Time relationship between metamorphism and deformation in Proterozoic rocks of the Lunavada region, Southern Aravalli Mountain Belt (India) - a microstructural study

The southern margin of the Aravalli Mountain Belt (AMB) is known to have un dergone polyphase deformation during the Mesoproterozoic. The Lunavada Grou p of rocks, which is an important constituent of the southern parts of AMB, reveals three episodes of deformation; D-1, D-2 and D-3 In this paper, int erpretations based on petrographic studies of schists and quartzites of the region are presented and the relationship between metamorphic and deformat ional events is discussed. It is established that from north to south, ther e is a marked zonation from chlorite to gamet-biotite schists. Metamorphism (M-1) accompanied D-1 and was progressive. M2-1 metamorphism associated wi th major part of D-2 was also progressive. However, M2-2 that synchronized with the waning phases of D-2 and early D-3 deformation was retrogressive. Porphyroblast-matrix relationships in the garnet-biotite schists of the reg ion have been useful in establishing these facts. The metamorphic rocks stu died were intruded by Godhra Granite during the late-D-3/post-D-3 event. Th e heat supplied by this granite resulted in static recrystallization and fo rmation of annealing microstructures in rocks close to the granite. It is e stablished that Grain Boundary Migration Recrystallization associated with dislocation creep and Grain Boundary Area Reduction were the two deformatio n mechanisms dominant in rocks lying far and close from the Godhra Granite, respectively. (C) 2001 Elsevier Science Ltd. All rights reserved.