Short-lived Arc Magmatism in the Arabia-Eurasia Collision Zone with Implications for Continental Crust Formation

Arc-continent collision plays a key role in the formation of continental crust. However, details on the processes remain unclear particularly in old collision zones where geologic records are incomplete. Here we present a high-resolution age and geochemical dataset of Late Cretaceous magmatic rocks from Elazig area, SE Turkey along the Arabia-Eurasia collisional orogen. Zircon U-Pb ages obtained by SIMS and LA-ICPMS from 17 samples constrain a short magma duration from 83 to 73 Ma. All the rocks show relative depletions in HFSE (Ti, Nb and Ta), similar to arc lavas from subduction zones. They are heterogeneous (SiO₂ = 45-78 wt.%), varying from low-K tholeiitic to calc-alkaline and shoshonitic composition with associated progressive enrichments in LREE and LILE, and change in radiogenic isotopic ratios, such as whole-rock εHf(t) values from +16 to -2. The Elazig magmatism can be explained specifically by a tectonic setting that switched rapidly from an intra-oceanic subduction to arc-continent collision within this part of Tethys where numbers of continental ribbons were present. The geochemical and isotopic variations can be attributed to melting of subducted sediments or mélange diapirs in the mantle wedge, with involvement of the continental materials increasing from 0.5 to 8 vol.%. It is evident that, while the intra-oceanic subduction gave rise to the tholeiitic arc crust from 83 Ma, the soon subsequent arc-continent collision in the region served as an efficient mechanism that transformed the juvenile arc crust toward a more mature continental crust. We argue that similar scenarios may have taken place worldwide in the early stage of collisional orogens, as also exemplified by the present-day Australia-Eurasia collision zone.