地震火山地层学及其在我国火山岩盆地中的应用

Applications of seismic volcanostratigraphy to the volcanic rifted basins of China

火山地层,物源来自于地下,搬运和分散方式有岩浆流、碎屑流、空落堆积及它们的再搬运,是不同于所有沉积地层的"异化地层".与层序地层学研究沉积地层类似,火山地层学着重研究火山岩系的层序界面和内部充填样式,通过地震层序分析刻画成因地层单元和地层对比关系.应用地震火山地层学在南海北部陆缘带识别出向海倾斜反射(SDR)、向陆流、外高和供给岩墙等表征火山裂谷陆缘的地震-地质单元;在松辽盆地识别出组-段-旋回三级层序界面,和垂向加积、侧向前积、披盖沉积、造丘和穿切五种充填样式.目前,火山地层学研究分为陆内和陆缘两个方向.陆内盆地的中小尺度地震相-火山岩相的研究精度高;而陆缘盆地大尺度地震-地质单元的成果更具普适性.二者取长补短、互为借鉴,将成为今后地震火山地层学研究的重要方向.

Materials comprising volcanogenic successions are derived from erupted components and transported by lava/pyroclastic flows and fallout as well as reworking processes. Their buildups are substaintial allostratigraphy and quite different from all kind of sedimentary sequences. The same with sequence stratigraphy for sedimentary rocks, voleanostratigraphy focuses on filling patterns confined by sequence boundaries, and depicts geological features and correlation of the successions in a volcanic basin. Some volcanic seismic facies units, including inner seaward dipping reflectors （SDR）, landward flows, outer high and feeder dikes, were recognized in northern margin of the South China Sea based on the concepts of seismic volcanostratigraphy, indicating volcanic rifted margin. For volcanogenic successions of the Songliao Basin, it was realized that there are three types of sequence boundaries, in descending order of formation, member, and volcanic cycle, and that there are five patterns of basin filling i.e. aggradation, progradation, draping, mounding and cutting. Inland basins and continental margins are two branches concerning the applications of seismic volcanostratigraphy. By comparison, intrafacies components/components associations （4^th tier） and facies associations （3^rd tier） were three-dimensionally described in inland basins. On the other hand, seismic facies （2^nd tier） like SRD and landward flows were globally developed in the marginal basins （cf. first tier heterogeneity is on the scale of graben）. Optimizing combination of the two branches will make seismic volcanostratigraphy more fruitful.