Deep komatiite signature in cratonic mantle pyroxenite
We present new and compiled whole-rock modal mineral, major and trace element data from extremely melt depleted but pyroxenite and garnet(-ite)-bearing Palaeoarchean East Greenland cratonic mantle, exposed as three isolated, tectonically strained orogenic peridotite bodies (Ugelvik, Raudhaugene and...
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ftunivutrecht:oai:dspace.library.uu.nl:1874/365197 2023-07-23T04:19:04+02:00 Deep komatiite signature in cratonic mantle pyroxenite Spengler, Dirk van Roermund, Herman L.M. Drury, Martyn R. Structural geology and EM Structural geology & tectonics 2018-06 application/pdf https://dspace.library.uu.nl/handle/1874/365197 en eng 0263-4929 https://dspace.library.uu.nl/handle/1874/365197 info:eu-repo/semantics/ClosedAccess Archean Cratonic mantle Garnet-pyroxenite Komatiite Pyroxene exsolution Geology Geochemistry and Petrology Article 2018 ftunivutrecht 2023-07-02T02:28:17Z We present new and compiled whole-rock modal mineral, major and trace element data from extremely melt depleted but pyroxenite and garnet(-ite)-bearing Palaeoarchean East Greenland cratonic mantle, exposed as three isolated, tectonically strained orogenic peridotite bodies (Ugelvik, Raudhaugene and Midsundvatnet) in western Norway. The studied lithologies comprise besides spinel- and/or garnet-bearing peridotite (dunite, harzburgite, lherzolite) garnet-clinopyroxenite and partially olivine-bearing garnet-orthopyroxenite and -websterite. Chemical and modal data and spatial relationships between different rock types suggest deformation to have triggered mechanical mixing of garnet-free dunite with garnet-bearing enclosures that formed garnet-peridotite. Inclusions of olivine in porphyroclastic minerals of pyroxenite show a primary origin of olivine in olivine-bearing variants. Major element oxide abundances and ratios of websterite differ to those in rocks expected to form by reaction of peridotite with basaltic melts or silica-rich fluids, but resemble those of Archean Al-enriched komatiite (AEK) flows from Barberton and Commondale greenstone belts, South Africa. Websterite GdN/YbN, 0.49-0.65 (olivine-free) and 0.73-0.85 (olivine-bearing), overlaps that of two subgroups of AEK, GdN/YbN 0.25-0.55 and 0.77-0.90, with each of them being nearly indistinguishable from one another in not only rare earth element fractionation but also concentration. Websterite MgO content is high, 22.7-29.0 wt%, and Zr/Y is very low, 0.1-1.0. The other, non-websteritic pyroxenites overlap-when mechanically mixed together with garnetite-in chemistry with that of AEK. It follows an origin of websterite and likely all pyroxenite that involves melting of a garnet-bearing depleted mantle source. Pyroxene exsolution lamellae in the inferred solidus garnet in all lithological varieties require the pyroxenites to have crystallized in the majorite garnet stability field, at 3-4 GPa (90-120 km depth) at minimum 1,600°C. Consequently, we interpret ... Article in Journal/Newspaper East Greenland Greenland Utrecht University Repository Greenland Midsundvatnet ENVELOPE(6.699,6.699,62.681,62.681) Norway |
institution |
Open Polar |
collection |
Utrecht University Repository |
op_collection_id |
ftunivutrecht |
language |
English |
topic |
Archean Cratonic mantle Garnet-pyroxenite Komatiite Pyroxene exsolution Geology Geochemistry and Petrology |
spellingShingle |
Archean Cratonic mantle Garnet-pyroxenite Komatiite Pyroxene exsolution Geology Geochemistry and Petrology Spengler, Dirk van Roermund, Herman L.M. Drury, Martyn R. Deep komatiite signature in cratonic mantle pyroxenite |
topic_facet |
Archean Cratonic mantle Garnet-pyroxenite Komatiite Pyroxene exsolution Geology Geochemistry and Petrology |
description |
We present new and compiled whole-rock modal mineral, major and trace element data from extremely melt depleted but pyroxenite and garnet(-ite)-bearing Palaeoarchean East Greenland cratonic mantle, exposed as three isolated, tectonically strained orogenic peridotite bodies (Ugelvik, Raudhaugene and Midsundvatnet) in western Norway. The studied lithologies comprise besides spinel- and/or garnet-bearing peridotite (dunite, harzburgite, lherzolite) garnet-clinopyroxenite and partially olivine-bearing garnet-orthopyroxenite and -websterite. Chemical and modal data and spatial relationships between different rock types suggest deformation to have triggered mechanical mixing of garnet-free dunite with garnet-bearing enclosures that formed garnet-peridotite. Inclusions of olivine in porphyroclastic minerals of pyroxenite show a primary origin of olivine in olivine-bearing variants. Major element oxide abundances and ratios of websterite differ to those in rocks expected to form by reaction of peridotite with basaltic melts or silica-rich fluids, but resemble those of Archean Al-enriched komatiite (AEK) flows from Barberton and Commondale greenstone belts, South Africa. Websterite GdN/YbN, 0.49-0.65 (olivine-free) and 0.73-0.85 (olivine-bearing), overlaps that of two subgroups of AEK, GdN/YbN 0.25-0.55 and 0.77-0.90, with each of them being nearly indistinguishable from one another in not only rare earth element fractionation but also concentration. Websterite MgO content is high, 22.7-29.0 wt%, and Zr/Y is very low, 0.1-1.0. The other, non-websteritic pyroxenites overlap-when mechanically mixed together with garnetite-in chemistry with that of AEK. It follows an origin of websterite and likely all pyroxenite that involves melting of a garnet-bearing depleted mantle source. Pyroxene exsolution lamellae in the inferred solidus garnet in all lithological varieties require the pyroxenites to have crystallized in the majorite garnet stability field, at 3-4 GPa (90-120 km depth) at minimum 1,600°C. Consequently, we interpret ... |
author2 |
Structural geology and EM Structural geology & tectonics |
format |
Article in Journal/Newspaper |
author |
Spengler, Dirk van Roermund, Herman L.M. Drury, Martyn R. |
author_facet |
Spengler, Dirk van Roermund, Herman L.M. Drury, Martyn R. |
author_sort |
Spengler, Dirk |
title |
Deep komatiite signature in cratonic mantle pyroxenite |
title_short |
Deep komatiite signature in cratonic mantle pyroxenite |
title_full |
Deep komatiite signature in cratonic mantle pyroxenite |
title_fullStr |
Deep komatiite signature in cratonic mantle pyroxenite |
title_full_unstemmed |
Deep komatiite signature in cratonic mantle pyroxenite |
title_sort |
deep komatiite signature in cratonic mantle pyroxenite |
publishDate |
2018 |
url |
https://dspace.library.uu.nl/handle/1874/365197 |
long_lat |
ENVELOPE(6.699,6.699,62.681,62.681) |
geographic |
Greenland Midsundvatnet Norway |
geographic_facet |
Greenland Midsundvatnet Norway |
genre |
East Greenland Greenland |
genre_facet |
East Greenland Greenland |
op_relation |
0263-4929 https://dspace.library.uu.nl/handle/1874/365197 |
op_rights |
info:eu-repo/semantics/ClosedAccess |
_version_ |
1772181860069146624 |