Abstract
Volcanic rocks in seamounts of the South China Sea consist mainly of alkali basalt, tholeiitic basalt, trachyandesitic pumice, dacite, etc. Inclusions in the minerals of the volcanic rocks are mainly amorphous melt inclusions, which reflects that the volcanic rocks are characterized by submarine eruption and rapid cooling on the seafloor. Furthermore, fluid-melt inclusions have been discovered for the first time in alkali basalts and mantle-derived xenoliths. indicating a process of differentiation between magma and fluid in the course of mantle partial melting. Alkali basalts and inclusions may have been formed in this nonhomogeneous system.
Rock-forming temperatures of four seamounts were estimated as follows: the Zhongnan seamount alkali basalt 1155 ∼ 1185 °C; the Xianbei seamount alkali basalt 960 ∼ 1200 °C; tholeiitic basalt 1040 ∼ 1230 °C; the Daimao seamount tholeiitic basalt 1245 ∼ 1280 °C; and the Jianfeng seamount trachyandestic pumice 880 ∼ 1140 °C. Equilibrium pressures of alkali basalts in the Zhongnan and Xianbei seamounts are 13.57 and 8.8 × 108 Pa, respectively. Pyroxene equilibrium temperatures of mantle xenoliths from the Xianbei seamount were estimated at 1073 ∼ 1121 °C, and pressures at (15.58 ∼ 22.47)×108Pa, suggesting a deep-source (e.g. the asthenosphere) for the alkali basalts.
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This project was financially supported by the National Natural Science Foundation of China and Guangzhou Marine Geology Survey.
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Zhaolin, L., Zhili, Q., Shecai, Q. et al. A study on the forming conditions of basalts in seamounts of the South China Sea. Chin. J. of Geochem. 13, 107–117 (1994). https://doi.org/10.1007/BF02838511
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DOI: https://doi.org/10.1007/BF02838511