Crust–mantle interactions and remelting of mica-rich residues in the lower crust: a new petrogenetic model for the southern Jinshajiang–Red River K-rich igneous belt, SW China

The Cenozoic potassic granitoids render the Sanjiang area one of the most promising regions for metal resources in eastern Tibet and southwestern China. To elucidate the genesis of the Cenozoic potassium-rich magmatism and its sources, this study presents new geochronological, geochemical, and Sr – Nd – Hf isotopic data for the shoshonitic intrusions from Habo in the Lüchun<b>–</b>Jinping area, southeastern Yunnan. The lamprophyres have high MgO and transition metal contents, high Mg# values and enriched isotopic characteristics, with similar neoproterozoic two-stage whole-rock Nd and zircon Hf model ages. These characteristics indicate that they originated from the Neoproterozoic subduction-related metasomatized subcontinental lithospheric mantle (SCLM). The Habo intrusive complex contains mafic microgranular enclaves (MMEs) that have the petrographic and geochemical characteristics of magma mixing. Based on geochemical and isotopic data analysis of granitoids from the Lüchun – Jinping area, we have identified potassic endmembers of crust-derived felsic melts originating from metasedimentary sources. The trace elemental and isotopic characteristics of these felsic endmembers are consistent with those of coeval lamprophyres, suggesting that their sources were reformed by neoproterozoic partial melting processes and mantle-derived fluids. Consequently, the potassium granitoids originate through the remelting of neoproterozoic mica-rich residues in the lower crust with varying degrees of mafic melts hybridization in the source areas, fractional crystallization, and magma mixing processes. Integrating the geological and geophysical data, we propose a geodynamic model for the Eocene shoshonitic magmatism: (a) The neoproterozoic and triassic oceanic subduction reformed the regional SCLM and the lower crust, produced the metasomatic SCLM and fusible mica-rich residues in the lower crust; (b) The Cenozoic partial melting of pre-existing metasomatized SCLM and fusible crustal materials produced the mantle-derived and crust-derived melts, as well as their mixtures in different proportions, triggered by asthenosphere upwelling. This study provides new insights into the role of crust–mantle interactions in potassium-rich magmatism.