LATE PALEOZOIC TECTONIC EVOLUTION ALONG CONVERGENT MARGIN IN NORTHERN TARIM BLOCK, NORTHWEST CHINA: CONSTRAINED BY BASIN-FILL AND PROVENANCE RECORDS

Based on stratigraphic correlation between nowaday basins and orogens, more complete Devonian-Carboniferous profiles, located between the northern margin of Tarim block and South Tianshan (TST belt), Northwest China, are investigated from basin-fill sequences in the paper. Alkaline basalt, radiolarian chert and turbidite, with enveloped acidic volcanic rocks and isolated platform carbonates in fault contact, are developed in Devonian through Early Visean of Early Carboniferous. However, relatively shallow carbonate and terrigenous clastic rocks, with mixed sedimentary strata in conformable contact, distinctly deposit in Late Visean of Early Carboniferous through Late Carboniferous, indicating ocean-continent transformation occurred. The research further focuses on sandstone components, detrital heavy minerals and detrital zircon geochronological data. Devonian through Early Visean of Early Carboniferous, unstable and varied detrital assemblages, with some detrital zircons approximately similar to their sandstone strata age, occur in the TST belt, showing chaotic deposition and relatively short source-sink systems limited in active continental margin. For Late Visean of Early Carboniferous through Late Carboniferous, sandstone records are characterized by relatively higher mature sandstone components, with an amount of detrital zircons respectively indicating basement ages of Tarim continental block and special 390~460Ma ages of positive εHf(t) related to crust growth, which mainly attributes to the complex orogen provenance type and middle-short source-sink systems, probably reflecting deposition in residual sea. No evident orogeny evidences are found from basin-fill records in the studied area till Late Carboniferous even Permian, and especially relatively deep-water sedimentation once again developed in early Late Carboniferous, though the South Tianshan ocean had closed after Visean Phase. As a whole, the Late Paleozoic tectonic evolution along convergent margin in northern Tarim block is clearly characterized by relatively short-lived ocean basin but long-lived residual sea, which probably is a responsive to distinct micro-continental margin rifting, archipelagic ocean closure and micro-continent convergence in the Central Asia tectonic domain.