K-Ar chronology and geochemistry of mafic dikes in the Huangmeijian area, Anhui and their geological significances

On the basis of field geological survey and indoor comprehensive analysis, this study discussed ore-forming age, genesis and tectonic setting of diabase porphyrite of Huangmeijian pluton in the Huangmeijian area using K-Ar chronology, geochemistry and Sr-Nd isotope geochemistry. K-Ar dating results show that the diabase porphyrite formed in ～107 Ma and should be the product of the early Cretaceous magmatic activity. The diabase porphyrite formed later than volcanic rocks and intrusive rocks in the area, but is consistent with that of U mineralization, indicating that the emplacement of diabase porphyrite was likely the last stage of magmatism and uranium mineralization may be genetically related to the diabase porphyrite. Geochemical characteristics indicate that the diabase porphyrite is rich in potassium, large ion lithophile elements(K, Rb, U and Pb)and light rare earth elements, and the loss of high field intensity elements(Nb, Ta, P and Ti), with high I_sr and negative ε_Nd(t)value, suggesting characteristic of mantle-enriched source. The diabase porphyrite was formed from partial melting of enriched mantle due to subduction metasomatism under the tectonic background of crustal extension and lithospheric thinning, indicating that the region was still in an extensional tectonic environment at ～107 Ma.