Garnet compositions as recorders of P-T-t history of metamorphic rocks

Massimiliano Tirone, Jibamitra Ganguly

Research output: Contribution to journalArticle

24 Citations (Scopus)

Abstract

On the basis of tests made in recent studies, we conclude that the simultaneous solutions of the equilibrium conditions of garnet-biotite Fe-Mg exchange and Grs = Plag + Aluminosilicate + Qtz (GASP) reactions, as formulated on the basis selected experimental data and well constrained thermodynamic mixing properties of garnet and plagioclase, offer robust estimates of P-T conditions of metapelitic assemblages that consist of the above minerals. Additional calculations are presented to show the compatibility of the retrieved P-T conditions of natural assemblages with the aluminosilicate phase diagram. We also calculate the minimum grain sizes of garnets that should be used for the calculation of the peak metamorphic P-T (Pp, Tp) conditions, using reasonable initial guessed values of minimum cooling rate and maximum Tp. To retrieve the thermal history of metapelites, we have developed a finite difference scheme for modeling multicomponent diffusion profiles in garnet, incorporating provisions for continuous nucleation and growth. This has been interlinked with a genetic algorithm that permits retrieval of the temperature vs. time path of metapelites through modeling of the zoning profiles in garnets, keeping several model parameters as floating variables. The numerical code has been applied to retrieve the T-t history of the low pressure-high temperature Royke metamorphic belt, Japan, by modeling the concentration profiles of Fe, Mn, Mg and Ca of garnets of different sizes that have been inferred to have developed by a process of continuous nucleation and growth.

Original languageEnglish (US)
Pages (from-to)138-146
Number of pages9
JournalGondwana Research
Volume18
Issue number1
DOIs
StatePublished - Jul 2010

Fingerprint

metamorphic rock
garnet
history
metapelite
aluminosilicate
nucleation
modeling
genetic algorithm
zoning
low pressure
biotite
plagioclase
grain size
thermodynamics
diagram
cooling
mineral
temperature
calculation

Keywords

  • Diffusion profiles
  • Garnet
  • Geothermobarometry
  • Metamorphism
  • Tectonics
  • Thermodynamics

ASJC Scopus subject areas

  • Geology

Cite this

Garnet compositions as recorders of P-T-t history of metamorphic rocks. / Tirone, Massimiliano; Ganguly, Jibamitra.

In: Gondwana Research, Vol. 18, No. 1, 07.2010, p. 138-146.

Research output: Contribution to journalArticle

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