https://scholars.lib.ntu.edu.tw/handle/123456789/431810
標題: | LA-ICP-MS zircon U-Pb age and Hf isotope data from the granitic rocks in the Iwakuni area, Southwest Japan: re-evaluation of emplacement order and the source magma | 作者: | Mateen T. Okamoto K. SUN-LIN CHUNG Wang K.-L. Lee H.-Y. Abe S. Mita Y. Rehman H.U. Terabayashi M. Yamamoto, Hiroshi |
關鍵字: | granitic rocks;Hf isotope;Ryoke Belt;San-yo Belt;U-Pb age | 公開日期: | 2019 | 卷: | 23 | 期: | 6 | 起(迄)頁: | 917-931 | 來源出版物: | Geosciences Journal | 摘要: | U-Pb-Hf isotopes of zircons from the granitic intrusive rocks in the Iwakuni area of Southwest Japan are determined by LA-ICP-MS analysis. The Gamano Granodiorite belonging to the Older Ryoke Granites of the Ryoke Belt yielded U-Pb mean age of 92.3 ¡Ó 2.6 Ma (MSWD = 1.8). The Namera Granite belonging to the Younger Ryoke Granites of the Ryoke Belt yielded U-Pb mean age of 106.3 ¡Ó 1.6 Ma (MSWD = 2.3). The Shimokuhara Granite belonging to the Hiroshima Granites of the San-yo Belt yielded U-Pb mean age of 103.8 ¡Ó 1.5 Ma (MSWD = 0.32). A granite porphyry sample taken from about 15 m thick dike discordantly intruded into pelitic schist of the Ryoke metamorphic rocks yielded U-Pb mean age of 92.5 ¡Ó 1.6 Ma (MSWD = 0.63). Hf isotope data, obtained from the same dated zircon grains, show initial 176Hf/177Hf isotopic ratios referred to as ¡§£`Hf(t)¡¨ generally ranging between¡V4.8 and +1.1 except an anomalously low value (¡V15.0) from an inherited core. The £`Hf(t) values, calculated with average crustal 176Lu/177Hf ratio of 0.015, correspond to Hf isotope crustal model ages between 1474 to 1087 Ma (Mesoproterozoic). The Gamano Graodiorite has long been regarded to be a syn-tectonic intrusion, but the zircon ages and £`Hf(t) values are similar to those of the post-tectonic granite porphyry dike. The results of this study together with available U-Pb zircon ages of granitic rocks in the Iwakuni area reported elsewhere reveal that the order of emplacement indicated by the U-Pb zircon ages are much discrepant with the traditional classification, the Older Ryoke, the Younger Ryoke. It is better to refrain from the use of ¡§Older¡¨ and ¡§Younger¡¨ for the collective names of the granitic intrusive bodies. ? 2019, The Association of Korean Geoscience Societies and Springer. |
URI: | https://scholars.lib.ntu.edu.tw/handle/123456789/431810 | ISSN: | 12264806 | DOI: | 10.1007/s12303-019-0003-1 |
顯示於: | 地質科學系 |
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