The role of Arc-Arc Collision in Accretionary Orogenesis: Insights From 320 Ma Tectono-sedimentary Transition in the Karamaili Area, NW China

Understanding the tectono-sedimentary evolution of the Karamaili orogenic belt and reflective collisional processes between the Junggar and Yemaquan blocks in NW China is critical for assessing the role of arc-arc collision during accretion forming Central Asian Orogenic Belt. An integrated multidisciplinary investigation has been conducted on the Carboniferous strata across the Karamaili suture zone. Three Carboniferous tectonostratigraphic units in the Karamaili orogenic belt were identified, that is, Early Carboniferous clastic sequences, clastic-volcanic sequences, and Late Carboniferous carbonate-clastic sequences. The deposition of the Early Carboniferous strata in the northern Junggar block was controlled by normal faults in an extensional setting, accompanied with sediment supplies from the Junggar block. The Upper Carboniferous is distributed in the Junggar block and at the southern margin of the Yemaquan block, unconformably overlain by rift sequences. This unit shows a foreland-type depositional pattern typical for a contractional regime and gained the detritus from the Yemaquan block. Such tectono-sedimentary evolution corresponds to a 350-330 Ma rifting event in the Junggar arc and a 330-320 Ma collision event between the Junggar and Yemaquan arcs prior to the onset of intraplate rifting at 320 Ma. Given the temporal-spatial distributions of the arc and rift magmatism in the southern Junggar area, we propose that two phases of rifting were likely associated with slab rollback of the subducting North Tianshan oceanic plate. The Karamaili collision may transfer crustal shortening to the southern margin of the Junggar arc resulting in coupling across the plate boundary, implying that arc-arc collision is a possible mechanism for driving accretionary orogenesis. Key Points Two phases of rifting and an intervening contraction developed in the Karamaili area during Carboniferous time The collision event between the Junggar and Yemaquan arcs took place at 330-320 Ma Arc-arc collisional processes have close links and feedbacks with accretionary tectonics at plate margin