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Conversion of titanite to rutile during the albitization of granitoids from the Sakar Batholith, SE Bulgaria: Experimental studies

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Published/Copyright: March 9, 2026
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Abstract

Petrological studies of the Sakar granitoid batholith (SE Bulgaria) have revealed that rutile-rich aggregates were formed from titanite during albitization and desilification of the granitoid at ∼600 °C and ∼300 MPa. Titanite conversion to rutile has been tested experimentally. Four experiments involving fluid-aided alteration of titanite in a granitic system were conducted using cold-seal pressure vessels on a hydrothermal line at 280 MPa and 600 °C. The starting material included titanite, fluorapatite, and a powdered, unaltered, natural granite from the Sakar Batholith. Four Na-bearing aqueous fluids (NaCl+H2O, NaF+H2O, Na2Si2O5+H2O, and 2 M NaOH) were used. Rutile was formed from titanite in experiments involving NaCl+H2O (RT-1) and NaF+H2O (RT-2). The mineral assemblage formed in RT-1 consisted of rutile, Ti-Th-U oxides, and monazite, whereas in RT-2 rutile, fluorite, lorenzenite, albitized plagioclase, REE-enriched rims on fluorapatite, and a glass formed. Rutile did not form in experiments involving Na2Si2O5+H2O or 2 M NaOH. The comparison between natural observation and the experimental results supports the premise that a NaCl+H2O fluid could have been responsible for the conversion of titanite to rutile during albitization, which further supports the role of NaCl-bearing fluids during the albitization of granitoids in general at mid- to upper-crustal pressures in the presence of alkali-bearing fluids. This implies that the geochemical relationship between rutile and titanite is more a function of the chemistry of the fluid and host rock, especially if they are Na-rich, rather than the P-T conditions. Subsequently, rutile formed from titanite can be used as a geochronometer for dating the process responsible for both the formation of the rutile and the metasomatism of the rock. Detrital rutile is commonly thought to mostly originate from medium- to high-pressure igneous and metamorphic source rocks. Formation of rutile during albitization and desilification of granitoids under relatively high-temperature hydrothermal conditions in the upper crust has implications regarding rutile provenance studies of areas sourced by regionally albitized quartzofeldspathic rocks.

Acknowledgments and Funding

Anna Gumsley and Ianko Gerdjikov were supported by the Bulgarian National Science Fund project no. KP-06-N74/1.

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Received: 2024-12-23
Accepted: 2025-07-29
Published Online: 2026-03-09
Published in Print: 2026-03-30

© 2026 Mineralogical Society of America

Articles in the same Issue

  1. Uncovering the mineral assemblages of six major gold deposit types: A machine learning approach to big data analytics of a global mineralogical database
  2. Infrared spectroscopy of natural Type Ib diamond: Insights into the formation of Y-centers and the early aggregation of nitrogen
  3. Microstructural and chemical responses of lunar pyroxene to shock shearing under low-to-moderate shock conditions
  4. Genesis of jordanite-geocronite solid solution series in the Huize Pb-Zn deposit, SW China: Implications for fluid evolution in the late mineralization stage
  5. How fluids control beryllium mineralization in a magmatic-hydrothermal system: Evidence from mica geochemistry and quartz-beryl O isotopes
  6. Toward the continuous series of HgS-ZnS solid solutions: Zn-rich metacinnabar assemblages in the Vorontsovskoe gold deposit, Northern Urals, Russia
  7. Molecular-level insights into mechanisms of Li enrichment and occurrence in natural clay-bauxite
  8. Conversion of titanite to rutile during the albitization of granitoids from the Sakar Batholith, SE Bulgaria: Experimental studies
  9. Kimberlite emplacement conditions through experimentally produced reaction rims on ilmenite macrocrysts
  10. Raman spectroscopic investigation of ianthinite U24+UO24O6(OH)4H2O45H2O, a rare mixed-valence uranium oxide hydrate
  11. A Zr-Hf geothermometer for magmatic zircon: New experiments and formulation
  12. (Li,Na)-P substitution in garnet: An indicator of ultrahigh-pressure conditions in subducted continental crust
  13. Book Review
  14. American Mineralogist thanks the Reviewers for 2025
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