Details
| Original language | English |
|---|---|
| Pages (from-to) | 108-117 |
| Number of pages | 10 |
| Journal | Earth and Planetary Science Letters |
| Volume | 443 |
| Early online date | 29 Mar 2016 |
| Publication status | Published - 1 Jun 2016 |
Abstract
The Bushveld Complex (South Africa) is the largest layered intrusion on Earth and plays a considerable role in our understanding of magmatic differentiation and ore-forming processes. In this study, we present new geochemical data for apatite-hosted multiphase inclusions in gabbroic cumulates from the Bushveld Upper Zone. Inclusions re-homogenized at high-temperature (1060-1100 °C) display a range of compositions in each rock sample, from iron-rich (35 wt.% FeOtot; 28 wt.% SiO2) to silica-rich (5 wt.% FeOtot; 65 wt.% SiO2). This trend is best explained by an immiscible process and trapping of contrasted melts in apatite crystals during progressive cooling along the binodal of a two-liquid field. The coexistence of both Si-rich and Fe-rich immiscible melts in single apatite grains is used to discuss the ability of immiscible melts to segregate from each other, and the implications for mineral and bulk cumulate compositions. We argue that complete separation of immiscible liquids did not occur, resulting in crystallization of similar phases from both melts but in different proportions. However, partial segregation in a crystal mush and the production of contrasting phase proportions from the Fe-rich melt and the Si-rich melt can be responsible for the cyclic evolution from melanocratic (Fe-Ti-P-rich) to leucocratic (plagioclase-rich) gabbros which is commonly observed in the Upper Zone of the Bushveld Complex where it occurs at a vertical scale of 50 to 200 m.
Keywords
- Apatite, Bushveld, Immiscibility, Layered intrusion, Melt inclusion, Troctolite
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geophysics
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
- Earth and Planetary Sciences(all)
- Earth and Planetary Sciences (miscellaneous)
- Earth and Planetary Sciences(all)
- Space and Planetary Science
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In: Earth and Planetary Science Letters, Vol. 443, 01.06.2016, p. 108-117.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Immiscible iron- and silica-rich liquids in the Upper Zone of the Bushveld Complex
AU - Fischer, Lennart A.
AU - Wang, Meng
AU - Charlier, Bernard
AU - Namur, Olivier
AU - Roberts, R. James
AU - Veksler, Ilya V.
AU - Cawthorn, R. Grant
AU - Holtz, François
N1 - Funding Information: This project was supported by a DAAD -Doktorandenstipendium for L.A. Fischer. B. Charlier and O. Namur acknowledge support from the Alexander von Humboldt Foundation . We acknowledge the German Science Foundation for the support of the research work. I.V. Veksler has been supported by DFG grant VE 619/2-1 and RSF grant No. 14-17-00200 . The reviews of C. Tegner, J. VanTongeren and an anonymous reviewer helped to improve the quality of this paper. P.E. Wolff and C. Zhang from the Leibniz Universität Hannover, and S. Feig and K. Goemann from the University of Tasmania are thanked for support with EPMA and FE-SEM. We acknowledge C. Glotzbach, C. Wangenheim and L. Lindner, Institut für Geologie, Leibniz Universität Hannover, for providing mineral separation, and A. Woodland and T. Terhaar, Goethe University Frankfurt, for SELFRAG. V.S. Kamenetsky, A. Husen, and S. Sykora are thanked for discussions and their comments. Publisher Copyright: © 2016 Elsevier B.V.. Copyright: Copyright 2016 Elsevier B.V., All rights reserved.
PY - 2016/6/1
Y1 - 2016/6/1
N2 - The Bushveld Complex (South Africa) is the largest layered intrusion on Earth and plays a considerable role in our understanding of magmatic differentiation and ore-forming processes. In this study, we present new geochemical data for apatite-hosted multiphase inclusions in gabbroic cumulates from the Bushveld Upper Zone. Inclusions re-homogenized at high-temperature (1060-1100 °C) display a range of compositions in each rock sample, from iron-rich (35 wt.% FeOtot; 28 wt.% SiO2) to silica-rich (5 wt.% FeOtot; 65 wt.% SiO2). This trend is best explained by an immiscible process and trapping of contrasted melts in apatite crystals during progressive cooling along the binodal of a two-liquid field. The coexistence of both Si-rich and Fe-rich immiscible melts in single apatite grains is used to discuss the ability of immiscible melts to segregate from each other, and the implications for mineral and bulk cumulate compositions. We argue that complete separation of immiscible liquids did not occur, resulting in crystallization of similar phases from both melts but in different proportions. However, partial segregation in a crystal mush and the production of contrasting phase proportions from the Fe-rich melt and the Si-rich melt can be responsible for the cyclic evolution from melanocratic (Fe-Ti-P-rich) to leucocratic (plagioclase-rich) gabbros which is commonly observed in the Upper Zone of the Bushveld Complex where it occurs at a vertical scale of 50 to 200 m.
AB - The Bushveld Complex (South Africa) is the largest layered intrusion on Earth and plays a considerable role in our understanding of magmatic differentiation and ore-forming processes. In this study, we present new geochemical data for apatite-hosted multiphase inclusions in gabbroic cumulates from the Bushveld Upper Zone. Inclusions re-homogenized at high-temperature (1060-1100 °C) display a range of compositions in each rock sample, from iron-rich (35 wt.% FeOtot; 28 wt.% SiO2) to silica-rich (5 wt.% FeOtot; 65 wt.% SiO2). This trend is best explained by an immiscible process and trapping of contrasted melts in apatite crystals during progressive cooling along the binodal of a two-liquid field. The coexistence of both Si-rich and Fe-rich immiscible melts in single apatite grains is used to discuss the ability of immiscible melts to segregate from each other, and the implications for mineral and bulk cumulate compositions. We argue that complete separation of immiscible liquids did not occur, resulting in crystallization of similar phases from both melts but in different proportions. However, partial segregation in a crystal mush and the production of contrasting phase proportions from the Fe-rich melt and the Si-rich melt can be responsible for the cyclic evolution from melanocratic (Fe-Ti-P-rich) to leucocratic (plagioclase-rich) gabbros which is commonly observed in the Upper Zone of the Bushveld Complex where it occurs at a vertical scale of 50 to 200 m.
KW - Apatite
KW - Bushveld
KW - Immiscibility
KW - Layered intrusion
KW - Melt inclusion
KW - Troctolite
UR - http://www.scopus.com/inward/record.url?scp=84961742949&partnerID=8YFLogxK
U2 - 10.1016/j.epsl.2016.03.016
DO - 10.1016/j.epsl.2016.03.016
M3 - Article
AN - SCOPUS:84961742949
VL - 443
SP - 108
EP - 117
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
SN - 0012-821X
ER -