HR: 0800h
AN: V41C-0726    [Abstracts]
TI: Interlayered High-P Granulites and Eclogites, Fiordland, New Zealand
AU: * De Paoli, M
EM: made9180@mail.usyd.edu.au
AF: University of Sydney, School of Geosciences University of Sydney, Sydney, NSW 2006, Australia
AU: Clarke, G
EM: geoffc@mail.usyd.edu.au
AF: University of Sydney, School of Geosciences University of Sydney, Sydney, NSW 2006, Australia
AU: Klepeis, K
EM: Keith.Klepeis@uvm.edu
AF: University of Vermont, Department of Geology University of Vermont, Burlington, VT 05405-0122, United States
AU: Turnbull, I
EM: I.Turnbull@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, Crown Research Institute, Dunedin, 9010, New Zealand
AB: As lithospheric plates are subducted and thickened, rocks are metamorphosed under high- P and UHP conditions to produce granulite and eclogite facies metamorphic rocks. Serendipitous circumstances may facilitate chemical equilibrium at such conditions, but it is rarely entirely achieved. Granulites and eclogites can preserve, in their distinctive mineral assemblages and textures, a record of the pressure, temperature and deformation conditions experienced during subduction, crustal thickening, and subsequent exhumation. Granulite facies rocks reflect the highest temperature conditions, whereas eclogite facies rocks are most commonly associated with subduction and reflect highest-pressure conditions associated for orogenic metamorphism. Eclogite facies assemblages may also reflect upper-mantle conditions. Rocks that record assemblages from both the granuilte and eclogite facies, evidence of the garnulite-eclogite facies transition, are extremely rare. These types of rocks are of interest as they represent the deepest parts of Earth's crust affected by orogenesis and encapsulate processes related to nascent crust and lower crust - upper mantle interaction. Fiordland, New Zealand, offers a unique cross-section through the lower crust root of a Cretaceous magmatic arc. We have recently identified a suite of unusual rocks that contain interlayered eclogite and granulite facies assemblages. On the basis of published literature, rocks with assemblages similar to those occur in relatively few localities - the Bohemian massif (Czech Republic) and the Western Gneiss Region (Norway). Peak metamorphic conditions accompanied by the formation of penetrative gneissic textures displaying interstitial partitions of mafic to felsic bearing assemblages - garnet-omphacite-rutile (mafic) and antiperthite-plagioclase-quartz-rutile-kyanite (felsic). Preliminary thermobarometric results for these uncommonly well preserved high- P high- T orthopyroxene-bearing rocks indicate P~17-19kbar, and T~850-920°C. The metamorphic P- T-t path of these peculiar rocks will be constrained through forward modeling utilizing XRF bulk rock data in conjunction with phase equilibria employing the program THERMOCALC (Powell, 1998). Calculated pseudosections to constrain peak and retrograde conditions reflected by changes in mineral composition and reaction textures; they have proven to be a powerful tool as both the stability of mineral assemblages and mineral compositions can be considered simultaneously. THERMOCALC also offers the potential to study other important physiochemical issues such as the development local-scale chemical potential gradients and volume change during the formation of these unique outcrops.
DE: 1099 General or miscellaneous
DE: 3625 Petrography, microstructures, and textures
DE: 3652 Pressure-temperature-time paths
DE: 3660 Metamorphic petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting