Middle Valley

N Guaymas Basin 14 Middle Valley 43 Escanaba Trough 32 Atlantic II Red Sea 53... 

Butterfield, V.A., McDuff, R.E., Franklin, J. and Wheat, C.G. (1994) Geochemistry of hydrothermal vent fluids from Middle Valley, Juan de Fuca Ridge. In Mottl, M.J., Davis, E.E., Fi.sher, A.T. and Slack, J.F. (eds.). Proceedings of the Ocean Drilling Program. Sci. Proc., 139, 395-410. 

Goodfellow, W.D. and Blaise, B. (1988) Sulfide formation and hydrothermal alteration of hemipelagic sediment in Middle Valley, northern Juan de Fuca Ridge. Can. Mineral, 26, 675-696. 

Simoneit BRT, Lipid/bitumen maturation by hydrothermal activity in sediments of Middle Valley, Leg 139, in Mottl M, Davis E, Fisher A, Slack] (eds.). Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 139, College Station, TX Ocean Drilling Program, pp. 447- 65, 1994. 

Rushdi Al, Simoneit BRT, Hydrothermal alteration of organic matter in sediments of the Northeastern Pacific Ocean Part 1. Middle Valley, Juan de Fuca Ridge, Appl Geochem 17 1401—1428, 2002. 

These omit sedimented covered and um hosted. ° Includes Guaymas, Escanaba, Middle Valley. Includes Rainbow, Lost City, kvd unpublished data for Logatchev. Compilation from Ishibashi and Urabe (1995). 

Cragg, B.A., Summit, M. and Parkes, RJ. (2000) Bacterial profiles in a sulfide mound (Site 1035) and an area of active fluid venting (Site 1036) in hot hydrothermal sediments from Middle Valley (Northeast Pacific), in Proceedings of the Ocean Drilling Program, Initial Reports, vol. 169 (eds R.A. Zierenberg, Y. Fouquet, DJ. Miller and W.R. Normark), pp. 1—18 [online]. 

Stable isotopic data for vent fluids from selected hydrothermal areas are presented in Table 1. Except as referenced, these data have been generated in USGS studies over the last 18 years and have a high degree of internal consistency. Stable isotope data from the southern East Pacific Rise, some of the more recent data from 9-10°N on the East Pacific Rise, data from the Lucky Strike vent field on the Mid-Atlantic Ridge, and data from pore fluids and hydrothermal minerals from ODP drilling at Middle Valley and Escanaba Trough are presented for the first time here. Chemical data in Table 1 from the southern East Pacific Rise, 9-10°N on the East Pacific Rise, and the Lucky Strike vent field are from Karen Von Damm and associates (Von Damm et al. 1995, 1997, and unpublished data). 

Two additional sedimented ridge Ir drothermal vent sites, Escanaba Trough and Middle Valley, show quite different ranges for CO2 in vent fluids (Fig. 11). 

Escanaba Trough Middle Valley Middle Valley subsurface... 

Escanaba Trough has a range from -12.2 to -3.9%o, and 5 C values increase with CO2 content, presumably due to increased magmatic contributions (Taylor 1992). The vent fluids at Middle Valley show a range from -38.9 to -10.6%o, indicating substantial contributions from pyrolysis of organic carbon in the sediments and dissolution of detrital biogenic carbonates (Taylor 1992). 

Figure 27 (right). Stable isotope data for whole rock samples of altered and unaltered sediments from Escanaba Trough and Middle Valley. 

Vent Field (Escanaba hole 1038), the Escanaba Trough Reference Hole (1037), which was drilled approximately 4.5 km from the nearest known hydrothermal activity, and from the Bent Hill Massive Sulfide system (holes 856 and 1035) in Middle Valley. These data show dramatic shifts in 5D and from -100 to -40 and from 15 to 5, respectively. Using the equations of Taylor (1974), relatively high w/r mass ratios of about 3-7 are indicated, as expected for the significant change in the 5D and of the muds. This w/r... 

Figure 28. Schematic cross-section of the Bent Hill Massive Sulfide and the ODP Mound, Middle Valley. Modified from Fouquet et al. (1998), ODP Sci Results 169 used with permission of the Ocean Drilling Project.

However, this is only one approach to estimate permeabilities from porosities and mean grain sizes. Other empirical relations exist, particularly for regions with hydrocarbon exploration (e.g. Gulf of Mexico, Bryant et al. 1975) or fluid venting (e.g. Middle Valley, Fisher et al. 1994) which compute depth-dependent permeabilities from porosity logs or take the grain size distribution and clay content into account. 

Figure 3 Schematic vertical distribution of typically hydrothermal clay minerals in the sedimentary systems of (A) the Galapagos spreading center, and (B) the Juan de Fuca Middle Valley. (Reproduced with permission from Buatier and Karpoff, 1995.)...

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