Metasomatic Origin of Lamellar-like Inclusions in Clinopyroxenes from Mantle Xenoliths of the Obnazhennaya Pipe (Kuoika Field, Yakutian Diamondiferous Province)

• Published in: Doklady earth sciences 2023-06, Vol.510 (2), p.422-427
• Main Authors: Korolev, N. M., Nikitina, L. P., Kuznetsov, A. B., Goncharov, A. G., Galankina, O. L., Shilovskikh, V. V., Vlasenko, N. S.
• Format: Article
• Language: English
• Subjects: Aluminum oxide; Calcium magnesium silicates; Chemical composition; Chromium; Diamonds; Diopside; Earth and Environmental Science; Earth Sciences; Enstatite; Garnet; Inclusions; Lamellae; Lamellar structure; Magnesium aluminum silicates; Mineral assemblages; Mineralogy; Minerals; Pipes; Recrystallization; Rocks, Igneous; Rutile; Solid solutions; Spinel group; Structures
• ISSN: 1028-334X; 1531-8354
• DOI: 10.1134/S1028334X23600445

The article reports new data on previously undescribed lamellar-like (linearly oriented) structures in clinopyroxenes from mantle xenoliths of garnet pyroxenites (Obnazhennaya pipe, Northern Siberia). The origin and mineral diversity of lamellar structures in xenoliths from the Obnazhennaya pipe are supposed to be related to a breakdown of solid solutions during a decrease of P–T parameters. Our study shows that metasomatic recrystallization of initial clinopyroxene with linear exsolution structures leads to the formation of new secondary mineral assemblages. The secondary clinopyroxene reproduces (inherits) frameworks with linearly oriented inclusions, which are morphologically similar to the primary exsolution structures. Thus, the pyroxenite xenoliths from the Obnazhennaya pipe contain two generations of mineral associations with lamellar structures: primary and secondary. The primary association is composed of diopside, containing lamellae of enstatite, pyrope, spinel and rutile. The secondary (metasomatic) clinopyroxene contains half as much Al 2 O 3 (3.4 wt %) and Na 2 O (1.7 wt %) and is enriched in MgO and CaO compared to the primary clinopyroxene. Nevertheless, the chemical composition of the secondary pyroxene still corresponds to diopside end-member. The metasomatic association comprises aligned pargasite (Al-rich amphibole) instead of orthopyroxene (enstatite) lamellae, and the secondary rutile is enriched in chromium (up to 3.1 wt % Cr 2 O 3 ) in contrast to rutile from the primary mineral assemblage.