Petrogenesis Of The Late Mesozoic Gabbros In The Eastern Jiangnan Orogen, South China: Characteristics Of The Lithospheric Mantle

As we know, mantle-derived mafic rocks can be used to effectively trace the nature of the mantle source and constrain the regional tectonic setting and evolution. Recently, a Late Mesozoic mafic intrusive body (Huangmao pluton) has been found in the eastern Jiangnan Orogen (EJO). In this study, we investigate this pluton using petrography, whole-rock geochemistry, Sr-Nd-Pb isotopes, and geochronology. The Huangmao pluton is primarily composed of a fine-grained gabbro-diabase, which is characterized by consistent SiO2, MgO, Fe2O3T, and TiO(2)contents. These gabbros exhibit continental crust-like trace element signatures, i.e., enriched in large-ion lithophile elements (LILE), Pb, and light rare earth elements (LREE), but depleted in high-field-strength elements (HFSE). In addition, the Huangmao gabbros have moderate initial(87)Sr/Sr-86 ratio (0.7065-0.7080) and slightly negative to weakly positive epsilon(Nd)(t) value (-2.06 to +0.84). Finally, U-Pb zircon dating confirms that the Huangmao pluton was emplaced in the Late Jurassic (152.6 +/- 3.1 Ma). Through an integrated geochemical analysis, these Late Mesozoic gabbros were genetically originated from an enriched lithospheric mantle source, which formed by a metasomatic reaction between mantle peridotite and sediment-derived felsic melt. Consequently, the lithologies of the metasomatite were predominantly pyroxenites with a small amount of pyroxene-rich peridotites. Considering the large distance between the modern trench and the EJO, the flat-slab subduction and rollback model of the palaeo-Pacific Plate is the most reasonable interpretation of the geodynamic setting that resulted in Late Mesozoic magmatism in the EJO.