Terminal Suturing Between the Tarim Craton and the Yili-Central Tianshan Arc: Insights From Melange-Ocean Plate Stratigraphy, Detrital Zircon Ages, and Provenance of the South Tianshan Accretionary Complex

摘要

New field relations and U-Pb ages of detrital zircons from Middle Devonian-Upper Triassic sedimentary rocks in the South Tianshan constrain the time and style of terminal suturing between the Tarim Craton and the Yili-Central Tianshan arc. The variety of melange blocks set within diagnostic thrust-imbricates demonstrates that basalts, limestones, cherts, and sandstones belong to the Ocean Plate Stratigraphy (OPS) of an accreted oceanic plate. The imbricated OPS structure is further confirmed by our observation of lateral juxtaposition of Lower Carboniferous meta-sandstones and Upper Carboniferous sandstones. Detrital zircon ages from Middle Devonian to Lower-Middle Triassic rocks show no input from the Tarim Craton, but rather derivation from the Yili-Central Tianshan arc or from isolated seamounts/oceanic plateaus within the South Tianshan oceanic plate. The integrated field observations and sediment provenance indicate that these rocks belong to the South Tianshan accretionary complex. The Upper Triassic sandstones show a mixed provenance from the Tarim Craton and the Yili-Central Tianshan arc suggesting that the final subduction of the South Tianshan oceanic plate lasted until its terminal collision to the Tarim craton in the Late Triassic. Our work not only supports continuous northward subduction of the South Tianshan oceanic plate, but also indicates that the cryptic terminal suture between the Tarim Craton and the Yili-Central Tianshan arc is situated on the southern boundary of the South Tianshan accretionary complex, providing new constraints on the final amalgamation of the Altaid orogen. This multi-disciplinary study demonstrates an optimum means of unraveling the complex framework and tectonic evolution of an accretionary orogen.