SUMMARY

Source features and melting conditions of Cenozoic basalts at Pleiku

Nguyễn Hoàng

The Pleiku basalt centre is one of the Vietnamese Cenozoic basalt plateaus that were formed after the cessation of the East Sea Basin opening and the uplift of the South Central Việt Nam. This basalt plateau occurred through several eruption episodes, from about 9 Ma to 0.32 Ma, with different periods of quiescence in between, producing lavas with a secular changing from voluminous, high-SiO₂, low-FeO* quartz and olivine tholeiites, to less voluminous, low-SiO₂, high-FeO* olivine, sub-alkaline and alkali basalts, and generally higher incompatible element concentration from older to younger lavas. The first trend is interpreted as an effect of decreasing melt fraction with increasing pressure, while the second is probably a function of source fertility. Comparison of primitive calculated basalts with parameterized experimental melt compositions shows segregation pressures ranging from 10 kbar for old eruptives up to 30 kbar for younger lavas.