High-Alumina Pyroxenite Xenoliths from Quaternary Basalt of Spitsbergen Island: Evidence for Continental Crust Delamination

The origin of spinel–garnet pyroxenite from xenoliths in Quaternary basaltoids of Spitsbergen Island (Svalbard Archipelago) is discussed. The rocks have a high concentration of Al 2 O 3 and MgO and low Cr. The primary magmatic association Spl–Opx–Cpx and the high Al content in pyroxenes provide evid...

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Bibliographic Details
Published in:Doklady earth sciences 2019-04, Vol.485 (2), p.413-417
Main Authors: Koreshkova, M. Yu, Marin, Yu. B., Nikitina, L. P., Downes, H., Tokusheva, A., Goncharov, A. G.
Format: Article
Language:English
Subjects:
Aluminum oxide
Archipelagoes
Basalt
Continental crust
Delamination
Earth and Environmental Science
Earth Sciences
Garnet
Geochemistry
Magma
Magnesium oxide
Melts
Phase transitions
Pyroxenes
Quaternary
Rock
Rocks
Silica
Silicon dioxide
Spinel
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Summary:The origin of spinel–garnet pyroxenite from xenoliths in Quaternary basaltoids of Spitsbergen Island (Svalbard Archipelago) is discussed. The rocks have a high concentration of Al 2 O 3 and MgO and low Cr. The primary magmatic association Spl–Opx–Cpx and the high Al content in pyroxenes provide evidence for the formation of these rocks as cumulates of hydrous basaltic melts in the lower crust at a pressure of ~1.2 GPa. Transformation of the texture from the magmatic hypidiomorphic to the metamorphic granoblastic and growth of garnet at the expense of spinel and high-alumina pyroxenes indicate transport of rocks to a depth below the spinel/garnet phase transition boundary in the Cr 2 O 3 -free CaO–MgO–Al 2 O 3 –SiO 2 system. The parameters of the Grt–Opx equilibrium range within 1060–1120°C and 2.2–2.6 GPa. Thus, magmatic pyroxenite was transported to a great depth into the mantle, which provides evidence for delamination in the region of the lower continental crust containing ultramafic cumulates.
ISSN:1028-334X
1531-8354
DOI:10.1134/S1028334X19040123