Petrology of gedrite-bearing rocks in mid-crustal ductile shear zones from the Eastern Ghats Belt, India |
| |
| Authors: | Dasgupta Sengupta PR Sengupta Ehl & Raith |
| |
| Institution: | Department of Geological Sciences, Jadavpur University, Calcutta-700 032, India (;), Mineralogisch-Petrologisches Institut der Universität Bonn, Poppelsdorfer Schloss, D-53115 Bonn, Germany |
| |
| Abstract: | A suite of metapelitic, basic and quartzofeldspathic rocks intruded by enderbitic gneiss from the southernmost tip of the Eastern Ghats Belt, India, and metamorphosed at c. 750–800 °C, 6 kbar, were subjected to repeated ductile shear deformation, hydration, cooling and accompanying alkali metasomatism along narrow shear zones. Gedrite-bearing assemblages developed in the shear zones traversing metapelitic rocks. Interpretation of the reaction textures in an appropriate P–T grid in the system FMASH, an isothermal–isobaric μ H2O– μ Na2O grid in the system NFMASH, and geothermobarometric data suggest a complex evolutionary history for the gedrite-bearing parageneses. Initially, gedrite-bearing assemblages were produced due to increase in μ Na2O at nearly constant but high μ H2O accompanying cooling. Gedrite was partially destabilized to orthopyroxene+albite due to progressively increasing μ Na2O. During further cooling and at increased μ H2O a second generation of gedrite appeared in the rocks. |
| |
| Keywords: | alkali metasomatism ductile shearing Eastern Ghats gedrite |
|
|
