赣东北近东西向岩浆岩带地球化学特征及构造背景研究

发布时间：2018-12-08 21:09

【摘要】：华南板块由华夏地块和扬子地块在新元古代早期沿江南造山带碰撞拼合形成,经历了自中元古代以来多次造山运动和多期岩浆活动,华南中生代岩浆岩对研究华南板块的区域构造及地质演化等科学问题有重要意义。区域上岩浆岩按时代划分后大都为北东、北北东向分布,但在江西省东北部发育一近东西向的岩浆岩带,其大地构造位置处于扬子地块的东南部、江南造山带的东段。本文在前人研究的基础上通过翔实的野外工作,采集了该岩浆岩带的系列样品,开展岩石学、年代学、岩石地球化学及岩浆氧逸度研究,讨论其成岩机制及其构造背景。年代学方面,该岩浆岩带中的岩体锆石年龄基本一致,形成时代在130~135Ma,都处于白垩纪。其中,样品D009-1和D011-6与其他样品的锆石年龄相差3Ma,反映了一次岩浆涌动作用。所以,取样的4个岩体属于同一期次的岩浆活动,该岩浆岩带形成于燕山期早白垩世。通过锆石的元素含量来计算岩浆氧逸度,结果表明该岩浆岩带的岩浆氧逸度低,平均都低于FMQ,反映了岩体的形成环境为还原型。地球化学方面,样品的Si2O含量在73.28~77.31,具铝强过饱和的特点。全碱含量较高,样品都落在高钾钙碱性系列中。微量元素和稀土元素分析显示,所有分析的样品都具有相似的REE分布形式,稀土元素配分曲线表现为轻稀土富集的右倾模式,样品的稀土含量在23.54~131.27之间,LREE/HREE比值范围在2.21~9.35。具有明显的Eu负异常,δEu范围在0.01~0.08之间,反映出壳源特征。且与皖南燕山中期岩体具有相似的地球化学特征,推测它们的来源一致,形成于同期岩浆活动。研究对象形成在大地构造背景由挤压向伸展转换的时期,岩石圈减薄,岩浆上涌,其成岩物质来源于地壳深部重融。
[Abstract]:The South China plate was formed by collision of Huaxia block and Yangtze block along the southern Yangtze orogenic belt in the early Neoproterozoic, and experienced many orogenic movements and magmatic activities since the Mesoproterozoic. Mesozoic magmatic rocks in South China are of great significance to the study of regional tectonics and geological evolution of the South China plate. The magmatic rocks in the region are mostly distributed in the north east and north east direction after dividing according to the age, but in the northeast of Jiangxi Province there is a magmatic rock belt near the east west direction. The tectonic position of the magmatic rock belt is located in the southeast of the Yangtze block and the eastern section of the Jiangnan orogenic belt. On the basis of previous studies, a series of samples have been collected from the magmatic zone through extensive field work. The petrology, geochronology, geochemistry and oxygen fugacity of magma have been studied, and the diagenetic mechanism and tectonic setting have been discussed. In terms of geochronology, the zircon ages of the magmatic rocks in this zone are basically the same, and the age of formation is 130135Ma. all of them are in the Cretaceous period. The zircon ages of samples D009-1 and D011-6 differ by 3 MaA, reflecting a magmatic gushing. Therefore, the four samples belong to the same stage of magmatic activity, and the magmatic belt was formed in the early Cretaceous of Yanshanian. The oxygen fugacity of magma is calculated by element content of zircon. The results show that the magmatic oxygen fugacity of the magmatic zone is low, and the average value is lower than that of FMQ, which reflects that the formation environment of the rock mass is reduced. In geochemistry, the Si2O content of the sample is 73.28 ~ 77.31, which is characterized by strong aluminum supersaturation. The total alkali content is high and the samples fall in the high potassium calc-alkaline series. The analysis of trace elements and rare earth elements showed that all the samples had similar REE distribution, and the distribution curve of rare earth elements showed the right tilting pattern of the enrichment of light rare earth elements, and the rare earth contents of the samples ranged from 23.54 to 131.27. The LREE/HREE ratio ranges from 2.21 to 9.35. There are obvious negative Eu anomalies and 未 Eu range from 0.01 to 0.08, which reflects the characteristics of crustal source. The geochemical characteristics are similar to those of the Yanshanian pluton in the south of Anhui, and their origin is the same as that of the Yanshanian rock body, which was formed during the same period of magmatic activity. The object of study was formed in the period of tectonic background transition from compression to extension, lithosphere thinning, magma upwelling, and its diagenetic material originated from deep thawing of the crust.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P588.1

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