| IBM型洋内弧的形成机制:以祁秦增生杂岩带为例 |
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| 引用本文： | 宋述光,杨立明.IBM型洋内弧的形成机制:以祁秦增生杂岩带为例[J].地球科学,2019,44(12):4167-4172. |
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| 作者姓名： | 宋述光 杨立明 |
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| 作者单位： | 北京大学地球与空间科学学院, 教育部造山带与地壳演化重点实验室, 北京 100871 |
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| 基金项目： | 国家重点基础研究发展计划项目2015CB856105国家自然科学基金项目91955202国家自然科学基金项目41572040中国地质调查局项目DD20190370 |
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| 摘 要： | 岛弧的形成和演化对于理解板块构造和大陆生长有重要意义.祁连山-西秦岭一带发育两条不同类型的弧岩浆岩带，其北侧为北祁连增生杂岩带，由蛇绿岩、高压变质岩和大陆型弧岩浆岩带组成，形成时代为520~440 Ma.岩浆岩以中酸性火山岩-侵入岩为主，部分地区发育典型双峰式火山岩.南侧为祁秦增生杂岩带，由寒武纪蛇绿岩（525~490 Ma）和奥陶纪IBM型洋内弧岩浆岩（470~440 Ma）组成，蛇绿岩以拉脊山-永靖洋底高原型蛇绿岩为代表，蛇绿岩的上部熔岩部分由夏威夷型苦橄岩、板内碱性玄武岩和板内拉斑玄武岩组成，为大洋板块内部地幔柱活动产物.洋内弧岩浆岩以高镁玄武岩、玄武安山岩、高铝安山岩、玻安岩为主，局部发育赞岐岩.祁秦增生杂岩带的蛇绿岩和弧火山岩组合很好地说明洋底高原与海沟碰撞和俯冲带阻塞是造成俯冲带起始和新的洋内弧形成和发展主要因素.
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| 关 键 词： | 寒武纪洋底高原型 奥陶纪洋内弧 祁秦增生杂岩带 岩石学 |
| 收稿时间： | 2019-09-23 |
Formation of the IBM-Type Intra-Oceanic Arc: An Example from the Qi-Qin Accretionary Belt,China |
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| Abstract: | Formation and evolution of the island/continental arcs are keys to understanding the plate tectonics and continent growth. In the Qilian and West Qinling, NW China, two different types of arc magmatic belts have been recognized. One is the North Qilian accretionary belt in the north, which consists of ophiolites, high-pressure metamorphic complex, and continental-type arc magmatic belt with ages of 520-440 Ma. The magmas are mainly intermediate to acid volcanics and intrusions. In the south is the Qi-Qin accretionary belt, which consists of Cambrian ophiolites (525-490 Ma) and Izu-Bonin-Mariana (IBM)-type intra-oceanic arc volcanic complexes (470-440 Ma). The Cambrian ophiolites are meanly composed of (1) the Hawaii-type picrite, (2) the within-plate alkaline basalt with intra-plate ocean-island-basalt (OIB) compositions, and (3) the within-plate tholeiitic basalt with enriched mid-ocean-ridge-basalt (E-MORB) compositions. The rock assemblage is best interpreted as an oceanic plateau of mantle plume within the Proto-Tethys ocean plate, obducted as ophiolitic fragments in the QQAB. The intraoceanic arc volcanic complexes are composed of high-Mg basalts, basaltic andesite, high-Al andesite, boninite and sanukite. Therefore, trench jam and subduction cessation caused by the arrival of an oceanic plateau are the primitive trigger for initiation of a new subduction zone with the development of younger volcanic sequence (~460-440 Ma). |
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