The Intra-Pontide Suture between the Istanbul and Sakarya zones was regarded debatably either as a Neotethyan Suture or a trace of the Rheic Suture in Turkey. Here, we present U-Pb ages and Lu-Hf isotopic compositions of detrital zircons from the Silurian to Triassic sandstones of the Istanbul Zone. Upper Silurian-Lower Devonian sandstone is dominated by Mesoproterozoic zircons (1950–900 Ma), with subordinate peaks at the latest Neoproterozoic to Silurian (750–420 Ma) and mid-Archean (2850–2750 Ma) confirming their Avalonian affinity. Detrital zircon ages from Carboniferous-Triassic sandstones show major peaks at Carboniferous-Early Permian (360–270 Ma) and Late Neoproterozoic–Cambrian (750–480 Ma) while Mesoproterozoic zircons are insignificant. The εHf(t) values of the detrital zircons exhibit a wide range from −21.3 to +11.7, and over 62% of zircon grains have negative values, largely coinciding with those of the Paleozoic igneous rocks in the Sakarya Zone. The Istanbul Zone is devoid of Carboniferous igneous and/or metamorphic rocks. Therefore, abundant Carboniferous zircons and the disappearance of the Mesoproterozoic zircons in the Carboniferous-Triassic sandstones of the Istanbul Zone require juxtaposition with a continental domain similar to the Sakarya and Strandja zones, which are characterized by widespread Carboniferous magmatism. We suggest that the Intra-Pontide Suture represents the trace of the Rheic Suture in Turkey, along which Avalonia and Armorica collided during the Early Carboniferous.