闻一多演讲
摘要
北祁连山是阿拉善地块和中祁连-柴达木地块之间的古生代造山带，也是我国洋内俯冲增生作用发育最充分、岩石记录保存最完整的区域之一。本文选择沿北祁连早古生代缝合带出露的火山岩进行了野外地质、岩石学、矿物学、元素地球化学、LA-ICP-MS锆石年代学研究工作，进而深入探讨了古祁连洋俯冲汇聚地质过程和演化历史。研究区位于青海省祁连县野牛沟乡一带，早古生代火山岩、次火山岩的岩石类型包括：流纹岩、英安岩、石英斑岩、安山岩、玄武岩和凝灰岩、火山碎屑岩等，中酸性火山岩和中基性火山岩常见互层状产出；火山岩层中还见有硅质岩、碳酸盐岩夹层，玄武岩常发生不同程度的蚀变。
通过对研究区火山岩的元素地球化学特征研究分析，揭示岩石K2O含量存在明显差异，依据中酸性岩K2O>2 wt%、中基性岩的K2O>1 wt%，可将研究区的火山岩划分出富K火山岩系列，其它（中酸性岩K2O<2 wt%、中基性岩的K2O<1 wt%）归属于低K火山岩系列。所有火山岩均呈现出不同程度Nb、Ta、Zr、Hf 和Ti亏损的岛弧火山岩特征，揭示它们均形成于岛弧环境，但低K火山岩系列中的流纹岩、玄武岩具有基本一致的近平坦型稀土配分型式和近平坦的微量元素蛛网图，显示主要为大洋岩石圈部分熔融形成熔浆的结晶产物；富K火山岩系列中的玄武岩和流纹岩则具有基本一致的右倾稀土配分型式和右倾微量元素蛛网图，其中LREE和大离子亲石元素明显富集，显示有大陆岩石圈物质的加入。通过综合对比研究，祁连洋早古生代俯冲-汇聚-碰撞过程中存在多期次幔源岩浆上侵、喷发作用，由于不同阶段
岩石圈结构和组成的差异，母岩浆成分明显不同，形成了高K和低K两套、均含有中基性和中酸性火山岩的岛弧火山岩系列，两个系列的火山岩沿主缝合带叠加产出。
通过LA-ICP-MS锆石U-Pb年代学研究，获得了富K火山岩系列玄武岩的成岩年龄，为482±2.7Ma。
综合研究认为北祁连地区弧火山岩包括：（1）富K岛弧火山岩系列，其形成于被动大陆边缘的洋-陆板块俯冲汇聚阶段，有明显的大陆岩石圈边缘物质加入，该期火山喷发年龄～482 Ma，也指示晚寒武末-早奥陶世早期由洋-陆俯冲汇聚引发的岩浆活动达到了峰期；（2）低K岛弧火山岩系列，岩石出露规模相对较小，推测其成岩时代稍晚，在晚奥陶世末-早志留世祁连洋闭合-碰撞造山（445Ma～428Ma）阶段，已俯冲至大陆岩石圈之下的洋壳残片因碰撞挤压作用发生了进一步部分熔融，形成的低K富Na熔浆基本沿原火山弧位置喷发，陆缘地壳增生加厚。
关键词：北祁连山，早古生代，岛弧，高钾火山岩，低钾火山岩
Abstract
The Northern Qilian Mountains is a Paleozoic orogenic belt between the Alashan terraneand the Qilian-Qaidam block. It is one of the most abundantly developedsubduction zones in the orogenic belts and saves one of the most integrated rock recordsin China. In this paper, the volcanic rocks ex
pod along the Early Paleozoic suture zone in the North QilianMountainsare studied by geology, petrology, mineralogy, elemental geochemistry and LA-ICP-MS zircon chronology measures to reveal theprocess and evolution history of convergence and subduction in ancient Qilian Ocean. The study area is located in the area of the YeniugoutoQingshuigou, Qilian County, Qinghai Province. The types of the early Paleozoic volcanic and sub-volcanic rocks include rhyolite, quartzite, quartz porphyry, andesite, basalt and tuff, volcanic clastic rocks.Intermediate-acidvolcanic rocks and intermediate-basic volcanic rocks are commonly interbedded. Siliceous rocks, carbonate mezzaninecan be found in volcanic rocks.And varying degrees of alteration often occur amongbasalts.
The elemental geochemical characteristics of the volcanic rocks in the study area reveal a significant difference in the K2O content of the rocks. According to the K2O>
2 wt% of the intermediate-felsic volcanic rocks and K2O> 1 wt% of the intermediate-basic volcanic rocks in the study area can be divided into the high-K volcanic rocks ries, the other (K2O<1 wt% of intermediate-basic volcanic rocks,
K2O < 2 wt% of the intermediate-felsic volcanic rocks) belongs to the low-K volcanic rocks ries. All
volcanic rocks show the characteristics of island arc volcanic rocks with different degrees of Nb, Ta, Zr, Hf and Ti loss, revealing that they are formed in the island arc environment.Butrhyolites and basaltsof the low-K volcanic rocks ries have the same near-flatREE distribution type and near-flat trace element spiderin general. It shows that the main oceanic lithosphere fud partially to form the crystalline product.Rhyolites and basalts of high-K volcanic rocks ries have the same right-leaningREE distribution type and right-leaning trace elements spider in general, where LREE and large ion lithophile elements are significantly enriched with the mixture of continental lithosphere materials. Through the
comprehensivelycomparative study, there are multiple mantle-derived magmatic uplifts and eruptionsin the subduction-convergence-collision process of the Qilian Mountains in the early Paleozoic. Due to the differences of the lithosphere structure, the compositions of the mother magma are obviously different. It forms high-K and low-K volcanic rocks, both of which contain the basic and the acid volcanic arc rock ries.The two ries of volcanic rocks are superimpod along the main suture belt when the eruption occurs.
The diagenetic age of the basalts ofhigh-K volcanic rock ries is 482±2.7Magiven by LA-ICP-MS zircon U-Pb chronology.
The comprehensive study suggests that the volcanic rocks in the Northern Qilian area include two different types. (1) The high-K island arc volcanic ries are formed
in the subduction zone of the passive continental margin;there are continental lithosphere materialsobviously. And the volcano eruption age is 482 Ma. (2)The scale of Low-K arc volcanic rocks ries expod is relatively small. The diagenetic era is speculated later thanthe formation of Qilian Ocean clod (445Ma～428Ma).The oceanic crust which has subducted under the continental partial is moltenin the continental strata due to the squeezed collision occurred at the end of the late Ordovician. The low-K and high-Na volcanic rocks erupt along the original volcanic arc path, and thickenthe crust of the continental margin.
Key words: North Qilian Mountains,Early Paleozoic,Island arc,High-Kvolcanic rocks, Low-Kvolcanic rocks
目录
1 前言 (1)
1.1 选题依据及研究意义 (1)
趣味数学100题
1.2 研究现状 (2)
1.3 关键问题与研究内容 (2)
1.3.1 关键问题 (2)
1.3.2 研究内容和目的 (3)
糖画1.4 技术路线 (3)
1.5 完成的实物工作量 (4)
2 区域地质概况 (5)
2.1 区域构造 (5)
2.1.1 构造单元划分 (5)
2.1.2 主要断裂 (6)
2.2 地层 (7)
2.3 岩浆岩 (10)
3 岛弧火山岩区地质概况 (11)
3.1 北祁连弧盆系特征 (11)
3.1.1 走廊弧后盆地 (12)
3.1.2 肃南-天祝蛇绿混杂岩带 (12)静寂的近义词
翡翠手镯怎么挑3.1.3 走廊南山岛弧带 (12)
3.2 火山岩分布特征 (13)
3.2.1 北祁连弧火山岩分布 (13)
3.2.2 祁连县岛弧火山岩 (15)
3.2.3 白银岛弧火山岩 (15)
4 岩石学特征 (17)
4.1 香子沟-野牛沟-边麻沟火山岩 (17)
4.2 火山岩主要类型及特征 (17)
4.2.1 中-基性火山岩的岩石学特征 (17)
4.2.2 中-酸性火山岩的岩石学特征 (20)
5 元素地球化学特征 (23)
5.1 岩石地球化学分析方法 (23)
5.1.1 主量元素测定 (23)
5.1.2 微量元素测定 (23)
2021国庆5.2 主量元素 (24)
5.2.1 高钾的岛弧火山岩主量元素特征 (28)
5.2.2 低钾的岛弧火山岩主量元素特征 (29)
5.3 微量元素成分特征 (31)
5.3.1 高钾的岛弧火山岩微量元素特征 (37)
5.3.2 低钾的岛弧火山岩微量元素特征 (38)
香蕉功效5.4 稀土元素特征 (39)
5.4.1 高钾的岛弧火山岩稀土元素特征 (40)
5.4.2 低钾的岛弧火山岩稀土元素特征 (41)
整式除法
6 U-Pb同位素年代学特征 (45)
6.1 测试方法 (46)
6.2 北祁连造山带古生代火山岩的锆石U-Pb年龄及其意义 (47)
7 岩石构造环境成因 (53)
8 结论 (55)
致谢 (57)
参考文献 (59)
附录 (62)
