Hogbomite in sappherine-bearing rocks from the Bamble Sector, south Norway

Hogbomite in sappherine-bearing rocks from the Bamble Sector, south Norway

Visser, D.
Thijssen, P.M.H

Molengraaff Fonds

1991

Hogbomite is reported from two upper-amphibolite and granulite-facies, sapphirine-bearing, Al-Mg-Fe-rich and silica-poor lens-shaped layers within the Bamble Sector, south Norway. Primary assemblages, indicating peak metamorphic conditions of 773-844 °C at 7 kbar (Mg-Fe exchange thermometry), are spinel-sapphirine-biotite-gedrite, spinel-corudum-sapphirine-cordierite and orthopyroxene-biotite-cordierite-plagioclase. Hogbomite formed by hydrousalteration and oxidation of primary spinel and rutile and/or ilmenite according to the generalised reaction: spinel + ilmenite/rutile ± sapphirine ± gedrite + H2O + O2 = hogbomite ± corundum ± magnetic ± chlorite. Suggested conditions of hogbomite formation are 550-620 °C and 6-7 kbar. The hogbomites contain 10.2-14.7 wt.% MgO, 0-0.3 wt. % ZnO , 58.9-62.1 wt.% Al2O3 and 15.6-17.6 wt. % Fe as FeO. The two hogbomites may belong to different polytypes, as suggested by their differing TiO2 (9.9-10.1 versus 5.7- 5.8 wt.%) and calculated Fe3+ - and H2O-contents. The partitioning of Zn between spinel and hogbomite is not uniform and is considered to depend upon prevailing fO2 and aH2O.

http://resolver.tudelft.nl/uuid:b7735b57-e44c-47f6-98e2-04098454cbae

Utrecht University

Geoscience Reports

report

(c) the author(s)