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Geological indexes of hydrothermal venting

Edward T. Baker

Pacific Marine Environmental Laboratory, NOAA, Seattle, Washington

Journal of Geophysical Research, 101(B6), 13,741–13,753 (1996)
Not subject to U.S. copyright. Published in 1996 by the American Geophysical Union.

Fine-Scale Trends

Of the indexes given above, Enet, Axs, and us are available essentially continuously along all three ridge sections; AMC percent coverage is available only for the EPR. A comparison of Enet with the plume distribution (Figure 3) allows a test of the Francheteau and Ballard [1983] hypothesis that hydrothermal venting is favored at bathymetric highs. The agreement between Enet and plume location is robust on some segments (e.g., Endeavour, 9°17­10°05N) but weak on most. Correlations weaken considerably as the along-axis variability of Enet decreases with increasing us. In general, little venting occurs where Enet < ~0.35 km.

Agreement between Axs and plume distribution is better, particularly on faster spreading segments (Figure 3). Axs is more sensitive because at the fastest spreading rates its along-axis dynamic range remains higher than that of Enet. Virtually all significant plumes occur where Axs > ~3.5 km2, especially on the JDFR and the northern EPR.

The correlation between AMC and plume presence is less precise than either of the two bathymetric variables. In general, extensive venting occurs only where an AMC reflector is observed, although an observable AMC does not guarantee hydrothermal venting (Figure 3). Neither is there a clear relation between AMC depth and plumes. Apparent variations in AMC depth often result from slight wander of the ship track away from the narrow region of minimum thickness of layer 2A [Kent et al., 1993a, b].


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