Abstract
[1] Hydrologic models of the oceanic crust commonly assume that the uppermost igneous extrusive layer of the aquifer is thermally well mixed, although this assumption has not been rigorously tested. Here, the assumption of a thermally well-mixed aquifer is tested against the geological record using O isotope-derived crystallization temperatures of carbonates in the lavas as a record of the temperatures experienced by the aquifer. It is found that carbonate formation temperatures are higher than can be explained by a model of outcrop-to-outcrop flow in a well-mixed aquifer at four of the seven drilling locations analyzed. A poorly mixed aquifer is developed to further explore the crustal hydrology at these locations. Relative to a well-mixed aquifer, a poorly mixed aquifer can achieve higher average temperatures, develops larger lateral pressure gradients driving flow, and requires a lower permeability to achieve a given lateral fluid flux. O isotope data from most of the carbonate samples analyzed are consistent with temperatures achievable in a poorly mixed aquifer; those samples which are not consistent can be explained by plausible special circumstances (such as formation at a discharge zone, where ascending fluid may warm the uppermost aquifer).
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call