Detrital Zircon U-Pb-Hf Isotopes of Middle Neoproterozoic Sedimentary Rocks in the Altyn Tagh Orogen, Southeastern Tarim: Insights for a Tarim-South China-North India Connection in the Periphery of Rodinia

The location of the Tarim craton during the assembly and breakup of the Rodinia supercontinent remains enigmatic, with some models advocating a Tarim-Australia connection and others a location at the heart of the uni ﬁ ed Rodinia supercontinent between Australia and Laurentia. In this study, our new zircon U-Pb dating results suggest that middle Neoproterozoic sedimentary rocks in the Altyn Tagh orogen of the southeastern Tarim craton were deposited between ca. 880 and 760 Ma in a rifting-related setting slightly prior to the breakup of Rodinia at ca. 750Ma. A compilation of existing Neoproterozoic geological records also indicates that the Altyn Tagh orogen of the southeastern Tarim craton underwent collision at ca. 1.0-0.9Ga and rifting at ca. 850-600 Ma related to the assembly and breakup of Rodinia. Furthermore, in order to establish the paleoposition of the Tarim craton with respect to Rodinia, available detrital zircon U-Pb ages and Hf isotopes from Meso- to Neoproterozoic sedimentary rocks were compiled. Comparable detrital zircon ages (at ca. 0.9, 1.3-1.1, and 1.7Ga) and Hf isotopes indicate a close linkage among rocks of the southeastern Tarim craton, Cathaysia, and North India but exclude a northern or western Australian a ﬃ nity. In addition, detrital zircons from the northern Tarim craton exhibit a prominent age peak at ca. 830Ma with minor spectra at ca. 1.9 and 2.5Ga but lack Mesoproterozoic ages, comparable to the northern and western Yangtze block. Together with comparable geological responses to the assembly and breakup of the Rodinia supercontinent, we o ﬀ er a new perspective of the location of the Tarim craton between South China and North India in the periphery of Rodinia.


Introduction
Most paleomagnetic studies, in agreement with plumerelated magmatic rocks and glacial intervals, support the placement of the Tarim craton to the north or west of Australia in Neoproterozoic reconstructions of Rodinia [1][2][3][4]. In contrast, some authors [5][6][7] argue for a "missing link" con-Musgrave and Albany-Fraser blocks of western-central Australia [10,11], challenging a Tarim-western Australia linkage (e.g., [3]). Furthermore, ca. 1.0-0.6 Ga magmatic rocks from the northern Tarim craton have recently been reinterpreted to correlate with a long-lived subduction event [8,9]. Such subduction-related magmatism without any Grenville-age unconformity or metamorphism indicates that the Tarim craton was probably located in the periphery of Rodinia with its northern margin facing the circum-Rodinia subduction zones [8,9], rather than at the heart of Rodinia [6,7]. In addition, the recognition of ca. 940-900 Ma syncollisional magmatism and metamorphism from the Altyn Tagh orogen of the southeastern Tarim craton supports to interpret that this orogen is the suture between the Tarim craton and another block during the amalgamation of Rodinia (e.g., [12][13][14][15][16]). However, the location of the Tarim craton in the periphery of Rodinia remains enigmatic and subsequent dispersal of the Tarim craton from Rodinia is not fully understood.
This study first reports on middle Neoproterozoic sedimentary rocks of the Altyn Tagh orogen of the southeastern Tarim craton, which were probably deposited in a riftingrelated setting slightly earlier than the breakup of Rodinia due to the opening of the Proto-Tethys Ocean at ca. 750 Ma (e.g., [3,17]). We suggest the placement of the Tarim craton between South China and North India with respect to Rodinia, based on a comparison of available detrital zircon age spectra and Hf isotope compositions.
The sampled outcrop contains rock associations of phyllite and quartz schist with prevailing cleavage and foliation ( Figure 2(b)). It is associated with early Paleozoic sedimentary sequences in the matrix of the Lapeiquan ophiolitic mélange (Figure 2(a)). Due to the poor quality of the outcrop, the relationship of this outcrop with early Paleozoic sedimentary sequences was difficult to establish in the field. Nonetheless, a tectonic contact is inferred (Figure 2 Detrital zircons extracted from sample 17LQ50-1A show subhedral, subrounded, and well-rounded forms with aspect ratios of 1-3 ( Figure 3). They illustrate predominantly oscillatory zoning and subordinately homogeneous internal structures under cathodoluminescence (CL; Figure 3). Th (2-1926 ppm) and U (12-2765 ppm) contents are conspicuously variable with Th/U ratios of mostly >0.2 (Table DR1 in the GSA Data Repository (GSA Data Repository item 201Xxxx, analytical methods and results (Tables DR1 and  DR2) and compiled data (Table DR3) are available online at http://www.geosociety.org/pubs/ft20XX.htm or on request from editing@geosociety.org.)), indicative of a magmatic origin. Only six analytical spots have low Th/U ratios of 0.01-0.10 (Table DR1 in the GSA Data Repository), reflecting their metamorphic origin, as also indicated by their complex, heterogeneous CL images ( Figure 3). For <1000 Ma and >1000 Ma zircons, the 206 Pb/ 238 U and 207 Pb/ 206 Pb ages were adopted, respectively. One analysis with an unreasonable minus error was deleted for discussion ( Table DR1 in Table DR2 in the GSA Data Repository).

Depositional Age
The youngest zircon (888 ± 7 Ma) from sample 17LQ50-1A shows a subhedral, prismatic form with abraded edges (Figure 3), suggesting transportation before deposition to some extent. It indicates that sample 17LQ50-1A might have been deposited at some time posterior to ca. 888 Ma. In addition, the Suolak Formation of the North Altyn Tagh subduction-accretion belt [28,29] provides a reliable estimate of its minimum age. The Suolak Formation consists of basalt, basaltic breccia and tuff, intermediate to felsic tuff, rhyolite, and chert, in which a SHRIMP zircon U-Pb age of ca. 763 Ma was obtained from a basalt [28] and a LA-ICP-MS zircon U-Pb age of ca. 750 Ma was obtained from a rhyolite [29]. The studied quartz schist is distinct from the volcanic and volcaniclastic sequences of the Suolak Formation ( Figure 5) and does not contain any detrital zircons from the ca. 760-750 Ma volcanic rocks of the Suolak Formation [29]. Therefore, the studied sample was probably deposited earlier than the ca. 760-750 Ma Suolak Formation. In conclu-sion, sample 17LQ50-1A was probably deposited between ca. 880 and 760 Ma.
3 Lithosphere supracrustal material at ca. 910 Ma [12], which was more likely related to syncollision. Recycling of Mesoproterozoic supracrustal material is also supported by ca. 1.9-1.4 Ga zircon Hf isotope model ages and coeval inherited zircon cores in some ca. 940-900 Ma granitic rocks [14,15]. On the other hand, an active continental margin is also difficult to reconcile with the lack of typical arc-like products in the Altyn Tagh orogen, such as mafic-intermediate magmatic rocks and calc-alkaline granitoids. In addition, comparable ca. 1.0-0.9 Ga magmatic rocks are also distributed throughout the adjacent Qilian and Qaidam regions [14,58]. Therefore, an early Neoproterozoic (ca. 1.0-0.9 Ga) collisional orogen characterizes the southeastern Tarim craton, which is coincident with the late assembly of the Rodinia supercontinent.
Following early Neoproterozoic final assembly, the interior of Rodinia underwent rifting-related extension at ca. 825-750 Ma, leading to the development of anorogenic magmatic rocks in most Rodinia terranes but not forming new oceans (e.g., [3]). The Rodinia supercontinent had not broken up until ca. 750-600 Ma due to the diachronous opening of relevant ocean domains [3,17,57]. Among these oceans, the Proto-Tethys Ocean separating Tarim, South China, and North China from other East Asian blocks was opened as early as ca. 750 Ma [3,17]. Ca. 760-750 Ma basalt and rhyolite associations in the North Altyn Tagh subductionaccretion belt (Figure 1(c); [28,29]) are coincident with the opening of the Proto-Tethys Ocean leading to the separation of the Tarim craton from Rodinia. The studied sample 17LQ50-1A deposited between ca. 880 and 760 Ma probably correlates with a rifting-related extensional setting prior to the separation of the Tarim craton from Rodinia. All these Neoproterozoic sedimentary and volcanic rocks of the North

Lithosphere
Altyn Tagh subduction-accretion belt were probably preserved in response to a well-preserved ca. 0.8-0.6 Ga rift depression throughout the Tarim basin [59]. Other geological records indicating middle-late Neoproterozoic extension in the Altyn Tagh orogen (Figure 1(c) (Figure 1(c)) could be a potential source for the ca. 910 Ma detrital zircons in the studied sample. Some ca. 1497-1470 Ma diabase dikes were documented in the Kuluketage area of the northeastern Tarim craton [62,63], but these mafic rocks might not have been the primary source material for the ca. 1.4 Ga detrital zircons in our studied sample because zircons typically crystallize from magmas with greater than 60% SiO 2 with much lesser abundance in lower silica magmas (e.g., [64] Figure 4). Notably, a zircon age peak at ca. 758 Ma in Cathaysia is absent in the southeastern Tarim craton because the studied sample was deposited prior to 760 Ma and unlikely contains such a young age peak at ca. 758 Ma. In addition, ca. 940-900 Ma collision operating within the southeastern Tarim craton is consistent with ca. 1.0-0.9 Ga collision recording in the Wuyi-Yunkai domains along southeastern Cathaysia (Figure 7; [52,65]). The ca. 820-710 Ma sedimentation and bimodal magmatism due to the Nanhua rifting across South China [66][67][68] also matches well with the rifting-related records of the southeastern Tarim craton (see the above section).
A connection between the northern Tarim craton and the northern and western Yangtze block is indicated by the same prominent age spectrum at ca. 830 Ma and minor spectra at ca. 1.9 and 2.5 Ga of detrital zircons ( Figure 6). Another age peak at ca. 2.6-2.7 Ga in the northern and western Yangtze craton probably reflects the importance of ca. 2.6-2.7 Ga crystalline basement in the Yangtze craton [69,70], which is relatively rare in the Tarim craton. Moreover, a ca. 1.0-0.6 Ga active continental margin along the northern Tarim craton [8,9] is comparable to the ca. 1.0-0.7 Ga Panxi-Hannan belt along the northern and western peripheries of the Yangtze block [71,72]. Together they probably belong to the Neoproterozoic accretionary orogen along the northern margin of Rodinia [9,71,73].
Collectively, a Tarim-South China linkage can be established in the periphery of Rodinia (Figure 7). South China was assembled by the connection of the Yangtze and Cathaysia blocks at ca. 820-800 Ma [68] and occupied a position adjacent to North India and western Australia with respect to Rodinia (Figure 7), based on comprehensive geologic, geochemical, geochronological, paleomagnetic, and faunal data [73]. We further suggest a location of the Tarim craton between South China and North India (Figure 7), according to the following lines of evidence.
First, a North Indian affinity for the southeastern Tarim craton is indicated by the similar age spectra (at ca.  Figure 6: Probability curves for detrital zircon ages from the southeastern Tarim craton (this study; [18,30]), the northern Tarim craton, and relevant Rodinia terranes (Table DR3 in the GSA Data Repository). N: number of analyses.
6 Lithosphere and 1.7 Ga) and ε Hf ðtÞ values for detrital zircons (Figures 4  and 6). This inference is also supported by the ca. 940-900 Ma collisional orogen in the southeastern Tarim craton, which is comparable to the ca. 990-900 Ma Eastern Ghats belt in India (Figure 7). In addition, the late Neoproterozoic strata in the Greater and Lesser Himalaya terranes were accumulated along the passive margin of North India [74,75]. Their age spectra at ca. 1.2-0.9 and 1.7 Ga are consistent with our results (Figure 6), further demonstrating the close linkage between the southeastern Tarim craton and Great India ( Figure 7). Furthermore, the ca. 1.4 Ga detrital zircons with positive ε Hf ðtÞ values in the studied sample were probably derived from the Northern Prince Charles Mountains of East Antarctica [11,56] that exhibit a number of positive zircon ε Hf ðtÞ values at ca. 1.4 Ga ( Figure 4). Second, the ca. 1.0-0.6 Ga arc magmatic rocks along the northern Tarim craton are coeval with the ca. 1.0-0.8 Ga arc-related magmatic rocks of northwestern India and the ca. 800-720 Ma Andean-type arcs in the Seychelles and Madagascar [71,76,77], occupying the circum-Rodinia subduction-accretion system (Figure 7). Third, we argue against an Australian affinity for the Tarim craton in the reconstruction of Rodinia [1,2,4]. The age spectra in this study are different from those in northern or southern Australia, which are characterized by a predominant age population at ca. 1.7-1.6 Ga but devoid of 0.9 and 1.4-1.3 Ga ages ( Figure 6). A western Australian affinity is also questionable because western Australia lacks ca. 0.9 and 1.4 Ga detrital zircons from Meso-to Neoproterozoic sedimentary rocks ( Figure 6). Importantly, even younger Permian sedimentary rocks in western Australia also lack ca. 0.9 and 1.4 Ga detrital zircons (e.g., [78]), implying coherent absence of ca. 0.9 and 1.4 Ga events in western Australia. In addition, the Grenvillian (ca. 1.3-1.0 Ga) orogens extending from the Albany-Fraser belt to the Musgrave block in western to central Australia ( Figure 7) are significantly older than the Neoproterozoic orogens in the peripheries of Tarim, challenging a western Australian affinity for the Tarim craton.
This study first reported middle Neoproterozoic sedimentary rocks in the Altyn Tagh orogen of the southeastern Tarim craton related to a rifting-related setting slightly earlier than the breakup of Rodinia at ca. 750 Ma. A new perspective on the location of the Tarim craton between South China and North India in the periphery of Rodinia is advocated based on Neoproterozoic geological records and detrital zircon U-Pb-Hf isotopes.

Data Availability
All data and analytical methods have been attached in Supplementary Materials.

Conflicts of Interest
The authors declare that they have no conflicts of interest.

Acknowledgments
This study was financially supported by a NSFC Project (41730213), Grant-in-Aids for Scientific Research from Japan Society for the Promotion of Science (JSPS) to Prof. Toshiaki Tsunogae (18H01300) and Dr. Qian Liu (No. 19F19020), and an open project from the State Key Laboratory for Mineral Deposits Research, Nanjing University (No. 21-16-03). JSPS International Research Fellowship is much appreciated. We appreciate the great help from Lei Wu, Jianfeng Gao, and Liang Li in experimental analyses.  Table DR1: U-Pb dating results for detrital zircons from sample 17LQ50-1A and zircon standards GJ-1 and Plešovice.