Transition from oceanic subduction to continental collision: Insights from volcanogenic-sedimentary rocks of the Tannuola terrane (northern Central Asian Orogenic Belt)

Magmatism associated with oceanic subduction plays a dominant role in crustal growth during the Earth's evolution. The Tannuola terrane, situated in the northern Central Asian Orogenic Belt (CAOB), is a key area to understanding oceanic subduction and initial collision processes in the northern CAOB. In order to investigate the switch from subduction to collision settings, detailed field mapping, zircon SHRIMP U-Pb geochronological and whole-rock geochemical studies of volcanogenic-sedimentary rocks from the Tannuola terrane were carried out. Zircon U-Pb ages indicate multi-stage volcanism lasted at least 30 Ma from -540 to -510 Ma, that can be divided into three events: the late Ediacaran (before -540 Ma), the early Cambrian (-520 Ma) and the middle Cambrian (-510 Ma). These ages are interpreted to the initial, main and final stages of oceanic subduction during the late Proterozoic - early Paleozoic. During the late Ediacaran, tholeiitic basalts with high eNd(t) values (from +7.4 to +8.5) were emplaced. Likely forming by the 10 %-30 % partial melting of spinel - garnet mantle source during slab subduction. During the early Cambrian, transitional from tholeiitic to calc-alkaline basaltic rocks with eNd(t) value (+5.6) and coeval intermediate-felsic volcanic rocks with similar eNd(t) values (+5.9 and +6.5) formed. The early Cambrian basaltic rocks are interpreted to be derived by 10 %-30 % partial melting of a depleted mantle source metasomatized by slab-derived fluids released from the subducting oceanic slab. The middle Cambrian calc-alkaline basaltic rocks with eNd(t) value of +6.2 might be emplaced as a result of low (5 %-10 %) degree partial melting of a metasomatized mantle followed by fractional crystallization of clinopyroxene and plagioclase. Associated intermediate-felsic volcanic rocks with eNd(t) values from +6.0 to +6.8 were formed through fractionation of the juvenile Neoproterozoic sources. The middle Cambrian volcanism is interpreted to be triggered by the slab break-off during the transition to a collisional setting. (c) 2024 China University of Geosciences (Beijing) and Peking University. Published by Elsevier B.V. on behalf of China University of Geosciences (Beijing). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).