Study on lithogeochemistry of Middle Jurassic basalts from southern China represented by the Fankeng

来源 :Science in China(Series D:Earth Sciences) | 被引量 : 0次 | 上传用户:tttde123
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There exists an E-W trending Middle Jurassic volcanic zone in southern China. The Fankeng basalts in the Yongding basin of Fujian Province are considered to be a typical example. The Fankeng basalts have TiO2 contents in the range of 1.92%-3.21%. They are classified as high-Ti basalts. They also have higher total Fe (averaging FeO* = 11.09%). The Middle Jurassic Fankeng basalts from southwestern Fujian have obvious distinctive lithogeochemical features from early Cre- taceous basalts from southeastern coast of China. They have higher HFSE, such as Th, Nb, Ta, Zr and Ti. Their element ratios related with HFSE, such as Zr/Ba, La/Nb, La/Ta ,Zr/Y, Ti/Y, Ba/Nb, K/Ti and Rb/Zr are similar to those of OIB. The most samples have ε Nd(T) of-0.70-0.24, which are near chondrite. Some samples have higher ε Nd(T) of 1.87-3.55.Therefore, these basaltic magmas might be derived from depleted asthenospheric mantle. The lithogeochemical characteristics of the Fankeng basalts may be caused by interaction between asthenosphere and lithosphere at the time. The (Early-) Middle Jurassic basalts and gabbros from southeastern Hunan, southern Jiangxi and northern Guangdong provinces show similar geochemical features to those of the Fankeng basalts from the Yongding of Fujian. Occurrence of these OIB-type basalts in the area may be regarded as the petrological mark of upwelling of asthenosphere at the time. Upwelling of asthenosphere has led to tectonic extension and the formation of rifted basin in the area. The Fankeng basalts have the TiO2 content in the range of 1.92% -3.21%. The Fankeng basalts in the Yongding basin of Fujian Province are considered to be a typical example. The Fankeng basalts have TiO2 contents in the range of 1.92% -3.21%. They are classified as an EW trending Middle Jurassic volcanic zone in southern China. They also have higher total Fe (averaging FeO * = 11.09%). The Middle Jurassic Fankeng basalts from southwestern Fujian have obvious distinctive lithogeochemical features from early Cre- taceous basalts from southeastern coast of China. They have higher HFSE , such as Th, Nb, Ta, Zr and Ti. Their element ratios related with HFSE, such as Zr / Ba, La / Nb, La / Ta, Zr / Y, Ti / Y, Ba / Nb, K / Ti and The most samples have ε Nd (T) of-0.70-0.24, which are near chondrite. Some samples have higher ε Nd (T) of 1.87-3.55.Therefore, these basaltic magmas might be derived derived from depleted asthenospheric mantle. The lithogeochemical characteristics of the Fankeng basalts may be caused by interacti on between asthenosphere and lithosphere at the time. The (Early-) Middle Jurassic basalts and gabbros from southeastern Hunan, southern Jiangxi and northern Guangdong provinces show similar geochemical features to those of the Fankeng basalts from the Yongding of Fujian. Occurrence of these OIB- type basalts in the area may be considered as the petrological mark of upwelling of asthenosphere at the time. Upwelling of asthenosphere has led to tectonic extension and the formation of rifted basin in the area.
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