| Autor: |
B. Sarbas, G.C. Amstutz, Manfred Schidlowski, U. Goerg, J.D. Arneth |
| Rok vydání: |
1985 |
| Předmět: |
|
| Zdroj: |
Geochimica et Cosmochimica Acta. 49:1553-1560 |
| ISSN: |
0016-7037 |
| DOI: |
10.1016/0016-7037(85)90260-1 |
| Popis: |
Amphibolite-grade metasediments from the Mgama Hills region, Kenya, contain conspicuous quantities of graphite, most probably derived from organic progenitor materials. The highest graphite contents (5.1–20.4%) are found in schists whereas calcite marbles intercalated in the sequence contain relatively low amounts (0.1–2.0%). The graphitic constituents are consistently enriched in 13 C relative to common sedimentary organic material, with the highest isotopic ratios in graphite from the marbles ( δ 13 C = −7.3 ± 5.0%.; n = 10). Carbon isotope fractionations between calcite and graphite mostly vary between 3.3 and 7.1‰, which comes close to both empirically recorded and thermodynamically calculated fractionations in the temperature range of the upper amphibolite facies (550–650°C). However, larger values occasionally encountered in the marbles suggest that complete isotopic equilibrium is not always attained in amphibolite-facies metamorphism. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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