Late Paleozoic Chingiz and Saur Arc Amalgamation in West Junggar (NW China): Implications for Accretionary Tectonics in the Southern Altaids

The Saur-Chingiz Belt (SCB) in northern West Junggar is regarded as the amalgamation zone of the Saur and Chingiz arcs. It contains diagnostic rocks of accretionary origin, providing critical information about the evolution of the southern Paleo-Asian Ocean. We recognize various lithologies in the SCB, including an ophiolitic melange, turbidites, conglomerates, rhyolites, breccias, and diorites, and investigate the structures of the Hebukesaier ophiolitic melange. Kinematic analysis indicates top-to-the-N thrusting. A coarse-grained gabbro (ca. 490 Ma) and a fine-grained gabbro (ca. 318 Ma) have normal mid-ocean ridge basalt (N-MORB)-type geochemical signatures, and three groups of pillow basalts exhibit N-MORB, enriched mid-ocean ridge basalt (E-MORB), and ocean island basalts (OIB) fingerprints, respectively. Detrital zircons in tuffs, conglomerates, and turbidites associated with the Hebukesaier melange display predominant ages of 410-440 Ma, which are consistent with the age of the Chingiz Arc. This suggests that the mafic rocks (ophiolitic components) in the Hebukesaier melange were generated at a mid-ocean ridge and were later accreted to the Chingiz Arc, which formed above a southward-dipping subduction zone that consumed the Paleo-Asian Ocean.The predominant zircon age peaks of turbidites from the Saur area, north of the Hebukesaier melange, range from 326 to 360 Ma, which areconsistent with a provenance from the Saur Arc. The distinctive detrital zircons of the Chingiz and Saur arcs indicate that the northern boundary of the Hebukesaier melange is the tectonic boundary between the Chingiz and Saur arcs. We suggest that Paleo-Asian Ocean closed before Late Triassic as indicated by a diorite vein (ca. 218 Ma) that intruded the Hebukesaier melange.