【作者】 王金荣；

【导师】 汤中立；

【作者基本信息】 兰州大学 ， 地质工程， 2006， 博士

【摘要】 北祁连构造带是世界上典型的造山带之一，是研究板块构造演化及其地球动力学过程的理想场所。在早古生代时期，北祁连东段壳幔相互作用活跃，岩石圈层圈物质及能量交换强烈，岩浆成矿作用显著，为国内外地质学家所关注。综合地质研究结果表明，北祁连东段由北至南可分为阿拉善古陆缘、老虎山弧后盆地残留体、白银陆缘弧、北祁连俯冲杂岩带、中祁连地块等构造岩石单元；在新元古代晚期—早古生代早期，北祁连造山带东段发生了裂解裂谷作用，以发育大陆拉班玄武岩到碱性玄武岩为特征，到早中寒武世—早中奥陶世，北祁连东段经历了古大洋扩张、俯冲消减、碰撞造山的重要构造事件，形成了白银陆缘弧和老虎山弧后盆地。岩石学、地球化学研究结果首次揭示并证实：1) 位于阿拉善古陆缘、老虎山弧后盆地残留体北侧的屈吴山银硐梁早古生代花岗闪长岩是埃达克岩，它们具有富Na贫K，SiO₂＞56 w％，Al₂O₃＞15 w％，Na₂O＞4.0 w％（4.51％～4.92w％），K₂O（1.96～2.77 w％），Na₂O／K₂O=1.63～2.40，属钙碱性侵入岩；高Sr(599～691×10^-6)低Y(6.3～8.1×10^-6)，Sr／Y＞40（81～94），Y／Yb＞10(Yb＜1.9×10^-6)，La/Yb＞20（22～45），富集轻稀土元素（LREE），亏损重稀土元素（HREE），（La/Yb）_N＞10（16～32），轻微负Eu异常（Eu／Eu*平均为0.94），∑REE～85～112×10^-6，与典型的环太平洋埃达克岩比较，它们具有更高的Mg^#（58～64，平均59）和相容元素Ni(31～38×10^-6)和Cr(35～43×10^-6)含量，因此被归入高镁埃达克岩，其形成于年轻而热的老虎山弧后盆地俯冲板片在消减过程中发生部分熔融，并与地幔橄榄岩发生明显交代作用；2) 侵入于白银陆缘弧火山岩中的早古生代晚期—晚古生代早期黑石山斜长花岗岩、花岗斑岩为埃达克质岩，其具有高Sr低Y型（Sr／Y＞40），富集LREE，亏损HREE（La／Yb＞20），无Eu负异常或轻微正异常（Eu／Eu^*=1.0-1.19），其成因是在北祁连东段进入后造山伸展构造阶段，由加厚的下地壳中基性岩石在地幔底侵作用下发生部分熔融的产物，但其富Na贫K而有别于中国东部燕山期由非板片熔融形成的富K贫Na的埃达克质岩。本文确定了白银厂矿田火山岩是早古生代北祁连古大洋俯冲产生的陆缘弧岩浆作用的结果，玄武岩主要源自岩石圈地幔部分熔融，而含矿岩系一流纹岩则来源于镁铁质下地壳部分熔融与地幔物质混合作用的产物。更多还原

【Abstract】 The North Qilian Orogenic Belt, as one of the typical orogenic zones in the world, is a key region for studying plate tectonic evolution and geodynamic processes. In the development of geosciences, geologists have been always paying close attention to the very mobile interaction between crust and mantle, intensive interchange processes of the lithospheric materials and energy, and remarkable magmatic mineralization in the eastern section of the North Qilian during early Paleaozoic period. The study results of comprehensive geology show that the eastern section of North Qilian may been divided into the Alaxa Paleo-continental margin, Laohushan back-arc basin remnant, Baiyin continental marginal arc, subducted complex zone of the North Qilian, and the Central Qilian Block from north to south, and that the eastern section of the North Qilian was obviously characterized by the tectonic processes of rifting with continental tholeiite to alkaline basalts from late period of Neoproterozoic to early period of Early Paleaozoic, and by tectonic evolution of the spreading, subduction of the paleo-Qilian ocean, forming Baiyin continental marginal arc and Laohushan back-arc basin, to finally plate collision and orogeny. The study results of petrology and geochemistry are to originally reveal and demonstrate: 1) the early Paleozoic granodiorites from Yindongliang in Quwushang, located in the Alaxa Paleo-continental margin, north of Laohushan back-arc basin remnant, are adakites, similar to the typical adakites from circum-Pacific region. They have high Al₂O₃ （>15% （w %））, Na₂O (>4.0% （4.51% - 4.92% （w %））, Na₂O/K₂O = 1.63- 2.40, and SiO₂>56% （w %）, and low K₂O contents （1.96-2.77 % （w %） ）, belonging to calc-alkaline series; and high Sr (599—691× 10^-6) low Y (6.3-8.1 ×10^-6)andYb (Yb<1.9×10^-6)contents, Sr/Y>40（81-94）, Y/Yb>10, La/Yb>20 （22-45）, and but with higher Mg^# （58 - 64） , Ni (31-38 ×10^-6) and Cr (35-43 ×10^-6) contents compared with the typical adakites, so called as high-Mg adakite,更多还原