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Published September 2018 | Supplemental Material
Journal Article Open

Ultrahigh-temperature osumilite gneisses in southern Madagascar record combined heat advection and high rates of radiogenic heat production in a long-lived high-T orogen

Abstract

We report the discovery of osumilite in ultrahigh‐temperature (UHT) metapelites of the Anosyen domain, southern Madagascar. The gneisses equilibrated at ~930°C/0.6 GPa. Monazite and zircon U–Pb dates record 80 Ma of metamorphism. Monazite compositional trends reflect the transition from prograde to retrograde metamorphism at 550 Ma. Eu anomalies in monazite reflect changes in fO_2 relative to quartz–fayalite–magnetite related to the growth and breakdown of spinel. The ratio Gd/Yb in monazite records the growth and breakdown of garnet. High rates of radiogenic heat production were the primary control on metamorphic grade at the regional scale. The short duration of prograde metamorphism in the osumilite gneisses (<29 ± 8 Ma) suggests that a thin mantle lithosphere (<80 km) or advective heating may have also been important in the formation of this high‐T, low‐P terrane.

Additional Information

© 2018 John Wiley & Sons Ltd. Issue Online: 02 August 2018; Version of Record online: 26 April 2018; Accepted manuscript online: 01 April 2018; Manuscript accepted: 25 March 2018; Manuscript received: 10 September 2017. Funding Information: Division of Earth Sciences. Grant Number: NSF‐EAR‐1348003. University of California, Santa Barbara. Grant Number: NSF‐EAR‐1348003.

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August 21, 2023
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