Unraveling the protolith origin of high-pressure and low-temperature (HP-LT) metamorphic rocks is the key to understanding the tectonic evolution of active continental margins. A comprehensive study, including field observations, geochemical analyses and zircon U-Pb geochronological dating, was conducted on the Lanling HP-LT terrane to determine its protolith origin and the presubduction paleogeography of the Paleo-Tethys Ocean. The metabasites can be divided into two geochemical groups: Group A samples exhibit low TiO2 values (1.15–1.81 wt%) and subalkaline basalt affinity with rare earth element (REE) distribution patterns and trace element abundances similar to enriched mid-ocean ridge basalts (E-MORB); Group B samples have higher TiO2 values (2.75–3.32 wt%) and show alkaline basalt affinity and ocean island basalt (OIB) geochemical signatures. Lanling metabasites are likely derived from a long-depleted mantle source combined with crustal contamination based on the following evidence: (1) positive εNd(t) values (+4.8 to +5.6) and a scattered distribution of Isr(t) values (0.704684 to 0.710999), (2) abundant Precambrian zircon grains, and (3) a volcanic arc trend in the tectonic discrimination diagram. Zircon U–Pb dating yields a timing of ca. 272–241 Ma for the protolith age of the Lanling eclogites. The protoliths of the OIB- and E-MORB-type metabasites in Lanling are postulated to be ocean island magmatites and basaltic crust of the Paleo-Tethys Ocean, respectively. Moreover, the Lanling quartzose schists contain only ancient detrital zircons with ages of >500 Ma and show protolith lithostratigraphy and provenance similar to those of the late Paleozoic clastic flysch in the South Qiangtang block (SQB). Based on the above observations and other geological evidence, a hypothetical model of the Permian–Triassic ocean island and adjacent abyssal submarine fan in the Paleo-Tethys Ocean is proposed to explain the protolith origin of the Lanling HP-LT terrane and the presubduction paleogeography in central Qiangtang.