Late Paleozoic subduction and collision processes during the amalgamation of the Central Asian Orogenic Belt along the South Tianshan suture zone

Abstract

The provenance of late Paleozoic siliciclastic sedimentary strata on the northern margin of the Tarim Craton and the South Tianshan Orogenic Belt provides important insights into subduction and collision processes during the formation of the southern Central Asian Orogenic Belt. Detrital zircons from Carboniferous and Permian sedimentary rocks in the South Tianshan belt show two predominant age populations of 500–400 and 305–270Ma, and three subordinate clusters around ~2.5Ga, 2.0–1.7Ga, and 1.2–0.6Ma. Such age patterns are similar to major magmatic episodes in the Tarim Craton but are distinct from those in the Central Tianshan–Yili Block, implying that the Carboniferous–Permian strata in the South Tianshan belt were deposited on the northern margin of the Tarim Craton. These data, in combination with Carboniferous passive margin deposition along the South Tianshan and northern Tarim regions and intense arc magmatism in the Central Tianshan area, support the northward subduction of the South Tianshan oceanic crust. The abrupt decrease of zircon εHf(t) values at ~310Ma indicates the tectonic transformation from oceanic subduction to continental collision. However, syn- and post-collisional sediments in the South Tianshan and northern Tarim regions did not contain detritus from the Central Tianshan–Yili Block, as evidenced by the absence/paucity of 380–310Ma detrital zircons in the late Paleozoic strata and by the stratigraphic record in the regions. Insignificant surface erosion and uplifting during the collision and (ultra-)high-pressure rock exhumation require divergence in the frontal wedge. We propose that the switch from a convergent to a divergent regime was triggered by the arrival of the Tarim mantle plume in the latest Carboniferous, which possibly had profound effects on regional sedimentation and exhumation of (ultra-)high-pressure rocks in the orogenic belt.