Titanium in phengite : a geobarometer for high temperature eclogites - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Contributions to Mineralogy and Petrology Année : 2010

Titanium in phengite : a geobarometer for high temperature eclogites

E. Auzanneau
  • Fonction : Auteur
M.W. Schmidt
  • Fonction : Auteur
J.A.D. Connolly
  • Fonction : Auteur

Résumé

Phengite chemistry has been investigated in experiments on a natural SiO2-TiO2-saturated greywacke and a natural SiO2-TiO2-Al2SiO5-saturated pelite, at 1.5-8.0 GPa and 800-1,050A degrees C. High Ti-contents (0.3-3.7 wt %), Ti-enrichment with temperature, and a strong inverse correlation of Ti-content with pressure are the important features of both experimental series. The changes in composition with pressure result from the Tschermak substitution (Si + R2+ = Al-IV + Al-VI) coupled with the substitution: Al-VI + Si = Ti + Al-IV. The latter exchange is best described using the end-member Ti-phengite (KMgTi[Si3Al]O-10(OH)(2), TiP). In the rutile-quartz/coesite saturated experiments, the aluminoceladonite component increases with pressure while the muscovite, paragonite and Ti-phengite components decrease. A thermodynamic model combining data obtained in this and previous experimental studies are derived to use the equilibrium MgCel + Rt = TiP + Cs/Qz as a thermobarometer in felsic and basic rocks. Phengite, rutile and quartz/coesite are common phases in HT-(U)HP metamorphic rocks, and are often preserved from regression by entrapment in zircon or garnet, thus providing an opportunity to determine the T-P conditions of crystallization of these rocks. Two applications on natural examples (Sulu belt and Kokchetav massif) are presented and discussed. This study demonstrates that Ti is a significant constituent of phengites that could have significant effects on phase relationships and melting rates with decreasing P or increasing T in the continental crust.

Dates et versions

hal-00448569 , version 1 (19-01-2010)

Identifiants

Citer

E. Auzanneau, M.W. Schmidt, D. Vielzeuf, J.A.D. Connolly. Titanium in phengite : a geobarometer for high temperature eclogites. Contributions to Mineralogy and Petrology, 2010, 159 (1), pp.1-24. ⟨10.1007/s00410-009-0412-7⟩. ⟨hal-00448569⟩
27 Consultations
0 Téléchargements

Altmetric

Partager

Gmail Facebook X LinkedIn More