Researches On The Geological And Geochemical Features And The Petrogenesis Of Gejiu Complex, Yunnan Province

In Mid-Late Yanshanian, magmas were intensively active which generated a series of basic, acid and alkaline complex in Gejiu, Yunnan Province. Some scholors have worked on them for many years, but their petrogenesis are deficient. Thus, we take Shenxianshui granites, Kafang granites and Jiasha gabbro-monzonites as main objects. By using XRF, ICP-MS and EMPA-1600 analysis methods, we have described their geochemical characters of Gejiu complex in details, and made some primary conclusions as followings:1. Gabbro-monzonites of Jiasha are enriched in LILE, LREE, relatively depleted in HREE and characterized by alkaline-rich and slight Eu-depletion, indicating their enriched-mantle sources; but they have characteristics, by comparison to OIB, with depletion of some elements (Nb, Ta, Ti et al.) which suggest crust's contamination.2. Granites generally have characters of high SiO₂, Al₂O₃, (K₂O+Na₂O) (especially K₂O). The content of Al₂O3, Fe₂O₃T, MgO, CaO, P₂O₅ and TiO₂ are negatively linear with that of SiO₂. When the content of SiO₂ is over 70%, the variation of K₂O and Na₂O is negligent.3. As for rock types, the values of A/CNK of granites vary from 0.92 to 1.08, attributed to I-type granites; granites of Gejiu formed from continental collision environment, concretely from late-collision or post-collision geological environment; their material sources are mainly from crust with characters of mixing between basic and acid sources.4. According to the pilot studies, granites generated by re-melting of lower continental crust, which is related to basaltic magma's underplating.