FY 1995
Tectonic and volcanic controls on hydrothermal processes at the mid-ocean ridge: An overview based on near-bottom submersible studies
Fornari, D.J., and R.W. Embley
In Seafloor Hydrothermal Systems: Physical, Chemical, Biological, and Geological Interactions, S.E. Humphris, R. Zierenberg, L. Mullineaux, and R. Thomson (eds.), AGU, Washington, D.C., Geophysical Monograph 91, doi: 10.1029/GM091p0001, 1–46 (1995) |
| The crestal area of the mid-ocean ridge (MOR) is a stratigraphically complex and dynamic environment where new lithosphere is created through intrusive and extrusive igneous activity. Magmatic processes at ridge crests also provide the energy to drive hydrothermal circulation of seawater through the oceanic crust. These result in rock-water interactions which give rise to low-temperature (<∼200°C) and high-temperature (200°C–∼400°C) venting at seafloor depths ranging between approximately 3600 m to 840 m (this depth range encompasses all known high-temperature MOR crest axial vent sites in slow- to superfast-spreading environments), and contribute substantively to the Earth's heat budget. Rock-water interaction and exhalation of mantle volatiles also affect the chemical composition of the world's ocean. The permeability structure of young oceanic lithosphere controls how hydrothermal circulation will manifest itself both locally and regionally. The interplay between intrusive and extrusive igneous activity, and the inferred causal relationships between spreading-rate-controlled tectonism and the physical properties of young crust (i.e. brittle vs. ductile behavior) all influence the permeability of young ocean crust. Slow- to intermediate-rate spreading MOR constructional morphology is dominated by pillow lavas and large-scale tectonic features, while fast- and superfast-spreading ridge crests have a greater proportion of lobate, sheet and ponded lava flows erupted at high effusion rates and more subdued (<100 m high) tectonic features. The volcanic effusion style and resulting stratigraphy at MOR crests also imparts a controlling influence on the permeability structure of the shallow crust (upper ∼300 m), and influences the location of hydrothermal vents. |
