Abstract
Kornerupine, (□, Mg, Fe)(Al, Mg, Fe) 9 (Si, Al, B) 5 O 21 (OH, F), is known from only five mafic or ultramafic settings worldwide (of the >70 localities overall). We report a sixth occurrence from Akarui Point in the Lützow-Holm Complex, East Antarctica, where two ruby corundum (0.22-0.34 wt% Cr 2 O 3 )-plagioclase lenses are found at the same structural level as boudinaged ultrabasic rocks in hornblende gneiss and amphibolite. Ion microprobe analyses of kornerupine give 13-59 ppm Be, 181-302 ppm Li, and 5466-6812 ppm B, corresponding to 0.38-0.47 B per 21.5 O; associated sapphirine also contains B (588-889 ppm). Peak metamorphic conditions are estimated to be 770-790 °C and 7.7-9.8 kbar. Kornerupine encloses tourmaline and plagioclase, which suggests the prograde reaction tourmaline (1) + plagioclase (>An34) + sapphirine ± spinel → kornerupine + corundum (ruby) + plagioclase (>An82)+(fluid or melt). Alternatively, kornerupine and tourmaline could have formed sequentially under nearly constant P-T conditions during the infiltration of fluid that was originally B-bearing, but then progressively lost Na (or gained Ca) and B through reaction with mafic rocks. Kornerupine later reacted with H 2 O-CO 2 fluid in cracks at P-T conditions in the andalusite stability field: kornerupine+ plagioclase+ (Na, K, ± Si in fluid) → tourmaline + biotite + corundum (sapphire)+ magnesite+andalusite + (Ca in fluid). Secondary tourmaline differs from the included tourmaline in containing less Ti and having a higher Na/(Na + Ca + K) ratio. There are two possible scenarios for introducing B into the lenses: (1) infiltration of boron-bearing aqueous fluids released by prograde breakdown of muscovite in associated metasedimentary rocks; (2) hydrothermal alteration of mafic and ultramafic rocks by seawater prior to peak metamorphism. The latter scenario is consistent with an earlier suggestion that Akarui Point could be part of an ophiolite complex developed between the Yamato-Belgica and Rayner complexes.
| Original language | English |
|---|---|
| Pages (from-to) | 351-375 |
| Number of pages | 25 |
| Journal | Geological Society Special Publication |
| Volume | 308 |
| DOIs | |
| Publication status | Published - Dec 1 2008 |
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All Science Journal Classification (ASJC) codes
- Water Science and Technology
- Ocean Engineering
- Geology
Cite this
Kornerupine sensu stricto associated with mafic and ultramafic rocks in the Lützow-Holm Complex at Akarui Point, East Antarctica : What is the source of boron? / Kawakami, T.; Grew, E. S.; Motoyoshi, Y.; Shearer, C. K.; Ikeda, Takeshi; Burger, P. V.; Kusachi, I.
In: Geological Society Special Publication, Vol. 308, 01.12.2008, p. 351-375.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Kornerupine sensu stricto associated with mafic and ultramafic rocks in the Lützow-Holm Complex at Akarui Point, East Antarctica
T2 - What is the source of boron?
AU - Kawakami, T.
AU - Grew, E. S.
AU - Motoyoshi, Y.
AU - Shearer, C. K.
AU - Ikeda, Takeshi
AU - Burger, P. V.
AU - Kusachi, I.
PY - 2008/12/1
Y1 - 2008/12/1
N2 - Kornerupine, (□, Mg, Fe)(Al, Mg, Fe) 9 (Si, Al, B) 5 O 21 (OH, F), is known from only five mafic or ultramafic settings worldwide (of the >70 localities overall). We report a sixth occurrence from Akarui Point in the Lützow-Holm Complex, East Antarctica, where two ruby corundum (0.22-0.34 wt% Cr 2 O 3 )-plagioclase lenses are found at the same structural level as boudinaged ultrabasic rocks in hornblende gneiss and amphibolite. Ion microprobe analyses of kornerupine give 13-59 ppm Be, 181-302 ppm Li, and 5466-6812 ppm B, corresponding to 0.38-0.47 B per 21.5 O; associated sapphirine also contains B (588-889 ppm). Peak metamorphic conditions are estimated to be 770-790 °C and 7.7-9.8 kbar. Kornerupine encloses tourmaline and plagioclase, which suggests the prograde reaction tourmaline (1) + plagioclase (>An34) + sapphirine ± spinel → kornerupine + corundum (ruby) + plagioclase (>An82)+(fluid or melt). Alternatively, kornerupine and tourmaline could have formed sequentially under nearly constant P-T conditions during the infiltration of fluid that was originally B-bearing, but then progressively lost Na (or gained Ca) and B through reaction with mafic rocks. Kornerupine later reacted with H 2 O-CO 2 fluid in cracks at P-T conditions in the andalusite stability field: kornerupine+ plagioclase+ (Na, K, ± Si in fluid) → tourmaline + biotite + corundum (sapphire)+ magnesite+andalusite + (Ca in fluid). Secondary tourmaline differs from the included tourmaline in containing less Ti and having a higher Na/(Na + Ca + K) ratio. There are two possible scenarios for introducing B into the lenses: (1) infiltration of boron-bearing aqueous fluids released by prograde breakdown of muscovite in associated metasedimentary rocks; (2) hydrothermal alteration of mafic and ultramafic rocks by seawater prior to peak metamorphism. The latter scenario is consistent with an earlier suggestion that Akarui Point could be part of an ophiolite complex developed between the Yamato-Belgica and Rayner complexes.
AB - Kornerupine, (□, Mg, Fe)(Al, Mg, Fe) 9 (Si, Al, B) 5 O 21 (OH, F), is known from only five mafic or ultramafic settings worldwide (of the >70 localities overall). We report a sixth occurrence from Akarui Point in the Lützow-Holm Complex, East Antarctica, where two ruby corundum (0.22-0.34 wt% Cr 2 O 3 )-plagioclase lenses are found at the same structural level as boudinaged ultrabasic rocks in hornblende gneiss and amphibolite. Ion microprobe analyses of kornerupine give 13-59 ppm Be, 181-302 ppm Li, and 5466-6812 ppm B, corresponding to 0.38-0.47 B per 21.5 O; associated sapphirine also contains B (588-889 ppm). Peak metamorphic conditions are estimated to be 770-790 °C and 7.7-9.8 kbar. Kornerupine encloses tourmaline and plagioclase, which suggests the prograde reaction tourmaline (1) + plagioclase (>An34) + sapphirine ± spinel → kornerupine + corundum (ruby) + plagioclase (>An82)+(fluid or melt). Alternatively, kornerupine and tourmaline could have formed sequentially under nearly constant P-T conditions during the infiltration of fluid that was originally B-bearing, but then progressively lost Na (or gained Ca) and B through reaction with mafic rocks. Kornerupine later reacted with H 2 O-CO 2 fluid in cracks at P-T conditions in the andalusite stability field: kornerupine+ plagioclase+ (Na, K, ± Si in fluid) → tourmaline + biotite + corundum (sapphire)+ magnesite+andalusite + (Ca in fluid). Secondary tourmaline differs from the included tourmaline in containing less Ti and having a higher Na/(Na + Ca + K) ratio. There are two possible scenarios for introducing B into the lenses: (1) infiltration of boron-bearing aqueous fluids released by prograde breakdown of muscovite in associated metasedimentary rocks; (2) hydrothermal alteration of mafic and ultramafic rocks by seawater prior to peak metamorphism. The latter scenario is consistent with an earlier suggestion that Akarui Point could be part of an ophiolite complex developed between the Yamato-Belgica and Rayner complexes.
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UR - http://www.scopus.com/inward/citedby.url?scp=72049102632&partnerID=8YFLogxK
U2 - 10.1144/SP308.17
DO - 10.1144/SP308.17
M3 - Article
AN - SCOPUS:72049102632
VL - 308
SP - 351
EP - 375
JO - Geological Society Special Publication
JF - Geological Society Special Publication
SN - 0305-8719
ER -