SUMMARY

A preliminary report on Rb-Sr, Sm-Nd age determination and isotopic composition
for pelitic gneiss from Pô Kô and eclogite samples from Điện Biên area, Việt Nam

T. Miyamoto, Y. Osanai, N. Nakano, M. Owada,
Nguyễn Thị Minh, Dương Đức Kiêm, Trần Ngọc Nam

Rubidium and strontium isotope compositions of pelitic gneiss from Pô Kô area define an internal isochron with age of 229 ± 1 Ma and ⁸⁷Sr/⁸⁶Sr initial ratio of 0.73963 ± 0.00005. This age shows the last geothermal activity in the Ngọc Linh Complex, Kon Tum Massif. The initial ratio shows that its protolith was old crustal deposits.

Samarium and neodymium isotope compositions of whole rock and mineral fractions of eclogitic rock (050830T03A) could not define any isochron. A cause for this result is probably modification of isotope composition during alteration after peak metamorphism.