Independent determination of the heat capacity of the sapphirine used in this study is currently underway. It is expected that extrapolation of this data to the results of this study will result in the derivation of a heat capacity function for natural sapphirine from 0-1573K. Incorporation of this into existing thermodynamic datasets should allow the quantitative determination of the position of sapphirine-bearing reactions in petrogenetic grids relevant to ultra-high temperature metamorphism in natural systems. The Archean Napier Complex of Antarctica is one of the best documented UHT terrains, long recognised as having experienced temperatures in excess of 1000°C followed by a long period of near-isobaric cooling at deep crustal levels. However, the early history of the terrain, the timing of deformation and metamorphism, and the tectonic processes responsible for the generation of the extreme temperatures of metamorphism, have not been resolved (e.g. Ellis, 1987; Harley, 1989; Sandiford, 1989; Hensen and Motoyoshi, 1992). Mineral textural relationships linked to deformation features from a range of localities in and around Amundsen Bay are consistent with peak metamorphic conditions of 900-1100°C at 0.8-1.1 GPa during intense lower crustal extension. Rare decompression textures from widely spaced localities attest to decompression of the whole terrain to depths equivalent to the base of a normal thickness crust after peak metamorphism, while still under UHT conditions, and indicate that intense lower crustal extension and UHT metamorphism occurred synchronously with crustal thickening. Retrograde reactions textures may have been produced either by isobaric cooling, or by later granulite facies metamorphic event/s, or both. Mineral reaction textures and structural features support a tectonic model of lithosphere delamination for the development of UHT metamorphism, in the Napier Complex. This model involves the detachment of the lower part of the mantle lithosphere during continental collision, allowing upwelling of hot asthenosphere material directly beneath the crust, which in turn results in intense extensional deformation of the lower crust and lateral expulsion of melts.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:652514 |
| Date | January 2000 |
| Creators | Hollis, Julie Alison |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/15035 |
Page generated in 0.0021 seconds