- Names
-
- Alexander V. Golovin
- Igor S. Sharygin
- Andrey V. Korsakov
- Title
- Origin of alkaline carbonates in kimberlites of the Siberian craton: Evidence from melt inclusions in mantle olivine of the Udachnaya-East pipe
- Abstract
- Alkaline carbonates hexagonal zemkorite $(Na,K)_2Ca(CO_3)_2$ and orthorhombic shortite $Na_2Ca(CO_3)_3$ were found among groundmassminerals in kimberlites from some localitiesworldwide, including the unserpentinised units of the Udachnaya-East kimberlite. However, the source of alkalis and the origin of the unusual minerals in these kimberlites remain highly debatable. It is generally considered that they have hydrothermal or metasomatic originwhile sodiummay come from a crustal source. Orthorhombic nyerereite $(Na,K)_2Ca(CO_3)_2$ and shortite were identified as daughter phases in secondarymelt inclusions (MI) in olivine fromthe deepest mantle xenoliths (i.e., sheared peridotites) and in olivine xenocrysts derived from disintegratedmantle rocks fromthe Udachnaya-East pipe by Raman spectroscopy and SEM-EDS. Themelt, hosted as the inclusions in olivine,was entrapped at a mantle depth. On the basis of similar mineralogy ofMI to groundmass of the unserpentinised kimberlites, we suggest relation ofMI to the Udachnaya kimberlite melts. The MI solidus temperature is as high as 500 °С. Generally,MI nyerereite is considered as a magmatic mineral but experiments show it to be stable at relatively low temperatures (LT) T ≤ 360 °С. Thus, strictly speaking, it is a subsolidus mineral formed from high-temperature (HT) (T < 800 °С) hexagonal $(Na,K)_2Ca(CO_3)_2$ carbonate. Shortite is also a subsolidus mineral, which may form by several subsolidus reactions in multicomponent systems, such as kimberlites, while breakdown of the HT hexagonal phase $(Na,K)_2Ca(CO_3,SO_4)_2$ into $Na_2Ca(CO_3)_3$ (shortite) and $K_3Na(SO_4)_2$ (aphthitalite) is the basic mechanism. The solidus temperature for the Udachnaya-East kimberlite is about 300 °С indicating that LT orthorhombic nyerereite may crystallise directly from the melt as well. Thus, $(Na,K)_2Ca(CO_3)_2$ and $Na_2Ca(CO_3)_3$ carbonates in the groundmass of the unserpentinised Udachnaya-East kimberlites are of magmatic/subsolidus origin. This scenario for the origin of Na-K-Ca and Na-Ca carbonates in the Udachnaya-East kimberlites may have implications for other kimberlites elsewhere.
- Keywords
- Raman spectroscopy, MIR, band position, minerals, carbonates, Nyerereite, Shortite, zemkorite, aphthitalite, Na2Ca(CO3)2, Na2Ca2(CO3)3, (Na,K)2Ca(CO3)2, K3Na(SO4)2, inclusions, Udachnaya-East pipe, Siberia, Earth Science
- Content
- band list data, spectral data, earth sciences
- Year
- 2017
- Journal
- Chemical Geology
- Volume
- 455
- Pages
- 357 - 375
- Pages number
- 21
- Document type
- article
- Publication state
- published
- Doi
- 10.1016/j.chemgeo.2016.10.036
- Identifiers
-
- bibcode: 2017ChGeo.455..357G