Groundwater helium: An indicator of active tectonic regions along Narmada River, central India

Results of a survey of dissolved helium, fluoride and electrical conductivity in groundwater from across the main stem of the Narmada River, between Bharuch in the west and Amarkantak in the east, are reported. This survey was undertaken to identify active tectonic regions, based on locations of high helium concentrations, interpreted as indicative of upward migration of deep fluids. Existence of deep fluids in this region has been hypothesised earlier based on various geophysical studies in the Narmada Rift Basin — a major tectonic feature in central India. Samples with high helium concentration are clustered in two broad regions with known intersecting faults, indicating the possibility of plumes with high helium concentration being injected into shallower groundwater in these regions, facilitated by these faults and fractures. Locations of groundwater samples having excess fluoride remarkably correspond to these two clusters of excess helium. This suggests a possible commonality between the causal factor of excess helium and higher fluoride in groundwater, which needs to be further investigated.