相山碎斑熔岩岩石特征及其成因探讨

Characteristics and Genesis of Porphyroclastic Lava Rock in Xiangshan

相山主体岩石碎斑熔岩在岩石成因、岩相归属上长期以来有多种不同的看法,原因在于碎斑熔岩边缘相具有熔结凝灰岩甚至是凝灰岩的特点,过渡相具有熔岩的特征,中间相具有潜火山岩的特征,并且各种相之间呈渐变过渡关系。笔者从碎斑熔岩的岩石矿物组成,稀土、微量元素及同位素特征,提出了碎斑熔岩是由基底变质岩重熔而形成的观点。从斑晶钾长石的低结构态和出溶机理,认为碎斑熔岩的形成环境接近于火山岩和潜火山岩,而与深成岩差别较大。碎斑熔岩中斑晶多呈碎裂状,与火山口内隐爆作用有关,因此将该岩石归属于火山侵出相。

Due to the transitional characteristics of porphyroclastic lava rock in Xiangshan of Jiangxi province,there are a variety of views on its genesis,petrographic attribution.This is because the marginal facies of the porphyroclastic lava is with ignimbrite and tuff characteristics,its transition phase has the characteristics of lava,and its intermediate phase has the feature of sub-volcanic rocks,further more,different texture of the rocks bears transition relationship.By the study of mineral composition,REE pattern,trace elements,isotopes,we put forward that the porphyroclastic lava is formed by the remelting of basement metamorphic rocks.The rocks was believed to be formed in the environment similar to volcanics and subvolcanics,and quite different to plutonic rocks due to the features of low-structure of potassium feldspar phenocrysts and solution mechanism,because the porphyroclastic lava phenocrysts occurs as fragments and maybe related to cryptoexplosion.Therefore the rocks was believed to belong to the volcano extrusive facies.