Holocene basaltic rocks of the Jingpohu area are located in the “Crater Forest” and Hamatang districts to the northwest of the Jingpohu Lake. Although there is only a distance of 15 km between the two districts, the...Holocene basaltic rocks of the Jingpohu area are located in the “Crater Forest” and Hamatang districts to the northwest of the Jingpohu Lake. Although there is only a distance of 15 km between the two districts, their petrological characteristics are very different: alkaline olivine basalt without any megacrysts in the former, and leucite tephrite with Ti-amphibole, phlogopite and anorthoclasite megacrysts in the latter. On the basis of their geochemical characteristics, the two types of basaltic rocks should belong to weakly sodian alkaline basalts. But leucite tephrite is characterized by higher Al2O3, Na2O and K2O, higher enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), lower MgO and CaO, compatible elements and moderately compatible elements and lower Mg*values and Na/K ratios in comparison with alkaline olivine basalt. However, the two types of basaltic rocks have similar Sr, Nd, Pb isotopic compositions, which suggests that the mantle beneath the Jingpohu area was homogeneous before undergoing some geological processes about 3490 years ago. As the activity of the mantle plume led to different degrees of metasomatism, extreme mantle source heterogeneities occurred beneath the Jingpohu area. In comparison with alkaline olivine basalt, the leucite tephrite was derived from the more enriched mantle source region and resulted from strong metasomatism.展开更多
Seismicity in the Jingpohu volcanic area was investigated based on the seismic data recorded by the mobile seismic network consisting of 14 stations equipped with 24-bit broad-band 3- component seismographs around Cra...Seismicity in the Jingpohu volcanic area was investigated based on the seismic data recorded by the mobile seismic network consisting of 14 stations equipped with 24-bit broad-band 3- component seismographs around Crater Forest, Results show that there appears certain seismicity in Jingpohu and its adjacent areas with a low activity level and most of the recorded earthquakes are the volcanic-tectonic ones, The results of location indicate a dominant focal depth of 10km - 30kin, most of the earthquakes are smaller than ML2,0, and are concentrated in the area of ＂ Crater Forest＂ and on the Dunhua-Mishan fault which runs through the volcanic area. At station No. 2, which has better observation conditions, two types of events, likely associated to volcanism, were recorded; their waveform characteristics are somewhat similar to that of the long-period volcanic event and the volcanic tremor, but with different feature of frequencies.展开更多
文摘Holocene basaltic rocks of the Jingpohu area are located in the “Crater Forest” and Hamatang districts to the northwest of the Jingpohu Lake. Although there is only a distance of 15 km between the two districts, their petrological characteristics are very different: alkaline olivine basalt without any megacrysts in the former, and leucite tephrite with Ti-amphibole, phlogopite and anorthoclasite megacrysts in the latter. On the basis of their geochemical characteristics, the two types of basaltic rocks should belong to weakly sodian alkaline basalts. But leucite tephrite is characterized by higher Al2O3, Na2O and K2O, higher enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), lower MgO and CaO, compatible elements and moderately compatible elements and lower Mg*values and Na/K ratios in comparison with alkaline olivine basalt. However, the two types of basaltic rocks have similar Sr, Nd, Pb isotopic compositions, which suggests that the mantle beneath the Jingpohu area was homogeneous before undergoing some geological processes about 3490 years ago. As the activity of the mantle plume led to different degrees of metasomatism, extreme mantle source heterogeneities occurred beneath the Jingpohu area. In comparison with alkaline olivine basalt, the leucite tephrite was derived from the more enriched mantle source region and resulted from strong metasomatism.
基金The research was jointly sponsored by National Natural Science Foundation (GrantNo. 40474049)the Public Welfare Research Fund ofMinistry of Science andTechnology of China (2001DIA10003)
文摘Seismicity in the Jingpohu volcanic area was investigated based on the seismic data recorded by the mobile seismic network consisting of 14 stations equipped with 24-bit broad-band 3- component seismographs around Crater Forest, Results show that there appears certain seismicity in Jingpohu and its adjacent areas with a low activity level and most of the recorded earthquakes are the volcanic-tectonic ones, The results of location indicate a dominant focal depth of 10km - 30kin, most of the earthquakes are smaller than ML2,0, and are concentrated in the area of ＂ Crater Forest＂ and on the Dunhua-Mishan fault which runs through the volcanic area. At station No. 2, which has better observation conditions, two types of events, likely associated to volcanism, were recorded; their waveform characteristics are somewhat similar to that of the long-period volcanic event and the volcanic tremor, but with different feature of frequencies.
