Geochemical Characteristics of Diorite Porphyrite in Dawu Area, Western Dabie and Its Tectonic Significance

Basic magmas can reflect the nature of mantle source region, genetic environment and formation and evolution process. Through the detailed field geological survey and rock geochemical analysis, we discuss the nature, genesis and tectonic environment of the magma source area of regional diorite porphyrite. The geochemical analysis of the whole rock shows that the SiO₂ content of the diorite porphyrite samples is 49.97%～55.01%, belonging to the medium−basic rock series, the MgO content is 4.63%～5.49%, and the Mg^# content is 60.17～90.19, the Nb/Ta value of the sample is 13.06～18.47, and the Zr/Hf value is 40.09～44.05, indicating that the magma source area of the diorite porphyrate may be from the enriched mantle. In addition, The LREE/HREE ratio is 9.45～13.97, and the diorite porphyrite samples show a steep−right diorite, and they are enriched in high field strength elements (Nb, Ta, Hf, Ti) and rich in large ion lithophile elements Sr. It is suggested that porphyrite may have been influenced by fluid metasomatism of subducted plates during the formation process. The field outcrops show that diorite porphyrite dikes intrude into granitic porphyry dikes (forming age is 130.8±1.8 Ma), so the emplacement time of dikes may be early Cretaceous. In the discrimination diagram of Zr−Ti tectonic environment, the diorite porphyrite samples fall in the intraplate basalt area. Combined with the regional tectonic background, we believe that the diorite porphyrite should be formed in the post−orogenic extension environment.