浙江左溪石英闪长岩成因的元素地球化学证据

左溪石英闪长岩赋存于浙江绍兴-江山断裂带中,其平均化学成分近似于出露在其北西侧的元古界双溪坞群;不同岩性的元素含量及比值具有线性演化关系,相似于不均一的二元混合物。对造岩元素及稀土元素含量的模拟计算表明:双溪坞群50%部分熔融的熔体相与残留相按不同混合比组成的混合相,相当于岩体中的不同岩性。因此,“部分熔融-不均一混合”的模型可以较好地解释岩体所具有的元素地球化学特征。

ELEMENTAL GEOCHEMICAL EVIDENCE FOR THE PETROGENESIS OF THE ZHUOXI QUARTZ-DIORITE, ZHEJIANG PROVINCE

Zhuoxi quartz-diorite body, which is situated in the Shaoxing-Jiangshan deep fault zone, is composed of quartzdiorite, gneissic quartz-diorite, gneissic diorite, plagioclase-amphibolite and others. The average chemical composition is similar to that of the Proterozoic Shuangxiwu spitite-keratophyre, which is situated near the Zhuoxi body. The contents and ratios of elements in difterent lithologies of the body vary in a linear evolutionary relationship, as that in a imhomogeneous binary mixttre. The calculatiens to simulate the contents of lock-forming and rare earth elements indicate that the residual phase produced by a 50% partial melting of the Shuangxiwu group has a chemical composition almost the same as that of the pyroxene-plagioclase-amphibolite in the Zhuoxi body. The mixtures composed of the melting phase and the residual phase in different mixing percentages correspond to the different lithologies in the body. Therefore, the authors regard partial melting of Shuangxiwu group-inhomogeneous mixing of the melting phase and the residual phase as the suitable petrogenetic model to explain the elemental geochemistry of the Zhoxi quartz-diorite body.