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Abstract

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.

Item Type:	Article
Authors/Creators:	Halpin, JA and White, RW and Clarke, GL and Kelsey, DE
Keywords:	electron microprobe monazite dating; granulite facies; Rayner Complex; sapphirine; THERMOCALC
Journal or Publication Title:	Journal of Petrology
DOI / ID Number:	10.1093/petrology/egm020
Additional Information:	The definitive publisher-authenticated version is available online at: www.oxfordjournals.org
Item Statistics:	View statistics for this item

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