Phase relationships in grunerite-garnet-bearing amphibolites in the systemCFMASH, with applications to metamorphic rocks from the Central Zone of the Limpopo Belt, South Africa.

Zeh, A. and Holland, T. J. B. and Klemd, R. (2005) Phase relationships in grunerite-garnet-bearing amphibolites in the systemCFMASH, with applications to metamorphic rocks from the Central Zone of the Limpopo Belt, South Africa. Journal of Metamorphic Geology, 23. pp. 1-17. DOI 10.1111/j.1525-1314.2005.00554.x

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Abstract

A petrogenetic grid in the model system CaO–FeO–MgO–Al2O3–SiO2–H2O is presented, illustrating the phase relationships among the minerals grunerite, hornblende, garnet, clinopyroxene, chlorite, olivine, anorthite, zoisite and aluminosilicates, with quartz and H2O in excess. The grid was calculated with the computer softwarethermocalc, using an upgraded version of the internally consistent thermodynamic dataset HP98 and non-ideal mixing activity models for all solid solutions. From this grid, quantitative phase diagrams (P–T pseudosections) are derived and employed to infer a P–T path for grunerite–garnet-bearing amphibolites from the Endora Klippe, part of the Venetia Klippen Complex within the Central Zone of the Limpopo Belt. Agreement between calculated and observed mineral assemblages and garnet zonation indicates that this part of the Central Zone underwent a prograde temperature and pressure increase from c. 540 °C/4.5 kbar to 650 °C/6.5 kbar, followed by a post-peak metamorphic pressure decrease. The inferred P–T path supports a geotectonic model suggesting that the area surrounding the Venetia kimberlite pipes represents the amphibolite-facies roof zone of migmatitic gneisses and granulites that occur widely within the Central Zone. In addition, the P–T path conforms to an interpretation that the Proterozoic evolution of the Central Zone was controlled by horizontal tectonics, causing stacking and differential heating at c. 2.0 Ga.

Item Type: Article
Uncontrolled Keywords: 2005 PUBL 2005 AREP IA47
Subjects: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Divisions: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Journal or Publication Title: Journal of Metamorphic Geology
Volume: 23
Page Range: pp. 1-17
Identification Number: 10.1111/j.1525-1314.2005.00554.x
Depositing User: Sarah Humbert
Date Deposited: 12 Aug 2010 11:08
Last Modified: 23 Jul 2013 10:00
URI: http://eprints.esc.cam.ac.uk/id/eprint/1890

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