阿拉斯加麥金利系列岩體之鋯石定年與地球化學研究
Plutonic rocks in the Central Alaska Range were emplaced during importantectonic events including the end of Late Cretaceous-Paleocene arc magmatism, theerminal phase of terrane accretion, the Kula ridge subduction, regional strike-slipaulting, oroclinal rotation of western Alaska, and Eocene resump...
| Main Authors: | , |
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| Other Authors: | , |
| Format: | Thesis |
| Language: | Chinese English |
| Published: |
2008
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| Subjects: | |
| Online Access: | http://ntur.lib.ntu.edu.tw/handle/246246/182874 http://ntur.lib.ntu.edu.tw/bitstream/246246/182874/1/ntu-97-R95224108-1.pdf |
| Summary: | Plutonic rocks in the Central Alaska Range were emplaced during importantectonic events including the end of Late Cretaceous-Paleocene arc magmatism, theerminal phase of terrane accretion, the Kula ridge subduction, regional strike-slipaulting, oroclinal rotation of western Alaska, and Eocene resumption of arcagmatism along the proto-Aleutian arc system. Here we report the first set ofA-ICPMS and SHRIMP zircon U-Pb ages for granitoids from (1) the McKinleyequence, (2) the Composite Plutons and (3) the Foraker Pluton, central Alaska Range.wo peraluminous granites from the McKinley Sequence yielded 206Pb/238U ages of2±1 and 60±1 Ma; an A-type granite from the same area gave age of 64±1 Ma. Tworanodiorites from the Composite Plutons and a granite from the Foraker Pluton gaveges of 69±1, 67±1 and 37±1 Ma, respectively.he age results indicate that the Composite Plutons and the McKinley Sequenceranites are older than previously reported and that the McKinley granites can beivided into two magma suites that consist of peraluminous and A-type compositionsccurring at ca. 62-60 and 64 Ma, respectively. Nd and Sr isotope data suggest aemporal change in the magma’s isotopic compositions, with the Foraker graniteshowing higher and more heterogeneous εNd(T) values that range from about +6 to -2nd the Composite and McKinley Sequence granitoids showing lower and lesseterogeneous εNd(T) values from +1 to -3. Besides, zircon Hf isotopic data of theated samples show that a granite from the Foraker plutons has the highest zirconHf(T) values from +15 to +10, in contrast to the Composite plutons that showpparently lower zircon εHf(T) values from +4 to -3. Peralumous and A-type granitesrom the McKinley Sequence have zircon εHf(T) values from +2 to -5 and +8 to +1,espectively.he Composite and McKinley Sequence plutonic rocks are interpreted as productsf the ending phase of Late Cretaceous-Paleocene arc magmatism. The peraluminousranites from the McKinley sequence may have been sourced from the remnantantle wedge, previously responsible for generating the Composite plutons andarlier arc magmas. Besides, generation of the A-type granites can be attributed to theroclinal rotation of western Alaska and ridge subduction that started around 64 Ma, aechanism that may also have resulted in broadly coeval volcanism in the nearbyantwell basin and northern Talkeetna Mountains. The Foraker pluton are interpreteds the product of renewed magmatism along the proto-Aleutian arc, in response toorth or northwestward subduction of the Pacific plate during 45-30 Ma. 致謝. i文摘要 ii文摘要 iv錄. vi目. viii目. ix、緒論 1.1 區域地質背景 1.1.1 Wrangellia composite terrane 1.1.2 Southern margin composite terrane 2.1.3 Kahiltna assemblage 3.1.4 Composite岩體、McKinley Sequence與Foraker岩體簡介 4.1.4.1 Composite岩體 4.1.4.2 McKinley Sequence 4.1.4.3 Foraker岩體 4.2 晚白堊紀至新生代於南阿拉斯加的岩漿活動 5.2.1 Late Cretaceous and early Tertiary magmatism 6.2.2 Middle Tertiary magmatism 6.2.3 Late Cenozoic volcanism 6.3 研究動機與目的 7.3.1 研究動機 7.3.2 研究目的 8、分析方法 9.1 岩樣採集位置 9.2 岩石薄片觀察 11.3 主量元素分析 11.3.1 主量元素分析步驟 11.3.2 燒失量測量 12.4 微量元素分析 12.4.1 微量元素測量之樣本處理 12.4.2 以ICP-MS測量USGS標準樣結果 13.5 鍶-釹同位素組成分析 16.5.1 標本前置處理 16.5.2鍶-釹同位素化學分離流程 16.5.2.1 第一分離柱 17.5.2.2 鍶純化分離柱 18.5.2.3 第二分離柱 18.5.3 以MC-ICP-MS測量標準樣結果 20.6 鋯石鈾-鉛定年分析 22.6.1 LA-ICP-QMS樣品靶(target)的製備 22.6.1.1鋯石的黏貼 22.6.1.2環氧樹脂的配置與灌注 22.6.1.3打磨與拋光 23.6.1.4樣品靶的顯微照相 23.6.2 SHRIMP樣品靶(target)的製備 24.6.3 鈾-鉛定年分析 24.7 鋯石鉿同位素分析 25、南阿拉斯加McKinley Sequence及相鄰岩體分析結果 28.1 定年資料 28.1.1 McKinley Sequence、Composite岩體與Foraker岩體 28.1.2 Reindeer Hills與Matanuska Valley 29.2 地球化學分析結果 39.2.1 Composite岩體 39.2.2 McKinley Sequence 46.2.3 Foraker岩體 49.3 鍶-釹同位素分析結果 50.4 鋯石鉿同位素分析結果 54、南阿拉斯加McKinley Sequence及相鄰岩體之岩石成因 59.1 火成岩與地質事件年代對比關係 59.2 鍶-釹同位素討論 61.2.1 Composite岩體與McKinley Sequence 61.2.2 McKinley Sequence中的A型花崗岩 62.2.3 Foraker岩體 62.2.4 與相鄰岩體對比 64.3 岩石成因 66.3.1 Late Cretaceous (emplacement of the Composite plutons) 66.3.2 Early Tertiary (emplacement of the McKinley Sequence) 66.3.3 Mid-Tertiary (emplacement of the Foraker pluton) 67、結論 69、參考文獻 71 |
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