KâAr age data for southeast Asian Cenozoic basalts and trapped melt consolidated at depth (see Latin et al., 1993). concluded ... submarine activity along the eastern seaboard (Koloskov .... collected by Vietnamese and Soviet scientists during ..... 2O. 2·94. 2·81. 2·57. 2·89. 2·97. 2·94. 2·84. 2·84. 2·45. 2·87. 2·77. K 2O. 1·19.
JOURNAL OF PETROLOGY
VOLUME 39
NUMBER 3
PAGES 369–395
1998
Petrogenesis of Cenozoic Basalts from Vietnam: Implication for Origins of a ‘Diffuse Igneous Province’ NGUYEN HOANG∗ AND MARTIN FLOWER† DEPARTMENT OF GEOLOGICAL SCIENCES, UNIVERSITY OF ILLINOIS AT CHICAGO (M/C 186), 845 W. TAYLOR STREET, CHICAGO, IL 60607-7059, USA
RECEIVED JULY 8, 1996; REVISED TYPESCRIPT ACCEPTED AUGUST 28, 1997
low-viscosity thermal boundary layer (TBL), and caused upward penetration and polybaric melting of TBL–asthenosphere columns.
Basalt magmatism occurred throughout east and southeast Asia after the early Tertiary India–Asia collision. This activity does not conform to the ‘Large Igneous Province’ model in view of lower eruption and melt production rates, wide dispersal of centres and the apparent absence of deep mantle upwelling. Age data for Vietnamese plateau basalts reflect spatial–temporal patterns consistent with a rotating stress field rather than suprahotspot lithosphere migration. For most of the volcanic centres there are two eruptive episodes: an early series formed by highSiO2, low-FeO∗ quartz and olivine tholeiites—large melt fractions of refractory (lithosphere-like) mantle—and a later series made up of low-SiO2, high-FeO∗ olivine tholeiites, alkali basalts and basanites—smaller melt fractions of more fertile (asthenospherelike) mantle. Comparison of Mg-15 normalized basalt compositions with parameterized anhydrous and hydrous experimental melt compositions allowed calculation of melt segregation pressures and temperatures. Computed for anhydrous conditions these range from
