Factors effecting the stability field of Ca-poor pyroxene and the origin of the Ca-poor minimum in Ca-rich pyroxenes from tholeiitic intrusions

摘要: Ca-poor pyroxene ceases to crystallise towards the end of fractionation in tholeiitic intrusions and is usually replaced by Fe-rich olivine. Using data Nicholls et al. (1971), $$a_{{\text{SiO}}_2 }$$ at which olivine can coexist has been calculated different temperatures pressures. From these calculations it clear that Fe/Mg ratio last from a melt increased raising temperature or pressure crystallisation. The pyroxene-Fe-rich relationship also dependent on melt. In magmas before quartz, inicreasing their will raise crystallise. If magma so high SiO2 saturation reached appearance cumulus olivine, any further increase not influence stability field pyroxene. replacement requires reach level a FeO late its fractionation. fractionates with an FeO depletion trend, Ca-rich reaction initiated K-feldspar results marked reduction amount anorthite crystallising magma. This increases a CaO