Petrogenesis of cordierite-orthoamphibole assemblages from the Springton region,South Australia |
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Authors: | Jo Arnold Michael Sandiford |
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Affiliation: | (1) Department of Geology and Geophysics, University of Adelaide, GPO Box 498, Adelaide, South Australia |
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Abstract: | Textural evidence for the partial breakdown of staurolite-biotite and andalusite-biotite assemblages to cordierite-orthoamphibole implies high temperature metasomatic depletion of K2O in semi-pelitic rocks from Springton, South Australia. The origin of the reaction textures is discussed with reference to K2O-T diagrams derived from the topologically equivalent K2O–(-H2O) diagram showing both discontinuous and Fe–Mg continuous reactions. The involvement of fluids in the metasomatic process is implied by the scale of K2O removal and suggests that the outcrop pattern of cordierite-gedrite rocks reflects, at least in part, a heterogeneous distribution of advecting fluids in the metamorphic pile at high temperatures.Mineral abbreviations used in text and figures ab albite - alm almandine - als aluminosilicate - and andalusite - anth anthophyllite - bt biotite - cd cordierite - fe-bt Fe-rich biotite - fe-cd Fe-rich cordierite - fe-oa Fe-rich orthoamphibole - fe-st Fe-staurolite - gt garnet - ksp potassium feldspar - ky kyanite - mg-cd Mg-rich cordierite - mg-oa Mg-rich orthoamphibole - mg-st Mg-rich staurolite - mu muscovite - oa orthoamphibole - phl phlogopite - plag plagioclase - py pyrope - sill sillimanite - st staurolite - v vapour |
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