北秦岭-祁连结合带扫帚滩辉长岩年代学、地球化学特征及其地质意义

发布时间：2018-05-21 19:26

本文选题：秦祁结合带 + 早古生代　；参考：《地球化学》2017年03期

【摘要】：对北秦岭-祁连结合带关山地区扫帚滩辉长岩进行了系统的岩石学、年代学和地球化学研究。扫帚滩辉长岩的LA-ICPMS锆石U-Pb同位素年龄为(436±3.8)Ma(n=15,MSWD=1.5)。岩石地球化学特征显示该岩体属于钙碱性岩石系列:SiO_2含量为46.32%~52.89%,TiO_2含量有两组区间(1.24%~1.37%和2.11%~2.55%),富Na_2O(2.17%~2.48%),贫K_2O(0.36%~0.62%),Na_2O/K_2O比值介于5.43~6.03之间,里特曼指数σ变化于0.79~2.15之间;岩石的Mg#值为42.65~57.28,分异指数DI=20.92~30.89,固结指数SI=23.68~35.04,表明岩浆分异程度较低。稀土元素分布模式和微量元素原始地幔标准化图解均呈现出两种明显的形态:洋中脊玄武岩型(MORB)和岛弧玄武岩型(IAB)。其中MORB型呈LREE富集的右倾型,(La/Yb)N=1.88~2.51,δEu变化于0.84~1.00之间,IAB型表现出明显的La-Nd及高场强元素(HFSE)负异常,(La/Yb)N=1.57~2.26,δEu介于0.96~1.03之间。结合区域地质背景,认为扫帚滩辉长岩是兼具MORB和IAB型组分的共生基性岩,该岩体可能形成于弧后盆地构造环境,这一结论对于研究秦祁结合带构造演化具有重要意义。
[Abstract]:A systematic petrological, chronological and geochemical study of the broomstick gabbro in the Guanshan area of the North Qinling Qilian Junction Zone has been carried out. The LA-ICPMS zircon U-Pb isotopic age of the broomstick gabbro is 436 卤3.8m ~ (15) MSWD ~ (1. 5). The petrogeochemical characteristics show that the body belongs to the calc-alkaline rock series, with a content of 46.32% and 52.89% TiO2. There are two groups of sections: 1.240.37% and 2.111.37% and 2.110.55%, rich in Na _ 2O _ 2O _ (2.17) and 2.48 ~ (th), K _ 2O _ (0.36) 0.360.62 ~ (2) Na _ 2O / K _ 2O / K _ 2O = 5.43 ~ 6.03, and the Richter 蟽 _ (蟽) between 0.79 and 2.15; and the ratio of K _ 2O to Na _ 2O / K _ 2O is between 5.43 and 6.03, and the Rytmann index is between 0.79 and 2.15. The Mg# value of the rocks is 42.65 ~ 57.28, the differentiation index is 20.92 ~ 30.89 and the consolidation index is 23.68 ~ 35.04, which indicates that the degree of magmatic differentiation is low. The REE distribution pattern and the primitive mantle standardized diagram of trace elements show two distinct forms: the mid-oceanic ridge basalt type (MORBB) and the island arc basalt type (Iab). Among them, the MORB type is a right dip type with LREE enrichment, and the 未 EU type is between 0.84 and 1.00, and the 未 EU type shows obvious negative La-Nd and high field strength element (HFSE) negative anomaly La / Yb ~ (+) N _ (1.57) ~ (2.26), and 未 EU is between 0.961.03 and 0.96 ~ (1.03). Combined with the regional geological background, it is considered that the Shuangruotan gabbro is a symbiotic basic rock with both MORB and IAB components, which may be formed in the tectonic environment of the back-arc basin. This conclusion is of great significance for the study of the tectonic evolution of the Qinqi-Qi-binding belt.
【作者单位】：西北大学大陆动力学国家重点实验室/地质学系;
【基金】：国家自然科学基金(41421002,41102037) 全国优秀博士论文作者专项资助(201324) 陕西省青年科技新星项目(2014KJXX-60)
【分类号】：P588.124;P597.3

【相似文献】