By Lesley Porcelli

The National Science Foundation awarded a research grant to Jay Thomas, associate professor in the Department of Earth and Environmental Sciences, for his project, “Revisiting the water-saturated granite solidus." Thomas is collaborating on the project with Michael Ackerson, research geologist at the Smithsonian Institution’s National Museum of Natural History.

The team’s preliminary dataset shows that granitic composition magmas solidify at 600 to 650°C, which is 70 to 100°C lower than the widely accepted temperatures determined using rudimentary methods in the 1950s. Granitic rocks are important because the Earth’s continental crust has a granitic composition. Granite solidification temperatures vary with depth (pressure), thus defining a fundamental phase boundary on Earth known as the granitic water-saturated solidus (G-WSS), that separates melt-free metamorphic rocks (i.e., completely solid) from igneous rocks that contain melt. Redefining the G-WSS will transform longstanding views on granite formation processes, continental crust formation, development of volcanic systems, thermal structure in terrestrial bodies, plate tectonics, and innumerable aspects in hard-rock petrology, and will affect explorations of economically important ores.

Thomas will conduct a series of lab-based experiments to redefine the G-WSS, and then apply observations to rocks contained in the Smithsonian Institution’s National Museum of Natural History collections. In addition, the grant will provide research opportunities for high school students from underserved communities in Washington, D.C. and Ph.D. students. Thomas and Ackerson will also produce a series of educational experiences to teach visitors to the National Mall how ancient magmatic systems generated the stones that were used to construct some of the National Mall’s most famous monuments and buildings.