摘要
大村和古龙岩体产于扬子地块与华夏地块拼合带的西南段,对剖析华南区域构造演化具有重要的地质意义。对大村和古龙岩体的石英闪长岩样品进行LA-ICP-MS锆石U-Pb测年,获得^(206)Pb/^(238)U年龄加权平均值分别为438±1Ma和435±2Ma,说明2个岩体均形成于加里东期。大村和古龙岩体具有钙碱性、准铝质-过铝质特征的I型花岗岩。锆石的ε_(Hf)(t)值主要集中在0^+4之间,二阶段模式年龄(T_(DM2))主要集中在1.15~1.45Ga之间,指示物源主要来自中元古代新生的基性下地壳物质。根据大村和古龙岩体的地球化学、Hf同位素组成、岩体发育暗色微粒包体等特征,结合区域地质情况,认为其是在陆内碰撞造山期后伴随岩石圈局部伸展-减薄,软流圈高温地幔物质上涌,导致中元古代新生的基性下地壳部分熔融形成的酸性岩浆和幔源岩浆在源区不同程度的混合形成母岩浆,随后又经历了一定程度的分异演化最终固结成岩。
The Dacun and Gulong plutons were found in the southwest orogenic belt of the Yangtze block and the Cathaysia block,and the pluton has important geological significance in analyzing the regional tectonic evolution of South China. In this paper, two quartz diorite samples were collected from Dacun pluton and Gulong pluton for LA-ICP-MS zircon U-Pb dating, respectively,which yielded U-Pb ages of 438±1Ma and 435±2Ma, indicating that the Dacun pluton and Gulong pluton were both formed in Caledonian orogeny. The data show that the Dacun pluton and Gulong pluton belong to I-type granite which has calc-alkaline and aluminous-peraluminous features. The Hf isotopic compositions of zircons show that the rocks have ε_(Hf)(t) values from 0 to +4, and T_(DM2)(Hf) model ages are mainly concentrated in the range of 1.15~1.45 Ga, implying that the magma was derived from the basic lower crust material, and the lower crust was formed in the Mesoproterozoic. According to geochemical features of the Dacun and Gulong plutons, Hf isotopic composition, and the dark particles-bearing pluton, in combination with regional geological conditions, the authors hold that, after the intracontinental collision orogenic period, the Dacun and Gulong plutons were formed along with the locallithosphere stretching-thinning, the upwelling of high temperature mantle materials from the asthenosphere, and the partial melting of the basic lower crust in the Mesoproterozoic. In the process of melting, there existed mixture of the upwelling mantle-derived magma formed in the source area at different levels, thus leading to the generation of parental magma. And then the magma experienced a certain degree of differentiation and evolution, finally forming rocks through solidification.
出处
《地质通报》
CAS
CSCD
北大核心
2017年第2期224-237,共14页
Geological Bulletin of China
基金
中国地质调查局项目<桂东-粤西成矿带地质矿产调查>(编号:D20160035)
