Mesozoic volcanic rocks in the lower reaches of the changjiang river

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Mesozoic magmatic activities in the eastern part of China were closely related to the mutual movement of the Eurasian and Kula plates. Mesozoic volcanic rocks can be divided into the southern, central and northern petrological regions. The Changzhou-Yueyang deep fault in the south and the Baodi-Changli-Jinzhou fault in the north are the main boundaries between them and extend in a roughly NEE direction.Mesozoic volcanic basins distributed in the lower reaches of the Changjiang River are located near the boundary line between the southern and central petrological regions. Based on the association of volcanic rocks they can be divided into four volcanic belts. From south to north they are as follows: (I) Guangde-Liyang-Wuxi volcanic belt; (II) Fanchang-Lishui-Zhenjiang volcanic belt; (III) Huaining-Luzong-Ningwu volcanic belt; (IV) Chuxian-Jinhu volcanic belt. These volcanic belts are nearly parallel with the Changzhou-Yueyang deep fault.Their major-element chemical variation, strontium, oxygen and sulphur isotopes and REE suggest that the dacite-rhyolitic magma in volcanic belt (I) was generated by anatexis of the lower part of the continental crust, and the andesitic magma in the volcanic belts (III) and (IV) might be generated by fusion of the upper mantle mixed with some other materials in the subducted zone under great compression, at 1200°–1250°C, with sufficient water. The “trachyandesite-latite rock series” is very different from the shoshonitic one and, it might be the product of the interaction of alkali-enriched andesitic magma with gypsum-salt beds. The volcanic rocks in belt (II) exhibit a transitional character.