Structure, Sedimentary Inclusions, and Hydrothermal Alteration of a Latite Intrusion

The latite intrusion near Port Kembla, New South Wales, is a flat-topped laccolith intruded into marine tuffaceous sediments of Permian age. Systematic study of internal structures revealed that movement in the direction of primary flow structures continued into post-consolidation and post-alteration stages. Contact relations and structures of included sediments indicate that the country rocks were unconsolidated at the time of intrusion, and because of this the margin of the intrusion was irregular during its growth. This resulted in the inclusion of sedimentary material in zones broadly oriented in planes of flow foliation both where these were steep over the feeder and flat near outer margins. At the same time tension joints formed in still fluid but very viscous latite, and unconsolidated sediments were injected into the fractures. Hydrothermally altered zones in the latite are characterized by an abundance of sedimentary sheet inclusions, and the alteration was caused mainly by absorption, before com...