中文摘要：

长江中下游地区繁昌火山盆地在早白垩世先后发育3个喷发旋回：中分村旋回、赤沙旋回和蝌蚪山旋回。其中蝌蚪山旋回下段以凝灰质粉砂岩为主，中段为玄武岩和流纹质凝灰岩互层，上段以流纹岩为主。蝌蚪山玄武岩中的辉石既存在斑晶中也存在于基质中，这两种辉石在成分上有明显的差异，从斑晶辉石的核部到边部再到基质的核部，化学成分由富镁向富铁演化，显示出拉斑玄武岩系列的特点，辉石成因的判别图解表明其寄主岩浆为板内拉斑玄武岩，但其化学成分的变化趋势又表明岩浆在结晶分异的过程中向着碱性系列演化。根据单斜辉石与熔体平衡原理计算出玄武岩形成时的温度约为1100℃，压力约为400MPa，相应的深度约为15km，证明岩浆在地壳中有过短暂的停留，并在上地壳部位发生分离结晶作用后喷出地表快速冷凝形成蝌蚪山玄武岩。

英文摘要：

Three eruptional cycles occurred in the early Cretaceous in Fanchang volcanic basin which is located in the Middle-lower Yangtze River Region, they are Zhongfencun cycle, Chisha cycle and Kedoushan cycle respectively. The lower part of Kedoushan cycle consists predominantly of tuffaceous aleurolite,midpart consists of basalt interbedded with rhyolitic tuff,and the up- per part is composed predominantly of rhyolite. Clinopyroxene exists both in phenocryst and matrix,which have obvious differences in composition. Chemical composition changes from Mg-en- richment to Fe-enrichment from the core of acteristics of tholeiite series. Clinopyroxene to the rim of phenocrysts and matrix, revealing chardiscrimination diagrams show that the host magma is inner-plate tholeiite,but the variation tendency of its chemical composition shows that the magma was evolved to the alkaline series during the process of crystallization differentiation. According to the clinopyroxene-melting equilibrium principle, the crystallization temperature and pressure of the clinopyroxene in Kedoushan basalts are calculated, 1 100 ℃ and 400 MPa temperature and pressure are obtained,which correspond a relevant depth about 15 km,indicating that the magma stayed in the crust for a short time and then formed the Kedoushan basalts with a rapid cooling after the process of fractional crystallization in the upper crust.