The Estimation Of Temperature And Oxygen Fugacity For Igneous Rocks

Oxygen fugacity, as same as temperature, pressure and composition of the melt, is the most basic physical and chemical parameters of the magma. It reflects the magma redox state, and directly decide the valence of key metallogenic elements, such as control the sulfur in the form of S2- and SO42- to affect the porphyry copper deposit, so oxygen fugacity is also one of the important parameters of magmatic mineralization ability. With the progress of testing technology in recent years, to estimate oxygen fugacity by in-situ zircon trace elements has been paid more and more attention. Because of zircon’s high closure temperature, strong weathering and erosion resistance, it can maintain the chemical characteristics of its formation, now, zircon is widely used in situ U-Pb isotope dating, in situ Hf-O isotopic tracer, in situ trace element analysis and so on, which provide great convenience for the estimation of zircon’s oxygen fugacity and formation temperature.In this paper, three tectonic units-the middle and lower Yangtze River, Jiangnan uplift zone and Dabie orogenic belt are involved. Based on their chronology stages of mesozoic magmatic rocks, we make statistical analyses and comparison of oxygen fugacity and temperature for representative samples in each stage, so as to summary their rule and feature. Besides, we also estimate oxygen fugacity in different way, especially using modified m-estimator to fitting Ce3+ distribution coefficient.For the middle and lower Yangtze River, we carried out a detailed analysis. The analysis reveals that:oxygen fugacity for the four stages of magmatic rock in the middle and lower Yangtze River are high, and the first stage is similar to the fourth stage, the second stage is close to the third stage, and from the first stage to the fourth stage, the magmatic oxygen fugacity from high to lower, then rising trend, accordingly, the temperature increased first and then decreased. these corresponds with that, the first stage is adakitic, the third stage is A-type granite, and the fourth stage is adakitic.And for the Jiangnan uplift and the Dabie orogenic belt, we do the same estimation and statistics, but lack of the whole rock’s trace elements in these two area, we use the data from other papers as substitute, which does not affect the results of the comparison. Three stages magmatic oxygen fugacity in Jiangnan uplift and the Dabie orogenic belt are from early to late decreased gradually, and temperature is Just the opposite, which also correspond with adakitic rocks and A-type granite in these two area.