西藏澤當桑格達角閃輝長巖體的發(fā)現(xiàn)：雅魯藏布江閉合時間的證據(jù)
發(fā)布時間：2019-01-06 14:51
【摘要】：印度板塊與歐亞大陸碰撞導致了新特提斯洋的閉合,但是對于其閉合的時間前人從不同的角度提供了多種解釋。澤當蛇綠巖套是雅魯藏布江縫合帶東段最大的蛇綠巖塊體,本文研究的澤當桑格達角閃輝長巖體侵位于蛇綠巖中,主要由細粒角閃輝長巖、斑狀角閃輝長巖、巨晶角閃輝長巖、堆晶角閃輝長巖和角閃巖這5個單元組成。澤當?shù)貐^(qū)產(chǎn)出的角閃輝長巖體前人有多種命名,例如玄武巖、玄武巖、埃達克巖等,我們發(fā)現(xiàn)這些巖體時間是同一個巖體的不同部分。本論文通過詳細的研究表明其屬于侵入巖,并且在TAS圖解中,角閃輝長巖投影點幾乎全部落入輝長巖區(qū)內(nèi),屬于基性巖類。在澤當角閃輝長巖的哈克圖解中可知,角閃石是由其它巖漿帶入巖體,巖體中存在的大量角閃石與巖漿不平衡。巖體各巖石樣品微量元素總體分布趨勢相近,Cs、Rb、Th、K、Ba等大離子親石元素和La元素相對富集,Ta、Nb、Ti、Th等高場強元素虧損,Sr正異常,具有板塊俯沖環(huán)境中的島弧巖漿巖特征。球粒隕石標準化稀土配分型式較為一致,表明這些角閃輝長巖具有同源巖漿系列的特征。對于新特提斯洋的閉合時間,一直沒有取得一直的認識,而本文所發(fā)現(xiàn)的桑格達角閃輝長巖可以用來判斷印度板塊與亞洲板塊碰撞啟動和完成碰撞的時間。角閃輝長巖體侵位于蛇紋石化橄欖巖(被動陸緣)和安山巖(主動陸緣火山-沉積建造)之間,說明它形成于碰撞以后;角閃輝長巖富含大量揮發(fā)分,是弧巖漿的特點,據(jù)此可以證明其形成在碰撞之前的俯沖環(huán)境中。利用這二者的矛盾可以判斷,其形成于板塊碰撞早期,也就是新特提斯洋剛剛閉合的時間。鋯石U-Pb測年得到桑格達巖體的年齡,也就是新特提斯洋閉合的時間為47.6±2.2Ma。根據(jù)前人研究,西藏澤當蛇綠巖套形成于板塊俯沖環(huán)境,且鋯石的U-Pb年齡是154.9Ma±2.0Ma,說明板塊俯沖一直持續(xù)了至少110Ma左右,也就是新特提斯洋在這110Ma時間范圍內(nèi)一直在閉合。以北大西洋的平均擴張速率近34 mm/年作為新特提斯洋閉合的速率下限,計算得新特提斯洋規(guī)模下限為3470公里。
[Abstract]:The collision between the Indian plate and Eurasia resulted in the closure of the New Tethys Ocean, but many explanations were provided for the time of its closure from different angles. The Zedang ophiolite suite is the largest ophiolite block in the eastern segment of the Yalu Zangbo River suture zone. The Zedang Sangoda amphiolite intrusion in this paper is located in the ophiolite, mainly composed of fine-grained hornblende gabbro, porphyry hornblende gabbro, megacrystalline hornblende gabbro. The five units are composed of amphibolite and amphibolite. There are many names of the hornblende gabbro body in Zedang area, such as basalt, adakite and so on. We find that these rocks are different parts of the same rock mass in time. In this paper, it is shown by detailed research that it belongs to intrusive rocks, and in the TAS diagram, almost all the projection points of hornblende gabbro fall into the gabbro area and belong to the basic rock category. In the Huck diagram of Zedang hornblende gabbro it can be seen that hornblende is brought into the rock body by other magma and a large number of hornblende and magma are not in equilibrium in the rock mass. The general distribution trend of trace elements in rock samples is similar, the large ion lithophile elements and La elements such as Cs,Rb,Th,K,Ba are relatively enriched, the high field strength elements such as Ta,Nb,Ti,Th are depleted, and the Sr anomaly is positive. It has the characteristics of island arc magma in plate subduction environment. The standardized REE distribution patterns of chondrites are consistent, indicating that these hornblende gabbro have the characteristics of homologous magma series. The closing time of the New Tethys Ocean has not been always known, and the Sangda diorite found in this paper can be used to judge the time of initiation and completion of the collision between the Indian plate and the Asian plate. The amphiolite intrusion is between serpentine peridotite (passive continental margin) and andesite (active continental margin volcanic-sedimentary formation), indicating that it was formed after collision. The hornblende gabbro is rich in volatile matter and is characterized by arc magma, which can be proved to be formed in the subduction environment before collision. This contradiction can be used to judge that it was formed in the early stage of plate collision, when the New Tethys Ocean was just closed. Zircon U-Pb dating shows that the age of the Sangeda rock body, i.e., the closing time of the NeoTethys Ocean is 47.6 鹵2.2 Ma. According to previous studies, the Zedang ophiolite suite in Tibet was formed in the subduction environment of the plate, and the U-Pb age of zircon is 154.9Ma 鹵2.0 Ma, indicating that the subduction of the plate has lasted at least about 110Ma. That is, the New Tethys Ocean has been closed in this 110Ma time range. Taking the average expansion rate of the North Atlantic for nearly 34 mm/ years as the lower limit of the closure rate of the New Tethys Ocean, it is calculated that the lower limit of the New Tethys Ocean scale is 3470 km.
【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】：2017
【分類號】：P588.124;P542
，
本文編號：2402939
[Abstract]:The collision between the Indian plate and Eurasia resulted in the closure of the New Tethys Ocean, but many explanations were provided for the time of its closure from different angles. The Zedang ophiolite suite is the largest ophiolite block in the eastern segment of the Yalu Zangbo River suture zone. The Zedang Sangoda amphiolite intrusion in this paper is located in the ophiolite, mainly composed of fine-grained hornblende gabbro, porphyry hornblende gabbro, megacrystalline hornblende gabbro. The five units are composed of amphibolite and amphibolite. There are many names of the hornblende gabbro body in Zedang area, such as basalt, adakite and so on. We find that these rocks are different parts of the same rock mass in time. In this paper, it is shown by detailed research that it belongs to intrusive rocks, and in the TAS diagram, almost all the projection points of hornblende gabbro fall into the gabbro area and belong to the basic rock category. In the Huck diagram of Zedang hornblende gabbro it can be seen that hornblende is brought into the rock body by other magma and a large number of hornblende and magma are not in equilibrium in the rock mass. The general distribution trend of trace elements in rock samples is similar, the large ion lithophile elements and La elements such as Cs,Rb,Th,K,Ba are relatively enriched, the high field strength elements such as Ta,Nb,Ti,Th are depleted, and the Sr anomaly is positive. It has the characteristics of island arc magma in plate subduction environment. The standardized REE distribution patterns of chondrites are consistent, indicating that these hornblende gabbro have the characteristics of homologous magma series. The closing time of the New Tethys Ocean has not been always known, and the Sangda diorite found in this paper can be used to judge the time of initiation and completion of the collision between the Indian plate and the Asian plate. The amphiolite intrusion is between serpentine peridotite (passive continental margin) and andesite (active continental margin volcanic-sedimentary formation), indicating that it was formed after collision. The hornblende gabbro is rich in volatile matter and is characterized by arc magma, which can be proved to be formed in the subduction environment before collision. This contradiction can be used to judge that it was formed in the early stage of plate collision, when the New Tethys Ocean was just closed. Zircon U-Pb dating shows that the age of the Sangeda rock body, i.e., the closing time of the NeoTethys Ocean is 47.6 鹵2.2 Ma. According to previous studies, the Zedang ophiolite suite in Tibet was formed in the subduction environment of the plate, and the U-Pb age of zircon is 154.9Ma 鹵2.0 Ma, indicating that the subduction of the plate has lasted at least about 110Ma. That is, the New Tethys Ocean has been closed in this 110Ma time range. Taking the average expansion rate of the North Atlantic for nearly 34 mm/ years as the lower limit of the closure rate of the New Tethys Ocean, it is calculated that the lower limit of the New Tethys Ocean scale is 3470 km.
【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】：2017
【分類號】：P588.124;P542
，
本文編號：2402939
本文鏈接：http://sikaile.net/kejilunwen/diqiudizhi/2402939.html
最近更新
教材專著
