Seismic Imaging of a Continental Intraplate: Long-Term Persistence of Fossil Rifts and Hot Spots in the Central and Eastern United States

Abstract:

Seismic surface waves from the Transportable Array of Earthscope’s USArray are used to estimate phase velocity structure of 18 to 125s Rayleigh waves, then corrected for lateral crustal thickness variations (with CRUST1.0) and inverted to obtain three-dimensional crust and upper mantle structure of the Central and Eastern United States (CEUS) down to ~200 km. The obtained lithosphere structure confirms previously imaged features in the CEUS, e.g., the low seismic velocity signature of Proterozoic to Cambrian fossil rifts, the very low velocity at >150 km depth below an Eocene volcanic center in northwestern Virginia, and the very low velocity along a corridor stretching from eastern New York to New Hampshire. The model also reveals new features. The high-velocity Granite-Rhyolite Province sharply bounds the Grenville front at mid-lithosphere depth, suggesting that it acted as a backstop during the Grenville orogeny ca. 1.2 - 1.0 Ga. High-velocity mantle extending ∼ 200 km deep stretches from the Archean Superior Craton well into the Proterozoic terrains (Granite-Rhyolite, Mazatzal and Yavapai provinces). This is consistent with independent seismic velocity images and suggests that the thickness of Proterozoic lithosphere is generally ∼ 200 km. A deep low-velocity zone in central Texas is associated with the late Cretaceous Travis and Uvalde volcanic fields, and a similar deep low-velocity zone is located beneath the South Georgia Rift, which contains Jurassic basalts associated with the Central Atlantic magmatic province. Hotspot tracks may be associated with several of the low-velocity zones, and the central Texas, New York-New Hampshire, and southern Georgia zones may also be associated with the former rifted Laurentia margin. This suggests a systematic pattern whereby transient mantle thermal perturbations are accentuated near former failed rifts or rift margins.