本文選題：埃達(dá)克質(zhì)巖　切入點(diǎn)：地球化學(xué)　出處：《東華理工大學(xué)》2015年碩士論文

【摘要】：雅魯藏布江縫合帶是青藏高原一條重要的構(gòu)造界線,帶內(nèi)地質(zhì)現(xiàn)象復(fù)雜對(duì)于反演青藏高原演化具有重要意義。本文報(bào)道了縫合帶東段澤當(dāng)?shù)貐^(qū)羅布莎礫巖中的火山巖及相關(guān)巖石的年代學(xué)、巖石地球化學(xué)和同位素地球化學(xué)特征,試圖為反演青藏高原演化及印亞碰撞提供更多巖石學(xué)及地球化學(xué)證據(jù)。澤當(dāng)?shù)貐^(qū)羅布莎礫巖為一套磨拉石沉積建造,不整合沉積于岡底斯花崗巖之上。野外地質(zhì)調(diào)查證實(shí)其沉積物源確實(shí)存在明顯變化,反映了縫合帶兩側(cè)不同的構(gòu)造運(yùn)動(dòng)。在礫巖近底部筆者發(fā)現(xiàn)以英安質(zhì)晶屑玻屑凝灰?guī)r為主的火山巖夾層有局部向熔巖端元過渡的現(xiàn)象,含有含礫英安巖,呈層狀產(chǎn)出。LA-ICP-MS鋯石U-Pb同位素結(jié)果顯示羅布莎礫巖中該火山巖噴發(fā)時(shí)代為18.7±0.2Ma,屬于中新世前中前期。羅布莎礫巖下伏的岡底斯花崗巖鋯石U-Pb定年顯示其侵位時(shí)代為29.9±0.4Ma。綜合野外地質(zhì)關(guān)系及磨拉石快速沉積的特點(diǎn),大約在18.7Ma~29.9Ma之間羅布莎礫巖開始沉積。羅布莎礫巖中火山巖全巖地球化學(xué)顯示其為鉀玄巖系列,樣品富集輕稀土元素、虧損重稀土元素,具有弱的銪負(fù)異常,大離子親石元素富集,高場(chǎng)強(qiáng)元素虧損;Sr含量很高(平均405×10-6),Y含量很低(平均10.05×10-6),Sr/Y=36.40~43.21,屬于埃達(dá)克質(zhì)巖,來源于加厚下地殼部分熔融。全巖Sr-Nd-Pb同位素顯示樣品具有親特提斯洋殼屬性,εNd(t)介于-2.58~-3.36之間,年輕虧損地幔模式年齡TDM(Ga)=0.84Ga~0.91Ga,具有初生地殼特征,鋯石Lu-Hf同位素也顯示出相似特征,說明虧損地幔對(duì)源區(qū)貢獻(xiàn)較大,全巖Sr-Nd-Pb同位素及鋯石Lu-Hf同位素特征都表明該火山巖具有親特提斯洋屬性。澤當(dāng)?shù)貐^(qū)羅布莎礫巖中火山巖親新特提斯洋洋殼屬性說明俯沖的印度板塊在18.7±0.2Ma還沒有影響到該地區(qū)。通過與拉薩地塊西部超鉀質(zhì)巖的對(duì)比,可以進(jìn)一步說明拉薩地塊東西差異性,暗示印度板塊在該時(shí)期內(nèi)可能經(jīng)歷了一次快速的俯沖過程。
[Abstract]:The Yalu Zangbo River suture zone is an important tectonic boundary of the Qinghai-Tibet Plateau, and the complexity of geological phenomena in the belt is of great significance for inversion of the evolution of the Qinghai-Tibet Plateau.This paper reports the geochronological, petrogeochemical and isotopic geochemical characteristics of volcanic rocks and related rocks in the Luobusa conglomerate in the Zedang area of the eastern segment of the suture zone.This paper attempts to provide more petrological and geochemical evidence for inversion of the evolution of the Qinghai-Tibet Plateau and the India-Subcollision.The Luobusa conglomerate in Zedang area is a set of morlite sedimentary formation, which is unconformity deposited on Gangdis granite.The field geological investigation confirmed that the sediment source changed obviously, which reflected the different tectonic movements on the two sides of the suture zone.Near the bottom of the conglomerate, it is found that the intercalation of volcanic rock, which is dominated by vitreous tuff, has the phenomenon of partial transition to the end of molten rock, and contains conglomerate dolomite.The U-Pb isotopic results of LA-ICP-MS zircon show that the eruption age of the volcanic rocks in the Luobusa conglomerate is 18.7 鹵0.2 Ma.It belongs to the pre-Miocene period.The U-Pb dating of zircon from the Gangdese granite underlying the Luobusa conglomerate shows that its emplacement age is 29.9 鹵0.4 Ma.Combined with the field geological relationship and the characteristics of rapid deposition of molars, the Luobusa conglomerate began to deposit between 18.7Ma~29.9Ma.The whole rock geochemistry of the volcanic rocks in the Luobusa conglomerate shows that it is a series of potassium metamorphic rocks. The samples are rich in light rare earth elements, depleted in heavy rare earth elements, with weak europium negative anomalies and large ion lithophile elements.The high field strength element depleted Sr content is very high (average 405 脳 10-6) and the content of Y is very low (average 10.05 脳 10-6) Sr-P / Y ~ (36.40) ~ (43.21), which belongs to adakitic rock and originated from partial melting of thickened lower crust.The Sr-Nd-Pb isotopes of the whole rock show that the samples have the characteristics of pro-Tethys oceanic crust, 蔚 Ndndnt) between -2.58 and 3.36, and the young depleted mantle model age is 0.84Ga0.91 Ga, which shows the characteristics of the primary crust. The zircon Lu-Hf isotopes also show similar characteristics, indicating that the depleted mantle contributes a great deal to the source region.The Sr-Nd-Pb isotopic and zircon Lu-Hf isotopic characteristics of the whole rock indicate that the volcanic rock is characterized by the Tethys oceanic property.The neo-Tethys oceanic crust properties of volcanic rocks in the Robesa conglomerate in the Zedang area indicate that the subducted Indian plate has not affected the area at 18.7 鹵0.2Ma.The comparison with the ultrakalitic rocks in the western Lhasa block can further explain the east-west difference of the Lhasa block suggesting that the Indian plate may have experienced a rapid subduction process in this period.
【學(xué)位授予單位】：東華理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：P588.14;P597.3

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