Physical properties of upper oceanic crust: Ocean Drilling Program Hole 801C and the waning of hydrothermal circulation
| Autor: | Tetsuro Hirono, Richard D. Jarrard, Robert A. Pockalny, Lewis J. Abrams, Roger L. Larson |
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| Rok vydání: | 2003 |
| Předmět: |
Atmospheric Science
Soil Science Aquatic Science Oceanography Deep sea Hydrothermal circulation Geochemistry and Petrology Oceanic crust Earth and Planetary Sciences (miscellaneous) Petrology Earth-Surface Processes Water Science and Technology Basalt geography geography.geographical_feature_category Ecology Paleontology Drilling Forestry Crust Geophysics Igneous rock Volcano Space and Planetary Science Geology |
| Zdroj: | Journal of Geophysical Research: Solid Earth. 108 |
| ISSN: | 0148-0227 |
| Popis: | [1] The hydrologic evolution of oceanic crust, from vigorous hydrothermal circulation in young, permeable volcanic crust to reduced circulation in old, cooler crust, causes a corresponding evolution of geophysical properties. Ocean Drilling Program (ODP) Hole 801C, which obtained the world's oldest section of in situ, normal oceanic crust, provides the opportunity to examine relationships among hydrologic properties (porosity, permeability, fluid flow), crustal alteration, and geophysical properties, at both core plug and downhole log scales. Within these upper crustal basalts, fluid flux in zones with high porosity and associated high permeability fosters alteration, particularly hydration. Consequently, porosity is correlated with both permeability and a variety of hydration indicators. Porosity-dependent alteration is also seen at the log scale: potassium enrichment is strongly proportional to porosity. We extend the crustal alteration patterns observed at Hole 801C to a global examination of how physical properties of upper oceanic crust change as a function of age based on global data sets of Deep Sea Drilling Project and ODP core physical properties and downhole logs. Increasing crustal age entails macroporosity reduction and large-scale velocity increase, despite intergranular velocity decrease with little microporosity change. The changes in macroporosity and velocity are significant for pillows but minor for flows. Matrix densities provide the strongest demonstration of systematic age-dependent alteration. On the basis of observed decreases in matrix density that are proportional to the logarithm of age, approximately half of all intergranular-scale crustal alteration occurs after the first 10–15 Myr. Apparently, crustal alteration continues, at a decreasing rate, throughout the lifetime of oceanic crust. |
| Databáze: | OpenAIRE |
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