Abstract:

Advances in analytical techniques lead to increasing application of non-traditional stable isotope in the investigation of high-temperature processes, such as magmatic differentiation, core formation, and early solar nebula evaporation and condensation. Although titanium (Ti) is a very important transition metal element occurring widely on Earth and other Earth-like planets, Ti stable isotope has received little attention to date. This is because Ti is relatively insoluble in sub-critical aqueous fluids and is highly refractory, i.e., resistant to later modification or resetting by metamorphism or alteration. Its isotopic variations have seldom been measured. Recent advances in double spike technique and the development of multi-collector inductively coupled plasma (MC-ICPMS) make it possible to acquire Ti isotopes with high precision. As a result, significant fractionation of Ti stable isotope has been found in natural samples. The large fractionation has important implications for the measurement and application of Ti isotopes, with great potential in tracing various geological processes. In this review, we summarized the recent advances, important applications and future directions of Ti isotope geochemistry. We start with a brief summary on nomenclatures and analytical methods, followed by Ti isotopic compositions of chondrites and Bulk Silicate Earth (BSE), then with a summary on the magnitude and mechanisms of Ti isotopic fractionation during magmatic differentiation at high temperatures. It seems that Ti isotopes can serve as high-fidelity tracers of magmatic evolution and genesis of ancient igneous rocks and Earth's crust. Finally we highlight future work needed to advance the research and applications of Ti isotope geochemistry.

Key words: titanium, titanium isotopes, mass-dependent isotope fractionation, geochemical tracer