中酸性硅酸盐熔体-水体系氢同位素分馏的压力效应

对0．2－2000MPa条件下钠长石熔体，钾长石熔体以及0．2－150MPa条件下流纹岩熔体－－水体系的氢同位素分馏实验数据进行了筹压拟合，发现硅酸盐熔体与水之间的氢同位素分馏存在显著的压力效应，在800，1000和1200度条件下对钠长石熔体，水体系和流夺熔体－－水体系氢同位素分馏压力方程进行的等温拟合表明，只有在特定的压力条件下才可以用钠长石熔体－水体系来近似流纹岩熔体－－水体系的氢同位素分馏行为，当压力超过临界值时，硅酸盐熔体－水体系氢同位素分馏会发生变化，本文拟合的硅酸盐熔体－水体系氢同位素分馏等值线在P－T空间的形态变化特征与矿物－水体系存在较大差异，依据流纹岩熔体与水之间氢同位素分馏的压力效应，成功地模拟了美国西部Glass Creek流纹岩δD值和水含量变化规律与岩浆去气之间的关系。

Pressure effect on hydrogen isotope fractionation between intermediate-acidic silicate melts and water

Experimental data for hydrogen isotope fractionatins between albitic,K-feldspar,and rhyolitic melts and water vary aystematically with pressure from0.2to 2000 Mpa.Pressre equations for albitic and rhyoliticmelt-water systems are fitted accordingly under isothermal conditions of 800,1000,and1200C.The results show that the behavior of hydrogen isotoe fractionationin the albitic melt-water system cannot be analogouslyaplied to that inthe rhyolitic melt-watersstem except at particular pressures.There is crossover in hydrogenisotope fractionation between silicate melts and waater when the experimentaal pressure is higher than the critical value.Teh contours of hydrogen isotoe fractionation between silicate melts and water are constructed in P-Tspace,which are aparently different from those for brucite-water system.interms of pressure effect on hydrogen isotope fractionation in the rhyolitic melt-water system,the unusual variability in the &Dvalues and h2o contemts of the Glass creek rhyolites from western umited states are successfully modeled in the course of magmatic degassing .