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Formation of sapphirine and corundum in scapolitised and Mg‐metasomatised gabbro
Author(s) -
Engvik Ane K.,
Austrheim Håkon
Publication year - 2010
Publication title -
terra nova
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.353
H-Index - 89
eISSN - 1365-3121
pISSN - 0954-4879
DOI - 10.1111/j.1365-3121.2010.00929.x
Subject(s) - geology , geochemistry , plagioclase , metasomatism , gabbro , cordierite , metamorphic rock , phlogopite , igneous rock , mantle (geology) , chemistry , quartz , paleontology , biochemistry , catalysis
Terra Nova, 22, 166–171, 2010 Abstract Sapphirine [(Mg 3.41 Fe 0.11 Al 4.45 )(Al 4.55 Si 1.45 )O 20 ] and corundum are found as inclusions (<0.2 mm) in Cl‐rich scapolite (Me 24‐25 ) and plagioclase (An 20‐24 ) in the metasomatised parts of the Ødegården gabbro, Bamble sector, South Norway. Microtextural relationships suggest that the overall reaction plagioclase + Mg + Cl = sapphirine + corundum + scapolite + Ca + Fe took place in two stages possibly related to infiltration of two metasomatic fronts. Gresen analyses support that the scapolitisation was combined with a strong Mg metasomatism and removal of Fe and Ca on a whole‐rock scale. The ferromagnesian minerals associated with sapphirine in the scapolite metagabbro have especially high Mg ratios (orthopyroxene #Mg = 0.96; phlogopite #Mg = 0.95; amphibole #Mg = 0.81–0.87; clinopyroxene #Mg = 0.95). This is much higher than in biotite (#Mg = 0.60) and clinopyroxene (#Mg = 0.78–0.81) in the unscapolitised parts of the gabbro and comparable with that found in sapphirine‐bearing, orthoamphibole–cordierite schists in the region, suggesting that they also formed by metasomatism. A metasomatic origin for the sapphirine has consequences for models of crustal growth and metamorphic history.