Reappraising the Provenance of Early Neoproterozoic Strata in the Southern–Southeastern North China Craton and Its Implication for Paleogeographic Reconstruction

: The early Neoproterozoic sediments in the southern–southeastern (S-SE) North China Craton (NCC) are critical in paleogeographic reconstruction. We present new detrital zircon U–Pb–Hf data of ﬁve sandstone samples from the Sangwon Supergroup in SE-NCC and the Wufoshan Group in S-NCC. We integrate published zircon U–Pb data to appraise their provenance. The new dataset constrains the maximum depositional age of the Sangwon Supergroup to be ca. 1.0 Ga. The similar provenance transition and the comparable sequence stratigraphy imply that the Wufoshan Group could be an extension of the Xuhuai–Dalian–Pyongnam basins in the SE NCC with a maximum depositional age of ca. 1.0 Ga. The zircon age spectra of the successions show four major populations at ca. 2.5 Ga, ca. 2.0–1.8 Ga, ca. 1.6–1.4 Ga, ca. 1.3–1.0 Ga, with rare >2.5 Ga grains. The Archean– Paleoproterozoic grains could be derived from the NCC, which is conﬁrmed by their ε Hf(t) values. After a review of the possible paleocontinental reconstructions, we suggest that the ca. 1.6–1.0 Ga grains with different ε Hf(t) values (mostly positive) were from the southwestern Congo craton, supporting a NCC–SW Congo/SE NCC-S S ã o Francisco connection at ca. 0.9 Ga.

It is well-known that there are widespread, early Neoproterozoic sedimentary successions along much of the southern and southeastern margins of the NCC (Figure 1).Recently, the quality and quantity of detrital zircon geochronology have begun to provide essential constraints on the clastic provenance of these marginal basins in the NCC, which may enhance the unraveling of the tectonic evolution and paleogeographic reconstruction [17][18][19][20][21][22][23][24].The increasing magnitude of the zircon-dating dataset permits the use of new statistical technics to identify trends in the spatial and temporal evolution of provenances of these basin successions [25,26].In this contribution, we compile existing detrital zircon U-Pb datasets and add new U-Pb-Hf isotopic systematics of data of key samples from two focused successions (i.e., the Sangwon Supergroup in Pyongnam Basin, SE margin of the craton, and the Wufoshan Group in Xiong'er Basin, S margin; Figure 2), aiming to: (1) evaluate possible correlations of stratigraphy in the two regions and all the basins along the S-SE margin of the craton, (2) constrain provenance evolution of the relevant successions, and (3) infer the paleogeographic configuration of the NCC with the Rodinia supercontinent.[19] and (c) Songshan area [20].
From ca. 1.8 Ga to 0.9 Ga, the NCC was stable, represented by multiple stages of basin formation [38], i.e., the Xiong'er rift along the southern margin of the NCC, the Yanliao rift in north-central NCC, the Bayan Obo rift in northwestern NCC, and the Xuhuai (-Dalian-Pyongnam) rift along the eastern margin of the NCC (Figure 1b).Several cogenetic (with the rifting) igneous events have been recognized [38,39]: (I) the ca.

Sangwon Supergroup in the Pyongnam Basin, SE-NCC
Early Neoproterozoic sedimentary successions were widely developed along much of the southeastern NCC (Figure 1d), including the Sangwon Supergroup (System) in Pyongnam Basin (North Korea), Yongning-Wuxingshan-Jinxian groups in Dalian Basin, Penglai and Tumen groups in the Jiaolai Basin and west Shandong, and Huaihe-Langan/Bagongshan-Xuhuai groups in Xuhuai Basin (Figure 3).Overlying the Paleoproterozoic Jiao-Liao-Ji belt, they show a distinct SW-NE trend and are separated from each other by the Phanerozoic Tan-Lu fault and Bohai Bay.In the reconstructions by reversing the sinistral displacement of the Tan-Lu fault, these early Neoproterozoic sedimentary basins are juxtaposed [40,41].
The Sangwon Supergroup of Pyongnam Basin consists of ca.8000 m thick sedimentary rocks that underwent low greenschist metamorphism [42,45].It is composed of the Jikhyon, Sadangu, Muckchon, and Myoraksan groups from the bottom-up (Figure 3).The Jikhyon Group comprises four formations (the Jangbong, Obongri, Jangsusan, and Ansimryong formations from the bottom-up) and comprises conglomerate, quartz sandstone, schist, and phyllite, with a total thickness of about 3000 m [42].It was mostly developed in the southern Pyongnam Basin, called the South Type.In the northern Pyongnam basin, the Jikhyon Group is relatively thin, called the North Type [42].The Sadangu Group comprises three formations (the Unjoksan, Tokjaesan, and Chongsokturi from the bottom upward), featured by stromatolite limestone and dolomite [42].The Mukchon group comprises three formations (the Solhwasan, Okhyonri, and Mukchon) with mainly quartz sandstone, phyllite, and marl.The Myoraksan series is made of carbonate rocks (limestones and dolomites) in the lower part and silty phyllites in the upper part [42].
Sariwon mafic dykes and sills (belonging to the Dashigou LIP) widely intruded into the Sangwon Supergroup.Precise baddeleyite U-Pb dating has shown that these mafic intrusions were emplaced at ca. 0.9 Ga [40], giving a minimum age limit for Sangwon Supergroup.In addition, detrital zircon U-Pb dating yields the maximum depositional age of ca.1.0 Ga for the Jikhyon Group [19,50].

Wufoshan Group in the Xiong'er Basin, S-NCC
In the Songshan area of the Xiong'er Basin, the Wufoshan Group unconformably covers the metamorphic Archean-Paleoproterozoic basement (Figure 2c).It is composed of terrestrial clastic-carbonate succession recording river delta-coastal-neritic environments [43].The Wufoshan Group is subdivided into Ma'anshan, Puyu, Luotuopan, and Hejiazhai formations.The Ma'anshan Formation mainly comprises fleshy red and grayish-white quartz sandstone with a small amount of silty shale and lenticular conglomerates [45].The basal conglomerate is common and about 3-20 m thick.Structures like cross-beddings, ripple marks, and mud cracks are well-developed in the Ma'anshan Formation.The overlying Puyu Formation is characterized by variegated shales and siltstones, with a stable thickness of ~130 m [43].The Luotuopan Formation, conformably sitting on the Puyu shales, consists of quartz sandstones and sandstone-conglomerates with a thickness of 30-40 m [45].The Hejiazhai Formation is composed of fine sandstones, shales, thin-bedded limestones, and stromatolitic limestones, with a thickness of ~330 m in the typical profile [43].

Zircon U-Pb Isotopes and Trace Elements
Fresh portions of the samples were powdered to 80-mesh, and then zircon grains were extracted using conventional heavy liquids and magnetic methods.Hand-picked zircons under a binocular microscope, together with the standard 91500, GJ-1, were subsequently mounted on adhesive tape.They were enclosed in epoxy resin and polished 1/3 to 1/2 to expose the grain centers.Then, the CL images of the zircons were obtained at Wuhan SampleSolution Analytical Technology Co., Ltd. to check the internal structures and exposed surfaces to understand their origins and identify suitable dating targets for LA-ICP-MS analysis (Figure 4).

125°21′0.6″, N 38°4′47.4″). Sample NK10
126°51′7.1″,N 39°11′46.6″).They were both quartz sandstones of ---- Zircon U-Pb dating and trace elements were measured by LA-ICP-MS at the Wuhan SampleSolution Analytical Technology Co., Ltd., Wuhan, China.Laser sampling was performed using a 193 nm GeoLasPro laser ablation system that consists of a COMPexPro 102 ArF excimer laser and a MicroLas optical system.Ion-signal intensities were acquired using an Agilent 7700e ICP-MS.The diameter of the spot was set to 32 µm and 24 µm for different sizes of zircon grains.The repetition was also set as 5 Hz and 4 Hz, respectively.Each analysis incorporated a background acquisition of approximately 20 s followed by 40 s of data acquisition from the sample.Reference zircon GJ1, 91500, Plešovice, and glass NIST SRM 610 were used as external reference standards for U-Pb dating and trace elements, respectively.The 91500 was analyzed twice every six analyses for both tests.A date processing app, ICPMSDataCal 11.8 [53], was utilized for offline raw data selection, integration of background and analyte signals, time-drift correction, and quantitative calibration for U-Pb dating.Concordia diagrams and probability density plots (PDPs) were plotted using Isoplot 4.0 [54].

Zircon Lu-Hf Isotopes
In situ zircon Hf isotope analysis was carried out at the Sample Solution Analytical Technology Co., Ltd., Wuhan, China, using a GeoLas-193 laser-ablation microprobe attached to a Neptune Plus multi-collector (MC) ICP-MS.Spots for Hf analysis were undertaken as closely as possible to the U-Pb analysis spots.The ablation protocol employed a spot diameter of 44 µm.Zircon standard 91500, GJ-1, Plešovice, and TEM were measured as external calibration to evaluate the analytical reliability.The standard zircon Plešovice was analyzed twice every 5-10 sample analyses.The present-day chondritic ratios of 176 Hf/ 177 Hf = 0.282772 and 176 Lu/ 177 Hf = 0.0332 (Blichert-Toft and Albarède, 1997) were adopted to calculate the εHf(t) values.Raw data were processed using the ICPMSDataCal 11.8 [53].

Zircon U-Pb Dating
The LA-ICP-MS zircon U-Pb dating and Th and U compositions of the five samples are supplied in Supplementary Table S1.Age disconcordance > 10% and error > 80 Ma (1σ) were utilized as filters to preclude some valueless ages, and they are not further discussed below.For zircon grains older than 1.0 Ga, 207 Pb/ 206 Pb ages were applied, whereas 206 Pb/ 238 U ages were selected for zircon grains younger than 1.0 Ga.The Th/U values are shown in Figure 5. Age probability distribution diagrams are shown in Figure 6. -

WFS2110-1: Puyu Formation Silty Shale
The sizes of the zircon grains in Sample WFS2110-1 are relatively small, mostly at ca. 50 µm or smaller (Figure 4a).55 spots randomly selected from 300 zircon grains were dated, and only 25 spots are valid after filtration.Their Th/U values are all >0.25 (Figure 5).Ages range from 1837 Ma to 2929 Ma, with distinct peaks at ca. 2.1 Ga and ca.2.5 Ga (Figure 6f).

WFS2110-2: Lower Lutuopan Formation Sandstone
More than 2000 zircon grains were separated from sample WFS2110-2.They were mainly ca. 100 µm in size and subrounded or round (Figure 4b).In CL images, most of them displayed clear oscillating zonings.A few grains also showed core-rim texture, implying later thermal disturbance.A total of 90 analytical spots on 300 randomly selected grains were analyzed and two of them were abandoned because of low concordance.The remaining ages had a wide range between 1710 Ma to 2829 Ma, peaking at ca. 1.8 Ga and ca.2.4 Ga (Figure 6g).

WFS2110-3: Basal Hejiazai Formation Sandstone
Zircons from samples WFS2110-3 were 80-150 µm in size and were rounded or subrounded.Almost all grains displayed clear oscillatory zoning on CL images (Figure 4c).Dissolution depressions and cracks are common, with Th/U ratios of 0.19-2.25 (Figure 5).A total of 95 randomly selected spots were analyzed, and 94 valid concordant ages range from 1091 Ma to 2787 Ma, peaking at ca. 1100 Ma, 1200 Ma, and ca.1584 Ma (Figure 6h).

NK1015-1: Jangbong Formation, South Type
The zircon grain size of sample NK1015-1 was ca. 100 µm.In the CL image, most grains displayed clear oscillatory zoning and core-rim structure.Some had good roundness (Figure 4d).A total of 100 spots on 100 randomly selected grains were analyzed.All the 100 ages passed filtering, ranging from 2607 to 1820 Ma.In Figure 6i, they present a single peak at ca. 1.9 Ga.Their Th/U ratios were >0.15 (Figure 5), implying igneous origin.

NK1010-1: Jangbong Formation, North Type
The zircon grains in sample NK1010-1 were ca. 100 µm in size and had a good roundness shape.The CL images show that most grains had oscillating zonings (Figure 4e).After filtration, 97 ages with the high concordance were selected from 100 randomly tested spots were selected.Their ages had a wide range from Archean to late Mesoproterozoic.The Archaean and Paleoproterozoic grain ages peaked at ca. 2.6 Ga, while the middle Proterozoic grain ages were concentrated at ca. 1260 Ma, ca.1395 Ma, ca.1520 Ma, and ca.1650 Ma (Figure 6j).High Th/U values implied they had an igneous origin (Figure 5).

Zircon Hf Isotopes
Zircons from Sample WFS2110-1 were not further dated because of their small size.The analytical data of all the samples are displayed in Supplementary Table S2.The εHf(t) values of most zircons from sample NK1015-1 cluster between −2 and −6 with TDMC ages ranging from 2.5 Ga to 2.9 Ga (Figure 7).The εHf(t) values of the 1.6-1.0Ga zircons from Sample NK1010-1 were mainly positive, with minor negative ones.The εHf(t) values of the zircons from Sample WFS2110-2 (Luotuopan Fm.) range from −22.51 to +3.47.Both the ca.1.6 Ga and ca.1.2 Ga zircons from Sample WFS2110-3 (Hejiazhai Fm.) had large ranges of εHf(t) values.
-early Mesoproterozoic Xiong'er rift sequence, correlating with the ----Pb ages of the single youngest detrital zircons from the Ma'anshan Formation --nance of the Ma'anshan Formation has a strong affinity with NC  The youngest detrital zircon ages can provide constraints on the maximum depositional age and provide information for the regional stratigraphy correlation [54].In this study, we took the youngest single zircon age as an estimation of maximum depositional age in this contribution.
In Pyongnam, Samples NK1010-1 and NK1015-1 were collected from basal parts of the Jangbong Formation in the north and south margins of the Pyongnam basin, respectively.Their age distributions show a big difference, and the youngest single ages are 1820 ± 44 Ma and 1005 ± 72 Ma, respectively.We suggested that the 1005 ± 72 Ma could represent the maximum depositional age of the Sangwon Supergroup, consistent with the youngest 968 ± 25 Ma age of the Jangsan Formation in [19].The 1820 ± 44 Ma zircon grains could be caused by a regional discrepancy of provenances.

Revised Age of the Wufoshan Group
In the southern NCC, the Wufoshan Group was lithologically described as a late Paleoproterozoic-early Mesoproterozoic Xiong'er rift sequence, correlating with the Ruyang-Luoyu groups in the Mianchi-Queshan area [43,46,47,51,52].LA-ICP-MS 207 Pb/ 206 Pb ages of the single youngest detrital zircons from the Ma'anshan Formation include 1655 ± 22 Ma [46], 1793 ± 6.4 Ma [47], 1698 ± 47 Ma [55], and 1711 ± 39 Ma (this study).However, the upper two formations of the Wufoshan Group are constrained to be ca.1.0-0.95Ga [48,49] and this study, which extends the depositional chronospan of the Wufoshan Group to be 1.65-0.95Ga.Since the formations of the Wufoshan Group are conformably contact from bottom to top-such a large chronospan may be quite different from the actual depositional age of the Wufoshan Group.
Zircon age distributions depend on the geological setting of source areas.Provenance variation or transition could significantly affect age distributions of different horizons and regions.The age distribution difference between the lower and upper units of the Wufoshan Group could be simply caused by the provenance transition because the provenance of the Ma'anshan Formation has a strong affinity with NCC [47,50,56].However, ca.1.65-1.45Ga and 1.3-1.0Ga magmatic zircons are not common in the NCC basement.In Figure 8, the MDS plots reveal that this provenance transition generally occurred in the early Neoproterozoic basins in the southeastern NCC [26].Additionally, the Wufoshan Group and those successions in the southeastern NCC share a similar sequence stratigraphy (Figure 3) [42][43][44].We suggest that the Wufoshan Group could have also been deposited during ca.1.0-0.9Ga, correlating with those successions in the southeastern NCC, and consequently, it represents a western extension of the Xuhuai-Dalian-Pyongnam basins. ----------

Provenance Analysis
The detrital zircon U-Pb age spectra of sedimentary rocks from the target successions show four major populations at ca. 2.5 Ga, ca.2.0-1.8Ga, ca.1.7-1.5 Ga, and ca.1.3-1.1 Ga, and subordinate populations at ca. 1.4 Ga with rare >2.5 Ga grains (Figure 6k).The >2.5 Ga Archean grains are subordinate in all the dated samples from the successions and usually cluster between 2.8 and 2.6 Ga, with fewer >3.0 Ga, highly consistent with the coeval TTG gneisses and greenstones reported in the Eastern Block of the NCC (e.g., Luxi Complex in Western Shandong and Qixia Complex in Eastern Shandong; [57][58][59][60]).Among the detrital zircon age peaks, ca.2.5 Ga and ca.2.0 to 1.8 Ga are typical features of the NCC basement [31], which is also indicated by their εHf(t) values.In addition, ca.1.8-1.6Ga Xiong'er LIP and anorogenic magmatic association also developed in the northern and southern margin of the NCC [39].

Possible Paleocontinental Reconstructions
The variable amount of zircon detritus and their Lu-Hf data indicate that between 1.6 and 1.0 Ga, important periods of juvenile activity coupled with reworking occurred in the regions of provenance [19,20,22,24].Ca. 0.94-0.89Ga sills and dikes are widely distributed in the central and southeastern NCC [23,40,41,[76][77][78].This large-scale mafic intrusion event is an essential indicator for widespread continental lithospheric extension and thus could be a precursor of continental rifting events [79,80].This ca.0.94-0.89Ga magmatism could represent an early breakup phase of the Rodinia supercontinent [40,77,81].Additionally, the detrital zircon spectra are in an agreement with the extensional setting in the tectonic discrimination (Figure 9) [82].Therefore, the NCC should be connected to a continent that developed 1.6-1.0Ga multiphase large-scale magmatism.This continent split from the NCC during the sedimentation of early Neoproterozoic successions in the southern-southeastern NCC.It could also be the case that the NCC once developed in the Andean continental margin arc (orogenic belt) and experienced post-orogen extension.Still, this continental margin arc is not preserved.The zircon grains can therefore be derived from syn-collisional magmatism as well as a swath of older rock units caught in the orogenic margin and the cratonic foreland [82].In the literature, three paleocontinental reconstructions are particularly interesting to interpret the Mesoproterozoic provenances and tectonic of early Neoproterozoic successions in the southern-southeastern NCC.The first one connects the northern side of the NCC (present coordinate) with the Canadian shield, Baltica [83][84][85].It can explain the observation that the detrital zircon age spectrums of coeval sediments in the western Baltica and the NCC basins are quite similar.However, notable paleomagnetic data support that the northern side of the NCC was placed along the northwest side of Laurentia (present coordinates) in Rodinia [23,86].It needed a large drainage system across the Laurentia and the NCC that transported the Grenville-age detrital zircons in the Baltic and East Laurentia to the basins.Considering the large distance and weak NCC basement provenance record in most formations, the possibility of these exotic grains entering the basins through the craton is quite small.It is more likely that the ancient block was once adjacent to the southern-southeastern margin of the NCC and provided the provenance.
Microcontinental fragments with Precambrian basement comprising pre-orogenic components are common constituents of orogenic belts.The second reconstruction suggests a Grenvillian-aged orogeny (ca.0.9 Ga) between the North Qinling Terrane (NQT) and NCC occurred along the Kuanping suture [87,88].The post-collisional tectonics was consequently succeeded by orogenic collapse and extension [89,90].However, the Proterozoic NQT is characterized by a predominantly highly deformed and metamorphosed Paleoproterozoic basement, with a small amount of 1.4-1.0Ga Kuanping meta-basic volcanic rocks [91] and 1.37 Ga bimodal volcanic rocks of the Waitoushan Formation [92].The NQT itself has few rocks to be provenance of ca.1.6-1.4Ga detrital zircons.

Non-NCC Sources and Paleogeographic Reconstruction
Notably, most Precambrian paleocontinental reconstructions are generally cratonic pieces drawn with their present-day shapes [96].Old cratonic basements could be flanked or truncated by orogenic belts.Alternatively, when we carry out a paleocontinental reconstruction, vast tracts of marginal basements, which could have been reworked and intruded by orogenic plutons as well as juvenile magmatism, should also be taken into consideration [102].
Based on these several lines of evidence, we suggest the Mesoproterozoic zircon grains in the NCC basins could be derived from the southwest Congo block and its marginal orogenic belts.If some large depression, uplift, or other continents separated the southsoutheast NCC from the SF-CC, sediments eroded from the sources might not have been transported towards the basins in NCC.We infer a paleogeographic model that the south-east Congo could link to the southern NCC, while the southern São Francisco corresponded to the southeast NCC (Figure 11).The sediments eroded from the southwest Congo have been transported towards Xiong'er and Xuhuai basins and subsequently redistributed to other basins in southeast NCC by marine currents.Supplementarily, they could also get their clastic supply after a cycle of sedimentation and diagenesis of the upper Espinhaço sedimentary rocks [102,112].However, because of the unconformity between early and late Neoproterozoic basins in both cratons, the exact timing and mechanism of separating the two cratons remain unclear, which deserves further attention.[19,20,22] and this study.The SF-CC data are from [111][112][113][114].

- Figure 1 .
Simplified geological map of the Precambrian Geology of the NCC.(a) Paleoproterozoic accretion belts; (b) Meso-Neoproterozoic cratonic basins; (c) the Songshan area in S NCC; (d) the early Neoproterozoic basins in SE NCC.

Figure 4 .
Figure 4. CL images of the representative zircons from the tested samples.Spot diameter for sample WFS2110-1 is ~24 µm and the others are ~32 µm.

Figure 5 .
Figure 5. Th-U ratios of the tested zircons of the samples.

-
target successions.Ages are in Ma and ellipses show 1σ errors.-50 μm or smaller

Figure 6 .
Figure 6.U-Pb concordia and relative probability plots of detrital zircons of the samples from the target successions.Ages are in Ma and ellipses show 1σ errors.

Figure 7 .
Figure 7. Hafnium isotope characteristics of detrital zircons of the samples from the target successions.

1 .
Depositional Age of the Sangwon Supergroup

Figure 8 .
Figure 8. Multidimensional Scaling plots of existing samples from the early Neoproterozoic successions in south-southeast NCC [26].The serial number of the samples are the same as in Figure 2.

Figure 9 .
Figure 9. Detrital zircon age cumulative probability diagram for early Neoproterozoic sedimentary successions in NCC [82].The reported data are the same as compiled in Figure 3 and also are from this study.CA: crystallization age; DA: depositional age.1000 Ma was taken as the depositional age.(A) convergent setting; (B) collisional setting; (C) extensional setting

Figure 11 .
Figure 11.A speculation of paleogeographic reconstruction of the NCC in the early Neoproterozoic era [22].The possible extend of NCC follows [77].The possible extension of "broad" SF-CC follows [103].