Projet collaboratif du Geotop
A strong, rigid lithosphere consisting of tectonic plates that move over the Earth’s surface over geologic time is fundamental to modern understanding of plate dynamics and mantle convection. Lithosphere underlying continental crust is relatively buoyant compared to the mantle so is sequestered from the bulk of the Earth. Growth and development of continental lithosphere is therefore also key to understanding the evolution of the Earth’s internal structure and chemical evolution. However, the mechanism of lithospheric growth and stabilization remains controversial. Post-Archean growth of the continental crust appears to have occurred predominantly by the accretion onto the margins of older cratonic interiors of discrete blocks, or terranes, of crust that form in disparate settings, but the development of the mantle lithosphere underlying accreted terranes is less well understood. This is particularly problematic for Phanerozoic-aged crust, which is dominated by accretionary orogenic belts. Phanerozoic crust along the eastern margin of the North American plate developed by accretion of terranes and collision of continental plates during the Paleozoic Taconic, Acadian, and Alleghanian orogenies. Breakup of Pangea in the Mesozoic lead to rifting and the opening of the North Atlantic in the Early-Middle Jurassic. Geophysical observations show that the North American cratonic interior is underlain by thick (> 150 km) lithosphere, whereas east of Logan’s Line the lithosphere is < 100 km-thick. A variety of geophysical methods indicate the transition from thick to thin lithosphere is sharp and that the internal structure of the mantle lithosphere is different from east to west. This proposal will investigate the evolution of continental lithosphere in the Phanerozoic on the east coast of North America by addressing these complementary research questions:
- Has any mantle lithosphere formed beneath the accreted Phanerozoic terranes of eastern North America?
- How was the sub-continental lithosphere impacted by the rifting of Laurentia?
- What is the deformation state of the mantle lithosphere and how can this be integrated with modern geophysical observations?