The petrology of the south-western end of the Mt. Samson gabbro-granite complex

In the Upper Cedar Creek area a gabbro, "diorite", granodiorite, and granite complex is emplaced in the Silurian? Neranleigh-Fernvale Group. This is an orogenic belt, and the post-tectonic sequence is of basic rocks followed by acidic rocks. The gabbro is considered to be derived by the melting of a lower simatic layer. Heat developed by orogenesis and the intrusion of the gabbro, together with the introduction of the elements Na and Ca, caused a replacement of the sediments at depth, giving trondhjemitic rocks which were mobilized and intruded. Later potash metasomatism converted these to granodiorities, and, finally, to true mobilized granites. Contact metamorphism is discussed; especially the metamorphism by the gabbro of unusual slates, giving rise to olivine-bearing hornfelses.