P-T conditions of polymetamorphism in the central part of the Eastern Ghats mobile belt, India

Different P-T metamorphic parameters are recorded in compositionally heterogenous minerals of the metamorphic rocks of the central part of the Eastern Ghats mobile belt, India. These parameters can be deciphered by the methods of mineralogical thermobarometry, Using a system of internally consistent geothermometers, we detected four discrete retrograde metamorphic events in the region at the following temperatures (degrees C): (M1) 830-850, (M2) 765 +/- 25, (M3) 675 +/- 25, and (M4) 540 +/- 35 (at pressures 6.9 +/- 0.6, 5.7 +/- 0.4, 4.6 +/- 0.2, and similar to 3.0 kbar, respectively). The activation of metamorphic reactions and rock recrystallization processes at stages M2 and M3 was controlled by fluid flows rather than heat flows. These metamorphic events can 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 whole long-term period 2600-500 Ma was only about 10-15 km. A model of cyclic alternation of rest (subisobaric cooling)and activation periods (subisothermal decompression) is proposed to interpret the obtained data.