中国东部地区新生代岩浆活动对区域性CO_2形成时间的制约

中国东部地区新生代存在 4个岩浆活动期 :第一期 6 5～ 4 1Ma ,第二期 4 1～ 2 1Ma ,第三期 2 1～ 13Ma ,第四期 11Ma至今。对研究区内火山岩地球化学研究表明 ,古近纪早期火山岩以拉斑玄武岩和钙碱性玄武岩为主 ,后期特别是从沙三期开始逐渐转变为碱性岩石。火山岩中CO2 包裹体含量统计表明 ,沙三段 (Es3 )中CO2 含量明显高于其它几个岩性段 ,而碱性岩中CO2 的含量又明显高于拉斑玄武岩中的含量。沙三期是整个东部地区一个较重要的岩浆活动期和火山活动发生重大改变的时期 ,从沙三期到馆陶期形成的碱性岩具有最大的CO2 成藏潜力 ,沙三期及以后的火山岩与CO2 在空间上存在密切关系 ,因此沙三期到馆陶期是形成区内CO2 的主要时期。

CONSTRAINTS ON FORMATION TIME OF CO2 FROM CENOZOIC MAGMATISM IN EASTERN CHINA

There are four periods of magmatism in Eastern China, they are 65～41 Ma,41～21 Ma,21～13Ma,and 11～1Ma, respectively. The magmatic rocks for the first and second periods erupted within the rift basins. The magmatic rocks for the third and fourth periods occurred on the margins of the basins or along the Tanlu fault belt. The CO_2 derived from magma in Eastern China mainly formed in the pull-apart basins, and are consistent with the magmatic rocks formed during the first and second periods in space. The geochemical data of volcanic rocks from Jiyang depression indicate that magmatic rocks of early Teriary are mainly tholeiitic and calc-alkali. The rocks formed after Es_3 are all alkali rocks. The contents of CO_2 enclosure in volcanic rock from the Shengli Oil Field indicate that the contents of CO_2 in the volcanic rocks from Es_3 are observably higher than those from other rock units, and the CO_2 contents in the enclosures of alkali basalt are markedly higher than those of tholeiite. So the magmatism from Es_3 to Ng is the main period for the formation of CO_2.