Petrogenesis and Lithium Mineralization of the Ke’eryin Diorite-Granite-Spodumene Pegmatite Complex in the Songpan-Ganze Orogenic Belt (China)

Abstract Li-rich pegmatites are commonly associated with evolved magmatic suites in post-collisional settings with significant mantle input, yet the petrogenetic links between mantle-derived magmatism and crustal felsic melts remain poorly constrained. The Ke’eryin intrusive complex, located in the eastern Songpan–Ganze Orogenic Belt (SGOB), offers a rare opportunity to reconstruct the complete magmatic evolution from the emplacement of mantle-derived mafic melts to highly evolved spodumene-bearing pegmatites that host world-class lithium (Li) mineralization. Whole-rock geochemistry, Sr–Nd whole-rock isotopes, zircon Hf isotopes, and U–Pb ages of zircon, columbite-group minerals, and cassiterite reveal two temporally distinct but genetically linked magmatic phases: (1) an early mafic–intermediate suite of diorites and granodiorites (ca. 226–218 Ma), characterized by εHf(t) values of –8.6 to –1.6 and geochemical signatures of subcontinental lithospheric mantle (SCLM)-derived magmas; and (2) a younger felsic suite of leucogranites and pegmatites (ca. 216–210 Ma), displays chemical signatures, εNd(t) values (–11.4 to –4.7) and zircon εHf(t) values (–11.3 to –3.0) typical for sediments from old crustal sources. The continued intrusion of mantle-derived magmas established a deep crustal hot zone that triggered biotite-dehydration melting of metasedimentary rocks. This process generated peraluminous melts that were Li-rich because of the breakdown of biotite. Progressive fractional crystallization led to the enrichment in Li (up to 11300 μg/g), Rb, Cs, and Be, the depletion in Sr, Ba, and REEs, along with increasing SiO₂ contents. At advanced stages of differentiation, fluid enhanced the mobility of incompatible elements such as Li, Rb, and Cs. The ascent and emplacement of these evolved melts were facilitated by shear zones and extensional deformation. This study highlights the key role of sustained mantle heat input and fluid-mediated differentiation in driving extreme Li enrichment in felsic magmatic systems.