本文選題：義敦島弧帶 + 中生代巖漿巖�。� 參考：《成都理工大學(xué)》2017年碩士論文

【摘要】：義敦島弧帶位于西南三江構(gòu)造帶,夾于甘孜理塘縫合帶與金沙江縫合帶之間,伴隨著強(qiáng)烈的板塊構(gòu)造運(yùn)動(dòng),巖漿活動(dòng)比較頻繁,出露有大量的花崗巖,發(fā)育大量的具有高經(jīng)濟(jì)價(jià)值的礦床,是我國(guó)目前發(fā)現(xiàn)的尚且被保存的最為完整的古島弧構(gòu)造帶,因此對(duì)其進(jìn)行深入的研究,對(duì)西南三江區(qū)域構(gòu)造及成礦背景以及國(guó)民經(jīng)濟(jì)支撐,具有非常重要的意義。目前,前人對(duì)該區(qū)的研究大多集中于弧火山巖,而對(duì)義敦島弧帶出露的大量的中生代花崗巖的研究相對(duì)較少,對(duì)其形成時(shí)代的研究方法比較單一,較少運(yùn)用LA-MC-ICP-MS的U-Pb測(cè)年來(lái)厘定義敦島弧帶巖漿巖的形成時(shí)代,并劃分期次;同時(shí)在鋯石U-Pb測(cè)年的基礎(chǔ)之上,運(yùn)用LA-MC-ICP-MS對(duì)義敦島弧帶中生代巖漿巖進(jìn)行鋯石Hf同位素的特征的研究。本文以義敦島弧帶東部、中部、西部花崗巖的典型巖體為研究對(duì)象,對(duì)其進(jìn)行了野外地質(zhì)調(diào)查、巖石學(xué)特征、鋯石U-Pb年齡、主量元素、微量元素以及鋯石Hf同位素的詳細(xì)研究,并且結(jié)合前人的研究成果,對(duì)義敦島弧帶中生代巖漿巖的形成時(shí)代、源區(qū)及構(gòu)造演化進(jìn)行探討,最終得到以下幾點(diǎn)認(rèn)識(shí):1)義敦島弧帶286個(gè)巖漿鋯石U-Pb年齡結(jié)果顯示,義敦島弧帶中生代巖漿巖的形成年齡在216Ma到93Ma之間,主要集中于三疊紀(jì)和白堊紀(jì)兩個(gè)時(shí)代,其中中生代侏羅紀(jì)地層缺失,未見(jiàn)其出露;將其劃分為兩個(gè)明顯不同的巖漿活動(dòng)期次,其中一期在義敦島弧帶東部巖漿巖帶和中部斑巖帶,巖漿年齡為208Ma到216Ma,為印支晚期;另一期主要發(fā)育西部花崗巖,巖漿年齡為100Ma左右,為燕山晚期。2)義敦島弧帶東部花崗巖體主要為二長(zhǎng)花崗巖。二長(zhǎng)花崗巖為過(guò)鋁質(zhì),親石元素Ba、Sr含量高,相對(duì)富集大離子親石元素,Nb/Ta=12.35,接近于與地幔有關(guān)的堿性巖類Nb/Ta比值,為A型花崗巖巖類,表明該期花崗巖主要由富鋁的地殼物質(zhì)重熔所形成,同時(shí)有幔源巖漿的貢獻(xiàn)。綜上所述,可見(jiàn)義敦島弧帶東部花崗巖的源區(qū)為殼幔型。3)義敦島弧帶中部花崗斑巖體主要出露花崗閃長(zhǎng)斑巖、花崗斑巖。屬于高鉀鈣堿性系列,并且以準(zhǔn)鋁質(zhì)-過(guò)鋁質(zhì)巖石為主,暗示著下地殼或地幔的巖漿起源,表明義敦島弧中部斑巖巖漿有很大部分是來(lái)自于地殼或者地幔;親石元素Ba、Sr含量高,相對(duì)富集大離子親石元素;Nb/Ta=12.35,接近于與地幔有關(guān)的堿性巖類Nb/Ta比值,顯示為幔源特點(diǎn);稀土配分模式從整體上呈十分明顯的右傾型,重稀土相對(duì)于輕稀土發(fā)生明顯的虧損,Eu表現(xiàn)為相對(duì)較弱的負(fù)異常,根據(jù)其特點(diǎn)可以判斷為幔源。高場(chǎng)強(qiáng)元素中,Nb相對(duì)虧損,可以指示其源區(qū)為地幔。綜上所述,可見(jiàn)義敦島弧帶東部花崗巖的源區(qū)為殼幔型。4)義敦島弧帶西部花崗巖以高鉀鈣堿性-鉀玄巖、準(zhǔn)鋁質(zhì)-過(guò)鋁質(zhì)(偏過(guò)鋁質(zhì))巖石為主,表明該期花崗巖有富鋁的地殼物質(zhì)重熔的貢獻(xiàn),其產(chǎn)生于大陸碰撞構(gòu)造環(huán)境。從稀土配分模式圖解可以看出西部花崗巖的配分曲線整體上呈海鷗右傾型,Ba含量偏高,稀土元素Sm/Nd為0.2~0.3,低于陸殼平均值,輕、重稀土分餾程度相對(duì)于印支期花崗巖較低,并且具有十分明顯的Eu負(fù)異常。從Na2O-K2O圖解中可以看出,義敦島弧帶西部花崗巖主要為A型花崗巖,花崗巖源區(qū)為幔源。綜上所述,義敦島弧帶西部花崗巖具有地幔巖漿演化的特征,并受地殼不同程度的混染。5)對(duì)義敦島弧帶東部花崗巖、中部斑巖、西部花崗巖的巖漿鋯石Hf同位素?cái)?shù)據(jù)投點(diǎn)后發(fā)現(xiàn),其東部花崗巖、中部花崗斑巖的U-Pb年齡都集中于200Ma左右,但是東部花崗巖大多數(shù)落在了球粒隕石演化線CHUR附近及偏下的地方,其源區(qū)主要為較為古老的地殼;而中部花崗斑巖在球粒隕石演化線CHUR和虧損地幔演化線附近都有分布,說(shuō)明中部花崗斑巖源區(qū)既有虧損地幔的熔融,又有較為古老的地殼成分的貢獻(xiàn)。TDM2峰值為1.20Ga,在這個(gè)時(shí)期代表發(fā)生了強(qiáng)烈的殼幔分異事件。西部花崗巖的U-Pb年齡主要集中在100Ma左右,其在鋯石U-Pb年齡-εHf(t)圖中的分布特征與中部花崗斑巖類似,在球粒隕石演化線CHUR和虧損地幔演化線附近都有分布,代表了義敦島弧帶西部花崗巖為殼幔型花崗巖。這與十萬(wàn)大山地區(qū)花崗巖鋯石Hf哈同位素組成特征,具有較高的相似度,可以從某種程度上來(lái)反映義敦島弧帶花崗巖主要源自地殼物質(zhì)的重熔,只有極少部分虧損地幔物質(zhì)的參與。
[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.
【學(xué)位授予單位】：成都理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：P597;P588.1

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