Experimental Study On Melting Of Enstatite Chondrites At High Pressure

Isotopic evidences of Oxygen?Nitrogen?Osmium?Molybdenum?Ruthenium?Chromium and Titanium show that the enstatite chondrites may be one of the most important building blocks of the Earth.High temperature and high pressure melting experiments on enstatite chondrites provide important constraints for the formation and differentiation of the earth and planets,making it become a hot spot in the research field of Earth and planetary science.Previous studies show that the pressure and temperature have effects on crystallization sequence ? elements partitioning and isotopic fractionation.However,it should be note that oxygen fugacity(f O2)is also a key parameter to constrain the evolution and core-mantle differentiation at planetary early stage.Considering that enstatite chondrites are formed in highly reduced environment(IW-3~-8),silicon(Si)powder was added in starting materials to reduce f O2 in previous high pressure and temperature studies.However,in iron-sulfur(S)-silicon(Si)-carbon(C)system,the presence of Si will affect the solubility of S,C in molten iron.Adding Si in the system will have great effect on phase relations.In addition,chemical reagents were usually used as starting samples in previous studies.We think that the high temperature and high pressure experiments on natural enstatite chondrites can truly simulate the early evolution history of the earth,but the high pressure experiment with natural sample is rarely reported.Sample chamber is the key to control the oxygen fugacity in Experimental Petrology.It is necessary to select the reduced sample chamber for the high temperature and high pressure study of enstatite chondrites.However,there is no systematic data on oxygen fugacity control of different material chambers,and there are some controversies between graphite and Mg O sample chamber.In our work,two parts of experimental research were carried out.In the first part,high pressure and temperature experiments were conducted on synthetic enstatite chondrite samples by using different sample chambers(Mg O,graphite,boron nitride,Platinum and Chromium).The aim of this study is to investigate the f O2 condition imposed by the interested sample capsules without adding extra Si.Our experiment pressure and temperature are 1 GPa and 1700?,respectively.The heating duration is 3-20 minutes.Based on the results of the first part,we conducted high pressure and temperature melting experiments on the enstatite chondrite Sahara 97159 samples in the second part.The experimental pressure and temperature are 1 GPa and 1500~1600?,respectively.The heating duration is 80 minutes.Some conclusions were drawn below:(1)The oxygen fugacity level of different capsule materials are(from oxide to reduce): Mg O > graphite > boron nitride.Pt and metal chromium react strongly with samples under high temperature and high pressure,and are not suitable for metalsilicate-sulfide systems.(2)High pressure and temperature melting experiments of Sahara 97159 show that the liquidus temperature is between 1500~1600? at 1GPa and metallic drops coexist with molten silicate in run products.It means that the liquid outer core may be stratified in the planetary bodies formed under low pressure conditions,...