Geochemistry of Axial seamount lavas: Magmatic relationship between the Cobb hotspot and the Juan de Fuca Ridge

Journal Article · Fri Aug 10 04:00:00 EDT 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JB095iB08p12713· OSTI ID:5108385

Rhodes, J M; Morgan, C; Lilas, R A ^[1]

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1. Univ. of Massachusetts, Amherst (United States)

Axial seamount, located along the central portion of the Juan de Fuca Ridge axis and at the eastern end of the Cobb-Eickelberg seamount chain, is the current center of the Cobb hotspot. Lava chemistry and bathymetry indicate that Axial seamount is a discrete volcanic unit, with a more productive shallow magmatic plumbing system separate from the adjacent ridge segments. Despite this classic association of spreading center and hotspot volcanic activity, there is no evidence in the lavas for geochemical or isotopic enrichment typical of hotspot or mantle plume activity. The differences in composition between the Axial seamount lavas and the Juan de Fuca Ridge lavas are attributed to melting processes rather than to any fundamental differences in their mantle source compositions. The higher magma production rates, higher Sr, and lower silica saturation in the seamount lavas relative to the ridge lavas are thought to be a consequence of melt initiation at greater depths. The melting column producing the seamount lavas is thought to be initiated in the stability field of spinel peridotite, whereas the ridge lavas are produced from a melting column initiated at shallower levels, possibly within or close to the stability field of plagioclase peridotite. Implicit in this interpretation is the conclusion that the Juan de Fuca Ridge lavas, and by analogy most MORB, are generated at shallow mantle levels, mostly within the stability field of plagioclase peridotite. This interpretation also requires that for the upwelling mantle to intersect the solidus at different depths, the mantle supplying Axial seamount must be hotter than the rest of the Juan de Fuca Ridge. Axial seamount, therefore, reflects a thermal anomaly in the mantle, rather than a geochemically enriched ocean island basalt type mantle plume.

• OSTI ID: 5108385
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 95:B8; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

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ALKALINE EARTH METAL COMPOUNDS
ALKALINE EARTH METALS
BASALT
CALCIUM COMPOUNDS
CALCIUM OXIDES
CHALCOGENIDES
CHEMISTRY
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ELEMENTS
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IGNEOUS ROCKS
LAVA
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
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OXIDES
OXYGEN COMPOUNDS
PACIFIC OCEAN
PHASE TRANSFORMATIONS
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SEA-FLOOR SPREADING
SEAS
SILICA
SILICON COMPOUNDS
SILICON OXIDES
SODIUM COMPOUNDS
SODIUM OXIDES
STRONTIUM
SURFACE WATERS
VARIATIONS
VOLCANIC REGIONS
VOLCANIC ROCKS