【摘要】：正長斑巖是中蒙邊界中生代重要的巖漿記錄,其花崗巖年齡和地球化學特征對于揭示該時期的構造格局與演化歷史具有重要意義。本文對蒙古國東南部出露的正長斑巖進行鋯石的LA-ICP-MS定年,獲得鋯石U-Pb年齡為(170.6±1.7)Ma,表明該花崗巖形成于中—晚侏羅世�；◢弾r的元素地球化學研究結果表明:該花崗巖屬高鉀鈣堿性S型花崗巖;花崗巖具高硅特征,其Si O2質量分數為73.99%~74.28%,Al_2O_3為12.36%~14.30%,MgO為0.17%~0.45%,過鋁質;稀土元素總量為51.92×10~(-6)~58.32×10~(-6),稀土元素分布型式為具有明顯負銪異常的"燕型"曲線;在原始地幔標準化的微量元素蛛網圖中,Rb、Th、U、K、Zr、Hf和輕稀土元素(如La、Ce、Nd和Sm等)富集,Ba、Sr、P和Ti等元素強烈虧損,Nb和Ta具有中等—弱虧損特點;n(~(143)Nd)/n(~(144)Nd)初始比值較高(0.512320~0.512451),平均為0.512404;ε_(Nd)(t)為-4.6~-2.3,均為負值。主量、微量元素和同位素特征表明,該正長斑巖形成于同碰撞向后造山構造體制轉換過渡的伸展大地構造環(huán)境背景之下。地殼加厚作用和地殼物質部分熔融,很可能是形成本區(qū)花崗巖的兩個最主要的動力機制。
[Abstract]:Syenite porphyry is an important record of Mesozoic magma in the boundary of China and Mongolia. Its granite age and geochemical characteristics are of great significance to reveal the tectonic framework and evolution history of this period. The LA-ICP-MS dating of zircon from syenite porphyry in the southeast of Mongolia has been carried out. The zircon U-Pb age of (170.6 鹵1. 7) Ma, indicates that the granite was formed in the middle to late Jurassic. The results of elemental geochemistry show that the granite belongs to high potassium calc-alkaline S-type granite, the granite is characterized by high silicon content, and its Si O 2 mass fraction is 73.99 and 74.28%. The content of Al _ 2O _ 2O _ 3 is 12.36 ~ 14.30% and 0.17 ~ 0.45%, peraluminous. The total amount of rare earth elements is 51.92 脳 10 ~ (-6) (58.32 脳 10 ~ (-6), and the distribution pattern of rare earth elements is "swallow" curve with obvious negative europium anomaly. In the primitive mantle-standardized trace element cobweb map, RbTH, La,Ce,Nd, Sm, etc., are strongly depleted in elements such as La,Ce,Nd and Ti. NB and Ta are characterized by moderate to weak depletion (~ (143) Nd) / n (~ (144) Nd) initial ratio is higher (0.512 320 / 0. 512451), average is 0. 512 404; 蔚 _ (Nd) (t) is -4. 6 ~ 2. 3, all are negative values. The principal, trace elements and isotopic characteristics indicate that the syenite was formed in the context of an extensional tectonic environment during the transition from the same collision to the post-orogenic tectonic regime. Crustal thickening and partial melting of crustal materials are probably the two main dynamic mechanisms for the formation of granites in this area.
【作者單位】： 華北理工大學礦業(yè)工程學院地質系;中國科學院地質與地球物理研究所礦產資源研究重點實驗室;河北省地礦局第五地質大隊;造山帶與地殼演化教育部重點實驗室北京大學地球與空間科學學院;
【基金】：“十一五”科技支撐計劃重大項目(編號:2006BAB01A02) 校級博士科研啟動基金項目(編號:20164043)的成果~~
【分類號】：P597.3;P618.67

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