| Dredged rocks from an area of about 15 km² within the inner floor and on the adjacent walls of the Rift Valley were collected. Based on petrographic and chemical data, four types of basaltic rocks were recognized: (1) picritic basalts with olivine xenocrysts, Ti02 inf 0.6%, K20 inf 0.l%, (2) olivine basalts with olivine megacrysts, Ti02=0.8-1.5%, K20=0.1-0.2%, (3) highly phyric and moderately phyric plagioclase basalts with megacrystic plagioclase, Ti02 inf 1.3%, K20 inf 0.3%, and (4) pyroxene basalts with pyroxene > plagioclase, Ti02=0.8-1%, K20=0.2-0.4%. The Cr and Ni having high partition coefficients show different variation trends for each type of rock and their values decrease continuously as crystallization proceeds within each type of basalt. It... |
