Seafloor spreading centers?the volcanic ridges where Earth?s tectonic plates separate and form oceanic crust?are subdivided into ?segments? that represent basic units of volcanic crustal formation. Segments are typically tens to hundreds of kilometers long and form crust along their length but with decreased thickness toward the segment ends. Often the segments are offset from each other along shear zones called transform faults. The scars produced by transform faults, referred to as fracture zones, trace out the motion of the plates and are among the longest and most prominent features of ocean basins. The segmented nature of volcanic crustal production on seafloor spreading centers creates the large-scale structure of the seafloor and controls the way in which material from the shallow mantle flows, melts and is emplaced to form the layered oceanic crust that forms two-thirds of the surface of the Earth. Yet segmentation is a dynamic aspect of seafloor spreading and can evolve abruptly or progressively. Segments can form, grow, shorten or be eliminated by merging together with other segments. What controls this evolution has long been a subject of debate and controversy. Some models propose that large-scale variations in flow and temperature of the underlying mantle are important. Other models propose a predominant control by the motion of the tectonic plates themselves. This project will conduct a marine geophysical survey to examine what controls the formation, evolution and elimination of segmentation on the Reykjanes Ridge, a 1000-km-long seafloor spreading center in the North Atlantic Ocean south of Iceland. In order to study what may be controlling this evolution this project will map how the segments first formed following the abrupt change in plate motion and how they progressively re-merged to eliminate segmentation along the gradient in mantle melting away from Iceland. The project will support the training and education of a graduate student in the research and bring undergraduates and interns out on the research vessel for at sea experience and training. A movie will be made of the ridge segmentation evolution to help explain the processes involved in plate tectonics.
The Reykjanes Ridge is probably the best example of the systematic formation and elimination of segmentation and transform faults on Earth today. The project will survey two conjugate flank areas of the Reykjanes Ridge where segmentation and transform faults formed and were subsequently eliminated. The survey will span the area from near the Iceland shelf in the north to the Bight Fracture Zone in the south, encompassing the prominent gradient in mantle melting away from Iceland. The survey will use multibeam swaths and sub-bottom sonar profiles to map the tectonic and volcanic structure of the seafloor, towed magnetometer measurements to accurately map the magnetic lineations that date the crustal formation process, and ship gravimeter measurements to estimate crustal thickness changes. These data will be used to examine how variations in mantle melting and plate motion changes affect the formation, evolution and elimination of segmentation on mid-ocean ridges that frame the large-scale tectonic and crustal structure of entire ocean basins.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
