Event


Freshly brewed continental crust

Esteban Gazel,Cornell University

Nov 22, 2019 at | 358 Hayden Hall

Geoscience Colloquium

Earth’s crust is the life-sustaining interface between our planet’s deep interior and surface. Most “terrestrial” planets in the solar system have basaltic crusts similar to Earth’s oceanic crust, but the continental masses, areas of buoyant, thick silicic crust, are a unique characteristic of Earth. Therefore, understanding the processes responsible for the formation of continents is fundamental to reconstructing the evolution of our planet. We use geochemical and geophysical data to reconstruct the evolution of the Central American Land Bridge (Costa Rica and Panama), which evolved from an oceanic subduction system (where two oceanic plates collide) over the past 70 million years. We found that the geochemical signature of erupted lavas evolved to continental-like about 10 million years ago - coinciding with the onset of subduction of more enriched oceanic crust that originally formed above the Galapagos mantle plume. We also found that seismic P-waves (body waves) travel through the crust at velocities closer to the ones observed in continental crust world-wide. Finally, we developed a continental index based on global statistical analyses of all magmas produced today in oceanic arcs compared to the global average composition of continental crust to quantitatively correlate geochemical composition with the average P-wave velocity of arc crust globally, resulting in a strong correlation (r2=0.85). We concluded that although the formation and evolution of continents may involve many processes, melting enriched oceanic crust within a subduction zone - a process probably more common in the Archaean (~2.5-3.5 billion of years ago), where most continental landmasses formed - can produce juvenile continental crust, and thus solving this major unknown in the evolution of our planet.