Mineralogical and strontium isotopic record of hydrothermal processes in the lower ocean crust at and near the East Pacific Rise

Twenty on‐bottom gravity stations were taken with a LaCoste‐Romberg model G gravity meter inside the submersible Alvin, over a 6 km long cross‐strike profile which straddles the East Pacific Rise spreading center at 21°N. The residual Bouguer anomaly shows a 1.5 mGal low with a total half‐width of 1.7 km centered about the spreading axis and hydrothermal vents. Uncertainties in the ocean depth are believed to contribute a standard error of about 0.3 to 0.4 mGal for the gravity data. The observed elevation factor of 0.1552 mGal/m indicates that the upper ocean crust bulk density is [Formula: see text]. On the other hand, 90 rock samples give a density of [Formula: see text]. This suggests that the largescale porosity of the upper crust is 14 percent. The gravity anomaly was inverted to find the ideal body with the smallest maximum density contrast which satisfies the data and their associated errors. This body extends from the sea floor to 2 500 m depth and has a density contrast of [Formula: see text]. If the density contrast is allowed to be as large as [Formula: see text], the top of the ideal body can be as deep as 300 m and its bottom as deep as 1 300 m; alternatively with the body top at the sea floor, the bottom of the body can be no shallower than 500 m. The ideal body is, therefore, restricted to the dikes and flows of the upper ocean crust. The body is not thought to represent magma in the shallow crust, but rather fractured crust filled with heated seawater.

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East Pacific rise at 21°N: The volcanic, tectonic, and hydrothermal processes of the central axis

Earth and Planetary Science Letters ◽

10.1016/0012-821x(81)90081-9 ◽

1981 ◽

Vol 55 (1) ◽

pp. 1-10 ◽

Cited By ~ 113

Author(s):

Robert D. Ballard ◽

Jean Francheteau ◽

Tierre Juteau ◽

Claude Rangan ◽

William Normark

Keyword(s):

East Pacific Rise ◽

Central Axis ◽

East Pacific ◽

Hydrothermal Processes

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Sites 419423 and 426429: Ocean Crust Drilling on the East Pacific Rise and in the Siqueiros Fracture Zone

10.2973/dsdp.proc.54.107.1980 ◽

1980 ◽

Author(s):

Keyword(s):

Fracture Zone ◽

East Pacific Rise ◽

Ocean Crust ◽

East Pacific

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Mineralogical and strontium isotopic record of hydrothermal processes in the lower ocean crust at and near the East Pacific Rise

Hydrothermal processes and products on the Galapagos Rift and East Pacific Rise

Submarine Lava Flow Emplacement at the East Pacific Rise 9°50´N: Implications for Uppermost Ocean Crust Stratigraphy and Hydrothermal Fluid Circulation

Petrology and geochemistry of the lower ocean crust formed at the East Pacific Rise and exposed at Hess Deep: A synthesis and new results

Subsurface structure of a submarine hydrothermal system in ocean crust formed at the East Pacific Rise, ODP/IODP Site 1256

Crustal fissuring and its relationship to magmatic and hydrothermal processes on the East Pacific Rise crest (9°12′ to 54′N)

Origin of the sheeted dike complex at superfast spread East Pacific Rise revealed by deep ocean crust drilling at Ocean Drilling Program Hole 1256D

Halogens in altered ocean crust from the East Pacific Rise (ODP/IODP Hole 1256D)

On‐bottom gravity profile across the East Pacific Rise crest at 21° north

East Pacific rise at 21°N: The volcanic, tectonic, and hydrothermal processes of the central axis

Sites 419423 and 426429: Ocean Crust Drilling on the East Pacific Rise and in the Siqueiros Fracture Zone

Sites 419423 and 426429: Ocean Crust Drilling on the East Pacific Rise and in the Siqueiros Fracture Zone