TY - JOUR
T1 - Influence of phosphate on mobility and adsorption of REEs during weathering of granites in Thailand
AU - Sanematsu, Kenzo
AU - Kon, Yoshiaki
AU - Imai, Akira
N1 - Funding Information:
We express gratitude to Prof. Koichiro Watanabe, Dr. Yoshinobu Motomura and the students of Kyushu University and Chulalongkorn University for supporting fieldworks in Thailand and XRF analysis. We are grateful to Dr. Karsten Goemann and Dr. Sandrin Feig at the Central Science Laboratory in University of Tasmania for supporting the SEM works. We are also grateful to two anonymous reviewers for reading our manuscript and giving constructive comments. This study was supported by the Grant-in-Aid for Scientific Research (B) of No. 19253005 and Postdoctoral Fellowships for Research Abroad , that were funded by the Japan Society for Promotion of Science (JSPS).
Publisher Copyright:
© 2015 Elsevier Ltd.
PY - 2015/11/1
Y1 - 2015/11/1
N2 - The Permo-Jurassic North Thai (NT) Granites and the Late Cretaceous to Paleogene Western Province (WP) Granites in Thailand are contrasting in terms of tectonic settings and chemical compositions. The NT Granites, which are dominated by S-type features, are characterized by lower SiO2 contents and higher P2O5 contents than the WP Granites in this study. In order to compare the mobility and adsorption of rare earth elements (REEs) during weathering of the two granite suites, geochemical analyses were conducted on the granite and weathered granites. The weathered WP Granites show wider ranges of REEs+Y (REY) contents, percentages of ion-exchangeable REY and Ce anomalies than the weathered NT Granites. These results indicate that REEs were less mobile during weathering of the NT Granites than those of the WP Granites. The low mobility of REEs can be explained by the occurrences of residual monazite and secondary REE phosphates which immobilize REEs during weathering. Therefore, in the weathered NT Granites, REEs are mostly contained in the phosphate minerals. In contrast, the weathered WP Granites are dominated by ion-exchangeable REEs (adsorbed REEs) which are likely to exist on the surface of clays. Previous studies and our study results suggest that the ion-exchangeable REEs in the weathered granites were probably sourced from weatherable allanite, titanite, apatite and/or REE fluorocarbonate, and rarely from monazite and zircon, which are resistant to weathering. The weathered granites of low phosphate contents potentially show high percentages of ion-exchangeable REY, although they can be influenced by the degree of hydrothermal alteration or weathering of granites.
AB - The Permo-Jurassic North Thai (NT) Granites and the Late Cretaceous to Paleogene Western Province (WP) Granites in Thailand are contrasting in terms of tectonic settings and chemical compositions. The NT Granites, which are dominated by S-type features, are characterized by lower SiO2 contents and higher P2O5 contents than the WP Granites in this study. In order to compare the mobility and adsorption of rare earth elements (REEs) during weathering of the two granite suites, geochemical analyses were conducted on the granite and weathered granites. The weathered WP Granites show wider ranges of REEs+Y (REY) contents, percentages of ion-exchangeable REY and Ce anomalies than the weathered NT Granites. These results indicate that REEs were less mobile during weathering of the NT Granites than those of the WP Granites. The low mobility of REEs can be explained by the occurrences of residual monazite and secondary REE phosphates which immobilize REEs during weathering. Therefore, in the weathered NT Granites, REEs are mostly contained in the phosphate minerals. In contrast, the weathered WP Granites are dominated by ion-exchangeable REEs (adsorbed REEs) which are likely to exist on the surface of clays. Previous studies and our study results suggest that the ion-exchangeable REEs in the weathered granites were probably sourced from weatherable allanite, titanite, apatite and/or REE fluorocarbonate, and rarely from monazite and zircon, which are resistant to weathering. The weathered granites of low phosphate contents potentially show high percentages of ion-exchangeable REY, although they can be influenced by the degree of hydrothermal alteration or weathering of granites.
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U2 - 10.1016/j.jseaes.2015.05.018
DO - 10.1016/j.jseaes.2015.05.018
M3 - Article
AN - SCOPUS:84931287719
SN - 1367-9120
VL - 111
SP - 14
EP - 30
JO - Journal of Asian Earth Sciences
JF - Journal of Asian Earth Sciences
ER -