Phase relations in three charnockites from Pallavaram-Tambaram
- 56 Downloads
Chemical data on eight ferromagnesian silicates from a syenitic and two tonalitic charnockites from the type area near Madras show remarkably regular cation fractionation patterns. The distribution coefficients for magnesium-iron point to equilibration under granulite facies metamorphism. Orthopyroxene-garnet-biotite subsystem has been found to be of a near invariant nature, while the compositions of orthopyroxene and biotite in the nongarnetiferous tonalite are different. Analysis of phase equilibrium by Thompson type AFM projection strongly indicates that pressure, temperature and the chemical potential of water were constant for assemblages separated by large distances.
KeywordsSilicate Fractionation Phase Equilibrium Mineral Resource Large Distance
Unable to display preview. Download preview PDF.
- Holland, T. H.: The charnockite series, a group of Archaean hypersthenic rocks in peninsular India. Mem. Geol. Surv. India. 28, pt. 2, 119–249 (1900).Google Scholar
- Howie, R. A.: The geochemistry of the charnockite series of Madras, India. Trans. Roy. Soc. Edinburgh 62, pt. 3, 725–768 (1955).Google Scholar
- Kretz, R.: Some applications of thermodynamics to coexisting minerals of variable composition. Examples: Orthopyroxene — clinopyroxene and orthopyroxene-garnet. J. Geol. 69, 361–387 (1961).Google Scholar
- Machigad, B. S.: Some aspects of garnet-biotite equilibria in enderbites from Pallavaram, Madras. J. Karnatak Univ. 12, 25–40 (1967).Google Scholar
- Ray, S., Sahu, J. R.: Hypersthene diorites from the type charnockite area near Madras. Bull. Geoch. Soc. India (in press).Google Scholar
- Sahu, J. R.: Compositional characteristics and equilibrium relations in mineral assemblages of some acid charnockites. Unpublished D.I.I.T. Thesis, Indian Institute of Technology, Kharagpur, 52 p. (1969).Google Scholar
- Sen, S. K., Chakraborty, K. R.: Magnesium-iron exchange equilibrium in garnet-biotite and metamorphic grade. Neues Jahrb. Mineral., Abhandl. 108, 181–207 (1968).Google Scholar
- - Ray, S., Dasgupta, D.: Structure of the type charnockite area near Madras. J. Geol. Soc. India (in press).Google Scholar
- Subramaniam, A. P.: Charnockites of the type area near Madras — a reinterpretation. Am. J. Sci. 257, 321–353 (1959).Google Scholar
- Thompson, J. B.: The graphical analysis of mineral assemblages in pelitic schists. Am. Mineralogist 42, 842–858 (1957).Google Scholar