Potassium isotopic evidence for the petrogenesis of Precambrian granitoids and implications for early crustal evolution of the accretionary orogen

• 2.5 Ga granite sourced from melting of metasomatized mantle material and sediments. • 1881 Ma granite sourced from melting of ancient crust and metasomatized mantle. • 1843 Ma granite sourced from melting of thickened crust with ancient sediments. • K isotope is a potential tracer of granite petrogenesis and early crustal evolution. Stable potassium (K) isotopes are emerging as a novel geochemical tracer for investigating magmatic differentiation and source characteristics. This study presents the K isotopic analyses of Neoarchean–Paleoproterozoic granitoids from the Xing’an Massif, a key microcontinent within the eastern Central Asian Orogenic Belt (CAOB), providing new insights into the granitoid petrogenesis and early crustal evolution of this accretionary orogen. The 2568 Ma peraluminous A-type monzogranite exhibits significantly heavier δ 41 K values (−0.22 ‰ to −0.05 ‰) compared to the range of the upper continental crust. Subduction zones can effectively transfer heavy K isotopic signature to the mantle wedge through slab-derived fluids/melts. The monzogranite could be formed through co-melting and mixing of previously metasomatized mantle materials and recycled supracrustal metapelites, followed by high degree of fractional crystallization in a post-collisional extensional setting. Although both the 1881 Ma monzogranite and 1843 Ma syenogranite share geochemical affinities with adakites, their markedly different K isotopic compositions and distinct geochemical fingerprints point to substantial heterogeneity within their source regions. The 1881 Ma monzogranite shows more pronounced heavy K isotopic enrichment ( δ 41 K = −0.39 ‰ to −0.18 ‰) and elevated zircon δ 18 O values (7.28 ‰–8.93 ‰). These features demonstrate the incorporation of mantle components metasomatized by melts of altered oceanic crust (with elevated δ 41 K values) into the lower crustal source. In contrast, the 1843 Ma syenogranite displays ultrapotassic affinity with lighter K isotopic compositions ( δ 41 K = −0.45 ‰ to −0.38 ‰) and strongly negative zircon ε Hf ( t ) values (−11.5 to −10.2), indicating a thickened lower crustal source with contributions from ancient supracrustal sediments. Collectively, K isotopic compositions of the ca. 1.8 Ga adakitic granitoids overcome the limitations of traditional geochemical and isotopic proxies in revealing the complex granite petrogenesis, and they potentially provide evidence for a cycle of plate tectonics, from oceanic crust alteration at mid-ocean ridges through slab subduction to continental collision. The onset of plate tectonics promoted remelting of Archean igneous and sedimentary crust, generating abundant peraluminous and potassic granitoids during the late Archean to Paleoproterozoic and driving crustal compositional maturation in this accretionary orogen.