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- 北祁連造山帶牛心山花岡岩的鋯石SHRIMP U-Pb定年及其地質意義
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- Mineralogy and Geochemistry of Granitic Rocks from Chinmen, Liehyu and Dadan Islands, Fujian
- Structural Evolution in the Hsuehshan Range, Taiwan
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題 名 | 北祁連造山帶牛心山花岡岩的鋯石SHRIMP U-Pb定年及其地質意義=Zircon SHRIMP U-Pb Dating and Geological Significance of the Niuxinshan Granites in the North Qilian Orogenic Belt |
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作 者 | 郭春滿; 曾建元; 張建新; | 書刊名 | 國立臺灣博物館學刊 |
卷 期 | 65:3 2012.09[民101.09] |
頁 次 | 頁31-56 |
分類號 | 358.43 |
關鍵詞 | 北祁連; 花岡岩; 鋯石SHRIMP U-Pb定年; 構造演化; North Qilian; Granite; Zircon SHRIMP U-Pb dating; Tectonic evolution; |
語 文 | 中文(Chinese) |
中文摘要 | 牛心山外來移置地體為中國西北地區北祁連造山帶內眾多前寒武 變質基盤雜岩中出露面積較大的一個。過去的研究顯示,此變質基盤雜 岩體是屬於南方祁連地塊的外來移置地體,在早古生代期間曾經發生多 期次花岡岩岩漿的侵入。這些複雜的岩漿事件與祁連地塊之間構造關係 的釐清,可以為祁連造山帶的區域構造演化提供新的制約。本研究的4 個牛心山花岡岩具接近1之全岩ASI和A/CNK比值,高鹼和低Na2O含量, 反映I型花岡岩特徵。此4個樣本具相似之微量元素分佈型式,即LREE和 LILE富集與Eu、Ba、Nb、Sr和Ti負異常。其 87Sr/86Sr(460 Ma)與εNd(460 Ma) 初始值分別為0.704725-0.706973與-2.0-4.5。這些地球化學徵象是島 弧或活動大陸邊緣岩漿之特性。鋯石SHRIMP U-Pb定年得到加權平均 年齡為461±6和453±13 Ma,顯示花岡岩侵入體形成於中-晚奧陶紀時 期。綜合以上結果,我們認為在早古生代時期古祁連洋由北向南隱沒到 祁連地塊之下的過程中,引發了牛心山花岡岩岩漿體的侵入。 |
英文摘要 | Among the Precambrian metamorphic complexes in the North Qilian suture zone, northwest China, the Niuxinshan complex is characterized by a relatively large outcrop area. Previous studies showed that this metamorphic complex was an allochthonous block from the southern Qilian block. It was subjected to multi-episode of granitic intrusion during the early Paleozoic period. Understanding the structural relationship between these granitic intrusions and Qilian block, will provide new constraints on the regional tectonic evolution of the Qilian orogenic belt. In this study, 4 granite samples from the Niuxinshan allochthonous block have whole-rock ASI index and A/ CNK ratio close to 1 with high alkaline and low Na2O contents, reflecting the characteristics of I-type granitoids. All of them have similar trace element variation patterns with LREE and LILE enrichments and pronounced negative Eu, Ba, Nb, Sr, and Ti anomalies. The initial 87Sr/86Sr(460 Ma) andεNd(460 Ma) values distribute in the range of 0.704725-0.706973 and -2.0--4.5, respectively. These geochemical features are characteristics of magmas generated at island-arc or active continental margin. Zircon SHRIMP U-Pb dating resulted in similar formation ages of 461±6 and 453±13 Ma for two Niuxinshan granites, indicating that granitic magmatic intrusions occurred during Middle-Late Ordovician period. Based on the above-presented data, we suggest that the Niuxinshan granite intrusions may be related to southward subduction of the North Qilian oceanic plate under the Qilian block during early Paleozoic era. |
本系統中英文摘要資訊取自各篇刊載內容。