Rutile and its applications in earth sciences

Abstract

Rutile is the most common naturally occurring titanium dioxide polymorph and is widely distributed as an accessory mineral in metamorphic rocks ranging from greenschist to eclogite and granulite facies but is also present in igneous rocks, mantle xenoliths, lunar rocks and meteorites. It is one of the most stable heavy minerals in the sedimentary cycle, widespread both in ancient and modern clastic sediments. Rutile has a wide range of applications in earth sciences. It is a major host mineral for Nb, Ta and other high field strength elements, which are widely used as a monitor of geochemical processes in the Earth's crust and mantle. Great interest has focused recently on rutile geochemistry because rutile varies not only by bulk composition reflected, for instance, in its Cr and Nb contents but also by the temperature of crystallisation, expressed in the Zr content incorporated into the rutile lattice during crystallisation. Rutile geochemistry and Zr-in-rutile thermometry yield diagnostic data on the lithology and metamorphic facies of sediment source areas even in highly modified sandstones that may have lost significant amounts of provenance information. Rutile may therefore serve as a key mineral in sediment provenance analysis in the future, similar to zircon, which has been widely applied in recent decades. Importantly, rutile from high-grade metamorphic rocks can contain sufficient uranium to allow U–Pb geochronology and (U–Th)/He thermochronology. Furthermore, in situ Lu–Hf isotope analysis of rutile permits insights into the evolution of the Earth's crust and mantle. Besides that, rutile is also of great economic importance because it is one of the favoured natural minerals used in the manufacture of white titanium dioxide pigment, which is a major constituent in various products of our daily life. Heavy mineral sands containing a significant percentage of rutile are therefore the focus of exploration worldwide. This paper aims to provide an overview of the applications of rutile in earth sciences, based on a review of data published in recent years. After giving a summary of various rutile-bearing lithologies, the focus lies on rutile geochemistry, Zr-in-rutile thermometry, O isotope analysis, U–Pb geochronology, (U–Th)/He thermochronology and Lu–Hf isotope analysis. A final outline of the economic importance of rutile highlights the demand for further rutile-related research in earth sciences.