Alkaline carbon dioxide hydrotherms and strontium-containing travertines in the Songwe River valley (Tanzania)

This paper considers the thermal water of a group of springs in the Songve River valley, located 7-10 km downstream from the Panda Hill carbonatite ma ssif, and calcareous tuffs formed from this water. The authors relate these hydrotherms to the latest, Quaternary, alkaline magmatism which covered th e entire East-African rift system, including the Rukwa graben, along which the Songwe River flows. The thermal water contains carbon dioxide, alkalies, silicon, carbonates, a nd hydrocarbonates, mineralization being 3.3-3.4 g/l. By some geochemical c oefficients (Li/Rb, Sr/Li, Sr/Rb, rNa/rCl), this water differs from the the rmal water of other continental rift systems, in particular the Baikal Rift water. Using a microprobe permitted study of the carbonate minerals of the tuffs: main - calcite and aragonite and secondary dolomite and strontianite. The c alcites are characterized by extraordinarily high contents of Sr (up to 5.6 wt.% SrO) and Mg (up to 5 wt.% MgO). The aragonites also have high content s of Sr (11.5-36.8 wt. % SrO) and low contents of Mg (0.05-0.17 wt.% MgO) a nd form an isomorphous series with Ca-strontianite (46.8-54.2 wt.% SrO). Sometimes the tuffs contain terrigenous grains of quartz and feldspar and i mpurities of trona, halite, and hydromicaceous minerals.