The Geochemistry Of Basalts Of Woniusi At Baoshan Area In The West Of Yunnan, And Its Tectonic Implications

The basalts of Woniusi in the MaChang and DaoJieBa two places, in the city of BaoShan, YunNan, that as volcanic rocks, are recorded derectly the activities of plates, bearing some information of the lithosphere and the evolution of the mantle, are the main objects in Geodynamics. The basalts in MaChang and DaJieBa areas are prophyritic basalts, almond-shaped basalts and altered basalts and so on. The main structures are porphyritic texture, intergranular structure and intersertaltexture in ground substance and so on. The basalts of Woniusi in MaChang are mainly calc-alkaline rocks, belonging to tholeiitic seric; The basalts of Woniusi in DaoJieBa are calc-alkaline rocks and alkaline rocks, belonging to calc-alkaline series and alkaline series. The basalts in this two places contain higher calcium, low Ti, low potassium, belonging to Na-rich, poor potassium and Na-rich types, while they have high aluminum content, belonginging to an aluminum-based rocks. The analysis of the Mg content and SI index show that the local rising magma experienced fractional crystallization or partial melting of wall rocks. REE distribution carve was flat from right deviation type, LREE and HREE fractionating and enriching weakly of LREE. The overall convergence carve is similar to the types of the basalts of the active plate margin and the cala-alkaline basalts of the typical islands. The Eu and Ce elements are normal. It shows that the large ion lithophile element enrichment and some loss of high field strength elements in the trace element analysis of rocks, and Zr element significantly enriched, P element loss, what declared obviously that fractional crystallization of apatites with the petrography analysis. Cr, Ni, Co elements of basalts with low average suggested that their source region or the primary magma possibly contaminated by the crust, indicating magmatic source region heterogeneity. The ratios of Zr/Nb and Nb/Ta like that of the rhyolites of intracontionental extensional environment in DaXingAnLing, and the ratios of Th/Nb and Nb/Zr are similar to that of volcanic rocks of continental intraplate rift. Then in Permain, the local basalts were produced in the expanding environment of continental rift with the analysis of the basalts in the ancient environment, and they are mainly basalts of continental interiors and the orogenic belt, and the magmatism was afftered by the plates and the orogenic belt. Meanwhile Sibumasu micro block in Gondwanaland had lifted northwards and the ancient Asia landmass moved southwards, squeezed the sediment of Paleotethys between them, made up into a land of western YunNan, and formed the modern original landscape.