2-D numerical simulations of groundwater flow, heat transfer and 4He transport - implications for the He terrestrial budget and the mantle helium-heat imbalance

Our simulations also indicate that in order for both heat and He to be in steady-state in recently formed crust, the presence of an advective dominated regime is required (k ≥ 10− 16 m2). Under these conditions, only in total absence of contact with ASW (e.g., an atmospheric component provided by freshwater or seawater) is the total 4He / heat flux ratio expected to equal the radiogenic production ratio. Lower 4He / heat fluxes in an advective dominated regime require the incorporation of an ASW component. We argue that the observed low ocean mantle 4He / heat flux results, at least partially, from sea water incorporation within mid-ocean ridge basalts. Our simulations also suggest that 4He transport is in transient state in recently formed crust for permeabilities ≤ 10− 17 m2. Under these conditions, low to very low mantle He excesses and thus total He / heat fluxes of up to several orders of magnitude lower than the radiogenic production ratios are expected.