Controls of a strike-slip fault system on the tectonic inversion of the Mahu depression at the northwestern margin of the Junggar Basin, NW China

Journal Pre-proofs Controls of a strike-slip fault system on the tectonic inversion of the Mahu depression at the northwestern margin of the Junggar Basin, NW China Yuanyuan Liang, Yuanyuan Zhang, Shi Chen, Zhaojie Guo, Wenbin Tang PII: DOI: Reference:

S1367-9120(20)30004-3 https://doi.org/10.1016/j.jseaes.2020.104229 JAES 104229

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Journal of Asian Earth Sciences

Received Date: Revised Date: Accepted Date:

31 May 2019 31 December 2019 4 January 2020

Please cite this article as: Liang, Y., Zhang, Y., Chen, S., Guo, Z., Tang, W., Controls of a strike-slip fault system on the tectonic inversion of the Mahu depression at the northwestern margin of the Junggar Basin, NW China, Journal of Asian Earth Sciences (2020), doi: https://doi.org/10.1016/j.jseaes.2020.104229

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Controls of a strike-slip fault system on the tectonic inversion of the Mahu depression at the northwestern margin of the Junggar Basin, NW China Yuanyuan Lianga,b, Yuanyuan Zhanga*, Shi Chenb, Zhaojie Guoa, Wenbin Tanga a

Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth

and Space Sciences, Peking University, Beijing 100871, China b

State Key Laboratory of Petroleum Resources and Prospecting, College of Geosciences, China

University of Petroleum (Beijing), Beijing 102249, China; * Corresponding Author: [email protected]

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ABSTRACT The

marginal

fault

(Hongshanzui–Chepaizi),

system,

which

Ke–Bai

is

represented

by

(Karamay–Baikouquan),

the and

Hong–Che Wu–Xia

(Wuerhe–Xiazijie) sub-systems and developed in the northwestern margin of the Junggar Basin, NW China, is a key factor affecting the development characteristics of the Permian–Triassic strata and controlling the hydrocarbon accumulation in the area. In this study, based on the latest two-dimensional and three-dimensional seismic exploration data, regional geological background, and previous research results, the attributes and timing of this structural belt of the NW margin as well as the basin type related to it are clarified. The result shows that the above marginal fault system has dextral strike–slip features and is characterized by a high-angle master fault, branch faults, and short-axis plunging anticlines in an en échelon arrangement. The tectonic deformation is classified into two main periods: late Permian tectonic inversion and late Triassic reactivation. It is found that the late Permian tectonic inversion led to the migration of the depocenter in the Mahu Depression and was induced by the counterclockwise rotation of the Junggar block and West Junggar area relative to the western part of the Chingiz range in the late Paleozoic. The nose structures, fault blocks, and en échelon anticlines derived from the relevant thrust faulting and folding may account for the development of the main structural traps, which play an important role in the hydrocarbon accumulation in the NW margin of the Junggar Basin. Keywords: NW Junggar, tectonic attribute, strike-slip fault, Mahu Depression,

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tectonic inversion

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1. Introduction The Junggar Basin, as one of the major petroliferous basins in China, is a late Paleozoic, Mesozoic, and Cenozoic-superimposed basin and located at the junction of the Kazakhstan, Siberia, and Tarim blocks (Carroll et al., 1990; Şengör et al., 1993; Hendrix et al., 1994). The NW margin of this basin is bounded by the Zaire and Hala’alate mountains, with an area of approximately 1.03×104 km2. In recent years, research has shown that the marginal fault system represented by the roughly NE-SW trending Hong–Che (Hongshanzui–Chepaizi), Ke–Bai (Karamay–Baikouquan), and Wu–Xia (Wuerhe–Xiazijie) sub-systems is considered to be the key factor affecting the development characteristics of the Permian–Triassic strata and controlling the hydrocarbon accumulation in the area (Wei et al., 2005; Guan et al., 2008; Kuang et al., 2008). However, there is still no consensus on the activity of this marginal fault system, and whether the NW Junggar is a faulted depression or a foreland basin continues to be a relevant debate (Wu, 1986; Zhao, 1992; Cai et al., 2000; Chen et al., 2005; Fang et al., 2006; Kuang et al., 2006). The NW marginal fault system of the Junggar Basin is generally considered to be a large-scale thrust and nappe system related to the orogenic process in West Junggar (He et al., 2004). The Ke–Bai and Wu–Xia sub-systems are interpreted as imbricated thin-skinned fold-and-thrust belts (Wei et al., 2005; Guan et al., 2008; Kuang et al., 2008; Tan et al., 2008), and the NW Junggar is also classified as a foreland basin developed from the Permian to the Triassic period (Lai et al., 1999; Zhang et al., 2006). Another view is that the NW marginal fault

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system is a series of thrust structures originating from the inversion structures occurring between the Permian and Jurassic extensions (Meng et al., 2009). Contrastingly, some scholars suggest that this NW margin tectonic belt is an independent dextral strike–slip deformation unrelated to orogenic events (Shao et al., 2011; Zhang et al., 2011; Wang, 2012; Chen et al., 2016). In addition, there are differing views regarding the timing of this marginal fault system. Some scholars have suggested that the fault activity is from the Carboniferous to the Triassic periods (Lai et al., 1999; He et al., 2004). However, others have proposed that the marginal fault system is a short-term structure occurring between the late Permian and Triassic (Shao et al., 2011; Zhang et al., 2011). The Mahu Depression in the Junggar Basin is the main hydrocarbon generating unit and well known for its Permian and Triassic oil and gas pools in sandy conglomerate fans (Watson et al., 1987; Lei et al., 2005a, 2005b; Tang et al., 2014; He et al., 2017). The challenges in understanding the attributes of the marginal fault system in the NW margin of Junggar have led to the discrepancies in the structural properties and evolutionary process of its adjacent area. Whether the Mahu Depression is a foreland depression related to a foreland thrust belt or a pre-existing depression reformed by a subsequent thrust or strike–slip faulting activity is still being debated. Therefore, this study utilizes the latest exploration data of the NW margin of the Junggar Basin and systematically investigates the geometric and kinematic characteristics, dynamic mechanism of the NW margin fault system, and relationships

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between the mountains and the basin. 2. Geologic setting The Central Asian Orogenic Belt (CAOB), also called the Altaid Tectonic Collage, is one of the largest accretionary orogens in the world (Fig. 1a) (Şengör et al., 1993; Şengör and Natal'in, 1996; Yakubchuk, 2004; Xiao et al., 2010). The triangular-shaped Junggar Basin is located in the central part of the CAOB and bounded by the West Junggar in the west, Altai orogenic belt in the NE, and Tianshan mountain in the south. Stretching west from the north Xinjiang region is the Kazakhstan orocline bend. The Junggar block is located in the easternmost section of the Kazakhstan orocline bend (Feng et al., 1989; Yakubchuk, 2004; Windley et al., 2007), and west Junggar is the innermost region of the mountain bend. Different from most tectonic belts in north Xinjiang, which trend in a NW to west–NW direction or have a nearly west–east distribution (Zhao et al., 2014), the marginal fault system in west Junggar trends NE, parallel to the west boundary of the Junggar block. North Xinjiang was formed by a progressive southward amalgamation along with the evolution of the Paleo-Asian Ocean by the late Carboniferous period (Han et al., 2006; Zhang et al., 2013) (Fig. 1c). The Paleo-Asian Ocean in the west Junggar area, resulting from the resistance of the internal Junggar block and the protection from the unique boundary condition, did not completely close during the bending of the Kazakhstan orocline and was preserved as a remnant ocean basin in the late Devonian to Carboniferous periods (Zhu and Feng, 1994; Chen and Guo, 2010; Han and Zhao, 2018). However, this remnant ocean was gradually filled and closed during

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the Late Devonian (~360 Ma) and the whole Carboniferous periods (Chen and Guo, 2010; Chen et al., 2013, 2014). Consequently, the Junggar Basin emerged in its embryonic form, accepting fluvial and lacustrine clastic deposition during the Late Carboniferous and Permian periods (Buckman and Aitchison, 2004; Zhang et al., 2006; Meng et al., 2009). During the Mesozoic period, the west Junggar region experienced a compression-uplift (Zhao et al., 2014), most of which suffered from denudation, providing a sediment source for the Western Junggar Basin (Yang et al., 2015). Since the Neogene era, the northern Tianshan orogenic belt uplifted again owing to the strong compression resulting from the Indian–Eurasian collision (Molnar and Tapponnier, 1975). A large sinistral strike–slip fault zone, represented by the Barluk, Tuoli, and Darbut strike–slip faults, formed in the west Junggar region, which controls the present configuration of this area (Avouac et al., 1993; Hendrix et al., 1994) (Fig. 1b). The NE–SW trending marginal fault system at the northwestern margin of the Junggar Basin developed in front of the Zaire and Hala’alate Mountains, beginning with the Chepaizi area in the south and extending to the Xiazijie and Hongqiba areas in the north with approximately 400 km in length. This marginal fault system is subdivided into three segments with distinct structural forms: the Hong–Che, Ke–Bai, and Wu–Xia sub-systems, which are connected at the beginning and end and bulge outward toward the basin in an arc-shape.

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The Mahu Depression trending NEE is bounded by the Ke–Bai and Wu–Xia sub-systems and is a Carboniferous-Quaternary depression with a depositional thickness of more than 10 km (Lee, 1985; Carroll et al., 1990; Cao et al., 2005) (Fig. 1c). The Carboniferous strata are mainly composed of pyroclastic, volcanic, and clastic rocks. The Permian strata are classified into five formations from bottom up. The lower Permian Jiamuhe Formation (P1j) is dominated by volcanic rocks and pyroclastic rocks. The Fengcheng Formation (P1f) is composed of dolomitized limestone and clastic rock. The Middle Permian Xiazijie Formation (P2x) and the Lower Wuerhe (P2w) Formation are mainly composed of coarse-grained clastic rocks, with fluvial facies, and fan delta facies being dominant. The upper Wuerhe Formation (P3w) of the Upper Permian mainly consists of conglomerate, sandstone, siltstone, and mudstone. The Triassic sequence, including mainly clastic rocks, consists of three formations: the lower Triassic Baikouquan (T1b), middle Triassic Karamay (T2k), and upper Triassic Baijiantan (T3b) formations. The Jurassic sequence consists of the Badaowan (J1b), Sangonghe (J1s), Xishanyao (J1x), and Toutunhe (J1t) formations, and the Cretaceous sequence is composed of the Tugulu (K1tg) and Ailikehu (K2a) formations from bottom up (Fig. 2). 3. Dataset and method The primary source of data used in this study was acquired by the Xinjiang Oilfield Company. The data included the well-log data and the two-dimensional (2-D) and three-dimensional (3-D) seismic data. The 3-D seismic survey in the Wu–Xia area covered an area of 867 km2 (see Fig. 1c for the location). The seismic lines covered

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most of the region of the NW margin from the Hong–Che domain to the Wu–Xia domain. The 2-D seismic profiles (SE-trending and NE-trending) were approximately 30 km–170 km long and had a record length of 7500 ms two-way travel (TWT). Several representative seismic profiles perpendicular to the principal displacement zone (PDZ) strike were chosen to describe the strike–slip structural style along the NW marginal fault system. Combined with the 2-D seismic lines, the structural map of the NW margin fault system was drawn by using time slices of 3000 ms of the 3-D seismic and coherence cubes of high resolution and signal-to-noise ratio. 4. Structure characterization of the marginal fault system Based on the variations in the deformation style and composition along the strike, this NW margin fault structure can be divided from south to north into three segments: the Hong–Che, Ke–Bai, and Wu–Xia sub-systems. These have distinctive features in their combination patterns, geometric characteristics, and structural deformation intensities (Fig. 3). 4.1 Hongshanzui–Chepaizi sub-system The Hong–Che tectonic belt starts from the Changji Sag in the south, passes through the Chepaizi Uplift, and ends in the Hongshanzui cross-fracture. Referring to the outline geographic map, it separates the western Chepaizi Uplift and the eastern Changji Sag (Fig. 3). Our study mainly focused on the central and northern parts of the Hong–Che sub-system. On seismic profiles A-A’, B-B’, and C-C’ perpendicular to the fault strike, the Hong–Che fault is featured by two high-angle faults, serving as the boundary between

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the Chepaizi Uplift in the west and the Changji Sag in the east. Furthermore, it terminates upward against the bottom of J1b (Fig. 4). The Changji Sag, which is located in the footwall, has deposited complete Permian, Triassic, and Jurassic formations. The Chepaizi Uplift is dominated by a Carboniferous basement without distinctive reflectors and is covered by lower Cretaceous sediments, forming a regional angular unconformity. Simultaneously, the wedge-shaped Jurassic strata become thin and overlap the top of the uplift. Several parallel thrust faults and associated folds are developed in the Chaipaizi Uplift, which involve the Carboniferous and Permian strata, and are generally distributed in a step-like pattern. The intensity and the lift height of the associated folds gradually increase, and the folds tend to disappear from the south to the north, as shown in the cross-section (Fig. 4). Based on the occurrence and distribution of these faults, it is speculated that they may gradually converge to a large low-angle thrust fault in the deep zone. The Zhongguai Uplift is developed on the east side of the Changji Sag. In the profile, the Zhongguai thrust fault roughly dips to the NE, as revealed in section B-B’, separating the Changji Sag from the Zhongguai Uplift (Fig. 4b). Secondary faults with opposite occurrence are developed on the uplift, displacing the Jiamuhe (P1j) and Fengcheng (P1f) formations of the lower Permian. The upper part of the uplift suffers from erosion and forms an angular unconformity with the overlying Triassic sequence. 4.2 Karamay–Baikouquan sub-system

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The strike of the Ke–Bai sub-system in front of the Zaire mountain changes from the NE to the NEE, presenting a curvilinear PDZ. In the map view, several sets of secondary faults are generally arranged in an en échelon pattern trending NNW and NE, oblique to the primary Ke–Bai fault, indicating a right-lateral sense of slip (Fig. 3). In the seismic lines from D-D’ and F-F’, the Ke–Bai sub-system is represented as a slightly tilted positive flower structure controlled by the steeply dipping master fault and sub-faults (Figs. 5 and 6). The high-angle branch faults in both sides are symmetrically oriented to the master fault. The branch faults on the SE side exhibit “a reverse fault displacement”, whereas those on the NW side present a “normal fault displacement”. The coexistence of the normal and reverse faults corresponds to the theory of “separation in one profile” proposed by (Christie-Blick and Biddle, 1985), illustrating the presence of both normal- and reverse-separation faults in a given profile across the PDZ. 4.3 Wuerhe–Xiazijie sub-system The NEE-trending Wu–Xia sub-system is in front of the Hala’alate mountain and composed of two sub-units: the Wuerhe and Xiazijie sub-systems. Compared to the Hong–Che and Ke–Bai segments in the south, the structural deformation of the Wu–Xia sub-system is more complex. In this area, rows of faults buried by thick Mesozoic–Cenozoic strata have developed and include the Hashan, Xiahongbei, Wuerhe, Fengnan, and Xiahongnan faults (Fig. 3). In addition, the NE–SW Wuerhe and Xiazijie anticlines in an en échelon arrangement, are oriented obliquely to the strike of the Xiahongbei fault.

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The G-G' and H-H’ regional seismic profiles pass through the Heshituoluogai basin, Hala’alate mountain, and Wuerhe sub-system, and finally enters the interior of the Junggar Basin (Figs. 7 and 8). A SE-dipping strike–slip fault cuts down to the basement in the deep part of the Hala’alate mountain. On the east side of the primary fault plane, several NW-dipping, high-angle transpressional branch faults, including the Xiahongbei, Wuerhe, and Fengnan faults, coalesce downward with this deep primary fault. They present an asymmetric positive flower structure, and these branch faults further develop sub-secondary faults. The Permian strata have a fault contact relationship with the Carboniferous rocks separated by the Xiahongbei fault. The imbricated faults form a step-like fault block and are characteri zed by being steeper from bottom to top, revealing that the amplitude of displacement gradually decreases to the shallow layer. In addition, the Wunan, Wuerhe, and Fengnan anticlines are developed under the transpressional setting of the regional strike slip. The Wunan anticline plunged to the SW and upturned to the NE, which is truncated by the Xiahongbei fault and forms a nose-like structure (Fig. 7), resembling the classic example of a contractional fault-related fold (Zhang et al., 2011). Seismic line I-I’ passes through the Heshituoluogai basin, Hala’alate mountain, and Xiazijie slope belt (Fig. 9). In the profile, the Darbut fault, steeply deepening to the NW, is a large left-lateral strike–slip fault formed in the Cenozoic period caused by the Indo–European plate collision and marks a clear boundary between the Heshituoluogai basin and Hala’alate mountain (Molnar and Tapponnier, 1975; Yang et al., 2011). The Xiazijie anticline is characterized by relatively gradual limbs

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developed on the Xiahongnan thrust fault, deforming the pre-Triassic strata, and is parallel to the Wuerhe anticline in the plane map (Fig. 3). The back limb of the anticline is longer than the front limb, and the strata of the back limb gradually dip. This

strike–slip

associated

fold

shows

the

characteristics

of

a

trishear

fault-propagation fold (Erslev, 1991; Allmendinger, 1998). 5. Timing and structural attributes 5.1 Fault kinematics Significant dextral transpressional structural deformation characteristics have been demonstrated along the NW marginal fault system. In the profiles, the Hong–Che, Ke–Bai, and Wu–Xia fault structures are shown as positive flower structures composed of an almost vertical master fault and a series of high-angle branch faults. In the plane view, the PDZ is large-scale bow-shaped, extending from tens to hundreds of kilometers. Furthermore, the geometries of the tension and shear faulting or thrust faulting and the associated folding acting as an en échelon or parallel pattern at certain angles related to the PDZ evidence the right-lateral strike–slip of the margin fault system (Fig. 3). 5.1.1 Dextral strike–slip fault system of the Ke-Bai sub–system In the map view, the Ke–Bai sub-system exhibits a typical S-shaped configuration extending from the NNE to NE directions. Multiple sets of branches with a NE or NS-trend are observed oblique to the master fault, which indicates the right-lateral property of the Ke–Bai sub-system (Fig. 3). In the seismic profile view, this strike–slip fault belt is featured by steep primary fault planes and sub-symmetric

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splay fault planes, presenting a classic positive flower structure, which is typically related to the strike–slip faulting. Notably, the occurrence of the master fault oscillates along the fault strike, and the fault location becomes gradually close to the basin (Figs. 5, 6, and 10a). In addition, in the profile B-B’, the Ke–Bai fault presents a reverse fault, whereas in the adjacent seismic line C-C’, it exhibits a trend towards a normal fault. Furthermore, in the seismic lines D-D’ and E-E’, it presents a reverse fault again (Fig. 10a). Therefore, the strike–slip fault exhibits different dipping and uplift displacement along its strike, known as the dolphin effect and ribbon effect. These are caused by the differences in the rise and fall of the two plates in different positions owing to the change in the presence of the shallow layer of the strike–slip faults and their movement (Zolnai, 1991). 5.1.2 Dextral strike–slip fault system of the Wu–Xia sub-system The Wu–Xia sub-system, trending roughly EW, is characterized by wider deformation zones and more complex structural deformation than the neighboring Hong–Che and Ke–Bai fault segments. The deformation ranges from the Hala’alate mountain to the Mahu slope belt, with the development of Hashan and Xiahongbei high-angle strike–slip faults and Wuerhe, Fengnan, and Xiahongnan thrust faults. The associated thrusting folds, the NE trending Wunan, Wuerhe, and Xiazijie and Fengnan anticlines exhibit a NE or roughly EW direction arranged in an en échelon pattern. These indicate a dextral transpressional deformation along the Wu–Xia sub-system (Fig. 11). The Hashan, Xiahongbei, and Wuerhe secondary faults dipping steeply north as

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frontal faults gradually converge into the primary strike–slip fault plane, representing a large-scale asymmetric positive flower (Figs. 7 and 10b). In particular, the Wunan anticline is an associated fold governed by the Xiahongbei fault, and its back wing intersects the nearly east–west trending Xiahongbei fault (Fig. 7) at an acute angle, indicating the right-lateral property of the fault. 5.2 Timing Multiple suites of angular unconformities between the Jurassic–Cretaceous, Triassic–Jurassic, Permian–Triassic, and Carboniferous–Triassic formations are evident in the subsurface seismic profiles. These combined with the fault geometries can define a two-phase significant tectonic deformation along the NW marginal fault system in the late Paleozoic–Mesozoic period. The Hong–Che strike–slip fault and several parallel thrust faults terminate upward against the bottom of the Jurassic strata in the Chepaizi Uplift. The Triassic strata are missing, and the residual Carboniferous–Permian strata in the Chepaizi Uplift are strongly deformed, suffer from denudation, and are covered subsequently by the Jurassic and Cretaceous strata (Fig. 4). These features suggest that an intensive tectonic deformation occurred in the Hong–Che sub-system during the late Triassic period. In the Zhongguai Uplift, an angular unconformity is observed between the Upper Wuerhe Formation and the overlying lower Triassic strata (Fig. 4b). Accordingly, we infer that there might be one tectonic activity in the late Permian period, accounting for the uplift and compressive structures in the Hong–Che sub-system.

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The Ke–Bai sub-system is demonstrated to displace the Carboniferous–Triassic strata and results in a slight deflection of the lower Jurassic strata. The Permian strata are missing in the fault zone, but are preserved in the slope zone of the Mahu Depression. Further, a regional angular unconformity between the Upper Wuerhe Formation and the lower Triassic strata can be observed in the Mahu Depression (Figs. 5 and 6). In addition, several thrust faults are noted to develop in the Mahu Depression, terminating at the bottom of the Lower Wuerhe Formation (Fig. 5d). These features suggest an earlier stage tectonic deformation had occurred along this fault belt in the late Permian strata. Thus, the whole Permian strata in the fault zone are seen to be uplifted and suffer from erosion. The Mesozoic sedimentary strata are then deposited on the carboniferous basement and deform owing to the fault reactivation in a subsequent period. The Wu–Xia sub-system is consistent with the Hong–Che and Ke–Bai segments, and there are two distinct tectonic activities in the late Permian and late Triassic strata. The Permian and Triassic strata are noted to develop on the Wunan anticline with remarkable angular unconformities, and the Upper Wuerhe Formation suffers from denudation (Fig. 7). The growth strata of the Upper Wuerhe Formation are developed on the back limb of the Fengnan anticline, displaying a wedge-shaped thinning to the axis of the Fengnan anticline (Fig. 12a and b). In addition, a distinct angular unconformity between the Permian and Triassic strata can also be observed on the arched area of the Xiazijie anticline (Fig. 9). Furthermore, the tilted Jurassic strata overlap the deformed Permian–Triassic formations, forming a regional unconformity.

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In summary, two-stage tectonic activities are demonstrated according to the regional unconformities and growth strata. The Hong–Che, Ke–Bai, and Wu–Xia dextral transpressional marginal fault systems were initially formed in the first stage. This activity is also supported by the evidence from the paleo-stratigraphy, paleo-hydrology, and paleo-magnetism data of the NW margin (Watson et al., 1987; Graham et al., 1990; Novikov, 2013; Tang et al., 2014; He et al., 2017, 2018). The second stage occurred during the late Triassic period, when the NW marginal fault system was reactivated and superimposed on the previous deformation; however, the activity intensity was remarkably decreased. 6. Evolution of the NW margin Marked by the occurrence of numerous A-type granites and intermediate–basic dyke swarms, West Junggar and even the entire northern Xinjiang area entered a post-collisional setting by the late Carboniferous (Han et al., 1999, 2010; Li et al., 2004; Zhou et al., 2008; Chen and Guo, 2010; Zhang J.E. et al., 2011; Zhang Y.Y. et al., 2013). The NW margin of the Junggar Basin during the early Permian experienced an intracontinental basin stage under an extension setting, forming the primeval Mahu Depression. The seismic sections also demonstrate the early Permian structural characteristics are rift-related. The thickness of the early Permian strata is observed to typically change significantly on the two sides of the faults within the marginal fault system of the Mahu Depression. This indicates the formation of graben and half-graben structures (Figs. 5d, 7, and 8). The thickness of the early Permian strata gradually

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increases from the Mahu Depression to the northwestern mountain system (Figs. 6–8), which is controlled by the pre-existing normal faults. Early Permian depocenter may not be in the Mahu Depression but far away near the Zaire and Hala’alate mountain systems (Figs. 14a and 15a). The Permian strata stop abruptly in front of the marginal fault system, being absent within the fault zone, and Triassic strata unconformably overlie on the pre-Permian basement rocks. It suggests the occurrence of a tectonic inversion in the NW margin during the late Permian period. This is also manifested by the strong deformation of the Carboniferous–Permian formations observed in the Chepaizi Uplift (Fig. 4), absence of Permian strata in the Zaire mountain (Figs. 5 and 6), and notable unconformity between the Permian and Triassic strata in the Wu–Xia sub-system (Figs. 7-9) and in the Mahu Depression. The upper Permian growth strata is noted to have developed locally (Fig. 12), with simultaneous occurrence of reverse faults along the pre-existing weak fault zone. In addition, the thickness of the Upper Permian to Triassic formations, increases gradually from the piedmont to the Mahu Depression, and then decreases to the top of the Luliang Uplift (Figs. 6–8). The migration of the depocenter in the Mahu Depression reveals the uplift of the Zaire and Hala’alate mountains in the NW margin during the late Paleozoic period (Figs. 14b and 15b). Under the late Permian tectonic inversion, the uplift area was strongly denuded, the sediment supply was enhanced, and numerous large alluvial fans and fan delta systems were formed around the Mahu slope (Watson et al., 1987; Lei et al., 2005a, 2005b; Tang et al., 2014; He et al., 2017). Subsequently, the NW margin entered a

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period of extensional subsidence during the Triassic period. The basin gradually expanded and the strata overlapped on the eroded Carboniferous and Permian strata (Figs. 14c and 15c). The late Carboniferous granites (~310 Ma) were unconformably overlain by the basal conglomerates of the Upper Triassic Baijiantan (T3b) Formation, which was flat without any deformation (Meng et al., 2009). The marginal fault system was reactivated during the late Triassic period, when the surrounding framework of mountain and basin were basically shaped (Figs. 14d and 15d). Subsequently, since the Jurassic period, it entered a stable stage of subsidence depression. The Jurassic strata further expand on the base of the Triassic strata. The Cretaceous and Paleogene strata exhibit two sets of reflecting layers with good continuity and southward tilting (Figs. 14e, 15e and 15f). The multi-stage activities of the marginal fault system in the NW margin of the Junggar Basin have played a key role in controlling the hydrocarbon accumulation. The late Permian tectonic inversion results in the denudation of the thick hydrocarbon source rocks of the lower Permian strata. However, the uplift of the mountains associated with the tectonic inversion might facilitate the development of the fan deposition of the mid-upper Permian and Triassic strata as high-quality reservoirs. The faulted noses, blocks, and en échelon anticlines caused by the relevant thrust faulting and folding may account for the development of the main structural traps in west Junggar. The Permian and Mesozoic strata in the Mahu slope are completely preserved, with multi-stage unconformity, probably resulting in numerous stratigraphic lithologic traps. These traps were basically completed in the late Triassic,

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and the source rocks in the Mahu Depression entered the stage of large-scale hydrocarbon generation and expulsion after the Triassic period. This demonstrates a good configuration relationship and plays an important role in hydrocarbon accumulation. 7. Dynamic mechanism West Junggar evolved in a distinct manner in the late Paleozoic strata: a remnant ocean basin was preserved and gradually filled with sediments from the Devonian to Carboniferous periods (~310 Ma) (Zhu and Feng, 1994; Chen and Guo, 2010; Chen et al., 2013, 2014; Han and Zhao, 2018), and West Junggar and most of the area in North Xinjiang subsequently entered the post-collision extensional stage (Cai et al., 2000; Fang et al., 2006; Meng et al., 2009). The NW margin of the Junggar Basin does not have the conditions for the development of large-scale foreland thrust systems because it differs from the traditional subduction–collisional orogenic model. Based on the background of the regional compression from Tarim and Siberia, during the late Paleozoic period, scattered blocks in north Xinjiang gradually collaged from the south to the north (Han and Zhao, 2018). Owing to the resistance of the internal Junggar block and the protection from the distinct boundary condition during the bending of the Kazakhstan orocline, the relative shear movement or oblique compression between the Junggar block and West Junggar dominated, resulting in the development of the NE-trending strike–slip structure parallel to the western boundary (Chen et al., 2013, 2014). Moreover, our study shows that the tectonic belt of the NW margin of the

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Junggar Basin is a dextral strike–slip thrust belt, and the main active period is between the late Permian and late Triassic period. The Carboniferous strata and granites on the north side of the NW margin were strongly uplifted and exposed to the surface due to the convergent strike–slip activity from the late Permian to late Triassic periods and then were covered by the late Jurassic and Cretaceous strata (Fig. 1c). The counterclockwise rotation of the Junggar block relative to the Chengiz arc were proposed based on the comprehensive study of palaeomagnetism and geochronology in the Tacheng basin of West Junggar (Metelkin et al., 2009; Choulet et al., 2013; Yi et al., 2015). This event was a significant intracontinental deformation in the West Junggar––Kazakhstan region, and considered to induced the formation of the right-lateral strike–slip fault in the NW margin of the Junggar Basin (Fig. 13b). 8. Conclusions (1) The marginal fault system along the NW margin of the Junggar Basin can be subdivided into three segments from the south to the north: the Hongshanzui–Chepaizi, Karamy–Baikouquan, and Wuerhe–Xiazijie sub-systems. It is characterized by a typical strike–slip structural deformation. The right-lateral strike–slip property was demonstrated. (2) The marginal fault system has two-stage significant activities: late Permian and late Triassic. The late Permian activity of this NW marginal fault system led to the tectonic inversion of the early Permian rift-related depression. The late Permian tectonic inversion was induced by the counterclockwise rotation of the Junggar block and West Junggar area relative to the western part of the Chingiz range in the late

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Paleozoic period. The late Triassic reactivation shaped the final framework of mountain–basin structural patterns in the Mahu Depression. (3) The faulted noses, blocks, and en échelon arranged anticlines derived from the relevant thrust faulting and folding may account for the development of the main structural traps in West Junggar. Acknowledgments This study is funded by the National Science and Technology Major Project of China (No. 2017ZX05008001). We would like to thank Editor-In-Chief Prof. Meifu Zhou, Miss Diane Chung and two anonymous reviewers for the constructive comments and suggestions in improving this manuscript.

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References References Allmendinger, R.W., 1998. Inverse and forward numerical modeling of trishear fault‐propagation folds. Tectonics 17, 640-656. Avouac, J., Tapponnier, P., Bai, M.H., You, H., Wang, G.A., 1993. Active thrusting and folding along the northern Tien Shan and late Cenozoic rotation of the Tarim relative to Dzungaria and Kazakhstan. Journal of Geophysical Research: Solid Earth 98, 6755-6804. Buckman, S., Aitchison, J.C., 2004. Tectonic evolution of Palaeozoic terranes in west Junggar, Xinjiang, NW China. Geological Society, London, Special Publications 226, 101-129. Cai, Z.X., Chen, F.J., Jia, Z.Y., 2000.Types and tectonic evolution of Junger Basin. Earth Science Frontiers 7, 431-440 (in Chinese with English abstract). Cao, J., Zhang, Y.J., Hu, W.X., Yao, S.P., Wang, X.L., Zhang, Y.Q., Tang, Y., 2005. The Permian hybrid petroleum system in the northwest margin of the Junggar Basin, northwest China. Marine and Petroleum Geology 22, 331-349. Carroll, A.R., Liang, Y.H., Graham, S.A., Xiao, X.H., Hendrix, M.S., Jinchi, C., McKnight, C.L., 1990. Junggar basin, northwest China: trapped Late Paleozoic ocean. Tectonophysics 181, 1-14. Chen, F.J., Wang, X.W., Wang, X.W., 2005. Prototype and tectonic evolution of the Junggar basin, northwestern China. Earth Science Frontiers 12, 77 (in Chinese with English abstract).

23

Chen, S., Guo, Z.J., 2010. Time constraints, tectonic setting of Dalabute ophiolitic complex and its significance for Late Paleozoic tectonic evolution in West Junggar. Acta Petrologica Sinica 26, 2336-2344 (in Chinese with English abstract). Chen, S., Guo, Z.J., Pe-Piper, G., Zhu, B.B., 2013. Late Paleozoic peperites in West Junggar,

China,

and

how

they

constrain

regional

tectonic

and

palaeoenvironmental setting. Gondwana Research 23, 666-681. Chen, S., Guo, Z.J., Qi, J.F., Xing, X.R., 2016. Three-stage strike-slip fault systems at northwestern margin of Junggar Basin and their implications for hydrocarbon exploration. Oil & Gas Geology 37, 322-331 (in Chinese with English abstract). Chen, S., Pe Piper, G., Piper, D.J., Guo, Z.J., 2014. Ophiolitic mélanges in crustal‐scale fault zones: Implications for the Late Palaeozoic tectonic evolution in West Junggar, China. Tectonics 33, 2419-2443. Choulet, F., et al., 2013. First Triassic palaeomagnetic constraints from Junggar (NW China) and their implications for the Mesozoic tectonics in Central Asia. Journal of Asian Earth Sciences 78, 371-394. Christie-Blick, N., Biddle, K.T., 1985. Deformation and basin formation along strike-slip faults. Society of Economic Paleontologists and Mineralogists, Special Publication 37, 1-34. Erslev, E.A., 1991. Trishear fault-propagation folding. Geology 19, 617-620. Fang, S.H., Jia, C.Z., Guo, Z.J., Song, Y., Xu, H.M., Liu, L.J., 2006. New view on the Permian evolution of the Junggar Basin and its implications for tectonic

24

evolution. Earth Science Frontiers 13, 108 (in Chinese with English abstract). Feng, Y., Coleman, R.G., Tilton, G., Xiao, X., 1989. Tectonic evolution of the west Junggar region, Xinjiang, China. Tectonics 8, 729-752. Graham, S.A., Brassell, S., Carroll, A.R., Xiao, X., Demaison, G., McKnight, C.L., Liang, Y., Chu, J., Hendrix, M. S., 1990. Characteristics of selected petroleum source rocks, Xianjiang Uygur Autonomous Region, Northwest China (1). AAPG Bulletin 74, 493-512. Guan, S.W., Li, B.L., Hou, L.H., He, D.F., Shi, X., Zhang, Y.Q., 2008. New hydrocarbon exploration areas in footwall covered structures in northwestern margin of Junggar Basin. Petroleum Exploration & Development 35, 17-22 (in Chinese with English abstract). Han, B.F., He, G.Q., Wang, S., 1999. Post-collisional mantle-derived magmatism, underplating and implications for basement of the Junggar Basin. Science in China Series D: Earth Sciences 42, 113-119 (in Chinese with English abstract). Han, B.F., Guo, Z.J., Zhang, Z.C., Zhang, L., Chen, J.F., Song, B., 2010. Age, geochemistry, and tectonic implications of a Late Paleozoic stitching pluton in the North Tian Shan suture zone, Western China. Geological Society of America Bulletin 122, 627-640. Han, B.F., Ji, J.Q., Song, B., Chen, L.H., Zhang, L., 2006. Late Paleozoic vertical growth of continental crust around the Junggar Basin, Xinjiang, China (Part I): timing of post-collisional plutonism. Acta Petrologica Sinica 22, 1077-1086 (in Chinese with English abstract).

25

Han, Y.G., Zhao, G.C., 2018. Final amalgamation of the Tianshan and Junggar orogenic collage in the southwestern Central Asian Orogenic Belt: constraints on the closure of the Paleo-Asian Ocean. Earth-Science Reviews 186, 129-152. He, D.F., Yin, C., Du, S.K., Shi, X., Ma, H.S., 2004. Characteristics of structural segmentation of foreland thrust belts—A case study of the fault belts in the northwestern margin of Junggar Basin. Earth Science Frontiers 11, 92-101. He, D.F., Wu, S.T., Zhao, L., Zheng, M.L., Li, D., Lu, Y., 2018. Tectono-Depositional Setting and Its Evolution during Permian to Triassic around Mahu Sag, Junggar Basin. Xinjiang Petroleum Geology 39, 35-47 (in Chinese with English abstract). He, M., Zhang, L.W., Liu, Y., Li, T.D., Zhang, W., 2017. Sedimentary system and environment research on the Triassic strata in northwest Junggar Basin. Geological Bulletin of China 36, 1032-1042 (in Chinese with English abstract). Hendrix, M.S., Dumitru, T.A., Graham, S.A., 1994. Late Oligocene-early Miocene unroofing in the Chinese Tian Shan: An early effect of the India-Asia collision. Geology 22, 487-490. Jahn, B., 2000. Massive granitoid generation in Central Asia: Nd isotope evidence and implication for continental growth in the Phanerozoic. Episodes 23, 82-92. Kuang, J., Qi, X.F., 2006. The structural characteristics and oil-gas explorative direction in Junggar Foreland Basin. Xinjiang Petroleum Geology 27, 5-9 (in Chinese with English abstract). Kuang, J., Zhang Y.Q., Hou, L.H., 2008. Exploratory targets of Karamay-Baikouquan

26

buried structural belt in northwestern margin of Junggar Basin. Xinjiang Petroleum Geology 29, 431-434 (in Chinese with English abstract). Lai, S.X., Huang, K., Chen, J.L., Wu, J., Qian, W.C., Chen, S.P., Xu, H.M., 1999. Evolution and oil/gas accumulation of late Carboniferous and Permian foreland basin in Junggar Basin. Xinjiang Petroleum Geology 20, 293-297 (in Chinese with English abstract). Lee, K.Y., 1985. Geology of the petroleum and deposits in the Junggar Basin, Xinjiang Uygur Autonomous Region, northwest China. US Geological Survey Open-File Report 53, 85-230. Lei, D.W., Chen, G.Q., Liu, H.L., Li, X., Abulimit., Tao, K.Y., Cao, J., 2017. Study on the Forming Conditions and Exploration Fields of the Mahu Giant Oil (Gas) Province, Junggar Basin. Acta Geologica Sinica 91, 1604-1619 (in Chinese with English abstract). Lei, Z.Y., Bian, D.Z., Du, S.K., Wei, Y.J., Ma, H., 2005a. Characteristics of fan forming and oil-gas distribution in west-north margin of Junggar Basin. Acta Petrolei Sinica 26, 8-12 (in Chinese with English abstract). Lei, Z.Y., Lu, B., Wei, Y.J., Zhang, L.P., Shi, X., 2005b. Tectonic evolution and development and distribution of fans on northwestern edge of Junggar Basin. Oil & Gas Geology 26, 86-91 (in Chinese with English abstract). Li, X.Z., Han, B.F., Ji, J.Q., Li, Z.H., Liu, Z.Q., Yang, B., 2004. Geology, geochemistry and K–Ar ages of the Karamay basic-intermediate dike swarm from Xinjiang, China. Geochimica 33, 574-584 (in Chinese with English

27

abstract). Metelkin, D.V., Vernikovsky, V.A., Kazansky, A.Y., Wingate, M.T.D., 2009. Late Mesozoic tectonics of Central Asia based on paleomagnetic evidence. Gondwana Research 18(2), 400-419. Meng, J.F., Guo, Z.J., Fang, S.H., 2009. A new insight into the thrust structures at the northwestern margin of Junggar Basin. Earth Science Frontiers 16, 171-180 (in Chinese with English abstract). Molnar, P., Tapponnier, P., 1975. Cenozoic tectonics of Asia: effects of a continental collision. Science 189, 419-426. Novikov, I.S., 2013. Reconstructing the stages of orogeny around the Junggar basin from the lithostratigraphy of Late Paleozoic, Mesozoic, and Cenozoic sediments. Russian Geology and Geophysics 54, 138-152. Şengör, A.M.C., Natal'in, B.A., Burtman, V.S., 1993. Evolution of the Altaid tectonic collage and Palaeozoic crustal growth in Eurasia. Nature 364, 299–307. Şengör, A.C., Natal'in, B.A., 1996. Turkic-type orogeny and its role in the making of the continental crust. Annual Review of Earth and Planetary Sciences 24, 263-337. Shao, Y., Wang, R.F., Zhang, Y.Q., Wang, X., Li, Z.H., Liang, H., 2011. Strike⁃ slip structures and oil—gas exploration in the NW margin of the Junggar Basin, China. Acta Petrolei Sinica 32, 976-984 (in Chinese with English abstract). Tan, K.J., Zhang, F., Wu, X.Z., Wang, Z.J., Geng, Mei., 2008. Basin-range coupling and hydrocarbon accumulation at the northwestern margin of the Junggar Basin.

28

Natural Gas Industry 28, 10-13 (in Chinese). Tang, Y., Xu, Y., Qu, J.H., Meng, X.C., Zhou, Z.W., 2014. Fan-delta group characteristics and its distribution of the Triassic Baikouquan reservoirs in Mahu sag of Junggar basin. Xinjiang Petroleum Geology 06, 628-635 (in Chinese with English abstract). Wang, R.F., 2012. Karamay-Xiazijie strike-slip structure in northwestern margin of Junggar Basin. Doctorial Dissertation. Zhejiang, Zhejiang University. Watson, M.P., Hayward, A.B., Parkinson, D.N., Zhang, Z.M., 1987. Plate tectonic history, basin development and petroleum source rock deposition onshore China. Marine and Petroleum Geology 4, 205-225. Wei, G.Q., Jia, C.Z., Li, B.L., 2005. Particularity and diversity of the foreland basins in the central and western China and the natural gas exploration in the foreland basins. Geological Journal of China Universities 11, 552-557 (in Chinese with English abstract). Windley, B.F., Alexeiev, D., Xiao, W., Kröner, A., Badarch, G., 2007. Tectonic models for accretion of the Central Asian Orogenic Belt. Journal of The Geological Society 164, 31-47. Wu, Q.F., 1986. Growth stage, classification of structural units and cause of partial tectonic of Junggar Basin. Xinjiang Petroleum Geology 7, 30-37 (in Chinese). Xiao, W.J., Huang, B.C., Han, C.M., Sun, S., Li, J.L., 2010. A review of the western part of the Altaids: a key to understanding the architecture of accretionary orogens. Gondwana Research 18, 253-273.

29

Yakubchuk, A., 2004. Architecture and mineral deposit settings of the Altaid orogenic collage: a revised model. Journal of Asian Earth Sciences 23, 761-779. Yang, G., Wang, X.B., Li, B.L., Shi, X., 2011. Transpression and wrench faults of northwestern margin of Junggar Basin. Chinese Journal of Geology 46, 696-708 (in Chinese with English abstract). Yang, Y. T., Song, C. C., Sheng, H., 2015. Jurassic tectonostratigraphic evolution of the Junggar basin, NW China: A record of Mesozoic intraplate deformation in Central Asia. Tectonics 34, 86-115. Yi, Z.Y., Huang, B.C., Xiao, W.J., Yang, L.K., Qiao. Q.Q., 2015. Paleomagnetic study of Late Paleozoic rocks in the Tacheng Basin of West Junggar (NW China): Implications for the tectonic evolution of the western Altaids. Gondwana Research 27(2), 862-877. Zhang, C.J., He, D.F., Wu, X.Z., Shi, X., Luo, J.N., Wang, B.Y., Yang, G., Guan, S.W., Zhao, X., 2006. Formation and evolution of multicycle superimposed basins in Junggar Basin. China Petroleum Exploration 1, 55-66 (in Chinese with English abstract). Zhang, J.E., Xiao, W.J., Han, C.M., Ao, S.J., Yuan, C., Sun, M., Geng, H.Y., Zhao, G.C., Guo, Q.Q., Ma, C., 2011. Kinematics and age constraints of deformation in a Late Carboniferous accretionary complex in Western Junggar, NW China. Gondwana Research 19, 958-974. Zhang, Y.Q., Wang, X., Liu, J.S., Liang, H., Li, Z.H., Wang, R.F., 2011. Wuerhe-Xiazijie strike-slip structure and petroleum exploration significance in

30

northwestern margin of Junggar Basin. Xinjiang Petroleum Geology 32, 447-450 (in Chinese with English abstract). Zhang, Y.Y., Pe-Piper, G., Piper, D.J.W., Guo, Z.J., 2013. Early Carboniferous collision of the Kalamaili orogenic belt, North Xinjiang, and its implications: Evidence from molasse deposits. Geological Society of America Bulletin 125, 932–944. Zhao, B., 1992. Formation and evolution of Junggar Basin. Xinjiang Petroleum Geology 13, 191-196 (in Chinese with English abstract). Zhao, S.J., Li, S.Z., Liu, X., Suo, Y.H., Dai, L.M., Lou, D., Sun, W.J., Li, T., Wang, X.B., Yang, Z., 2014. Intracontinental orogenic transition: Insights from structures of the eastern Junggar Basin between the Altay and Tianshan orogens. Journal of Asian Earth Sciences 88, 137-148. Zhou, J., Ji, J.Q., Han, B.F., Ma, F., Gong, J.F., Xu, Q.Q., Guo, Z.J., 2008. Ar-40/Ar-39 Geochronology of mafic dykes in north Xinjiang. Acta Petrologica Sinica 24, 997-1010 (in Chinese with English abstract). Zhu, B.Q., Feng, Y.M., 1994. Plate tectonics and evolution in west Junggar of Xinjiang. Xinjiang Geology 12, 91–105 (in Chinese with English abstract). Zolnai, G., 1991. Continental wrench-tectonics and hydrocarbon habitat. Gsw Books, 161: I-II.

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Figures and tables Fig 1. Sketch maps (a) Showing the tectonic location of the Junggar Basin in the CAOB (modified from Şengör et al., 1993; Jahn, 2000). (b) Digital elevation model of the North Xinjiang area showing the major faults and tectonic units. (c) Geologic map of the northwest margin fault system of the Junggar Basin. The grey lines show the distribution of the 2-D seismic lines. The irregular border denotes the scope of the 3-D seismic survey. Fig 2. Generalized stratigraphy of the NW Junggar Basin (modified from Cao et al., 2005; Lei et al., 2017) Fig 3. Simplified structural map of the NW margin fault system for the bottom surface of the Cretaceous strata, exhibiting the paleo-structures buried by the thick Cenozoic sediments. The strike–slip fault belt of the NW margin is distributed in a bow-shaped pattern, which is composed of three uinits consisting of the Hong–Che, Ke–Bai, and Wu–Xia sub-systems. Fig 4. Interpreted seismic profiles A-A’, B-B’, and C-C’ across the Hong–Che sub-system. See Fig. 3 for the location. Fig 5. (a) Uninterpreted and (b) interpreted seismic profile D-D’ across the southern segment of the Ke–Bai sub-system. (c) Uninterpreted and (d) Interpreted seismic profile E-E’ across the southern segment of the Ke–Bai sub-system and the Mahu Depression. See Fig. 3 for the location. Fig 6. (a) Uninterpreted and (b) interpreted seismic profile F-F’ across the northern segment of the Ke–Bai sub-system, Mahu Depression, and the Luliang Uplift. See Fig. 3 for the location. Fig 7. (a) Uninterpreted and (b) interpreted seismic profile G-G’ across the Heshituoluogai basin, Hala’alate mountain, Wuerhe fault zone, Mahu Depression, and

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Luliang Uplift. See Fig. 3 for the location. Fig 8. (a) Uninterpreted and (b) interpreted seismic profile H-H’ across the Wu–Xia sub-system and the Mahu Depression. See Fig. 3 for the location. Fig 9. (a) Uninterpreted and (b) interpreted seismic profile I-I’ across the Heshituoluogai basin, Hala’alate mountain, and Xiazijie anticline. See Fig 3 for the location. Fig 10. 3-D conceptual model of the right-lateral strike-slip structural systems in the Ke–Bai and Wu–Xia sub-systems. Fig 11. (a) Uninterpreted 3-D seismic time slice and (b) interpreted 3-D coherence slice of 3000 ms in the Wu–Xia area showing the distinct distribution of the faults and related folds of this strike–slip structure. Fig 12. Detailed analysis of the seismic profiles in the Wuerhe anticlines. The growth strata developed on the limbs of the anticlines are marked in yellow. Fig 13. Diagrams illustrating the tectonic evolution of the west Junggar and surrounding terranes in the late Carboniferous (~310 Ma) and late Permian–late Triassic (~250 Ma) periods (Modified from Chen et al., 2014, 2016). (a) A remnant ocean basin was preserved in west Junggar during the bending of the Kazakhstan orocline under the resistance of the Junggar block and surrounding boundary. The relative motion between the Junggar block and ocean basin caused NW trending left-slip fault zones within the remnant ocean basin. (b) The counterclockwise rotation of the Junggar block relative to the Chengiz arc induced the right-lateral strike-slip fault in the NW margin of the Junggar Basin. Fig 14. Schematic 3-D conceptual model delineating the tectonic evolution of the northwestern margin of the Junggar Basin since the Permian. The five main stages of deformation include: (a) Post-collision rifting in the Early Permian; (b)

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Transpressional tectonic inversion in the Late Permian; (c) Short-term extensional subsidence during the Early-Middle Triassic; (d) The reactivation in the Late Triassic; (e) Regional subsidence with southward tilting in the Post-Triassic. Fig 15. Sketch diagram showing the structural evolution of the Hong-Che, Ke-Bai and Wu-Xia sub-systems since the Permian. Six main stages of deformation include: (a) Post-collision in the Early Permian; (b) Transpressional tectonic inversion in the Late Permian; (c) Short-term extensional subsidence during the Early-Middle Triassic. (d) Reactivation in the Late Triassic; (e) Late Jurassic compressional thrusting; (f) Regional subsidence with southward tilting since the Cretaceous.

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Highlights:  The marginal fault system along the NW Junggar Basin is a dextral strike-slip fault system.  This strike-slip fault system was active in the Late Permian and Late Triassic.  The activity of the fault system resulted in the tectonic inversion of the Mahu Depression.

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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:

We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled.

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Yuanyuan Liang: Writing - Original Draft Yuanyuan Zhang: Writing - Review & Editing, Supervision, Funding acquisition, Conceptualization Shi Chen: Conceptualization Zhaojie Guo: Validation Wenbin Tang: Investigation

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Author agreement: We declare that this manuscript is original, has not been published before and is not currently being considered for publication elsewhere. We confirm that the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed. We further confirm that the order of authors listed in the manuscript has been approved by all of us. We understand that the Corresponding Author is the sole contact for the Editorial process. She is responsible for communicating with the other authors about progress, submissions of revisions and final approval of proofs. Regards, Yuanyuan Liang Yuanyuan Zhang

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