Concentration, behavior and storage of H/sub 2/O in the suboceanic upper mantle: implications for mantle metasomatism
Mid-ocean ridge basalt glasses from the Pacific-Nazca Ridge and the northern Juan de Fuca Ridge were analyzed for H/sub 2/O by gas chromatography. Incompatible element enriched (IEE) glasses have higher H/sub 2/O contents than depleted (IED) glasses. H/sub 2/O increases systematically with decreasing Mg/Mg + Fe/sup 2 +/ within each group. Near-primary IED MORBs have an average of about 800 ppm H/sub 2/O, while near-primary IEE MORBs (with chondrite normalized Nb/Zr or La/Sm approx. 2) have about 2100 ppm H/sub 2/O. If these basalts formed by 10-20% partial melting then the IED mantle source had 100-180 ppm H/sub 2/O, while the IEE source had 250-450 ppm H/sub 2/O. The ratio H/sub 2/O/(Ce + Nd) is fairly constant at 95 +/- 30 for all oceanic basalts from the Pacific. During trace element fractionation in the suboceanic upper mantle, H/sub 2/O behaves more compatibly than K, Rb, Nb, and Cl, but less compatibly than Sm, Zr and Ti. H/sub 2/O is contained mostly in amphibole in the shallow upper mantle. At pressures greater than the amphibole stability limit, it is likely that a significant proportion of H/sub 2/O is contained in a mantle phase which is more refractory than phlogopite at these pressures. The role of H/sub 2/O in mantle enrichment processes is examined by assuming that an enriched component was added. The modeled concentrations of K, Na, Ti and incompatible trace elements in this component are high relative to H/sub 2/O, indicating that suboceanic mantle enrichment is caused by silicate melts such as basanites and not by aqueous fluids.
- Research Organization:
- Univ. of British Columbia, Vancouver (Canada)
- OSTI ID:
- 5065123
- Journal Information:
- Geochim. Cosmochim. Acta; (United States), Vol. 52:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
BASALT
CHEMICAL COMPOSITION
GEOCHEMISTRY
PARAGENESIS
EARTH MANTLE
HYDROTHERMAL ALTERATION
MAGMA SYSTEMS
ROCK-FLUID INTERACTIONS
OCEANIC CRUST
CHLORINE
GAS CHROMATOGRAPHY
HYDROTHERMAL SYNTHESIS
MAGMA
MAGMATISM
NOBELIUM
PACIFIC OCEAN
POTASSIUM
RUBIDIUM
TITANIUM
WATER
ZIRCONIUM
ACTINIDES
ALKALI METALS
CHEMISTRY
CHROMATOGRAPHY
EARTH CRUST
ELEMENTS
GEOTHERMAL SYSTEMS
HALOGENS
HYDROGEN COMPOUNDS
IGNEOUS ROCKS
METALS
NONMETALS
OXYGEN COMPOUNDS
ROCKS
SEAS
SEPARATION PROCESSES
SURFACE WATERS
SYNTHESIS
TRANSITION ELEMENTS
TRANSPLUTONIUM ELEMENTS
TRANSURANIUM ELEMENTS
VOLCANIC ROCKS
580400* - Geochemistry- (-1989)