Closure Time of the Junggar‐Balkhash Ocean: Constraints From Late Paleozoic Volcano‐Sedimentary Sequences in the Barleik Mountains, West Junggar, NW China

Abstract

The Junggar‐Balkhash Ocean was a major branch of the southern Paleo‐Asian Ocean. The timing of its closure is important for understanding the history of the Central Asian Orogenic Belt. New sedimentological and geochronological data from the Late Paleozoic volcano‐sedimentary sequences in the Barleik Mountains of West Junggar, NW China, help to constrain the closure time of the Junggar‐Balkhash Ocean. Tielieketi Formation (Fm) is dominated by littoral sediments, but its upper glauconite‐bearing sandstone is interpreted to deposit rapidly in a shallow‐water shelf setting. By contrast, Heishantou Fm consists chiefly of volcanic rocks, conformably overlying or in fault contact with Tielieketi Fm. Molaoba Fm is composed of parallel‐stratified fine sandstone and sandy conglomerate with graded bedding, typical of nonmarine, fluvial deposition. This formation unconformably overlies the Tielieketi and Heishantou formations and is conformably covered by Kalagang Fm characterized by a continental bimodal volcanic association. The youngest U‐Pb ages of detrital zircons from sandstones and zircon U‐Pb ages from volcanic rocks suggest that the Tielieketi, Heishantou, Molaoba, and Kalagang formations were deposited during the Famennian‐Tournaisian, Tournaisian‐early Bashkirian, Gzhelian, and Asselian‐Sakmarian, respectively. The absence of upper Bashkirian to Kasimovian was likely caused by tectonic uplifting of the West Junggar terrane. This is compatible with the occurrence of coeval stitching plutons in the West Junggar and adjacent areas. The Junggar‐Balkhash Ocean should be finally closed before the Gzhelian, slightly later or concurrent with that of other ocean domains of the southern Paleo‐Asian Ocean.

The Ediacaran to Early Palaeozoic evolution of the Junggar–Balkhash Ocean: A synthesis of the ophiolitic mélanges in the southern West Junggar terrane, NW China

“…There has been a long‐standing dispute among tectonic divisions within the WJT (see a review and figure 2 in Liu, Han, Chen, et al, ), which is partly due to the fact that the WJT's ophiolitic mélanges do not always occur in linear belts (Figure b) and their specific tectonic implications remain relatively unexamined. Here, we follow the widely accepted division scheme, as proposed by Choulet et al (), Choulet et al (), Z. Xu et al (), Chen, Han, et al (), Liu, Han, Chen, et al (), and Ren et al (), with an emphasis on the importance of utilizing known ophiolitic mélanges in dividing the tectonic units.…”

“…These two ophiolitic mélanges are composed mainly of ~414–385 Ma N‐MORB, E‐MORB, and arc‐like gabbros (e.g., Xu et al, ; Yang, Li, Gu, et al, ; Zhu, Chen, & Qiu, ) and Late Devonian radiolarian‐bearing cherts (Zong, Wang, Jiang, & Gong, ). These blocks of diverse tectonic origins were thought to have been welded together during the final oceanic subduction, probably within a remnant Junggar–Balkhash Ocean (Chen et al, ; Li et al, ; Liu, Han, Chen, et al, ; Q. Q. Xu et al, ).…”

“…The southern WJT is largely bounded by the Ediacaran–Early Palaeozoic BMT ophiolitic mélange (Liu, Han, Chen, et al, ; Ren et al, ), dismembered by the NE–SW trending Barleik, Mayile, and Darbut faults (Figures b and a). In the following section, we summarize the petrology, geochronology, and geochemistry of the BMT ophiolitic mélange.…”

“…(a) Simplified tectonic map of the Central Asian Orogenic Belt (modified after Han, Guo, Zhang, et al, ) with the approximate location of Figure b. (b) Tectonic map of the West Junggar terrane (modified after Bureau of Geology and Mineral Resources of Xinjiang Uygur Autonomous Region (BGMRXUAR), ; Liu, Han, Chen, et al, ) with the approximate location of Figure . WJT = West Junggar terrane [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…As a key region of the south‐western CAOB, the West Junggar terrane (WJT) of NW China is sandwiched between the Char suture zone to the north and the North Tianshan suture zone to the south and marks the site of consumption of one major south‐western branch of the PAO, the Junggar–Balkhash Ocean (Filippova et al, ; Li, He, Qi, & Zhang, ; Liu, Han, Chen, et al, ). Current studies have shown that the WJT (Figure b) is characterized by nearly complete Neoproterozoic–Palaeozoic records and excellent exposure of dismembered ophiolitic mélanges and intra‐oceanic arcs (e.g., Buckman & Aitchison, ; Choulet et al, ; Han, Guo, & He, ; Han, Ji, Song, Chen, & Zhang, ; Liu et al, ; Liu, Han, Ren, et al, ; Liu, Han, Chen, et al, ; Liu, Han, Gong, & Chen, ; Ren et al, ; Ren, Han, Guan, Liu, & Wang, ; Xu et al, ; Xu, Han, Ren, Zhou, & Su, ; Yang, Li, Santosh, et al, ). Based on available age data, the Barleik–Mayile–Tangbale (BMT) ophiolitic mélange (Figure b) in the southern WJT is considered to contain the oldest known WJT's ophiolitic gabbros (Jian, Liu, Shi, & Zhang, ; Kwon, Tilton, Coleman, & Feng, ; Ren et al, ; Wen, Zhao, Liu, & Liu, ; Weng et al, ; Yang, Li, Santosh, et al, ) and blueschist and garnet amphibolite blocks (Liu et al, ; Ren, ; Zhang, ) in the entire WJT.…”