Multiple Generations of Granite in the Fosdick Mountains, Marie Byrd Land, West Antarctica: Implications for Polyphase Intracrustal Differentiation in a Continental Margin Setting

• Published in: Journal of Petrology
• Main Authors: Korhonen, F. J., Saito, S., Brown, M., Siddoway, C. S., Day, J. M. D.
• Format: Text
• Language: English
• Published: Oxford University Press 2010
• Subjects: Original Papers; West Antarctica; Byrd; Marie Byrd Land; Fosdick Mountains; Antarc*; Antarctica
• Online Access: http://petrology.oxfordjournals.org/cgi/content/short/51/3/627; https://doi.org/10.1093/petrology/egp093

Production of granite in the middle to lower crust and emplacement into the middle to upper crust at convergent plate margins is the dominant mechanism of crustal differentiation. The Fosdick Mountains of West Antarctica host migmatitic paragneisses and orthogneisses corresponding to the middle to lower crust and granites emplaced as dikes, sills and small plutons, which record processes of intracrustal differentiation along the East Gondwana margin. U–Pb chronology on magmatic zircon from granites reveals emplacement at c . 358–336 Ma and c . 115–98 Ma, consistent with a polyphase tectonic evolution of the region during Devonian–Carboniferous continental arc activity and Cretaceous continental rifting. The gneisses and granites exposed in the Fosdick migmatite–granite complex were derived from Early Paleozoic quartzose turbidites of the Swanson Formation and Ford Granodiorite suite calc-alkaline plutonic rocks, both of which are widely distributed outside the Fosdick Mountains and have affinity with rock elsewhere in East Gondwana. Granites of both Carboniferous and Cretaceous age have distinct chemical signatures that reflect different melting reactions and accessory phase behavior in contrasting sources. Based on whole-rock major and trace element geochemistry and Sr–Nd isotope compositions, Carboniferous granites with low Rb/Sr are interpreted to be products of melting of the Ford Granodiorite suite. Extant mineral equilibria modeling indicates that the Ford Granodiorite suite compositions produce melt volumes >10 vol. % at temperatures above biotite stability, involving the breakdown of hornblende + plagioclase, consistent with the high CaO and Na 2 O contents in the low Rb/Sr granites. The Carboniferous low Rb/Sr granites show a sequence from near-melt compositions to compositions with increasing amounts of early crystallized biotite and plagioclase and evidence for apatite dissolution in the source. Carboniferous granites derived from the Swanson Formation are scarce, suggesting that the significant ...