长江下游火山岩的二个变异趋势及其形成机制

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。

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

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.