Petrogenesis Of High-Ti And Low-Ti Basalts In Emeishan

Emeishan flood basalt is one of many regions in which Geo-science circles are interested. Many geologists have researched the geology, geochemistry, geophysics of Emeishan basalt; not only doing the fruitful work about its distribution scope, the active time limit, rock association, petrochemistry and lithogeochemistry aspects ; but also doing the thorough research to its magmatic process, magmatic character, mantle source characteristics, accumulating the rich material. But to some key scientific questions understanding still remains disagreed, or waits for further discusses.This article takes the author in the Yunnan northwest Binchuan - Yongsheng -Lijiang area and the Yunnan northeast Lu Dian - Dongchuan area to gain material as a foundation, unified predecessor's correlation data, through the petrography, the petrochemistry, the rare-earth element, the trace element and Nd, Sr, Pb isotope aspect system research, and preliminarily analyzed its magmatic processing, mantle source characteristic, its evolved mechanism of the Emeishan basalt and discussed correlative questions of low-Ti basalts and high-Ti basalts above scientific question. Obtaining main progress as follows:1. Distribution scope of the Emeishan basalt is quite broad, and the most main rock type is low-Ti basalts and high-Ti basalts, and has the few picritic basalts, picrites and meymechites.2. The petrochemical compositions of these volcanic rock basically belong to the tholeiitic series, a little basalts to the calc-alikalic series. They enrich in LILEs and LREEs at different degrees, and deplete relatively to HREEs, REEs fractionate evidently, compatible elements (Co, V, Cr, Ni) deplete significantly.3. Low-Ti basalt magma was obviously contaminated by continent crust, in a larger extent than high-Ti basalt magma. And influences of contamination on Sr isotope and LILEs are more evident than those on Nd isotope and REEs. Nd and Sr isotope prove that contamination materials are mainly metamorphic rocks of lower continent crust, but also have minor rocks of upper continent crust. That the samples were not contaminated shows Nd and Sr isotopic compositions of moderately depleted mantle.