Facies models for ancient volcanic successions

Abstract

The preceding chapters have laid the groundwork for this chapter, by emphasising processes and products in modern volcanic terrains, which are extremely important in understanding equivalent elements in ancient terrains. Any study in modern terrains is only half complete if the relevance to the rock record is ignored. The majority of workers in volcanic terrains are not working in modern successions, but are geologists (most of them exploration or survey geologists) trying to make sense of discontinuously outcropping, variably deformed, metamorphosed and hydrothermally altered successions. Therefore, in this chapter we try to bring together what has been presented in previous chapters to construct general but workable facies models. These serve to represent significant associations of facies and, if possible, their spatial and genetic relationships, and to summarise, however schematically, the palaeoenvironmental—palaeogeographic context. If this can be done, then such facies models may have predictive value for ancient successions and in basin analysis studies involving volcanic successions. We also consider the influences that modify original facies characteristics in ancient successions, including the effects of erosion, alteration, metamorphism and diagenesis.