本文選題：碳酸巖 + 地球化學(xué)特征　； 參考：《石家莊經(jīng)濟(jì)學(xué)院》2015年碩士論文

【摘要】：前人對張北地區(qū)碳酸巖的研究主要集中在二道邊碳酸巖筒,本次對張北漢諾壩地區(qū)野外地質(zhì)調(diào)查發(fā)現(xiàn)了黑腦包一帶有碳酸巖脈產(chǎn)出,規(guī)模十幾米至一百多米,與堿性玄武巖及其中的地幔橄欖巖包體密切共生。本文通過巖相學(xué)、礦物學(xué)、巖石地球化學(xué)分析結(jié)果研究張北地區(qū)碳酸巖巖石成因。研究表明張北二道邊碳酸巖筒和黑腦包碳酸巖脈的碳酸巖均為含CaO較高的方解石碳酸巖,主要礦物為方解石,次要礦物為鎂橄欖石、斜方輝石、單斜輝石及鉻尖晶石。局部脈狀碳酸巖可能與包含的幔源包體進(jìn)行交代,而使MgO的含量增加。研究區(qū)碳酸巖普遍具有結(jié)晶柱狀結(jié)構(gòu),說明碳酸巖為火成成因。微量稀土元素地球化學(xué)特征與甘肅禮縣新生代噴發(fā)碳酸巖特征相似。碳酸巖及方解石的Sr元素與Ta、Zr、Hf元素含量特征與火成成因碳酸巖的特征一致。筆者推測張北漢諾壩地區(qū)碳酸巖是富CO_2的硅酸巖巖漿液態(tài)不混溶作用形成,硅酸鹽熔體先噴出地表形成堿性玄武巖,受后期熱應(yīng)力影響產(chǎn)生大量裂隙,碳酸鹽熔體隨后灌入先固結(jié)的堿性玄武巖中,形成黑腦包脈狀碳酸巖,呈脈狀穿插于玄武巖和地幔橄欖巖中。當(dāng)分溶的碳酸鹽熔體具備較大壓力時(shí)就會沖破上覆地層,產(chǎn)生爆破式噴發(fā),形成二道邊的爆破碳酸巖筒。富CO_2的硅酸巖巖漿演化過程中斜長石由于結(jié)晶分異作用晶出,造成巖漿低Eu特征,碳酸鹽熔體與硅酸鹽熔體溶離后繼承了低Eu的特征,可能是張北漢諾壩地區(qū)碳酸巖Eu負(fù)異常的原因。推測方解石單礦物稀土元素Eu正異常是由巖漿噴發(fā)活動造成物質(zhì)不均一性導(dǎo)致的。
[Abstract]:Previous studies of carbonatite in Zhangbei area were mainly focused on the two sides of the carbonatite tube. This field geological survey of Hannouba area in Zhangbei has found that carbonatite veins are produced in the area of Hannoba in Zhangbei, with a scale of 10 to more than 100 meters.It is closely associated with alkaline basalt and mantle peridotite xenoliths.In this paper, the petrogenesis of carbonatite in Zhangbei area is studied by the results of petrographic, mineralogical and petrogeochemical analysis.The results show that the carbonatite in both the Carbonate tube of Erdaobian in Zhangbei and the carbonatite in the Kuronaobao vein are calcite carbonate rocks with high CaO content. The main minerals are calcite, the secondary minerals are mafic olivine, clinopyroxene, clinopyroxene and chromium-spinel.The local vein carbonate may be metasomorphic with the contained mantle xenoliths, thus increasing the content of MgO.Carbonatite in the study area generally has crystalline columnar structure, indicating that carbonatite is the origin of pyrogeny.The geochemical characteristics of trace rare earth elements are similar to those of Cenozoic eruptive carbonatite in Lixian County Gansu Province.The contents of Sr element and Tazrzru HF element in carbonatite and calcite are consistent with those of pyrogenic carbonatite.The authors speculate that carbonatite in Hanooba area of Zhangbei is formed by liquid immiscible process of CO_2 rich silicate magma, and silicate melt first ejects from the surface to form alkaline basalt, and a large number of cracks are produced under the influence of late thermal stress.Carbonate melts are then poured into preconsolidated alkaline basalts to form black-brain encrusted carbonatites interlaced in basalts and mantle peridotite.When the dissolved carbonate melt has a high pressure, it will break through the overlying strata and produce a blasting eruption, forming a blasting carbonatite tube with two sides.In the process of magma evolution of silicalite rich in CO_2, plagioclase is characterized by crystallization differentiation, which results in low EU characteristics of magma, and inherits the character of low EU after dissolution of carbonate melt and silicate melt.It may be the cause of negative EU anomaly of carbonatite in Hannoba area, Zhangbei.It is inferred that the positive anomaly of EU in calcite monmineral is caused by the material heterogeneity caused by magmatic eruption.
【學(xué)位授予單位】：石家莊經(jīng)濟(jì)學(xué)院
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：P588.245

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