Discovery of New Methane-bearing Hyperalkaline Springs in the Serpentinized Dun Mountain Ophiolite, New Zealand
Friday, 19 December 2014
The production of H2 and CH4 following serpentinization is considered a fundamental process for the origin/sustenance of microbial life, with several implications in astrobiology and petroleum geology. In recent years an increasing number of gas seeps or springs, with dominantly abiotic CH4, have been discovered in land-based serpentinized peridotites worldwide. We report the discovery of a new site in the Dun Mountain Ophiolite (DMO), New Zealand. This is the second gas-bearing peridotite discovered so far in NZ, after Poison Bay which was documented in the 1990s. The DMO area is characterized by active and present-day low temperature serpentinization driven by meteoric water, a common process in ophiolites. A localised area of hyperalkaline (pH >11.6) and reduced (-243.4 mV) waters contain relatively high concentrations of dissolved calcium (43.2 ppm) aiding in carbonate precipitation. Directly above these waters flux measurements by closed chamber methods reveal CH4 emission rates exceeding 2800 mg m-2day-1. The δ13C values of CH4 suggest the presence of a dominant abiotic gas component (e.g. -32.7 ‰ VPDB). Additionally, an unusual clear to black gel is released from less alkaline springs elsewhere in the DMO. The origin and nature of this gel-like material is currently unknown.