P-T CONDITIONS OF POLYMETAMORPHISM IN THE CENTRAL PART OF THE EASTERNGHATS MOBILE BELT, INDIA

Different P-T metamorphic parameters are recorded in compositionally h eterogenous minerals of the metamorphic rocks of the central part of t he Eastern Ghats mobile belt, India. These parameters can be deciphere d by the methods of mineralogical thermobarometry, Using a system of i nternally consistent geothermometers, we detected four discrete retrog rade metamorphic events in the region at the following temperatures (d egrees C): (M1) 830-850, (M2) 765 +/- 25, (M3) 675 +/- 25, and (M4) 54 0 +/- 35 (at pressures 6.9 +/- 0.6, 5.7 +/- 0.4, 4.6 +/- 0.2, and simi lar to 3.0 kbar, respectively). The activation of metamorphic reaction s and rock recrystallization processes at stages M2 and M3 was control led by fluid flows rather than heat flows. These metamorphic events ca n be attributed to main tectonothermal events dated at 2600, 2200-1900 , 1180-950, and 620-500 Ma. During these events, tangent motions were dominant in the region, while the vertical displacement during the who le long-term period 2600-500 Ma was only about 10-15 km. A model of cy clic alternation of rest (subisobaric cooling)and activation periods ( subisothermal decompression) is proposed to interpret the obtained dat a.