Despite the presence of a large area of andesite in the Sayaburi Province of Laos, it has received very little attention. Based on a combination of detailed field investigations, geochronology and geochemical analysis...Despite the presence of a large area of andesite in the Sayaburi Province of Laos, it has received very little attention. Based on a combination of detailed field investigations, geochronology and geochemical analysis, this study aims to explore the geochemical, Sr-Nd isotopic, and source rock characteristics, as well as the genesis and tectonic setting of the andesite in this region. In the Sayaburi Province, the andesite zircon U-Pb age is(241.2±1.2) Ma. The andesite rock is classified in the metaluminous-weak peraluminous calc-alkaline series. The light rare-earth elements(LREEs) are enriched and characterized by clear fractionation, whereas heavy rare-earth elements(HREEs) are relatively depleted and have no signs of fractionation. The average δEu is 0.96 with weak-or-no Eu anomalies. It is enriched in large ion lithophile elements such as Rb and K, while depleted in high field-strength elements such as Nb, Ta, P and Ti. For andesites in the Sayaburi Province, the(87Rb/86Sr)t value ranges in 0.702849-0.704687, the εNd(t) value is between 3.53 and 4.77, the tDM(t) value ranges in 633-835 Ma, and the tDM2(t) ranges in 625–724 Ma. The results based on the synthesis of petrology, geochemistry, and regional tectonic background studies show that 1) the andesitic magma source in the study area is an enriched mantle, which is modified by subduction zone fluids;2) the geotectonic background environment of the andesite in Sayaburi area is the continental island arc environment and related to the tectonic evolution of Jinghong–Nan–Uttaradit back-arc basin, which reflects that the magmatic source is enriched with a mantle wedge component modified by a subduction zone fluid(or melt).展开更多
In this paper,we introduce the tectonic setting,historical earthquake focal mechanisms and geodynamic environment of Tienshan and its neighboring regions, and draw a conclusion that large earthquakes in the Tienshan s...In this paper,we introduce the tectonic setting,historical earthquake focal mechanisms and geodynamic environment of Tienshan and its neighboring regions, and draw a conclusion that large earthquakes in the Tienshan seismic zone are governed mainly by the pushing from Hindu Kush-Pamir syntax. Secondly,the relationship of large earthquakes in the Hindu Kush-Pamir region and the Tienshan seismic zone is investigated,and synchronization features are found existing in the grouped large earthquakes between the large earthquakes in two regions. The relationship between intermediate-focus large earthquakes in Hindu Kush-Pamir and shallow large earthquakes in the Tienshan seismic zone is also discussed. The same synchronization characteristics are found,and the intensity and frequency of intermediate-focus earthquakes are fiercer, while large earthquakes in the Tienshan seismic zone are more intense,with a wider distribution range. The above results confirm the geodynamic correlativity between Hindu Kush-Pamir and the Tienshan seismic zone from the viewpoint of seismicity.展开更多
基金Projects(DD20160107,DD20150742)supported by the China Geological SurveyProject supported by the International Scientific Plan of the Qinghai-Xizang(Tibet)Plateau of Chengdu Center,China Geological Survey
文摘Despite the presence of a large area of andesite in the Sayaburi Province of Laos, it has received very little attention. Based on a combination of detailed field investigations, geochronology and geochemical analysis, this study aims to explore the geochemical, Sr-Nd isotopic, and source rock characteristics, as well as the genesis and tectonic setting of the andesite in this region. In the Sayaburi Province, the andesite zircon U-Pb age is(241.2±1.2) Ma. The andesite rock is classified in the metaluminous-weak peraluminous calc-alkaline series. The light rare-earth elements(LREEs) are enriched and characterized by clear fractionation, whereas heavy rare-earth elements(HREEs) are relatively depleted and have no signs of fractionation. The average δEu is 0.96 with weak-or-no Eu anomalies. It is enriched in large ion lithophile elements such as Rb and K, while depleted in high field-strength elements such as Nb, Ta, P and Ti. For andesites in the Sayaburi Province, the(87Rb/86Sr)t value ranges in 0.702849-0.704687, the εNd(t) value is between 3.53 and 4.77, the tDM(t) value ranges in 633-835 Ma, and the tDM2(t) ranges in 625–724 Ma. The results based on the synthesis of petrology, geochemistry, and regional tectonic background studies show that 1) the andesitic magma source in the study area is an enriched mantle, which is modified by subduction zone fluids;2) the geotectonic background environment of the andesite in Sayaburi area is the continental island arc environment and related to the tectonic evolution of Jinghong–Nan–Uttaradit back-arc basin, which reflects that the magmatic source is enriched with a mantle wedge component modified by a subduction zone fluid(or melt).
基金jointly sponsored by the National Key Technology R&D Program(2012BAK19B01-04)the Special Fund of Youth Working Group,Institute of Earthquake Science,China Earthquake Administration
文摘In this paper,we introduce the tectonic setting,historical earthquake focal mechanisms and geodynamic environment of Tienshan and its neighboring regions, and draw a conclusion that large earthquakes in the Tienshan seismic zone are governed mainly by the pushing from Hindu Kush-Pamir syntax. Secondly,the relationship of large earthquakes in the Hindu Kush-Pamir region and the Tienshan seismic zone is investigated,and synchronization features are found existing in the grouped large earthquakes between the large earthquakes in two regions. The relationship between intermediate-focus large earthquakes in Hindu Kush-Pamir and shallow large earthquakes in the Tienshan seismic zone is also discussed. The same synchronization characteristics are found,and the intensity and frequency of intermediate-focus earthquakes are fiercer, while large earthquakes in the Tienshan seismic zone are more intense,with a wider distribution range. The above results confirm the geodynamic correlativity between Hindu Kush-Pamir and the Tienshan seismic zone from the viewpoint of seismicity.
