HR: 0800h
AN: T21A-0512    [Abstracts]
TI: Oxidised Eclogites and Garnet-Blueschists from Oman: PT Path Modelling in the NCFMASHO System.
AU: * Warren, C J
EM: clare.warren@earth.ox.ac.uk
AF: Oxford University, Department of Earth Sciences Parks Road, Oxford, Ox1 3PR United Kingdom
AU: Waters, D J
EM: dave.waters@earth.ox.ac.uk
AF: Oxford University, Department of Earth Sciences Parks Road, Oxford, Ox1 3PR United Kingdom
AU: Searle, M P
EM: mike.searle@earth.ox.ac.uk
AF: Oxford University, Department of Earth Sciences Parks Road, Oxford, Ox1 3PR United Kingdom
AU: Parrish, R R
EM: rrp@nigl.nerc.ac.uk
AF: NIGL, BGS Keyworth, Nottingham, NG12 5AA United Kingdom
AB: Eclogites and garnet-blueschists exposed at the deepest structural levels of the Oman Mountains in north-eastern Saih Hatat, Oman, are evidence for the subduction of the Arabian continental margin. Their peak pressures have been a matter of debate for over a decade, with initial thermobarometric estimates in excess of 20 kbar, based on garnet-clinopyroxene-phengite barometry and the presence of radial cracks around quartz inclusions in garnet, questioned by some workers. The high pressure minerals (glaucophane/crossite, omphacite, epidote) contain significant amounts of ferric iron, postulated to displace the stability fields of the eclogite and blueschist assemblages to less extreme conditions. In this study we have calculated phase diagrams and pseudosections in the model system NCFMASHO, using the program THERMOCALC and the thermodynamic database of Holland and Powell, which incorporates data for Fe$^{3+}$ -bearing end members. We find that the phase compositions and modal abundances for typical bulk compositions are successfully matched at pressures of $\sim$22 kbar for the eclogites and $\sim$18 kbar for the garnet blueschists. This supports the original high P estimates for the eclogites, and indicates that crossitic amphibole and aegirine-rich pyroxene do not necessarily reflect less extreme conditions. The data set and activity models are applicable to other oxidised HP and UHP mineral assemblages.
DE: 3660 Metamorphic petrology
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting