本文關(guān)鍵詞： 玳瑁海山及鄰近陸域 玄武巖 地化分析 構(gòu)造演化　出處：《中國地質(zhì)大學(xué)(北京)》2015年博士論文　論文類型：學(xué)位論文

【摘要】：玳瑁海山位于南海海盆北部,其16.7-14.4Ma的噴發(fā)年齡與南海海盆擴張的結(jié)束時段(～15.5Ma)大體相當(dāng),而且提供了現(xiàn)存南海海山唯一的MORB型玄武巖樣品,從年代學(xué)和巖石地球化學(xué)角度衡量都具有難以替代的分析價值。南海及其鄰近陸域在新生代存在兩次重大構(gòu)造-巖漿事件：發(fā)生于古新世末至晚始新世(60-～40Ma)的三水盆地和中中新世以后(15Ma)的我國雷瓊地區(qū)與越南中部的嵬嵩-呵叻地區(qū)。本文為考察南海演化各階段的基本特點,利用當(dāng)前能夠獲得的南海擴張前(三水盆地)、擴張晚期(玳瑁海山)和擴張停止之后(雷瓊、]嵩地區(qū))的玄武巖樣品,在建立基于LA-ICP-MS技術(shù)的高精度分析方法,對樣品中70個元素進行分析,其中特別包括含量為ppb級別的親鐵元素和親硫元素。力圖將不同時段和不同地域的分析結(jié)果納入同一過程體系,通過對比研究建立它們在深部和構(gòu)造上的關(guān)聯(lián)。玳瑁海山的MOBR型樣品來自DM虧損端元,而所有OIB型玄武巖樣品均源自一個DM和EM2的雙端元混合源區(qū)。其中,DM源區(qū)類似MORB虧損地幔源區(qū)而EM2源區(qū)則來自俯沖的洋殼物質(zhì)再循環(huán)。研究區(qū)火山巖源區(qū)的部分熔融深度和潛在溫度均低于深部地幔柱成因的夏威夷或冰島玄武巖；而相較于南海北、西部陸緣玄武巖源區(qū),玳瑁海山則更低。此外,樣品中親鐵及親硫元素,特別是W的含量也明顯低于深源熱點型OIB,進一步說明研究區(qū)幔源EM2組分并非來自下地幔深部或核幔邊界。對應(yīng)南海及其相鄰陸域火山巖巖石地球化學(xué)特征所約束的源區(qū)深部過程,本研究認(rèn)為：在中新生代之交,由于華南大陸巖石圈的大規(guī)模減薄和水平位移,誘使研究區(qū)的某些地點軟流圈顯著抬升,加大上地幔熔融量并形成大量巖漿在三水盆地廣泛噴發(fā),構(gòu)成淺源地幔柱和主動型大陸裂谷表象,與其后的南海張裂本來存在機制關(guān)聯(lián)。但是南海海盆的擴張最終還是由印度板塊擠入歐亞大陸的“擠出效應(yīng)”所控制,強烈的大陸塊體的遷移運動“壓制”并取代淺源地幔柱的“熱點效應(yīng)”成為南海開裂的主控因素；強勢的構(gòu)造拉張運動使得巖石圈發(fā)生分熔,并對洋殼和海山的形成提供物質(zhì)來源。南海擴張停止后,區(qū)域邊界條件發(fā)生改變,導(dǎo)致類似三水與軟流圈關(guān)系密切的“淺源熱點”現(xiàn)象在雷瓊、昆嵩、呵叻等地“復(fù)蘇”。
[Abstract]:The tortoiseshell seamounts are located in the northern part of the South China Sea basin, and the eruption age of 16.7-14.4 Ma is roughly similar to that of 15.5Ma at the end of the South China Sea basin extension. The only MORB basalt samples are provided in the seamounts of the South China Sea. There are two major tectonic-magmatic events in the South China Sea and its adjacent continental areas during the Cenozoic: from the end of Paleocene to the late Eocene (from the end of Paleocene to the late Eocene) (from the late Paleocene to the late Eocene). The Sanshui basin of 60-40 Ma and the Raiqiong area of China and the Wei Song-Kalat area of central Vietnam. The basic characteristics of the evolution stages in the South China Sea are discussed in this paper. Basalt samples from the South China Sea before (Sanshui basin), late expansion (hawksbill seamounts) and after the extension (Leiqiong,] Yunsong area) are used. A high precision analysis method based on LA-ICP-MS was established to analyze 70 elements in the sample. In particular, it includes the content of ppb level of iron and sulfur elements, trying to bring the results of different time and different regions into the same process system. The MOBR type samples of the tortoiseshell seamounts are derived from DM depleted end elements. All OIB basalt samples are derived from a mixed source of DM and EM2. The DM source region is similar to the MORB depleted mantle source region, while the EM2 source region is derived from the subducted oceanic crust material recycling. The partial melting depth and potential temperature of the volcanic source region in the study area are lower than those in Hawaii, where the deep mantle plume was formed. Or Icelandic basalt; Compared with the northern part of the South China Sea, the tortoiseshell seamounts are lower than those in the northern part of the South China Sea. In addition, the contents of Fe and S, especially W, in the samples are obviously lower than those in the deep-source hot spot type OIB. It is further explained that the EM2 component of mantle source in the study area is not derived from the lower mantle or the core mantle boundary, and corresponds to the deep source process restricted by the geochemical characteristics of volcanic rocks in the South China Sea and its adjacent continental regions. This study suggests that at the turn of Mesozoic and Cenozoic, the large scale thinning and horizontal displacement of the continental lithosphere in South China induced a significant uplift of the asthenosphere in some locations in the study area. Increasing the amount of melting of the upper mantle and forming a large amount of magma erupting widely in the Sanshui basin, forming the shallow mantle plume and active continental rift surface. However, the expansion of the South China Sea basin is ultimately controlled by the "crowding effect" of the Indian plate into Eurasia. The strong migration movement of continental block "suppresses" and replaces the "hot spot effect" of shallow mantle plume as the main controlling factor of South China Sea cracking. The strong tectonic extensional movement caused the lithosphere to melt and provided material source for the formation of oceanic crust and seamounts. After the South China Sea extension stopped the regional boundary conditions changed. Leading to similar Sanshui and soft circle close relationship between the "shallow hot spot" phenomenon in Lei Qiong, Kunsong, Kulat, and other places, "recovery."
【學(xué)位授予單位】：中國地質(zhì)大學(xué)(北京)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：P588.145;P736.1

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