本文選題：大別山　切入點：金紅石　出處：《中國科學技術大學》2016年博士論文　論文類型：學位論文

【摘要】：位于中國東部的大別蘇魯造山帶是由三疊紀時華南板塊與華北板塊碰撞而形成的。郯城-廬江斷裂帶將大別蘇魯造山帶分成兩部分,分別為西部的大別造山帶和東部的蘇魯造山帶�？率⒑徒饎偸陌l(fā)現(xiàn)及對冷卻歷史的研究表明華南板塊曾經(jīng)俯沖到地幔深度(100km),而后快速折返至地表。本論文的樣品采自位于中大別中溫超高壓變質(zhì)帶的雙河和碧溪嶺地區(qū),所選取的樣品為新鮮榴輝巖及退變質(zhì)榴輝巖,旨在以金紅石和鐵同位素為切入點,通過對比新鮮榴輝巖和退變質(zhì)榴輝巖中的痕量元素地球化學和同位素地球化學數(shù)據(jù),探討在折返階段的退變質(zhì)過程中元素和同位素的地球化學行為。本論文的第一個工作主要研究雙河地區(qū)的大顆粒金紅石的精細結(jié)構、微量元素含量、氧同位素組成、拉曼光譜等地球化學參數(shù)。相比于退變質(zhì)榴輝巖中的大顆粒金紅石,石英脈中的金紅石具有更高含量的V和U,更低含量的Nb、Ta、Cr和W。兩種產(chǎn)狀的金紅石具有相似的氧同位素值、Zr/Hf、Zr、Hf和Mo含量。石英脈中的金紅石具有更低的Nb/Ta值,指示脫水反應時產(chǎn)生的流體相較殘留相具有較大的Ta分配系數(shù)。退變質(zhì)榴輝巖中的大顆粒金紅石周圍存在退變質(zhì)的產(chǎn)物榍石,在金紅石和榍石的邊界,觀測到Nb從榍石向金紅石的“反擴散”現(xiàn)象。拉曼光譜及EBSD的結(jié)果顯示,兩個表現(xiàn)為大顆粒金紅石的整個晶體方向并不一致,分成不同晶體方向的小顆粒金紅石以及線狀的膝折帶。鏡下觀察和實驗結(jié)果顯示,大顆粒的金紅石的形成過程應該有四個階段,分別是：1)小顆粒金紅石的形成；2)在金紅石塑性的情況下,形成塑性膝折帶；3)金紅石由轉(zhuǎn)為脆性后,受到應力作用而形成脆性膝折帶；4)在后期,金紅石的物理破裂。本論文的第二個工作研究了碧溪嶺超高壓榴輝巖巖體的全巖和單礦物的鐵同位素組成與鐵價態(tài)組成,以示蹤在折返過程中的氧逸度等地球化學參數(shù)變化。穆斯堡爾譜結(jié)果顯示,退變質(zhì)榴輝巖中的Fe~(3-)/ΣFe值比新鮮榴輝巖的Fe~(3+)/EFe值高,指示退變質(zhì)反應和流體交代過程中氧逸度的升高。碧溪嶺榴輝巖的全巖的鐵同位素組成相對均一,δ~(56)Fe值的變化范圍是從0.00±0.07‰到0.16±0.07‰。如此均一的鐵同位素組成是從其原巖,即地幔玄武質(zhì)巖漿的堆晶體中繼承的,反映了在板塊俯沖折返過程中其鐵同位素組成改變不大。石榴石具有相對均一的鐵同位素組成(δ~(56)Fe值為-0.08±0.07‰到0.02±0.07‰),而共存的綠輝石具有相對變化較大的鐵同位素組成(δ~(56)Fe值為0.15±0.07‰到0.47±0.07‰)。同時,綠輝石也具有變化范圍更大的Fe~(3+)/∑Fe值(0.367±0.025到0.598±0.024),指示綠輝石可能在峰期變質(zhì)之后的折返過程中受到改造。相比于新鮮榴輝巖中的綠輝石(～0.37),退變質(zhì)榴輝巖中的綠輝石具有更高的Fe~(3+)/ΣFe值(0.54-0.60),而兩種榴輝巖中的石榴石的Fe~(3+)/ΣFe值相對均一(0.039±0.013到0.065±0.022)。研究表明,石榴石中相對均一的鐵同位素組成及三價鐵含量指示石榴石在退變質(zhì)反應中受到的改造很小,基本保留了其峰期變質(zhì)的δ~(56)Fe值和Fe~(3+)/ΣFe值。因為Fe和Mg在石榴石和綠輝石的擴散速率類似,而且已有的研究表明石榴石和綠輝石之間的Mg同位索在峰期變質(zhì)時達到了平衡,因此可以推定石榴石和綠輝石之間的Fe同位素在峰期變質(zhì)時也應該達到了平衡。退變質(zhì)榴輝巖中升高的三價鐵比值及變化的△56Fe綠輝石-石榴石指示退變質(zhì)過程中氧逸度高的流體交代作用會導致綠輝石的鐵同位素組成上升。計算擬合的結(jié)果表明,在600-650℃時,綠輝石中的Fe~(2+)和Fe~(3+)之間的鐵同位素分餾值為～0.98%。。擬合結(jié)果整理成礦物內(nèi)的溫度計的形式為：δ~(56)Fe~(3+)_(綠輝石)-δ~(56)Fe~(2+)_(綠輝石)=75-84×10~4/T~2(T為開爾文溫度)。
[Abstract]:Chinese is located in the eastern Dabie Su Lu orogenic belt was formed by the Triassic collision of Southern China plate and North China plate formed. The Su Lu Dabie orogenic belt is divided into two parts of Tancheng - Lujiang fault zone, respectively for the western part of the Dabie orogenic belt and the eastern part of the Su Lu orogenic belt. Coesite and diamond discovery and Research on the cooling history that was Southern China plate subduction to mantle depths (100km), and then rapid exhumation to the surface. The samples were collected from the Dabie is located in the middle temperature ultra high pressure metamorphic belt in Shuanghe and Bixiling area, selected samples of fresh eclogite and retrograde eclogite, to rutile and Fe isotopes as a breakthrough by contrast, fresh eclogite and retrograde Eclogite in the trace element and isotope geochemistry data, explore the retrograde metamorphism in the exhumation stage of elemental and isotopic geochemistry for For the fine structure of large particles. Jin Hongshi is the first work of this thesis mainly studies the Shuanghe area. The contents of trace elements, oxygen isotope composition, the Raman spectra of geochemical parameters such as large particles. Jin Hongshi compared to Eclogite in the Jin Hongshi quartz vein has a higher content of V and U, lower the content of Nb, Ta, Cr and W. two kinds of occurrence of Jin Hongshi with oxygen isotope values similar to that of Zr/Hf, Zr, Hf and Mo. The content of Jin Hongshi in quartz vein has a lower Nb/Ta value, indicating the fluid dehydration reaction compared with Ta residual phase distribution coefficient is greater. There is the product of retrograde titanite Eclogite in the large particles around Jin Hongshi, Jin Hongshi and sphene boundary, observed Nb from titanite to Jin Hongshi's "anti diffusion phenomenon. Raman spectra and EBSD results show that the performance of two large granular rutile crystal whole The body direction is not consistent, divided into different crystal orientation of small particles and Jin Hongshi linear kink band. Observation and experimental results under the microscope showed that the formation process of Jin Hongshi particles should have four stages, respectively is: 1) the formation of small particles of Jin Hongshi; 2) Jin Hongshi in the plastic case, plastic forming knee fold belt; 3) by Jin Hongshi to brittle stress, and the formation of brittle kink band; 4) in the later period, Jin Hongshi's physical rupture. The second work of Bixiling eclogite rocks of whole rock and mineral iron isotope composition and valence state of iron composition, oxygen fugacity in the tracer and other geochemical parameters during the exhumation process changes. The Mossbauer spectrum showed that the Eclogite in the Fe~ (3-) / Sigma Fe value than fresh eclogite Fe~ (3+) /EFe value is high, indicating retrograde metamorphic reactions and fluid metasomatism in the process of oxygen 閫稿害鐨勫崌楂，

本文編號：1595564