本文選題：巖漿巖 + 鋯石U-Pb年齡��； 參考：《中國地質(zhì)大學(北京)》2015年碩士論文

【摘要】：雅布賴山復式巖基位于內(nèi)蒙古阿拉善北部,該巖基包括花崗巖、花崗閃長巖、正長花崗巖等侵入巖以及英安巖等火山巖。LA-ICP-MS鋯石U-Pb測年結果顯示,花崗閃長巖(280±1 Ma)、正長花崗巖(286±1 Ma)和和英安巖(275±2 Ma)形成于早二疊世,而英云閃長巖(272±2 Ma)形成于中二疊世。鋯石Hf同位素測試結果顯示,除了正長花崗巖的部分鋯石的εHf(t)為正值,暗示其形成過程中可能受到新生地殼物質(zhì)或虧損地幔的混染,雅布賴山地區(qū)巖漿巖的鋯石絕大部分具有負的εHf(t)值(-12.97~+1.7)和相對古老的地殼模式年齡(TDM2=2.1~1.2 Ga),表明這些巖漿巖的源區(qū)主要為古老的地殼物質(zhì),這與典型的古老陸塊上發(fā)育的酸性巖漿巖一致。地球化學分析結果表明,雅布賴山地區(qū)花崗閃長巖和正長花崗巖具有相似的微量和稀土元素組成,都顯示出輕稀土相對富集和重稀土相對虧損的特征,并且具有微弱-中等的Eu負異常;而英云閃長巖則表現(xiàn)了一定程度的Eu正異常,且相比前兩者具有較高的Sr/Y值(300)。排除巖漿在侵位過程中圍巖同化混染作用的影響,而中上地殼酸性侵入巖的結晶分異作用也難以形成如此高的Sr/Y值,因而英云閃長巖高Sr/Y特征可能是源區(qū)特征的反映。考慮到斜長石、角閃石和黑云母均不能明顯影響Sr/Y值,所以造成英云閃長巖與鄰區(qū)中酸性侵入巖地球化學差異的原因可能是其源區(qū)存在石榴子石。結合前人研究資料,雅布賴山地區(qū)和以東的諾爾公-紅古爾玉林一帶,以及華北北緣廣泛分布的晚古生代巖漿巖形成了一條近東西向展布的巖漿巖帶,這條巖漿巖帶可能處于同一構造環(huán)境之下,與古亞洲洋的閉合、俯沖或俯沖之后的伸展作用相關。
[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 鹵1 Ma), syenite (286 鹵1 MaA) and andalite (275 鹵2 Ma) were formed in the early Permian, while the Yingyun diorite (272 鹵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.
【學位授予單位】：中國地質(zhì)大學(北京)
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：P588.1

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