赣南中生代火山活动时代及岩浆来源

THE MESOZOIC VOLCANIC AGE AND THE SOURCE OF MAGMA IN SOUTH JIANGXI

同位素地质研究表明，赣南中生代火山活动分属侏罗纪和白垩纪两大旋回，火山地层的时序为菖蒲组（Ｊ２），鸡笼嶂组（Ｊ３），路迳金伯利角砾岩（Ｋ１），赣州组（Ｋ１２－Ｋ２１），版石组（Ｋ２２）；火山岩浆属壳幔混源型，不同活动时期壳幔组分比例呈规律性变化，是板内深断裂作用的产物。

By means of the isotope geology study of the Gannan Mesozoic volcanic basin system, the authors come to the following conclusions:1 ) The isGtope age span of the Mesozoic volcanic activity in Gannan ranges from 176to 72 Ma (The early and middle Jurassic Period to the end of the late Cretaceous Period). There is a clear distinction between the Jurassic Period and the volcanic activity in the Jurassic Period and that in the Cretaceous Period. The volcanic activity in the Jurassic Period was very strong and it became weaker and weaker from southwest to northeast. and finally disappeared in a basin. The volcanos erupted intermittently in the Cretaceous Period. The center of the volcanic activity shifted from the east to the west. The chronological age order of the upper layer igneous rocks is:Yongpu Group: The age span ranges from 176 to 60, with crest value of 175Ma. It belongs to JI or J2 type.Jilongzhang Group: The age span ranges from 154 to 138 Ma, with the crest value of 140 to 150 Ma. It belongs to the J3 type.Anyuan Group: the age span ranges from 140 to 132 Ma and judging by some related materials, it can be classified as the K1 type.Ganzhou Group: The age span ranges from 85 to 106 Ma, with two crest values,85 Ma and 106 Ma, which goes in the direction of the two faults running from north to east. It belongs to K1 and K2 type.Banshi Group: The age span ranges from 72 to 79 Ma. It belongs to K2 type 2 ) The volcanic magma in Gannan prefecture is the mixture of crust and mantle. The proportion of the crust and mantle distribution shows a regular pattern in accordance with the different periods of the volcanic sctivity. The thickness of the crust of the Yongpu Group averages 63, Jilongzhang Group 56, Ganzhou Group 63, Banshi Group 70. Generally speaking, the thickness of the crust increases from early volcanic activity to the late volcanic activity.The formation background of the volcanic activity in the Gannan prefecture is partly due to the diving of the volcanic activity plate in the southeast coastal areas. It is caused by the action of the three faults in the Gannan prefecture.