Geochemical and isotope composition of tungsten (u182W): comparative analysis between bulk rock and mineral phases in silicated rocks

Short-lived system chronometers provide evidence for the rapid and early differentiation of planet Earth. In particular, the hafnium¹⁸²Hf – tungsten ¹⁸²W system (t_1/2 = 8.9 Ma) has been used to constrain the age of core formation and silicate differentiation taking advantage of the geochemical differences between these two elements during geological processes. For example, during core formation, W, which is a siderophile element, was attracted into the Earth’s core, while Hf, being a lithophile element, was concentrated into the silicate portion of the Earth. This contrasting difference in the behavior of these elements resulted in distinct ¹⁸²Hf/¹⁸²W isotopic ratios in both reservoirs, which are now reflected in the ¹⁸²W/¹⁸⁴W isotopic compositions of the samples derived from these reservoirs. The purpose of this work is to try to develop a new method for obtaining W isotope data for silicate rocks. The current bulk-rock analysis requires the use and preparation of large amounts of rock powder due to the very low W concentrations in most samples. Here, we propose a new methodology that may generate less costs and optimize the current method by replacing bulk-rock isotopic analysis with that of mineralogical fraction. In this study, we determined W concentrations (and other trace elements) of individual mineral phases from different types of rock by LA-ICP-MS. Our preliminary results reveal that titanium (Ti) - rich minerals, such as rutile and ilmenite, have systematically more elevated W concentrations than the other minerals. Rutile, in particular, captures most of the W in the rock. Replacing bulk rock isotopic analyses with analyses of Ti-rich minerals would require significantly less material to process. It is expected to obtain and compare results of W isotopic compositions of both the bulk rock and the Ti-rich mineral fraction.