| 滇西新生代富碱斑岩的岩石特征与成因 |
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| 引用本文： | 邓万明,黄萱.滇西新生代富碱斑岩的岩石特征与成因[J].地质科学,1998,33(4):412-425. |
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| 作者姓名： | 邓万明 黄萱 |
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| 作者单位： | 中国科学院地质研究所 北京 100029 |
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| 摘 要： | 对滇西金沙江-墨江缝合带中段新生代富碱斑岩的岩石地球化学和同位素组成的研究表明,这一套岩石形成在板内造山后的剪切和拉张构造环境,是壳-幔混合层物质部分熔融,快速上升浅部定位所形成。本区壳-幔过渡带可能是先期生成的一种富集源区。文中还讨论了壳-幔过渡带的成因及富碱斑岩岩浆活动与岩石圈演化的关系。
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| 关 键 词： | 富碱斑岩 壳－幔混合层 岩石圈演化 板内变形 |
| 收稿时间： | 1997-03-27 |
| 修稿时间： | 1997-03-27; |
PETROLOGICAL CHARACTERISTICS AND GENESIS OF CENOZOIC ALKALI RICH PORPHYRY IN WEST YUNNAN, CHINA |
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| Deng Wanming\ Huang Xuan\ Zhong Dalai.PETROLOGICAL CHARACTERISTICS AND GENESIS OF CENOZOIC ALKALI RICH PORPHYRY IN WEST YUNNAN, CHINA[J].Chinese Journal of Geology,1998,33(4):412-425. |
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| Authors: | Deng Wanming\ Huang Xuan\ Zhong Dalai |
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| Institution: | Institute of Geol. Chinese Academy of Sciences, Beijing, 100029 |
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| Abstract: | Four Cenozoic porphyry groups occuring at north segment of the Jinsha river suture zone have been studied in petrology, petro-geochemistry, chronology and isotopic components. These rocks include mostly syenite porphyry, monzonitic porphyry, granitic porphyry and a few trachytic porphyry. Most porphyries belong to the alkalic calc series in petrochemistry formed in the post-collision environment, and are charactrized by LREE-rich distribution patterns without Eu anomaly. The apparent ages of the alkali-rich porphyries range from 26.5 to 37.6Ma according to K/Ar dating of whole-rocks. A few xenoliths such as amphibolite, garnet-bearing amphibolite, P1-hornblende gneiss etc. have been discovered in some rock bodies. These shards may represent ancient basemental metamorphic rocks from mid lower continental crust beneath the Yangtze plate. According to isotopic analytical results, (87Sr/86Sr)i of porphyries, amphibolites and basalts are 0.7073(average), 0.7065—0.7071 and 0.7058—0.7065; εNd(t) are -3.4—-6.3,-2.1—-7.4 and -3.3(average),respectively. Pb isotopic compositions of these samples also show a little differences. In brief, these values are situated just in a transitional position between a depleted mantle source and a typical crustal source. There are evidence that the porphyritic magma was derived from partial melting of the EMII type source, i.e. so-called “crust-mantle mixed layer” within subcontinental lithosphere. It is demonstrated by geophysical researches that there is a “crust-mantle mixed layer”, which has an average V p velocity of 7.70—7.80 km/sec with about 10 km thickness in the study area. Moreover, a high thermal anomaly and an obvious asthenospheric upwelling have been already proved. It is possible that the genesis of the “crust-mantle mixed layer” is related closely to formation of the Jinsha-Ailaoshan plate suture zone. It seems likely that some oceanic sediments and terrigenous materials were brought into the mantle accreting wedge along subduction zone during the closure of the “Jinsha oceanic lithosphere” about 220—250 Ma ago. In other words, the crustal mass has participated in a recycling chemical process within the continental upper mantle. But the partial melting of the EMII type source and intrusion or extrusion of the magmas upwards might be controlled by intraplate deformation mechanisms since the Paleogene. |
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| Keywords: | Alkali rich porphyry Crust mantle mixed layer Lithosphere evolution Intraplate deformation |
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