The following model equilibria have been observed in metapelites from the Diti Formation of the Central Limpopo belt.
(Mg,Fe)2Si2O6Orthopyroxene+2 Al2SiO5Sillimanite+SiO2Quartz=(Mg,Fe)2Al4Si5O18Cordierite2(Mg, Fe)3Al2Si3O12Garnet+4Al2SiO5Sillimanite+5SiO2Quartz=3(Mg,Fe)2Al4Si5O18Cordierite2(Mg, Fe)3Al2Si3O12Garnet+3SiO2Quartz=(Mg,Fe)2Al4Si5O18Cordierite+2(Mg, Fe)2Si2O6Orthopyroxene5(Mg, Fe)2Si2O6Orthopyroxene+10Al2SiO5Sillimanite=4(Mg,Fe)2Al4Si5O18Cordierite+2(Mg,Fe)2Al2O4Spinel

An internally consistent thermodynamic data set in the MAS system for constituent phases has been derived which is also consistent with both calorimetric data and experimental equilibria. Microprobe analyses of the phases present in the Limpopo metapelites have been applied to equilibrium equations derived from this data set, and conditions of P = 4–5 kbar, T > 670°C are implied assuming aH2O = 0. Application of published cordierite-free thermobarometers both from the pelites and interlayered mafic granulites, provides similar P–T conditions (P = 3.5–5 kbar, T = 750±50°C) indicating that metamorphism was virtually dry. Conditions of aH2O < 0.5 are also implied by analysis of equilibria involving hydrous phases.

Decompression reactions are observed both in this and in earlier studies of supracrustal rocks from the Central Limpopo Belt, and a period of essentially isothermal uplift is suggested, which raised crustal blocks from depths of about 40 km to 15 km. One possible speculation is that such rapid uplift results from a phase of extensional tectonics which occurred between 2600 and 3150 Ma.

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