Mid–Neoproterozoic collision of the Tarim Craton with the Yili–Central Tianshan Block towards the final assembly of Supercontinent Rodinia: A new model

The Central Asian Orogenic Belt (CAOB) has been considered as an archetype of an accretionary orogenic belt that developed through steady–state subduction–accretion processes, punctuated by short–lived, microcontinent, island arc, and oceanic plateau collision events, between 1000 Ma and 250 Ma. Here, we present a new tectonic model for a mid–Neoproterozoic (~830–790 Ma) collisional orogeny, which resulted in the suturing of the Tarim, Central Tianshan, and Yili continental blocks during the final assembly of Supercontinent Rodinia. Using the Neoproterozoic stratigraphic, magmatic, and metamorphic rock records of these blocks and their detrital zircon histories and zircon Hafnium isotope, we show that: (1) the Tarim and Yili-Central Tianshan blocks evolved as separate tectonic entities throughout the early Neoproterozoic (Tonian), as indicated by major differences in the magmatic and metamorphic records of their early Neoproterozoic and older crystalline basement units; (2) these blocks share similar mid–Neoproterozoic mafic and felsic magmatic assemblages that are overlain by similar Cryogenian and Ediacaran sedimentary sequences, which contain detrital zircons derived from the compatible provenances; and (3) a subduction zone dipping away from the Tarim Craton and beneath the southern margin of the Yili–Central Tianshan Block (YCTB) to the north brought them together in a collisional front around 830–790 Ma, resulting in syn–collisional magmatism, followed by lithospheric–scale extension, bimodal magmatism, and continental rifting. The last two phases are integral parts of the assembly and breakup histories of Rodinia. The latest Neoproterozoic (600–550 Ma) rift–drift and seafloor spreading tectonics led to the opening of the South Tianshan Ocean between the Tarim Craton and the YCTB, and to the development of extensive conjugate passive margins along them. The proposed mid–Neoproterozoic collisional orogeny during the final stages of the Rodinia buildup is compatible with the regional geology of the southern CAOB, providing a new perspective against the ruling hypothesis of steady–state subduction–accretion tectonic evolution of the CAOB, and should be tested with future field-based structural, geochronological, and isotope geochemistry studies in the region.