TY - JOUR

T1 - Origin of alkaline carbonates in kimberlites of the Siberian craton

T2 - Evidence from melt inclusions in mantle olivine of the Udachnaya-East pipe

AU - Golovin, Alexander V.

AU - Sharygin, Igor S.

AU - Korsakov, Andrey V.

N1 - Publisher Copyright: © 2016 Elsevier B.V.

PY - 2017/4/20

Y1 - 2017/4/20

N2 - Alkaline carbonates hexagonal zemkorite (Na,K)2Ca(CO3)2 and orthorhombic shortite Na2Ca2(CO3)3 were found among groundmass minerals in kimberlites from some localities worldwide, 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 origin while sodium may come from a crustal source. Orthorhombic nyerereite (Na,K)2Ca(CO3)2 and shortite were identified as daughter phases in secondary melt inclusions (MI) in olivine from the deepest mantle xenoliths (i.e., sheared peridotites) and in olivine xenocrysts derived from disintegrated mantle rocks from the Udachnaya-East pipe by Raman spectroscopy and SEM-EDS. The melt, hosted as the inclusions in olivine, was entrapped at a mantle depth. On the basis of similar mineralogy of MI to groundmass of the unserpentinised kimberlites, we suggest relation of MI 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(CO3)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(CO3,SO4)2 into Na2Ca2(CO3)3 (shortite) and K3Na(SO4)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(CO3)2 and Na2Ca2(CO3)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.

AB - Alkaline carbonates hexagonal zemkorite (Na,K)2Ca(CO3)2 and orthorhombic shortite Na2Ca2(CO3)3 were found among groundmass minerals in kimberlites from some localities worldwide, 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 origin while sodium may come from a crustal source. Orthorhombic nyerereite (Na,K)2Ca(CO3)2 and shortite were identified as daughter phases in secondary melt inclusions (MI) in olivine from the deepest mantle xenoliths (i.e., sheared peridotites) and in olivine xenocrysts derived from disintegrated mantle rocks from the Udachnaya-East pipe by Raman spectroscopy and SEM-EDS. The melt, hosted as the inclusions in olivine, was entrapped at a mantle depth. On the basis of similar mineralogy of MI to groundmass of the unserpentinised kimberlites, we suggest relation of MI 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(CO3)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(CO3,SO4)2 into Na2Ca2(CO3)3 (shortite) and K3Na(SO4)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(CO3)2 and Na2Ca2(CO3)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.

KW - Alkaline carbonate

KW - Carbonatite

KW - Kimberlite

KW - Mantle xenolith

KW - Melt inclusion

KW - Nyerereite

KW - Raman spectroscopy

KW - Shortite

KW - OLDOINYO-LENGAI

KW - LITHOSPHERIC MANTLE

KW - UNALTERED KIMBERLITES

KW - PERIDOTITE XENOLITHS

KW - CALCITE CARBONATITE

KW - FLUID INCLUSIONS

KW - NATROCARBONATITE LAVA

KW - CHEMICAL-COMPOSITION

KW - MAGMA EVOLUTION

KW - CANADA-GOLD-MINE

UR - http://www.scopus.com/inward/record.url?scp=85006825769&partnerID=8YFLogxK

U2 - 10.1016/j.chemgeo.2016.10.036

DO - 10.1016/j.chemgeo.2016.10.036

M3 - Article

AN - SCOPUS:85006825769

VL - 455

SP - 357

EP - 375

JO - Chemical Geology

JF - Chemical Geology

SN - 0009-2541

ER -