|
|||||
|
|
Hydration, 18O enrichment and oxidation during ocean floor hydrothermal metamorphism of ophiolitic metabasic rocks from E. Liguria,Italy |
|
| Authors: | ETC Spooner RD Beckinsale PC England A Senior |
| Institution: | 2. Department of Geology and Mineralogy, University of Oxford, Parks Road, Oxford OX1 3PR, England;3. Institute of Geological Sciences, Geochemical Division, 64-78 Gray''s Inn Road, London WC1X 8NG, England;4. Geologisch en Mineralogisch Institut der Rijksuniversiteit. Garenmarkt, Leiden Holland, The Netherlands |
| Abstract: | During ocean-floor hydrothermal metamorphism of a 225 m thick allochthonous Jurassic sequence of ophiolitic pillow lavas and underlying material in E. Liguria, Italy, the rocks were hydrated, enriched in 18O and oxidised. H2O+ contents increased from ~0.3 to 3.8 wt.%, δ18O values increased from ~ +6‰ to values as high as +13.2‰, and (1) increased from 0.18 to ratios as high as 1.0. Both δ18O values and oxidation ratios decrease in the original direction of increasing depth. Pillow margins are consistently more enriched in 18O and are more oxidised than cores.These observations are qualitatively interpreted in terms of a non-isothermal, heterogeneous reaction model of interaction of basalt with oxygen-bearing sea water during flow through the packed bed of pillows. Fluid flow approximated undirectional downward motion, and occurred in the recharge part of a cycle of single pass convection. Mass transfer through the pile was by flow (infiltration metasomatism), whereas intra-pillow mass transfer was diffusional. Oxygen isotope exchange and oxidation did not occur under conditions of perfect incremental equilibrium. An integrated bulk volumetric water/rock ratio of ~2 × 103:1 is estimated from the oxidation profile. |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ | |