Mesozoic crust-mantle interaction in the East Kunlun Orogenic Belt, northern Tibetan Plateau: Constraints from the Tuolahai granodiorite and MMEs

Crust-mantle interaction occurs widely in orogenic belts, exerting a crucial role in understanding the petrogenesis of igneous rocks and the geodynamic processes of orogenic evolution. The East Kunlun Orogenic Belt (E-KOB), as a typical subduction-accretionary orogenic belt, underwent a prolonged subduction-accretionary evolutionary process from the Early Paleozoic to the Triassic, accompanied by multi-stage magmatic activity. A set of granodiorites with mafic microgranular enclaves (MMEs) outcropped in the Tuolahai of the Central Kunlun Belt is key to revealing the crust-mantle interaction correlated with subduction or collision in the E-KOB. In this study, petrological, mineral chemical, whole-rock and isotopic geochemical, and geochronological investigations were conducted on the Tuolahai host granodiorites and MMEs to investigate their petrogenesis, magma source, and tectonic significance. The zircon UPb geochronology suggests comparable crystallization ages of 247 ± 2 Ma and 246 ± 2 Ma for the host granodiorite and MMEs, respectively. The host granodiorites are primarily composed of medium-to-coarse plagioclase, amphibole, quartz and biotite. Geochemically, they exhibit calc-alkaline and metaluminous, with enrichment in LILEs, and slight depletion in HFSEs, belonging to I-type granites. They display negative ε_Nd(t) (−5.89 to −5.27) and ε_Hf(t) (−4.77 to −2.25), along with comparatively young two-stage Nd and Hf model ages (1.44–1.49 Ga and 1.41–1.57 Ga, respectively). These geochemical features suggest that the granodiorites originated predominantly from juvenile mafic lower crust, with contributions from deep mantle-derived materials, while experiencing minor upper crustal contamination during their ascent. Compared to the granodiorites, the MMEs exhibit a finer-grained texture composed of plagioclase, amphibole, biotite and quartz. Geochemically, they display lower SiO₂ (50.12–54.13 wt%), higher MgO (4.13–5.29 wt%), ΣREE contents, similar rare earth element patterns, and ε_Nd(t) (−5.59 to −5.10), but distinctly different ε_Hf(t) (−7.68 to −0.14) values. Considering that the sharp contact, the plagioclase and amphibole xenocrysts in the MMEs are compositionally similar to those in the host rock, we propose that the MMEs represent products of magma mingling, with their sources primarily originating from mantle materials, indicating formation through the partial melting of an enriched lithospheric mantle. Comprehensive petrology, geochemistry and mineral chemistry indicate that the Tuolahai batholith is a product of crust-mantle interaction, where the upwelling of enriched lithospheric mantle led to partial melting of the mafic lower crust, forming hybrid magma and MMEs. Together with the regional geological data, all the above lines of evidence allow us to propose that the Tuolahai granodiorites and the associated MMEs were formed through crust-mantle interaction during the northward subduction of the Paleo-Tethys Ocean.