长江下游火山岩的二个变异趋势及其形成机制

Two Variation Trends and Their Genesis of the Volcanic Rocks in the Lower Reach of the Yangtze River

长江下游地区若干盆地不同旋回火山岩的化学成分存在２个不同的变异趋势，即富硅趋势和富钾趋势。富硅趋势主要由分离结晶作用形成的。富钾趋势的成因较为复杂。庐枞富钾趋势的形成与分离结晶作用有关，溧水富钾趋势涉及分离结晶与混染作用。而宁芜富钾岩石是由独立的母岩浆形成的。

Composition of volcanic rocks from some basins in the lower reach of the Yangtze River shows two variation trends, Si-enrichment trend and K-enrichment trend. Major element and trace element characteristics of volcanic rocks and quantitative modelling indicate that formation of all Si-enrichment trends in the region can be explained by fractional crystallization. K-enrichment trends from various basins are, however, different in their genesis. K-enrichment trend from Luzhong basin is formed through fractional crystallization. Formation of K-enrichment trend from Lishui involves both fractional crystallization and assimilation. In Ningwu basin, K-rich rocks have no genetic relation with the early erupted aandesitic rocks and might be derived from an independent parent magma.