Hydrothermal Alteration of Oceanic Crust
Near-axis hydrothermal circulation removes a significant portion of the heat from crystallization and cooling of the plutonic lower oceanic crust. Therefore, the mechanism of lower oceanic crust accretion is closely related to the strength and distribution of hydrothermal circulation at mid-ocean ridges. Interaction with hydrothermal fluids can also substantially modify the chemical and isotopic composition of altered oceanic crust. The strength and distribution of near-axis hydrothermal circulation remain a matter of debate.
Oxygen and strontium isotopes are sensitive tracers of hydrothermal alteration. Previous studies that examined ophiolites and fault-uplifted seafloor oceanic crust sections all suggest high-temperature hydrothermal alteration of lower oceanic crust. In contrast, I examined a suite of gabbroic xenoliths from the Hualalai Volcano, Hawaii, which represent samples of in situ lower oceanic crust. The O and Sr isotope compositions of these gabbros suggest minimal hydrothermal alteration.
Gao, R., Lassiter, J. C., Barnes, J. D., Clague, D. A., & Bohrson, W. A. (2016). “Geochemical Investigation of Gabbroic Xenoliths from Hualalai Volcano: Implications for Lower Oceanic Crust Accretion and Hualalai Volcano Magma Storage System.” Earth and Planetary Science Letters, 442, 162-172.
