本文關鍵詞： 藏南 雙峰式火山巖 超鎂鐵質巖 基性脈巖 SHRIMP鋯石定年 地球化學　出處：《中國地質大學(北京)》2015年碩士論文　論文類型：學位論文

【摘要】：藏南隆子地區(qū)桑秀組中發(fā)育一套以英安巖和粗玄巖為主的雙峰式火山巖組合,英安巖的SHRIMP鋯石U-Pb年齡為134.9±2.3Ma,成巖時代為早白堊世。地球化學證據(jù)表明,粗玄巖富Ti O2、TFe O和P2O5,無明顯HFSE虧損,英安巖Th、Nb、Zr、Y含量較高,而相對虧損P和Ti,Eu的負異常明顯。粗玄巖可能是Kerguelen地幔柱與巖石圈地幔相互作用的產物,而英安巖的形成與地殼深熔作用有關。藏南地區(qū)廣泛發(fā)育近東西向的基性巖墻群,其中哲古地區(qū)輝石巖以夾層形式產于輝長巖中,對哲古基性巖進行SHRIMP鋯石U-Pb定年,得出輝長巖和輝石巖加權平均年齡分別為131.71±2.7Ma(2σ,MSDW=2.8)和135.0±2.4Ma(2σ,MSDW=2.1),輝石巖的結晶時代早于輝長巖約4Ma。元素地球化學研究表明,輝長巖Si O2含量為50.85%,Ti O2含量為1.45%,Mg O含量為10.05%,全鐵含量為8.57%,鎂數(shù)為71.33。輝石巖Si O2含量為48.28%,Ti O2含量為2.02%,Mg O含量為18.68%,全鐵含量為13.08%,鎂數(shù)為78.76。輝長巖和輝石巖K2O含量較高,分別為0.68和0.81,Eu的虧損不明顯,相對虧損Nb、Ta等元素,稀土分布型式與板內洋島玄武巖(OIB)類似。其形成與同時期的地幔熱事件關系密切,并在上升過程中可能受到了地殼物質的混染。藏南隆子-古堆一帶廣泛發(fā)育近東西走向的基性脈巖尚未得到很好的約束,對基性脈巖做了較為系統(tǒng)的地質年代學和巖石地球化學研究,3個基性脈巖的SHRIMP鋯石U-Pb年齡為133-140.9Ma,代表了輝長巖的結晶年齡,元素地球化學研究表明,基性脈巖屬于鈣堿性-堿性系列,總體富Ti O2,平均含量為3.08,LREE富集,輕重稀土分異較為明顯,LILE略為富集,HFSE虧損不明顯,屬被動大陸邊緣構造環(huán)境。
[Abstract]:A set of bimodal volcanic assemblages consisting mainly of dolomite and trachyte are developed in the Sangxiu formation of southern Tibet. The SHRIMP zircon U-Pb age of the dolomite is 134.9 鹵2.3 Ma.The diagenetic age is early Cretaceous. Geochemical evidence shows that, The coarse rocks are rich in TIO _ 2, TFE _ O and P _ 2O _ 5, and have no obvious HFSE depletion. The contents of Thnbszru _ Y are relatively high, while the relative depletion of P and Ti-EU are obvious. The coarse rocks may be the product of interaction between Kerguelen mantle plume and lithospheric mantle. The formation of dolomite is related to deep crustal melting. In southern Tibet, there are widely developed near-east-west basic-dike groups, in which pyroxenite occurs in gabbro in the form of intercalation, and the SHRIMP zircon U-Pb dating is carried out for the geostrophic rocks. The weighted mean ages of gabbro and pyroxenite are 131.71 鹵2.7 Ma ~ (2 蟽) and 135.0 鹵2.4 Ma ~ (2 蟽) respectively. The crystallization age of pyroxenite is earlier than that of gabbro about 4 Ma.Elemental geochemistry study shows that. The content of Sio _ 2 in gabbro is 50.85, the content of TIO _ 2 is 1.45 and the content of MgO is 10.05, the content of total iron is 8.57, the amount of magnesium is 71.33. The content of Sio _ 2 in pyroxenite is 48.28, and the content of TIO _ 2 is 2.02mg _ O, the content of total iron is 13.08, the content of magnesium is 78.76. The content of K _ 2O in gabbro and pyroxenite is higher. The depletion of 0.68 and 0.81 EU is not obvious, and the REE distribution pattern is similar to that of OIBB, and the REE distribution pattern is closely related to the mantle thermal events in the same period. During the process of uplift, it may be contaminated by crustal materials. The basic dike rocks, which are widely developed in the area of Longzi to Gudui in the south of Tibet, have not been well constrained by the east-west trend. The geochronology and geochemistry of the basic dikes have been systematically studied. The SHRIMP zircon U-Pb ages of the three basic dikes are 133-140.9 Ma, which represent the crystallization age of gabbro. The basic dike rocks belong to the calc-alkaline alkaline series, which are rich in TIO _ 2, and the average content is 3.08% LREE, and the difference between light and heavy rare earth elements is relatively obvious. The Lile is slightly enriched and the loss of HFSE is not obvious. It belongs to the passive continental margin tectonic environment.
【學位授予單位】：中國地質大學(北京)
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：P588.1;P597.3

【參考文獻】

相關期刊論文 前3條

1 李金陽;楊經綏;徐向珍;郭國林;陳松永;李天福;任玉峰;左國朝;;新疆南天山東段庫茲山基性超基性巖特征和成因探討[J];中國地質;2011年04期

2 張招崇,王福生,郝艷麗,JohnJ.Mahoney;峨眉山大火成巖省中苦橄巖與其共生巖石的地球化學特征及其對源區(qū)的約束[J];地質學報;2004年02期

3 朱弟成,潘桂棠,莫宣學,王立全,廖忠禮,江新勝,耿全如;特提斯喜馬拉雅桑秀組英安巖鋯石SHRIMP年齡及其意義[J];科學通報;2005年04期

，

本文編號：1551673