青海阿木尼克牦牛山组火山岩地球化学与成因研究
发布时间：2018-07-29 07:16
【摘要】：柴北缘缝合带属于秦祁昆造山系的一部分,在早古生代时期经历了原特提斯洋的闭合,洋-陆俯冲作用和后期碰撞造山作用,弧盆体系发育。晚志留世至早泥盆世时期,沿柴达木盆地边缘广泛发育的牦牛山组地层磨拉石建造,代表了造山作用的基本结束。近些年大量的地球化学研究证据,对其年龄下限进行了约束,而缺少对其年龄上限的认识。阿木尼克地区位于柴北缘缝合带北部,其境内出露大量牦牛山组火山岩。对其岩石学特征、岩石地球化学特征的进行综合研究,有助于认识早古生代洋盆闭合后,盆地进入陆相演化阶段,柴北缘的构造演化。并且通过对牦牛山组上层火山岩年代学研究,约束牦牛山组地层形成的时间上限。本文通过野外地质调查和室内镜下薄片鉴定及地球化学分析等手段,对该套火山岩进行了岩石学及岩石地球化学特征研究,并进行了构造环境判别、岩浆源区、成因及演化的探讨。研究区牦牛山组火山岩岩石类型主要为火山碎屑岩和熔岩类,韵律及旋回特征明显。岩相学特征主要表现为喷发相、爆发相、溢流相、局部少量喷发沉积相。古火山机构保存较好,其中以阿木尼克山和达达肯乌拉山南两处保存最为完整。另外,熔岩类火山岩表现出陆相溢流的特征,具有典型的柱状节理,横截面多呈四边形。根据SiO2的含量,将研究区牦牛山组火山岩分为两类:一类为中性火山岩类,SiO2含量53.94~61.88%;一类为中酸性火山岩类,SiO2含量62.99~76.61%。相对而言,前者氧化物含量较后者多,后者表现出高K的特征。两者同时表现出低Ti,TiO2范围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范围5.38~9.86%,里特曼指数δ:1.45~4.54,基本集中于钙碱性范围内。微量元素表现为富集大离子亲石元素(LILE),亏损高场强元素(HFSE),两类火山岩都表现为Nb、Sr的负异常。中酸性火山岩类P、Ti、Ba负异常明显,两者表现Th、La、Ce、Nd、Zr、Hf、Y的相对正异常。稀土元素特征为轻稀土富集,重稀土亏损,中酸性火山岩类Eu呈明显负异常。稀土标准化曲线表现出似安第斯型火山岩特征。对研究区牦牛山组上部英安岩、流纹岩锆石LA-ICP-MS U-Pb测年结果显示其年龄在369.2±3.3Ma-392.4±3.3Ma之间,属于中晚泥盆世。火山岩岩相学及地球化学特征显示:研究区牦牛山组火山岩形成于板内拉张环境,具岛弧火山岩特征,判断其形成于弧后盆地拉张。岩浆源区为俯冲洋壳含水流体交代的富集楔形地幔,岩浆上升过程中与硅铝质地壳底部发生较强同化混染作用。
[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 卤3.3Ma-392.4 卤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.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P588.14
[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 卤3.3Ma-392.4 卤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.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P588.14
【参考文献】
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1 衣健;唐华风;王璞s，
本文编号：2151922
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