Petrological Evolution of the Pangidi Granulites, Eastern Ghats, India: Evidence for decompressive and cooling retrograde trajectories
Dharma Rao, C. V.
published: Jul 22, 1998
ArtNo. ESP154017303003, Price: 29.00 €
The Pangidi granulite Complex is a high grade supracrustal sequence located in the southern part of the Eastern Ghats belt of India. It comprises a spectrum of rock types ranging from pelitic granulites, two-pyroxene granulites, retrogressed orthopyroxene granulites and spinel granulites. Reaction textures and compositional characteristics document several mineral reactions involving formation and breakdown of garnet in these diverse rock types. In pelitic granulite, dehydration melting of biotite in presence of quartz indicates reaction of Bt + Sil + Qtz = Grt + Kfs + melt. In two-pyroxene granulites, breakdown of prograde hornblende to Opx + Pl and Symplectites of Opx + Pl around Grt are interpreted as products of near isothermal decompression. Similarly, the Opx + Pl symplectites in these granulites indicate an early breakdown of garnet during decompression by the reaction Grt + Qtz = Opx + Pl. Subsequently, coronal garnet was produced in the orthopyroxene and spinel granulites by the reaction, Opx + Pl = Grt + Qtz, replacing the 'earlier' porphyroblastic garnet during near isobaric cooling. Mineral reaction textures with different garnet habits, and thermobarometric data define a retrograde P-T path during which a mild decompression representing an early portion of the P-T trajectory was followed by near isobaric cooling. The deduced P-T path may have originated in overthickened crust owing to collision.