Revealing the link between A-type granites and hottest melts from residual metasedimentary crust

Among S-, I-, and A-type granites, the latter are the most debated in terms of origin, and metasedimentary crust is usually discarded as a potential source. Here we tackle this issue by adopting an in-source perspective, rather than focusing on the final product (granite), documenting the occurrence...

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Bibliographic Details
Published in:Geology
Main Authors: B. B. Carvalho, O. Bartoli, B. Cesare, M. Satish-Kumar, M. Petrelli, T. Kawakami, T. Hokada, M. Gilio
Other Authors: Carvalho, B. B., Bartoli, O., Cesare, B., Satish-Kumar, M., Petrelli, M., Kawakami, T., Hokada, T., Gilio, M.
Format: Article in Journal/Newspaper
Language:English
Published: Geological Society of America 2023
Subjects:
Antarc*
Antarctica
East Antarctica
Online Access:https://hdl.handle.net/11577/3496983
https://doi.org/10.1130/G51097.1
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/51/9/845/624382/Revealing-the-link-between-A-type-granites-and
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Summary:Among S-, I-, and A-type granites, the latter are the most debated in terms of origin, and metasedimentary crust is usually discarded as a potential source. Here we tackle this issue by adopting an in-source perspective, rather than focusing on the final product (granite), documenting the occurrence of pristine melt inclusions (MIs) in garnet from residual metapelitic ultrahigh-temperature (UHT) granulite from East Antarctica. Coexistence of sapphirine + quartz, phase equilibria calculations, and Zr-in-rutile thermometry indicate that MIs trapped UHT melts formed at peak conditions (930–1000 °C) from a residual metapelitic source. MIs are granitic with weakly peraluminous to weakly peralkaline affinity, ferroan character, high alkali contents, high K/Na and Ga/Al, and low Ca, Ba, Sr, and H2O concentrations. These features and geochemical modeling indicate that MIs represent primary melts for high-SiO2 A-type granites. Therefore, MIs reveal the missing link between A-type granites and the hottest metasedimentary crust. Voluminous amounts of slightly peraluminous, high-SiO2 A-type granites can be produced in large, residual UHT terranes such as those of eastern Gondwana. Our results provide a wider view of processes responsible for granite formation and show that a larger variety of granites must be considered in models of the effects of UHT anatexis on crustal differentiation.

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