【摘要】：滇西三江地區(qū)位于喜馬拉雅-特提斯構造域的東端與環(huán)太平洋構造域的匯合部,受到太平洋板塊、印度洋板塊和歐亞板塊的共同影響,經(jīng)歷了特提斯形成演化、印度-歐亞大陸碰撞以及高原隆升的復雜過程。區(qū)內(nèi)發(fā)育的臨滄復式花崗巖基是區(qū)域出露面積最大的復式巖基,是古特提斯構造域中的重要單元,本文在野外調(diào)研的基礎上,對位于臨滄復式花崗巖基北緣的云南鳳慶西老黃墳中酸性侵入巖巖石學、元素地球化學等方面的研究,結(jié)合區(qū)域上已有成果,旨在對其成因和形成時代以及區(qū)域構造巖漿演化提供約束。研究發(fā)現(xiàn)鳳慶西老黃墳巖體位于大勐龍變質(zhì)帶上,主要巖性為黑云母石英閃長巖,局部間夾有花崗閃長巖,呈不規(guī)則狀、孤島狀或條帶狀分布于主巖體中,燕山晚期花崗巖呈小巖體侵位其中。巖石表面風化較重,主要表現(xiàn)為綠泥石化、硅化、鉀化、鈉黝簾石化、絹云母化。部分地段受韌性剪切的變形變質(zhì)作用影響尚有部分糜棱巖化、初糜棱巖化巖石。礦物化學分析顯示,巖石中的斜長石為中酸性斜長石;黑云母為鎂質(zhì)黑云母,但具有向鐵質(zhì)黑云母過渡的趨勢;角閃石主要為陽起石和鎂鈉閃石,為變質(zhì)及交代成因的角閃石。以上特征表明該巖體在結(jié)晶成巖過程中一定程度上受到富硅堿流體交代蝕變及燕山期淺動力變質(zhì)作用。元素地球化學分析顯示,該巖體的SiO2含量為64.2%~69.56%,平均為66.83%,K2O/Na2O為1.51~27.42,平均為9.25,A/CNK為1.025~2.906,平均為1.87,總體顯示SiO2含量偏高,該巖體為過鋁質(zhì)高鉀鈣堿性花崗巖,具有明顯的輕稀土富集,重稀土虧損,大離子親石元素相對富集,過渡元素相對虧損的特征。以上特征進一步表明該巖漿過程與板片俯沖碰撞過程中伴隨深部流體交代作用有關。結(jié)合Zr-TiO2、黑云母TFeO/(TFeO+MgO)-MgO、1000Ga/Al2O3-K2O/MgO、CaO/Na2O-Al2O3/TiO2、Rb/Ba-Rb/Sr和La/Sm-La等圖解判斷鳳慶西老黃墳巖體并非單一殼源巖漿經(jīng)簡單結(jié)晶分異而來,而是經(jīng)歷了復雜構造-巖漿作用,分離結(jié)晶作用很明顯,由此推測該巖體是由地殼部分熔融的鈣堿性花崗巖漿,先經(jīng)過分離結(jié)晶作用,再經(jīng)過多次脈動和伴隨快速運移的低程度結(jié)晶分異形成的,在結(jié)晶過程中受到了一定程度的地幔流體的交代作用。鳳慶西老黃墳巖體與其他地區(qū)臨滄花崗基印支期及二疊紀巖體有著不同的巖相學特征,但有著相似的地球化學特征,進一步推測三者可能為相同或相近源區(qū)的巖漿作用的產(chǎn)物。其源巖為雜砂巖。形成環(huán)境為后碰撞。綜合研究認為,鳳慶西老黃墳巖體可能形成于二疊紀,屬臨滄復式花崗巖基過渡演化的巖體組成部分,是昌寧-孟連洋閉合,蘭坪-思茅陸塊與保山陸塊碰撞過程的產(chǎn)物。其主體形成機制上表現(xiàn)為在洋殼板塊俯沖消減導致大陸對接后碰撞條件下引發(fā)深部上地殼部分熔融的陸殼改造產(chǎn)物。
[Abstract]:The Sanjiang area in western Yunnan is located at the eastern end of the Himalayan Tethys tectonic domain and the confluence of the circum-Pacific tectonic domain. It is influenced by the Pacific plate, the Indian Ocean plate and the Eurasian plate, and has undergone the Tethys formation and evolution. Complex processes of India-Eurasia collision and plateau uplift. Lincan-type granite base developed in this area is the largest outcropping area and an important unit in the paleoTethys tectonic domain. The petrology and elemental geochemistry of acidic intrusive rocks in Laowangfen, Fengqing County, Yunnan Province, located in the northern margin of Lincang complex granite base, have been studied. The purpose of this paper is to provide constraints on the origin and formation of magma and the evolution of regional tectonic magma. It is found that the Laowangfen rock body in the west of Fengqing is located in the Damenglong metamorphic belt. The main lithology is biotite quartz diorite, and there is a granodiorite intercalated locally, which is irregular, isolated island or striped in the main rock mass. The late Yanshanian granite emplaced in small rock mass. The weathering of the rock surface is heavy, mainly manifested as green mud fossilization, silicification, potassium, sodium tetrahedrite and sericite. Some mylonitization and primary mylonitization are affected by ductile shear deformation and metamorphism. The mineral chemistry analysis shows that the plagioclase in the rocks is intermediate acid plagioclase, the biotite is magnesia biotite, but has the tendency of transition to ferric biotite, and the amphibole is mainly actinolite and magnesium sodium amphibole, which are metamorphic and metasomatic hornblende. The above characteristics indicate that the rock mass is subjected to the metasomatic alteration of silicon-rich fluid and the shallow dynamic metamorphism of Yanshanian period to some extent during the process of crystallization and diagenesis. The element geochemistry analysis shows that the SiO2 content of the rock mass is 64.2 ~ 69.56, the average value is 66.83K _ 2O / Na _ 2O = 1.51n 27.42, and the average value is 9.25% A / C / N = 1.025 / 2.906, with an average value of 1.87, respectively. The SiO2 content is relatively high, and the rock mass is peraluminous high potassium calc-alkaline granite with obvious characteristics of light rare earth enrichment, heavy rare earth deficiency, relative enrichment of large ion lithophile elements and relative depletion of transition elements. The above characteristics further indicate that the magmatic process is related to the metasomatism of deep fluids during plate subduction and collision. Combined Zr-TiO2, biotite TFeO/ (TFeO MgO)-MgO,1000Ga/Al2O3-K2O/MgO,CaO/Na2O-Al2O3/TiO2, Rb/Ba-Rb/Sr and La/Sm-La diagrams show that the Xihuangfen rock body is not a single crust magma through simple crystallization differentiation, but experienced complex tectonic-magmatism, and the separation and crystallization process is very obvious. It is inferred that the rock mass is formed by the calc-alkaline granite magma partially melted in the crust, which is separated and crystallized first, then through multiple pulsations and low-degree crystallization differentiation accompanied by rapid migration. In the process of crystallization, the mantle fluid is responsible for the metasomatism to some extent. The Laowangfen pluton in the west of Fengqing has different lithofacies characteristics from other Lincang granitic and Permian rocks, but it has similar geochemical characteristics. It is further speculated that the three bodies may be the product of magmatism of the same or similar source area. The source rock is complex sandstone. The forming environment is a rear collision. It is considered that the Laowangfen rock body in the west of Fengqing may have been formed in the Permian period and is a part of the transitional evolution of the Lincang complex granite base. It is the result of the Changning-Menglian ocean closure and the collision process between the Lanping-Simao continental block and the Baoshan block. Its main formation mechanism is the product of continental crust transformation which caused partial melting of deep upper crust under the condition of subduction and subduction of oceanic crust plate resulting in collision after continental docking.
【學位授予單位】：成都理工大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：P588.121

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