Ti-Bearing Minerals: from the Ocean Floor to Subduction and Back.

This article investigates the stability and trace element chemistry of titanium-bearing minerals—titanite, rutile, and ilmenite—in metamafic rocks with mid-ocean ridge basalt (MORB) affinity, spanning from oceanic crust formation through subduction-related high-pressure (HP) metamorphism. It demonstrates that rutile can be stable at low pressure and high temperature (HT-LP) conditions in ocean-floor amphibole-bearing gabbros, contrary to previous experimental constraints, while titanite is stable at low temperature, HP (LT-HP) conditions such as in blueschist and some eclogite facies rocks. The study identifies bulk-rock Ti/Ca and Ca/Al ratios as key controls on the titanite-to-rutile transition and establishes trace element proxies—such as La/Sm, Nb, Yb, and V in titanite, and V/Nb, Cr, Sc, and Nb in rutile—that can discriminate HP from LP metamorphic conditions. These findings offer new geochemical tools for using detrital Ti-bearing minerals to trace HP metamorphic histories in both modern and ancient orogenic settings.