Hydrothermal venting in magma deserts: The ultraslow-spreading Gakkel and Southwest Indian Ridges

摘要: [1] Detailed hydrothermal surveys over ridges with spreading rates of 50–150 mm/yr have found a linear relation between rate and the spatial frequency venting, but validity this at slow ultraslow is unproved. Here we compare plume along three sections Gakkel Ridge (Arctic Ocean) Southwest Indian (SWIR) to determine if activity similarly distributed among these ridge distributions follow hypothesized trend derived from fast ridges. Along Ridge, most apparent vent sites occur on volcanic highs, extraordinarily weak vertical density gradient deep Arctic permits plumes rise above axial bathymetry. Individual can thus be extensively dispersed axis, distances >200 km, ∼75% total length surveyed overlain by plumes. Detailed mapping points only 9–10 active in 850 however, yielding site Fs, sites/100 km length, 1.1–1.2. Plumes detected SWIR are considerably less extensive for two reasons: an paucity fields highs normal deep-ocean that prevents extended rise. western section (10°–23°E) identify 3–8 sites, so Fs = 0.3–0.8; previously 440 eastern (58°–66°E), 6 yield 1.3. Plotting (us) versus eight other sections, spanning global range rate, establish robust (Fs 0.98 + 0.015us), implying long-term heat supply first-order control distribution activity. Normalizing delivery basaltic magma suggests several times more efficient than faster-spreading supporting fields. This increased efficiency could derive some combination three-dimensional focusing centers, mining gabbroic intrusions direct cooling upper mantle, nonmagmatic supplied exothermic serpentinization.