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| Titel |
Nd isotopic composition of the granites with REE tetrad pattern |
| VerfasserIn |
Seung-Gu Lee, Yoshihiro Asahara, Tsuyoshi Tanaka, Nicolas Dauphas, SeungRyeol Lee |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250084190
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| Zusammenfassung |
| Rare earth elements (REEs) have received considerable attention in geochemistry and
cosmochemistry because of their similar chemical behaviors and their gradual changes in
ionic radii. Compared with Sr, REEs are relatively immobile during various kinds of
geological processes. As a result, Nd isotopes in the geologic systems are likely to be
changed less than Sr isotopes in the same geologic systems. Recently, a unique and
chemically coherent behavior of the rare earth elements (REEs) called as “tetrad effect”
from geological sample has spawned considerable interest in geologic systems.
The “tetrad” effect consists of four separate curves, encompassing four points,
La-Ce-Pr-Nd, Pm-Sm-Eu-Gd, Gd-Tb-Dy-Ho and Er-Tm-Yb-Lu, with Gd being an
element common to the second and the third tetrad. One of the characteristic of the
granites with REE tetrad effect is that the Nd model ages (TDM) are unreasonable
because they are negative or extremely old. The Muamsa and Weolaksan granites are
Cretaceous granites with REE tetrad effect, which occurs at the middle part of the
Ogcheon belt, South Korea. In order to survey Nd isotopic system in granites with REE
tetrad effect, we measured the whole Nd isotopic composition of the Muamsa and
Weolaksan granites with REE tetrad effect and without REE tetrad effect. As a result, we
could observe that the 143Nd/144Nd ratios of granites with REE tetrad pattern range
from 0.511907 to 0.511969, whereas those without REE tetrad pattern range from
0.511885 to 0.511920. And in plots of 87Rb/86Sr - 87Sr/86Sr and 147Sm/144Nd -
143Nd/144Nd diagrams, granites with REE tetrad pattern plotted at higher values than those
without REE tetrad pattern. However, we could not find anomalies of Nd isotopic
composition except 143Nd/144Nd. This suggests that there was no mixing or input
of the materials with different Nd isotopic composition during the formation of
REE tetrad effect. Our data indicate that REE tetrad effect might be product during
differentiation of granitic magma rather than hydrothermal water-rock interaction. |
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