Rashid M.u., Rehman H.U., Lee H.Y., Chung S.L., Das K., Zeb M.J., Ahmad N., Hussain M., Yamamoto H. . Tectono-magmatic evolution of the Ambela granitic complex, Northwest Himalayas, Pakistan:2025 · 記述言語： 日本語 出版者・発行元： Journal of Asian Earth Sciences Ambela Granitic Complex (AGC) is a dominant alkaline magmatic body exposed in the Peshawar Plain Alkaline Igneous Province of the NW Himalaya. However, its petrogenetic source was not clear till data. This study aims to investigate petrogenetic source and magma origin of AGC using whole-rock geochemistry, zircon U–Pb/Lu–Hf isotope and trace element geochemistry. Oscillatory-zoned zircons in AGC yielded <sup>206</sup>Pb/<sup>238</sup>U age spanning between 282 and 287 Ma, indicating granite emplacement during Permian. Positive εHf(t) values of + 1.4 to + 13.8 from zircons confirm mantle-derived juvenile material slightly mixed with continental crust. Whole-rock data show the studied rocks are ferroan, high-K calc-alkaline, and A-type granites. Chondrite-normalized REE patterns of zircon, characterized by LREE depletion, positive Ce and negative Eu anomalies, with elevated U/Yb, Sc/Yb and Nb/Yb ratios, indicate crystallization from an evolved, oxidized melt that underwent plagioclase fractionation in an anorogenic within-plate rift related setting. Zircon-saturation (722 to 858 °C) and Ti-in-zircon (692 to 820 °C) thermometry indicate high-temperature magmatism typical of granitic system. The petrogenetic sequence suggests that initial partial melting of lower crustal rocks was triggered by upwelling of the asthenosphere causing doming and crustal thinning, followed by magmatic differentiation that generated AGC rocks. The presence of mafic dykes in AGC, along with Panjal Trap basalts, represents bimodal magmatism, indicative of mantle plume input. The geochemical affinity and temporal overlap of AGC with the coeval widespread Permian magmatic episode in the Himalayan region suggest an intracontinental rifting related to the Cimmerian orogeny in the northern margin of Gondwana. DOI： 10.1016/j.jseaes.2025.106846 Scopus
山本 啓司, 磯﨑 行雄, 岡本 和明 . 中琉球の新たな地体構造単元「徳之島帯」 . 地学雑誌133 ( 6 ) 447 - 464 2024年12月 詳細を見る 担当区分： 筆頭著者, 責任著者 記述言語： 日本語 出版者・発行元： 公益2024 · 担当区分： 筆頭著者, 責任著者 記述言語： 日本語 出版者・発行元： 公益社団法人 東京地学協会 The latest geological and geotectonic aspects of Tokunoshima Island in Central Ryukyus are reviewed. The pre-Quaternary basement geology of the island is two-fold; i.e., the Cretaceous accretionary complex （Amagidake and Omo units） and the high-grade metamorphic unit newly named the Inokawadake metamorphic complex （IMC）. The former is correlated with the northern subbelt of the Shimanto belt in SW Japan. The IMC is composed of high-grade metamorphic rocks composed of pelitic–psammitic schists, with minor lenses of serpentinite and “dioritic gneiss” with Paleoproterozoic （ca. 1.8 Ga） zircons. In the southern half of the island, the IMC structurally overlies the Cretaceous AC as a klippe, which is separated probably by a subhorizontal fault. The IMC suffered from high-grade metamorphism up to the amphibolite facies, which is extremely rare in the Shimanto belt. A new geotectonic unit, the Tokunoshima belt, is newly proposed for the area of the IMC, which is limited to a mountainous domain in southern Tokunoshima Island. Based on the youngest detrital zircon U-Pb ages （ca. 60 Ma） from psammitic schists, the metamorphism of the IMC probably occurred in the Paleocene or later. Possible sites for the Paleocene or later heat source may include the San-in （Paleogene batholith） belt in SW Japan on the north and/or an unknown collided island arc system from the south. DOI： 10.5026/jgeography.133.447 Scopus CiNii Research
