Generation of REE-rich syenite-(carbonatite) complex through lithosphere-asthenosphere interaction: An in-situ Sr–Nd–O isotopic study of the Mesozoic Weishan pluton, Northern China.

[Display omitted] • In-situ Sr-Nd-O isotopic analyses of minerals are employed to constrain the nature of primary magmas in the Weishan syenite-(carbonatite) complex. • Both lithospheric and asthenospheric mantle have contributed to the generation of the Weishan complex. • Involvement of asthenosphere-derived components may play an important role in the enrichment of REE in the Weishan complex. Carbonatite-alkaline complexes are commonly derived from the mantle. However, whether the source is lithospheric or asthenospheric mantle remains debated. In order to better understand this issue, this paper conducts a Sr-Nd-O isotopic study on the Early Cretaceous, Weishan REE-rich syenite-(carbonatite) complex, Northern China. Two types of apatite are identified from the Weishan complex, namely magmatic and xenocrystic apatite. In-situ Sr-Nd isotopic analyses on magmatic apatite yielded (87Sr/86Sr) i from 0.70690 to 0.70719, and ε Nd (t) from −7.6 to −8.8. The pristine calcite from carbonatite has similar (87Sr/86Sr) i (0.70727–0.70739) with magmatic apatite. In-situ oxygen isotopic analyses on zircon yielded δ18O VSMOW (‰) from 5.9 to 6.7 ‰. Previous studies reveal that coeval, mantle lithosphere-derived rocks in the region have more enriched Sr (87Sr/86Sr i greater than 0.709) and Nd [ε Nd (t) 〈 −1 2] isotopes than the Weishan complex; whereas the asthenosphere-derived rocks in the region are characterized by depleted Sr-Nd isotopes (87Sr/86Sr i < 0.706; ε Nd (t) greater than 0) and low δ18O VSMOW values (mostly < 5.4 ‰). It is well known that Northern China experienced destruction in the Early Mesozoic, which was accompanied with asthenosphere upwelling along trans -lithosphere faults. Considering that the Weishan complex locates adjacent to the trans -lithosphere Tanlu fault, generation of the complex may be related to asthenosphere-lithosphere interaction. Notably, the Weishan complex differs from coeval REE-barren carbonatites in that its source involved asthenosphere-derived components; hence, involvement of asthenosphere-derived components may be important for the formation of such a REE-rich complex. In general, this study highlights the importance of lithosphere-asthenosphere interaction in supplying necessary heat and materials for the generation of the Weishan complex. [ABSTRACT FROM AUTHOR]