Along-strike Variations in Synrift Magmatism on the Eastern North American Margin

DESCRIPTION: Continental breakup to form new oceans is often accompanied by extensive outpouring of magmatism. Magmas may make continental breakup possibly by heating up and weakening continental tectonic plates. Volcanism associated with these events has also been associated with major extinction events on Earth. Despite the importance of magmatism during continental breakup, very little is known about the total volume of magmatism involved during rifting and how the volume varies between rift systems. The continental margin off the coast of the eastern U.S. is one of the best examples in the world of a continental breakup event associated with extensive magmatism. One of the biggest magmatic events in history occurred during the breakup of the supercontinent of Pangea and opening of the Atlantic Ocean. This project will involve the analysis of existing marine seismic data collected across the margin offshore North Carolina in 2014 to quantify the volume and distribution of magma frozen in the crust and how it relates to the structures that allowed breakup to occur. The project supports the training of an undergraduate student.

Magmatic intrusions contribute to the growth and modification of the crust of the Earth and strongly influence strain localization in a variety of tectonic settings. Despite this, very few constraints exist on the 3-D distribution of magmatic intrusions throughout the crust in a tectonic setting that can be used to understand the controls on their distribution and the consequences for crustal modification and deformation. This project focuses on magmatism in rifts, but the scientific questions apply across many tectonic settings. Do intrusions exploit pre-existing structures and/or are they focused in the areas of greatest crustal/lithospheric thinning? Does the volume of intrusions in magmatic rifts vary along strike and relate to segmentation at the mid-ocean ridge, or does voluminous magmatism overwhelm focusing mechanisms and result in a more uniform distribution of intrusions along the margin? A 3D seismic velocity model of the crust and uppermost mantle will be built in one of the type examples of magma-rich continental rifting: The Eastern North American Margin (ENAM). The NSF-GeoPRISMS Program supported the collection of active/passive, onshore/offshore seismic data across the ENAM in 2014. As a part of this experiment, data were also collected along and across the East Coast Magnetic Anomaly, which is thought to mark the location of significant synrift magmatism. The data provide excellent 3-D ray coverage of the ENAM area and will be used for 3-D travel time tomography. The resulting velocity model will be used to map the 3-D distribution of magmatic intrusions. This part of the margin is an excellent place to test competing ideas for controls on synrift magmatic addition to the crust.

OUTCOMES: Continental breakup to form new ocean basins is often accompanied by the extensive outpouring of magmas. These magmas may make continental breakup possible by heating up and weakening continents. Volcanism associated with these events has also been associated with major extinction events in Earth’s history. Despite the importance of magmatism during continental breakup, very little is known about the total volume of magmatism generated during rifting and how it varies throughout rift systems. One of our main tools for studying tectonic and magmatic processes is seismic imaging, where we use sound waves to create images of geological structures left behind by these events below Earth’s surface in the crust, including frozen magmas. Although continental rifting creates geological structures that vary in 3D, most existing constraints on crustal configuration of these systems come from 2D profiles. In this project, we used recently acquired seismic data from the Eastern North American Margin Community Seismic Experiment to create a 3D model of crustal velocity structure to constrain 3D patterns of magmatism and deformation. The continental margin off the eastern US is considered a type example of continental breakup event associated with extensive magmatism. One of the biggest magmatic events in Earth’s history occurred during the breakup of the supercontinent of Pangea and opening of the Atlantic Ocean. Our new models of Earth structure here reveal significant variability in the volume and distribution of synrift magmatism along the margin. These results suggest that rifting to form the Atlantic Ocean was associated with less magmatism than previously thought, consistent with other recent results. Furthermore, the variability in magmatism along the ancient rift may have influenced the way that continental breakup took place and initiated the organization of a new seafloor spreading system after rifting, which produced oceanic crust that floors the Atlantic Ocean. The results will be valuable for understanding similar processes in other rifts and designing future 3D imaging projects. An undergraduate student, graduate student and postdoctoral researcher received training and mentoring as a part of this project.