Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Xirouchakis, D. Articles by Andersen, D. J. Search for Related Content GeoRef GeoRef Citation

Assemblages with titanite (CaTiOSiO₄), Ca-Mg-Fe olivine and pyroxenes, Fe-Mg-Ti oxides, and quartz: Part I. Theory

¹ Earth Sciences and Solar System Exploration Division, NASA Lyndon B. Johnson Space Center, Mail Code SN2, Houston, Texas 77058, U.S.A.
² Department of Geosciences and Center for High Pressure Research, State University of New York at Stony Brook, Stony Brook, New York 11794-2100, U.S.A.
³ ConnectSouth, Inc., 9600 Great Hills Trail, Suite 250 East, Austin, Texas 78759, U.S.A.

Correspondence: ^* E-mail address: dxirouch{at}ems.jsc.nasa.gov

Critical evaluation of the thermodynamic data for titanite, in conjunction with a heat capacity equation that takes into account the P2₁/a A2/a transition and a more complete P-V-T data set for titanite, indicates that: (1) enthalpy of formation values greater than –2600 kJ/mol are not supported by calorimetry; (2) calculated internally consistent feasible solutions converge to enthalpy of formation from the elements values between –2608 and –2600 kJ/mol and 113 to 121 J/mol·K for the entropy; (3) the practice of adjusting the enthalpy of formation to fit phase equilibrium experiments may be erroneous, in contrast, it is the currently accepted entropy of 129.20 ± 0.84 J/mol·K that may need revision to a smaller value. Consequently, we optimize standard-state properties for end-member titanite (P2₁/a structure) consistent with the thermodynamic data in the program QUILF. In addition, we use a modified version of the program to calibrate equilibria among titanite (CaTiOSiO₄), Fe-Mg-Ti ilmenite and spinel, Ca-Mg-Fe pyroxenes and olivine, and quartz. Calculations at 1 and 3 kbar, and 650, 850, and 1100 °C, in the system CaO-MgO-FeO-Fe₂O₃-TiO₂-SiO₂, suggest that the

and

impose well defined f_O2, a_SiO2, and X_Fe^Opx restrictions to the assemblages (1) titanite + spinel phase + quartz, (2) titanite + orthopyroxene, (3) augite + ilmenite, and consequently titanite stability. The absence of quartz (a_SiO2< 1 with respect to Qz) favors the sub-assemblage Fe-Mg-Ti spinel + titanite over augite + ilmenite, and the latter over titanite + orthopyroxene. Nonetheless, in the absence of quartz, no titanite-bearing assemblage is stable relative to olivine + orthopyroxene + augite + ilmenite + Fe-Mg-Ti spinel. From the phase relations, we can also infer that in quartz-saturated rocks: (1) titanite can coexist with orthopyroxene only at low X_Fe^Opx values, regardless of f_O2 conditions, whereas the assemblage titanite + orthopyroxene + spinel phase requires high f_O2, relative Mg-enrichment (from high to moderate X_Fe^Opx), and temperatures 650 °C. (2) The association of titanite with a spinel phase is generally indicative of relatively oxidizing conditions. (3) The assemblage titanite + olivine requires f_O2 condition close to FMQ and relative Fe-enrichment (from moderate to high X_Fe^Opx), and temperatures 650 °C.

This article has been cited by other articles:

				Y. O. Mohammad and H. Maekawa Origin of titanite in metarodingite from the Zagros Thrust Zone, Iraq American Mineralogist, July 1, 2008; 93(7): 1133 - 1141. [Abstract] [Full Text] [PDF]

				M. A. W. Marks, J. Schilling, I. M. Coulson, T. Wenzel, and G. Markl The Alkaline-Peralkaline Tamazeght Complex, High Atlas Mountains, Morocco: Mineral Chemistry and Petrological Constraints for Derivation from a Compositionally Heterogeneous Mantle Source J. Petrology, June 1, 2008; 49(6): 1097 - 1131. [Abstract] [Full Text] [PDF]

				J. L. Anderson, A. P. Barth, J. L. Wooden, and F. Mazdab Thermometers and Thermobarometers in Granitic Systems Reviews in Mineralogy and Geochemistry, January 1, 2008; 69(1): 121 - 142. [Full Text] [PDF]

				R. P. Wintsch, M. J. Kunk, J. L. Boyd, and J. N. Aleinikoff P-T-t paths and differential Alleghanian loading and uplift of the Bronson Hill terrane, South Central New England Am J Sci, May 1, 2003; 303(5): 410 - 446. [Abstract] [Full Text] [PDF]