Melissa Kharkongor

I am working on a project that aims to establish apatite as a new tool to date mafic rocks. Mafic rocks are the most common type of igneous rocks on Earth, however, constraining the crystallization age of mafic rocks can be challenging. Apatite is a common accessory phase in mafic rocks, where zircons and other datable minerals are absent or low in abundance. It is amenable to dating using the U-Pb system, however, the U-Pb system in apatite has a relatively low closure temperature (~350°-550° C) and is therefore prone to resetting by later thermal and metasomatic events. In this study, a recently developed Lu-Hf dating method using laser ablation reaction-cell mass spectrometry is applied to apatite from mafic rocks. The Lu-Hf system in apatite has a higher closure temperature (~650°-750°C) compared to U-Pb, increasing the chances of obtaining primary crystallization ages.

Legacy samples from Australia, Brazil, Canada, Finland, India, and other areas will be chosen based on the availability of mafic rocks. These samples will be analysed for LA-ICP-MS U-Pb, Lu-Hf  and U-Pb ratios to construct a database of  ages that can be integrated with the zircon record to provide a more holistic description for how our planet developed.