Thermodynamics of lateral dike propagation: Implications for crustal accretion at slow spreading mid-ocean ridges

We consider solidification of hot fluid flowing through a rigid-wall channel of infinite extent. The calculated "thermal arrest" lengths are used to investigate the role of magma freezing in limiting the propagation distance of lateral dike intrusions. Our results demonstrate that for reasonable parameters the propagation distances of meter-wide dikes do not exceed the wavelength of crustal thickness variations or transform fault spacing along slow spreading ridges. This suggests that thermal controls on the crustal melt delivery system could be an important factor in modulating these variations. Unlike published results for a finite channel, which predict unlimited meltback of the channel walls if the prefreezing fluid velocity exceeds some critical value, any flow into an infinite channel will eventually freeze, provided that shear heating in the magma is negligible. The thermal arrest distances depend strongly on the average dike thickness h (∝h⁴ for dikes driven by an along-strike topographic slope and ∝ h² for dikes driven by an excess source pressure). Thermal erosion of the country rocks associated with lateral dike intrusions is likely to be confined to a very small region near the magma source. Substantial correlations between the along-strike bathymetry and geochemistry of the erupted lavas along individual ridge segments may be consistent with high-level basalt fractionation in the laterally propagating dikes.