Petrology of gedrite-bearing rocks in mid-crustal ductile shear zones fromthe Eastern Ghats Belt, India

A suite of metapelitic, basic and quartzofeldspathic rocks intruded by ende rbitic gneiss from the southernmost tip of the Eastern Ghats Belt, India, a nd metamorphosed at c. 750-800 degrees C, 6 kbar, were subjected to repeate d ductile shear deformation, hydration, cooling and accompanying alkali met asomatism alone narrow shear zones. Gedrite-bearing assemblages developed i n the shear zones tra traversing metapelitic rocks. Interpretation of the r eaction textures in an appropriate P-T grid in the system FMASH, an isother mal-isobaric mu(H20)-mu(Na2O) grid in the system NFMASH, and geothermobarom etric data suggest a complex evolutionary history for the gedrite-bearing p arageneses. Initially, gedrite-bearing assemblages were produced due to inc rease in mu(Na2O) at nearly constant but high mu(H2O) accompanying cooling. Gedrite was partially destabilized to orthopyroxene + albite due to progre ssively increasing mu(Na2O). During further cooling and at increased mu(H2O ) a second generation of gedrite appeared in the rocks.