| GEOCHEMISTRY OF EARLY CRETACEOUS TRACHYTES OF DONGLINGTAI FORMATION FROM THE XISHAN AREA, BEIJING： CONSTRAINTS ON MELTING OF LOWER MAFIC CRUST |
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| 作者姓名： | LI Xiaoyong * FAN Weiming GUO Feng WANG Yuejun and LI Chaowen |
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| 作者单位： | 1. Zhuzhou Institute of Technology，Zhuzhou，Hunan 412008，China; 2. Guangzhou Institute of Geochemistry，Chinese Academy of Science，Guangzhou，GD 510640，China; 3. Resource and Environmental Bureau of Chinese Academy of Sciences，Beijing 100864，China |
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| 基金项目： | 中国科学院资助项目，国家自然科学基金 |
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| 摘 要： | Felsic igneous rocks are of widespread magma types in continental orogenic belt, the petrologic genesis of which provides very important indication for understanding crustal evolution and melting geodynamic process within orogenic belt. Because of the differences of meltingdynamic condition, e.g. (1) composition of source rock; (2) physical chemistry conditions such as temperature, pressure etc.; (3) composition of residual phases and so on, felsic igneous rocks exhibit distinctly diverse petro…
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| 关 键 词： | 铁镁质壳 部分熔融 白垩纪 北京 粗面岩 |
GEOCHEMISTRY OF EARLY CRETACEOUS TRACHYTES OF DONGLINGTAI FORMATION FROM THE XISHAN AREA,BEIJING:CONSTRAINTS ON MELTING OF LOWER MAFIC CRUST |
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| LI Xiaoyong,*,FAN Weiming,GUO Feng,WANG Yuejun and LI Chaowen.GEOCHEMISTRY OF EARLY CRETACEOUS TRACHYTES OF DONGLINGTAI FORMATION FROM THE XISHAN AREA,BEIJING:CONSTRAINTS ON MELTING OF LOWER MAFIC CRUST[J].Geotectonicaet Metallogenia,2005,29(1):44-57. |
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| Authors: | Li Xiaoyong FAN Weiming GUO Feng Wang Yuejun Li Chaowen |
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| Abstract: | The early Cretaceous trachytes of Donglingtai Formation in Xishan, Beijing are characterized by slight Eu negative anomaly and significant enrichment in LREE, LILE (Ba, K and Sr) and depletion of Nb-Ta-Ti, Th-U. These trachytes have been highly enriched by Sr and Nd isotopic signatures (87Sr/86Sr(t)= 0.70638～ 0.70672, εNd(t) = -16.3～ -15.7), overlapping Sr-Nd isotopic range of late Mesozoic mafic igneous rocks in the region. Taking into account Nb-Ta fractionation and high Zr/Sm ratio for these trachytes, we consider that the trachytes of Donglingtai Formation are derived from the garnet-bearing amphibolite in the lower crust composed of garnet plagioclase ± amphibole ± pyroxene residual phases. On the basis of the melting experimental results of crustal materials and regional extensional tectonics during late Mesozoic, it is concluded that the thermal input from underplating basaltic melt results in the partial melting of lower continental crust to generate the trachytes of Donglingtai Formation. And the characteristics of high Sr and Ba for these trachytes suggest that part of underplating basalts should take a share in partial melting at least. |
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| Keywords: | mafic lower crust partial melting trachyte early Cretaceous Beijing Xishan |
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