义敦岛弧带中生代岩浆岩锆石铪同位素特征

发布时间：2018-06-03 20:10

本文选题：义敦岛弧带 + 中生代岩浆岩　；参考：《成都理工大学》2017年硕士论文

【摘要】：义敦岛弧带位于西南三江构造带,夹于甘孜理塘缝合带与金沙江缝合带之间,伴随着强烈的板块构造运动,岩浆活动比较频繁,出露有大量的花岗岩,发育大量的具有高经济价值的矿床,是我国目前发现的尚且被保存的最为完整的古岛弧构造带,因此对其进行深入的研究,对西南三江区域构造及成矿背景以及国民经济支撑,具有非常重要的意义。目前,前人对该区的研究大多集中于弧火山岩,而对义敦岛弧带出露的大量的中生代花岗岩的研究相对较少,对其形成时代的研究方法比较单一,较少运用LA-MC-ICP-MS的U-Pb测年来厘定义敦岛弧带岩浆岩的形成时代,并划分期次;同时在锆石U-Pb测年的基础之上,运用LA-MC-ICP-MS对义敦岛弧带中生代岩浆岩进行锆石Hf同位素的特征的研究。本文以义敦岛弧带东部、中部、西部花岗岩的典型岩体为研究对象,对其进行了野外地质调查、岩石学特征、锆石U-Pb年龄、主量元素、微量元素以及锆石Hf同位素的详细研究,并且结合前人的研究成果,对义敦岛弧带中生代岩浆岩的形成时代、源区及构造演化进行探讨,最终得到以下几点认识:1)义敦岛弧带286个岩浆锆石U-Pb年龄结果显示,义敦岛弧带中生代岩浆岩的形成年龄在216Ma到93Ma之间,主要集中于三叠纪和白垩纪两个时代,其中中生代侏罗纪地层缺失,未见其出露;将其划分为两个明显不同的岩浆活动期次,其中一期在义敦岛弧带东部岩浆岩带和中部斑岩带,岩浆年龄为208Ma到216Ma,为印支晚期;另一期主要发育西部花岗岩,岩浆年龄为100Ma左右,为燕山晚期。2)义敦岛弧带东部花岗岩体主要为二长花岗岩。二长花岗岩为过铝质,亲石元素Ba、Sr含量高,相对富集大离子亲石元素,Nb/Ta=12.35,接近于与地幔有关的碱性岩类Nb/Ta比值,为A型花岗岩岩类,表明该期花岗岩主要由富铝的地壳物质重熔所形成,同时有幔源岩浆的贡献。综上所述,可见义敦岛弧带东部花岗岩的源区为壳幔型。3)义敦岛弧带中部花岗斑岩体主要出露花岗闪长斑岩、花岗斑岩。属于高钾钙碱性系列,并且以准铝质-过铝质岩石为主,暗示着下地壳或地幔的岩浆起源,表明义敦岛弧中部斑岩岩浆有很大部分是来自于地壳或者地幔;亲石元素Ba、Sr含量高,相对富集大离子亲石元素;Nb/Ta=12.35,接近于与地幔有关的碱性岩类Nb/Ta比值,显示为幔源特点;稀土配分模式从整体上呈十分明显的右倾型,重稀土相对于轻稀土发生明显的亏损,Eu表现为相对较弱的负异常,根据其特点可以判断为幔源。高场强元素中,Nb相对亏损,可以指示其源区为地幔。综上所述,可见义敦岛弧带东部花岗岩的源区为壳幔型。4)义敦岛弧带西部花岗岩以高钾钙碱性-钾玄岩、准铝质-过铝质(偏过铝质)岩石为主,表明该期花岗岩有富铝的地壳物质重熔的贡献,其产生于大陆碰撞构造环境。从稀土配分模式图解可以看出西部花岗岩的配分曲线整体上呈海鸥右倾型,Ba含量偏高,稀土元素Sm/Nd为0.2~0.3,低于陆壳平均值,轻、重稀土分馏程度相对于印支期花岗岩较低,并且具有十分明显的Eu负异常。从Na2O-K2O图解中可以看出,义敦岛弧带西部花岗岩主要为A型花岗岩,花岗岩源区为幔源。综上所述,义敦岛弧带西部花岗岩具有地幔岩浆演化的特征,并受地壳不同程度的混染。5)对义敦岛弧带东部花岗岩、中部斑岩、西部花岗岩的岩浆锆石Hf同位素数据投点后发现,其东部花岗岩、中部花岗斑岩的U-Pb年龄都集中于200Ma左右,但是东部花岗岩大多数落在了球粒陨石演化线CHUR附近及偏下的地方,其源区主要为较为古老的地壳;而中部花岗斑岩在球粒陨石演化线CHUR和亏损地幔演化线附近都有分布,说明中部花岗斑岩源区既有亏损地幔的熔融,又有较为古老的地壳成分的贡献。TDM2峰值为1.20Ga,在这个时期代表发生了强烈的壳幔分异事件。西部花岗岩的U-Pb年龄主要集中在100Ma左右,其在锆石U-Pb年龄-εHf(t)图中的分布特征与中部花岗斑岩类似,在球粒陨石演化线CHUR和亏损地幔演化线附近都有分布,代表了义敦岛弧带西部花岗岩为壳幔型花岗岩。这与十万大山地区花岗岩锆石Hf哈同位素组成特征,具有较高的相似度,可以从某种程度上来反映义敦岛弧带花岗岩主要源自地壳物质的重熔,只有极少部分亏损地幔物质的参与。
[Abstract]:The Yi don island arc belt, located in the southwest Sanjiang tectonic belt, is sandwiched between the Ganzi Litang suture zone and the suture zone of Jinsha River. With the strong plate tectonic movement, the magmatic activity is more frequent, a large number of granites are exposed, and a large number of high economic deposits are developed, which are the most intact ancient islands found in China at present. The deep study of the arc tectonic zone is of great significance to the regional tectonic and metallogenic background of Southwest Sanjiang and the support of the national economy. At present, most of the previous studies on this area have concentrated on the arc volcanic rocks, and a large number of Mesozoic granites exposed to the Yi don island arc are relatively few, and they are formed in the era of its formation. The method of research is relatively simple, and the U-Pb dating of LA-MC-ICP-MS is less used to define the age of the formation of the magmatic rocks in the Dun island arc zone and to divide the period. At the same time, on the basis of the zircon U-Pb dating, the characteristics of the zircon Hf isomer of the Mesozoic magmatic rocks in the igton island arc zone are studied by LA-MC-ICP-MS. The typical rock mass of granite in the central and western regions of China is the research object, and a detailed study of its field geological survey, petrological characteristics, zircon U-Pb age, principal elements, trace elements and zircon Hf isotopes is carried out in detail, and the formation age, source and tectonic evolution of Mesozoic Mesozoic Magmatic rocks in the Yi Dun island arc zone are carried out in combination with previous research results. The following points are discussed: 1) 1) the results of 286 magmatic zircon ages in the eigun island arc show that the age of Mesozoic Magmatic Rocks of the eigun island arc zone is between 216Ma and 93Ma, mainly concentrated in two times of the Triassic and Cretaceous, of which the Mesozoic Jurassic layer was absent and no exposure was found, and it was divided into two distinct differences. The same magmatic activity period, one in the eastern magmatic rock belt and the middle porphyry zone in the east of the yidon island arc zone, the magma age is 208Ma to 216Ma, the late Indo branch, the other mainly developed in the Western granite, the magma age is about 100Ma and the late Yanshan.2), the granite in the east of the yidon island arc zone is mainly two long granite. The two granites are over. The content of aluminum, Ba and Sr is high, and is relatively rich in large ion stone elements, and Nb/Ta=12.35 is close to the Nb/Ta ratio of the alkaline rock related to the mantle, which is a A type granite rock. It indicates that the granite is mainly formed by the remelting of the crust material of the rich aluminum, and the contribution of the mantle derived rock slurry. The source area of the rock is the crust and mantle type.3) and the granitic porphyry in the middle of the igton island arc zone is mainly exposed to the granodiorite and granite porphyry. It belongs to the high potassium calc alkaline series and is mainly paralic - peraluminous rocks, suggesting the magma of the lower crust or mantle, indicating that the magma in the middle of the middle of the Yi Town arc is mostly derived from the crust or earth. The content of Ba and Sr is high and is relatively rich in large ion stone elements; Nb/Ta=12.35, which is close to the Nb/Ta ratio of the basic rocks related to the mantle, shows the characteristics of the mantle source, and the REE distribution pattern is obviously right leaning from the whole, and the heavy rare earth has a significant loss relative to the light rare-earth, and the Eu shows a relatively weak negative anomaly. The characteristics can be judged to be the mantle source. In the high field and strong elements, the Nb relative loss can indicate that the source area is the mantle. To sum up, it can be seen that the source area of the granite in the eastern part of the yitun island arc zone is the crust and mantle type.4) and the granite in the Yun island arc zone is characterized by high potassium calcalc basalite and paralic peralalic (partial peraluminous) rocks. The contribution of aluminum rich crustal material remelting is born in continental collision tectonic environment. From the diagram of rare earth distribution pattern, it can be seen that the distribution curve of the granite in the western region shows the right tilt of the seagull, the Ba content is high and the rare earth element Sm/Nd is 0.2~0.3, which is lower than the average of the continental crust, and the degree of heavy rare earth fractionation is lower than that of the granites of the Indo Chinese period. And it has a very obvious negative Eu anomaly. From the Na2O-K2O diagram, it can be seen that the granite in the west of the Yi Dun island arc is mainly A type granite, and the source area of the granite is the mantle source. In summary, the granite in the western part of the Yi Dun island arc zone has the characteristics of mantle magma evolution and is affected by different degrees of the crust in the east of the Yi Town arc zone. After the magmatic zircon Hf isotopic data from the porphyry and Western granite, it is found that the U-Pb age of granite in the eastern part of the granite and the central granitic porphyry is concentrated around 200Ma, but the eastern granite is mostly located near and below the CHUR of the chondrite evolution line, and its source area is mainly the older crust, and the central granite porphyry. The distribution of the chondrite evolution line CHUR and the evolution line of the depleted mantle shows that the source area of the granite porphyry in the central part of the central granite porphyry has both the melting of the depleted mantle and the contribution of the ancient crustal composition to the peak of the.TDM2 peak of 1.20Ga. In this period, a strong crust and mantle differentiation event occurred. The U-Pb age of the Western granite is mainly concentrated in 100Ma. The distribution of the zircon U-Pb age - epsilon Hf (T) map is similar to that of the central granite porphyry. It is distributed near the chondrite evolution line CHUR and the evolution line of the depleted mantle. It represents the crust mantle granite in the west of the Yi Town arc zone, which is characterized by the composition of the zircon Hf isotopes of the zircon in the one hundred thousand great mountains. The similarity can reflect to some extent that the granites of the Yi Dun island arc belt are mainly derived from remelting of crustal materials, and only a small proportion of depleted mantle materials participate.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P597;P588.1

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