Titanium (Ti) is one of the most important elements in element chemostratigraphy, due to its mineral associations. So, what are the element-mineral links of Ti?
Titanium (symbol Ti; atomic number 22; relative atomic mass 47.867) [Link to webelements.com]
Ti has three main oxidation states, +2, +3, +4, with +4 being the most common one.
There are five naturally occurring Ti isotopes (46Ti, 47Ti, 48Ti, 49Ti, and 50Ti), with 48Ti being the most abundant one.
Common element substitutions for Ti are Nb and Ta.
In geochemical analysis, titanium is commonly reported in its oxide form as TiO2 in weight percent [wt.%].
Common element-mineral links of Ti
Most common element-mineral links: heavy minerals, such as rutile/anatase/brookite (TiO2), ilmenite (FeTiO3), titanite (or sphene) (CaTiSiO5), and titanomagnetite (Fe”(Fe”’,Ti)2O4). Ti can also (beside others) be incorporated in traces into the crystal lattice of amphibole, pyroxene, garnet, biotite, illite, and chlorite.
Ti in siliciclastic sediments
In most siliciclastic sediments Ti is present in only low concentrations, with TiO2 concentrations commonly <1%. The concentrations are driven by the presence of detrital oxides and silicates such as chlorite.
Nb (niobium) and Ta (tantalum) substitute for Ti in the crystal lattices of Ti-bearing heavy minerals. Ratios between these elements may thus be used as provenance indicators.
On the other hand, Ti may substitute for Mg or Fe in silicates, resulting in the relative enrichment of Ti in amphibole and mica.
Heavy minerals, such as the Ti-oxides, are commonly found in the silt-size fractions of siliciclastic rocks (e.g., Morton & Hallsworth, 1999), and Ti (as well as Nb and Ta) is therefore often relatively enriched in this grain size fraction.
Being associated with relatively stable (heavy) minerals, which are very resistant to weathering, Ti thus may become enriched in weathering profiles and bauxite and laterite horizons, where it is commonly present in Ti-bearing detrital heavy minerals and/or authigenic anatase, and TiO2 can reach concentrations of 2-3%.
Ti in carbonates
In carbonates, Ti concentrations are commonly very low, but can get enriched in stylolites (together with Al, Si, K, and Fe; e.g. Hassan, 2007).
Ti in igneous rocks
Basic (gabbro, dolerite, basalt) and intermediate igneous rocks (diorite and andesite) have TiO2 concentrations commonly around 1-3% and are mainly associated with pyroxenes (particularly (titan-)augite) and other mafic minerals, such as amphibole, ilmenite, titanite (or sphene), and titanomagnetite. Therefore, elevated Ti (TiO2) concentrations may be indicative of mafic (TiO2 >1%) and ultramafic (> 2%) igneous rocks, compared to felsic (TiO2 ~0.2%) rocks.