HR: 1340h
AN: T33B-1370    [Abstracts]
TI: Correlations Between Hydrothermal Venting and Axial Magma Chamber Characteristics
AU: * Baker, E T
EM: edward.baker@noaa.gov
AF: NOAA/PMEL, 7600 Sand Point Wy NE, Seattle, WA 98115, United States
AB: The principal power sources for high-temperature hydrothermal venting have long been thought to be heat mined from solidified magma ("hot rock"), as by a propagating cracking front, and heat supplied conductively from an unsolidified magma body ("axial magma chamber"). However, nearly all high-temperature vents have been found at, or near, locations where seismic studies have imaged an AMC. This association seems especially true on fast-spreading ridges, where lengthy seismic transects have been conducted on several ridge sections. To test the robustness of this association, I here review data from all six multi-segment ridge sections, ranging from 170- 560 km in length, where detailed surveys of both the AMC and hydrothermal plumes have been conducted. The sections include the southern East Pacific Rise (14°-18° S) (560 km), Galapagos Spreading Center (380 km), Juan de Fuca Ridge (365 km), Valu Fa/Eastern Lau Spreading Center (360 km), northern EPR (9° - 12° N) (307 km), and northern EPR (15.3° -16.8° N) (170 km). These sections include a total of 21 2nd or 3rd order tectonic segments. At the section scale, there is no significant correlation (r² = 0.05) for a least-squares fit between percent AMC coverage and percent plume coverage (p_h). Removing the hotspot-affected GSC, however, increases r² to 0.61. This finding is consistent with evidence showing that hydrothermal activity on hotspot-affected ridges is markedly less than normal ridges of similar spreading rate. The correlation between mean AMC depth below the seafloor and p_h for all six sections is high (r² = 0.58), and improves to r² = 0.87 if the Valu Fa/ELSC section is excluded. The AMC is unusually deep and the crustal structure along this section is unique along among midocean ridges, perhaps because of its proximity (40-100 km) to the Kermadec volcanic arc. At the individual segment scale, the same correlations are much less robust. AMC coverage vs. p_h decreases to r² = 0.15 whether or not the Galapagos data are included. AMC depth vs. p_h decreases to r² = 0.3 whether or not the Valu Fa/ELSC data are included. This analysis demonstrates that the correlation between the spatial density of venting and the spatial extent or depth of an AMC is weak on the small segment scale but significant at the multi-segment scale. This pattern is the same as found between p_h and spreading rate on the small and multi-segment segment scales. In contrast, at both scales venting is more sensitive to AMC depth than AMC extent, a correlation likely linked to the observation that the AMC shallows as spreading rate increases. It may be that p_h increases with spreading rate not simply because of a higher magma budget, but also because heat extraction becomes more efficient as AMC depth decreases.
DE: 3035 Midocean ridge processes
DE: 8135 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8424)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting