RE: Rift, Helium, Hydrogen, Tanzania31 Jan 2024 21:45
Why the reported increase in temperature may be vital
3.4.4 Lake Tanganyika and Lake Rukwa area
Geothermometric estimates of sublacustrine hydrothermal vents (53-103°C) at Lake Tanganyika have yielded reservoir temperatures of >200 °C for samples of the NaHCO3-Pemba and NaCl-Cape Banza geothermal systems, respectively (Tiercelin et al. 1993, Pflumio et al. 1994). However, the fluid geothermometric data is not conclusive. Rare earth element patterns (only available for Cape Banza; Barrat et al. 2000) do not show a positive cerium anomaly as expected for high-temperature fluids. Crustal strontium isotope data of Cape Banza fluids are more radiogenic than those of the lake, confirming the basinal brine component in the fluid mixture (Barrat et al. 2000). The only indication for a magmatic heat source is the 13C range of CO2 (Botz & Stoffers 1993), which might indicate a subvolcanic alkali-basaltic dike intrusion. However, this possible intrusion is not yet confirmed by high mantle helium concentrations. A magmatic helium signature at Pemba would have implications also for geothermal systems on the Tanzanian side of Lake Tanganyika (Figure 7a). Uvinza (crustal gas composition, Walker 1969; long residence time, Figure 4b) and comparable Ivuna basinal brines (dominating crustal He isotope composition, Pik et al. 2006) are without magmatic heat source. However, direct heat use could enhance salt production at Ivuna site during the rainy season.