發(fā)布時間：2018-03-24 14:23

  本文選題：中國　切入點：東南　出處：《中國科學(xué)技術(shù)大學(xué)》2017年博士論文

【摘要】：板內(nèi)玄武巖的起源和成因已經(jīng)持續(xù)爭論了數(shù)十年,至今仍在不斷引起地球化學(xué)家討論與關(guān)注。板內(nèi)玄武巖具有的富集地球化學(xué)特征往往被地球化學(xué)家和地幔源區(qū)中來自地球淺部圈層再循環(huán)物質(zhì)聯(lián)系起來。中國東部地區(qū)新生代廣泛發(fā)育板內(nèi)玄武巖,為研究再循環(huán)物質(zhì)組分在大陸板內(nèi)玄武巖源區(qū)的貢獻,以及俯沖活動對板內(nèi)玄武巖的影響提供了可能。當前已有的研究表明中國東部新生代玄武巖源區(qū)中富集組分的可能來自于:(1)俯沖板塊中的再循環(huán)洋殼或者大洋沉積物;(2)中生代拆沉的加厚大陸下地殼/巖石圈地幔;(3)具有富集特征大陸巖石圈地幔。中國東部地區(qū)自中生代以來經(jīng)歷了復(fù)雜的地質(zhì)過程。中國東部地區(qū)自中生代以來經(jīng)歷了多期次的俯沖事件,地球物理地震圖像表明俯沖的太平洋板塊至今還滯留在地幔過渡帶(MTZ)中,同時,地球物理地震圖像證據(jù)也表明在長白山和海南島地區(qū)可能存在有地幔柱結(jié)構(gòu)。中國東部地區(qū)的復(fù)雜地質(zhì)歷史背景為研究不同地質(zhì)背景下的玄武巖源區(qū)的差別提供了可能。中國東南沿海新生代板內(nèi)玄武巖下部的三種不同地幔結(jié)構(gòu)特征:地球物理地震圖像表明中國東南沿海地區(qū)北部地區(qū)(浙江地區(qū)與江西地區(qū))下的地幔過渡帶里有滯留的太平洋俯沖板塊存在;中部地區(qū)(福建與廣東北部)的MTZ深度的地震波異常逐漸減弱直至消失;海南島與雷州半島有地幔柱結(jié)構(gòu)存在。水和Ce在巖漿和地幔礦物中的分配行為相近似,其比值在巖漿演化過程(部分熔融和分離結(jié)晶)中不會發(fā)生明顯改變,同時,不同種類的再循環(huán)物質(zhì)組分具有不同的H20/Ce比值,并且區(qū)別于DMM的H20/Ce比值。如果將玄武巖的H20/Ce與Ba/Th、Nb/La、Ce/Pb等微量元素比值相結(jié)合,可以判斷其地幔源區(qū)是否有再循環(huán)物質(zhì)存在,以及源區(qū)再循環(huán)物質(zhì)組的來源。同時,地表再循環(huán)物質(zhì)大多經(jīng)歷過淺部的低溫反應(yīng),通常具有與普通地幔迥異的氧同位素比值(δ18O),以鑒別再循環(huán)物質(zhì)存在與否。Liu et al.(2015 a和b)采用H20/Ce和δ18O聯(lián)合示蹤的方法提示出華北克拉通的新生代玄武巖中再循環(huán)物質(zhì)組份的存在。為了確定中國東南沿海地區(qū)新生代玄武巖中是否存在再循環(huán)物質(zhì)及其來源,本文分析了采自中國東南沿海地區(qū)具有不同地質(zhì)背景的新生代玄武巖的主微量元素組成、Sr-Nd-Pb放射性成因同位素組成、單斜輝石斑晶的水含量、主量元素組成、氧和Li同位素組成。隨后,依據(jù)O'Leary etal.(2010)提出的單斜輝石斑晶成分與水分配系數(shù)關(guān)系的經(jīng)驗方程,由單斜輝石斑晶主量元素組成計算出水在單斜輝石斑晶與玄武巖熔體中的分配系數(shù),進而反演出玄武巖漿的"原始"水含量,為中國東南沿海地區(qū)新生代玄武巖源區(qū)中富集組分的來源提出了新線索和制約:(1)浙江新生代玄武巖水含量分布范圍為1.3-2.6%,與島弧玄武巖和弧后盆地玄武巖的水含量一致。浙江新生代玄武巖主要噴發(fā)于兩個時代:20-27 Ma以及晚于11Ma。兩個時期噴發(fā)的玄武巖具有迥異的地球化學(xué)特征。偏老的玄武巖采自于西壟(XL)地區(qū),具有更高的堿含量、微量元素含量、La/Yb、Ce/Pb和Nb/La比值,更低的硅鋁含量,以及H20/Ce和Ba/Th比值。西壟玄武巖可以在蛛網(wǎng)圖上的觀察到強烈的K、Pb、Zr、Hf和Ti負異常,以及Nb(Ta)正異常。較年輕的新昌玄武巖(包括高坪(GP)和雙彩(SC)兩個地區(qū))具有比西壟玄武巖低的堿含量、微量元素含量、La/Yb、Ce/Pb和Nb/La比值,更高的硅鋁含量,以及更高的 H2O/Ce 和 Ba/Th 比值。Ba/La、H20/Ce、Nb/La、Ce/Pb 與 Ba/Th 之間協(xié)同的變化關(guān)系表明西壟新生代玄武巖源區(qū)除了虧損地幔以外還有再循環(huán)洋殼組分存在,新昌新生代玄武巖的源區(qū)除了 DMM與再循環(huán)洋殼組分以外,還含有再循環(huán)大洋沉積物組分。再循環(huán)物質(zhì)組分在浙江新生代玄武巖源區(qū)的連續(xù)變化表明在20-11Ma之間有新的再循環(huán)物質(zhì)的持續(xù)供給與加入。華南自中生代以來只受西向的太平洋俯沖的影響,因此浙江新生代玄武巖源區(qū)連續(xù)加入的再循環(huán)物質(zhì)組分只可能來源于滯留在地幔過渡帶內(nèi)的太平洋俯沖板塊。(2)福建新生代玄武質(zhì)巖石噴發(fā)或侵位于17Ma之后,其微量元素組成與GP和SC的浙江玄武巖相類似。明溪(MX)和石衡(SH)玄武巖在蛛網(wǎng)圖上具有明顯的Th、U、Pb、K、Zr、Hf和Ti負異常,而白琳(BL)輝綠巖在蛛網(wǎng)圖中不具有明顯的K、Zr、Hf和Ti異常。與浙江玄武巖都具有高水含量特征不同,福建地區(qū)三個采樣點的玄武質(zhì)巖石水含量差異較大:SH玄武巖的水含量為1.3-2.4%;MX玄武巖的水含量為0.3-0.5%;BL地區(qū)的輝綠巖的由于單斜輝石中的H經(jīng)歷過擴散,其表觀水含量為1.9%-2.1%。明溪新生代玄武巖的水含量明顯低于其他浙江和福建地區(qū)的新生代玄武巖,表明水在上地幔的分布具有明顯的不均一性。福建新生代玄武質(zhì)巖石中的單斜輝石斑晶具有高于普通地幔的δ18O值,表明其源區(qū)有再循環(huán)物質(zhì)組分的存在。最高的δ18O值出現(xiàn)在具有中等Si/Al和Ca/Al比值的單斜輝石斑晶中,表明多種含有不同比例再循環(huán)物質(zhì)組分的巖漿后混合。福建玄武質(zhì)巖石的H2O/Ce、Ba/La、Nb/La、Ce/Pb和Ba/Th之間協(xié)變關(guān)系,表明福建地區(qū)新生代玄武質(zhì)巖石的源區(qū)同樣存在再循環(huán)的大洋物質(zhì)組分。盡管現(xiàn)存的地球物理學(xué)證據(jù)表明,MX和SH下并沒有與滯留于于MTZ的俯沖太平洋板片,但是這些再循環(huán)組分可能來自于已經(jīng)下沉到地幔的俯沖大洋板片在上幔的零星殘留。如果考慮到福建玄武質(zhì)巖石的放射成因同位素并非過于富集,這些"消失"的俯沖大洋板片的年齡不可能太老,太平洋俯沖的可能性依然最大。(3)相對于浙江和福建新生代玄武巖,海南新生代玄武巖在微量元素蛛網(wǎng)圖上表現(xiàn)出多種類型的OIB-like特征,包括類似HIMU和類似EM的特征,表明海南玄武巖的源區(qū)相對于浙江和福建新生代玄巖源區(qū)具有更大的不均一性和復(fù)雜性。相對MORB而言,海南新生代玄武巖具有更富集的Sr-Nd-Pb放射成因同位素特征和不同于典型地幔值(+5.7‰)的δ18O值,表明其源區(qū)存在有再循環(huán)物質(zhì)。雷虎嶺(LH)新生代玄武巖單斜輝石斑晶的Li同位素剖面分析結(jié)果表明其在結(jié)晶后經(jīng)歷了 Li擴散,其與馬鞍嶺(ML)以及Sanjiaoyuan(SJY)近乎完全"干"的水含量特征并不是其源區(qū)的原始特征,而可能是單斜輝石斑晶結(jié)晶后H丟失的結(jié)果。在去掉受H丟失影響的樣品后,LH,大洋(DY)和�；�(FJT)玄武巖水含量分別為2.7%、1.3%以及2.6%。LH玄武巖具有類似HIMU的微量元素特征、高δ18O、低Ba/Th與H20/Ce比值表明其地幔源區(qū)存在再循環(huán)上部洋殼組分,少量的低δ18O單斜輝石斑晶表明除再循環(huán)部洋殼組分外,其源區(qū)可能還含有少量的再循環(huán)大洋下地殼的輝長巖組分。DY和FJT玄武巖的高Ba/Th、δ18O和H2O/Ce比值特征則表明其源區(qū)可能含有再循環(huán)的大洋洋殼和沉積物組分�？偟目磥�,具有不同地幔結(jié)構(gòu)的中國東南沿海新生代玄武巖源區(qū)都有再循環(huán)的洋殼物質(zhì)組分存在。中國東南沿海新生代玄武巖通常都具有與島弧玄武巖和弧后盆地玄武巖相類似的高水含量,即使這些玄武巖具有不同的放射性成因Sr-Nd-Pb同位素比值和微量元素特征。放射性成因Sr-Nd-Pb同位素比值和微量元素的變化表明中國東南沿海不同地區(qū)的玄武巖的地幔源區(qū)中的再循環(huán)大洋物質(zhì)組分組成不同,最有可能是受到了西向的俯沖的太平洋板塊的影響。
[Abstract]:The origin and genesis of intraplate basalt has been debated for decades, still continue to cause geochemist discussion and attention. With the enrichment of intraplate basalt geochemistry are Geochemists and mantle sources in shallow layers of material recycling from Earth linked. The eastern region of Cenozoic China widely developed for Inouchi Xuantakeiwa. Study on the recycling of material components in the continental intraplate basalt source contribution, provides the possibility and influence of subduction activities on intraplate basalt. The current research shows that Chinese Eastern Cenozoic basalt source region in the enriched components may come from: (1) the subducting plate of recycled oceanic crust or oceanic sediments; (2) the Mesozoic lower crust, and thickened sink / lithospheric mantle; (3) with enrichment characteristics of continental lithospheric mantle in the eastern region of China. Since the Mesozoic in experience The complicated geological process. In the eastern region of China experienced many times since Mesozoic subduction events, geophysical seismic images show that the subduction of the Pacific plate still stranded in the mantle transition zone (MTZ), at the same time, geophysical seismic image evidence also shows that there might be a mantle plume structure in Changbai Mountain and Hainan Island area. Provide the difference may be complex geological history background of Eastern China as research under different geological background of basalt source area. Three different mantle structure Chinese along the southeast coast of Cenozoic Basalt in the lower part of the plate: geophysical seismic images show that the northern coastal area of Southeast China (Zhejiang area and Jiangxi area) of the mantle transition zone. There are stranded in the subduction of the Pacific plate; the central region (Fujian and Northern Guangdong) seismic wave MTZ depth anomaly gradually weaken until disappeared; the sea The South Island and the Leizhou Peninsula exist mantle plume structure. The distribution behavior of water and Ce in magma and mantle mineral phase in the approximation, the ratio in the process of magmatic evolution (partial melting and fractional crystallization) will not change obviously, at the same time, different kinds of material recycling groups with different H20/Ce ratio, H20/Ce ratio and difference in DMM. If the H20/Ce and Ba/Th basalts of Nb/La, Ce/Pb and other trace element ratio combination, can determine whether the mantle source region have recycled material existence, and the source area of recycled substances group. At the same time, the surface of recycled substances have experienced low temperature shallow, usually with oxygen isotope ratios and ordinary different mantle (delta 18O), to identify the presence and absence of recycled substances (2015 a.Liu et al. and b) by H20/Ce and delta 18O combined tracer indication of the North China Craton Cenozoic basalts Recycle components. In order to determine the existence of recycled substances and new sources of the southeast coastal area of Chinese on behalf of Xuan Wuyan, this paper analyzes the main trace elements collected from the coastal area of Southeast China with different geological background of the new generation of Xuan Wuyan's composition, Sr-Nd-Pb radiogenic isotopic composition, water content of clinopyroxene phenocrysts, major elements composition, oxygen and Li isotope composition. Then, according to O'Leary etal. (2010) proposed empirical equations clinopyroxene phenocryst composition and water distribution coefficient, by Dan Xiehui phenocrysts major element composition distribution coefficient calculation of water in clinopyroxene phenocrysts and Xuan Wuyan in the melt, to reverse the "primitive basaltic magma" water content, put forward new clues and control for the source of the new enrichment group in southeast coastal areas of China generation Xuan Wuyan source region: (1) the new generation of Zhejiang Xuan Wuyan The distribution range of water content is 1.3-2.6%, and the water content of consistent basin basalts and arc Shima Xuantakeiwa. Zhejiang Cenozoic basalts mainly erupted in two times: the geochemical characteristics of 20-27 Ma and two 11Ma. later than the period of eruption of the basalt is different. The older basalts collected from the west ridge (XL) area, has alkali content is higher, the content of trace elements La/Yb, Ce/Pb, and Nb/La ratio, silicon aluminum content lower, and H20/Ce and Ba/Th ratio. The west ridge basalt in the spider diagram of the observed strong K, Pb, Zr, Hf and Ti negative anomalies, and Nb (Ta) is abnormal. The younger the basalt of Xinchang (including Gaoping (GP) and Shuangcai (SC) two area) with west ridge basalts with low alkali content, La/Yb content of trace elements, Ce/Pb, Nb/La and the ratio of silicon, aluminum content higher, and higher H2O/Ce and Ba/Th ratios of.Ba/La, H20/Ce, Nb/La, Ce/Pb and B The relationship between a/Th showed synergistic ridge Cenozoic source region of West Xuan Wuyan in addition to depleted mantle besides recycled oceanic crust components exist, the source area of Xinchang new generation of Xuan Wuyan in addition to the DMM and recycled oceanic crust components, also containing recycled oceanic sediment components. The recycling material group changes continuously in Zhejiang new generation Xuan Wuyan source the show at 20-11Ma between the continuous supply of new material recycling and join. Effects of Southern China since Mesozoic only by westward subduction of the Pacific, so the recycle group of Zhejiang new generation Xuan Wuyan source area continuous addition only may be derived from the mantle transition zone in the stranded in the subduction of the Pacific plate. (2) after the eruption of basaltic rocks or invade Fujian Cenozoic is located in 17Ma, the trace element composition similar to GP and SC in Zhejiang. Mingxi basalt (MX) and Shi Heng (SH) Xuan Wuyan in the spider net With Th, Pb, K map U, Zr, Hf and Ti negative anomalies, and Bai Lin (BL) - has no obvious K in the spider diagram of Zr, Hf and Ti anomalies. And Zhejiang basalt are characterized by high water content in different regions of Fujian, the three sampling points of basaltic rock water content is quite different: the water content of SH basalt is 1.3-2.4%; water content MX basalt is 0.3-0.5%; BL region because of diabase in clinopyroxene H through diffusion, its apparent water content water content 1.9%-2.1%. Mingxi Cenozoic basalts from Zhejiang and Fujian was significantly lower than that in other regions of the Cenozoic basalts, shows that water inhomogeneity in the distribution of upper mantle. The Fujian Cenozoic basaltic rocks in clinopyroxene phenocrysts with delta 18O is higher than that of normal mantle values showed that the source region of recycle material composition. 8 18O the highest value appeared in medium and Si/Al The ratio of the grouper clinopyroxene crystal Ca/Al, showed that many components with different proportion of recycled magma mixing. Fujian basaltic rock H2O/Ce, Ba/La, Nb/La, Ce/Pb and Ba/Th between the covariant relations, indicating that the oceanic material formation in Fujian area of Cenozoic basaltic rocks in the source region are also recycled. Although the physics of the earth the existing evidence suggests that MX and SH were not associated with the subduction of the Pacific plate held in MTZ, but these recycling components may come from the already sinking to the subducted oceanic slab mantle in the mantle of the scattered residue. If taking into account the radiogenic isotope basaltic rocks in Fujian are not too rich, these "dive the ocean plate disappeared" film age may not be too old, the possibility of the subduction of the Pacific is still the largest. (3) compared with the Zhejiang and Fujian Cenozoic basalts, Hainan Cenozoic basaltic rocks in the trace Element spider diagram showing OIB-like characteristics of various types, including features like HIMU and similar EM, showed that the source region of Hainan basalts relative to Zhejiang and the Fujian Cenozoic dolerite source region is uneven and greater complexity. Compared with MORB, the Hainan Cenozoic basaltic rocks have isotopic characteristics of Sr-Nd-Pb radiation causes more enrichment and different from the typical mantle value (+5.7%) of the 18O values, show that the source region has recycled material. Lei Huling (LH) Li isotope profile analysis results of Cenozoic basalts indicate that the clinopyroxene Shi Banjing experienced Li diffusion after crystallization, and the Saddle Ridge (ML) and Sanjiaoyuan (SJY) the original features almost completely "dry" water content is not in the source area, and may be clinopyroxene phenocryst after crystallization. In the result of the loss of H removed by H lost samples, LH, ocean (DY) and Fuji (FJT) Tian Xuan Wu rock water content were 2.7%, 1.3% and 2.6%.LH characteristics of trace elements in basalt is similar to HIMU, high Ba/Th and low 18O value, H20/Ce ratio showed that the recycling of the upper oceanic crust component on the mantle source region, a low delta 18O clinopyroxene phenocrysts showed that except the shell group were divided into.DY ocean recirculation, and FJT basalts the high Ba/Th group gabbro in the source area may also contain a small amount of recycled oceanic crust, Delta 18O and H2O/Ce ratios show that the source region containing recycled oceanic crust and sediment components. In general, the new oceanic crust group in southeast coastal Chinese generation basalt source areas with different structures of the mantle the recycle. China along the southeast coast of the Cenozoic basalts are usually with high water content and Shima Xuantakeiwa back arc basin basalt is similar, even if these basalts have different radioactivity into Because of the Sr-Nd-Pb isotope and trace element characteristics. Indicating that the change of radiogenic Sr-Nd-Pb isotope and trace elements of recycled oceanic material group in different areas of southeast coastal China basalt mantle source region of different components, most likely to be affected by the west to the Pacific plate subduction.

【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：P588.145
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本文編號：1658687