【摘要】 <正> 我国东南沿海的火山岩地区,例如浙江、福建、江西等省,分布着一种具有特殊地质意义而在成因上又有争议的岩石——碎斑熔岩。50年代,这种岩石被普遍确定为花岗斑岩、微花岗岩或花岗岩类侵入体的边缘相带。60年代以后,岩石学工作者将其归属于火山岩或次火山岩。总之,到目前为止,对这类岩石的岩相归属、岩石命名和成因尚有不同的意见。争论的问题大体上包括二个方面:其一,关于“粒状碎斑熔岩”,有角岩化熔结凝灰岩及次火山岩相、碎屑熔岩相、侵出相等不同观点;其二,关于“粒状碎斑熔岩”外围的一套与之呈过渡关系的岩石,有定为熔结凝灰岩,也有定为凝灰熔岩,相应地其成因机理说法也就很不一致。碎斑熔岩问题,是从1:20万区域地质测量和普查找矿中提出来的,随即引起了人们广泛的兴趣。正确认识碎斑熔岩不仅具更多还原

【Abstract】 Granular porphyroclastic lavas, a volcanic rock type with a special geological significance and in dispute on its genetic mechanism, are a series of rocks distributed in the volcanic rock belt of southeastern China and characterized by porphyroclastic texture for phenocrysts and vitric-felsitic-microgranular texture for matrix.Based on the detailed study of the typical porphyroclastic lava bodies and the regional investigatio.n in the whole area, the authors summarized the principle features of this rock series as follows: 1 . porphyroclastic lavas are widespread in the whole area, composing a member of volcanic intrusive complex distributed in clusters along the regional faults; 2 . the lavas lie in a definite part of volcanic structure representing products of evolution from negative volcanic structure to positive one; 3. most of them formed in the late period of the first volcanic cycle (147~120m.y ago),belonging to the late Jurassic-early Cretaceous epoch with only one exception found in eastern Fujian province that formed in the second volcanic cycle (87 m.y ago); 4 .the occurrence of porphyroclastic lava bodies shows a characteristic of extrusion-effusion, the contact between the porphyroid porphyroclastic lava and the peri-pheric vitric porphyroclastic lava is transitional and no intrusive contact with other rocks has been found yet; 5 . the porphyroclastic lava bodies show variation in facies from outer (or upper) part to inner (or deep) part, i.e. the gradual transition from hyalo-porphyroelstic lava to fel-sitic porphyroclastic lava and porphyroid porphyroclastic lava; 6 . the rocks are rich in phenocrysts, the proportions of phenocrysts are corresponding to the chemical classification of the rocks; 7. the rocks are complicated in texture, the porphyroclastic texture is their typomorphic texture; 8. the minerals show a characteristic of multiple-generation, the analysis of the texture state of feldspars indicate that the alkali felddspars belong to sanidine and orthoclase, the plagioclases are in wide range of composition (An = 30- 40) and the ordering degree is 20~50.In the light of macroscopic geology and microscopic features, the authors formed the viewpoints on petrographic facies and genetic model of porphyroclastic lava as follows.1. The disputed microgranula porphyroclastic lavas are neither the product of post-intrusion thermal metamorphism of welded tuff, nor the subvolcanic or effusive facies, in fact they belong to the internal facies of a large or composite extrusive periclinal terrain.2 . The vitric porphyroclastic lavas in a transitional relation with the porphyroid porphyroclastic lavas are the ignimbrite of liquation origin, not the ash flow tuff, so the term "tuff lava" should be abandoned. They might form the marginal facies of a large or composite dome, the small lateral dome and veined extrusive body, or the effusive facies in transitional relation with the normal lavas.3 . The origin model of large porphyroclastic lava bodies could be generalized in term of "three facies in one" characterized by the formation of extrusion and extrusion to effusion isometric dome and linear phacolith.4. The geological events of porphyroclasl ic lavas and the related rocks can be divided into four stages, i.e. the stage of volcanism before the formation of porphyroclastic lavas, the stage of the formation of porphyroclastic lavas, the stage of intrusion after the formation of porphyroclastic lavas and the stage of uplift and erosion.5 . The mechanism of the formation of porphyroclastic lava includes crystallization of phenocrysts and their corrosion, liquation in shallow magma chamber, cataclasm of phenocrysts, emplacement and cooling of lavas, ana postmagmatic gaseous phase crystallization and recrystalliza-tion. The difference in supercooling gradient during extrusion and effusion of magma is the predominant factor for the formation of model "three facies in one", and the lithophile volatile components play an important role in the liquation of magma.更多还原