The Contact Metamorphism and Related Phenomena in the Neighbourhood of Marulan, New South Wales

Abstract

1. The contact metamorphic effects produced by the intrusion of quartz-monzonite into the Silurian limestone of the Marulan district, New South Wales, are described.2. The rocks are divided broadly into marbles, hornfelses, skarns, and hybrid diopside-rocks. The first two groups are interpreted as being due to the recrystallization of limestone containing impurities which have reacted with the lime of the sediments to give lime-silicates and certain other minerals. The view is taken that only a very minor amount of pneumatolytic metamorphism followed the main thermal change. The skarns are shown to be due to the metasomatic replacement of recrystallized limestone by magmatic solutions rich in iron and silica, which were also responsible for the deposition of iron-oxides in cracks.The hybrid rocks are explained as developing from limited marginal assimilation of limestone by the quartz-monzonite magma.