SUMMARY
Geochemistry of Late Cenozoic basalts in Việt
Phạm Tích Xuân , Nguyễn Hoàng, Lee Hyun Koo
The Late
Cenozoic basalts consist of two main series related to two eruptive episodes.
The early episode (bN1-N21) comprises voluminous tholeiitic
and olivine basalts, erupted from extensional fissures. The late episode (bN22-Q), formed by central
eruptions, comprises mainly alkaline basalts. The lower series basalts are
characterized by high SiO2, low TiO2, FeO*, Na2O+K2O
and P2O5, while the upper series basalts have low SiO2,
high TiO2, FeO*, Na2O+K2O and P2O5
and usually have higher contents of incompatible elements. Diversity of
compositions of basalts was due to the difference of melt generation conditions
(P-T, fluid), degree of partial melting or heterogeneous of sources. The lower
series were generated under intensive extension of territory (high degree of
partial melting), in shallow mantle (low pressure). In contrast, the upper
series were generated under limited extension of territory (low degree of
partial melting), in deeper mantle (high pressure). The differentiation in
intensity and appearance of W-E extension is the cause of feature of
distribution of late Cenozoic basalts: most of the eruptive centres are
concentrated in the southern part of