Development of a Modern-Style Trench-Arc-Backarc System in the Proto-Tethys Ocean (Qilian Orogenic Belt, NW China)

Abstract

The development of trench-arc-backarc (TABA) systems is uniquely associated with modern-style plate tectonics on Earth. The Qilian orogenic belt in NW China records the evolution history of the Proto-Tethys Ocean at the transition time from the Proterozoic to Phanerozoic. This paper presents systematic studies of petrography, U-Pb chronology and geochemistry on various rocks from a MOR-type ophiolite belt, active continental margin and back-arc basin in the Qilian orogenic belt to address the development of a modern-style TABA system. Arc magmas include felsic intrusions with ages of 530–477 Ma and felsic-mafic arc volcanic rocks with ages of 506–439 Ma, showing distinctive features of typical magmatic rocks formed at an Andean-type continental margin. The back-arc basin is recorded by a 490–448 Ma SSZ-type ophiolite with boninite, and Silurian turbidite flysch formation. We establish a three-stage tectonic history from the initiation of subduction to the formation of a mature Japan-Sea-type back-arc basin at the active continental margin in the Early Paleozoic era. (1) Northward subduction of Proto-Tethys Ocean initiated and the Andean-type continental arc developed at ~530–500 Ma with continual crustal thickening; (2) a tectonic transition occurred from an Andean-type active continental margin to a West Pacific-type active continental margin at ~500–490 Ma with rapid thinning of crust to ~35 km, and (3) mature ocean basins and back-arc-basin (BAB) ophiolites were formed in the back-arc extensional environment at ~ 490–450 Ma.

Petrogenesis of Syn-Collisional Adakitic Granitoids and Their Copper Mineralization Potential in the North Qilian Suture Zone

“…530 Ma, and to have closed at ca. 445 Ma followed by the continental collision, as indicated by the ophiolites, eclogites, and arc basaltic-andesitic lava in the NQSZ [25,35]. Accordingly, the ca.…”

“…The northwest-trending NQSZ is situated in the northern part of the Qinghai-Tibet Plateau, located between the Alashan block to the north and the Qilian block to the south and offset by the Altun Tagh fault to the west (Figure 1a). It has long been recognized as a typical Early Paleozoic suture zone that records a complete Wilson cycle from continental rifting to seafloor spreading, oceanic subduction, the extension of the back-arc basin, and to ultimately a continental collision and mountain collapse in the Neoproterozoic to early Paleozoic era [25,34,35]. It has been subdivided into three tectonic-magmatic subunits, i.e., the southern mid-ocean ridge (MOR)-type ophiolite belt (ca.…”

“…530-440 Ma), and the northern back-arc basin ophiolite-volcanic belt (ca. 517-450 Ma) (Figure 1a) [25,[34][35][36].…”

Tectonic Evolution of the Proto‒Tethys in the Early Devonian: Insights From the Turbidite in the North Qilian Belt, NW China

“…The northern ophiolite belt extends from Jiugequan through Biandukou to the Laohushan area, and consists of ultramafic rocks, mafic cumulates, N-MORB basalts, cherts, island-arc basalt, lawsonite-blueschists, blueschists and Cambrian to Devonian sedimentary rocks. The oceanic crustal fragments have magmatic zircon U-Pb ages of 490-450 Ma (D. Fu et al, 2020Fu et al, , 2023Meng et al, 2010;Qian et al, 2001;Qiao et al, 2023;S. Song et al, 2013;S.…”

“…The Jiugequan lawsonite-blueschists yield glaucophane and muscovite 40 Ar/ 39 Ar ages of 415-413 Ma (Lin et al, 2010) and the Laohushan blueschists yield phengite and glaucophane 40 Ar/ 39 Ar plateau ages of 455 ± 0.6 Ma and 432-425 Ma (D. Fu et al, 2022), respectively. Basalts and gabbros feature N-MORB to volcanic arc basalt geochemical affinities, indicating a supra-subduction zone tectonic setting, such as those associated with subduction initiation, forearc extension, or a back-arc basin (D. Fu et al, 2020Fu et al, , 2022Meng et al, 2010;Qiao et al, 2023;S. Song et al, 2013;Xia & Song, 2010;Xia et al, 2003Xia et al, , 2012Xiao et al, 2009).…”