Successive geothermal, volcanic-hydrothermal and contact-metasomatic events in island-arc basalts, South Shetland Islands

摘要

Hydrothermal alteration in volcanic arcs occurs in diverse settings and may involve magmatic, marine, lacustrine or ground waters driven by tectonic or thermal events. King George Island, part of the South Shetland Island Cainozoic volcanic arc, contains an 80 km long zone of propylitized volcanic rocks wit numerous occurrences of quartz veining, silicic, sericitic, argillic and advanced argillic alteration. On Barton Peninsula a basaltic tuff and lava sequence (49-44 m.y.), cut by a small, high-level, diorite-granodiorite pluton (42-41 m.y.), contains these alteration types, previously interpreted as a single, porphyry copper-type, system. However, field relations, mineralogies, textures and new geochemical data reveal three, possibly four, distinct hydrothermal events.