Probing the `Zircon Zip': Geochronology (FT and SHRIMP)

Abstract

Zircon megacrysts are associated with gem ruby- sapphire deposits along a 12 000 km long zone, from eastern Australia in the south, through South East Asia, to far eastern Russia in the north. Representative zircons were studied from some 6 sites along this zone. This is just a small part of a much broader ongoing study of this zone whose occurrence must be due to some fundamental plate tectonic process. The time relationship between zircon crystallisation at depth, and transport to the surface via basaltic magmas was studied using zircon FT, U-Pb zircon SHRIMP techniques, and published basalt ages. The results show that for some fields, zircon crystallisation and transport to the surface were almost coeval events, whilst for others, zircons crystallised as much as 200 Ma before later transport.