A Lombart

A Siegel

C Villa

J Bascou

H Pillet

C Sauret

Evaluation of a scapula spinal marker cluster to track the scapula kinematics during manual wheelchair propulsion

Keywords: shoulder, kinematics, wheelchair, pseudo-kinematics

Introduction

Manual wheelchair (MWC) propulsion is a constraining mode of locomotion for the musculoskeletal system. It results that 30-70% of the MWC users suffer from musculoskeletal disorders, in particular at the shoulder joints [START_REF] Finley | Prevalence and identification of shoulder pathology in athletic and nonathletic wheelchair users with shoulder pain: A pilot study[END_REF]. Hence, there is a high interest in investigating shoulder biomechanics during MWC locomotion. However, tracking the scapula motion during MWC locomotion is not obvious because high soft tissue artifact can occur using skin markers. Some studies reported the use of a scapula locator during pseudo-kinematics acquisitions and showed a non-negligible motion of the scapula during MWC propulsion [START_REF] Koontz | Scapular range of motion in a quasi-wheelchair push[END_REF]. However, this methodology cannot be used to track dynamically the scapula during MWC locomotion. For that purpose, others methods were developed, such as multiple-calibration method (de Groot and Brand 2001). Nevertheless, this method can be time consuming for the patient. Finally, other studies used a technical cluster composed of at least 3 markers placed on the acromion [START_REF] Shaheen | Effects of attachment position and shoulder orientation during calibration on the accuracy of the acromial tracker[END_REF] or on the scapula spine [START_REF] Prinold | Scapula kinematics of pull-up techniques: Avoiding impingement risk with training changes[END_REF]. These techniques seem to be efficient for tracking the scapula orientation but failed for the translation [START_REF] Naaim | Effect of various upper limb multibody models on soft tissue artefact correction: A case study[END_REF]. In addition, validation data did not concern MWC locomotion.

The goal of this study was to evaluate the accuracy of a spinal marker cluster to track the scapula motion during MWC locomotion.

Material and methods

Sequential-kinematics acquisitions of 46 scapulae were obtained from 10 subjects who participated to 2 or 3 measurements sessions where both scapulae were tracked. During each session, the subject was equipped with reflective markers on the manubrium, the xyphoid process, the spinous processes of both the 7th cervical and the 8th thoracic vertebrae, and on both acromions. A technical scapula spinal marker cluster (SSMC) equipped with 3 markers was also placed on the spine of each scapula. For right and left sides, four static acquisitions were performed with the subject sat in a MWC, reproducing the initial contact of the hand with the handrim (IC), the contact of the hand at the top of the handrim (TC), the final contact (FC) and an elevation of the arm of 30° in the plane of the scapula (Elev30). During each acquisition, a scapula locator [START_REF] Shaheen | Effects of attachment position and shoulder orientation during calibration on the accuracy of the acromial tracker[END_REF]) was placed by an experimenter on 3 palpated anatomical landmarks: Angulus Acromialis (AA), Trigonum Scapulae (TS) and Margo Medialis (MM). Locations of all the markers and the scapula locator were acquired simultaneously with a 13-cameras optoelectronic motion capture system (Vicon system, Oxford Metrics Inc., UK).

Anatomical frames of the thorax and the scapula as well as the scapulothoracic rotations (yxz) were calculated according to the ISB recommendations. A segmental optimization based on the SSMC and the acromion was performed taking the TC pose as a reference. This allowed the scapula registration during the others poses (IC, FC and Elev30) and the comparison of the reconstructed positions with those obtained with the scapula locator.

Root mean square distances (RMSD) between palpated and simulated landmarks of the scapula were computed. Differences in orientation of the scapula (palpated vs reconstructed) and in origin location (here placed at AA) were calculated and expressed through the RMSD.

CONTACT a. lombart antoine.lombart@free.fr; C. sauret christophe.sauret@ensam.eu

Conclusions

This study aimed at evaluating the validity of a scapula spine marker cluster to track the scapula motion during MWC propulsion. The results showed non-negligible uncertainties, even if they remained below the motion of the scapula. This was found both for rotation and location. If the uncertainties reported in the present study are slightly higher than these reported in the literature [START_REF] Naaim | Effect of various upper limb multibody models on soft tissue artefact correction: A case study[END_REF], it must be kept in mind that our reference, i.e. scapula locator, is not free of uncertainty (gold standard remains intracortical pins).

Finally, the use of multibody kinematics optimization instead of segmental optimization would allow avoiding dislocation phenomenon but the validity of this method remains to be evaluated.

Results and discussion

RMSD between reconstructed and palpated markers (Figure 1) ranged from 1.5 to 28.5 mm (mean: 8.4 mm; SD: 4.7 mm) for IC; from 1.1 to 48.5 mm (mean 13.8 mm; SD: 8.0 mm) for FC; and from 3.4 to 53.7 mm (mean: 20.7 mm; SD: 11.6 mm) for Elev30. Obviously, the largest errors were found for the furthest markers (TS and MM) from the set composed of the SSMC and the acromion marker.

Across the four static poses, the mean orientation of the scapula ranged from -5.9° ± 7.3° to 0.4° ± 6.6° for up/downward rotation (range: -23.7° to 31.0°); from 27.4° ± 5.9° to 34.8° ± 6.9° for int/external rotation (range: 10.5° to 51.9°); and from -26.6° ± 5.7° and -16.1° ± 5.1° for ant/posterior tilt (range: -37.5° to -3.6°). Hence, in average, ranges of angular motion of the scapula across the 3 investigated poses were 6.3° for up/downward rotation, 7.4° for int/external rotation and 10.5° for tilt.

Angular RMSD between palpated and registered scapulae (Figure 2) was 5.3° ± 3.6° (range: 0.9° to 16°) for up/ downward rotation; 3.3° ± 2.1° (range: 0.4° to 9.8° for int/ external rotation; and 5.5° ± 3.5° (range: 0.6° to 15.6°) for tilt. Globally, these results are slightly higher than the existing literature using the acromial marker cluster combined with segmental optimization [START_REF] Naaim | Effect of various upper limb multibody models on soft tissue artefact correction: A case study[END_REF].

Differences in origin location ranged from 6.1 to 12.6 mm in average for the 3 positions. However, this error could reach 13.6 mm for IC, 17.4 mm for FC and 24.7 mm for Elev30. Nevertheless, this result remains in accordance with the existing literature, where it was noted that the acromial marker cluster combined with segmental optimization often results in large dislocation between the scapula and the clavicle [START_REF] Naaim | Effect of various upper limb multibody models on soft tissue artefact correction: A case study[END_REF].

Figure 1 .

 1 Figure 1. rmsd between reconstructed and palpated landmarks (mm, aa and ts) for the iC, FC and elev30 poses.

Figure 2 .

 2 Figure 2. angular rmsd between palpated and reconstructed scapulae following up/downward rotation (x), int/external rotation (y) and tilt (z) for the iC, FC and elev30 poses.


Chaolei Yan

Liangshu Shu

Michel Faure

Yan Chen

Renbo Huang

Time constraints on the closure of the Paleo-South China Ocean and the Neoproterozoic assembly of the Yangtze and Cathaysia blocks: insight from new detrital zircon analyses

Keywords: South China, Jiangnan Orogenic Belt, Neoproterozoic unconformity, Sibao Group, Detrital zircon geochronology

The South China Block was built up by the assembly of the Yangtze and Cathaysia blocks along the Neoproterozoic Jiangnan Orogenic Belt. The timing of the Jiangnan Orogeny remains controversial. The widespread orogeny-related Neoproterozoic angular unconformity that separates the underlying folded Sibao (ca.1000-820 Ma) and overlying Danzhou (ca.800-720 Ma) Groups was investigated. Six sedimentary samples, below and above the unconformity in three distal localities (Fanjingshan, Madiyi, and Sibao) yield detrital zircon with U-Pb ages ranging from 779±16 Ma to 3006±36 Ma, with a prominent peak at ca. 852 Ma. The youngest ages of 832±11 Ma and 779±16 Ma are revealed for the underlying Sibao and overlying Danzhou Groups, respectively. The detrital zircon U-Pb age relative probability plot of the Jiangnan Orogen matches well with those of the Yangtze and Cathaysia blocks since ca. 865 Ma.

Integrating geological, geochemical and geochronological results, we suggest that the Paleo-South China Ocean began to subduct under the Yangtze block at ca. 1000 Ma, and was partly closed at ca. 865 Ma. Afterwards, the Yangtze and Cathaysia blocks initially collide at 865 Ma, forming the Jiangnan Orogen. This collision resulted in not only the folding of the Sibao Group, but also sediment deposition in a syn-collisional setting, which makes the upper part of the Sibao

Introduction

The Jiangnan Orogen plays a key role in the tectonic framework of the South China Block, making the Neoproterozoic collision between the Cathaysia and Yangtze blocks. Over the past decades, advances in research on the Jiangnan Orogen led authors to propose several controversial tectonic models. The presence of remnants of oceanic crust and the well-defined suture zones make the eastern sector of the Jiangnan orogen commonly acknowledged as a collision belt (e.g., Li et al., 2007;[START_REF] Zhao | Precambrian geology of China[END_REF][START_REF] Charvet | The neoproterozoic-early paleozoic tectonic evolution of the South China Block: an overview[END_REF][START_REF] Shu | Early Paleozoic depositional environment and intracontinental orogeny in the Cathaysia Block (South China): implications from stratigraphic, structural, geochemical and geochronologic evidence[END_REF]Fig. 1). However, in the western part of the Jiangnan Orogen, some issues remain to be clarified.

One of the most debated questions is the timing of the collision between the Yangtze and Cathaysia blocks. Some researchers proposed that this collision took place at 1.2-1.1 Ga in the western part, but later in the eastern part at 1.0-0.96 Ga according to the tuff and basin study (Greentree et al., 2006). Li et al. (2007) proposed that the Jiangnan Orogen was related to the assembly of the Rodinia supercontinent during 1041-1015 Ma by the insight of mica 40 Ar/ 39 Ar dating of the Tianli schist in the Jiangxi Province. While some authors hold the view that the collision between the two blocks should be constrained at 1.0-0.86 Ga owing to the insights of ophiolites, and arc related rocks [START_REF] Shu | Kinematic and geochronology of the Proterozoic Dongxiang-Shexian ductile shear zone (Jiangnan region), South China[END_REF][START_REF] Ye | SHRIMP zircon U-Pb geochronological and whole-rock geochemical evidence for an early Neoproterozoic Sibaoan magmatic arc[END_REF]Li et al., 2008a[START_REF] Chen | Petrogenesis of the Pingshui keratophyre from Zhejiang: zircon U-Pb age and Hf isotope constraints [in Chinese with English abstract[END_REF]Li et al., , 2014;;[START_REF] Zheng | Rift melting of juvenile arc-derived crust: geochemical evidence from Neoproterozoic volcanic and granitic Reference Miaohou Zhejiang 828±4 Zircon LA-ICPMS U-Pb Xia[END_REF]. Meanwhile, considering the peak of detrital zircon of the Sibao Group (and its equivalents) as well as the peraluminous granites distributed along the Jiangnan

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Orogenic Belt, a school of researchers suggested that the collision of the Yangtze and Cathaysia blocks took place at 850-800 Ma [START_REF] Wang | Detrital zircon geochronology of Precambrian basement sequences in the Jiangnan orogen: dating the assembly of the Yangtze and Cathaysia Blocks[END_REF][START_REF] Wang | Geochronology and Hf isotopes of zircon from volcanic rocks of the Shuangqiaoshan Group, South China: Implications for the Neoproterozoic tectonic evolution of the eastern Jiangnan orogen[END_REF]Yao et al., 2014aYao et al., , 2014b)). Recently, more and more mafic rocks dated at 850-820 Ma, have been reported in the Jiangnan Orogen (Liu et al., 2015;Xia et al., 2015;Zhang et al., 2016;Sun et al., 2017). These rocks are interpreted as magmatic arc-related, consequently, the authors considered that the collision of the Yangtze and Cathaysia blocks did not started until 820 Ma. However, some authors considered that the sedimentary hiatus between the Sibao Group (and its equivalents) and Danzhou Group (and its equivalents) is the consequence of the Jiangnan Orogeny, leading the authors to propose that the collision should occur at ca. 830-800 Ma (Su et al., 2008;[START_REF] Zhao | Precambrian geology of China[END_REF][START_REF] Shu | Tectonic evolution of the eastern Jiangnan region, South China: New findings and implications on the assembly of the Rodinia supercontinent[END_REF].

In order to advance the debate on depositional time of the Sibao Group as well as the timing of the Jiangnan Orogeny, we have carried out detrital zircon dating above and below the Neoproterozoic unconformity in three distinct localities, and synthesized similar studies by integrating the new and previous data from the Jiangnan Orogen, the Yangtze and Cathaysia blocks, to improve the understanding of the Neoproterozoic tectonic evolution of the Jiangnan Orogenic Belt.

Geological setting

The general framework of the Jiangnan Orogen

The Jiangnan Orogenic Belt locates in the southeastern margin of the Yangtze Block, tracing the northwestward subduction of the Paleo-South China Ocean and the collision between the Yangtze and Cathaysia blocks (e.g., Guo et al., 1989;[START_REF] Shu | Plate Tectonic Evolution and the Kinematics of Collisional Orogeny in the Middle Jiangnan, Eastern China[END_REF][START_REF] Shu | Early Paleozoic depositional environment and intracontinental orogeny in the Cathaysia Block (South China): implications from stratigraphic, structural, geochemical and geochronologic evidence[END_REF][START_REF] Shu | Early Paleozoic and Early Mesozoic intraplate tectonic and magmatic events in the Cathaysia Block[END_REF]Li et al., 2007;[START_REF] Wang | Detrital zircon geochronology of Precambrian basement sequences in the Jiangnan orogen: dating the assembly of the Yangtze and Cathaysia Blocks[END_REF]Shu, 2012;[START_REF] Zhao | Precambrian geology of China[END_REF][START_REF] Charvet | The neoproterozoic-early paleozoic tectonic evolution of the South China Block: an overview[END_REF]Yao et al., 2014a; A C C E P T E D M A N U S C R I P T [START_REF] Yan | The Precambrian tectonic evolution of the western Jiangnan Orogen and western Cathaysia Block: Evidence from detrital zircon age spectra and geochemistry of clastic rocks[END_REF]Guo and Gao, 2017). The Paleo-South China Ocean subducted beneath the Yangtze Block since ca. 1000 Ma [START_REF] Wang | Detrital zircon geochronology of Precambrian basement sequences in the Jiangnan orogen: dating the assembly of the Yangtze and Cathaysia Blocks[END_REF][START_REF] Wang | Geochronology and Hf isotopes of zircon from volcanic rocks of the Shuangqiaoshan Group, South China: Implications for the Neoproterozoic tectonic evolution of the eastern Jiangnan orogen[END_REF]Yao et al., 2014b), and the final closure of the Paleo-South China Ocean resulted in the collision between the Jiangnan magmatic arc and the Cathaysia Block (Shu, 2012;Wang et al., 2012b). Numerous ultramafic, mafic magmatic (gabbro, diorite), and volcanic rocks, interpreted as ophiolites, dated from ca. 1000 Ma to ca. 870 Ma, distribute along the suture zone (BGMRAH, 1982;[START_REF] Bgmrjx | Regional Geology of Jiangxi Province[END_REF][START_REF] Manuscript A C C E P T E D M A N U S C R I P T Bgmrzj | Regional Geology of Jiangxi Province[END_REF]Xia et al., 2018). In the Dexing-Shexian area of eastern part of the Jiangnan belt, blueschists are dated at 866±14 Ma applying the K-Ar method on glaucophane [START_REF] A C C E P T E D M A N U S C R I P T Shu | Study on the high pressure metamorphic blueschist and its Late Proterozoic age in the Eastern Jiangnan belt[END_REF][START_REF] Shu | Kinematic and geochronology of the Proterozoic Dongxiang-Shexian ductile shear zone (Jiangnan region), South China[END_REF]. The collision led to intensive folding and faulting, but weak metamorphism of the Sibao Group and its equivalents (see Section 2.2;[START_REF] Bgmrgx | Regional Geology of Guangxi Autonomous Region[END_REF][START_REF] Bgmrhn | Regional Geology of Hunan Province[END_REF]. Afterwards, the Jiangnan Orogenic Belt was intruded by peraluminous granite plutons with ages ranging from from ca. 850 to ca. 805 Ma (peak at 830±10 Ma) (e.g., Xucun pluton, Jiuling pluton, Yuanbaoshan pluton, Sanfang pluton; Fig. 1) along the Jiangnan Orogen (Guo et al., 1989;Zhou et al., 2009;[START_REF] Zheng | Rift melting of juvenile arc-derived crust: geochemical evidence from Neoproterozoic volcanic and granitic Reference Miaohou Zhejiang 828±4 Zircon LA-ICPMS U-Pb Xia[END_REF]Yao et al., 2014b;Xin et al., 2017). After the formation of the South China Block, this continent started to rift probably reworking the preexisting faults related to the Jiangnan Orogeny, the Piangxiang-Qidong-Quanzhou-Longsheng suture zone in the middle Neoproterozoic turned into normal fault along the northern boundary of the middle Hunan extensional basin in the Nanhua Period [START_REF] Shu | Tectonic evolution of the eastern Jiangnan region, South China: New findings and implications on the assembly of the Rodinia supercontinent[END_REF]. The Nanhua rifting was coeval with the generation of ca. 800 Ma-750 Ma bimodal igneous rocks (Wang and Li, 2003;Li et al., 2018;Xia et al., 2018;[START_REF] Zheng | Rift melting of juvenile arc-derived crust: geochemical evidence from Neoproterozoic volcanic and granitic Reference Miaohou Zhejiang 828±4 Zircon LA-ICPMS U-Pb Xia[END_REF].

Afterwards, the South China was reworked by three prominent orogenic cycles in the Phanerozoic period, including the early Paleozoic, Triassic, and Jurassic-Cretaceous tectonic events [START_REF] Charles | The Montagne Noire migmatitic dome emplacement (French Massif Central): new insights from petrofabric and AMS studies[END_REF][START_REF] Charvet | The neoproterozoic-early paleozoic tectonic evolution of the South China Block: an overview[END_REF][START_REF] Shu | Early Paleozoic and Early Mesozoic intraplate tectonic and magmatic events in the Cathaysia Block[END_REF]Li et al., 2016a).

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Neoproterozoic stratigraphic sequences of the South China Block

In South China, the early Neoproterozoic strata (contemporary with the Sibao Group, ca. 1000-820 Ma, (Zhou et al., 2016)) are distributed geographically in three parts. One part that crops out in the northern and western boundaries of the Yangtze Block (Fig. 1) mainly consists of sandstone and mudstone (Wang and Li, 2003). The second part, exposed within the Jiangnan Orogen, is characterized by greywacke, sandstone, mudstone enclosing mafic and ultramafic blocks. This part is generally interpreted as the consequence of the subduction of the Paleo-South China Ocean (Zhou et al., 2009;Wang et al., 2012a;[START_REF] Shu | Early Paleozoic depositional environment and intracontinental orogeny in the Cathaysia Block (South China): implications from stratigraphic, structural, geochemical and geochronologic evidence[END_REF]Yao et al., 2014b). The third part is sporadically exposed in the Cathaysia Block, particularly in the northern part of the Fujian province. It is composed of terrigenous clastic rocks interlayered with volcanic rocks [START_REF] Bgmrfj | Regional Geology of Fujian Province[END_REF]Xu et al., 2010).

During the middle Neoproterozoic rifting (ca. 800-720 Ma) of the unified South China Block, more than 5 km-thick terrigenous and volcano-clastic series were deposited. Although the formation names, such as Banxi, Danzhou and Xiajiang Groups (ca. 800-720 Ma, (Zhou et al., 2016)) vary depending on the Provinces, they are petrographically and structurally equivalent [START_REF] Bgmrgz | Regional Geology of Guizhou Province[END_REF][START_REF] Bgmrgx | Regional Geology of Guangxi Autonomous Region[END_REF][START_REF] Bgmrhn | Regional Geology of Hunan Province[END_REF]. According to sedimentology, at that time, a littoral-neritic depositional environment characterized the whole South China Block (Shu, 2012). However, the water depth in the Jiangnan region was deeper than that in the Yangtze and Cathaysia regions (Wang and Li, 2003;Xu et al., 2010). The middle Neoproterozoic strata (ca. 800-720 Ma) are mainly composed of fine grain conglomerate, sandstone and siltstone, and widely exposed in the Jiangnan and the Cathaysia regions but rarely revealed in the Yangtze region [START_REF] Zhao | Precambrian geology of China[END_REF]Fig. 1).

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Comparison of the Sibao Group (and its equivalents) and Danzhou Group (and its equivalents) in the Jiangnan Orogenic Belt

The early Neoproterozoic and middle Neoproterozoic strata have different names in various places, e.g., the Sibao Group, Fanjingshan Group, Lengjiaxi Group, Shuangqiaoshan Group, Shangxi Group and Shuangxiwu Group of the early Neoproterozoic strata were named in the Guangxi province, Guizhou province, Hunan province, Jiangxi province, Anhui province and Zhejiang province, respectively, where the middle Neoproterozoic strata were named the Danzhou Group, Xiajiang Group, Banxi Group, Dengshan Group, Likou Group and Heshangzhen Group, correspondingly (BGMRAH, 1982;[START_REF] Bgmrgz | Regional Geology of Guizhou Province[END_REF][START_REF] Bgmrjx | Regional Geology of Jiangxi Province[END_REF][START_REF] Bgmrgx | Regional Geology of Guangxi Autonomous Region[END_REF][START_REF] Bgmrhn | Regional Geology of Hunan Province[END_REF][START_REF] Manuscript A C C E P T E D M A N U S C R I P T Bgmrzj | Regional Geology of Jiangxi Province[END_REF].

The deformation of the Sibao Group and its equivalents is characterised by N-S and NE-SW striking trending folds (Fig. 3). Tight folds with vertical axes are also common at the outcrop scale (Shu, 2012). The deformation is coeval with a low-grade regional metamorphism represented by low greenschist facies metamorphic rocks, such as slate, phyllite, and metavolcanic rocks. Locally, garnet-biotite micaschist and amphibole schist are observed [START_REF] Charvet | The neoproterozoic-early paleozoic tectonic evolution of the South China Block: an overview[END_REF][START_REF] Zheng | Rift melting of juvenile arc-derived crust: geochemical evidence from Neoproterozoic volcanic and granitic Reference Miaohou Zhejiang 828±4 Zircon LA-ICPMS U-Pb Xia[END_REF][START_REF] Yan | The Precambrian tectonic evolution of the western Jiangnan Orogen and western Cathaysia Block: Evidence from detrital zircon age spectra and geochemistry of clastic rocks[END_REF]Fig. 4). These strata were unconformably overlain by the Middle Neoproterozoic Danzhou Group and its equivalents basal conglomerate (Wang and Li, 2003;[START_REF] Wang | Detrital zircon geochronology of Precambrian basement sequences in the Jiangnan orogen: dating the assembly of the Yangtze and Cathaysia Blocks[END_REF]Fig. 3). On the contrary to the Sibao Group, the Danzhou Group and its equivalents display gentle folds and a very low grade metamorphism, or even no metamorphism (Fig. 4). The Sibao Group and its equivalents contain ultramafic and mafic magmatic rocks, and siliceous sedimentary rocks interpreted as olistoliths [START_REF] Yao | An early Neoproterozoic accretionary prism ophiolitic Mélange from the Western Jiangnan Orogenic Belt, South China[END_REF]. It is worthy to note that such mafic or ultramafic blocks are never observed in the Danzhou Group and its equivalents (Fig. 1).

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Ophiolitic mélange and magmatic events in the Jiangnan Orogenic Belt

Two ophiolitic mélanges in the eastern part of Jiangnan Orogenic Belt are generally accepted by the researchers. One is in the NE Jiangxi province, another is located near the Pingxiang-Jiangshan-Shaoxing fault, both of them are thought to be formed in an accretionary complex defining the ophiolitic suture of the Paleo-South China Ocean. The NE Jiangxi ophiolitic rocks yielded Sm-Nd isochron ages of 1024±30 Ma (gabbro) (Zhou et al., 1989) and 1034±24 Ma (ophiolitic mélange) [START_REF] Chen | Magmatism along the southeastern margin of the Yangtze block: Precambrian collision of the Yangtze and Cathaysia block of China[END_REF], SHRIMP zircon U-Pb ages of 968±23 Ma (ophiolitic mélange) (Li et al., 1994), and 970±21 Ma (plagiogranite) (Gao et al., 2009), and SIMS zircon U-Pb age of 993±12 Ma (gabbro) [START_REF] Shu | Early Paleozoic and Early Mesozoic intraplate tectonic and magmatic events in the Cathaysia Block[END_REF]. They yield that a Neoproterozoic marginal sea between the Zhanggong terrane and the Huaiyu terrane [START_REF] Shu | Plate Tectonic Evolution and the Kinematics of Collisional Orogeny in the Middle Jiangnan, Eastern China[END_REF][START_REF] Shu | SHRIMP zircon U-Pb age, litho and biostratigraphic analyses of the Huaiyu Domain in South China[END_REF][START_REF] Shu | Tectonic evolution of the eastern Jiangnan region, South China: New findings and implications on the assembly of the Rodinia supercontinent[END_REF]. Recently, [START_REF] Yao | An early Neoproterozoic accretionary prism ophiolitic Mélange from the Western Jiangnan Orogenic Belt, South China[END_REF] dated a gabbroic block enclosed in an ophiolitic mélange at 869±9 Ma (zircon, LA-ICP-MS) in the Longsheng area, in the western part of the Jiangnan Orogenic Belt (Fig. 1), which represents a Neoproterozoic suture zone of the Yangtze and the Cathaysia blocks. Accordingly, it is accepted that the subduction of the Paleo-South China Ocean under the Yangtze Block already began at ca. 1000 Ma and at least lasted until to ca. 869 Ma.Previous studies indicate that the subduction related rocks are relatively well exposed in the eastern Jiangnan Orogen: plagiogranite (970±21 Ma, zircon SHRIMP U-Pb, NE Jiangxi, Gao et al., 2009;905±14 Ma, zircon SHRIMP U-Pb, Zhejiang, Ye et al., 2007), andestic rocks (926± 15 Ma, zircon SHRIMP U-Pb, Zhejiang, Li et al., 2009), tonalite (913±15 Ma, zircon SHRIMP U-Pb, Zhejiang, [START_REF] Ye | SHRIMP zircon U-Pb geochronological and whole-rock geochemical evidence for an early Neoproterozoic Sibaoan magmatic arc[END_REF], basalt (904±8 Ma, zircon SHRIMP U-Pb, Zhejiang, Chen et al., 2009), rhyolite (891±12 Ma, zircon SHRIMP U-Pb, Zhejiang, Li et al., 2009), tuff (879±6 Ma, zircon LA-ICP-MS U-Pb, Jiangxi, [START_REF] Wang | Geochronology and Hf isotopes of zircon from volcanic rocks of the Shuangqiaoshan Group, South China: Implications for the Neoproterozoic tectonic evolution of the eastern Jiangnan orogen[END_REF], gabbro (875±8 Ma, zircon LA- Jiangxi, Zhang et al., 2013). However, ophiolites crop rarely out in the western Jiangnan Orogen: gabbro (869±9 Ma, zircon LA-ICP-MS U-Pb, Guangxi, [START_REF] Yao | An early Neoproterozoic accretionary prism ophiolitic Mélange from the Western Jiangnan Orogenic Belt, South China[END_REF].

A C C E P T E D M A N U S C R I P T ICP-MS U-Pb,
Numerous peraluminous granitic plutons crop out along the Jiangnan Orogenic Belt (Fig. 1).

Table 1 provides all ages obtained from this type of granitoids with a prominent peak at 830±10 Ma though their ages extent from ca. 850 to ca. 805 Ma. These granitoids are interpreted as lateto post-collisional plutons (see Section 5. 1;Song et al., 2015).

A ca. 800-750 Ma bimodal magmatism composed of basalts and rhyolites has been identified in the eastern Jiangnan Orogenic Belt (Ge et al., 2001;Li et al., 2008b;Wang et al., 2012b). The geochemistry of these rocks confirms the extensional setting of the South China Block since the middle Neoproterozoic. However, the bimodal magmatism is rarely reported in the western Jiangnan Orogenic Belt.

Samples collection and analytical procedures

Sample collection

We collected sandstone samples from both strata below and above the unconformity in three localities: Fanjingshan (Guizhou Province), Sibao (Guangxi Province) and Madiyi (Hunan Province) (Figs. 1, 2 and 3). GPS locations are provided in Table S1.

Analytical procedures

Whole-rock major element contents were analyzed by ARL-9900 X-ray fluorescence spectrometer (XRF) at the Testing Center of Shandong Bureau of China Metallurgical Geology Bureau. The uncertainties reported in this study are lower than 2% for major elements. Trace Zircons were separated from the crushed rocks using heavy liquid and magnetic techniques and then handpicked under a binocular microscope. The zircon grains were mounted in epoxy resin, and then polished and coated with gold. To reveal the internal textures of zircons, cathodoluminescence (CL) images were obtained using a JEOL JXA8230 electron probe microanalyzer at the Testing Center of Shandong Bureau of China Metallurgical Geology Bureau.

The laser ablation (LA)-ICP-MS analysis of zircon U-Pb isotopic compositions was performed at the Testing Center of Shandong Bureau of China Metallurgical Geology Bureau, using a ThermoX2 ICP-MS connected to a GeoLas Pro 193 nm laser ablation system. All analyses were carried out with a spot size of 30 μm or 20μm and a laser frequency of 10 Hz. Helium was used as the carrier gas to transport the ablated material. The detailed analytical procedure is described in Liu et al. (2010). All measurements were performed using zircon 91500 as the external standard with a 206 Pb/ 238 U age of 1065. 4±0.3 Ma (Wiedenbeck et al., 1995). We calibrated elemental contents with NIST610 as the external standard and 29 Si as the internal standard. The U-Pb ages were calculated from the raw signal data using the software ICPMSDataCal (ver.8.4). On account of the 204 Pb could not be measured owing to low signal and interference from 204 Hg in the gas supply, common lead correction was carried out using the EXCEL program common Pb correction [START_REF] Andersen | Correction of common Pb in U-Pb analyses that do not report 204 Pb[END_REF]. For zircons older than 1000 Ma, because of large amounts of radiogenic Pb, the 207 Pb/ 206 Pb age is more reliable than 206 Pb/ 238 U, whereas for zircons younger than 1000 Ma, as a result of the low content of radiogenic Pb and uncertainty of common Pb correction, the 206 Pb/ 238 U age is more reliable.

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Analytical results

Major and trace elements

The analytical results of major and trace elements of 13 representative samples are given in Table S2. Slate and phyllite of the Sibao Group and its equivalents show high SiO 2 (72.2-79.8 wt%), intermediate Al 2 O 3 (6.2-13.1 wt%). However, sandstone, metapsammite and slate of the Danzhou Group and its equivalents yield lower SiO 2 (66.2-77.1 wt%) and higher Al 2 O 3 (7.3-16.0 wt%). These two suites of strata have similar content in Fe 2 O 3, MgO and K 2 O. The most prominent character of all samples analyzed for geochemistry is that they display similar chondrite-normalized steep rare earth element (REE) patterns revealing obvious enrichment in light rare earth element (LREE) with respect to heavy rare earth element (HREE; Fig. 6A).

LREE/HREE values range from 6.2 to 16.3, and (La/Yb) N vary from 3.3 to 14.2 with an average of 8.2. All the samples reveal distinct negative Eu anomalies (Eu/Eu* value of 0.31-0.70, with an average of 0.53). On the upper crust normalized spidergrams (Fig. 6B), all samples exhibit strong negative Ba, Sr and Nb anomalies and the enrichment of Rb, Th and U, suggesting that the sedimentary rocks were derived from the upper crustal source (Taylor and McLennan, 1981;Sun and McDonough, 1989).

Zircon cathodoluminescence images

Representative cathodoluminescence (CL) images of detrital zircons of the six samples are shown in Fig. 7. In majority, the zircon grains are subhedral and euhedral, revealing that they are near source accumulation. Most of zircon grains display clear oscillatory zoning with granitic zircon feature, while three of them show broad banded structure with mafic zircon characters (n° 1933-12, 1933-32, 1714-32). Some zircon grains reveal thin luminescent overgrowth rims that appear bright in the CL images, displaying low Th/U ratios of 0.06-0.11 (Table S3) which are

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suggested as formed during metamorphism (Hoskin and Black, 2000;Corfu et al., 2003).

Interestingly, this phenomenon is found both within older cores (2529-946 Ma) and younger overgrowth rims (865-852 Ma).

Detrital zircon U-Pb ages

Sibao Group and its equivalents

Two hundreds and sixty-one zircon data yield good concordance (94%-99%) (Fig. 8 and Table S3). The Sibao Group and its equivalents reveal one significant peak at 853 Ma, one minor peak cluster ranging from 1900 Ma to 1500 Ma and one inconspicuous peak at ca. 2450 Ma, with the youngest age at 832 Ma (Fig. 9B).

The one collected in Fanjingshan (1933) yields ages in the range of 2176-834 Ma with a peak at 849 Ma. The ages of samples collected in Madiyi (1400) and Sibao (1714) range in 2645-832 Ma, and 3038-838 Ma, with distinct peaks at 861 Ma and 856 Ma, respectively. The peak clusters ranging from ca. 1000 Ma to ca. 870 look like a shoulder, lying behind the prominent peaks, and are remarkable in all of the three plots (Fig. 8).

Danzhou Group and its equivalents

Totally, we got 227 zircon ages for the Danzhou Group and its equivalents, most of them are concordant (92%-99%) (Fig. 8 and Table S3). In general, the age spectrum shows two obvious peaks at 850 Ma and 795 Ma, one minor peak cluster at ca. 1900-1500 Ma, and one minor peak at 2500 Ma as a whole, the relative probability plot reveals a good similarity with that of the Sibao Group and its equivalents except one significant peak at 795 Ma (Fig. 9D). Moreover, there is no detrital zircon age ranging from ca. 832 Ma to ca. 803 Ma recorded in the Danzhou Group and its equivalents (Fig. 9D).

Individually, the sample collected in Fanjingshan (1932) Fanjingshan and Madiyi (Fig. 8). However, the plot of the sample collected from Sibao reveals a different pattern and presents a significant age cluster at 903-850 Ma, two prominent peaks at 997 Ma and 796 Ma, one minor peak clusters at 1790-1617 Ma and one minor peak at 2507 Ma (Fig. 8).

Discussion

Comparison of the age spectra between the Sibao and Danzhou Groups and geological significance of the detrital zircon ages

The detrital zircon U-Pb age spectra of the Sibao and Danzhou Groups and their equivalents are given in Figs. 8 and9. In general, the age spectrum of the Sibao Group and its equivalents yields a distinct peak at 853 Ma and an obvious peak cluster ranges in 1000-870 Ma as a shoulder, with two minor peaks at 1700 Ma and 2500 Ma (Fig. 9A). The age spectrum of rocks from the Danzhou Group and its equivalents inherits the features of those of the Sibao Group and its equivalents, but also contains a younger peak at 795 Ma. Independently, the detrital zircon age spectra of the top sequence of the Sibao Group and its equivalents collected from three localities display a good comparability with a significant peak at ca. 855 Ma and an obvious peak cluster ranging from 1000 to 870 Ma. The ages ranging from ca. 1500 Ma to ca. 1000 Ma are rarely recorded except for that of the sample collected from the Sibao area (Fig. 8). In terms of the bottom of the Danzhou Group and its equivalents, the samples collected from Fanjingshan and Madiyi present two similar peaks at ca. 850 Ma and ca. 795 Ma.

However, the sample collected in the Sibao area presents a more complicated pattern that reveals

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A N U S C R I P T a main peak cluster ranging around 903-850 Ma with two peaks at 997 Ma and 796 Ma as shoulders. The spectra from all three areas also show prominent age peaks ranging from 1790 to 1617 Ma and at ~2507 Ma. It is worth noting that the detrital zircon age spectrum of the Danzhou Group sample collected from the Sibao area is different with those collected from the Fanjingshan and Madiyi areas, as it displays multiple peaks with respect to the other two. The zircon age distribution pattern of the Sibao sample can be traced in the detrital zircon spectrum of the Cathaysia Block (Fig. 10C). From the geographical point of view, the Sibao area is closer to the collision boundary than the Fanjinshan and Madiyi ones (Fig. 1), therefore, we may infer that the detritus in the Danzhou Group of the Sibao area was partly supplied by the Cathaysia Block.

The various detrital zircon ages have different geological significances. Some xenocrystic zircons dated at ca. 2600-2400 Ma in the lamprophyric and basaltic rocks have been found in Hunan, Hubei and Guizhou provinces, in the eastern and northern Yangtze Block (Zheng et al., 2006;Wang et al., 2012b). Detrital zircons with similar ages have been reported in the areas of Wuyi, southern Jiangxi and northern Guangdong provinces, Cathaysia Block (Gan et al., 1996;Yu et al., 2006Yu et al., , 2009)). The minority of detrital zircons dated at ca. 2500 Ma in this study might correspond to the period of global continental growth at the end Archean-early Paleoproterozoic, which was already proposed by [START_REF] Yao | Detrital zircon U-Pb geochronology, Hf-isotopes and geochemistry-new clues for the Precambrian crustal evolution of Cathaysia block South China[END_REF]. Similarly, the detrital zircon ages at ca. 1900-1500 Ma are interpreted to be linked with the Columbia supercontinent (Rogers and Santosh, 2002;[START_REF] Ye | SHRIMP zircon U-Pb geochronological and whole-rock geochemical evidence for an early Neoproterozoic Sibaoan magmatic arc[END_REF]. The detrital zircons ranging from 1500 Ma to 1000 Ma are abundant in the Cathaysia Block but rare in the Yangtze Block (Fig. 10A), which can be related to the Rodinia supercontinent and Grenville Orogeny [START_REF] Ye | SHRIMP zircon U-Pb geochronological and whole-rock geochemical evidence for an early Neoproterozoic Sibaoan magmatic arc[END_REF]. However, the detrital zircon spectra of the Yangtze Block and Jiangnan Orogen show a distinct differentiation across the time

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point at 1000 Ma (Fig. 10), suggesting that a gradually enhanced magmatism should have occurred after that time. Besides, igneous rocks dated at ca. 1000-870 Ma are widely reported in the Jiangnan Orogenic Belt (Xin et al., 2017 and references therein), indicating that the Jiangnan region was an active magmatic zone. Based on the geological facts (i.e., ca. 1.0 Ga subduction related arc magmatism, see Section 2.4) and the analysis of detrital zircon age spectra in this study, we suggest that the Paleo-South China Ocean started to subduct at ca. 1000 Ma (Fig. 11).

In this study, a few zircons with core-rim structure are observed (Fig. 7), the light luminescence rims suggest a hydrothermal event (Hoskin and Schaltegger, 2003;Dubińska et al., 2004), in the range of 865-852 Ma, which are produced by metamorphism and related to the collision of the Yangtze and Cathaysia blocks. The emplacement of regional numerous S-type granite plutons, dated at 830-820 Ma along the Jiangnan Orogen, formed by the melting of a continental crust. It is widely accepted that the S-type granite is product of the crustal partial melting, and related to a collision, however, it is still questionable whether this type of granite is generated and emplaces in the syn-collision or post-collision setting (Mass et al., 1997;Clemens et al., 2003;Collins and Richard, 2008;Song et al., 2015). Though the generation of crustal partial melting largely depends on the water content in the initial crustal materials, the melting temperature varies with the pressure, i.e. higher pressure versus higher melting temperature. Therefore, it is more difficult to melt crustal material and generate magma in a syn-collision compressive context than in the post-collision decompressive one. Moreover, the transport and intrusion of magma could be less easier in a shortening context than in an extensive one. The S-type granites from the Variscan and Himalayan orogens present good examples of the emplacement mechanism of the acidic magma. The study on the S-type granite from the Sanfang and Yuanbaoshan plutons, localised in the western part of the Jiangnan Orogenic Belt, reveals that the magma was

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A N U S C R I P T generated and emplaced posterior to the main phase of the collision and in the lower stress environment. Consequently, the emplacement of regional numerous S-type granite plutons, dated at 830-820 Ma along the Jiangnan Orogen, produced by the crustal partial melting, implies the ending (or late stage) of the orogeny. Afterwards, the absence of a magmatic activity during the interval of the 820-803 Ma (Fig. 9D) may suggest that the Jiangnan Orogen was in a tectonic quiet period. The newly formed South China block began to rift around 800-780 Ma, marked by the abundant bimodal magmatism [START_REF] Wang | Detrital zircon geochronology of Precambrian basement sequences in the Jiangnan orogen: dating the assembly of the Yangtze and Cathaysia Blocks[END_REF]. The youngest zircon, dated at 779 Ma, in the bottom of the Danzhou Group may record the starting time of the deposition of the Danzhou Group in the Jiangnan region.

Comparison of the detrital zircon age spectra of Neoproterozoic strata in the South

China Block

In order to characterize the detrital zircon age spectra originated from the Neoproterozoic strata of the Yangtze Block, Jiangnan Orogen and Cathaysia Block, we collected thousands of available detrital zircon age data (Table S4) from early Neoproterozoic (Sibao Group and its equivalents), middle Neoproterozoic (Danzhou Group and its equivalents) and late Neoproterozoic strata (Sinian and its equivalents, ca. 720-540 Ma, [START_REF] Bgmrgx | Regional Geology of Guangxi Autonomous Region[END_REF][START_REF] Bgmrhn | Regional Geology of Hunan Province[END_REF]) in three regions, mainly including the eastern Yangtze Block (northern Guizhou, northern Hunan and western Hubei provinces), whole Jiangnan Orogen (Anhui, Jiangxi, Hunan, northern Guangxi and eatern Guizhou provinces) and Cathaysia Block (Fujian, Guangdong, southeastern Hunan and southeastern Guangxi provinces) (Fig. 10I).

As shown in Fig. 10, the pattern of the detrital zircon age spectrum of the Jiangnan Orogen is almost consistent with that of the Yangtze Block, but significantly different from that of the Cathaysia Block (Figs. 10A, 10B and 10C). A prominent view shows that both relative

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probability plots of zircon age distribution from the Yangtze Block and Jiangnan Orogen display an increasing trend from 1000 Ma to ca. 850 Ma (Figs. 10E and10F). However, the contemporaneous peak cluster in the Cathaysia Block seems quite different from the former two (Fig. 10G). In addition, the ca. 1.0 Ga ophiolitic mélange and arc related magmatism heralded an intervening ocean (i.e., Huaiyu marginal sea, [START_REF] Shu | Plate Tectonic Evolution and the Kinematics of Collisional Orogeny in the Middle Jiangnan, Eastern China[END_REF][START_REF] Shu | Tectonic evolution of the eastern Jiangnan region, South China: New findings and implications on the assembly of the Rodinia supercontinent[END_REF] between the Yangtze and Cathaysia blocks. Consequently, we may qualitatively infer that the Cathaysia Block was not in contact with the Yangtze Block at ca. 1000 Ma (Fig. 11). S-type granites, dated at ca. 850-820 Ma, are widely distributed in the Jiangnan Orogenic Belt (Shu, 2012;Yao et al., 2014b;Xin et al., 2017 and references therein). However, rare contemporaneous magmatic event is known within the Yangtze and Cathaysia blocks. These plutons formed through the melting of a continental crust emplaced at the end of the Jiangnan collision. Nevertheless, we notice that the zircon age peak cluster from ca. 850 Ma to 820 Ma can be observed in the age spectra of both the Yangtze and Cathaysia blocks (Figs. 10E and10G). A possible interpretation is that these ca. 850-820 Ma detrital zircons were derived from the S-type granites in the Jiangnan Orogen. S-type granite indicates the late stage of the Jiangnan Orogeny, thus the collision between the Yangtze and Cathaysia blocks should have occurred before 850 Ma. Furthermore, the relative probability plots of zircon age distribution from the Yangtze Block, Jiangnan Orogen and Cathaysia Block show that the proportion of the Jiangnan Orogen is approximately equal to the sum of those of the Yangtze and Cathaysia blocks in the range of ca. 865-820 Ma (Figs. 10D and10H). This result can be interpreted as the Jiangnan Orogen was the unique source provider for the eastern Yangtze Block and western Cathaysia Block in the period from ca. 865 to 820 Ma. In other words, we propose that the collision between the Yangtze and Cathaysia blocks probably started at ca. 865 Ma and ended at ca. 820

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Ma. Such a 45 Myr orogenic duration is similar with some well known orogenic belts, such as the Variscan and Himalayas. (e.g. [START_REF] Chung | Tibetan tectonic evolution inferred from spatial and temporal variations in post-collisional magmatism[END_REF]Faure et al., 2008;[START_REF] Charles | The Montagne Noire migmatitic dome emplacement (French Massif Central): new insights from petrofabric and AMS studies[END_REF]Martinez-Catalan et al., 2014).Nevertheless, some researchers proposed that the collision took place after ca. 820 Ma, owing to the geochronology result of previously thought subduction related gabbro and diorite (ca. 850-820 Ma) in both the eastern and western parts of the Jiangnan Orogen (Zhou et al., 2009;Liu et al., 2015;Xia et al., 2015;Sun et al., 2017). However, the CL images of the dated zircons show oscillatory zoning (typical feature of acidic magma zircon) rather than broad bands (typical feature of mafic magma zircon) (Wu and Zheng, 2004). In addition, these zircons are anhedral instead of euhedral shaped. Consequently, these zircons cannot be considered as magmatic ones and were probably captured, as xenocrysts from the late to post-orogenic peraluminous granites, which are widely distributed along the Jiangnan orogenic belt, during the mafic magmatism in the Neoproterozoic Nanhua rifting period.

Moreover, recent study reveals that the final closure of the Paleo-South China Ocean is unisochronous in the western and eastern parts of the Jiangnan region [START_REF] Shu | Tectonic evolution of the eastern Jiangnan region, South China: New findings and implications on the assembly of the Rodinia supercontinent[END_REF], which approaches the understanding of the tectonic evolution of the Jiangnan Orogenic Belt.

Significance of the geochemistry and sedimentation record of the Sibao Group

The Sibao Group and its equivalents are mainly composed of phyllite, slate, greywacke, and low mature arkose. However, the Danzhou and its equivalents, unconformably covering the Sibao Group and its equivalents, consist mainly of a suite of conglomerate, slate, sandstone and carbonate (BGMRAH, 1982;[START_REF] Bgmrjx | Regional Geology of Jiangxi Province[END_REF][START_REF] Bgmrgx | Regional Geology of Guangxi Autonomous Region[END_REF][START_REF] Bgmrhn | Regional Geology of Hunan Province[END_REF]. Although the weathering and metamorphism may affect the geochemical character of the source rocks, the immobile elements can be still traced as a provenance indicator (Singh, 2009;Wang et al., 2012a). In the Hf-La/Th plot (Fig. 5A), most samples of the Sibao Group and its equivalents

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A N U S C R I P T cluster around the average compositions of andesite, TTG, felsic volcanic rock and granite, which are the source providers for the Sibao Group and its equivalents (Floyd and Leveridge, 1987). The tonalite-trondhjemite-granite (TTG) crust has been acknowledged as formed in a subduction zone (Senshu et al., 2009;Hoffmann et al., 2012;Zhang and Zhai, 2012). In the plot of tectonic setting discriminant, all the samples of the Sibao Group and its equivalents drop in the active continental margin field (Fig. 5B), suggesting that the sources of Sibao Group and its equivalents were more likely deposited in an active continental margin [START_REF] Bhatia | Plate tectonics setting of sandstones and geochemical composition of sandstones[END_REF]. The prominent trace and rare earth elements characters of the Sibao Group and its equivalents show distinct enrichment in light rare earth element (LREE) with respect to heavy rare earth element (HREE), and yield strong negative Ba, Sr and Nb anomalies (Fig. 6). These features suggest that the top sequence of the Sibao Group sediments was derived from an upper crustal source.

Considering the depositional environment of the Sibao Group and its equivalents, there are some controversial issues, such as the time span of the depositional process and the tectonic setting during the accumulation of the Sibao Group and its equivalents.

The majority of researchers acknowledged that the upper limit of the Sibao Group and its equivalents ranges around 835 Ma to 815 Ma (Wang et al., 2010a(Wang et al., , 2012a;;[START_REF] Zhao | Precambrian geology of China[END_REF][START_REF] Zheng | Rift melting of juvenile arc-derived crust: geochemical evidence from Neoproterozoic volcanic and granitic Reference Miaohou Zhejiang 828±4 Zircon LA-ICPMS U-Pb Xia[END_REF]Yao et al., 2014a;Su et al., 2018). However, there is no general agreement on the initial time of the sedimentation of the Sibao Group and its equivalents. A school of researchers suggested that the Sibao Group and its equivalents initiate to deposit at around 1.0 Ga according to detrital zircon trace of the Sibao Group and its equivalents (Shu, 2012;[START_REF] Zhao | Precambrian geology of China[END_REF]Yao et al., 2014a). Nevertheless, some authors pointed out that the maximum depositional age of the Sibao Group and equivalents is ca. 870 Ma [START_REF] Wang | Detrital zircon geochronology of Precambrian basement sequences in the Jiangnan orogen: dating the assembly of the Yangtze and Cathaysia Blocks[END_REF]Zhou et al., 2009;Su et al., 2018) by using of the youngest detrital zircon age of the

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"bottom" sequence of the Sibao Group. However, the sampling sites are about 2000 meters above the bottom according to their stratigraphic column. It could be a workable way to trace the bottom depositional age of the Sibao Group and equivalents by analyzing the detrital zircon spectrum. In this study, we propose that the maximum depositional age of the Sibao Group is at ca. 1000 Ma, when the detrital zircon spectra become distinct (Figs. 8,9 and 10B).

Concerning the sedimentation setting of the Sibao Group and its equivalents, most of the researchers hold the view that the Sibao Group and its equivalents were accumulated in a backarc basin (Wang et al., 2010a(Wang et al., , 2012a;;Shu, 2012;Yao et al., 2014b;Zhang and Wang, 2016), while some others proposed that they were deposited in a foreland basin [START_REF] Wang | Detrital zircon geochronology of Precambrian basement sequences in the Jiangnan orogen: dating the assembly of the Yangtze and Cathaysia Blocks[END_REF]Zhou et al., 2009). In all these tectonic interpretations, they suggested that the collision of the Yangtze and Cathaysia blocks (i.e. the Jiangnan Orogeny) took place after the end of the sedimentation of the Sibao Group and its equivalents.

However, in this study, we propose some new perspectives. As a great number of arc related magmatic rocks are exposed along the Jiangnan Orogen, we argue that the Paleo-South China Ocean started to subduct northwestwards (present coordinates) beneath the Yangtze Block since around 1000 Ma. Combined with the zircon spectra analysis of the Sibao Group and its equivalents, we suggest that the Sibao Group and its equivalents were formed along with the subduction of the Paleo-South China Ocean. Some oceanic crust relics were scratched and involved into the Sibao deposits during the ongoing subduction. Thus, the lower part of the Sibao Group is considered as an accretionary complex. Meanwhile, the mafic rocks related with arc magmatism intruded into the Sibao Group and its equivalents (Zhou et al., 1989;[START_REF] Chen | Petrogenesis of the Pingshui keratophyre from Zhejiang: zircon U-Pb age and Hf isotope constraints [in Chinese with English abstract[END_REF][START_REF] Zheng | Rift melting of juvenile arc-derived crust: geochemical evidence from Neoproterozoic volcanic and granitic Reference Miaohou Zhejiang 828±4 Zircon LA-ICPMS U-Pb Xia[END_REF]Yao et al., 2014b[START_REF] Yao | An early Neoproterozoic accretionary prism ophiolitic Mélange from the Western Jiangnan Orogenic Belt, South China[END_REF]Fig. 1). Associated with the analysis of the geochemistry, we propose that in the subduction period from 1.0 Ga to 865 Ma (see Sections 5.1

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A N U S C R I P T and 5.2), the Sibao Group and its equivalents were deposited in an active continental margin zone (Fig. 11).

The youngest detrital zircon is dated around 830-820 Ma in the Sibao Group and its equivalents (Su et al., 2018 and references therein, and this study), which is consistent with the geological fact that the Sibao Group and its equivalents are intruded by the ca. 830-820 Ma Stype granitic plutons in the Jiangnan Orogen.

Therefore, we suggest that the tectonic setting of the sedimentation of the Sibao Group and its equivalents can be divided into two stages. Firstly, at ca. 1000-865 Ma, it deposited in an active continental margin. Secondly, around 865-820 Ma, after the collision of the Yangtze and Cathaysia blocks, the Sibao Group and its equivalents were accumulated during the crustal thickening. By an ɛHf(t) study in the Anleilin and Xiushui formations (equivalent to the Sibao Group), Li et al. (2016b) showed that the negative ɛHf(t) values increase along the stratigraphic sequence from the bottom to the top, indicating that the Sibao Group and its equivalents received more and more crustal derived materials during its deposition in the early Neoproterozoic, which implies that the Sibao Group and its equivalents had experienced a tectonic setting transition from an active continental margin to continental collision. In other words, the Sibao Group and its equivalents have recorded both the subduction and collision events.

Afterwards, the Danzhou Group and its equivalents began to accumulate at ca. 780 Ma. The bottom sequence inherited the bulk geochemical signature of the Sibao Group and its equivalents (Figs. 5 and6), except that the rocks from the Danzhou and its equivalents present higher Al 2 O 3 and lower SiO 2 contents than those from the Sibao Group and its equivalents probably owing to the mechanical sorting and chemical changes related to transportation (Fralick and Kronberg, 1997).

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Geodynamic evolution of the South China Block in the Early Neoproterozoic

The Jiangnan Orogenic Belt was built up due to the convergence of the Paleo-South China Ocean and the collision between the Yangtze and Cathaysia blocks (Shu, 2012;[START_REF] Charvet | The neoproterozoic-early paleozoic tectonic evolution of the South China Block: an overview[END_REF], but its geodynamic evolution process is still debated. In this study, according to the geological evidence, zircon geochronology and whole rock geochemical study of the Sibao and Danzhou Groups and their equivalents, a possible spatial and temporal tectonic evolution model of the Early Neoproterozoic geological events can be suggested in the following.

As the detrital zircon spectra show a distinct differentiation across 1000 Ma (Fig. 10), it may suggest that a significant magmatism should have occurred after that time. The ophiolitic mélange, gabbro and oceanic plagiogranite dated at ca. 1000 Ma in the eastern part of the Jiangnan Orogen indicates that the subduction of the Paleo-South China Ocean took probably place after that time (Zhou et al., 1989;[START_REF] Chen | Magmatism along the southeastern margin of the Yangtze block: Precambrian collision of the Yangtze and Cathaysia block of China[END_REF]Li et al., 1994;Gao et al., 2009;[START_REF] Shu | Early Paleozoic and Early Mesozoic intraplate tectonic and magmatic events in the Cathaysia Block[END_REF]. The mafic rocks dated at 935 Ma together with the volcanic rocks ranging in 880-870 Ma are arc related (Yao et al., 2014b and references therein;Xin et al., 2017 and references therein), as well as the ca. 869 Ma ophiolitic gabbro [START_REF] Yao | An early Neoproterozoic accretionary prism ophiolitic Mélange from the Western Jiangnan Orogenic Belt, South China[END_REF] and ca. 866 Ma blueschist [START_REF] A C C E P T E D M A N U S C R I P T Shu | Study on the high pressure metamorphic blueschist and its Late Proterozoic age in the Eastern Jiangnan belt[END_REF], indicating that the subduction of the Paleo-South China Ocean was ongoing during the ca. 1000-865 Ma. In addition, the spectra analysis of detrital zircon age in this study points out that the subduction of the Paleo-South China Ocean probably started at ca. 1000 Ma and ended at ca. 865 Ma. During this period, the Sibao Group and its equivalents were accumulated in the active continental margin setting (Fig. 11).

Afterwards, the Yangtze and Cathaysia blocks began to collide, the changes in temperature ending of the Jiangnan Orogeny. In the period of ca. 865-820 Ma, the upper part of the Sibao Group and its equivalents were deposited in a syn-collisional setting (Fig. 11).

The evidence that rare magmatic imprint was traced in the ca. 820-800 Ma period may suggest that the Jiangnan Orogenic Belt was, at that time, probably situated in a tectonically quiet period. Then, in the ca. 800-760 Ma period, the Nanhua rifting was accompanied by both A-type granites plutonism and mafic intrusive rocks (Li et al., 2008b;Wang et al., 2012b). The unconformity between the Sibao Group (and its equivalents) and Danzhou Group (and its equivalents) marks the initial time of the Nanhua rifting in the Jiangnan Orogen area. The youngest zircon age dated at ca. 780 Ma in the bottom sequence of the Danzhou Group (and its equivalents) suggests that the Danzhou Group and its equivalents started their deposition at that time.

Conclusions

This study aims to explore the collision of the Yangtze and Cathaysia blocks. We have carried out detrital zircon dating and geochemistry study near the Neoproterozoic unconformity in three distinct localities, and synthesized studies by integrating the new and previous data from the Jiangnan Orogen, the Yangtze and Cathaysia blocks, to further understand the Neoproterozoic tectonic evolution of the Jiangnan Orogenic Belt.

Six sedimentary samples yield detrital zircon with U-Pb ages ranging from 779±16 Ma to 3006±36 Ma, with a prominent peak at ca. 852 Ma. The youngest ages of 832±11 Ma and 779±16 Ma are revealed for the underlying Sibao and overlying Danzhou Groups, respectively.

Geochemistry study reveals that the sources of the Sibao Group were derived from the upper crustal material with active continental marginal affinity, and the Danzhou Group inherits the Integrating the new results in the detrital zircon dating, geology and geochemistry from three localities in the western part of the Jiangnan Orogen, and previous geochronology data from the Yangtze, Jiangnan and Cathaysia regions, we can conclude the following main results from this study:

(1) The subduction of the Paleo-South China Ocean started at ca. 1000 Ma and ended at ca. 865 Ma;

(2) The Jiangnan Orogenic Belt was built up due to the assembly of the Yangtze and Cathaysia blocks between ca. 865 and 820 Ma;

(3) The deposition of the Sibao Group lasted from ca. 1000 Ma to 820 Ma;

(4) The angular unconformity between the Sibao and Danzhou Groups could take place at ca. 820-800 (or 780) Ma;

(5) The Danzhou Group and its equivalents began to deposit since ca. 780 Ma in the western Jiangnan Orogen area. Table 1. Dating of the S-type granite plutons in the Jiangnan Orogenic Belt.

Table

A C C E P T E D M A N U S C R I P T

Table 1 Dating of the S-type granite plutons in the Jiangnan Orogenic Belt Pluton Area (province) Age (Ma) Method

  elements and rare earth elements (REE) were measured by ICP-MS (Finnigan Element II) at the Testing Center of Shandong Bureau of China Metallurgical Geology Bureau. International standards (GBW07105 and GBW07122) were used to define the analytical precision and A C C E P T E D M A N U S C R I P T accuracy throughout the analytical processes for ICP-MS. The uncertainties are lower than 5% for trace elements.

  yields ages in the range of 2803-A C C E P T E D M A N U S C R I P T 779 Ma. As for the samples collected in Madiyi (1399) and Sibao (1714-1), they show ages ranging in 2997-783 Ma and 2562-796 Ma intervals, respectively. Two distinct peaks, ca. 850 Ma and ca. 795 Ma, are displayed in the relative probability plot of the sample collected from

  and fluid property possibly resulted in the metamorphism in the zircon which are traced at 865-852 Ma in this study. Abundant 830-820 Ma peraluminous late orogenic granites indicate the A C C E P T E D M A N U S C R I P T

  S C R I P Tgeochemical signature of the Sibao Group. The Yangtze, Jiangnan and Cathaysia regions have a good consistency since ca. 865 Ma from the synthesized analysis of the detrital zircon age relative probability plots.

  .W.O., Black, L.P., 2000. Metamorphic zircon formation by solid state recrystallization of protolith igneous zircon. Journal of Metamorphic Geology 18, 423-439. doi:10.1046/j.1525-1314.2000.00266.x Hoskin, P.W.O., Schaltegger, U., 2003. The composition of zircon and igneous and metamorphic petrogenesis. Reviews in mineralogy and geochemistry 53, 27-62. doi:10.2113/0530027 Li, J.H., Dong, S.W., Zhang, Y.Q., Zhao, G.C,, Johnston, S.T., Cui, J.J., Xin, Y.J., 2016a. New insights into Phanerozoic tectonics of south China: part 1, polyphase deformation in the Jiuling and Lianyunshan domains of the central Jiangnan Orogen. Journal of Geophysical Research: Solid Earth 121 (4), 3048-3080. doi:10.1002/2015jb012778 Li, J.Y., Wang, X.L., Zhang, F.F., Zhou, X.H., Shu, X.J., 2016b. A rhythmic source change of the Neoproterozoic basement meta-sedimentary sequences in the Jiangnan Orogen: Implications for tectonic evolution on the southeastern margin of the Yangtze block. Precambrian Research 280, 46-60. doi:10.1016/j.precamres.2016.04.012 Li, L.M., Lin, S.F., Xing, G.F., Jiang, Y., Xia, X.P., 2018. Geochronology and geochemistry of volcanic rocks from the Jingtan Formation in the eastern Jiangnan Orogen, South China: constraints on petrogenesis and tectonic implications. Precambrian Research 309, 166-180. doi:10.1016/j.precamres.2017.02.012Li, W.X., Li, X.H., Li, Z.X., Lou, F.S., 2008a. Obduction-type granites within the NE Jiangxi Ophiolite: Implications for the final amalgamation between the Yangtze and Cathaysia Blocks. GondwanaResearch 13, 288-301. doi:10.1016/j.gr.2007.12.010 Li, X.H., Zhou, G., Zhao, J., Fanning, C.M., Compston, W., 1994. SHRIMP ion microprobe zircon U-Pb age of the NE Jiangxi ophiolite and its tectonic implications [in Chinese with English abstract]. Geochimica (Beijing) 23, 125-131. doi:10.1007/BF02838521 A C C E P T E D M A N U S C R I P T rocks in the Jiangnan orogen, South China. Precambrian Research 163, 351-383. doi:10.1016/j.precamres.2008.01.004 Zhou C.M., 2016. Neoproterozoic lithostratigraphy and correlation across the Yangtze block, South china. Journal of Stratigraphy 40 (2), 120-135. Zhou, J.C., Wang, X.L., Qiu, J.S., 2009. Geochronology of neoproterozoic mafic rocks and sandstones from northeastern guizhou, south china: coeval arc magmatism and sedimentation. Precambrian Research 170, 27-42. doi:10.1016/j.precamres.2008.11.002 Zhou, X.M., Zhou, H.B., Yang, J.D., Wang, Y.X., 1989. Sm-Nd isochron age of the ophiolite suite in Shexian county, Anhui province and its geological significance. Chinese Science Bulletin 35, 208-212.

Figure captions Figure 1 .

 captions1 Figure captions

Figure 2 .

 2 Figure 2. Geological sketch maps and cross-sections with sampling locations for (A) the

Figure 3 .

 3 Figure 3. Representative field photos and geologic sketch maps. (A) Unconformity between the

Figure 4 .

 4 Figure 4. Representative photomicrographs of the samples. (A) Photomicrograph of Sample

Figure 5 .

 5 Figure 5. (A) Source rock discrimination diagrams for the samples on Hf versus La/Th (modified

Figure 7 .

 7 Figure 7. Representative cathodo-luminescence images of zircons of the samples from the

Figure 8 .Figure 9 .

 89 Figure 8. U-Pb age concordia plots and histograms and relative probability plots for the zircon of

Figure 10 .

 10 Figure 10. Comparison of the U-Pb age histograms and relative probability plots derived from

Figure 11 .

 11 Figure 11. Geodynamic evolutionary model for the Jiangnan region in the Early Neoproterozoic.

Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10

 2345678910 Figure 2

Figure 11

 11 Figure11

Acknowledgments

We wish to express our appreciation to Lin P.J. for the help during the work of zircon dating and geochemistry analysis. This study is supported by National Fundamental Research Program of China (973 Program, No. 2012CB416701) and National Natural Science Foundation of China (Nos. 41772204, 41572200).

Dubińska, E., Bylina, P., Kozłowski, A., Dörr, W., Nejbert, K., Schastok, J., Kulicki, C., 2004  The Jiangnan Orogenic Belt was built up due to the assembly of the Yangtze and Cathaysia blocks between ca. 865 and 820 Ma.

 The deposition of the Sibao Group lasted from ca. 1000 Ma to 820 Ma.