| The basement complex of the coastal batholith in Arequipa province, Peru, is a unique component of the crust at the root of the Neogene orogenic belt in the South American Andes. It’s also a critical tectonic rock unit for understanding the early evolution of the South American continent. However, current investigations into its rock composition and tectonic deformation remain insufficient, with a notable lack of high-precision age data, which has become a significant obstacle to fully comprehending its tectonic history. Detailed geological investigations conducted in the Atico-Chala region revealed that the basement gneiss consists of supracrustal rocks and metamorphic plutonic rocks. These rocks have experienced ductile shear deformation and amphibolite to granulite facies metamorphism. Layered plagioclase-hornblende gneisses was identified in the supracrustal rocks. Integrated petrological, geochemical, zircon U-Pb geochronological, and Lu-Hf isotopic analyses indicate that the protolith corresponds to fine-basaltic volcanic lava, classified as either island arc tholeiitic basalt or oceanic island basalt. This classification aligns with geochemical signatures indicative of subduction-related processes, specifically Nb-enriched basalts associated with oceanic plate subduction. LA-ICP-MS U-Pb zircon dating yielded a crystallization age of 1863 ± 8 Ma for the plagioclase amphibolite gneiss, followed by an initial metamorphic event at 1798 ± 58 Ma. The εHf(t) values range from -0.7～4.3, while the two-stage depleted mantle model ages (TDM2) vary between 2196 and 2467 Ma. These results suggest that the parent magma primarily originated from partial melting of deep mantle components, with minor contributions from ancient crustal material during magmatism. This study indicates that the basement gneiss formed during the late Paleoproterozoic orogeny (~1.86 Ga), likely in a continental margin arc or oceanic island setting on the eastern edge of the Nena supercontinent. Subduction of the oceanic lithosphere beneath this region triggered asthenospheric upwelling, leading to mixing with the depleted mantle wedge beneath the island arc and subsequent eruption of Nb-rich basalts. The first metamorphic transformation occurred during the early Paleoproterozoic consolidation period (~1.79 Ga), leading to the formation of Paleoproterozoic volcanic complexes. These geological features represent critical evidence for the preservation of tectonic remnants associated with the assembly of the Columbia supercontinent. |