【摘要】：本文通過對西大別大悟芳畈地區(qū)黑云母花崗巖和石英正長巖花崗巖兩種巖體的地球化學(xué)分析及U-Pb同位素測試,得到如下認(rèn)識:黑云母花崗巖和石英正長巖花崗巖總體特征相似,主量元素表現(xiàn)為高SiO2(平均77.2%)、過鋁質(zhì)(A/CNK指數(shù)在1.03~1.13),堿度率在5.43~7.23,屬堿性系列;ΣREE平均62.4×10-6,(Ce/Yb)N均值為0.67,(La/Yb)N均值為0.97,呈現(xiàn)平緩僅Eu虧損(δEu均值0.20)的"海鷗型";大離子親石元素Rb、Th、U、K等相對富集,高場強(qiáng)元素Nb、Ta、Sr、Ti等呈明顯的負(fù)異常,說明巖漿源巖以陸殼成分為主;Ga/Al均值為3.16,Zr+Nb+Ce+Y均值為578;鋯石飽和溫度為833~877℃,稀土元素飽和濃度溫度為773~862℃,表明初始巖漿溫度較高。上述特征說明,芳畈花崗巖為典型的A型花崗巖,形成于中上地殼的板內(nèi)伸展背景。用LA-ICPMS測得的黑云母花崗巖中鋯石的U-Pb年齡為773.0±1.6 Ma(MSWD=0.96,n=33),石英正長花崗巖形成的年齡為759.8±2.3 Ma(MSWD=1.6,n=28),表明其形成于新元古代洋陸俯沖的構(gòu)造背景,是這一時期大陸邊緣弧巖漿作用的產(chǎn)物。芳畈花崗巖體形成時代早于其外圍地層,是經(jīng)后期構(gòu)造改造形成的混雜巖帶,其巖漿作用與巖體外圍的銅成礦作用無直接聯(lián)系。
[Abstract]:Based on the geochemical analysis and U-Pb isotopic test of biotite granite and quartz syenite granite in Dabie Fangfan area, the authors have obtained the following conclusions: the general characteristics of biotite granite and quartz syenite granite are similar. The main elements are high SiO2 (77.2% average), peraluminous (A/CNK index 1.031.13), alkalinity (5.430.23), 危 REE (62.4 脳 10-6), (Ce/Yb) N (0.67), (La/Yb) N (0.97), which are "gull type" with a gentle Eu deficit (未 Eu mean 0.20), and relatively rich in large ion lithophile element Rb,Th,U,K, etc. The high field strength element Nb,Ta,Sr,Ti and so on show obvious negative anomalies, indicating that the main source rocks are continental crust composition, the average value of Ga / Al is 3.16% Zr Nb Ce Y is 578, the saturation temperature of zircon is 833 ~ 877 鈩，

本文編號：2203808