关键词: 火山岩, 火山岩相, 相模式, 地层单元, 火山地层学, 盆地

Abstract:  Volcanic facies model in the basin is an important basis for reservoir distribution and identification. There are still some problems including stratigraphic unit inconsistency, unsystematic drilling, and large differences between basins. It is necessary to establish a system of facies models of basic stratigraphic units. This paper summarizes the definitions of facies, lithofacies and volcanic facies. Volcanic facies are divided into three classification schemes, which are for geological mapping and mineral survey in field, modern volcanoes and volcanic rocks in basin. It is considered that it is preferancial to apply the modern volcanic research results to guide the study of volcanic facies in the basin. The deposited units of volcanostratigraphy highlight the elements of rock fabric and geometric shape, and the volcanic facies division scheme of 5 facies, 15 subfacies and 44 microfacies is summarized. The eruptive facies is divided into pyroclastic flow, base surge, volcaniclastic apron, and volcaniclastic diatreme subfacies. The effusive facies is divided into subaerial lava flow, subaqueous lava flow, and subaerial eruption-subaqueous emplacement lava flow subfacies. The extrusive facies is divided into subaerial lava dome, underwater lava dome, and early subaqueous-late subaerial lava dome subfacies. The volcano-sedimentary facies is divided into lahar and debris avalanche subfacies. The subvolcanic facies is divided into dikes, laccolith and sill/lopolith subfacies. The characteristics of the fabric and structure of each microfacies are pointed out. Lava with different chemical compositions can form the same subfacies or microfacies. For example, rhyolite and basalt can both form the braided lava flow subfacies of the subaerial lava flow, while rhyolite, dacite, andesite, and basalt can all form the subaerial lava dome. With respect to the reservoir potential, the braided lava flow microfacies is better than the various microfacies of the subaerial lava dome. Therefore, the classification scheme in this paper can establish a detailed correlation between the subfacies/microfacies and the reservoir, and can be suitable for reservoir prediction and volcanic facies comparison in the basin.

Key words: volcanic rocks, volcanic facies, facies model, stratigraphic unit, volcanostratigraphy, basin