云南大理小龙潭地区富碱斑岩体的地球化学特征与年代学研究

发布时间：2018-02-25 23:30

  本文关键词： 富碱斑岩 地球化学 年代学 大理 中国　出处：《昆明理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：小龙潭富碱斑岩体位于三江地区金沙江-哀牢山缝合带内,是金沙江-哀牢山富碱侵入岩带的重要组成部分。本文以小龙潭富碱斑岩体作为研究主体,利用岩石主微量元素数据分析了岩体的岩石地球化学特征,利用锆石U-Pb同位素测年技术,获得了岩体的成岩年龄。结合前人关于金沙江-哀牢山富碱侵入岩的研究资料,探讨了小龙潭富碱斑岩的成因与构造背景。(1)主量元素分析结果显示岩石具有Si02饱和(61.34%-67.07%),富碱(K20+Na2O=9.05%～12.45%)、高钾(K2O/Na2O=0.85～8.39),低Ti(TiO2含量0.27%～0.37%),属准铝质-过铝质岩石,总体为钾玄岩系列的岩石。(2)微量元素分析结果显示本区富碱斑岩富集Rb、Ba、K及LREE等大离子亲石元素,Ta、Zr、Hf、Nb、Ti等高场强元素相对亏损,具有十分明显的Ta、Nb、Ti负异常,显示出俯冲带幔源岩石的成分特点。(3)稀土元素分析结果显示富碱斑岩的亲稀土元素与重稀土元素存在明显的分馏,属于轻稀土元素富集,重稀土元素亏损型岩石。6 Eu在0.35-0.85之间,样品表现为中等程度的负铕异常,Ce异常不明显。(4)同位素研究表明本区岩体具有高的(87Sr/86Sr)i值和低的(I43Nd/I44Nd)i值,同时具有高放射性成因Pb同位素成分,显示出EMⅡ富集型地幔的源区特征。暗示小龙潭富碱斑岩起源于被地壳物质混染过的EMⅡ型地幔端元。(5)用锆石LA-ICP-MS U-Pb测年法获得滇西小龙潭地区石英正长斑岩的年龄为34.7+0.28Ma,可以把小龙潭富碱斑岩的形成时间确定为新生代。(6)地球化学特征显示小龙潭富钾斑岩具有壳幔混合特征,岩浆起源于经地壳物质在源区混染的富集岩石圈地幔。富集岩石圈地幔的形成与晚古生代-早中生代扬子板块俯冲有关。样品的w(La)-w(La)/w(Sm)图解表明小龙潭富碱斑岩为部分熔融成因。富碱岩浆的EMⅡ地幔源区的富挥发份的特征以及软流圈物质的上涌可能是导致富集岩石圈地幔部分熔融的主导因素。新生代亚欧陆壳与印度陆壳的碰撞导致岩石圈增厚,随之增厚的岩石圈地幔部分拆离岩石圈,导致软流圈上涌,为岩石圈地幔熔融提供热量,后碰撞期的走滑剪切作用诱发了岩浆的上侵。
[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，

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