EGU21-9657
https://doi.org/10.5194/egusphere-egu21-9657
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

High pressure, halogen-bearing melt in ultra-high temperature felsic granulites of the Central Maine Terrane, Connecticut (US)

Silvio Ferrero1,2, Jay J. Ague3, Patrick J. O'Brien1, Bernd Wunder4, Laurent Remusat5, Martin A. Ziemann1, and Jennifer Axler6
Silvio Ferrero et al.
  • 1Universität Potsdam, Institut für Geowissenschaften-Haus 27, Potsdam, Germany (sferrero@geo.uni-potsdam.de)
  • 2Museum für Naturkunde (MfN), Leibniz-Institut für Evolutions-und Biodiversitätsforschung, 10115 Berlin, Germany
  • 3Yale University, New Haven, CT, 06520-8109, US
  • 4Helmholtz-Zentrum Potsdam, GFZ, D-14473 Potsdam, Germany
  • 5Museum National d’Histoire Naturelle, Paris
  • 6Wellesley College, 106 Central Street – Wellesley, MA 02481

Inclusions of relic high pressure melts provide information on the fate of crustal rocks in the deep roots of orogens during collision and crustal thickening, including at extreme temperature conditions exceeding 1000°C. However, discoveries of high pressure melt inclusions are still a relative rarity among case studies of inclusions in metamorphic minerals. Here we present the results of experimental and microchemical investigations of nanogranitoids in garnets from the felsic granulites of the Central Maine Terrane (Connecticut, US). Their successful experimental re-homogenization at ~2 GPa confirms that they originally were trapped portions of deep melts and makes them the first direct evidence of high pressure during peak metamorphism and melting for these felsic granulites. The trapped melt has a hydrous, granitic, and peraluminous character typical of crustal melts from metapelites. This melt is higher in mafic components (FeO and MgO) than most of the nanogranitoids investigated previously, likely the result of the extreme melting temperatures – well above 1000°C. This is the first natural evidence of the positive correlation between temperature and mafic character of the melt, a trend previously supported only by experimental evidence. Moreover, it poses a severe caveat against the common assumption that partial melts from metasediments at depth are always leucogranitic in composition. NanoSIMS measurement on re-homogenized inclusions show significant amounts of CO2, Cl and F. Halogen abundance in the melt is considered to be a proxy for the presence of brines (strongly saline fluids) at depth. Brines are known to shift the melting temperatures of the system toward higher values, and may have been responsible for delaying melt production via biotite dehydration melting until these rocks reached extreme temperatures of more than 1000°C, rather than 800-850°C as commonly observed for these reactions.

How to cite: Ferrero, S., Ague, J. J., O'Brien, P. J., Wunder, B., Remusat, L., Ziemann, M. A., and Axler, J.: High pressure, halogen-bearing melt in ultra-high temperature felsic granulites of the Central Maine Terrane, Connecticut (US), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9657, https://doi.org/10.5194/egusphere-egu21-9657, 2021.

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