TY - JOUR

T1 - Kyanite-bearing eclogite xenoliths from the Udachnaya kimberlite, Siberian craton, Russia

AU - Radu, Ioana Bogdana

AU - Moine, Bertrand

AU - Ionov, Dmitri

AU - Korsakov, Andrey

AU - Golovin, Alexander

AU - Mikhailenko, Denis

AU - Cottin, Jean Yves

PY - 2017

Y1 - 2017

N2 - Xenoliths brought up by kimberlite magmas are rare samples of otherwise inaccessible lithospheric mantle. Eclogite xenoliths are found in most cratons and commonly show a range of mineral and chemical compositions that can be used to better understand craton formation. This study focuses on five new kyanite-bearing eclogites from the Udachnaya kimberlite pipe (367+5 Ma). They are fine-to coarse-grained and consist mainly of "cloudy" clinopyroxene (cpx) and garnet (grt). The clinopyroxene is Al,Na-rich omphacite while the garnet is Ca-rich, by contrast to typical bi-mineral (cpx+grt) eclogites that contain Fe- and Mg-rich garnets. The Udachnaya kyanite eclogites are similar in modal and major element composition to those from other cratons (Dharwar, Kaapvaal, Slave, West African). The kyanite eclogites have lower REE concentrations than bi-mineral eclogites and typically contain omphacites with positive Eu and Sr anomalies, i.e. a "ghost plagioclase signature". Because such a signature can only be preserved in non-metasomatised samples, we infer that they were present in the protoliths of the eclogites. It follows that subducted oceanic crust is present at the base of the Siberian craton. Similar compositions and textures are also seen in kyanite eclogites from other cratons, which we view as evidence for an Archean, subduction-like formation mechanism related to craton accretion. Thus, contrary to previous work that classifies all kyanite eclogites as type I (IK), metasomatized by carbonatite/kimberlitic fluids, we argue that some of them, both from this work and those from other cratons, belong to the non-metasomatized type II (IIB). The pristine type IIB is the nearest in composition to protoliths of mantle eclogites because it contains no metasomatic enrichments.

AB - Xenoliths brought up by kimberlite magmas are rare samples of otherwise inaccessible lithospheric mantle. Eclogite xenoliths are found in most cratons and commonly show a range of mineral and chemical compositions that can be used to better understand craton formation. This study focuses on five new kyanite-bearing eclogites from the Udachnaya kimberlite pipe (367+5 Ma). They are fine-to coarse-grained and consist mainly of "cloudy" clinopyroxene (cpx) and garnet (grt). The clinopyroxene is Al,Na-rich omphacite while the garnet is Ca-rich, by contrast to typical bi-mineral (cpx+grt) eclogites that contain Fe- and Mg-rich garnets. The Udachnaya kyanite eclogites are similar in modal and major element composition to those from other cratons (Dharwar, Kaapvaal, Slave, West African). The kyanite eclogites have lower REE concentrations than bi-mineral eclogites and typically contain omphacites with positive Eu and Sr anomalies, i.e. a "ghost plagioclase signature". Because such a signature can only be preserved in non-metasomatised samples, we infer that they were present in the protoliths of the eclogites. It follows that subducted oceanic crust is present at the base of the Siberian craton. Similar compositions and textures are also seen in kyanite eclogites from other cratons, which we view as evidence for an Archean, subduction-like formation mechanism related to craton accretion. Thus, contrary to previous work that classifies all kyanite eclogites as type I (IK), metasomatized by carbonatite/kimberlitic fluids, we argue that some of them, both from this work and those from other cratons, belong to the non-metasomatized type II (IIB). The pristine type IIB is the nearest in composition to protoliths of mantle eclogites because it contains no metasomatic enrichments.

KW - Craton

KW - Eclogite

KW - Kyanite

KW - Mantle

KW - Siberia

KW - Xenolith

KW - SOUTH-AFRICA

KW - LITHOSPHERIC MANTLE

KW - PERIDOTITE XENOLITHS

KW - ROBERTS-VICTOR-KIMBERLITE

KW - OBNAZHENNAYA KIMBERLITE

KW - CONSTRAINTS

KW - PROGRESSIVE METASOMATISM

KW - OCEANIC-CRUST

KW - GEOCHEMISTRY

KW - RE-OS

UR - http://www.scopus.com/inward/record.url?scp=85026663846&partnerID=8YFLogxK

U2 - 10.1051/bsgf/2017008

DO - 10.1051/bsgf/2017008

M3 - Article

AN - SCOPUS:85026663846

VL - 188

JO - Bulletin - Societie Geologique de France

JF - Bulletin - Societie Geologique de France

SN - 0037-9409

IS - 1-2

M1 - 7

ER -