Dr. Esteban Gazel, Associate Professor Department of Earth and Atmospheric Sciences Cornell University.
"The rocks that joined the Americas: Is there a connection with climate and evolution of life?"
Earth’s crust is the life-sustaining interface between our planet’s deep interior and surface. Basaltic crusts similar to Earth’s oceanic crust characterize terrestrial planets in the solar system while the continental masses, areas of buoyant, thick silicic crust, are a unique characteristic of Earth. The continental crust is also enriched in incompatible elements (elements that separate from the mantle during partial melting) and although it is a volumetrically minor layer it plays a major role in the fractionation and storage of those elements. Therefore, understanding the processes responsible for the formation of continents is fundamental to reconstructing the evolution of our planet. Analyzing modern analogues where “juvenile” continental crust is forming can provide a better understanding of the formation of continental crust in the past. The evolution of the Central American Land-Bridge (CALB, Costa Rica and Panama) was used as a natural laboratory to answer this fundamental question. Geochemical and geophysical data support the evolution of the CALB into a young continent as a result of the interaction of Galapagos Hotspot tracks with this subduction system. A global survey of intra-oceanic arcs was conducted with the goal of identifying where magmas with continental crust signatures have been produced and what processes control the composition of the volcanic output. Finally, a new geochemical continental index was developed to quantitatively correlate geochemical composition with available average arc P-wave velocity, resulting in a strong correlation (r2=0.87) between those two parameters. Our work suggests that although the origin and evolution of continents may require many processes, melting of enriched oceanic crust and reaction of these melts with the mantle wedge in a subduction system will result in juvenile continental crust production, a process that was probably more common in the Archean than today. In Central America the production of “juvenile” continental crust culminated with the closure of the Panama Seaway ~15 to 3 Ma. This closure resulted in global change of ocean circulation, separated marine species, and allowed the exchange of fauna between the Americas, making the evolution of the CALB not only relevant to the understanding of geologic processes, but also had considerable impacts on evolution of life and climate on the planet.