Abstracted/indexed

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.

The dating of carbonates by laser ablation ICP-MS is improved by an additional, newly characterised reference material, and adapted data evaluation protocols: The shape (diameter to depth) of the ablation crater has to be as similar as possible between the reference material used and the unknown samples. Otherwise an offset is introduced. Different carbonates have different ablation rates per laser pulse. With robust uncertainty propagation, precision can be as good as 2–3 %.

Our study presents the first seasonally laminated (varved) sediment record covering almost the entire Holocene in high-mountainous arid Central Asia. The established floating varve chronology is confirmed by two terrestrial radiocarbon dates, whereby aquatic radiocarbon dates reveal decreasing reservoir ages up core. Changes in seasonal deposition characteristics are attributed to changes in runoff and precipitation and/or to evaporative summer conditions.