RT Journal Article
T1 Challenges to rutile-based geoscientific tools: low-temperature polymorphic TiO2 transformations and corresponding reactive pathways
A1 Pinto, André Filipe Jorge
A1 Sánchez Pastor, Nuria
A1 Callegari, Ivan
A1 Pracejus, Bernhard
A1 Scharf, Andreas
AB Rutile, a common accessory mineral in a wide variety of rocks, is the most stable naturally occurring TiO2 polymorph. The relationship between its trace element composition and formation conditions has provided geoscientists with discriminant tools for fingerprinting geological processes, such as magmatic evolution and subduction zone metamorphism, alongside applications to the study of sediment provenance. In the present work, volcaniclastic rock samples belonging to Fara and Saiq Formations, outcropping in Jebel Akhdar mountains, Oman, are studied with Raman spectroscopy and Electron Microprobe (EMP) aiming: of (i) the identification of different naturally-occurring TiO2 polymorphs, (ii) the evaluation of their trace element contents in relation with hydrothermal alteration features, and (iii) the analysis of the mineral reactive pathways behind the observed textural relationships. Raman investigations demonstrated that interstitial, fine-grained TiO2 corresponds to anatase, whereas rutile occurs as isolated single grains. EMP determinations further revealed that an identified Nb-enrichment in anatase is coupled with a corresponding Nb-depletion in rutile. The combination of the obtained results with petrographic observations enabled unravelling the TiO2 reactive pathways affecting the studied samples. Thus, a coupled polymorphic dissolution-precipitation reaction assisting rutile-to-anatase conversion has been defined, together with the role of Nb in further stabilizing the structure of the lower temperature polymorph. Semi-quantitative thermometric considerations suggest that rutile substrates are likely of magmatic origin, whereas anatase formation is clearly associated with a lower temperature aqueous environment. The gathered results raise fundamental questions concerning the application of commonly used rutile-based geochemical and thermometric tools.
PB Nature Research
SN 2045-2322
YR 2020
FD 2020
LK https://hdl.handle.net/20.500.14352/6249
UL https://hdl.handle.net/20.500.14352/6249
LA eng
NO Ministerio de Economía y Competitividad (MINECO)
NO Research Committee of the German University of Technology in Oman
DS Docta Complutense
RD 12 abr 2025