Thermal State, Thickness, and Composition of the Lithospheric Mantle beneath the Upper Muna Kimberlite Field (Siberian Craton) Constrained by Clinopyroxene Xenocrysts and Comparison with Daldyn and Mirny Fields
| Autor: | Igor V. Yakovlev, Vladimir Malkovets, A. M. Dymshits, Igor S. Sharygin, Viktor K. Garanin, Sergey V. Potapov, Anastasia A. Gibsher, Taisia A. Alifirova, Sofya S. Vorobei |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2020 |
| Předmět: |
lcsh:QE351-399.2
010504 meteorology & atmospheric sciences kimberlite 010502 geochemistry & geophysics 01 natural sciences Mantle (geology) diamond Lithosphere geotherm Xenolith Petrology Geothermal gradient 0105 earth and related environmental sciences Peridotite Siberian craton geography geography.geographical_feature_category lcsh:Mineralogy Geology xenocryst Geotechnical Engineering and Engineering Geology Craton FITPLOT clinopyroxene Magmatism paleogeotherm Kimberlite mantle xenolith |
| Zdroj: | Minerals, Vol 10, Iss 549, p 549 (2020) Minerals Volume 10 Issue 6 |
| Popis: | To gain better insight into the thermal state and composition of the lithospheric mantle beneath the Upper Muna kimberlite field (Siberian craton), a suite of 323 clinopyroxene xenocrysts and 10 mantle xenoliths from the Komsomolskaya-Magnitnaya (KM) pipe have been studied. We selected 188 clinopyroxene grains suitable for precise pressure (P)-temperature (T) estimation using single-clinopyroxene thermobarometry. The majority of P-T points lie along a narrow, elongated field in P-T space with a cluster of high-T and high-P points above 1300 ° C, which deviates from the main P-T trend. The latter points may record a thermal event associated with kimberlite magmatism (a &ldquo stepped&rdquo or &ldquo kinked&rdquo geotherm). In order to eliminate these factors, the steady-state mantle paleogeotherm for the KM pipe at the time of initiation of kimberlite magmatism (Late Devonian&ndash Early Carboniferous) was constrained by numerical fitting of P-T points below T = 1200 ° C. The obtained mantle paleogeotherm is similar to the one from the nearby Novinka pipe, corresponding to a ~34&ndash 35 mW/m2 surface heat flux, 225&ndash 230 km lithospheric thickness, and 110&ndash 120 thick &ldquo diamond window&rdquo for the Upper Muna field. Coarse peridotite xenoliths are consistent in their P-T estimates with the steady-state mantle paleogeotherm derived from clinopyroxene xenocrysts, whereas porphyroclastic ones plot within the cluster of high-T and high-P clinopyroxene xenocrysts. Discrimination using Cr2O3 demonstrates that peridotitic clinopyroxene xenocrysts are prevalent (89%) among all studied 323 xenocrysts, suggesting that the Upper Muna mantle is predominantly composed of peridotites. Clinopyroxene-poor or -free peridotitic rocks such as harzburgites and dunites may be evident at depths of 140&ndash 180 km in the Upper Muna mantle. Judging solely from the thermal considerations and the thickness of the lithosphere, the KM and Novinka pipes should have excellent diamond potential. However, all pipes in the Upper Muna field have low diamond grades (< 0.9, in carats/ton), although the lithosphere thickness is almost similar to the values obtained for the high-grade Udachnaya and Mir pipes from the Daldyn and Mirny fields, respectively. Therefore, other factors have affected the diamond grade of the Upper Muna kimberlite field. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
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