U-Pb geochronology from Tonagh Island, East Antarctica:Implications for the timing of ultra-high temperature metamorphism of the Napier Complex

• Published in: Precambrian Research
• Main Authors: Carson, C. J., Ague, J. J., Coath, C. D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2002
• Subjects: East Antarctica; Ion probe; Napier Complex; U-Pb geochronology; Zircon; Napier; Tonagh Island; Antarc*; Antarctica; Enderby Land
• Online Access: https://hdl.handle.net/1983/fc98788c-f6ac-406f-9515-7a34b6725371; https://research-information.bris.ac.uk/en/publications/fc98788c-f6ac-406f-9515-7a34b6725371; https://doi.org/10.1016/S0301-9268(02)00023-2; http://www.scopus.com/inward/record.url?scp=0037096353&partnerID=8YFLogxK

Ion microprobe U-Pb zircon geochronology of an orthopyroxene-bearing felsic orthogneiss from central Tonagh Island, Enderby Land, East Antarctica provides insight into the chronological-metamorphic evolution of the Archaean Napier Complex, the details of which have been the source of debate for over two decades. The orthogneiss crystallised at 2626 ± 28 Ma, predating peak, ultra-high temperature (UHT) metamorphism and development of an intense regional S 1 gneissosity. Two subsequent episodes of zircon growth/resetting can be identified. A minor period of zircon growth occurred at 2546 ± 13 Ma, the regional significance and geological nature of which is unclear. This was followed by an episode of abundant zircon growth, as mantles on ∼ 2626 Ma cores and as anhedral grains, partly characterised by high Th/U (> 1.2), at ∼ 2450-2480 Ma. This age coincides with both lower and upper concordia intercept ages from other U-Pb zircon studies, and several Rb-Sr and Sm-Nd whole-rock isochron ages from the Napier Complex. We conclude that UHT metamorphism occurred at ∼ 2450-2480 Ma, and find no compelling evidence that UHT occurred much earlier as has been postulated. The zircon U-Pb data from this study also indicates a lower intercept age of ∼ 500 Ma, which coincides with the emplacement of Early Palaeozoic pegmatite swarms and synchronous infiltration of aqueous fluids into the southwestern regions of the Napier Complex.