Varieties of eclogites and their positions in the cratonic mantle lithosphere revealed by Jd-Di thermobarometry and trace element geochemistry
- 1Institute of Geology and Mineralogy SB RAS, Geology, Novosibirsk, Russian Federation (igor.ashchepkov@igm.nsc.ru)
- 2Alrosa Stock Company, Mirny, Russia
- 3Vienna University, A-1090Vienna, Austria
- 4Department of Earth and Planetary Sciences, Birkbeck College, University of London, UK
- 5Institute of Geochemistry SD RAS, Irkutsk, Russia
The PT conditions and position of different groups of eclogites in the subcratonic lithospheric mantle (SCLM) worldwide has been established using clinopyroxene Jd-Di thermobarometry for different cratons and kimberlite localities. Beneath Siberia, Fe-eclogites found within the 3.0-4.0 GPa and were probably formed in Early Archean times forming the base of the lithosphere. In the Middle and Late Archean, eclogites were melted during subduction creating restite and cumulates from partial melts traced ascending channels.
High-Mg eclogites (partial melts or arc cumulates) are related to low-T geotherms. Melt-metasomatized eclogites trace a high-T geotherm and are often close to the middle part of the mantle lithosphere. Abundant eclogitic diamond inclusions from Siberia also mostly belong to the middle part of the lithosphere.
Ca-rich eclogites from Precambrian kimberlites of India are located in the middle lithospheric mantle whereas those entrained in Phanerozoic magmas are derived from the lithosphere base. In the Wyoming craton, kimberlites carry eclogite xenoliths captured from the 4.0-2.5 GPa interval. In mantle lithosphere sampled by Proterozoic kimberlites, Ca-rich eclogites and grospydites occur in the 4.0-5.0 GPa interval. South Africa HT eclogite and diamond inclusions from the Proterozoic Premier kimberlites are derived from the deeper part of the mantle lithosphere and trace a high-T geotherm at depths of 7.0-4.0 GPa showing an increase in Fe upwards in the mantle section. Similar trends are common beneath the Catoca cluster kimberlites in Angola.
Mantle eclogites have clinopyroxenes and garnet trace element patterns with opposite inclinations determined by KDs with melts. Flatter and bell-like REE patterns with Eu anomalies? HFSE troughs and U, Pb peaks are common for MORB-type basaltic eclogites. High-Mg eclogites show less fractionated incompatible element patterns. LILE-enrichments and HFSE troughs are typical for kyanite-bearing eclogites. Clinopyroxenes from diamond-bearing eclogites show lower REE and troughs in Nb and Zr, peaks in Pb and U concentrations compared to barren eclogites with round smooth trace element patterns and small depressions in Pb and Ba.
Support: RFBR 19-05-00788, Russian Ministry of Education and Science
How to cite: Ashchepkov, I., Logvinova, A., Spetsius, Z., Ntaflos, T., Downes, H., Vladykin, N., and Ivanov, A.: Varieties of eclogites and their positions in the cratonic mantle lithosphere revealed by Jd-Di thermobarometry and trace element geochemistry, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1749, https://doi.org/10.5194/egusphere-egu21-1749, 2021.
