November 11, 2019
6:00 - 7:30 pm
Pellissippi State Technical Community College
10915 Hardin Valley Road, Knoxville
J.L Goins Administration Building
Faculty/Staff Dining Room
Modern Appalachian Topography, Product of Miocene to Recent Uplift: Not a Relic of Paleozoic Orogeny, And Not The "World's Oldest Mountain Chain"
Dr. Robert D. Hatcher, Jr.
UT Distinguished Scientist & Professor
Department of Earth and Planetary Sciences
and Science Alliance Center of Excellence
(Co-author is David C. Prowell)
We were taught in junior high the
Appalachians are an "old worn-down" chain, whereas the Rockies are a
"young rugged" range: some still believe that. Atlantic-Gulf Coastal
Plain stratigraphy, however, reveals several cycles of uplift and
erosion interrupted by carbonate deposition in the Mesozoic and
Cenozoic as the Atlantic and Gulf of Mexico opened. The Late
Triassic-Early Jurassic involved erosion, then Late Jurassic-Early
Cretaceous development of a carbonate platform. Renewed uplift of
southeastern North America spilled clastic sediments onto the
Atlantic and Gulf margins in the Late Cretaceous and Eocene.
Carbonate deposition resumed during the mid-Cenozoic, but
Appalachians uplift occurred in the late Miocene-Pliocene producing
the modern southern-central Appalachian topography, supplying
voluminous sediment to the Coastal Plain. Present-day topography and
drainage patterns indicate Paleozoic-early Mesozoic tectonics and
rock types play a minor role in modern topography: major drainages
that drain the western Appalachians head in the eastern Blue Ridge
and Piedmont. The 1.5->2 km maximum Appalachians height shifts from
the southern Appalachian Blue Ridge to the Virginia-West Virginia
Valley and Ridge. The Gray Fossil Site in northeastern Tennessee
contains a Miocene-Pliocene vertebrate assemblage in an ancient lake
that rests on a hilltop >100 m above the nearest drainage providing
a timeline for uplift.
Appalachian crust today remains >50 km thick beneath parts of the Valley and Ridge, Blue Ridge, and western Piedmont, but thins to <35 km from the central Piedmont suture eastward beneath the Coastal Plain from Virginia to Alabama. Late Jurassic to Early Cretaceous reversal of Triassic-Early Jurassic extension to ridge-push-related compression can account for Cretaceous uplift, but does not account for Miocene-Pliocene uplift.
Either deep or shallow mantle flow, or erosional processes and sediment deposition disturbing isostatic equilibrium, likely controlled late Mesozoic-early Tertiary and Miocene-Pliocene Appalachian uplift. Geophysical models involve tomographic data in southeastern North America that suggest flow and reveal a high-velocity, southeast-dipping descending mantle slab west of the Appalachians and a low-velocity mantle to the east.
Despite great strides in
tomographic resolution of mantle structure, the mismatch between
modern topography and tomographic data reconfirms our imperfect
understanding of mantle structure.
Dr. Robert D. Hatcher, Jr. is currently a Distinguished Scientist and Professor with the University of Tennessee in Knoxville, Tennessee. Dr. Hatcher's primary research goal is to gain a better understanding of the evolution of continental crust, mostly through the study of mountain chains and mature crust. Most of his research has been concentrated in the southern and central Appalachians, but large amounts of time have been spent visiting and studying other mountain chains, and Precambrian continental crust. His primary interest is in the mechanics and kinematics of large faults, which formed a natural transition into related long-term interests in the geologic controls of petroleum occurrence in the Appalachians, radioactive waste management, the causes of intraplate seismicity and geologic evidence for determination of recurrence intervals for intraplate earthquakes. While a structural geologist, most of his research is interdisciplinary, integrating stratigraphic, geochronologic, geochemical, and geophysical data into structural studies. As a field geologist, however, his field data form the basis for all other supporting studies. He has been involved for many years with geophysicists and geologists in other academic institutions and the USGS in the geologic interpretation of seismic reflection and potential field (aeromagnetic and gravity) data. From 1981 through 1983 (part of the Bechtel team), he participated in the Electric Power Research Institute-sponsored study of eastern seismicity, and during the late 1970s and early 1980s participated in the TVA-sponsored Southern Appalachian Tectonic Study (with S. S. Alexander and W. J. Hinze, 1979-1980). Current research support includes a Nuclear Regulatory Commission grant for study of the East Tennessee seismic zone (through 2015), a USGS EDMAP grant (detailed geologic mapping of stream terraces around Douglas Lake), and a National Park Service grant (detailed geologic mapping, Obed W & SR region).
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Page updated October 14, 2019