本文選題：鋯石LA-ICP-MS　切入點：U-Pb年齡　出處：《長江大學》2017年碩士論文　論文類型：學位論文

【摘要】：萬洋山巖體位于湘贛兩省交界地帶,出露面積約1400km2,呈巖基產(chǎn)出,巖體主體具有塊狀構造,斑狀似斑狀結構,為加里東期多階段巖漿活動的復式巖體,花崗巖主要巖石類型有黑云母二長花崗巖、黑云母花崗閃長巖和二云母二長花崗巖,以黑云母二長花崗巖分布面積最廣。針對萬洋山巖體缺乏高質(zhì)量的年齡數(shù)據(jù)和高精度的地球化學分析數(shù)據(jù),導致對華南地區(qū)動力學背景認識存在一定差異,本文在野外系統(tǒng)地質(zhì)調(diào)查的基礎上,采用先進的測試技術和方法,對萬洋山巖體的巖相學、同位素地質(zhì)學、地球化學、地質(zhì)年代學等方面進行深入研究,并且探討華南加里東期花崗巖形成的地質(zhì)背景。對巖體中黑云母二長花崗巖中樣品中的鋯石進行激光剝蝕-多接收器電感耦合等離子體質(zhì)譜(LA-ICP-MS)U-Pb定年,鋯石的16個測點206Pb/238U的加權平均年齡為(446±3.4)Ma(n=16,MSWD=0.15)(95%置信度),反映該巖體形成于晚奧陶世至早志留世。花崗巖巖體的主要礦物成分有斜長石、鉀長石、石英,次要礦物為黑云母。巖石地球化學表明巖體中Si O2的含量為65.91%~73.35%(平均值為69.50%),K2O的平均含量為3.19%~5.36%(平均值為4.20%),Na2O+K2O為5.90%~7.88%(平均值為6.76%),K2O/Na2O平均值為1.64,Al2O3平均值為13.81%,ASI平均值為1.09%�？傮w的TFeO(平均4.55%)含量偏高,鎂鐵比值(F/F+M)變化范圍較小,為0.67~0.73,集中在0.70左右,堿鈣指數(shù)(MALI)為2.72%~6.90%,變化范圍較大。萬洋山巖石樣品總體屬于高鉀鈣堿性過鋁質(zhì)花崗巖。微量元素組成中Ba、K、Sr、P、Ti表現(xiàn)出明顯的虧損,Rb、Th、U、Nb、Zr、Hf等則相對富集,具有較高的Rb/Sr比值(平均值為1.91%)和Rb/Nb比值(平均值為14.48%)。稀土元素總量中等(159.71×10-6~262.78×10-6),輕稀土富集明顯(LREE/HREE=6.16~10.01),具有明顯的右傾曲線,(La/Yb)N=6.37~12.17,具明顯的負Eu異常,δEu值為0.30~0.59,平均值為0.45。巖體的[n(87Sr)/n(86Sr)]i值為0.71223~0.72509,與S型花崗巖[n(87Sr)/n(86Sr)]i值范圍一致。εSr(t)值為117.5~299.9Ma,εNd(t)值為-9.39~-7.30,兩階段Nd模式年齡(TDM2)為1.77~1.94 Ga,與湘桂內(nèi)陸帶花崗巖的背景值(1.8~2.4 Ga)基本一致。巖石地球化學和同為素地球化學以均表明萬洋山巖體為來源于地殼的S型花崗巖,源巖為中上地殼變質(zhì)碎屑巖�；◢弾r氧化物和微量元素構造環(huán)境判別圖解指示巖體形成于后碰撞構造環(huán)境。結合前人對華南加里東期巖體的研究成果,推斷華南加里東期花崗巖巖體的具體形成機制為:受到全球板塊構造活動的影響,揚子板塊和華夏板塊趨于閉合,主要是沿著欽—杭斷裂帶。結果導致華南地區(qū)以淺海盆地為主的環(huán)境關閉,兩個板塊拼貼到一起導致地殼大面積的增厚。由于地殼的增厚可以導致產(chǎn)熱高的元素產(chǎn)生地球化學遷移,并且集中在增厚的區(qū)域。在足夠的溫度壓力下,結果導致中上地殼的局部熔融。在后碰撞時期,發(fā)生陸內(nèi)環(huán)境的伸展作用,巖石圈相對減薄,巖漿上涌并且侵位,最后形成該地區(qū)分布面積比較廣的殼源花崗巖。
[Abstract]:WANYANGSHAN Hunan pluton is located in the junction of two provinces area, the exposed area of about 1400km2, a batholith, rock body has a massive structure, porphyritic porphyritic structure, complex rock mass of Caledonian polystage magmatic activities, the main types of granite rock is biotite two feldspar granite, biotite granodiorite and two mica two granite, biotite granite with two long distribution area is the most widely used. According to the data analysis of age data of high quality and high precision of the geochemical WANYANGSHAN lack of rock mass, leading to the dynamic background of Southern China area there exist certain differences, based on the investigation of field geology on the test using advanced technology and methods, to 10000 the rock mass of isotope geology, petrography, geochemistry, geochronology and other aspects of in-depth research, and discuss the geological background of Southern China CALEDONIAN GRANITE formation of. Zircon samples biotite granite two in rock by laser ablation multi collector inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb dating of zircon, the 16 points 206Pb/238U weighted average age (446 + 3.4) Ma (n=16, MSWD=0.15) (95% confidence), the rock formed in the late Ordovician to Early Silurian. The main mineral composition of granite are plagioclase, K-feldspar, quartz, biotite. Secondary mineral content in rock Si O2 indicate that the rock geochemical 65.91%~73.35% (average of 69.50%), the average content of K2O is 3.19%~5.36% (average 4.20%), Na2O+K2O 5.90%~7.88% (average of 6.76%), the average K2O/Na2O value was 1.64, the average Al2O3 value was 13.81%, the average ASI 1.09%. overall TFeO (average 4.55%) high content of magnesium, iron ratio (F/F+M) range of small, 0.67~0.73, concentrated in about 0.70, calcium alkali index (M ALI)涓，

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