Sequential, syndeformational porphyroblast growth during Hercynian low-pressure/high-temperature metamorphism in the Canigou massif, Pyrenees |
| |
| Authors: | R L GIBSON |
| |
| Institution: | Department of Geology, University of the Witwatersrand, PO WITS, 2050, Johannesburg, South Africa |
| |
| Abstract: | The sequence of growth of garnet, staurolite and aluminosilicate in Fe-rich metapelitic rocks from the Canigou massif, Pyrenees, is established using evidence of inclusion, reaction and pseudomorphing textures between the different minerals, compositional zoning patterns in garnet and staurolite (that can be related to the KFMASH reaction grid), and the geometric relations between inclusion trails in the porphyroblasts and the matrix microstructures. The evidence indicates that garnet and staurolite commenced growth before aluminosilicate in all cases, even where all three are in textural equilibrium. Interpretation of the reaction textures between the porphyroblasts and of the compositional zoning in garnet and staurolite in terms of the KFMASH reaction grid indicates the importance of continuous reactions in the development of these phases. Some garnet and staurolite porphyroblasts underwent renewed growth during breakdown, producing rims enriched in Mn and Zn respectively. The presence of aluminosilicate in these assemblages (i.e. the absence of a clear andalusite-absent zone in the field) is attributed to a strong pressure-dependence for the aluminosilicate-producing reactions. Porphyroblast-matrix microstructural relations indicate that Hercynian metamorphism in the massif was synchronous with the development of the regional subhorizontal foliation (S3). |
| |
| Keywords: | aluminosilicates garnet sequential porphyroblast growth staurolite syndeformational growth |
|
|
