The Proterozoic P-T-t Evolution of the Kemp Land Coast, East Antarctica; Constraints from Si-saturated and Si-undersaturated Metapelites
Integrated metamorphic and geochronological data place new constraints on the metamorphic evolution of a Neoproterozoic orogen in east Antarctica. Granulite-facies rocks from a 150 km stretch of the Kemp Land coast reflect peak conditions involving T~870-990 ºC at P~7.4-10 kbar, with pressure increa...
| Published in: | Journal of Petrology |
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| Main Authors: | , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
2007
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| Subjects: | |
| Online Access: | https://eprints.utas.edu.au/6555/ https://eprints.utas.edu.au/6555/1/Halpin_et_al_2007.pdf http://petrology.oxfordjournals.org/cgi/content/full/48/7/1321 |
| Summary: | Integrated metamorphic and geochronological data place new constraints on the metamorphic evolution of a Neoproterozoic orogen in east Antarctica. Granulite-facies rocks from a 150 km stretch of the Kemp Land coast reflect peak conditions involving T~870-990 ºC at P~7.4-10 kbar, with pressure increasing westward towards an Archaean craton. Electron microprobe-derived (Th+U)-Pb monazite ages from metapelitic assemblages indicate that the major mineral textures in these rocks developed during the c. 940 Ma Rayner Orogeny. Complex compositional zoning in monazite suggests high-T recrystallization over c. 25 Myr. Diversity in metapelitic reaction textures reflects silica and ferromagnesian content: Si-saturated Fe-rich metapelites contain garnet that is partially pseudomorphed by biotite and sillimanite, whereas Si-saturated Mg-rich metapelites and Siundersaturated metapelitic pods have reaction microstructures involving cordierite enclosing orthopyroxene, garnet and/or sapphirine, cordierite+sapphirine symplectites around sillimanite and coarse-grained orthopyroxene+corundum separated by sapphirine coronae. Interpretations based on P-T pseudosections provide integrated bulk-rock constraints and indicate a clockwise P-T-t path characterized by a post-peak P-T trajectory with dP/dT~15-20 bar/ºC. This moderately sloped decompressive-cooling P-T path is in contrast to near-isothermal decompression P-T paths commonly cited for this region of the Rayner Complex, with implications for the post-collisional tectonic response of the mid- to lower crust within this orogenic belt. |
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