本文關(guān)鍵詞： 雅魯藏布縫合帶 日喀則弧前盆地 混雜巖 放射蟲(chóng) 侏羅紀(jì)-白堊紀(jì)　出處：《中國(guó)地質(zhì)大學(xué)(北京)》2016年博士論文　論文類(lèi)型：學(xué)位論文

【摘要】：雅魯藏布縫合帶位于青藏高原南部,代表了新特提斯洋消減閉合的部位。一直以來(lái),該縫合帶內(nèi)的蛇綠巖帶被公認(rèn)是新特提斯洋巖石圈的殘留。它們與雅魯藏布縫合帶中相關(guān)的海相地層共同記錄了新特提斯洋演化及印度與歐亞板塊碰撞過(guò)程。近年來(lái),國(guó)內(nèi)外學(xué)者在雅魯藏布縫合帶進(jìn)行了大量卓有成效的研究,為認(rèn)識(shí)新特提斯洋的演化提供了重要證據(jù)。但是,目前關(guān)于雅魯藏布縫合帶的研究重點(diǎn)集中在該蛇綠巖的同位素年代格架和地球化學(xué)屬性等方面,對(duì)該縫合帶內(nèi)海相地層的古生物學(xué)和沉積學(xué)等方面的研究相對(duì)薄弱,使得對(duì)新特提斯洋的演化缺乏系統(tǒng)認(rèn)識(shí)。本文以雅魯藏布縫合帶西段仲巴地區(qū)的侏羅-白堊紀(jì)含放射蟲(chóng)遠(yuǎn)洋硅質(zhì)(泥)巖以及中段日喀則弧前盆地白堊紀(jì)沖堆組底部硅質(zhì)巖為研究對(duì)象,開(kāi)展了古生物地層學(xué)、沉積學(xué)和鋯石U-Pb年代學(xué)等研究,取得了如下主要認(rèn)識(shí)。在雅魯藏布縫合帶西段仲巴地區(qū)混雜巖帶中實(shí)測(cè)了7條海相地層剖面。從其中放射蟲(chóng)硅質(zhì)巖中,鑒定出了中生代放射蟲(chóng)31個(gè)屬,42個(gè)種;識(shí)別出了4個(gè)侏羅紀(jì)放射蟲(chóng)組合和5個(gè)白堊紀(jì)放射蟲(chóng)組合。結(jié)合野外地質(zhì)觀察和構(gòu)造分析,本文將該地區(qū)傳統(tǒng)上被認(rèn)為是正常沉積地層的桑單林組、郭雅拉組和鹽多組理解為混雜巖,并將其分解為5個(gè)構(gòu)造巖組:馬泉河巖組、塔瓦巖組、爾捌巖組、衣桑巖組和踏弄巖組。根據(jù)江木那混雜巖中放射蟲(chóng)的年代序列,重建了大洋板塊地層格架,揭示了新特提斯洋在中侏羅世-早白堊世的演化過(guò)程,即在早阿普特期,從遠(yuǎn)洋放射蟲(chóng)硅質(zhì)巖轉(zhuǎn)變成陸源碎屑為主的泥巖,暗示了新特提斯洋開(kāi)始俯沖,與蛇綠巖年代學(xué)和地球化學(xué)研究成果吻合。而侏羅紀(jì)-白堊紀(jì)的放射蟲(chóng)年代,也否定了前人將該套地層定為始新世的認(rèn)識(shí)。在雅魯藏布縫合帶中段納蝦、群讓、則嘎普等地日喀則弧前盆地沖堆組海相地層實(shí)測(cè)了6條剖面。在其底部硅質(zhì)巖中鑒定出早白堊世放射蟲(chóng)18個(gè)屬,26個(gè)種,并識(shí)別出5個(gè)放射蟲(chóng)組合,顯示其時(shí)代為晚巴列姆-晚阿普特期,與仲巴地區(qū)硅質(zhì)泥巖時(shí)代一致。沖堆組上部碎屑巖在QFL圖解中,均落入未切割巖漿弧-過(guò)渡巖漿弧區(qū)域。而碎屑鋯石U-Pb年齡表現(xiàn)為顯著的110Ma的單峰分布,與岡底斯巖漿巖年齡峰值吻合,表明岡底斯可能是沖堆組碎屑物的主要源區(qū)。通過(guò)上述研究,并結(jié)合沖堆組與蛇綠巖沉積不整合的接觸關(guān)系,說(shuō)明新特提斯洋在早白堊世晚期開(kāi)始俯沖,日喀則弧前盆地開(kāi)始發(fā)育,并接受來(lái)自岡底斯島弧的碎屑物質(zhì)。
[Abstract]:The Yalu Zangbo suture zone, located in the southern part of the Qinghai-Tibet Plateau, represents the subduction and closure of the Neo-Tethys Ocean. The ophiolite belt in the suture zone is recognized as a remnant of the Neo-Tethys lithosphere. They are associated with the marine strata in the Yarlung Zangbo suture belt to record the evolution of the Neo-Tethys Ocean and the collision process between India and the Eurasian plate. Years ago. Scholars at home and abroad have done a great deal of fruitful research in the Yalu Zangbu suture zone, which provides important evidence for understanding the evolution of the New Tethys Ocean. At present, the study of Yalu Zangbo suture zone focuses on the isotopic chronological framework and geochemical properties of the ophiolite. The paleontology and sedimentology of marine strata in the suture zone are relatively weak. In this paper, the Jurassic-Cretaceous ocean-going siliceous (mud) containing radiolarian in the Zhongba area of the western section of the Yalu Zangbo suture belt is used to make a lack of systematic understanding of the evolution of the Neo-Tethys Ocean. Rocks and siliceous rocks at the bottom of the Cretaceous Chong heap formation in the Xigaze forearc basin in the middle segment are the objects of study. Paleontological stratigraphy, sedimentology and zircon U-Pb geochronology have been carried out. Seven marine stratigraphic sections have been measured in the melange belt in the western section of the Yalu Zangbo suture belt. 31 genera of radiolarian have been identified from the radiolarian siliceous rocks. 42 species; Four Jurassic radiolarian assemblages and five Cretaceous radiolarian assemblages have been identified. Combined with field geological observation and structural analysis, this paper considers this area to be a normal sedimentary formation of Sundanlin formation. The Guoyala formation and the Yanduo formation are understood as melange and decomposed into five tectonic formations: maquanhe formation, Tahuyan formation and lxxiyan formation. According to the age series of radiolarian in Jiangmona melange, the stratigraphic framework of oceanic plate was reconstructed, and the evolution of the NeoTethys ocean during the Middle Jurassic to early Cretaceous was revealed. That is, in the early Apt period, it changed from distant-water radiolarian siliceous rock to land-based clastic mudstone, which indicated that the new Tethys ocean began to subduction. The age of radiolarian from Jurassic to Cretaceous also negates the previous understanding that the strata were defined as Eocene. Six sections were measured in the marine stratigraphy of the chongdui formation in Xigaze forearc basin, etc. 18 genera and 26 species of early Cretaceous radiolarian were identified in the siliceous rocks at its bottom, and 5 radiolarian assemblages were identified. It shows that its age is the late Barreem-late Aputte epoch, which is consistent with the age of siliceous mudstone in Zhongba area. The upper clastic rocks of the Chongdui formation are in the QFL diagram. The U-Pb age of clastic zircon shows a significant single-peak distribution of 110 Ma, which coincides with the peak age of Gangdis magmatic rocks. It is suggested that Gangdis may be the main source of clastic material in the alluvial formation. Through the above study and the contact relationship between the alluvial formation and ophiolite deposits, it is concluded that the Neo-Tethys Ocean began to subduction in the late early Cretaceous. The Xigaze forearc basin developed and received debris from the Gangdis Island Arc.
【學(xué)位授予單位】：中國(guó)地質(zhì)大學(xué)(北京)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類(lèi)號(hào)】：P534.5;Q915

【參考文獻(xiàn)】

相關(guān)期刊論文 前10條

1 魏玉帥;李亞林;陳曦;王成善;李祥輝;李鑫;鐘瀚m，

本文編號(hào)：1474196