Why Are the Appalachian Mountains So High?

John Cipar, PhD Weston Observatory

Boston College April 16, 2014

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Adirondacks from Mt. Marcy, NY

High elevation (1630 m at summit)

Steep Topography (30 m at Lake Champlain)

Old Rocks from deep crust (1200 Ma Anorthosite, crystallized at 15-20 depth)

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Photo by Jef Renaud

Eastern North America Topography

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Adirondacks

Alleghany Plateau

Southern Appalachians

Northern Appalachians

Coastal Plain

Catskills

Central Appalachians

Blue Ridge

Canadian Shield

From Geological History of Jamestown, Rhode Island web site

Earth’s Interior

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• Pressure at center is 350 Gpa (3,500,00 atmospheres)

• Temperature at center: 5430 ⁰C (9800 ⁰F)

UC Berkeley Seismo Lab

Continents v. Oceans

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30-50 km Rigid & elastic

Continental crust

• Light granite: “floats” on surface • Formed by continental collision • Old (4000 My) to very young

Oceanic crust • Heavy basalt: subducts into mantle • Formed at mid-ocean ridges • Young <185 My to right now!

PhysicalGeography.net

Plate Tectonics

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• Continental Drift was first proposed by Alfred Wegner in 1912 • Strong geological evidence for drift, but no physical mechanism for moving the continents through the oceans • Modern theory of sea floor spreading /Plate Tectonics developed in 1950s -1970s

US Geological Survey

Plate Map

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Boston 2011 Tohoku, Japan earthquake

2004 Sumatra earthquake

Earth’s Dynamic Systems /W. Kenneth Hamblin and Eric H. Christiansen

Plate Boundaries

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Hawaiian Hot Spot

9 May 30, 2011

Subduction zones

10 Earth’s Dynamic Systems /W. Kenneth Hamblin and Eric H. Christiansen

Wilson cycle

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Lynn S. Fichter/James Madison University

Building the Appalachians: Precambrian to Paleozoic

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Geology of North America

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Geologic Map of Eastern North America

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“Suspect” Terranes

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Hibbard et al, 2006

Rodinia - 700 My

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Paul Hoffman, Science, v. 252, p. 1409

Laurentia

Passive Margin Early Cambrian - 550 My

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• Maps from Ron Blakely • Cross-sections from Virginia Geology web site and USGS

Amazonia (South America)

Laurentia (North America)

Iapetus Ocean

Taconic Orogeny Ordovician - 450 My

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Boston

Ron Blakely and USGS

Acadian Orogeny Devonian - 385 My

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Ron Blakely and USGS

Alleghany Orogeny Pennsylvanian & Permian - 290 My

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Africa

North America

The Paleozoic Appalachians were probably similar to today’s Himalaya Mountains

Boston

Ron Blakely and USGS

Rifting of Pangaea Triassic - 195 My

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North America

Africa

Ron Blakely and JMU

Triassic rifting: Opening of the Atlantic

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~200 My

~185My

Earth’s Dynamic Systems /W. Kenneth Hamblin and Eric H. Christiansen

“How many years can a mountain exist

Before it's washed to the sea?”

- Bob Dylan, Blowin’ in the Wind

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The Last 200 My

• Eastern North America is a “passive” margin

– Sedimentation along the Atlantic coast

– Far from active plate boundaries

• Passage over the Great Meteor hotspot 125-90 My

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Unsolved question is the persistence of high Appalachian topography to the present

Great Meteor Hotspot Track

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105 My

White Mountains 125-100 My

85 My

125 My

Hot spot in New England 125-100 My

McHone, 1996

North America 115 My ago

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Farallon plate

Atlantic Ocean

Greenland

Great Meteor hotspot

N o r t h A m e r i c a

Map by Ron Blakely

Evidence for Hotspot Uplift

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Crough, 1981

Devonian sediments are truncated

Thermochronology

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Apatite grain w/tracks

Assumed geothermal gradient converts temperature to depth

Apatite fission track (AFT) ages tell when a rock cooled through approximately 100 °C, or about 4-5 km depth.

New England AFT ages

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Roden-Tice and Tice, 2005

~70-125 My

125-178 My

125-178 My

Offshore sediments

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Sediment Supply to Atlantic Basins

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Pulse in sedimentation (& uplift?) ~15 My

Seismic structure of the Earth

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Stephen A. Nelson, Tulane University

S-wave velocities in New England

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Slow S-wave ≡ high T

Li et al (2002) Remnant of Great Meteor hot spot ?

Structure of North American mantle constrained by simultaneous inversion of multiple‐frequency SH, SS, and Love waves

Journal of Geophysical Research: Solid Earth Volume 116, Issue B2, B02307, 15 FEB 2011 DOI: 10.1029/2010JB007704 http://onlinelibrary.wiley.com/doi/10.1029/2010JB007704/full#jgrb16621-fig-0013

Tian, Yue, Ying Zhou, Karin Sigloch, Guust Nolet, and Gabi Laske (2011)

Map view Cross-section

Slow S –wave velocity in NH & VT

Farallon plate beneath North America

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High S velocity = • low temp • high density

eastern US

IRIS Earthscope TA Stations

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Incorporated Research Institutions in Seismology

The “Great” Unconformity near Alexandria Bay, NY

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540 My

1100 My

~560 My

Chris Murray, Thousand Islands Life web site

Saga of the Potsdam sandstone

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Questions?

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Further Reading • Mountain Press Roadside Geology Series

– Fr. James Skehan, S.J.: MA and CT/RI

• USGS Geology of the New York City Region – http://3dparks.wr.usgs.gov/nyc/index.html

• Geological Evolution of Virginia and the Mid-Atlantic Region – Lynn S. Fichter/James Madison University – http://csmres.jmu.edu/geollab/vageol/vahist/

• Geological History of Jamestown, Rhode Island – http://www.jamestown-ri.info/northern_appalachians.htm

• PhysicalGeography.net – http://www.physicalgeography.net/

• Ron Blakely Paleogeographic Maps – http://cpgeosystems.com/paleomaps.html

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Bibliography Crough, S.T. (1979). Hotspot epeirogeny, Tectonophysics, vol. 61, pp. 321-333.

Crough, S. Thomas (1981). Mesozoic hotspot epeirogeny in eastern North America, Geology, v. 9, pp. 2-6.

Duncan, R. A. (1984). Age Progressive Volcanism in the New England Seamounts and the Opening of the Central Atlantic Ocean, J. Geophys. Res., 89(B12), 9980–9990, doi:10.1029/JB089iB12p09980.

Ehlers, Todd A. and Kenneth A. Farley (2003). Apatite (U-Th)/He thermochronometry: methods and applications to problems in tectonic and surface processes, Earth and Planetary Science Letters 206 (2003) 1-14.

Furlong, Kevin P. and David S. Chapman (2013). Heat Flow, Heat Generation, and the Thermal State of the Lithosphere, Annu. Rev. Earth Planet. Sci. 2013. 41:385–410

Grand, Stephen P. and Rob D. van der Hilst (1997). Global Seismic Tomography: A snapshot of convection in the Earth, GSA Today, vol. 7, no. 4, pp. 1-7, (April, 1997).

Hibbard, J.P., van Staal, C.R., Rankin, D.W., and Williams, H., 2006, Lithotectonic map of the Appalachian orogen, Canada–United States of America: Geological Survey of Canada Map 2096A, scale 1:1,500,000.

Hoffman, Paul F. (1991). Did the Breakout of Laurentia Turn Gondwanaland Inside-Out?, Science 7 June 1991: 1409-1412. [DOI:10.1126/science.252.5011.1409]

Li, Aibing, Karen M. Fischer, Suzan van der Lee, and Michael E. Wysession (2002), Crust and upper mantle discontinuity structure beneath eastern North America, J. Geophys. Res., vol. 107, p. 2100, doi:10.1029/2001JB000190

McHone, J. Gregory and J. Robert Butler (1984). Mesozoic igneous provinces of New England and the opening of the North Atlantic Ocean, Geological Society of America Bulletin, July, 1984, v. 95, p. 757-765.

McHone, J. Gregory (1996). Constraints on the mantle plume model for Mesozoic alkaline intrusions in northeastern North America, Can. Mineral., v. 34, p. 325-334.

Pazzaglia, Frank J. and Mark T. Brandon (1996). Macrogeomorphic evolution of the post-Triassic Appalachian mountains determined by deconvolution of the offshore basin sedimentary record, Basin Research, vol. 8, pp. 255-278.

Pazzaglia, Frank et al (2006). Rivers, glaciers, landscape evolution, and active tectonics of the central Appalachians, Pennsylvania and Maryland, Geological Society of America Field Guides 2006; 8;169-197.

Poag, C. W. and W. D. Sevon (1989). A record of Appalachian denudation in post rift Mesozoic and Cenozoic sedimentary deposits of the U.S. middle Atlantic continental margin, Geomorphology, v. 2, pp. 119-127.

Roden-Tice, Mary K., Steven J. Tice, and Ian S. Schofield (2000). Evidence for Differential Unroofing in the Adirondack Mountains, New York State, Determined by Apatite Fission-Track Thermochronology, The Journal of Geology, 2000, volume 108, p. 155–169.

Roden-Tice, Mary K. and Steven J. Tice (2005). Regional-Scale Mid-Jurassic to Late Cretaceous Unroofing from the Adirondack Mountains through Central New England Based on Apatite Fission-Track and (U-Th)/He Thermochronology, The Journal of Geology, 2005, volume 113, p. 535–552.

Roden-Tice, Mary K., J. Dykstra Eusden Jr., and Robert P. Wintsch. "Apatite fission-track evidence for the Cretaceous development of kilometer-scale relief and steady-state Tertiary topography in New England" Geomorphology 141-142 (2012): 114-120.

Tian, Yue, Ying Zhou, Karin Sigloch, Guust Nolet, and Gabi Laske (2011). Structure of North American mantle constrained by simultaneous inversion of multiple-frequency SH, SS, and Love waves, J. Geophys. Res., vol. 116, B02307, 18p.

Williams, Harold, and Robert D. Hatcher, Jr (1982). Suspect terranes and acretionary history of the Appalachian orogeny, Geology, October, 1982, v. 10, p. 530-536

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