Petrogenesis of nephelinites from the Tarim Large Igneous Province, NW China: Implications for mantle source characteristics and plume–lithosphere interaction

• The Wajilitage nephelinite represents the last phase of magmatism of the TLIP.
• Magnesium isotope is reported for the Wajilitage nephelinite.
• Minor carbonatic enclaves are recognized in the nephelinite.
• A hybridized carbonated peridotite/eclogite source is proposed for the nephelinite.
• A plume-lithosphere interaction model is proposed to interpret the varity of complex rock types.

The nephelinite exposed in the Wajilitage area in the northwestern margin of the Tarim large igneous province (TLIP), Xinjiang, NW China display porphyritic textures with clinopyroxene, nepheline and olivine as the major phenocryst phases, together with minor apatite, sodalite and alkali feldspar. The groundmass typically has cryptocrystalline texture and is composed of crystallites of clinopyroxene, nepheline, Fe-Ti oxides, sodalite, apatite, rutile, biotite, amphibole and alkali feldspar. We report rutile SIMS U-Pb age of 268 ± 30 Ma suggesting that the nephelinite may represent the last phase of the TLIP magmatism, which is also confirmed by the field relation. The nephelinite shows depleted Sr-Nd isotopic compositions with age-corrected 87Sr/86Sr and εNd(t) values of 0.70348–0.70371 and + 3.28 to + 3.88 respectively indicating asthenospheric mantle source. Based on the reconstructed primary melt composition, the depth of magma generation is estimated as 115–140 km and the temperatures of mantle melting as 1540–1575 °C. The hotter than normal asthenospheric mantle temperature suggests the involvement of mantle thermal plume. The Mg isotope values display a limited range of δ26Mg from − 0.35 to − 0.55‰, which are lower than the mantle values (− 0.25‰). The Mg isotopic compositions, combined with the Sr-Nd isotopes and major and trace element data suggest that the Wajilitage nephelinite was most likely generated by low-degree partial melting of the hybridized carbonated peridotite/eclogite source, which we correlate with metasomatism by subducted carbonates within the early-middle Paleozoic convergent regime. A plume-lithosphere model is proposed with slight thinning of the lithosphere and variable depth and degree of melting of the carbonated mantle during the plume-lithosphere interaction. This model also accounts for the variation in lithology of the TLIP.