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°C at P ≈ 7·4–10 kbar, with pressure inc...
| Published in: | Journal of Petrology |
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| Main Authors: | , , , |
| Format: | Text |
| Language: | English |
| Published: |
Oxford University Press
2007
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| Subjects: | |
| Online Access: | http://petrology.oxfordjournals.org/cgi/content/short/48/7/1321 https://doi.org/10.1093/petrology/egm020 |
| 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°C 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 Si-undersaturated 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 d P /d T ≈ 15–20 bar/ °C. 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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