Imaging the Cratonic Lithosphere Beneath the Illinois Basin and the Adirondack Mountains

Date: 4/25/2019

Time: 11:45 AM

Room: Pike

Although cratons are usually thought to be relatively stable, basins and plateaus are widely distributed around the globe. Understanding the formation and evolution of these intractatonic features has significant implications on the modification of continental lithosphere in general. Here we investigate and compare the lithospheric structure beneath the Illinois Basin in the central United States and the Adirondack Mountains in the northeastern United States. We present a crustal thickness model beneath the Illinois Basin, using plane-wave migration of teleseismic receiver functions recorded by the Ozark, Illinois, Indiana, and Kentucky (OIINK) seismic array. For the Adirondack Mountains area and its vicinities, we construct a high-resolution crust and upper mantle shear-wave velocity model using full-wave ambient noise tomography. Beneath the central and southeastern Illinois Basin area, we image an unusually thick crust (up to 62 km), which contradicts to horizontal stretching or lithospheric flexural subsidence model. Multiple mechanisms may have thickened the crust. Remnants of ancient magmatic underplating might be the primary mechanism responsible for the density increase of the crust and, consequently, the subsidence at the surface due to negative buoyancy. In comparison, beneath the Adirondack Mountains, the velocity model reveals a distinctive low-velocity column immediately below the Moho. This anomaly is connected with the large-scale low-velocity volume beneath southern New England and eastern New York at greater depths, which may reflect asthenosphere upwelling induced by a combined effect of the Great Meteor hotspot and edge-driven convections. The buoyancy of the upwelling asthenosphere, together with possible thermal expansion, may have uplifted the Adirondack Mountains. The imaging results for both the Illinois Basin and the Adirondack Mountains suggest the dominance of vertical forces, primarily buoyancy, in the evolution of cratonic interiors.

Presenting Author: Xiaotao Yang

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