西大别芳畈花岗岩锆石U-Pb年龄、地球化学特征及其构造意义
发布时间：2018-08-25 19:00
【摘要】：本文通过对西大别大悟芳畈地区黑云母花岗岩和石英正长岩花岗岩两种岩体的地球化学分析及U-Pb同位素测试,得到如下认识:黑云母花岗岩和石英正长岩花岗岩总体特征相似,主量元素表现为高SiO2(平均77.2%)、过铝质(A/CNK指数在1.03~1.13),碱度率在5.43~7.23,属碱性系列;ΣREE平均62.4×10-6,(Ce/Yb)N均值为0.67,(La/Yb)N均值为0.97,呈现平缓仅Eu亏损(δEu均值0.20)的"海鸥型";大离子亲石元素Rb、Th、U、K等相对富集,高场强元素Nb、Ta、Sr、Ti等呈明显的负异常,说明岩浆源岩以陆壳成分为主;Ga/Al均值为3.16,Zr+Nb+Ce+Y均值为578;锆石饱和温度为833~877℃,稀土元素饱和浓度温度为773~862℃,表明初始岩浆温度较高。上述特征说明,芳畈花岗岩为典型的A型花岗岩,形成于中上地壳的板内伸展背景。用LA-ICPMS测得的黑云母花岗岩中锆石的U-Pb年龄为773.0±1.6 Ma(MSWD=0.96,n=33),石英正长花岗岩形成的年龄为759.8±2.3 Ma(MSWD=1.6,n=28),表明其形成于新元古代洋陆俯冲的构造背景,是这一时期大陆边缘弧岩浆作用的产物。芳畈花岗岩体形成时代早于其外围地层,是经后期构造改造形成的混杂岩带,其岩浆作用与岩体外围的铜成矿作用无直接联系。
[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，
本文编号：2203808
[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，
本文编号：2203808
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