Isotopic exchange in mineral-fluid systems; II, Oxygen and hydrogen isotopic investigation of the experimental basalt-seawater system

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doi: 10.1016/0016-7037(87)90334-6
Authors:Cole, David R.; Mottl, Michael J.; Ohmoto, Hiroshi
Author Affiliations:Primary:
Oak Ridge Natl. Lab., Geosci. Group, Oak Ridge, TN, United States
Other:
Hawaii Inst. Oceanogr., United States
Pa. State Univ., United States
Volume Title:Geochimica et Cosmochimica Acta
Source:Geochimica et Cosmochimica Acta, 51(6), p.1523-1538. Publisher: Pergamon, Oxford, International. ISSN: 0016-7037
Publication Date:1987
Note:In English. 53 refs.; illus. incl. 3 tables
Summary:O and H isotopic exchange reactions between oceanic tholeiite, natural sea-water and artificial sea-water at 300-500°C were investigated. The tholeiite was holocrystalline to glassy, but was crushed to approx 150 mu m. Water/rock mass ratios ranged 1-3, in runs lasting 167-576 days. In general, depletion of 18O and enrichment of D in the tholeiitic basalts occur at all T and the changes increase with increase of T, time and, to a lesser degree, glass content. The trends in isotopic shifts are related to mineralogical changes such as crystallization of smectite at 300°C and talc-actinolite at 400-500°C. In most cases, the final measured delta 18O and delta D of the basalt do not represent equilibrium values. Rate constants for O isotopic exchange between altered basalt and sea-water range from 10-9.5 to 10- 8.0 moles of O/m2 of solid surface/sec, for T of 300-500°C. An activation energy of 11.5 kcal/mole was calculated from these rate data. Using a closed-system model for O isotopes, the duration of fluid-rock isotopic equilibration in MORB-type systems is estimated to be a few hundred to a few thousand yr. H isotope fractionation between altered basalt and sea-water ranged from approx -74per mille at 300°, -62per mille at 400°, to -48per mille at 500°C. These fractionations probably attributable to exchange between sea-water and secondary minerals which are enriched in Fe. [R.K.H.]
Subjects:Basalts; D/H; Deuterium; Experimental studies; Fluid phase; Geochemistry; Halmyrolysis; Hydrogen; Igneous rocks; Isotopes; Lava; Minerals; O-18/O-16; Oxygen; Phase equilibria; Sea water; Solid phase; Stable isotopes; Volcanic rocks; Fractionation
Abstract Numbers:88M/0796
Record ID:1987080432
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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