Stability of high-Al titanite from low-pressure calcsilicates in light of fluid and host-rock composition
Titanite of variable Al and F content was found in granulite- to amphibolite-facies calcsilicates in Central Dronning Maud Land, Antarctica. The highest observed Al content corresponds to an X(Al) [= Al/(Al + Ti)] of 0.53. Previously, such high values of X(Al) were reported from high-pressure rocks,...
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ftmacquarieunicr:oai:https://researchers.mq.edu.au:publications/87791f07-6758-4b41-87a8-27d5dbe3a2de 2024-06-23T07:47:40+00:00 Stability of high-Al titanite from low-pressure calcsilicates in light of fluid and host-rock composition Markl, Gregor Piazolo, Sandra 1999-01 https://researchers.mq.edu.au/en/publications/87791f07-6758-4b41-87a8-27d5dbe3a2de http://www.scopus.com/inward/record.url?scp=0032957615&partnerID=8YFLogxK eng eng info:eu-repo/semantics/restrictedAccess Markl , G & Piazolo , S 1999 , ' Stability of high-Al titanite from low-pressure calcsilicates in light of fluid and host-rock composition ' , American Mineralogist , vol. 84 , no. 1-2 , pp. 37-47 . article 1999 ftmacquarieunicr 2024-05-29T23:48:40Z Titanite of variable Al and F content was found in granulite- to amphibolite-facies calcsilicates in Central Dronning Maud Land, Antarctica. The highest observed Al content corresponds to an X(Al) [= Al/(Al + Ti)] of 0.53. Previously, such high values of X(Al) were reported from high-pressure rocks, but the titanite of this study is from a low-pressure terrain. The compositional variations in titanite can be described for all samples by a set of three linearly independent exchange vectors added to the CaTiSiO 5 end-member titanite. In most rocks, these vectors are Al 1 F 1 Ti(-1O-1), Ti(-0.25)[](0.25)O(-1)OH 1 , and OH 1 F(-1); in one sample, the Ti(-0.25)[](0.25)O(-1)OH 1 vector is replaced by a Si(-0.25)[](0.25)O(-1)OH 1 vector. The actual amount of exchange along these vectors and, therefore, the amount of Al in titanite, depends on P and T, on the composition of the coexisting fluid phase in terms of its H 2 O/HF fugacity ratio, and on host rock composition in terms of Al 2 O 3 /TiO 2 activity ratio. It is inferred that, in suitable chemical environments, high-Al titanite is stable over a wide P-T range. Therefore, the Al content of titanite should not be used in geothermobarometry, even qualitatively. Additionally, because of the coupled substitutions Al 1 F 1 Ti(-1)O(-1) and Al 1 OH 1 Ti(-1)O(-1), the concentration of F in titanite is strongly dependent on the host rock chemistry. This rules out the easy use of titanite as a monitor of fluid composition. Article in Journal/Newspaper Antarc* Antarctica Dronning Maud Land Macquarie University Research Portal Dronning Maud Land |
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Open Polar |
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Macquarie University Research Portal |
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ftmacquarieunicr |
language |
English |
description |
Titanite of variable Al and F content was found in granulite- to amphibolite-facies calcsilicates in Central Dronning Maud Land, Antarctica. The highest observed Al content corresponds to an X(Al) [= Al/(Al + Ti)] of 0.53. Previously, such high values of X(Al) were reported from high-pressure rocks, but the titanite of this study is from a low-pressure terrain. The compositional variations in titanite can be described for all samples by a set of three linearly independent exchange vectors added to the CaTiSiO 5 end-member titanite. In most rocks, these vectors are Al 1 F 1 Ti(-1O-1), Ti(-0.25)[](0.25)O(-1)OH 1 , and OH 1 F(-1); in one sample, the Ti(-0.25)[](0.25)O(-1)OH 1 vector is replaced by a Si(-0.25)[](0.25)O(-1)OH 1 vector. The actual amount of exchange along these vectors and, therefore, the amount of Al in titanite, depends on P and T, on the composition of the coexisting fluid phase in terms of its H 2 O/HF fugacity ratio, and on host rock composition in terms of Al 2 O 3 /TiO 2 activity ratio. It is inferred that, in suitable chemical environments, high-Al titanite is stable over a wide P-T range. Therefore, the Al content of titanite should not be used in geothermobarometry, even qualitatively. Additionally, because of the coupled substitutions Al 1 F 1 Ti(-1)O(-1) and Al 1 OH 1 Ti(-1)O(-1), the concentration of F in titanite is strongly dependent on the host rock chemistry. This rules out the easy use of titanite as a monitor of fluid composition. |
format |
Article in Journal/Newspaper |
author |
Markl, Gregor Piazolo, Sandra |
spellingShingle |
Markl, Gregor Piazolo, Sandra Stability of high-Al titanite from low-pressure calcsilicates in light of fluid and host-rock composition |
author_facet |
Markl, Gregor Piazolo, Sandra |
author_sort |
Markl, Gregor |
title |
Stability of high-Al titanite from low-pressure calcsilicates in light of fluid and host-rock composition |
title_short |
Stability of high-Al titanite from low-pressure calcsilicates in light of fluid and host-rock composition |
title_full |
Stability of high-Al titanite from low-pressure calcsilicates in light of fluid and host-rock composition |
title_fullStr |
Stability of high-Al titanite from low-pressure calcsilicates in light of fluid and host-rock composition |
title_full_unstemmed |
Stability of high-Al titanite from low-pressure calcsilicates in light of fluid and host-rock composition |
title_sort |
stability of high-al titanite from low-pressure calcsilicates in light of fluid and host-rock composition |
publishDate |
1999 |
url |
https://researchers.mq.edu.au/en/publications/87791f07-6758-4b41-87a8-27d5dbe3a2de http://www.scopus.com/inward/record.url?scp=0032957615&partnerID=8YFLogxK |
geographic |
Dronning Maud Land |
geographic_facet |
Dronning Maud Land |
genre |
Antarc* Antarctica Dronning Maud Land |
genre_facet |
Antarc* Antarctica Dronning Maud Land |
op_source |
Markl , G & Piazolo , S 1999 , ' Stability of high-Al titanite from low-pressure calcsilicates in light of fluid and host-rock composition ' , American Mineralogist , vol. 84 , no. 1-2 , pp. 37-47 . |
op_rights |
info:eu-repo/semantics/restrictedAccess |
_version_ |
1802651811772891136 |