皖南中生代岩浆活动年代学格架和岩石成因

发布时间：2018-03-20 20:52

  本文选题：岩石成因　切入点：Hf-O同位素　出处：《合肥工业大学》2015年硕士论文　论文类型：学位论文

【摘要】：皖南地区位于扬子板块东南缘,江南隆起带东段。本文选取青阳-九华山复式岩体和太平-黄山复式岩体,开展主量元素、锆石U-Pb年代学和Hf-O同位素研究。LA-ICPMS锆石U-Pb定年结果显示青阳-九华山复式岩体与太平一黄山复式岩体分别可以划分为三个不同的期次,早期侵入产出的为花岗闪长岩(青阳岩体、太平岩体),形成年龄在149.3±2.4 Ma到138.3±1.4 Ma之_间；中期为二长花岗岩(青阳岩体、太平岩体),形成年龄在145.1±1.7 Ma到132.8±1.5 Ma之间;晚期为钾长花岗岩(九华山岩体、黄山岩体),形成年龄在134.9±2.6 Ma到128.4±1.4 Ma之间。结合已发表的其他高精度年代学数据表明,皖南地区燕山期岩浆作用可划分为三期,早期153～136 Ma、中期136～129 Ma和晚期129～122 Ma。早期花岗闪长岩Si02变化范围为66%～67%,MgO含量较低(1.2%～1.5%),全碱含量在7.1%至7.5%之间,K2O/Na2O1, A/CNK1, ANK属于高钾钙碱性系列,为准铝质Ⅰ型花岗岩；中期二长花岗岩具有较花岗闪长岩略高的Si02含量,在68%～69%之间,其它主量元素特征较类似,全碱含量在7.7%-8.6%之间, K2O/Na2O1, A/CNK1, ANK属于高钾钙碱性系列,为弱过铝质Ⅰ型花岗岩;晚期钾长花岗岩富硅(Si02=73%-77%),低钙(CaO=0.2%-0.8%), A/CNK1, ANK, K2O/Na2O1,同样为高钾钙碱性系列岩石,具有A型花岗岩特征。花岗闪长岩的锆石εHf(t)值在-9.54～-4.86之间,对应的δ18O值在6.68‰～8.42‰之间；二长花岗岩的锆石εHf(t)值在-11.40-9.43之间,对应的818O值在7.16‰～8.04‰之间；钾长花岗岩的锆石Hf-O同位素表现出不同的特征,九华山岩体的锆石εHf(t)值较低,为-7.62-4.78,锆石818O值介于7.03‰和8.84‰之间,而黄山岩体具有较九华山岩体略高的锆石εHf(t)值(-6.56～-1.20),锆石δ18O值介于6.27‰和8.34‰之间。主量元素和锆石Hf-O同位素综合研究表明,在太平洋板块低角度俯冲背景下,受到板片析出流体交代的岩石圈地幔发生部分熔融,玄武岩浆的底侵导致晚太古代-早元古代地壳也发生部分熔融,这两种岩浆发生不同程度的混合形成皖南早期花岗闪长岩-二长花岗岩岩体；随着俯冲板片的后撤和俯冲角度的加大,皖南地区的构造背景转变为弧后拉张,引起板撕裂形成板片构造窗,软流圈地幔物质沿着断裂上涌,部分熔融扬子地块中元古代基底,形成晚期钾长花岗岩。
[Abstract]:The southern Anhui area is located in the southeast margin of the Yangtze plate and the eastern section of the Jiangnan uplift belt. In this paper, the Qingyang-Jiuhuashan complex rock mass and the Taiping Huangshan complex rock mass are selected to carry out the main elements. Zircon U-Pb geochronology and Hf-O isotopic study. The results of LA-ICPMS zircon U-Pb dating show that the Qingyang-Jiuhuashan complex and Taiping-Huangshan complex can be divided into three different stages, and the early intrusions occurred in the granodiorite (Qingyang pluton). The formation age of Taiping rock body is 149.3 卤2.4 Ma to 138.3 卤1.4 Ma, the middle stage is monzogranite (Qingyang rock body, Taiping rock body), the age range is 145.1 卤1.7 Ma to 132.8 卤1.5 Ma, and the late stage is potassium feldspar granite (Jiuhuashan rock body). The formation age of Huangshan rock body ranges from 134.9 卤2.6 Ma to 128.4 卤1.4 Ma. The Yanshanian magmatism in southern Anhui can be divided into three periods, combined with other published high accuracy geochronological data. The range of Si02 variation of early granodiorite is 660.The Si02 content of early granodiorite is relatively low, and the total alkali content is between 7.1% and 7.5%. The content of K _ 2O / Na _ 2O _ 1, A / CNK _ 1 and ANK belong to high-potassium calc-alkaline series and quasi-aluminous I-type granite. The Si02 content of the monzomorphic granodiorite is slightly higher than that of the granodiorite, and between 68% and 69%, the other major elements are similar. The total alkali content is between 7.7% and 8.6%. K _ 2O / Na _ 2O _ 1, A / CNK _ 1 and ANK belong to the high-potassium calc-alkaline series and belong to weakly peraluminous I-type granite. The late K-feldspar granites are Si-rich in Si _ (02) ~ (73) ~ (-77) and low in calcium content (0.2 ~ 0.8). A / C _ (CNK1), ANK, K _ 2O / Na _ 2O _ (1), which is also a high-potassium calc-alkaline series, has the characteristics of A-type granite. The zircon 蔚 Hft value of granodiorite ranges from -9.54 to 4.86, and the corresponding 未 ~ (18) O value is between 6.68 鈥，

本文编号：1640754