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The Neoproterozoic Arabian‐Nubian Shield (ANS) is the best preserved and the largest exposed Neoproterozoic juvenile crust on Earth. While the lithology and early Sr and Nd isotopic data demonstrate that the ANS crust is overwhelmingly juvenile, pre‐ANS old zircon crystals have been increasingly recognized in the ANS igneous and sedimentary rocks, casting doubt on the “juvenility” of the ANS crust. In order to understand the origin of the old continental materials in the ANS and its roles in generation of juvenile oceanic arcs, we carry out for the first time an integrated in situ analysis of zircon U‐Pb age and Hf‐O isotopes for greywacke and felsic volcanic cobble samples from the Atud Formation in the Eastern Desert of northwestern part of the ANS. Our data indicate that the Atud Formation was deposited between ca. 720 and 700 Ma, concurrent with the production of oceanic arcs in the ANS. The Atud greywacke was derived from the erosion of a proximal arc terrane that contains numerous old continental crust materials. We identify for the first time a 755‐Ma felsic volcanic cobble from the Atud Formation that is derived from old continental materials during juvenile crust production, suggesting presence of an old continental crust substrate that underlies the ANS. Our work demonstrates that reworking of old continental crust played important roles in generation of oceanic arcs in the northwestern ANS that is likely much less juvenile than previously thought. Thus, the crustal growth rates calculated based on estimates of temporal island arc development need to be revised. The oceanic arc is generated by partial melting of a mantle wedge where one oceanic plate subducts beneath another. Given the presumed lack of continental crust within oceanic arcs, accretion of oceanic arcs is considered as manifesting rapid growth of continental crust. However, this classic viewpoint is questioned by identification of increasing numbers of old zircon in the modern oceanic arcs in the Pacific Ocean and ancient oceanic arcs in the Arabian‐Nubian Shield (ANS). In order to understand the origin of old continental materials in oceanic arcs and its roles in generation of juvenile oceanic arcs, we carry out an integrated in situ analysis of zircon U‐Pb age and Hf‐O isotopes for sedimentary rocks from the northwestern ANS. Our data indicate that the Atud greywacke was derived from the erosion of a proximal arc terrane containing numerous old continental materials. A 755‐Ma rhyolite cobble was derived from old continental materials during juvenile crust production, suggesting presence of an old continental crust substrate underlying the ANS. Reworking of old continental crust played important roles in generation of oceanic arcs in the ANS. Thus, the crustal growth rates calculated based on estimates of temporal island arc development need to be revised. Most detrital zircon grains from the Atud greywacke are not entirely crystallized from the juvenile crust‐derived magmasA 755‐Ma volcanic cobble is formed by remelting of an old continental crust substrate underlying a juvenile oceanic arc in ANSReworking of old continental crust played important roles in the generation of oceanic arc systems in the northwestern ANS