全文快速搜索:          
引用本文:郝增元,高鉴,王晨,刘旭东,李得成,王新亮. 北山造山带风雷山地区二长花岗岩LA-ICP-MS锆石U-Pb年龄及其构造背景[J]. 中国地质, 2020, 47(4): 1204-1219.
HAO Zengyuan,GAO Jian,WANG Chen,LIU Xudong,LI Decheng,WANG Xinliang. LA-ICP-MS zircon U-Pb dating and tectonic setting of the monzogranites in the Fengleishan area of Beishan orogenic belt, Inner Mongolia[J]. Geology in China, 2020, 47(4): 1204-1219(in Chinese with English abstract).
【打印本页】   【HTML】   【下载PDF全文】   查看/发表评论  下载PDF阅读器  关闭
←前一篇|后一篇→ 过刊浏览    高级检索
本文已被:浏览 109次   下载 117 本文二维码信息
码上扫一扫!
分享到: 微信 更多
北山造山带风雷山地区二长花岗岩LA-ICP-MS锆石U-Pb年龄及其构造背景
郝增元1, 高鉴2, 王晨1, 刘旭东3, 李得成1, 王新亮2
1.西安地质矿产勘查开发院, 陕西 西安 710010;2.内蒙古地质矿产勘查院, 内蒙古 呼和浩特 010010;3.陕西地矿物化探队, 陕西 西安 710010
摘要:
风雷山二长花岗岩位于北山北部的红石山—百合山—蓬勃山与芨芨台子—小黄山两条蛇绿混杂岩带之间,构造位置特殊。二长花岗岩LA-ICP-MS锆石U-Pb年龄加权平均值为(320±1)Ma,代表了其成岩年龄。岩石具有富SiO2、Al2O3的特征,里特曼指数(σ)为1.58~2.74(<3.3),碱度率(AR)为2.35~4.05,属于钙碱性花岗岩类,A/NCK=0.92~1.15,显示出偏铝质、过铝质岩浆的特征。稀土元素总量(ΣREE)较高,稀土配分模式呈轻稀土富集的右倾型[(La/Yb)N=4.60~8.83],轻稀土分异程度大于重稀土,所有样品均具有Eu负异常(δEu=0.56~0.88,平均为0.72);强烈富集强不相容元素Th、U和大离子亲石元素Rb、K,亏损高场强元素Nb、Ta、Ti、P。曲线形态与上地壳的相似,表明岩浆作用过程有上地壳物质的参与。高的Th含量(8.58~21.62 μg/g)及低的Nb/Ta值(8.75~15.72)指示岩浆源区主要为地壳。在Rb-(Nb+Y)及R1-R2等构造判别图解中样品大多数落入板块碰撞前火山弧花岗岩区,根据岩石共生组合特征,认为风雷山地区二长花岗岩为碰撞前陆缘弧岩浆作用的产物,与红石山—百合山—蓬勃山有限洋的洋壳俯冲作用有关。结合区域地质背景,推测红石山—百合山—蓬勃山有限大洋的闭合时间应晚于晚石炭世早期。
关键词:  北山造山带  锆石U-Pb年龄  地球化学  活动大陆边缘弧  地质调查工程  风雷山  内蒙古
DOI:10.12029/gc20200419
分类号:P588.12+1;P597
基金项目:中国地质调查局项目(1212011220462)资助。
LA-ICP-MS zircon U-Pb dating and tectonic setting of the monzogranites in the Fengleishan area of Beishan orogenic belt, Inner Mongolia
HAO Zengyuan1, GAO Jian2, WANG Chen1, LIU Xudong3, LI Decheng1, WANG Xinliang2
1.Xi'an Institute of Geological Survey and Mineral Exploration, Xi'an 710100, Shaanxi, China;2.Inner Mongolia Institute of Geological Survey and Mineral Exploration, Hohhot 010010, Inner Mongolia, China;3.Shaanxi Bureau of Geology and Mineral Resources, Xi'an 710100, Shaanxi, China
Abstract:
Monzogranites in Fengleishan are located in northern Beishan and situated between two ophiolitic mélange belts of Hongshishan-Baiheshan-Pengboshan and Jijitaizi-Xiaohuangshan, having a special tectonic affinity. Zircons from the monzogranites yielded a weighted mean LA-ICP-MS U-Pb age of (320±1) Ma, representing the intrusion age. The samples are characterized by high content of SiO2 and Al2O3 with Rittmann indexes of 1.58-2.74 (<3.3) and alkaline ratios of 2.35-4.05, belonging to calc-alkaline granitoids. Their A/NCK values range from 0.92 to 1.15 and display metaaluminous to peraalmuinous affinities. They have relatively high content of total REE and are characterized by LREE-enriched patterns ((La/Yb)N=4.60-8.83)and negative Eu anomalies (δEu=0.56-0.88, 0.72 in average). They also show strong enrichment of incompatible elements (e.g., Th and U) and large ion lithophile elements (e.g., Rb and K) but depletion of high field strength elements (e.g., Nb, Ta, Ti and P). Their normalized patterns are similar to those of upper continental crust (UPC), indicating participation of materials from the UPC in their magma source. High values of Th (8.58-21.62 μg/g) and low ratios of Nb/Ta (8.75-15.72) point to a crust-dominated magma source. On the tectonic discriminant diagrams of Rb-(Nb+Y) and R1-R2, most of the samples are plotted in the pre-collisional volcanic arc granite area. Based on associated lithological characteristics, it is proposed that monzogranites in the Fengleishan were formed by pre-collisional volcanic arc magmatism, which was related to oceanic crust subduction in the Hongshishan-Baiheshan-Pengboshan belt. Combined with regional geological background, it is inferred that the closure of the small ocean in the Hongshishan-Baiheshan-Pengboshan belt should postdate the early period of late Carboniferous.
Key words:  Beishan orogenic belt  zircon U-Pb age  geochemistry  active continental margin  geological survey engineering  Fengleishan  Inner Mongolia