Pervasive rehydration of granulites during exhumation - an example from the Pulur complex, Eastern Pontides, Turkey


Topuz G. , ALTHERR R.

MINERALOGY AND PETROLOGY, cilt.81, ss.165-185, 2004 (SCI İndekslerine Giren Dergi) identifier identifier

  • Cilt numarası: 81
  • Basım Tarihi: 2004
  • Doi Numarası: 10.1007/s00710-003-0034-0
  • Dergi Adı: MINERALOGY AND PETROLOGY
  • Sayfa Sayıları: ss.165-185

Özet

High-grade gneisses from the Pulur complex in NE Turkey bear evidence for biotite-dehydration melting at greater than or equal to820 degreesC and 0.7-0.8 GPa, melt segregation and near-isothermal decompression to 0.4-0.5 GPa. During further exhumation, the rocks underwent secondary pervasive rehydration at temperatures between similar to400 and 230 degreesC and fluid pressures between similar to0.3 and 0.1 GPa. Metamorphic peak conditions are dated at 331-327 Ma, while hydrothermal retrogression occurred significantly later at 315-310 Ma under static conditions. During the rehydration event, primary high-grade mineral assemblages including garnet, cordierite, sillimanite, spinel, biotite, plagioclase and ilmenite were extensively replaced by muscovite, paragonite, margarite, corundum, diaspore, chlorite, kaolinite, pumpellyite, prehnite, epidote, titanite, anatase, pyrite and chalcopyrite. Secondary mineral assemblages indicate that the infiltrating fluids were characterized by low fO(2), very low X-CO2 (<0.002), variable activities of Ca2+, K+, Na+ and H+ and relatively high activities of H2S and CH4. Quartz veins that might have acted as pathways for the fluids are rare. Ubiquitous veinlets consisting of (i) albite, (ii) chlorite+calcite+quartz or (iii) K-feldspar+calcite+quartz were formed after the pervasive rehydraton event by precipitation from aqueous solutions that were somewhat richer in CO2.