Evaluating models for lithospheric loss and intraplate volcanism beneath
the Central Appalachian Mountains
Abstract
The eastern margin of North America has been shaped by a series of
tectonic events including the Paleozoic Appalachian Orogeny and the
breakup of Pangea during the Mesozoic. For the past ~200
Ma, eastern North America has been a passive continental margin;
however, there is evidence in the Central Appalachian Mountains for
post-rifting modification of lithospheric structure. This evidence
includes two co-located pulses of magmatism that post-date the rifting
event (at 152 Ma and 47 Ma) along with low seismic velocities, high
seismic attenuation, and high electrical conductivity in the upper
mantle. Here, we synthesize and evaluate constraints on the lithospheric
evolution of the Central Appalachian Mountains. These include
tomographic imaging of seismic velocities, seismic and electrical
conductivity imaging along the MAGIC array, gravity and heat flow
measurements, geochemical and petrological examination of Jurassic and
Eocene magmatic rocks, and estimates of erosion rates from
geomorphological data. We discuss and evaluate a set of possible
mechanisms for lithospheric loss and intraplate volcanism beneath the
region. Taken together, recent observations provide compelling evidence
for lithospheric loss beneath the Central Appalachians; while they
cannot uniquely identify the processes associated with this loss, they
narrow the range of plausible models, with important implications for
our understanding of intraplate volcanism and the evolution of
continental lithosphere. Our preferred models invoke a combination of
(perhaps episodic) lithospheric loss via Rayleigh-Taylor instabilities
and subsequent small-scale mantle flow in combination with shear-driven
upwelling that maintains the region of thin lithosphere and causes
partial melting in the asthenosphere.