Hydrothermal cooling along the Eastern Lau Spreading Center: No evidence for discharge beyond the neovolcanic zone

摘要: Heat transported from the mantle beneath spreading centers creates an astonishingly narrow ribbon of convective heat discharge at plate boundaries, as apparently demonstrated by exhaustive exploration for hydrothermal sites over last three decades. Recent observations and models are now challenging this assumption exclusively axis-centric high-temperature venting. One example is proposal that intense cooling along vertical boundaries a broad low-velocity volume (LVV) hot crust could generate fluids several kilometers off axis. To test hypothesis substantial might occur beyond LVV, we conducted dense survey grid ridge surrounding seafloor (up to ±5 km) 175 km Eastern Lau Spreading Center Valu Fa Ridge (∼1800 track line). Our sampling array extended ∼50 400 m above bottom included light-scattering, oxidation-reduction potential, hydrographic sensors attached tow line IMI120 sonar mapping system. The surveys successfully mapped plumes vent fields in neovolcanic zone (∼±1.5 about axis) but did not detect evidence significant anywhere farther off-axis. At few locations on Ridge, however, record potential anomalies with density signatures imply low-temperature sources axial flank. Although these hundreds meters deeper than adjacent crest, they above, beyond, previously LVV. results thus do support simple picture ascending undiluted through However, cannot exclude possibilities largely unmapped LVV narrower here seen other ridges, formed channeled axis, or occurs only dispersed, very fluids. demonstrate predominantly exits within ribbon, regardless presence absence magma chamber.