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| Titel |
One atmosphere experimental study on the partitioning of the HFSE between olivine, pyroxene and lunar basaltic melts in the CMAS + Fe + Ti system |
| VerfasserIn |
Felipe Padilha Leitzke, Raúl O. C. Fonseca, Lina T. Michely |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250122517
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| Publikation (Nr.) |
 EGU/EGU2016-1565.pdf |
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| Zusammenfassung |
| Titanium is generally regarded as a minor element in the Bulk Silicate Earth (1265 μg/g),
with average and maximum TiO2 contents of 1.06 and 5.57 wt. %, respectively. In the Moon,
however, TiO2 can be found in concentrations as high as 17 wt. %. In order to better explain
this enrichment, petrogenetic models require precise knowledge of major and trace elements
fractionation under conditions similar to the ones that may have prevailed on the lunar
mantle. Previous studies show that Fe-Ti-O melt species may affect the fractionation of the
high-field strength elements (HFSE) between Fe-Ti oxides and silicate melt. However, there
is a scarcity of data on the behaviour of these elements between silicates and lunar mare
basalts with different TiO2 contents. To address this issue, we present results from an
experimental campaign on a HFSE-doped basalt in the CMAS system with different
amounts of Cr2O3 (0.1 – 1.5 wt.%), P2O5 (0.1 – 0.5 wt.%), FeO (0 -17 wt.%) and
TiO2 (1 – 21 wt.%). Experiments were carried out in a vertical tube gas-mixing
furnace with temperatures ranging from 1100 to 1300 ∘C and ΔFMQ from -5.2 to
+6.6. Major and trace elements were acquired with the EMP and LA-ICP-MS,
respectively.
Our results for DHFSEsilicate∕melt are in agreement with the literature for glasses
with ca. 1.0 wt.% TiO2. Nevertheless, DHFSEolv∕melt for 4+ and 5+ cations have
a negative correlation until ca. 4.8 wt. % TiO2 in the silicate glass and after that
values are constant until ca. 20 wt. % TiO2. This may be used to indicate that a melt
complex may be present, since DTiolv∕melt< 0.01. Regarding the DUolv∕melt, values
change by almost one order of magnitude from more incompatible at the more
oxidizing experiments, where the main species present is U6+ to relatively more
compatible at the more reducing experiments, where there is a greater contribution of
U4+. Results for DHFSEopx∕melt do not show any change over the range of TiO2
in the glass in this study, apart from the same behaviour observed in olivine for
DUopx∕melt. The most striking feature is the DHFSEcpx∕melt which varies by almost one
order of magnitude from low-Ti to high-Ti glasses. This behaviour is observed for
DZrcpx∕melt, DHfcpx∕melt, DTacpx∕melt and DThcpx∕melt and is surprisingly
less pronounced for DNbcpx∕melt. For the DUcpx∕melt, this trend is much more
pronounced on the experiments where U4+ predominates than U6+. The TiO2 in the
silicate glass is proportional to the TiO2 in the cpx, which reaches concentrations
up to 3.1 wt.% and substitutes both into the M1 and the T site. The IV Al on the
experiments is in agreement with lunar pyroxene data, with values lower than 0.07
apfu, indicating that Ca-Tschermak component was seldom present. Charge balance
mechanism is defined by the substitution of Ti4+ - 2Al3+. Our data represent an
improvement on the understanding of the fractionation of the HFSE in conditions similar to
the ones that may have prevailed during generation of high-Ti lunar mare basalts. |
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