钠质与钾质中酸性岩浆的成因:玄武质岩的高压熔融实验研究

ORIGIN OF THE SODIC AND POTASSIC INTERMEDIATE-ACID MAGMAS:MELTING EXPERIMENTS ON BASALTIC ROCKS AT HIGH PRESSURES

在温度850～1300℃，压力1．5～3．5GPa和含约2％水的条件下进行了碱性玄武岩和拉斑玄武质岩的熔融实验，实验和研究结果表明：①含饱和水的拉斑玄武岩在低的部分熔融程度下可以熔出花岗岩，而含不饱和水时只能熔出英云闪长质岩；②含不饱和水的钾质和钢质碱性玄武岩在低的部分熔融程度下分别可以熔融出花岗岩和奥长花岗岩。因此，太古宙广泛发育的奥长花岗岩说明当时的玄武岩质地壳是贫钾的，太古宙地壳不存在饱和水的岩浆源区，这意味着太古宙不存在大规模的板块运动。

Melting experiments on aIkalic and tholeiitic rocks containing about 2 % water were made at 850- 1300℃ and 1. 5-3. 5 GPa. The results showed that: (1 ) partial melting of tholeiitic rocks with saturated water would produce granitic magma, but only tonalitic magma with unsaturated water; (2) granitic and trondhjemitic magmas could be derived from lower partial melting of potas-sic and sodic alkali basalts with unsaturated water, respectively. So the fact that trondhjemite was developed during the Archean indicates that the basaltic crust at that time was lack of potassium and there were no magma sources with saturated water in the Archean crust, thus suggesting no large-scale plate movement during the Archean.