| 大别苏鲁地区层状地幔反射体及其解释 |
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| 引用本文： | 杨文采.大别苏鲁地区层状地幔反射体及其解释[J].地球物理学报,2003,46(2):191-196. |
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| 作者姓名： | 杨文采 |
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| 作者单位： | 中国地质科学院地质研究所，北京 100037 |
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| 基金项目： | 大陆科学钻探工程 (CCSDP)，国土资源部重点基础研究项目 (2 0 0 0 1 0 1 0 2 0 3) . |
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| 摘 要： | 深反射地震虽然己广泛应用于地壳上地幔调查，然而，来自地幔的反射体在全世界 都还比较少见，尤其是尚未有发现上地幔中多层水平反射体的报道. 近年来，作者用24s 的 深反射地震记录揭示了在大别苏鲁地区岩石圈地幔内存在5组水平的反射体, 表明该区具有 特殊演化作用形成的上地幔组构, 它们可随深度增加分别命名为M1到M5 . 这些反射体不仅 可在地震叠加剖面上看到，有时还可在野外单炮记录上看到. 反射体M1对应Moho面，而M5大 概与现今岩石圈底界对应，根据地热资料，苏鲁热岩石圈厚度约为78km. 其他3个反射体可 能是中生代岩石圈减薄诱发的壳幔作用的结果. 根据岩石学与地球化学的数据，在晚中生代 中国东部岩石圈的厚度约从150km减薄到约60km，在新生代又略微加厚到平均 78km. 这一减 薄作用引起岩浆底侵并在下地壳产生麻粒岩层，而早侏罗纪扬子克拉通向北的陆-陆俯冲又 在上地幔产生榴辉岩层. 在双程走时12s处的反射体M2 则是麻粒岩层与榴辉岩层的边界，它 也是古生代的 Moho面. 反射体 M3 出现在14s 前后，看来是榴辉岩层的底面, 它的下面应 保存有残留的古生代上地幔. 由于新老岩石圈地幔成分不同，其界面产生反射体 M4. 这种 多层岩石圈地幔反射体的存在表明，所研究地区的地幔结构与中国东部中生代岩石圈减薄作 用有关. 同时，由于20世纪80年代以来一直认为上地幔在反射地震上是相对透明的，多层反 射体的发现对这一认识是新的挑战, 表明采用爆炸震源与地震反射新技术有可能揭露岩石圈 地幔内部结构细节，这些细节也是地幔动力学作用的产物.
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| 关 键 词： | 深反射地震 地幔反射 岩石圈减薄 壳幔相互作用 中国东部 |
| 文章编号： | 0001-5733(2003)02-0191-06 |
| 收稿时间： | 2002-4-28 |
| 修稿时间： | 2002-11-8 |
LAYERED MANTLE REFLECTORS IN DABIE-SULU AREAS AND THEIR INTERPRETATION |
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| YANG WENCAI.LAYERED MANTLE REFLECTORS IN DABIE-SULU AREAS AND THEIR INTERPRETATION[J].Chinese Journal of Geophysics,2003,46(2):191-196. |
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| Authors: | YANG WENCAI |
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| Institution: | Institute of Geology, CAGS, 26 Baiwanzhuang Road, Beijing 100037, China |
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| Abstract: | Although the deep seismic reflection method has been widely applied to investigations of the crust and mantle, reflectors occurred in the mantle, espe cially multi layered reflectors, have been rarely reported. Recent 24s deep sei smic reflection records conducted by the author revealed 5 flat reflectors in the lithospheric mantle in Eastern China, indicating some importan t mantle fabrics that produced by special dynamic processes. They are named M1 t o M5 with increasing depth, and can be seen on both field single shot and stack ed records. The reflector M1 corresponds to the Moho discontinuity, whilst M5 sh ould be the reflection from the bottom of the current lithosphere that is about 78km deep according to geothermal measurements. The other three reflectors might result from interaction between the crust and mantle induced by the process of lithospheric thinning. Based on lithological and geochemical data, it is suggest ed that the lithosphere has been thinned from about 150km to about 60km in the l ate Mesozoic, and then has been thickened to about 78km during the Cenozoic. The thinning process produced a granulite layer in the old lower crust caused by ma gmatic underplating, whilst an eclogite layer beneath occurred owing to the subdu ction of the Yangtze craton during the early Mesozoic. The reflector M2 at about 12s TWT might result from the Paleozoic Moho that turned out to be the boundary between the granulite and eclogite facies. The reflector M3 at about 14s might correspond to the bottom of the eclogite layer, beneath which the old lithospher ic mantle remained. The old and the newly developed mantle may have different co mpositions, resulting in the reflector M4. The multi layered mantle reflectors demonstrate a typical mantle structure that correlates with the lithospheric thi nning process that occurred in Eastern China during the later Mesozoic. As the i dea of seismically transparent uppermost mantle has been widely accepted since t he late 1980s, the discovery of the multi layered mantle reflectors in the Dabi e Sulu areas of Eastern China implies that this idea can be challenged, suggest ing that reflection seismology with improved technology can provide more details related to some dynamic processes occurring in the lithospheric mantle. |
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| Keywords: | Dee pseismic reflection Mantle reflectors Lithospheric thinning Crust-mantle interaction Eastern China |
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