CONSTRAINTS ON GRENVILLE OROGENIC PROCESSES BENEATH CENTRAL AND EASTERN NORTH AMERICA FROM SEISMIC IMAGING OF CRUSTAL STRUCTURE (Invited Presentation)

The ca. 1 Ga Grenville orogeny was a protracted mountain-building event that culminated in the collision of Laurentia and Amazonia and the formation of the Rodinia supercontinent. While the expression of Grenville orogenesis in present-day crustal structure has been extensively investigated in eastern Canada, evidence for contemporaneous crustal deformation is less well established beneath the eastern United States. Furthermore, the interpretation of a geophysical lineament through the U.S. midcontinent, typically inferred to be the Grenville deformation front, has recently been called into question; an alternative hypothesis is that this feature actually corresponds to an eastern arm of the Midcontinent Rift. Here we present receiver function imaging using data from the Mid-Atlantic Geophysical Integrative Collaboration (MAGIC) experiment, a dense array of broadband seismometers across Virginia, West Virginia, and Ohio that was deployed as part of the EarthScope USArray. We see evidence for a crustal negative velocity gradient that dips gently (dip angle <10°) to the southeast and extends east from a location near the putative Grenville front in Ohio, terminating near the Appalachian Mountains. While we cannot date this feature, its location and characteristics are consistent with a shallowly dipping, seismically anisotropic intracrustal shear zone associated with collisional deformation, likely during Grenville orogenesis. The similarity between this feature and similar mid-crustal detachments in other orogens, both ancient (Appalachians) and modern (Himalayas), suggests that this style of crustal deformation has been common in continental collisional orogens across geologic time. We situate our crustal imaging from the MAGIC project in the context of other recent results from other EarthScope data in the eastern U.S., and discuss possible avenues for resolving ongoing controversies regarding the relative roles of the Midcontinent Rift and the Grenville Orogeny in shaping the lithospheric structure beneath the central and eastern U.S.