Abstract
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.
Highlights
Rutile, a common accessory mineral in a wide variety of rocks, is the most stable naturally occurring TiO2 polymorph
We focus on the mineralogical and chemical characterization of TiO2 phases included in volcaniclastic rocks belonging to Fara and Saiq formations (Jebel Akhdar mountains, Oman) with the purpose of: i) identify the different naturally-occurring TiO2 polymorphs, ii) evaluate their trace element contents in relation with hydrothermal alteration features, and iii) decipher the mineral reactive pathways behind the observed textural relationships
The overall primary mineralogical and textural arrangements are affected by widespread sericitization, silicification, carbonation, as depicted in Fig. 3a,b and the related hydrothermal alteration products correspond to the main matrix components
Summary
A common accessory mineral in a wide variety of rocks, is the most stable naturally occurring TiO2 polymorph. 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. The trace element contents of rutile provide a useful tool for geochemically fingerprinting processes such as magmatic evolution or high-pressure metamorphic systems[6,7]. The study of hydrothermal rutile knows fewer efforts in comparison to both metamorphic and magmatic origins, as indicated by scarcer references[15,16,17,18,19]. The main economical source of this mineral is globally exploited as rutile-enriched sands[26,27]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
