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

Abstract

The southern West Junggar terrane in the south‐western Central Asian Orogenic Belt (CAOB) is mainly composed of accretionary complexes and characterized by widespread outcrops of ophiolitic mélanges in the Barleik, Mayile, and Tangbale (BMT) areas, representing the site of consumption of the Junggar–Balkhash Ocean. However, due to a lack of comprehensive synthesis of the ophiolitic mélanges, the early evolution of the Junggar–Balkhash Ocean remains poorly understood. This paper first focuses on the little‐known Barleik ophiolitic blocks and associated pillow basalts and then integrates the Barleik, Mayile, and Tangbale ophiolitic mélanges into one model. Mineral and whole‐rock chemistry suggests that the Barleik ophiolitic blocks, including serpentinized dunite, clinopyroxenite, and gabbro, show supra‐subduction zone (SSZ) affinities, as indicated by high Cr# values (76–78) in spinels and strong depletion in Nb, Ta, Zr, and Hf, whereas the Barleik pillow basalts are alkaline and have high TiO2 contents (2.82–3.42 wt.%) and Nb–Ta enrichment, similar to ocean‐island basalt (OIB) lavas. Combined with published chronological and chemical data from ophiolites, metamorphic rocks, and arc plutons, we propose that the BMT Ediacaran to middle Cambrian ophiolitic gabbros were formed in a SSZ environment, implying a single Mariana‐type arc system within the Junggar–Balkhash Ocean, which was coeval with an Andean‐type arc system in the Kyrgyz North Tianshan, supporting an archipelagic model for the south‐western CAOB. By contrast, the BMT OIB‐type basalts are early Silurian in age, much younger than the SSZ‐type ophiolites, and can be interpreted as relicts of seamounts. Thus, a model involving the Ediacaran to Ordovician intra‐oceanic subduction and late Silurian to Early Devonian seamount accretion is helpful for clarifying the different components of the accretionary complexes in the southern West Junggar terrane.

Accretionary tectonics, deep structures and metallogeny of southern Altaids

“…Liu, Han, Xu, Ren and Chen (, this issue) in their research present a comprehensive synthesis of the ophiolitic mélanges within the southern West Junggar terrane, and constructed a model involving the Ediacaran to Ordovician intra‐oceanic subduction and late Silurian to Early Devonian seamount accretion. The model is quite helpful in clarifying the different components of the accretionary complexes in the southern West Junggar terrane.…”

Zircon U-Pb-Hf Isotopes and Whole-Rock Geochemistry of the “Kulumudi Formation” from the Laofengkou Area (West Junggar): Implications of the Construction of a Juvenile Arc in the Junggar–Balkhash Ocean

“…Moreover, compared w accepted Early-to-Middle-Devonian outer arc belt (OAB) with a Precambria basement, the basement nature of the Late-Devonian-to-Carboniferous inner remains debated [9,10,13]. [15]).…”

“…The WJT is characteri spread Paleozoic accretionary complexes and Carboniferous-Permian in (Figure 1b), and its formation was closely associated with the subduction a [14]). (b) Geological map of the West Junggar terrane (modified after [15]).…”

“…The WJT is characterized by widespread Paleozoic accretionary complexes and Carboniferous-Permian intrusive rocks (Figure 1b), and its formation was closely associated with the subduction and closure of the Junggar-Balkhash Ocean [2,7,[16][17][18]. Current research on the tectonic evolution of the WJT Minerals 2024, 14, 14 3 of 16 focuses on the Ediacaran-Early Paleozoic [15,17,19,20] and Carboniferous-Permian periods [14,18,21]. It is generally accepted that the Ediacaran-Early Paleozoic evolution of the WJT was dominated by a single or multiple intra-oceanic arc(s) [15,17,19,20,22,23].…”

“…the Junggar-Balkhash Ocean [2,7,[16][17][18]. Current research on the tectonic evolution of t WJT focuses on the Ediacaran-Early Paleozoic [15,17,19,20] and Carboniferous-Permia periods [14,18,21]. It is generally accepted that the Ediacaran-Early Paleozoic evolution the WJT was dominated by a single or multiple intra-oceanic arc(s) [15,17,19,20,22,23 Previous work showed that the WJT was a place of active convergence during the Ear Carboniferous [24,25], while the Late Carboniferous-Permian tectonic setting was su gested to be a post-collisional [25][26][27] or continuous normal/ridge-related subduction sy tem [7,28,29].…”