【摘要】：柴北緣縫合帶屬于秦祁昆造山系的一部分,在早古生代時(shí)期經(jīng)歷了原特提斯洋的閉合,洋-陸俯沖作用和后期碰撞造山作用,弧盆體系發(fā)育。晚志留世至早泥盆世時(shí)期,沿柴達(dá)木盆地邊緣廣泛發(fā)育的牦牛山組地層磨拉石建造,代表了造山作用的基本結(jié)束。近些年大量的地球化學(xué)研究證據(jù),對(duì)其年齡下限進(jìn)行了約束,而缺少對(duì)其年齡上限的認(rèn)識(shí)。阿木尼克地區(qū)位于柴北緣縫合帶北部,其境內(nèi)出露大量牦牛山組火山巖。對(duì)其巖石學(xué)特征、巖石地球化學(xué)特征的進(jìn)行綜合研究,有助于認(rèn)識(shí)早古生代洋盆閉合后,盆地進(jìn)入陸相演化階段,柴北緣的構(gòu)造演化。并且通過(guò)對(duì)牦牛山組上層火山巖年代學(xué)研究,約束牦牛山組地層形成的時(shí)間上限。本文通過(guò)野外地質(zhì)調(diào)查和室內(nèi)鏡下薄片鑒定及地球化學(xué)分析等手段,對(duì)該套火山巖進(jìn)行了巖石學(xué)及巖石地球化學(xué)特征研究,并進(jìn)行了構(gòu)造環(huán)境判別、巖漿源區(qū)、成因及演化的探討。研究區(qū)牦牛山組火山巖巖石類型主要為火山碎屑巖和熔巖類,韻律及旋回特征明顯。巖相學(xué)特征主要表現(xiàn)為噴發(fā)相、爆發(fā)相、溢流相、局部少量噴發(fā)沉積相。古火山機(jī)構(gòu)保存較好,其中以阿木尼克山和達(dá)達(dá)肯烏拉山南兩處保存最為完整。另外,熔巖類火山巖表現(xiàn)出陸相溢流的特征,具有典型的柱狀節(jié)理,橫截面多呈四邊形。根據(jù)SiO2的含量,將研究區(qū)牦牛山組火山巖分為兩類:一類為中性火山巖類,SiO2含量53.94~61.88%;一類為中酸性火山巖類,SiO2含量62.99~76.61%。相對(duì)而言,前者氧化物含量較后者多,后者表現(xiàn)出高K的特征。兩者同時(shí)表現(xiàn)出低Ti,TiO2范圍0.1~1.12%,平均值0.41%,低P2O5含量0.019%~0.33%,平均值0.11%,FeO*含量0.70~7.16%,平均值2.81%,ALK范圍5.38~9.86%,里特曼指數(shù)δ:1.45~4.54,基本集中于鈣堿性范圍內(nèi)。微量元素表現(xiàn)為富集大離子親石元素(LILE),虧損高場(chǎng)強(qiáng)元素(HFSE),兩類火山巖都表現(xiàn)為Nb、Sr的負(fù)異常。中酸性火山巖類P、Ti、Ba負(fù)異常明顯,兩者表現(xiàn)Th、La、Ce、Nd、Zr、Hf、Y的相對(duì)正異常。稀土元素特征為輕稀土富集,重稀土虧損,中酸性火山巖類Eu呈明顯負(fù)異常。稀土標(biāo)準(zhǔn)化曲線表現(xiàn)出似安第斯型火山巖特征。對(duì)研究區(qū)牦牛山組上部英安巖、流紋巖鋯石LA-ICP-MS U-Pb測(cè)年結(jié)果顯示其年齡在369.2±3.3Ma-392.4±3.3Ma之間,屬于中晚泥盆世�；鹕綆r巖相學(xué)及地球化學(xué)特征顯示:研究區(qū)牦牛山組火山巖形成于板內(nèi)拉張環(huán)境,具島弧火山巖特征,判斷其形成于弧后盆地拉張。巖漿源區(qū)為俯沖洋殼含水流體交代的富集楔形地幔,巖漿上升過(guò)程中與硅鋁質(zhì)地殼底部發(fā)生較強(qiáng)同化混染作用。
[Abstract]:The suture zone in the northern margin of Qaidam is a part of the Qinqi-Kun orogenic system, which experienced the closure of the Paleozoic Tethys ocean, ocean-continental subduction and late collision orogeny, and the development of the arc basin system in the early Paleozoic period. From late Silurian to early Devonian the formation of Yak Niushan formation developed extensively along the margin of Qaidam Basin represents the end of orogeny. In recent years, a great deal of geochemical research evidence has restricted the lower age limit of its age, but it lacks the understanding of its age upper limit. The Amunik area is located in the northern suture zone of the northern margin of Chai, where a large number of yak volcanic rocks are exposed. A comprehensive study of the petrological and geochemical characteristics of the basin is helpful to the understanding of the tectonic evolution of the basin in the northern margin of Qaidam after the closure of the early Paleozoic ocean basin. The upper volcanic rock chronology of the Yak Niushan formation is studied to limit the upper limit of the formation time. In this paper, the petrology and petrogeochemical characteristics of this set of volcanic rocks are studied by means of field geological survey, microscopic sheet identification and geochemical analysis, and the tectonic environment and magmatic source region are distinguished. Discussion on Origin and Evolution. In the study area, the volcanic rock types of Yaniushan formation are mainly volcanic clastic rocks and lava types, with obvious rhythmic and cyclic characteristics. The lithofacies are mainly characterized by eruptive facies, explosive facies, overflow facies and a small amount of eruptive sedimentary facies. The ancient volcanic institutions are well preserved, among which the Amunic Mountain and the Southern Dadakenullah Mountain are the most complete ones. In addition, lava volcanic rocks show the characteristics of continental overflow with typical columnar joints and quadrilateral cross sections. According to the content of SiO2, the volcanic rocks of Yak Niushan formation in the study area are divided into two types: one is neutral volcanic rock, the content of SiO2 is 53.94 (61.88), the other is the content of SiO2 of intermediate and acidic volcanic rocks (62.99m 76.61). Relatively speaking, the content of oxides in the former is higher than that in the latter, and the latter shows the characteristics of high K. At the same time, they showed the range of low TiTiTiTiO20.1 ~ 1.12, the average value of 0.41, the low P2O5 content of 0.019 and 0.33, the average of 0.11 and the content of Feo * 0.70 and 7.16, the average value of 2.81ALK in the range of 5.389.86. the Littmann index of 未 -1.450.4.54 was basically concentrated in the calc-alkaline range. The trace elements are characterized by the enrichment of large ion lithophile element (LILE), depleted high field strength element (HFSE), and both types of volcanic rocks show negative anomalies of NB + Sr. There are obvious negative anomalies of PnTiTI-Ba in intermediate-acid volcanic rocks, both of which show the relative positive anomalies of the Th _ (Lac) NdCe ~ (2 +) Zr ~ (+) HfU _ (Y). REE is characterized by LREE enrichment, heavy REE depletion and EU negative anomalies in intermediate-acid volcanic rocks. The REE standardization curve shows the characteristics of Andes-like volcanic rocks. The LA-ICP-MS U-Pb dating of zircon from the upper part of the yak Niushan formation in the study area shows that the zircon age is between 369.2 鹵3.3Ma-392.4 鹵3.3Ma, which belongs to the Middle and late Devonian. The petrological and geochemical characteristics of the volcanic rocks show that the volcanic rocks of the Yaniushan formation in the study area were formed in the intraplate extensional environment and have the characteristics of the island arc volcanic rocks, which are judged to have formed in the extensional basin behind the arc. The magma source area is the enriched wedge-shaped mantle of fluid metasomatism of subducted oceanic crust, which is strongly assimilated and mixed with the bottom of Si-Al crust during the magma rising.
【學(xué)位授予單位】：成都理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：P588.14

【參考文獻(xiàn)】

相關(guān)期刊論文 前10條

1 衣健;唐華風(fēng);王璞s，

本文編號(hào)：2151922