Modeling multiple melt loss events in the evolution of an active continental margin

• Published in: Lithos
• Main Authors: Korhonen, Fawna, Saito, S., Brown, M., Siddoway, C.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier Science BV 2010
• Subjects: Mineral equilibria modeling; Melt loss; East Gondwana; Migmatites; Partial melting; Pacific; West Antarctica; Antarc*; Antarctica
• Online Access: https://hdl.handle.net/20.500.11937/38152; https://doi.org/10.1016/j.lithos.2009.09.004

The Fosdick migmatite–granite complex in West Antarctica records evidence for crustal melting during two periods of tectonism along the East Gondwana margin. Initial high-temperature metamorphism in the Devonian–Carboniferous (M1) was broadly contemporaneous with emplacement of calc-alkaline arc magmas during Pacific-style accretionary margin convergence. This event involved metamorphism of arc plutonic rocks soon after their emplacement and partial melting and migmatization of host metasedimentary rocks. Preservation of M1 garnet-bearing assemblages and mineral equilibria modeling of the metasedimentary rock and calc-alkaline plutonic rock protolith compositions regionally exposed constrain conditions of M1 metamorphism to 820–870 °C and 7.5–11.5 kbar. A second anatectic event during the Cretaceous (M2) resulted in metamorphism of plutonic rocks and partial melting of fertile metasedimentary rocks that had remained at a high enough structural level to have been subsolidus during the first anatectic event, and a metamorphic overprint on now residual paragneisses characterized by the growth of M2 cordierite after garnet, and after biotite + sillimanite. Mineral equilibria modeling of para- and orthogneiss compositions in the Fosdick migmatite–granite complex constrain conditions of M2 metamorphism to 830–870 °C and 6–7.5 kbar.We use the results of mineral equilibria modeling to assess the constituents of the Fosdick migmatite–granite complex as melt sources and as domains of melt transfer and melt accumulation during the two anatectic events. Modeling the range of metasedimentary rock protolith compositions shows that ~ 4–25 vol.% melt was produced at the conditions of M1 metamorphism, although most compositions would have been fertile enough to reach the melt connectivity transition (~ 7 vol.%) leading to the development of a melt extraction pathway and subsequent melt loss. The preservation of peak-M1 assemblages in the paragneiss is consistent with melt loss, and modeling based on a representative protolith ...