大山次火山岩中岩浆熔离结构的元素分布特征及成岩模式

ELEMENT DISTRIBUTION FEATURES OF THE MAGMATIC LIQUATION TEXTURE AND PETROGENETIC MODEL OF DASHAN SUBVOLCANIC ROCK,ZHEJIANG PROVINCE

主要利用电子探针对大山次火山岩中岩浆熔离形成的结构单元一“浆屑”及基质两者间的元素分布特征进行了研究，Ｎａ、Ｋ、Ｆｅ、Ｓｉ等元素的面扫描分析及线扫描分析结果显示“浆屑”中富含金属元素Ｎａ、Ｋ、Ｆｅ等，贫Ｓｉ，基质中富含Ｓｉ，贫金属元素Ｎａ、Ｋ、Ｐｅ等。结合熔体结构分析及热力学计算，笔者讨论了大山次火山岩岩浆熔离的可能性及成岩模式。

Composed of ' the magma fragment', 'shard' and groundmass the Dathan subvolcanic rock is apparently the same as a welded tuff in characteristics under unaided eye and polarizing mieroscope. But, it has been found under polarizing microscope that the boundary between the magma fragments, shards and groundmass in a welded tuff is clear and obvious, and 'the magma fragments', 'shards' and groundmass in Dashan subvolcanic rock can be transitional to each other, and the phenocrystals are oriented. The microtextures of the groundmass in both Dashan subvolcanic rock and a welded tuff observed in SEM are quite different. The pyroclastic texture can be seen in the groundmass of a welded tuff. The groundmass of Dashan subvolcanic rock shows a lavatic texture. The authors studied the elements distribution feature between 'the magma fragment' and groundmass in Dashan subvolcanic rock by using EPMA (Electron Probe Microanalyzer). The Tesults of element area scanning analysis and line scanning analysis show the difference of composition between 'the magma fragment' and groundmass.' The magma fragment' is rich in Na,K, Fe, and poor in Si. The groundmass is rich in Si, and poor in Na, K, Fe. So, the authors thought that this subvolcanic rock was not a welded tuff, but a lava with the magmatic liquation banding. Based on the structure of magmatic melt and its thermodynamic the authors discussed the petrogenetic model of this subvolcanic rock.