Reaction Textures and Metamorphic Evolution of Quartz-Free Granulites from Namlekonda (Karimnagar), Andhra Pradesh, Southern India
2008; Taylor & Francis; Volume: 50; Issue: 11 Linguagem: Inglês
10.2747/0020-6814.50.11.1008
ISSN1938-2839
Autores Tópico(s)High-pressure geophysics and materials
ResumoQuartz-free granulites form a new locality in Namlekonda (Karimnagar), occurring as enclaves within a granite-gneiss complex and charnockites with sharp contacts. They occur as biotite-rich, dark colored rocks with well-defined schistosity. The assemblages in Namlekonda are as follows: (i) biotite-sapphirine -spinel-cordierite-orthopyroxene -corundum-potash feldspar; (ii) corundum- chlorite-spinel-magnetite ± biotite-cordierite; and (iii) biotite-andulasite-corundum-chlorite ± cordierite. Interpretation of multiphase reaction textures in conjunction with mineral chemical data and topology in the (Fe, Mg)O-(Al2O3-K2O)-(SiO2-6K2O) system is consistent with the following reactions: Bt1 + Crn1 = Spl1 + Kfs +V Phl (in Bt1) + Crn1 = East (in Bt2) + Spl1 + Crd1 Phl (in Bt1) + Crn1 = East (in Bt2) + Spr1 + Crd1 Crd1 + Bt2 + Crn1 = Spr1 + Kfs + H2O Spr1 = Crd2 + Spl1 + Crn2 Opx + Spr1 = Spl1 + Crd2 Opx + Crn1 = Spl1 + Crd2 Spr2 + H2O = Chl + Spl2 + Crn2 Crd2 + Crn2 ± Kfs + H2O = And ± Bt3 ± Chl. The P-T evolution of these quartz-free granulites has been constrained through the use of conventional geothermobarometry, THERMOCALC, and thermodynamically calibrated MAS equilibria. P-T conditions of metamorphism from different pertinent calibrations are estimated to be around 6-7 kbar and 700-800°C, respectively. The prograde P-T path is interpreted from different reaction textures and thermobarometric estimates.
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