The northern Ford ranges in Marie Byrd Land, Antarctica, record events and processes that transformed a voluminous succession of Lower Paleozoic turbidites intruded by calc-alkaline plutonic rocks into differentiated continental crust along the margin of Gondwana. In this study the Fosdick migmatite?granite complex will be used to investigate crustal evolution through an integrated program of fieldwork, structural geology, petrology, mineral equilibria modeling, geochronology and geochemistry. The PIs propose detailed traverses at four sites within the complex to investigate Paleozoic and Mesozoic orogenic cycles. They will use petrological associations, structural geometry, and microstructures of host gneisses and leucogranites to distinguish the migration and coalescence patterns for remnant melt flow networks, and carry out detailed sampling for geochronology, geochemistry and isotope research. Mafic plutonic phases will be sampled to acquire information about mantle contributions at the source. Mineral equilibria modeling of source rocks and granite products, combined with in situ mineral dating, will be employed to resolve the P?T?t trajectories arising from thickening/thinning of crust during orogenic cycles and to investigate melting and melt loss history.
Broader impacts: This work involves research and educational initiatives for an early career female scientist, as well as Ph.D. and undergraduate students. Educational programs for high school audiences and undergraduate courses on interdisciplinary Antarctic science will be developed.
The major goals of this project were to: characterize the pattern of a remnant melt flow network in the deep crust that enabled the transfer granite magma to the shallow crust; to develop a petrogenetic model for the evolution and temporal succession of granites associated with crustal differentiation; to determine the variation in the depth–temperature–time evolution of active plate margin crust during mountain building and collapse; to evaluate regional ‘sinks’ for melt produced at depth within the crust; and, to investigate the field context of mafic rocks and acquire samples of these and xenoliths from young volcanic vents for use in a future project. Additionally, components of the project were designed as research topics for graduate student training. Among the outcomes of this project, two graduate students at the University of Maryland earned degrees as follows: Caitlin R. Brown, Petrogenesis of peraluminous granites from the Fosdick Mountains, Marie Byrd Land, West Antarctica, MS degree, December 2013; and, Christopher John Anthony Yakymchuk, Anatexis and crustal differentiation: Insights from the Fosdick migmatite–granite complex, West Antarctica, PhD degree, July 2014. Chris Yakymchuk enjoyed valuable experience in extreme conditions via 2 seasons of fieldwork in the Fosdick Mountains of Marie Byrd Land in West Antarctica. Both students received training in cutting edge analytical techniques in geochemistry and both have been involved in writing up their research for publication in the peer-reviewed scientific literature. This training will ensure that they contribute at a high level to the future of our society. Specific scientific outcomes include: the demonstration of power-law behavior of a remnant melt flow network in the deep crust, which is consistent with the hypothesis that intracrustal differentiation by partial melting and granite magmatism is scale-invariant and represents a self-organized critical system; the demonstration of prominent arc-parallel and arc-normal variations in the mechanisms and timing of crustal reworking vs crustal growth along the former active margin of the late-Precambrian supercontinent Gondwana; the demonstration that partial melting and melt drainage from deep crust in mountain belts has important consequences for the behavior of the principal geochronometers, zircon and monazite, used to evaluate rates of processes and for the tectonic behavior of these belts; and, the demonstration that granites in remnant melt flow networks represent clogging of magma transport channels through the middle crust as melt drainage slowed, whereas larger bodies of granite at shallower levels in the crust record collapse of sub-horizontal partially-crystallized layers of magma by filter pressing and melt loss during vertical shortening associated with doming and exhumation of the basement rocks in the Fosdick Mountains. This outcomes of project, together with the previous work by our team, has raised the bar in terms of what can be done in complex basement terrains, and our papers published in the peer-reviewed scientific literature serve as a "best-case how-to" guide for others to follow in the study of high-metamorphic-grade granite source terrains.
