Studies of Igneous and Tectonic Textures and Layering in the Rocks of the Gosse Pile Intrusion, Central Australia

Abstract

The Gosse Pile mafic-ultramafic intrusion is a laycred igneous body, the upper part of which was involved in localized ductile deformation (low angle faulting) soon after crystallization. A complete gradation between rocks showing typically igneous textures and layering and those showing typically tectonic, or metamorphic, textures and layering can be observed. Textures and preferred orientations in the undeformed part of the intrusion are very similar to those found in other layered igneous bodies. Orthopyroxenes show very strong preferred orientations in some parts of the body. The metamorphic textures and layering of the deformed rocks are identical to ‘flow-layering’ which is used as an essential criterion for distinguishing ‘alpine-type’ from ‘stratiform’ bodies. The Gosse Pile Body thus demonstrates that at least some of the ‘alpine-type’ bodies may be produced byin situ deformation of ‘stratiform’ bodies.