The Cambrian initiation of intra-oceanic subduction in the southern Paleo-Asian Ocean: Further evidence from the Barleik subduction-related metamorphic complex in the West Junggar region, NW China. (1st June 2016)

• Record Type: Journal Article
• Authors: Liu, Bo; Han, Bao-Fu; Xu, Zhao; Ren, Rong; Zhang, Jin-Rui; Zhou, Jing; Su, Li; Li, Qiu-Li
• Is Part Of: Journal of Asian earth sciences. Number 123(2016)
• Page Start: 1
• Page End: 21
• Publication Date: 2016-06-01
• Subjects: Intra-oceanic subduction -- Subduction initiation -- Cambrian -- Blueschist -- West Junggar -- Paleo-Asian Ocean; Earth sciences -- Asia -- Periodicals; Sciences de la terre -- Asie -- Périodiques; Earth sciences; Asia; Periodicals; 555.05
• DOI: 10.1016/j.jseaes.2016.03.015
• Languages: English
• ISSNs: 1367-9120

Abstract

Graphical abstract: Highlights: Barleik subduction-related metamorphism occurred in Middle-Late Cambrian. The protoliths are intra-oceanic arc andesite and seamount basalt. Initial subduction of the southern PAO started during the Early Cambrian. Abstract: In this study, we present new evidence from the Barleik subduction-related metamorphic complex in the southern West Junggar region, northwestern China, for the Cambrian initiation of intra-oceanic subduction in the southern Paleo-Asian Ocean. The Barleik metamorphic complex is mainly composed of blueschist and amphibolite blocks within an ophiolitic mélange and their protoliths are calc-alkaline andesite and alkali and tholeiitic basalts. The calc-alkaline andesite has a zircon U–Pb age of 502 ± 2 Ma, obtained from magmatic cores of zircon grains, and shares geochemical features similar to the 515–485 Ma intra-oceanic arc magmatic rocks in the West Junggar region. By contrast, the alkali and tholeiitic basalts have trace element features similar to ocean island and enriched mid-ocean ridge basalts, respectively. Rutile and sodic–calcic amphibole from the amphibolite have a U–Pb age of 502 ± 25 Ma and a 40 Ar/ 39 Ar age of ∼504 Ma, respectively, which are in good agreement within errors with a 40 Ar/ 39 Ar age of 492 ± 4 Ma for phengite from the blueschist. These metamorphic ages of ∼500 Ma are interpreted to represent the timing of Pacific-type subduction-related metamorphism and are also compatible with ages of the oldest supra-subduction zone ophiolites (531–512 Ma) and intra-oceanic arc plutons (515–485 Ma) in the southern West Junggar region. Being one of the oldest subduction-related metamorphic complexes (509–490 Ma) in the southern Central Asian Orogenic Belt, the Barleik metamorphic complex, together with the oldest arc plutons, definitely indicate the initial intra-oceanic subduction in the southern Paleo-Asian Ocean at least in the Early Cambrian.