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Oxygen isotope ratios in eclogites from kimberlites
Science (New York, N.Y.)
|June 4, 1971
Summary
Oxygen isotope variations in Roberts Victor kimberlite eclogites reveal fractional crystallization processes. Early crystal accumulates show higher oxygen-18, while residual liquids have lower values, indicating pressure-dependent crystal-melt partitioning.
Area of Science:
- Geochemistry
- Petrology
- Isotope Geology
Background:
- Eclogitic xenoliths provide insights into Earth's mantle processes.
- Oxygen isotope compositions (delta(18)O) are sensitive tracers of geological processes.
Purpose of the Study:
- To investigate the causes of oxygen isotope variations in Roberts Victor kimberlite eclogites.
- To understand the role of fractional crystallization and crystal-melt partitioning in eclogite formation.
Main Methods:
- Analysis of oxygen isotope compositions (delta(18)O) in eclogitic xenoliths.
- Comparison of isotopic data with mineralogical and textural observations.
Main Results:
- Oxygen isotope compositions range from 2 to 8 per mil relative to standard mean ocean water (SMOW).
- Variations are attributed to fractional crystallization, with high delta(18)O in early cumulates and low delta(18)O in residual liquids.
- Crystal-melt partitioning is estimated to exceed 3 per mil and is pressure-dependent.
Conclusions:
- Fractional crystallization is a key process controlling oxygen isotope signatures in these eclogites.
- Increased crystal-melt partitioning occurred after melt formation but before crystallization.
- The findings provide new constraints on the conditions of eclogite formation and evolution.
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