Abstracted/indexed

Using a relatively new dating technique, in situ Rb-Sr geochronology, we constrain the ages of two generations of mineral assemblages from the Tropicana Zone, Western Australia. The first dated at ca. 2535 Ma is associated with exhumation of an Archean craton margin and gold mineralization. The second, dated at ca. 1210 Ma, has not been previously documented in the Tropicana Zone. It is probably associated with Stage II of the Albany-Fraser Orogeny and additional gold mineralization.

Geologic dating methods generally do not directly measure ages. Instead, interpreting a geochemical measurement as an age requires a middle layer of calculations and supporting data, and the fact that this layer continually improves is an obstacle to synoptic analysis of geochronological data. This paper describes a prototype data management and analysis system that addresses this obstacle by making the middle-layer calculations transparent and dynamic to the user.

The integration of zircon geochemistry and U-Pb geochronology (petrochronology) allows us to further our understanding of magmatic processes and here we could reconstruct the ~ 300 kyr evolution of the magma reservoir that sourced the magmas, fluids and metals to form the Batu Hijau porphyry Cu-Au deposit. The application of in-situ LA-ICP-MS and high-precision CA-ID-TIMS geochronology to the same zircons further allowed an assessment of the strengths and limitations of the different techniques.

We show results from a new type of ion detector technology for mass spectrometry that allows us to measure ion beams more precisely. This technology expands the range of ages we can measure using a single instrument, and makes it possible measure those ages – including all required corrections and adjustments – with more confidence. We show measurements of widely-used standard materials for Ar/Ar, including air and synthetic standard gas, to illustrate the capabilities of the new detectors.

Baddeleyite (ZrO₂) is a commonly used mineral in U-Pb dating, but limited insight into discordance makes age interpretation difficult. We show that preferential 206Pb loss plays an important role for baddeleyite discordance, and present strategies to obtain more accurate ages by high precision and high spatial resolution methods. Based on microtextural observations, we present an interpretation guideline that helps to distinguish among seven different types of baddeleyite-zircon intergrowths.