Petrogenesis of late Mesoproterozoic granitoids in the Miyi–Yuanmou region: implications for the tectonomagmatic evolution of SW China

Considerable debates still persist over the petrogenesis and magma source affinities of Late Mesoproterozoic granitoids in the Miyi–Yuanmou region. To resolve these uncertainties, this study presents comprehensive geochemical and isotopic constraints, with key conclusions outlined below: (1) The granitoids are enriched in large-ion lithophile elements (e.g. Rb, Th, U, K, Pb) and remarkably depleted in Sr, Nb, Ta, Ti, and P relative to the Normal Mid-Ocean Ridge Basalt (N-MORB). (2) The bulk trace element distribution patterns exhibit OIB-like geochemical affinities (3) The granitoids display widely variable εNd(t) values (−9.9 to +4.4, avg. −2.1) and ancient two-stage TDM2 model ages, indicating that ancient continental crust served as the dominant magma source; by contrast, the predominantly positive zircon εHf(t) values (−4.4 to +16.6, avg. +5.1) and their consistency with coeval mafic rocks demonstrate extensive mantle-derived material incorporation. Such Nd–Hf isotopic decoupling reflects variable degrees of crust–mantle interaction during magma evolution. (4) The granites are dominantly A2-type granitoids with minor A1-type and S-type geochemical fingerprints, recording a transitional tectonic–magmatic environment. (5) Integrating REE patterns, trace element spidergrams, Nd–Hf isotopic compositions, trace element modelling, and field geological observations, the studied granitoids were generated by binary magma mixing between lower continental crust (LCC)-derived crustal melts and mantle-derived magmas.