LA-ICP-MS U–Pb ages of detrital zircons from clastics of the undated fore-arc sedimentary unit (FAS) along the Shangdan Suture and the Middle–Upper Devonian Liuling Group in the South Qinling belt are used to establish the maximum depositional age and provenance of these tectonic units which were deposited on both sides of the Shangdan suture zone between the North China Block (NCB) and South China Block (SCB). The new data and geological evidence show that the FAS was deposited in a fore-arc basin with an exclusive source of the clastics in the North Qinling Belt (NQB). The depositional age of FAS is limited by the youngest U–Pb 455Ma-ages of detrital zircons from clastics and the intrusive age of 435±7Ma of mafic dykes between the Late Ordovician–Early Silurian, while the NCB was still separated from the SCB by the Shangdan Ocean. However, detrital zircon U–Pb ages from six samples of the Middle Devonian Liuling Group indicate sources in both NQB and SCB suggesting pre-Middle Devonian collision of NCB and SCB. All results indicate deposition of the FAS in a forearc setting upon an active continental margin during Late Ordovician–Early Silurian, while the Middle–Upper Devonian Liuling Group represents a marine foreland basin after closure of the Shangdan Ocean. Together with the unconformity between Middle Devonian and pre-Devonian strata, this reveals still evolving subduction and accretion on the southern side of the NQB during the Ordovician-Early Silurian, and the Early Devonian collision between the NCB and SCB. Display omitted ► Detrital zircon ages reveal ca. 455–435 Ma sedimentation in a for-arc basin. ► For-arc basin exclusively received clastics from North Qinling (North China Block). ► Collision between South and North China blocks occurred during Early Devonian. ► Middle Devonian foreland basin received clastics from both South and North China blocks.