本文關(guān)鍵詞： 富堿斑巖 地球化學(xué) 年代學(xué) 大理 中國　出處：《昆明理工大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

【摘要】：小龍?zhí)陡粔A斑巖體位于三江地區(qū)金沙江-哀牢山縫合帶內(nèi),是金沙江-哀牢山富堿侵入巖帶的重要組成部分。本文以小龍?zhí)陡粔A斑巖體作為研究主體,利用巖石主微量元素數(shù)據(jù)分析了巖體的巖石地球化學(xué)特征,利用鋯石U-Pb同位素測年技術(shù),獲得了巖體的成巖年齡。結(jié)合前人關(guān)于金沙江-哀牢山富堿侵入巖的研究資料,探討了小龍?zhí)陡粔A斑巖的成因與構(gòu)造背景。(1)主量元素分析結(jié)果顯示巖石具有Si02飽和(61.34%-67.07%),富堿(K20+Na2O=9.05%～12.45%)、高鉀(K2O/Na2O=0.85～8.39),低Ti(TiO2含量0.27%～0.37%),屬準(zhǔn)鋁質(zhì)-過鋁質(zhì)巖石,總體為鉀玄巖系列的巖石。(2)微量元素分析結(jié)果顯示本區(qū)富堿斑巖富集Rb、Ba、K及LREE等大離子親石元素,Ta、Zr、Hf、Nb、Ti等高場強元素相對虧損,具有十分明顯的Ta、Nb、Ti負異常,顯示出俯沖帶幔源巖石的成分特點。(3)稀土元素分析結(jié)果顯示富堿斑巖的親稀土元素與重稀土元素存在明顯的分餾,屬于輕稀土元素富集,重稀土元素虧損型巖石。6 Eu在0.35-0.85之間,樣品表現(xiàn)為中等程度的負銪異常,Ce異常不明顯。(4)同位素研究表明本區(qū)巖體具有高的(87Sr/86Sr)i值和低的(I43Nd/I44Nd)i值,同時具有高放射性成因Pb同位素成分,顯示出EMⅡ富集型地幔的源區(qū)特征。暗示小龍?zhí)陡粔A斑巖起源于被地殼物質(zhì)混染過的EMⅡ型地幔端元。(5)用鋯石LA-ICP-MS U-Pb測年法獲得滇西小龍?zhí)兜貐^(qū)石英正長斑巖的年齡為34.7+0.28Ma,可以把小龍?zhí)陡粔A斑巖的形成時間確定為新生代。(6)地球化學(xué)特征顯示小龍?zhí)陡烩洶邘r具有殼�；旌咸卣�,巖漿起源于經(jīng)地殼物質(zhì)在源區(qū)混染的富集巖石圈地幔。富集巖石圈地幔的形成與晚古生代-早中生代揚子板塊俯沖有關(guān)。樣品的w(La)-w(La)/w(Sm)圖解表明小龍?zhí)陡粔A斑巖為部分熔融成因。富堿巖漿的EMⅡ地幔源區(qū)的富揮發(fā)份的特征以及軟流圈物質(zhì)的上涌可能是導(dǎo)致富集巖石圈地幔部分熔融的主導(dǎo)因素。新生代亞歐陸殼與印度陸殼的碰撞導(dǎo)致巖石圈增厚,隨之增厚的巖石圈地幔部分拆離巖石圈,導(dǎo)致軟流圈上涌,為巖石圈地幔熔融提供熱量,后碰撞期的走滑剪切作用誘發(fā)了巖漿的上侵。
[Abstract]:The Xiaolongtan alkali-rich porphyry is located in the Jinshajiang-Ailaoshan suture zone in Sanjiang area, and is an important part of the Jinshajiang-Ailaoshan alkali-rich intrusive rock belt. In this paper, the Xiaolongtan alkali-rich porphyry rock mass is taken as the main body of study. The geochemistry characteristics of the rock mass are analyzed by using the data of main trace elements of rocks, and the diagenetic age of the rock mass is obtained by using zircon U-Pb isotopic dating technique, which is combined with the previous research data on the alkali-rich intrusive rocks in Jinshajiang-Ailaoshan. In this paper, the origin and tectonic setting of the alkali-rich porphyry in Xiaolongtan are discussed. The results of main element analysis show that the rock has Si02 saturation of 61.34- 67.07, alkali-rich K20 Na2O9.059.050.4545, high potassium K _ 2O / Na _ 2O 0.858.39, low Ti(TiO2 content 0.270.37m, which belongs to quasi-aluminite-peraluminous rock, and is characterized by high K _ 2O / Na _ 2O _ (0.858.39) and low Ti(TiO2 content (0.27 ~ 0.37m), which is a kind of quasi-aluminum-peraluminous rock. The results of trace element analysis for the rocks of the kaleite series show that the alkali-rich porphyry in this area is rich in large ion lithophile elements, such as LREE, LREE and so on, which are relatively depleted in high field strength elements, such as the high field strength elements such as Ta-Nb-Ti, and have very obvious negative anomalies of Ta-Nb-Ti. The results of REE analysis show that the alkali-rich porphyry rocks have distinct fractionation of REE and heavy REE, which belong to the enrichment of LREE, and the REE depleted rocks range from 0.35-0.85, and the REE analysis results show that the REE of mantle derived rocks in the subduction zone is characterized by a significant fractionation of REE from heavy REE rich porphyry rocks. The sample shows moderate negative EU anomaly ce anomaly. The isotopic study shows that the rock mass in this area has a high ~ (87) Sr ~ (%) ~ (86) Sr ~ (-) I value and a low ~ (43) ND / I ~ (44) ND ~ (1) I value, and a high radiogenic Pb isotopic composition. This indicates that the source region of the EM 鈪，

本文編號：1535624