矿床地球化学国家重点实验室知识库

Mafic-layered intrusions and sills and spatially associated andesitic basalts are well preserved in the Funing area, SW China. The 258±302Ma-layered intrusions are composed of fine-grained gabbro, gabbro and diorite. The 260±302Ma sills consist of undifferentiated diabases. Both the layered intrusions and volcanic rocks belong to a low-Ti group, whereas the diabases belong to a high-Ti group. Rocks of the high-Ti group have FeO, TiO 2 and P 2 O 5 higher but MgO and Th/Nb ratios lower than those of the low-Ti group. They have initial 87 Sr/ 86 Sr ratios (0.706–0.707) lower and 07Nd (611.5 to 610.6) higher than the low-Ti equivalents (0.710–0.715 and 619.6 to 614.0, respectively). The high-Ti group was formed from relatively primitive, high-Ti magmas generated by low degrees (7.3 –9.5%) of partial melting of an enriched, OIB-type asthenospheric mantle source. The low-Ti group may have formed from melts derived from an EM2-like, lithospheric mantle source. The mafic rocks at Funing are part of the Emeishan large igneous province formed by a mantle plume at 6526002Ma.