阿拉善盟雅布赖山地区晚古生代岩浆岩的地球化学特征及构造意义

发布时间：2018-05-16 11:03

本文选题：岩浆岩 + 锆石U-Pb年龄　；参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：雅布赖山复式岩基位于内蒙古阿拉善北部,该岩基包括花岗岩、花岗闪长岩、正长花岗岩等侵入岩以及英安岩等火山岩。LA-ICP-MS锆石U-Pb测年结果显示,花岗闪长岩(280±1 Ma)、正长花岗岩(286±1 Ma)和和英安岩(275±2 Ma)形成于早二叠世,而英云闪长岩(272±2 Ma)形成于中二叠世。锆石Hf同位素测试结果显示,除了正长花岗岩的部分锆石的εHf(t)为正值,暗示其形成过程中可能受到新生地壳物质或亏损地幔的混染,雅布赖山地区岩浆岩的锆石绝大部分具有负的εHf(t)值(-12.97~+1.7)和相对古老的地壳模式年龄(TDM2=2.1~1.2 Ga),表明这些岩浆岩的源区主要为古老的地壳物质,这与典型的古老陆块上发育的酸性岩浆岩一致。地球化学分析结果表明,雅布赖山地区花岗闪长岩和正长花岗岩具有相似的微量和稀土元素组成,都显示出轻稀土相对富集和重稀土相对亏损的特征,并且具有微弱-中等的Eu负异常;而英云闪长岩则表现了一定程度的Eu正异常,且相比前两者具有较高的Sr/Y值(300)。排除岩浆在侵位过程中围岩同化混染作用的影响,而中上地壳酸性侵入岩的结晶分异作用也难以形成如此高的Sr/Y值,因而英云闪长岩高Sr/Y特征可能是源区特征的反映。考虑到斜长石、角闪石和黑云母均不能明显影响Sr/Y值,所以造成英云闪长岩与邻区中酸性侵入岩地球化学差异的原因可能是其源区存在石榴子石。结合前人研究资料,雅布赖山地区和以东的诺尔公-红古尔玉林一带,以及华北北缘广泛分布的晚古生代岩浆岩形成了一条近东西向展布的岩浆岩带,这条岩浆岩带可能处于同一构造环境之下,与古亚洲洋的闭合、俯冲或俯冲之后的伸展作用相关。
[Abstract]:The Yablaishan complex rock base is located in the northern part of Alashan, Inner Mongolia. The U-Pb dating results show that the rock base includes granite, granodiorite, syenite, and volcanic rocks such as dolomite. LA-ICP-MS zircon dating results show that the rock base consists of granite, granodiorite, syenite and other volcanic rocks. The granodiorite (280 卤1 Ma), syenite (286 卤1 MaA) and andalite (275 卤2 Ma) were formed in the early Permian, while the Yingyun diorite (272 卤2 MaA) was formed in the Middle Permian. The results of zircon HF isotopic measurements show that the 蔚 Hfft) of some zircons except for syenite is positive, suggesting that the zircon may be mixed by neo-crustal material or depleted mantle during its formation. The zircons of the magmatic rocks in the Yablaishan area are mostly of negative 蔚 Hftt values of -12.97 ~ 1.7) and the relatively old crustal model age of TDM2 / 2.1Ga-1.2GaGA, indicating that the source regions of these magmatic rocks are mainly ancient crustal materials. This is consistent with the acid magma developed on typical ancient landmasses. The geochemical analysis results show that granodiorite and syenite in the Yablaishan area have similar composition of trace and rare earth elements, showing the characteristics of relative enrichment of light rare earth elements and relative depletion of heavy rare earth elements. There is a weak to medium negative EU anomaly, while the quartz diorite shows a certain degree of positive EU anomaly, and has a higher Sr/Y value than the former two. Excluding the influence of the assimilation of the surrounding rock during the emplacement of magma, it is difficult for the crystallization differentiation of acid intrusive rocks in the upper and middle crust to form such a high Sr/Y value, so the high Sr/Y characteristics of Yingyun diorite may be the reflection of the characteristics of the source region. Considering the plagioclase, amphibole and biotite can not obviously affect the Sr/Y value, so the geochemical difference between the quartz diorite and the intermediate-acid intrusive rocks in the adjacent area may be due to the existence of garnet in the source area. Based on the previous research data, the late Paleozoic magmatic rocks, which are widely distributed in the Yablai Mountain area, the Norgon-Honggueryulin area to the east and the northern margin of North China, form a magmatic belt near the east-west direction. This magmatic belt may be located in the same tectonic environment, which is related to the closure, subduction or extension of the Paleo-Asian Ocean.
【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】：2015
【分类号】：P588.1

【参考文献】