Fuping and Hengshan areas, and some are redeposit from the erosion of the lower sequences in the Hutuo Group. Near the Wutai Mountains, 2.4−2.3 Ga intrusives are locally distributed in the Lüliang (Geng et al., 2006; Zhao et al., 2008), Hengshan (Kröner et al., 2005) and Fuping areas (Liu et al., 2002), implying that the zircons in the clastic rocks were derived from complexes in these three areas. 2.0−1.9 Ga magmatism has not been reported in Wutai, but is found locally in the Hengshan (Kröner et al., 2006) and Lüliang areas (Geng et al., 2006; Zhao et al., 2008), which are likely sources for the ca. 1.98 Ga zircon population in the Guojiazhai Subgroup. 6.2. Redefining the depositional ages of the Hutuo Group The Hutuo Group is considered to be the classic example of Paleoproterozoic stratigraphy in the NCC (Bai, 1986; BGMRSP, 1989). Conventional TIMS zircon U-Pb dating from metabasalt in the Qinshicun Formation yielded an upper intercept 207

Pb/206Pb age of 2366+103/-94 Ma (Wu et al., 1986), which indicated that

deposition in the Hutuo Group was initiated in the early Paleoproterozoic. However, the Hutuo Group basalts are continental volcanic rocks that captured a large amount of ca. 2.5 Ga zircons when erupting (Du et al., 2010a). The five different zircon grains from the Qingshicun basalt, however, cluster close to the lower intercept (Wu et al.,

1986), and therefore the upper intercept age is not very accurate, and cannot be considered to provide a reliable age for the volcanic rock. Based on a 2549±22 Ma granitic pluton intruding into the Doucun Subgroup (Bai et al., 1992), Li and Kusky (2007) proposed that the Doucun Subgroup formed in the Neoarchean and considered that the interval between the Doucun and Dongye Subgroups represented the boundary of the late Archean and Paleoproterozoic. There is little doubt, however, that the Hutuo Group uncomformbaly overlies the late Archean Wutai Complex (Bai, 1986; BGMRSP, 1989; Miao et al., 1999; Wu et al., 2008; Guo et al., 2011; Du et al., 2010a, 2012a). In addition, zircon U-Pb ages from pebbles in the Sijizhuang conglomerate at the base of the Doucun Subgroup range from 2500 Ma to 2566 Ma, suggesting that Sijizhuang Formation was deposited after 2.5 Ga (Zhang et al., 2006; Wu et al., 2008; Du et al., 2012a). Additionally, Du et al. (2010) obtained a zircon

207

Pb/206Pb age of

2140±14 Ma from metamorphosed basaltic andesite in the Sijizhuang Formation, indicating that deposition of the Hutuo Group started in middle Paleoproterozoic, which is further supported by the detrital zircons (2140−2180 Ma) in the Sijizhuang Formation and felsic volcanics (2087±9 Ma) in the Qingshicun Formation (Wilde et al., 2004b; Du et al., 2011; Liu et al., 2011). These results constitute strong evidence against the proposal that the Hutuo Group was deposited between 1900 Ma and 1800 Ma (Faure et al., 2007; Trap et al., 2009, 2012). In this paper, we got a strong peak of ca. 2140 Ma from sandstone in the upper sequence of the Sijizhuang Formation, which constrains the maximum depositional age of the Sijizhuang Formation in Jiangcun area to be not older than 2140 Ma. Considering the Hutuo Group deposition

is coeval with 2.2−2.0 Ga magmatism along the TNCO, we further propose that the time of initial deposition of the group is ca. 2.2 Ga, which is about 350−300 Ma younger than the Wutai Group (Du et al., 2010a, 2011, 2015a). Wilde et al. (2004b) obtained two zircon U-Pb ages of 2180±5 Ma and 2087±9 Ma from a felsic tuffaceous rock in the Qingshicun Formation and proposed that the younger age (2087±9 Ma) represented the crystallization age of the volcanic rock. Provided that the volcanic lithics in the Wenshan sandstone come from the Doucun Subgroup (Du et al., 2011; this paper), we confine the period of the Doucun Subgroup deposition to be from 2.2 Ga to 2.07 Ga. Detrital zircons from a lithic quartz greywacke (HT45-1) at the base of the Wenshan Formation form a strong peak of ca. 2066 Ma, consistent with the result from another sandstone in the same formation (Du et al., 2011), which suggests the Dongye Subgroup was deposited after 2.07 Ga. Liu et al. (2011) obtained a zircon 207

Pb/206Pb age of 1877±24 Ma from one grain in the Jianancun Formation and

suggested that the middle to upper section of the Dongye Subgroup (from Jianancun to Tianpengnao Formation) and the Guojiazhai Subgroup were deposits after 1.88 Ga. However, previous work and our study reveal that Doucun and Dongye Subgroups underwent the similar deformation, which is resulted in both being unconformably overlain by the Guojiazhai Subgroup (Bai, 1986; Miao et al., 1999; Wu et al., 2008; Guo et al., 2011; Du et al., 2011, 2015a), and both the Jianancun and Hebiancun Formations are dominantly composed of dolomite with widespreads occurrenance of stromatolites, suggesting a similar sedimentary environment. On the other hand, the

new metamorphic ages in Wutai, Fuping, Hengshan and Huai’an areas indicate that1.95−1.8 Ga interval corresponds to a collisional orogenic process along the TNCO that lead to the ultimate cratonization of the NCC (Zhao et al., 2012 and references therein; Qian et al., 2013, 2015; Wei et al., 2014; Zhang et al., 2016). It is therefore unreasonable to separate the upper Dongye Subgroup from the lower sequences and ascribe it to deposition after 1.88 Ga (Liu et al., 2011). Due to a lack of volcanic rocks in the upper sequences of the Dongye Subgroup, it is difficult to define the depositional period of this group. The lithological associations from the Doucun to Dongye Subgroups are conglomerate, sandstone, slate, and carbonate, and indicate deposition in an extensional environment (Du et al., 2011), which is likely contemporaneous with the 2.2−2.0 Ga rift-related magmatism along the TNCO (Du et al., 2015b, 2016a, and references therein). Thus, we infer that deposition of the Dongye Subgroup probably lasted until ca. 2.0 Ga and spanned 2.07 Ga to 2.0 Ga. The Guojiazhai Subgroup unconformably overlies the Dongye Subgroup (Fig.5k; Bai, 1986; BGMRSP, 1989; Du et al., 2011) and comprises, from the bottom up, siltstone, sandstone and conglomerate, which contrast with the sedimentary sequences of the Doucun and Dongye Subgroups. Therefore, this unit should be separated from the lower sequences and renamed as the Guojiazhai Group (Wu et al., 2008; Du et al., 2011). Due to dominant presence of clastic rocks, the depositional interval of the Guojiazhai Group is also difficult to constrain. The youngest detrital zircon from sandstone at the bottom of the Xiheli Formation yielded a 207Pb/206Pb age of 1958±10 Ma (with 99% concordance) (Du et al., 2011). In this paper, we also obtain a large

amount of zircons from different samples with age ranging from 2.0−1.91 Ga, further indicating that the Guojiazhai Group was deposited after 1.9 Ga. The Guojiazhai Group comprises, from the bottom up, siltstone, sandstone and conglomerate, likely deposited during the orogenic process (Bai, 1986), which must be earlier than the late Paleoproterozoic mafic dykes (1.78−1.75 Ga; Peng et al., 2005, 2008) and the Changcheng Group (Lu et al., 2008). Therefore, we suggest that the Guojiazhai Group was deposited between 1.9−1.8 Ga, and was related to the process of finial cratonization in the NCC (Du et al., 2011; Liu et al., 2011). 6.3. Depositional settings of the Hutuo Group and constraints on the Paleoproterozoic evolution in the TNCO As mentioned in the introduction, the Paleoproterozoic evolutionary process along the TNCO is still the subject of intense debate. Different opinions have been put forward to interpret the tectonic setting of the Hutuo Group (Kusky and Li, 2003; Li and Kusky, 2007; Faure et al., 2007; Liu et al., 2011; Du et al., 2010a, 2011, 2012a, 2015b). Some researchers consider the Hutuo Group to represent the Qinglong-Wutai foreland basin to rifting sequences developed over the 2.5 Ga to 1.9 Ga interval following collision between EB and WB along the COB, mainly based on the sedimentary associations, deformation features and some Sm-Nd whole rock and single zircon U-Pb ages (Kusky and Li, 2003; Li and Kusky, 2007). Conversely, other have cited the detrital zircons in the Hutuo Group and tectonic deformations in Hengshan, Wutai, and Fuping Complexes to suggest that the Hutuo Group represents back-arc to retro-arc foreland basin sequences deposited in the middle to late

Paleoproterozoic (Zhang et al., 2006; Liu et al., 2011) or a late Paleoproterozoic foreland basin deposit (<1.9 Ga) in the TNCO (Faure et al., 2007; Zhao et al., 2008; Trap et al., 2009, 2012; Li et al., 2010). Additionally, in view of the volcanic and sedimentary rocks in the Hutuo Group and the coeval magmatism in the TNCO, Du et al. (2009, 2010, 2011, 2012a, 2015b) propose that the Hutuo Group likely formed in a rift-related environment in the middle Paleoproterozoic. In a foreland basin, sedimentary facies typically grade from fluvial/alluvial systems near the orogenic belt to shallow marine clastic environments farther away from the mountains, with typical deposition of flysch sequences by turbidity currents (Li and Kusky, 2007). On the other hand, the sequences in a typical foreland basin can generally be subdivided into lower deep-water turbidite or flysch facies, a shallow-marine molasses and, finally, terrestrial molasses separated by unconformities (Sinclair, 1997). Given that the basin is progressively filled by synorogenic deposits, it evolves from early submarine to late terrestrial sedimentation associated with upward coarsening and thickening sequences, derived from the orogenic belt or forebulge (Condie, 1997; Li and Kusky, 2007). Although an unconformity occurs between the Wutai Group and the Hutuo Group, the initial deposition in the Hutuo Group occurred at about 2.2 Ga and has no relationship with 2.5 Ga and/or 1.9−1.8 Ga orogenic process (Du et al., 2010a, 2011, 2015b; Liu et al., 2011). Meanwhile, the sequences in the Doucun and Dongye Subgroups are conglomerate, sandstone, slate and carbonate (Bai, 1986; Miao et al., 1999; Du et al., 2011, this paper), which is far from the upwards coarsening sediments, in the foreland basin (Condie, 1997).

Therefore, we argue against the Hutuo Group as either a ca. 2.5 Ga or a 1.9−1.8 Ga foreland basin along the TNCO (Li and Kusky, 2007; Faure et al., 2007; Trap et al., 2009, 2012). In a back-arc basin, deposition is generally dominated by pelagic, hemipelagic clays, and biogenic carbonate and silica sediments in a deep water facies setting (Klein, 1985; Ingersoll, 1988; Condie, 1997). In addition, clastic rocks in back-arc basins contain mainly volcanoclastic sands derived from the island arc (Dickinson et al., 1983, 1985; Bhatia and Crook, 1986; Packer and Ingersoll, 1986; Ingersoll, 1988; Sun et al., 2008; Du et al., 2013b) and detrital zircons with ages close to the depositional age of the sediment are predominate (Sun et al., 2008; Cawood et al., 2012; Du et al., 2013b). Furthermore, basalts from back-arc basins usually exhibit compositions ranging from MORB to IAB (Stern et al., 1990; Hawkons, 1995; Taylor and Martinez, 2003). The clastic components in sandstones from the Doucun and Dongye Subgroups, however, mainly contain quartz grains with subordinate to minor feldspar, granitic and sedimentary lithic fragments, but lack volcanoclastic components. On the other hand, the provenance of the sandstones is chiefly cratonic, but not volcanic arc in nature (Fig. 7; Dickinson et al., 1983, 1985). The detrital zircons are clearly derived mainly from the late Archean basement and contemporaneous Paleoproterozoic intrusive rocks, which is contrary to the nature of sediments in back-arc basins, but similar to continental rift sediments chiefly composed of arkoses, feldspathic sandstones and conglomerates derived from the craton and/or uplifted old blocks (Condie, 1997; Mendoza-Rosales et al., 2010; Cawood et al., 2012). In addition, basalts in the Qingshicun Formation (Doucun

Subgroup) and Hebiancun Formation (Dongye Subgroup) also display within-plate features (Sun et al., 1992; Du et al., 2009, 2015b). Therefore, it is reasonable to postulate that the dominant sequences in the Hutuo Group, namely the Doucun and Dongye Subgroups, formed in a continental rift setting (Du et al., 2011, 2015b; this paper), identical to that of sediments in the Gantaohe Group (Du et al., 2016b). However, the Guojiazhai Subgroup, from the base upwards, shows a coarsening sequence which contrasts with sediments in the lower units (Bai, 1986; Du et al., 2011). Additionally, some clastic components in this subgroup are from the lower sequences of the Hutuo Group (Fig 5m-p). These sedimentary facies and associations in the Guojiazhai Subgroup are identical with those of sediments in foreland basins (Condie, 1997). Therefore, we are favor previous interpretations that the Guojiazhai Subgroup represents a local molasse formed between mountains (Bai, 1986) during closure of the 1.9−1.8 Ga rifting-related basin that is related to the final cratonization of the NCC (Du et al., 2011). 6.4. Unveiling crustal growth and reworking in the Central TNCO As shown above, zircon Lu-Hf isotopes, combined with U-Pb ages from the clastic rocks in the Hutuo Group, can be used to reveal the crustal growth and/or reworking in the Wutai, Hengshan and Fuping areas. The substantial geochronological database confirms that the Wutai Complex is mainly composed of 2560−2520 Ma granitic gneisses and 2533−2513 Ma volcanic-sedimentary rocks, accompanied by small scales 2.2−2.1 Ga granites (Wilde et al., 2004a, 2005), and Hengshan and Fuping Complexes are dominated by 2520−2480 Ma TTG gneisses with minor 2.7 Ga

gneisses and 2.3−2.0 Ga granites (Cheng et al., 2004; Guan et al., 2002; Zhao et al., 2002; Kröner et al., 2005; Han et al., 2012; Lu et al., 2014). Based on the arc-related geochemical features of the ca. 2.5 Ga gneisses and volcanic rocks, some researchers have proposed that the Hengshan-Wutai-Fuping successions were the product of a late Archean island arc at the margin of the Eastern Block (Guan et al., 2002; Liu et al., 2002; Zhao et al., 2002), which was tectonically interleaved during a major continental collisional event at 1.95−1.8 Ga via the amalgamation of the Eastern and Western Blocks of the North China Craton along the Trans-North China Orogen (Zhao and Zhai, 2012 and references therein; Qian et al., 2013, 2015; Wei et al., 2014; Zhang et al., 2016). However, Zhai and Santosh (2011) proposed that the NCC initially formed a craton via the amalgamation of several micro-blocks in the late Archean. In the clastic rocks of the Hutuo Group, 645 detrital zircons, including previous published data (Du et al., 2011), show a large variation in εHf(t) values on a 207

Pb/206Pb ages versus εHf(t) diagram (Fig. 16A). A small number of grains with ca.

2.5 Ga ages have high positive εHf(t) values greater than the 0.75εHf contemporaneous depleted mantle, and

207

of

Pb/206Pb ages identical with single stage

model ages (Fig. 16B), which indicates these zircons were derived from juvenile crust and represented some degree of crustal growth at the end of late Archean (Belousova et al., 2010). Most of the zircons lie between 0.75 times the depleted mantle and Chondrite, indicating that the parent rocks were derived from the partial melting of young crust or from depleted mantle mixing with old crust (Fig. 16A). Additionally,

some 2.2−2.0 Ga zircons and a small number of ca.2.5 Ga crystals exhibit lower εHf(t) values, deviating from contemporaneous depleted mantle, and their single stage model ages are much older than their

207

Pb/206Pb ages (Supplementary table 2; Fig. 16B),

which indicate the 2.2−2.0 Ga crustal reworking in central Trans−North China Orogen, consistent with the extensive occurrence of the 2.2−2.0 Ga granitoid rocks in these areas (Du et al., 2016a and reference therein). Zircon two stage model ages TDMC show a wide range from 2.0 Ga to 3.7 Ga and dominantly span from 2.6 Ga to 2.9 Ga (Fig. 16C). Whole rock Sm-Nd and zircon Lu-Hf isotopes indicate that the NCC witnessed intensive crustal growth from 2.9 Ga to 2.6 Ga with a peak of ca. 2.7 Ga (Wu et al., 2005; Geng et al., 2012). Significantly, ca. 2.7 Ga TTG gneisses and supracrustal rocks occur widely the in western and eastern parts of Shandong province (Zhuang et al., 1997; Du et al., 2003, 2010b; Jahn et al., 2008; Wan et al., 2011; Wang et al., 2012). In addition, a rapidly growing number of 2.7 Ga rocks are identified along the TNCO, such as at Fuping (Guan et al., 2002; Han et al., 2012; Lu et al., 2014), Hengshan (Kröner et al., 2005), Zanhuang (Yang et al., 2013); Zhongtiao (Zhu et al., 2013), Taihua (Liu et al., 2009), and Huoqiu (Wan et al., 2010b). Additionally, 2.7 Ga TTG gneiss is also reported in Wuchuan, Inner Mongolia (Ma et al., 2013). In summary, multiple lines of evidences indicate that 2.7 Ga rocks are widespread in the NCC (Wan et al., 2014), which is similar to the intensive 2.7 Ga tectonic-thermal event found on different cratons around the world (Condie, 1998; 2000). However, ca. 2.5 Ga magmatism is also widespread in the North China Craton and represents an

episode of intensive crustal reworking in late Archean (Geng et al., 2010, 2012). As previously discussed, detrital zircons from the Hutuo Group suggest the intensive crustal growth of 2.7 Ga in central Trans-North China Orogen. 7. Conclusions Based on the clastic components, zircon U-Pb ages and Lu-Hf isotope compositions of clastic rocks from the Hutuo Group, we can draw the following conclusions. (1) The Doucun and Dongye Subgroups show different types of sedimentary sequences compared with those of the Guojiazhai Subgroup. Sandstones in the Doucun and Dongye Subgroups were dominantly derived from a combination of cratonic and recycled orogenic provenances. Sandstones in the Guojiazhai Subgroup were mainly derived from a single source, however, which corresponds to a recycled orogenic provenance. Detrital zircons in the clastic rocks from Doucun and Dongye Subgroups are dominated by ca. 2.5 Ga and 2.2−2.0 Ga populations with minor 2.7 Ga. Their ca. 2.5 Ga and 2.7 Ga zircons were mainly derived from the late Archean Wutai, Fuping and Hengshan Complexes, along with minor contributions from the Zanhuang Complex, and the 2.2−2.0 Ga zircons were sourced from local Paleoproterozoic granites with some contribution from lower sequence of the Hutuo Group. In contrast, zircons in the Guojiazhai Subgroup show three main peaks at 2180 Ma, 2400 Ma, and 1980 Ma, which indicate that Paleoproterozoic intrusives in the Lüliang area are their dominant source with some contributions from the Wutai, Fuping and Hengshan Complexes.

(2) The youngest zircons in the Sijizhuang Formation sandstone yielded 207

Pb/206Pb ages of ca. 2140 Ma. Considering the thick layers of conglomerate at the

base of the Hutuo Group and the 2140±14 Ma basaltic andesite in the Sijizhuang Formation, we infer that the initial deposition of the group occurred at ca. 2.2 Ga. Sedimentation in the Doucun and Dongye Subgroups was likely contemporaneous with 2.2−2.0 Ga magmatism in the North China Craton and occurred over a similar time span. The youngest zircon in the Guojiazhai Subgroup is ca. 1.9 Ga and the unit is demonstrably earlier than the Changcheng Group and 1.78−1.75 Ga mafic dykes. Therefore, the Guojiazhai Subgroup was deposit at 1.9−1.8 Ga. (3) Detrital components in the Hutuo Group sandstones are mainly quartz grains with minor feldspar and lithic fragments. The Doucun and Dongye Subgroups were deposited in a shallow water environment, which is distinct from the sediments in back-arc basins but similar to those of rift-related basins within cratons. The Guojiazhai Subgroup was likely deposited during closure of the rifting-related basin. (4) Detrital zircons in the Hutuo Group show a large variation in εHf(t) values. A small number of ca. 2.5 Ga grains have high positive εHf(t) values and

207

Pb/206Pb

ages that are identical with the single stage model ages, suggesting crustal growth at the end of late Archean. Most 2.7−2.5 Ga, 2.4−2.3 Ga and 2.2−2.0 Ga zircons show 207

Pb/206Pb ages that are much younger than their single stage model ages (TDM1),

indicating intensive crustal reworking at these times. Their two stage Hf model ages (TDM C) mainly concentrate at 2.9−2.6 Ga, which is distribution similar to that of crustal growth in the North China Craton.

Acknowledgments We would like give our gratitude to Drs. ChunrongDiwu, Xiaoming Liu, ChunliGuo and KejunHou for the zircon U-Pb and Lu-Hf analyses and to the journal editor, Prof. Guochun Zhao, and two reviewers for their critical comments. This work was financed by the National Natural Science Foundation of China (Grant No. 41172171), the China Scholarship Council (File No. 201409110015), China Geological Survey (12120114021501 and DD20160121), and the National Commission on Stratigraphy of China (1212011120142).

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Figure 1

Three subdivision of the North China Craton. ( after Zhao et al., 1999a, b)

Figure 2

Geological map of the Wutai Complex in the Trans-North China Orogen

(after Wilde et al., 2004a)

Figure 3

Geological sketch map of the Hutuo Group in Wutai Complex (after Wu et

al., 2008).

Figure 4 The stratigraphic column of the Hutuo Group in Wutai Complex. (after Bai et al., 1986; Miao et al., 1999; Du et al., 2011)

Figure 5

Outcrop photos of the Hutuo Group in Wutai Complex.

(a) Quartz porphyry pebble in the Sijizhuang Formation, Jiancun area, (b) Ripple structure in sandstone of the Nantai Formaton, (c) Cross bedding in the sandstone of the Wenshan Formation, (d) Stromatolites kept in upper sequences of the Wenshan Formation, (e) Ripple structures in sandsonte of the Hebiancun Formation, (f) Flute marks structure in sandstone of the Hebiancun Formation, (g) Sedimentary breccia in carbonate of the Hebiancun Formation, (h) Brown oxide crust kept in basalt of the Hebiancun Formation, (i), (j) Stromatolites kept in carbonates of the Huaiyincun and Beidaxing Formations, (k) The Guojiazhai Subgroup unconformably overlying the Dongye Subgroup, (l) Ripple structure in sandstone of the Xiheli Formation, (m) Conglomerate with purple sandstone pebbles in Heishanbei Formation, (n),(p) Conglomerate with dolomite pebbles in the Diaowangshan Formation, and the stromatolites kept in pebbles.

Figure 6 Microphotos of sandstones in the Hutuo Group. Abbreviations are as in Table 1.

Figure 7

Q-F-L and Qm-F-Lt triangles for framework modes of sandstones in the

Hutuo Group (Dickinson, 1985).

Figure 8

Representative zircons CL images from detrital rocks in the Doucun

Subgroup. Yellow-outlined white circles represent the locations of U-Pb dating, and red dashed circles represent the positions of Lu-Hf isotopic analyses.

Figure 9

U-Pb Concordia and histogram with frequency distribution diagrams of

zircons from clastic rocks in the Doucun Subgroup.

Figure 10

207

Pb/206Pb age vs. εHf(t) diagrams of zircons from clastic rocks in the

Hutuo Group.

Figure 11

Representative zircons CL images from detrital rocks in the Dongye

Subgroup. Yellow-outlined white circles represent the locations of U-Pb dating, and red dashed circles represent the positions of Lu-Hf isotopic analyses.

Figure 12

U-Pb Concordia and histogram with frequency distribution diagrams of

zircons from clastic rocks in the Dongye Subgroup.

Figure 13

Representative zircons CL images from detrital rocks in the Guojiazhai

Subgroup. Yellow-outlined white circles represent the locations of U-Pb dating, and red dashed circles represent the positions of Lu-Hf isotopic analyses.

Figure 14

U-Pb Concordia and histogram with frequency distribution diagrams of

zircons from clastic rocks in the Guojiazhai Subgroup.

Figure 15

207

Pb/206Pb age histograms with frequency distribution diagrams of

zircons from clastic rocks in the Hutuo Group.

Figure 16

207

Pb/206Pb ages vs. εHf(t) plots (a),

207

Pb/206Pb ages vs. TDM1 plots (b),

and two stage model ages (TDM C) histogram of zircons from the Hutuo Group (after Belousova et al., 2010) (c).

Table 1 Definition of point and recalculated mode parameters Counted parameters Qp = polycrystalline quartz grains Qm = monocrystalline quartz grains P = plagioclase feldspar K = potassium feldspar Lvf = volcanic lithic with felsic texture Lvm = volcanic lithic with microlithic texture Lvl = volcanic lithic with lathwork texture Lvv = vitric volcanic lithic Lp = plutonic lithic Lss = siltstone/shale sedimentary-lithic Lsc = carbonate grain Lmv = metavolcanic-lithic grain Lms = metamorphic-lithic grains except Lmv M = phyllosilicates H = heavy minerals Misc = miscelaneous and unidentified grains Recalculated parameters Q = Qm+Qp F = P+ K Lv = Lvf+Lvm+Lvl+Lvv+Lp Ls = Lss+Lsc Lm = Lmv+Lms L = Lv+Ls+Lm+Misc Lt = Lv+Ls+Lm+Qp+Misc

Table 2 Statistics on the detrital grains in sandstones of the Hutuo Group Sampl e

Q F Lv Ls Lm Q-F-L Qm-F-Lt Subgrou Formatio Q Q Lv Lv Lv Lv L Ls Ls Lm Lm MH % % %Q % ps ns P K %F %F p m f m l v p s c v s Q L m Lt

HT18 -1

Sijizhua 36 1 42 54 ng 8 9

HT19 -1

Sijizhua 25 1 32 23 ng 5 3

HT57 -1 HT59 -1

Sijizhua 41 3 42 90 ng 1 8 Sijizhua 50 12 6 56 ng 8 1 5

HT58 -6

Sijizhua 39 2 23 58 16 ng 1 7

7

Sijizhua 45 13 41 9 ng 0 4

1

HT65 -1

Doucun

1 1

2 5 4 6

7

1 5 1 1 18 20 4

5

37

78. 13. 13. 8 70.1 16 1 9 9

4

75. 23. 9.5 15 67.1 9.5 5 4

9

75. 15. 15. 13. 9.3 71.1 3 5 5 5

12

75. 22. 22. 2 69.6 8.3 9 1 1

2

15 1

71. 21. 21. 6.5 69.7 8.5 8 8 8

4

9

80. 14. 14. 5 78.2 7.4 5 4 4 64

HT66 -2

Sijizhua 43 3 13 43 1 5 1 5 ng 4 7

3

HT67 -1

Sijizhua 33 8 14 58 ng 2 1

3

3 5

1

14

HT09 -1

Dashilin 42 2 15 17 g 6 0

4 2

1 5

3 1

1

HT23 -1

Wenshan 8

HT23 -3

Wenshan

HT23 -4

Wenshan

HT24 -3

Dongye

49 3

1

53 0

6

52 2 2

18 17 40 1 6

12 1

Hebianc 49 6 un 1

5

1

25. 10. 25. 12. 61.4 7 4 7 9

87. 7.3 5.2 84.5 7.3 8.1 5 81. 18. 19. 0 80.3 0 6 4 7

38

1 4

69. 19. 10. 19. 16. 63.4 9 8 3 8 8 66. 11. 17. 22 60.1 22 7 2 9

13

15

Sijizhua 37 4 11 75 11 ng 8 3

3

1

43

HT65 -2

5

2

15

8

94. 0.2 5.5 94.1 0.2 5.7 3 98. 0.4 0.7 97.8 0.4 1.9 9

3 4

5

97. 0 2.7 96.1 0 3.9 3

HT62 -1

Hebianc 39 10 un 6

5

3

98. 0 1.9 95.7 0 4.3 1

HT62 -2

Hebianc 55 21 un 7

2

6

98. 0 1.4 95.1 0 4.9 6

HT68 -1 HT26 -2

Hebianc 35 1 un 9 37 Xiheli 9 2

HT26 -3 HT26 -4

Guojiaz hai

Xiheli Xiheli

2 1 12 4 6

6 6

52 5

2

97. 0 2.2 97.6 0 2.4 8 81. 18. 20. 0 79.3 0 2 8 7

16

39 8

1 15 13 4

2 44 33 3

11

74. 25. 28. 0 71.3 0 2 8 7

15

33 8

2 10

1 72 6

21

74. 25. 28. 0 71.3 0 5 5 7

Sampl e

Q F Lv Ls Lm Q-F-L Qm-F-Lt Subgrou Formatio Q Q Lv Lv Lv Lv L Ls Ls Lm Lm MH % % %Q % ps ns P K %F %F p m f m l v p s c v s Q L m Lt

HT26 -5

Xiheli

HT26 -6

Xiheli

HT51 -3

Xiheli

HT52 -1

Xiheli

HT53 -1 HT47 -1 HT48 -1

Guojiaz hai

12

34 3

3 6

9

29

40 5

3

3

8

41 9

17

17

50 8

Heishan 38 40 bei 7 Heishan 44 60 bei 2 Heishan 43 18 bei 7

61

3

81. 18. 21. 0 78.3 0 1 9 7

31

13 2 4

89. 10. 16. 0 83.5 0 5 5 5

11

80

17

77. 22. 24. 0 75.9 0 4 6 1

33 1 1 2

5 25 7

15

11

9

8

7

3

1

1 2

1 1

1

79. 20. 22. 0 77.1 0 7 3 9 95. 13. 0 4.5 86.6 0 5 4 96. 0 3.5 85 0 15 5 99. 0 0.9 95.2 0 4.8 1

Highlight: Zircons from a sandstone in lower sequence of the Hutuo Group yielded a youngest age of 2140 Ma. The Provenance of the clastic rocks was mainly from the late Archean basements and 2.2−2.0 Ga intrusives in central TNCO. The Doucun and Dongye Subgroups formed from 2.2 Ga to 2.0 Ga in rift-related environment. The Guojiazhai Subgroup deposited during the closure of the rifting-related basin in 1.9−1.8 Ga. 2.6 −2.9 Ga represents intensive crustal growth in Central TNCO.