How did the peripheral subduction drive the Rodinia breakup: Constraints from the Neoproterozoic tectonic process in the northern Tarim Craton

How did the peripheral subduction drive the Rodinia breakup: Constraints from the Neoproterozoic tectonic process in the northern Tarim Craton

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Journal Pre-proofs How did the peripheral subduction drive the Rodinia breakup: Constraints from the Neoproterozoic tectonic process in the northern Tarim Craton Rong Ren, Shu-Wei Guan, Shui-Chang Zhang, Lin Wu, Hong-Yu Zhang PII: DOI: Reference:

S0301-9268(19)30408-5 https://doi.org/10.1016/j.precamres.2020.105612 PRECAM 105612

To appear in:

Precambrian Research

Received Date: Revised Date: Accepted Date:

19 July 2019 5 December 2019 6 January 2020

Please cite this article as: R. Ren, S-W. Guan, S-C. Zhang, L. Wu, H-Y. Zhang, How did the peripheral subduction drive the Rodinia breakup: Constraints from the Neoproterozoic tectonic process in the northern Tarim Craton, Precambrian Research (2020), doi: https://doi.org/10.1016/j.precamres.2020.105612

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How did the peripheral subduction drive the Rodinia breakup: Constraints from the Neoproterozoic tectonic process in the northern Tarim Craton

Rong Ren a*, Shu-Wei Guan a, Shui-Chang Zhang a, Lin Wu b, Hong-Yu Zhang c a

Research Institute of Petroleum Exploration and Development, Petrochina, Beijing

100083, China b

Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing

100037, China c

Institute of Earth Sciences, China University of Geosciences, Beijing 100083, China

* Corresponding author: Tel: +86 10 8359 7706 E-mail address: [email protected]

ABSTRACT The peripheral or exterior subduction is known to drive the breakup of Rodinia; however, the geodynamic driving mechanism remains controversial, which may result from the slab retreat or the slab avalanche-induced superplume impingement. We report here new constraints on the Neoproterozoic tectonic process whether the northern Tarim Craton at the NW margin of Rodinia was subduction- or mantle plume-dominated that further sheds light on how the peripheral subduction drove the Rodinia breakup. A tectonic transition from the Cryogenian arc and backarc rift to the Ediacaran passive margin characterized northern Tarim, as indicated by the distinct

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detrital zircon geochronological, geochemical, and structural-sedimentary features between the Ediacaran and Cryogenian sequences. This rejects the mantle plume-dominated evolution, but supports a Neoproterozoic evolving subduction process at the northern Tarim margin, where an advancing subduction (830-780 Ma) evolved into a retreating subduction (<780 Ma) in response to the retreat of the subducting Pan-Rodinia oceanic slab. The retreat-induced backarc rifting resulted in the opening of the northern Tarim rift between 760 and 740 Ma and the Cryogenian to Ediacaran tectonic transition. The peripheral subduction along the northern Tarim margin had thus caused no rifting before 780 Ma, which was also impossible to induce the >780 Ma rifting events in the supercontinent interior. These findings imply a composite peripheral subduction-driving mechanism for the Rodinia breakup. The slab retreat probably occurred as the dominant breakup driving force at the supercontinent margins, with less impact to the supercontinent interior; however, another geodynamic driver such as the deep subduction-induced plume impingement may account for the interior rifting and breakup. In addition, a zircon U-Pb age of 636±2 Ma obtained from tufflava constrains the Tereeken diamictite to correlate with the Marinoan glaciation that further indicates a rapid and globally synchronous termination of the Neoproterozoic “Snowball Earth”. Keywords: Neoproterozoic, peripheral subduction, driving mechanism, Rodinia breakup, rifting, Tarim

1. Introduction

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Multicycle assembly and breakup of supercontinents are known to characterize the Earth since the Archean. Specifically, the assembly and breakup of Rodinia have profound impact on the teconic, sedimentary, climate, and biological evolutions of the major cratons during the Neoproterozoic (Hoffman et al., 1998; Hoffman, 1999; Li et al., 2008, 2013; Cawood et al., 2010, 2016; Zhao et al., 2018). Unraveling the mechanism and process of the Rodinian assembly and breakup is, therefore, of great significance in understanding the evolutions of the various earth spheres. It is generally thought that the peripheral or exterior subduction zones would form around the supercontinent such as Rodinia, Gondwana, and Pangea in response to the global plate kinematic adjustments after the collision and aggregation of the constituent continents (Collins and Pisarevsky, 2005; Cawood and Buchan, 2007; Cawood et al., 2016). In other word, the convergence or subduction had migrated from between the aggregating continents to the supercontinent margins. Multiperiod rifting events were induced by this peripheral subduction, i.e., top-down process (Murphy and Nance, 2003, 2013), leading to the final breakup of Rodinia during the Cryogenian to Early Cambrian (Li et al., 2008, 2013; Cawood et al., 2016; Zhao et al., 2018). However, controversy remains in the geodynamic driving mechanism of breakup related to the peripheral subduction. It may result from the retreat of the subducting slab, which made the overlying supercontinent in an extension state and experience rifting; meanwhile, the plume-related magmatic activities were minor and localised in time and space (Cawood et al., 2016 and references therein). Alternatively, the multiperiod superplume activities, resulting from the subducted slab avalanches in the

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core-mantle transition zone and the thermal insulation of both the subducted slabs and overlying supercontinent, accounted for the supercontinent breakup and widespread plume-related magmas (Li et al., 2008, 2013; Nosova et al., 2011; Zhang et al., 2018). As one of the major cratons in China, the Tarim Craton has been demonstrated to be extensively involved in the assembly and breakup processes of Rodinia (Fig. 1a-c; Zhang et al., 2007, 2009, 2010, 2013, 2019; Lu et al., 2008; Xu et al., 2013a, b; Ge et al., 2014; Gao et al., 2015; Ren et al., 2018; Zhao et al., 2018). Most of the paleomagnetic data and supercontinent reconstruction results show that the Tarim Craton was located at the northwestern margin of Rodinia during the Neoproterozoic (Fig. 1b; Li et al., 2008, 2013; Ge et al., 2014; Zhao et al., 2014, 2018; Tang et al., 2016; Zhang et al., 2019), although an alternative “missing-link” location at the heart of Rodina was proposed recently by Wen et al. (2017, 2018). This implies that it may record both the peripheral subduction and interior rifting events of Rodinia. Moreover, a dispute between plume- and subduction-based models has been long-standing for the Neoproterozoic tectonic evolution at northern Tarim (e.g. Zhang et al., 2007, 2009, 2011a, b, 2013; Xu et al., 2013a, b; Ge et al., 2014; Tang et al., 2016; Ren et al., 2018). It is thus a better palce to reveal the breakup driving mechanism related to the peripheral subduction, i.e., plume or slab retreat for Rodinia. Integrated with the previous data, the Neoproterozoic sedimentary and magmatic records in the Quruqtagh region, northern Tarim (Figs. 1c and 2) are mainly focused in this paper to unravel the subduction- or mantle plume-dominated tectonic evolution of northern Tarim and how the peripheral subduction drove the Rodinia breakup.

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2. Geological setting The Tarim Craton, located in northwestern China, is surrounded by arcuate mountains to constitute a typical basin-mountain coupling system (Fig. 1a and c). Its northern and southern borders are the Tianshan Mountains and the West Kunlun-Altyn Tagh Mountains, respectively. It consists of the Eoarchean to early Neoproterozoic basement and the overlying Cryogenian to Cenozoic sedimentary sequences, with a prolonged and complicated evolution process (Lu et al., 2008; Xu et al., 2013b; Zhang et al., 2013, 2019; Lin et al., 2015; Ge et al., 2018). The unified Tarim basement formed by the amalgamation between the southern and northern Tarim blocks during the early Neoproterozoic (ca. 825 Ma; Xu et al., 2013b; Zhang et al., 2019). Intense rifting, magmatic, and sedimentary activities subsequently occurred in response to the Rodinia breakup from the Cryogenian to Ediacaran (Fig. 3a-c; Lu et al., 2008; Xu et al., 2013b; Lin et al., 2015; Ren et al., 2018; Zhang et al., 2019). It should be noted that the Cryogenian (herein ca. 740-635 Ma) and Ediacaran (635-542 Ma) are also correspondingly known as the Nanhua and Sinian periods in China. The Quruqtagh region at northeastern Tarim has extensive Neoproterozoic plutonic and volcanic outcrops and thus, is a key place for unraveling the magmatic activities and tectonic evolution (Figs. 1c and 2). Previous geochronological data have revealed that the Neoproterozoic magmatism concentrated in three major episodes: 1) 830-780 Ma episode that consists of adakitic and I-type granitoids as well as mafic-ultramafic-carbonatite complex; 2) 780-720 Ma episode that is predominated

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by mafic dykes, bimodal volcanic and intrusive rocks, mafic-ultramafic complex, and A-type granites; and 3) 660-600 Ma episode that includes quartz syenites, syenogranites, S-type granites, mafic dykes, and intermediate-mafic volcanics (Zhang et al., 2007, 2009, 2011a; Zhu et al., 2008, 2011; Xu et al., 2009, 2013a, b; Gao et al., 2010; Cao et al., 2011, 2014; Long et al., 2011; Ge et al., 2012, 2014; He et al., 2014a, 2019; Tang et al., 2016; Chen et al., 2017; Xiao et al., 2019). These mafic to felsic magmatic rocks generally show LILEs enrichment and HFSEs depletion resembling those in the subduction setting. However, they have been employed to support the disctinct mantle plume (Zhang et al., 2007, 2009, 2013; Long et al., 2011; Xu et al., 2013b) and subduction models (Ge et al., 2014; Tang et al., 2016; Chen et al., 2017) for the Neoproterozoic tectonic evolution at northern Tarim. The Neoproterozoic rift should thus be correspondingly generated by the plume and subduction activities. The Quruqtagh region also has a relatively intact Neoproterozoic rift sequence in a thickness up to 6000m (Figs. 2 and 3a). It is unconformably underlain by the Tonian Pargangtag group and the ca. 780 Ma granites crosscut by 773 Ma mafic dykes (Zhang et al., 2009; Long et al., 2011). The Beiyixi Formation at the bottom is featured by a rapidly fining-upward sequence, and 740 Ma bimodal volcanics in a thickness up to 1000m occur at the lower part (Xu et al., 2009), probably marking the rifting peak. The presence of volcanics at the upper part of the Altungol and Tereeken formations further suggests intense Cryogenian rifting (Xu et al., 2009; He et al., 2014a). The rifting may have diminished in the Ediacaran, and the volcanics are observed locally. The Ediacaran sequence has parallel or angular and parallel

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unconformable contacts with the Cryogenian sequence and the Early Cambrian Xishanbrak Formation, respectively. These features, together with the seismic data in the interior of the Tarim basin, have revealed a typical dual structure with distinct structural and sedimentary characteristics for the Neoproterozoic rifts (Ren et al., 2018; Wu et al., 2018). The Cryogenian rifting basin has a wedge-shaped rapid filling structure, and the Ediacaran depression is occupied by extensive overlapping sediments. Moreover, the Beiyixi, Altungol, Tereeken, and Hankalchough diamictite-cap carbonate couplets have been proposed to correlate with the multiperiod global or regional glaciations related to the Neoproterozoic “Snowball Earth” event, although controversy remains in the age of the Tereeken diamictite (Fig. 3a; Xiao et al., 2004; Xu et al., 2009; Gao et al., 2010; He et al., 2014a).

3. Sampling and analytical methods As mentioned above, a large number of geochronologic and geochemical data have been reported on the Neoproterozoic magmatic and sedimentary rocks in the Quruqtagh region. Here we performed complementary analyses on volcanics in the Tereeken and Xishanbrak formations and the Ediacaran clastic rocks to systematically discuss the Neoproterozoic tectonic evolution at northern Tarim. 3.1. Sampling 3.1.1 Volcanics The volcanic samples were collected at the Qiakmaktieshi section to the north of the Xingdi Fault (Fig. 2). The Tereeken Formation has a thickness of about 500m that

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consists mainly of massive or layered diamictites, siltstones, and mudstones. Dropstones occur occasionally, indicating ice-raft facies for the diamictites (Fig. 4a). Dull gray-green intermediate to mafic volcanic and pyroclastic rocks including breccia-conglomerate lava and tufflava are present at the upper part, whose thickness reaches above 100m at some places (Figs. 3a and 4b). They were then overlain by the diamictites and cap carbonates in an ascending order (Figs. 3a and 4c). The tufflava sample was located about 70m below the cap carbonate (N41°26′2.40ʺ, E87°48′14.04ʺ), and has a porphyritic texture with <5% phenocrysts of quartz and feldspar. The Xishanbrak Formation at the bottom of the Lower Cambrian disconformably overlies the diamictite-cap carbonate couplet of the Ediacaran Hankalchough Formation (Figs. 3a). Its lower part is composed of phosphorus-bearing silicolites interbedded with mafic volcanics, and the upper part is predominated by silicolites. The volcanics have a varying thickness from 0 to 200m in different outcrops. A basalt sample was collected at the bottom of the Xishanbrak Formation (Fig. 4d; N41°18′12.72ʺ, E87°45′14.10ʺ). It has a greyish-green appearance but a gray-black fresh part, ophitic or intersertal-intergranular textures, and local carbonatization with penetration of calcite veins. Secondary mineral alterations were recognized in thin sections (Fig. 4e). Pyroxene is mostly replaced by chlorite and epidotite. Plagioclase is commonly subjected to sericitization and clayzation and thus, in a turbid appearance. Carbonatization occasionally occurs. However, it is noteworthy that the volcanics have not

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experienced deformation. 3.1.2 Clastic rocks The clastic rock samples were also collected at the Qiakmaktieshi section (Fig. 2). The sampled sequences include the Zhamokti, Yukengou, and Shuiquan formations. The

Zhamokti

Formation

consists

mainly

of

sandstones,

siltstones,

and

silty mudstones, and cap carbonate occurs at the bottom; the Yukengou Formation is occupied by fine-grained clastic deposits of neritic facies; and the Shuiquan Formation is mainly composed of neritic carbonate and clastic deposits. Fine-grained sandstone samples were collected near the bottom of the Zhamokti and Yukengou formations and the top of the Shuiquan Formation (Fig. 3a). In general, the Ediacaran sandstone samples consist of quartz (>70%) and minor detritus, feldspar, muscovite, and epidotite (Fig. 4f-h). 3.2. Analytical methods 3.2.1 Zircon U-Pb geochronology Zircon grains were selected by conventional heavy liquid and magnetic techniques, and were then mounted in epoxy resin and polished to expose the center. Subsequent to photographing under a microscope, Cathodoluminescence (CL) images were acquired using a Scanning Electron Microscope for further analysis of the internal structures and the determination of dating domains. Zircon laser ablation-inductively coupled plasma-mass spectrometer (LA-ICP-MS) U-Pb dating was performed on an Agilent 7500a ICP-MS connected to an 193 nm excimer laser ablation system of American New Wave UP 193SS at China University

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of Geosciences, Beijing. The spot diameter was 25 or 36 μm, and the analytical laser frequency was 10Hz. Zircon 91500 was used as standard to calculate U-Pb ages, and zircon 91500B (1065.4±0.6 Ma, Wiedenbeck et al., 1995) and QINGHU (159.5±0.2 Ma, Li et al., 2013) were used as monitoring standard with analytical weight mean ages of 1062.8±4.8 and 161.8±1.4 Ma, respectively. Common Pb corrections were made according to Anderson (2002). The weighted mean U-Pb ages and concordia plots and ages at 2σ level were all processed using the software ISOPLOT (Ludwig, 2003). Analyses with >10% discordance were excluded in age plotting and calculation. 3.2.2 Whole-rock major and trace elements Rock samples were carefully selected, crushed, and then ground to a particle size below 200 mesh (~80 μm). Major and trace elements were acquired at the Acme Analytical Laboratories Ltd., Canada. Abundances of major oxides were obtained on a 0.2 g sample analyzed by ICP-emission spectrometry following a lithium metaborate/tetraborate fusion and dilute nitric digestion. Loss on ignition (LOI) is weight difference after ignition at 1000 °C. Rare earth and refractory element abundances were determined by ICP-MS with the same procedure as major oxides. Another 0.5 g split was digested in aqua regia and analyzed by ICP-MS to report precious and base metals including Pb. Duplicate analyses of the samples and standards (SO-18, DS8, and OREAS45CA) yielded relative standard deviations <10% for most trace elements and <20% for V, Cr, Co, Ni, Th, and U. The related diagrams were plotted in the software Minpet.

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4. Results 4.1. Zircon U-Pb ages Representative CL images are given in Fig. 5. Zircon LA-ICP-MS U-Pb age data of the volcanic and clastic rocks are listed in Supplementary Tables 1 and 2, respectively. 4.1.1 Volcanics The majority of zircons from the tufflava sample (KL-12) of the Tereeken Formation are euhedral or subhedral, and show clear oscillatory zoning on CL images, suggesting a magmatic origin. 30 analyses were performed on these oscillatory zonings, 26 of which yield a weighted mean

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Pb/238U age of 636±2 Ma (n = 26,

MSWD = 0.098) that represents the age of the tufflava (Fig. 6a). The other four analyses of 740-671 Ma have a large deviation from the main age population, and are possibly attributed to the capture of older zircons from the wall rock. Zircons from the basalt sample (KL-4) of the Xishanbrak Formation have multiple structures that indicate a variety of origins (Supplementary Figure 1). 9 analyses with ≤10% discordance range from 734 to 265 Ma, in which four analyses with Th/U ratios of 0.77-0.54 give a weighted mean

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Pb/238U age of 541±6 Ma (Fig. 6b; n = 4,

MSWD = 0.083). Though not valid enough, this age is nearly consistent with the potential deposition age of the Xishanbrak Formation at the bottom Lower Cambrian and thus, represents the formation age of the basalt. The 734 Ma grain (Th/U = 0.47) is identified as xenocryst, and the other dispersive ages with low Th/U ratios (0.44-0.15) may result from Pb loss or contamination.

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4.1.2 Clastic rocks Detrital zircons from the Zhamokti (KL-37), Yukengou (KL-20), and Shuiquan (KL-24) sandstone samples are largely rounded, with length to width ratios of 1:1 to 2:1. On CL images, the zircons show various internal structures, including sector, annular, and banded oscillatory zonings as well as homogeneous structure. The zircon grains were analyzed randomly, avoiding inclusion and fractures, for wholly obtaining the crystallization ages and reducing the analytical biases (e.g. selection of old versus young zircons). 281 analyses with ≤10% discordance from the three sandstone samples yield an age range from 2747 to 601 Ma. The zircon ages overall show a multimodal distribution pattern with main peak ages at ca. 1900 and 830 Ma as well as minor peak ages between 766 and 721 Ma (Fig. 7). The zircon sources for the ca. 1900 Ma population include magmatic (high Th/U >0.2) and metamorphic (low Th/U <0.2) rocks, and the other populations are mainly derived from magmatic rocks (high Th/U >0.2). 4.2. Major and trace elements of bulk-rock samples Major (wt.%) and trace element (ppm) compositions of the bulk-rock samples are listed in Supplementary Table 3. The sandstone samples of the Zhamokti, Yukengou, and Shuiquan formations have similar major and trace element features. The major element contents and ratios are characterized by minor variations, with SiO2 of 78.26-84.68 wt.%, MgO of 0.41-1.09 wt.%, Fe2O3 of 1.57-4.07 wt.%, Al2O3 of 7.47-10.77 wt.%, CaO of 0.15-0.27 wt.%, TiO2 of 0.25-0.44 wt.%, and K2O/Na2O ratio of 0.4-0.7. The small variation is also present for the immobile trace elements

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during the late weathering and metamorphic processes, including Th (3.8-6.4 ppm), Sc (4-6 ppm), Co (1.9-5.0 ppm), Zr (usually >200 ppm), Hf (2.8-7.7 ppm), and REEs (La=13.9-19.5 ppm).

5. Discussion 5.1 New age constraint on the Neoproterozoic Tereeken diamictite and its correlation The Quruqtagh region at northern Tarim is a typical place where four layers of Neoproterozoic diamictites have been intactly preserved on the Earth (Fig. 3a). These diamictites mark the global or regional glaciations of the Neoproterozoic “Snowball Earth” (Xiao et al., 2004; Xu et al., 2009; He et al., 2014a). Previous geochronological data of the volcanics have confined the Beiyixi, Altungol, and Hankalchough diamictites to form at 740-725, 725-655, and 615-541 Ma that correspond to the Kaigas, Sturtian, and Gaskiers glaciations, respectively (Xu et al., 2009; Gao et al., 2010; He et al., 2014a). Controversy remains in the age of the Tereeken diamictite and its global correlation. A zircon U-Pb age of 705±10 Ma was reported for the pillow basalt at the top of the Tereeken Formation in the Moheershan section (Gao et al., 2010); however, it contradicts with both the ca. 655 Ma volcanics of the underlying Altungol Formation and the ca. 615 Ma volcanics of the overlying Zhamokti Formation (Fig. 3a; Xu et al., 2009; He et al., 2014a). It thus probably represents the age of zircon xenocrysts in the basalt. In this study, a reconcilable zircon U-Pb age of 636±2 Ma has been obtained from the tufflava at the upper Tereeken Formation in the Qiakmaktieshi section (Figs. 2 and 6a). This new age

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constrains that the Tereeken diamictite formed between 655 and 636 Ma, and is temporally identical to the ca. 650-635 Ma Nantuo diamictite in South China (Fig. 3a and d; Condon et al., 2005; Bao et al., 2018). The Tereeken diamictite, therefore, marks the Neoproterozoic global Marinoan glaciation. This correlation is consistent with the Marinoan-type δ13C chemostratigraphic pattern (i.e., ca. -5‰ at the base and slightly decreasing upsection) of the cap dolostone overlying the Tereeken diamictite (Xiao et al., 2004). Meanwhile, the rapid and globally synchronous termination of the Marinoan glaciation is further evidenced by the 636±2 Ma tufflava age at the upper Tereeken Formation (this study) in the low-middle latitude Tarim Craton (Li et al., 2013; Zhao et al., 2014, 2018) together with the coincident volcanic ages from the glacial-postglacial transitional strata throughout the high to low latitudes (635.5±1.2 Ma at the upper Ghaub diamictite in Namibia, Hoffmann et al., 2004; 635.2±0.6 Ma at 2 m above the Nantuo diamictite in South China, Condon et al., 2005; 636.4±0.5 Ma at the uppermost Cottons Breccia Formation in South Austrilia, Calver et al., 2013). More specifically, the presence of tens of meters-thick sediments of ice-raft facies between the 636±2 Ma volcanics and the cap carbonate (Figs. 3a and 4a, c) suggests a high accumulation rate and thus rapid deglaciation in a short duration. 5.2 Evidence for the Cryogenian to Ediacaran tectonic transition The magmatic rocks have long been employed as a robust tool for unraveling the Neoproterozoic tectonic evolution at northern Tarim. However, there remains a currently unsolvable dispute on the interpretation of tetctonic setting, i.e., mantle

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plume or subduction for the Neoproterozoic magmatic rocks that generally show LILEs enrichment and HFSEs depletion (Zhang et al., 2007, 2009, 2011a; Long et al., 2011; Ge et al., 2012, 2014; Xu et al., 2013b; Tang et al., 2016; Chen et al., 2017). The alternative sedimentary evidence is thus employed in an attempt to constrain the tectonic evolution. As discussed below, a tectonic transition from the Cryogenian arc and backarc rift to the Ediacaran passive margin has been first indicated by the distinct geochronological, geochemical, and structural-sedimentary features between the Ediacaran and Cryogenian sequences in northern Tarim. 1) Detrital zircon geochronology. Detrital zircon ages of clastic rocks are capable of reflecting the tectonic setting of a sedimentary basin by plotting the distribution of difference between the crystallization age of individual detrital zircon grains and the deposition age of the sediment (Cawood et al., 2012). This method is particularly useful for the ancient basins that have been intensely reworked to obscure the basin prototype. In the Quruqtagh region, abundant zircon U-Pb ages of volcanics enable to determine the deposition ages of the Neoproterozoic sequences. The Beiyixi Formation has an initial deposition at ca. 740 Ma, as constrained by the 740-739 Ma bimodal volcanics at the lower part (Fig. 3a; Xu et al., 2009; Gao et al., 2010). Deposition ages of >656, 636-615, <615, and 615-580 Ma are correspondingly confined for the Altungol, Zhamokti, Yukengou, and Shuiquan formations by the 656-615 Ma volcanics (Xu et al., 2009; He et al., 2014a; this study) and the probable correlation of the Hankalchough diamictite to the ca. 580 Ma Gaskier glaciation (Fig. 3a). Herein the maximum or average deposition ages, i.e., 660, 625, 615, and 600 Ma

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were adopted respectively. Geochronological results show that the detrital zircon age spectra of the Ediacaran clastic rocks in Quruqtagh are similar to those in the rift and post-rift passive margin, in other word, the detrital zircon ages are much older with less than 5% within 150 Ma of the deposition age (Figs. 8 and 9; Cawood et al., 2012). On the contrary, the Cryogenian clastic rocks are characterized by detrital zircon age spectra with a high proportion of ages close to the deposition age (< 150 Ma) and minor older grains (<50%), resembling those in the arc and backarc basins at convergent margin (Figs. 8 and 9; Zhang et al., 2011c; He et al., 2014a). The backarc basin is further preferred by the bimodal age spectra and a higher proportion of older zircon ages (Fig. 8). This is because that the forearc and trench basins in the arc system usually have unimodal age spectra, whereas the backarc basins have increasing input of older detritus from the adjacent craton (Cawood et al., 2012). Notably, it appears that the age peaks of the Cryogenian and Ediacaran clastic rocks are similar, suggesting a common source from the two major magmatic-metamorphic event groups in northern Tarim (1900 and 830-720 Ma); however, the latter shows increasing older age proportions and difference values between the crystallization and deposition ages (Figs. 8 and 9). These differences are unlikely to simply result from the difference in deposition ages because if the Cryogenian and Ediacaran clastic rocks formed in a same tectonic setting, subduction for instance, a similar high proportion of zircon ages close to the deposition age is expected to occur in response to the widespread synsedimentary arc magmatism. The presence of minor younger magmatic zircons close to the deposition age in the Ediacaran sequences is thus

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inconsistent with a subduction setting but compatible with the small-scale magmatic activity in passive margin, just as the fewer Ediacaran magmatic outcrops in northern Tarim (Xu et al., 2013a; Ge et al., 2014). The detrital zircon age differences, therefore, probably reflect the change of tectonic setting from the Cryogenian to Ediacaran. 2) Geochemical characteristic. The major and trace elements of clastic rocks have also been frequently employed to constrain the tectonic setting in which the basin forms (e.g. Bhatia, 1983; Bhatia and Crook, 1986; Roser and Korsch, 1986; McLennan, 1993; Spalletti et al., 2008; Verma and Armstrong-Altrin, 2013). The Hf, Zr/Sc, Th/Sc, La/Th, La/Sc, and Co/Th values indicate that the Neoproterozoic clastic rocks in the Quruqtagh region are mostly sourced from felsic rocks, with partial contribution of recycling sediments (Fig. 10a). Specifically, the Ediacaran clastic rocks show a more obvious sedimentary recycling feature. The sandstones of the Zhamokti, Yukengou, and Shuiquan formations have high SiO2 and Zr values and low Co content resembling those in the passive margin (Fig. 10b-e; this study). In contrast, the Cryogenian sandstones have subduction-related major and trace element features, as indicated by the plotting in active continental margin or arc regions of the various tectonic discrimination diagrams (Fig. 10b-e; Zhang et al., 2011b). This is consistent with the correspondingly low and high SiO2 and K2O/Na2O values of the Cryogenian and Ediacaran clastic rocks as well as the increasing SiO2/Al2O3 value from the Cryogenian to Ediacaran in the Aksu region, NW Tarim (Figs. 3b and 10; Ding et al., 2015). As a whole, the increase in SiO2, SiO2/Al2O3, K2O/Na2O, and Zr values reflects an increase in composition maturity of the younger clastic rocks (i.e., more quartz and

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zircon) that are compatible with the tectonic transition from the Cryogenian active margin to the relatively stable Ediacaran passive margin. Otherwise, immature sediments would form in response to the intense tectonic and magmatic activities if the Cryogenian subduction continued to the Ediacaran. 3) Structural-sedimentary pattern. Besides the above constraints from outcrops, seismic and drilling well data in the interior of the Tarim basin are integrated to further reveal the tectono-sedimentary transition from the Cryogenian to Ediacaran. Seismic reflections and drilling stratigraphic columns overall show that the Cryogenian and Ediacaran sequences have a typical dual structure with distinct structural and sedimentary patterns in northern Tarim (Figs. 3a, b and 11). The Cryogenian sequence occurs as a nearly EW-striking narrow band in the plane (Fig. 1c; Ren et al., 2018; Wu et al., 2018), and is dominated by a series of grabens or half grabens to form a

wedge-shaped

structure

in profile

(Fig. 11a). This

structural-sedimentary pattern, together with the rapidly fining-upward deposits and bimodal volcanics (in a thichness up to 1000m) in outcrops, argues for the presence of rifting activities in northern Tarim during the Cryogenian. The Cryogenian sequence is thus likely to form in a backarc rift at convergent margin in view of the subduction-related detrital zircon age and geochemical features. On the contrary, the Ediacaran sequence is characterized by extensive overlapping sediments in small thickness and wide distribution onto both the Cryogenian sequence and cratonic basement (Fig. 11a and b) that should deposit in a relatively stable setting. Especially, the widespread late Ediacaran carbonates in the basin interior and outcrops (Figs. 3

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and 11b) are indicative of the presence of a passive margin. In general, the distinct structural-sedimentary patterns between the Cryogenian and Ediacaran sequences support the tectonic transition from the Cryogenian arc and backarc rift to the Ediacaran passive margin. Moreover, it needs to be emphasized that the Cryogenian to Ediacaran tectonic transition is consistent with the distinct geochemical features between the Cryogenian and Ediacaran magmatic rocks in northern Tarim. The Cryogenian mafic dykes, mafic-ultramafic complex, and bimodal magmatic rocks show generally pronounced Nb-Ta negative anomalies that are typical of the subduction-related magma (Xu et al., 2005; Zhang et al., 2009, 2012; Tang et al., 2016; Chen et al., 2017), in contrast to the oceanic island basalt (OIB)-type geochemical characteristics with no obvious Nb-Ta negative anomalies of the Ediacaran basalts (Xu et al., 2013a; Ren et al., 2018) that are compatible with an intraplate passive margin setting. 5.3 A Neoproterozoic evolving subduction system at the northern Tarim margin Competing models have been proposed for the Neoproterozoic tectonic evolution at the northern margin of the Tarim Craton, in which it may be predominated by the mantle plume activities (Zhang et al., 2007, 2009, 2013; Long et al., 2011; Xu et al., 2013b) or occurred as a constituent part of the circum Rodinia subduction system (Ge et al., 2014; Tang et al., 2016; Chen et al., 2017). Combined with the regional data, the latter subduction model is overall preferred in this study; however, the Cryogenian to Ediacaran tectonic transition argues for an evolving subduction process at the northern Tarim margin.

19

Most of the paleomagnetic and geological evidence indicates that the Tarim Craton was located at the northwestern margin of Rodinia with the northern part facing the Pan-Rodinia Ocean (also known as the Mirovoi Ocean) during the Neoproterozoic (Fig. 1b; Zhan et al., 2007; Li et al., 2013; Zhao et al., 2014, 2018; Tang et al., 2016; Chen et al., 2017; Zhang et al., 2019). The circum Rodinia subduction system had formed along the northern Tarim margin as early as 900 Ma (Ge et al., 2014; He et al., 2019) in response to the Rodinia assembly and global plate kinematic adjustment (e.g. Li et al., 2013; Cawood et al., 2016). A “missing-link” model with the Greater Tarim Block at the heart of Rodinia has also been recently proposed (Wen et al., 2017, 2018). However, this model is largely paleomagnetic data-based, and has trouble in explaining: 1) the presence of the Neoproterozoic Aksu blueschist at NW Tarim that reflects the subduction of an oceanic slab to experience high-P metamrohism between 790 and 760 Ma (Zhang et al., 2009, 2014; Lu et al., 2017); 2) the 830-790 Ma high-pressure granulite facies metamorphism under peak conditions of 700-810℃ and 1.0-1.2 GPa at NE Tarim that probably resulted from the rapid burial of arc basalts and surface sedimentary rocks in a subduction setting (He et al., 2012; Ge et al., 2016); and 3) the subduction-related detrital zircon age and geochemical features of the Cryogenian clastic rocks that formed in a backarc rift at convergent margin (this study). All these geological data indicate a prolonged duration of the Neoproterozoic subduction along the northern Tarim margin at least until 760 Ma, even throughout the Cryogenian. This supports a peripheral position with the presence of a wide oceanic basin to the north (present coordinate) for Tarim, contradicting with

20

the assumption of an interior position. Therefore, subsequent to the amalgamation between the northern and southern Tarim blocks that formed the unified Tarim Craton (Xu et al., 2013b; Zhang et al., 2019), the northern Tarim margin was occupied by a southward advancing subduction-accretion system between 830 and 780 Ma (Fig. 12a; Ge et al., 2014), as marked by the arc magmatic activities peaking at 830-780 Ma (Zhang et al., 2007; Long et al., 2011; Xu et al., 2013b; Ge et al., 2014), the 820-790 Ma high-pressure granulite facies metamorphism (He et al., 2012; Ge et al., 2016), the 800-790 Ma thickened crust-derived adakitic granitoids (Long et al., 2011), and the 790-760 Ma high-P metamrohism of the Aksu blueschist (Zhang et al., 2009, 2014; Lu et al., 2017). In view of the presense of blueschist-bearing accretionary complex in the Aksu region, the NW Tarim margin should lie more approximate to the circum Rodinia subduction zone than the Quruqtagh region where arc plutons had a wide distribution (Fig. 12a). The advancing subduction-accretion process is further supported by the abrupt increase in melting pressure and decrease in primary magma temperature of the Quruqtagh granitoids at ca. 820 Ma (Ge et al., 2014 and references therein). This remarkable temperature reduction, nevertheless, argues against the presence of mantle plume activites that should result in a synchronous temperature rise at northern Tarim (e.g. Zhang et al., 2007, 2009; Long et al., 2011; Xu et al., 2013b). The emergence of 773-759 Ma mafic dyke swarms (Zhang et al., 2009) marked that the northern Tarim Craton began to experience extension since ca. 780 Ma (Fig. 12b). A persistent subduction of the Pan-Rodinia oceanic slab beneath northern Tarim is

21

indicated by the subduction-related detrital zircon age and geochemical features of the Cryogenian clastic rocks (Figs. 8-10). The transition from the previous compression to extension thus probably resulted from the retreat of the subducted Pan-Rodinia oceanic

slab,

with

the

replacement

of

the

advancing/compressional

by

retreating/extensional subdution. It needs to be emphasized that the emplacement of the Aksu blueschist and intrusion by 760 Ma mafic dykes (Zhang et al., 2009, 2014) imply a probable termination of subduction in the Aksu region; however, the subduction may migrate and continue to the north. The slab retreat-induced backarc rifting had the climax to initiate the northern Tarim rift in the early Cryogenian (Fig. 12c), as represented by the voluminous bimodal volcanics and rapidly fining-upward sequence of the Beiyixi Formation (Fig. 3a; 740-725 Ma, Xu et al., 2009). Moreover, the seismic data have revealed that the northern backarc rift extends in a nearly EW striking (present coordinate), perpendicular to the subduction direction, in the interior of the Tarim Basin (Fig. 1c; Ren et al., 2018; Wu et al., 2018). These subduction retreat and backarc rifting processes are consistent with the great decrease in melting pressure and increase in primary magma temperature of the Quruqtagh granitoids at ca. 740 Ma (Ge et al., 2014 and references therein) that probably indicate the presence of asthenosphere upwelling beneath northern Tarim. The northern Tarim Craton evolved into the passive continental margin stage during the Ediacaran (Fig. 12d), as indicated by the passive margin-type detrital zircon geochronological, geochemical, and structural-sedimentary features of the Ediacaran sequence (Figs. 8-10; this study). It may result from the persistent slab retreat and

22

oceanward migration of the backarc rifting center that led to the separation of the Middle Tianshan Terrane from Tarim and the opening of the South Tianshan Ocean as a composite backarc basin (Ge et al., 2014; Ren et al., 2017, 2018). The age data of the Dalubayi, Hongliuhe, and Yueyashan ophiolites show that the South Tianshan Ocean to the north of Tarim had existed from the Ediacaran to Cambrian (Fig. 1c; Yang et al., 2005; Zhang and Guo, 2008; Ao et al., 2012; Ren et al., 2017). More specifically, the Dalubayi ophiolite that formed in the oceanic island setting had corresponding zircon U-Pb ages of 590±11 and 600±15 Ma for the gabbro and basalt (Yang et al., 2005), suggesting the opening of South Tianshan Ocean prior to 600 Ma. The establishment of the Ediacaran to Cambrian passive margin is further supported by the OIB-type geochemical characteristics of the 615-541 Ma basalts in northern Tarim (Xu et al., 2013a; Ren et al., 2018). These intraplate magmatic events were likely attributed to either the mantle upwelling in the late stage of the superplume activity (Xu et al., 2013a) or the ongoing asthenosphere upwelling initiated by the previous backarc extension (Fig. 12d). An analogue to the Neoproterozoic backarc rifting process in northern Tarim is that of the late Mesozoic to Cenozoic backarc rifts in East Asia, which also show an oceanward migration in response to retreat of the subducting Pacific oceanic slab (e.g. Ren et al., 2002). In East Asia, the oceanward migration of the episodic backarc rifting successively gave rise to the formation of the late Jurassic to Cretaceous Songliao intracontinental rifting-depression basin, the development of the Paleogene Bohai Bay continental marginal basin, and the Neogene extension of the Japan Sea

23

and South China Sea (Ren et al., 2002). 5.4 Implications for the geodynamic driving mechanism of the Rodinia breakup It is generally thought that the peripheral subduction around supercontinent (the top-down process; Murphy and Nance, 2003, 2013) accounted for the final breakup of Rodinia (Li et al., 2008, 2013; Cawood et al., 2016). However, the breakup driving mechanism related to the peripheral subduction remains controversial. It may result from the retreat of the subducting slab that made the overlying supercontinent experience rifting (Cawood et al., 2016) or from the superplume impingement induced by avalanches of the subducted slab (Li et al., 2008, 2013; Nosova et al., 2011). The Tarim Craton at the northwestern Rodinia margin has recorded both the Neoproterozoic peripheral subduction and interior rifting events and thus, is an ideal palce to reveal the geodynamic driving mechanism of the supercontinent breakup. As shown by the North Atlantic margin and the Red Sea as well as the 2D numerical modeling results, the magmatic rifting (magmatism and dyke intrusion associated with LIP-large igneous province) often precedes the tectonic rifting (rift initiation and first sedimentation) by 1-20 Ma when the supercontinent rifts (Bialas et al., 2010). This time difference is inversely proportional to the rate of magmatic injection (Bialas et al., 2010). In Tarim, therefore, the Neoproterozoic northern backarc rift probably initiated between 760 and 740 Ma, as constrained by: 1) the 773-759 Ma mafic dyke swarms (Zhang et al., 2009) that unconformably underlie the Cryogenian rift sequences; and 2) the 740 Ma bimodal volcanics and >725 Ma fining-upward sequence of the Beiyixi Formation (Xu et al., 2009) that represent the earliest rift

24

depositions (Fig. 3a). However, the Neoproterozoic rifts have been advocated to have distinct initiation timing and spatial distribution in southern and northern Tarim (Fig. 1c; Ren et al., 2018; Wu et al., 2018). The southern rift probably initiated between 800 and 780 Ma, i.e., at least 20 Ma earlier based on: 1) the 802 Ma mafic dyke swarm and 783 Ma bimodal magmatic rocks at the southern margin of the Tarim Basin (Zhang et al., 2006, 2010); and 2) the >800 Ma deformed and metamorphic basement sequence and <800 Ma undeformed-unmetamorphic rift sequence (Fig. 3c; Zhang et al., 2016, 2019). As mentioned previously, the northern margin of the Tarim Craton was occupied by a southward advancing accretionary orogeny prior to 780 Ma (Fig. 12a). It means that only compressional stress was transmitted to the interior of the supercontinent, which impossibly led to synchronous rifting in the Tarim Craton and the supercontinent interior. The circum-Rodinia subduction along the northern Tarim margin had thus caused no rifting before 780 Ma. The 800-780 Ma magmatic and tectonic rifting events in southern Tarim, therefore, suggest the presence of another rifting driving mechanism, in which the mantle pume is a candidate. Actually, the early Neoproterozoic mantle plume activity has been confirmed by the OIB-type geochemical characteristics of the 800-780 Ma mafic dyke and gabbro (Zhang et al., 2006, 2010) as well as the geochemical features of the Cryogenian clastic rocks resembling those in continental rift (Tong et al., 2013). This plume impingement and accompanied rifting accounted for the opening of the southern Tarim rift and started the prelude of the fragmentation of Tarim from Rodinia. The northern Tarim margin evolved into a retreating accretionary system since 780 Ma (Fig. 12b). The backarc

25

rifting led to the initiation of the northern rift between 760 and 740 Ma and the subsequent tectonic transition from the Cryogenian backarc rift to the Ediacaran passive margin (Fig. 12c and d). As seen in Tarim, the rifting induced by the retreat of the subducting Pan-Rodinia oceanic slab was not widely distributed, in other word, the rifting centers were localised at the supercontinent margins, far from the interior (Fig. 13). This is consistent with the new numerical modeling result that the extensional stress induced by subduction retreat concentrates in a narrow zone at the supercontinent boundary and has far less impact to the supercontinent interior (Zhang et al., 2018). Globally, the initial Rodinia rifting (marked by the 825-820 Ma rift magmatism and depositions in South China, Wang and Li, 2003; Wang et al., 2007; Li et al., 2008, 2013) was preceded by the peripheral subduction initiation (marked by the 980-920 Ma Valhalla accretionary orogeny along the northeastern margin of Laurentia, Cawood et al., 2010, 2016) for at least 100 Ma. This provides sufficient time for the Pan-Rodinia oceanic slab to subduct into the deep mantle and even the core-mantle transition zone (D” layer) to induce superplume activities and subsequent interior breakup of the supercontinent (Fig. 13). Moreover, the plume push stress has been proven to be about three times larger than the stress generated by slab retreat at the center half of the supercontinent (Zhang et al., 2018). It is thus more feasible to drive the interior rifting and breakup through the plume push and the gravitational collapse caused by plume rise and heating (Fig. 13). As the Earth's most recent supercontinent, the multi-stage breakup process of Pangea demonstrates that mantle plume activities

26

play a pivotal role in continental breakup (Ernst et al., 2013, 2016). In Rodinia, the 780 Ma Gunbarrel magmatic event and the 720 Ma Franklin LIP in northwestern Laurentia have been proposed to be related to mantle plumes (Ernst et al., 2013, 2016). More prominently, the radiating Franklin dolerite dyke swarm converges towards the northern margin of Laurentia, marking a probable mantle plume centre and potential breakup margin (Ernst et al., 2013, 2016). These events may be temporally equivalent to rifting along the Laurentian margin, with the former associated with rifting during opening of the Paleo-Pacific Ocean (Harlan et al., 2003). Late Neoproterozoic magmatic activity (630-550Ma) along the East Laurentian margin has also been linked to a plume source based on the similarities to OIBs (Puffer, 2002). This plume event resulted in the breakup of the southeastern Laurentia margin and the opening of the Iapetus Ocean at ca. 600 Ma, though the rifting may have initiated as early as ca. 750 Ma (Cawood et al., 2001; Zhao et al., 2018). Admittedly, the slab retreat would assist the supercontinent breakup and occur as the dominant rifting force at supercontinent margins, just as the case of the Tarim Craton in this study (Figs. 12 and 13). This slab retreat-induced marginal rifting has also been demonstrated to account for the formation of backarc basins and ribbon-like microcontinents or terranes at the margins of Gondwana and Pangea (e.g. Stampfli et al., 2013). The Ganderia, Avalonia, and Hunia terranes were successively detached from Northern Gondwana to initiate the Rheic Ocean in response to the peripheral oceanic slab retreat from the Late Cambrian to Ordovician; the rollback of the Rheic oceanic slab to the north of the Galatian superterrane had triggered the opening of the

27

backarc rifts and the Paleo-Tethys Ocean since the Early Devonian; and the Cimmerian continent was rifted from Gondwana to open the Neo-Tethys backarc ocean by the retreat of the Paleo-Tethys oceanic slab during the initial breakup of Pangea in the Permian (Stampfli et al., 2013 and references therein). All these imply a more complicated and composite peripheral subduction-driving mechanism for the supercontinent breakup than the slab retreat or the plume impingement alone.

6. Conclusion 1) A zircon U-Pb age of 636±2 Ma was obtained for the tufflava at the upper part of the Tereeken Formation in the Tarim Craton. The Tereeken diamictite is thus constrained to form in response to the Marinoan glaciation, which further indicates a rapid and globally synchronous termination of the Neoproterozoic “Snowball Earth”. 2) The Ediacaran sequence has detrital zircon geochronological, geochemical, and structural-sedimentary features resembling those in the passive margin, whereas the Cryogenian sequence resembles those in the backarc rift. This distinction implies a tectonic transition from the Cryogenian arc and backarc rift to the Ediacaran passive margin at northern Tarim. 3) The northern Tarim margin was occupied by an early Neoproterozoic advancing subduction system (830-780 Ma) that evolved into a retreating subduction since 780 Ma. The backarc rifting induced by the Pan-Rodinia oceanic slab retreat accounted for the initiation of the northern Tarim rift between 760 and 740 Ma and the Cryogenian to Ediacaran tectonic transition.

28

4) A composite peripheral subduction-driving mechanism for the Rodinia breakup is demonstrated by the Neoproterozoic subduction and rifting processes in the northern Tarim Craton. The peripheral slab retreat may occur as the dominant rifting and breakup driving force at the supercontinent margins, with less impact to the supercontinent interior; however, another geodynamic driver such as the deep subduction-induced plume impingement probably accounted for the interior rifting and breakup.

Acknowledgement Thanks are given to Xiao-Bo Wang, Zhi-Lin Yang, and Duan Zhong for their help in the field investigation and photography. This work was supported by the National Key Research and Development Program of China (2017YFC0603101), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA14010101), and the PetroChina Company Limited program (2018A-01).

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Figure captions Fig. 1 (a) Simplified tectonic map of the Tarim Craton and adjacent regions with the approximate location of Fig. 1c; (b) location of the Tarim Craton in Rodinia at 800-750 Ma showing that its northern part faced to the Pan-Rodinia Ocean (modified after Zhao et al., 2018); and (c) sketch tectonic map of the Tarim Basin and adjacent areas (modified from Lu et al., 2008) with the approximate location of Fig. 2. The Neoproterozoic Tarim rifts are shown in (c) with a north-south differentiated spatial distribution (Ren et al., 2018; Wu et al., 2018).

Fig. 2 Geologic map of the Quruqtagh region at the northern Tarim Craton.

Fig. 3 Stratigraphic correlation of the Cryogenian and Ediacaran sequences in (a) the

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Quruqtagh and (b) Aksu regions at northern Tarim, (c) the Tiekelik region at southern Tarim, and (d) South China (according to Wang and Li, 2003; Zhao et al., 2014; Ren et al., 2018).

Fig. 4 Field photos (a-d) and photomicrographs (e-h, cross-polarized light) of the Neoproterozoic magmatic and clastic rocks in the Quruqtagh region, northern Tarim. (a) dropstone in diamictite of the Tereeken Formation; (b) tufflava at the upper part of the Tereeken Formation; (c) Tereeken diamictite

overlain by cap

dolomite at the bottom of the Zhamokti Formation; (d) basalt layer interbedded in silicalite at the bottom of the Xishanbrak Formation; (e) Tereeken tufflava; sandstone: (f) Zhamokti, (g) Yukengou, and (h) Shuiquan formations.

Fig. 5 Representative CL images of zircons from the Neoproterozoic to Cambrian magmatic and clastic rocks in this study. The three numbers for each zircon successively respresent spot number,

206

Pb/238U or

207

Pb/206Pb age, and Th/U

ratio. The scales are all 50 μm in length.

Fig. 6 U-Pb concordia diagrams of zircon ages for the (a) Tereeken tufflava and (b) Xishanbrak basalt.

Fig. 7 Combined U-Pb concordia and relative probability density-histogram plots of detrital zircon ages for the Neoproterozoic clastic rocks in this study.

Fig. 8 Normalized probability and histogram plots of detrital zircon U-Pb ages from the Neoproterozoic clastic rocks in the Quruqtagh region, northern Tarim. Data

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are compiled and listed with references (this study; Zhang et al., 2011c; He et al., 2014a) in Supplementary Table 2.

Fig. 9 Cumulative proportion plot of the difference between the crystallization age of detrital zircons and the deposition age of the Neoproterozoic sequences in the Quruqtagh region, northern Tarim. Data sources are as the same as those in Fig. 8.

Fig. 10 Major and trace element discrimination diagrams for the Neoproterozoic clastic rocks at northern Tarim. (a) Th/Sc-Zr/Sc (McLennan, 1993), (b) K2O/Na2O-SiO2 (Roser and Korsch, 1986), (c) high silica rock [(SiO2)adj=63-95 wt. %] major-element (Verma and Armstrong-Altrin, 2013), and (d) Th-Sc-Zr/10 and (e) Th-Co-Zr/10 (Bhatia and Crook, 1986). Data are compiled and listed with references (this study; Zhang et al., 2011b; Ding et al., 2015) in Supplementary Table 3.

Fig. 11 (a) seismic reflections and (b) drilling stratigraphic columns in the interior of the Tarim basin showing distinct structural-sedimentary patterns between the Cryogenian and Ediacaran sequences. The seismic section and drilling well locations are shown in Fig. 1c.

Fig. 12 Neoproterozoic to Cambrian tectonic evolution at the northern margin of the Tarim Craton. (a) 830-780 Ma: the northern Tarim margin was occupied by a southward advancing subduction that occurred as a constituent part of the circum Rodinia subduction system; (b) 780-760 Ma: the northern Tarim Craton began to

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experience extension in response to the retreat of the subducting Pan-Rodinia oceanic slab; (c) after 760 Ma: the slab retreat-induced backarc rifting had the climax to initiate the northern rift; (d) the Ediacaran to Cambrian: the northern Tarim margin evolved into a passive margin due to the persistent slab retreat and oceanward migration of the backarc rifting center. The section location is shown in Fig. 1b.

Fig. 13 A composite peripheral subduction-driving mechanism for the supercontinent breakup (modified after Zhang et al., 2018). The slab retreat probably occurred as the dominant rifting and breakup driving force at the supercontinent margins, whereas another geodynamic driver such as the plume impingement induced by deep subduction may account for the interior rifting and breakup.

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Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

A tectonic transition from the Cryogenian arc-backarc rift to Ediacaran passive margin characterized northern Tarim. The mantle plume-dominated evolution is rejected, but a Neoproterozoic evolving subduction process is supported. A composite Rodinia breakup mechanism includes slab retreat-driving marginal and plume-driving interior breakups.

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The 636±2 Ma tufflava age constrains Tereeken diamictite to correlate with the Marinoan glaciation.

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