| 拉脊山蛇绿混杂带结构组成、形成时代与形成过程 |
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| 引用本文：付长垒,闫臻.2017.拉脊山蛇绿混杂带结构组成、形成时代与形成过程[J].地球学报,38(s1):29-32. |
| DOI：10.3975/cagsb.2017.s1.09 |
| 摘要点击次数: 1866 |
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| 基金项目:中国地质调查局项目(编号: 1212011120159; 121201140880001; 12120115069401; 12120115027001; 121201102000150020; DD20160022);国家自然科学基金项目(编号: 41272221; 41372207) |
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| 中文摘要:祁连造山带是原特提斯洋闭合过程中, 阿拉善和柴达木地块在青藏高原东北缘拼合的产物。它是由蛇绿岩残片、海山、岛弧、弧前/弧后盆地等多个构造单元构成的典型增生型造山带, 表现出在多个元古代微陆块周围分布有蛇绿岩和岛弧火山岩的特征。蛇绿混杂带广泛分布于北祁连和南祁连中, 在南祁连主要出露寒武纪玄武岩、安山岩、辉长岩、超基性堆晶岩、硅质岩、灰岩、砂岩和少量地幔橄榄岩, 呈现出蛇绿混杂带的典型特征, 其中拉脊山蛇绿混杂带是该蛇绿混杂带的最大组成部分。因此, 拉脊山蛇绿混杂带的来源和形成构造背景对研究祁连造山带构造演化具有重要的意义。由于构造的复杂性以及系统的野外和岩石学方面研究的缺乏, 拉脊山蛇绿混杂带的岩石组合、同位素年龄和构造背景仍然不清楚, 从而严重制约了区域构造演化的认识。例如, 前人根据灰岩中三叶虫化石将拉脊山地区火山-沉积岩系划归于寒武纪, 然而其它岩石单元的同位素年龄和来源信息相对缺乏, 而且灰岩究竟是本地岩块还是老的异地岩块仍有待进一步研究。岩石地球化学分析结果显示表明寒武纪玄武岩具有MORB、WPB或者OIB的特征, 且部分玄武岩具有岛弧亲缘性。因此, 大陆裂谷、弧后盆地、多阶段抬升构造窗或俯冲-增生杂岩等模式相继被提出。这些分歧严重影响了我们对祁连造山带和原特提斯洋构造演化的认识。究其根本原因, 是由于缺乏将蛇绿岩和岛弧形成视为沟-弧-盆体系演化过程中一个具有成因联系的有机体对其进行综合分析。 |
| 中文关键词:拉脊山 混杂带 SSZ型蛇绿岩 活动大陆边缘 构造演化 |
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| The Composition, Age and Tectonic Setting of Lajishan Ophiolitc Mélange |
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| Abstract:The Qilian orogenic belt formed as a result of closure of the Proto-Tethyan Ocean and amalgamation of the Alashan and Qaidam continental blocks along the NE margin of Tibet. It is a classic accretionary orogen in that it consists of various accreted terranes, such as ophiolites, seamounts and island arcs. A dis-tinctive structural feature is the multitude of Protero-zoic microcontinental blocks and slivers, that appear to separate the numerous ophiolite/arc complexes. Ophiolitic mélanges are widely distributed within both the North and South Qilian blocks. In the South Qilian block, Cambrian basalt, andesite, gabbro, ul-tramafic cumulate rocks, chert, limestone, sandstone and rare mantle peridotites are well-exposed and dis-play characteristic features of an ophiolitic mélange. The Lajishan ophiolitic mélange is the largest single zone within the belt. Therefore, its origin and tectonic setting are of a great importance for understanding the tectonic evolution of the orogen. Due to structural complexity, lack of systematic field and petrologic studies, exact lithological assemblages, isotopic ages and tectonic settings remain unclear making regional correlations difficult. For instance, vol-cano-sedimentary units in the Lajishan are assigned to the Cambrian based on trilobite faunas from lime-stones. However, isotopic ages for other lithologies and provenance data are lacking, and whether the limestones are autochthonous or older allochthonous blocks slumped into younger sequences remains to be determined. Geochemical data indicate that the Cam-brian-aged basalts are mainly transitional between MORB and WPB or OIB with some exhibiting is-land-arc affinity. Therefore, several models such as a continental rift, back-arc basin, multi-staged uplifting structure window and a subduction-accretionary com-plex have been proposed. These discrepancies sig-nificantly affect the Cambrian tectonic evolution of the Qilian orogenic belt and the Proto-Tethys Ocean. The fundamental reason lies in lack of combing the ophiolite and island arc as parts of trench-arc-basin systems. |
| keywords:Lajishan mélange SSZ ophiolite active continental margin tectonic evolution |
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