Variation of Fe, Al, and F Substitution in Titanite (Sphene)

Titanite is an important mineral in petrochronology studies. Understanding chemical signatures of titanite from different environments can provide significant data unraveling the complex histories recorded their textures and compositions. Using a database over 8500 analyses both literature (3829) our own (4900), we found that ratio Fe/Al useful for separating igneous (Fe/Al typically close to 1:1 almost always > 1:2) metamorphic < with few exceptions. Volcanic grains also be separated plutonic due shorter crystallization compositions clustered more tightly terms Fe, Al, F. Compositions rocks often have later or hydrothermal overgrowths are not on volcanic titanite. ratios silica-undersaturated 1:2 include highest ratios. Although they overlap field normal titanite, other elements (particularly high levels Nb low Y) allow them separated. In most rocks, except formed mafic rocks. ultrahigh pressure (eclogite facies) tend lowest ratios, 1:8. pegmatitic scatter widely even within single fluids highly variable Charge balancing metamorphic, hydrothermal, Fe+3 Al+3 substitution into Ti+4 site largely accomplished by coupled F− O−2. However, charge imbalance appears mainly REE+3 Y+3 Ca+2 lesser contribution F−.