Transcript By Alyson Churchill Overview • The Green Mountains extend from Vermont’s northern to southern border, and provide evidence for both pervasive and complex.

By Alyson Churchill
Overview
• The Green Mountains extend from Vermont’s northern to
southern border, and provide evidence for both pervasive
and complex geologic activity.
• The deposition of the basement complex and subsequent
sedimentation form the base of the Green Mountains.
• They record the activity of ancient plate tectonics and were
heavily influenced by the Taconic and Acadian Orogenies.
• The breakup of Pangaea is recorded in the Green Mountains
through evidence of extensional tectonics.
• Glaciation during the Pleistocene was very influential.
• Geomorphologic processes continue to change the Green
Mountains.
Figure 1: A map of the geo-physiographic
provinces of Vermont, with the Green
Mountain Province highlighted in the central
part of the state (from Doolan, 1996).
Underlying Basement Complex
• Core of the Green Mountains consists of Precambrian
Grenville basement rocks derived from previously
deposited sediments-these comprised the ancient
Grenville Mountains.
• After the erosion of the Grenville Mountains, a major
rifting event resulted in multiple episodes of magmatic
activity and the first significant sediment input into
basins.
• Formation of the Iapetus Ocean deposited marine
sediments.
• A thick cover of mud was then deposited on top of the
marine sediments, with its source being deep ocean
sediments to the east.
Figure 2: Simplified map of the geology of
Vermont, including the Proterozoic
basement rocks and subsequent depositions
(from Coish, 2010).
Uplift of the Green Mountains-the Taconic
Orogeny
• The Taconic Orogeny-collision of an island arc with the North
American continent.
• This thrust Cambrian-Ordovician rock units onto the Laurentian
continental margin, resulting in pervasive deformation and
high-grade metamorphism
• A deep sedimentary basin developed after the Taconic Orogeny,
recycling the sediments of structures produced by it.
Figure 3: Diagram reconstructing orogenic activity as a result of plate tectonics
during the Tectonic Orogeny. C1-C3 detail the closing of the Iapetus Ocean by the
subduction of oceanic crust under a trench, with mountains developing as a result
of sediment accumulation along the continental margin (from Doolan, 1996).
The Acadian Orogeny - Continuing
Deformation
• The Acadian Orogeny-collision of one or more microcontinents
and island arcs with North America.
• This produced deformation and metamorphism of more intense
magnitudes, refolding previously deformed structures within
the Green Mountains.
• Large amounts of heat and pressure melted the material within
the convergence zone, producing vast quantities of granite.
Figure 4: Reconstruction of collisional tectonics during the Acadian
orogeny. D1-D2 detail the development of a new basin as well as the uplift
of Vermont due to continent collisions (from Doolan, 1996).
Mesozoic Era Extension
• The breakup of Pangaea formed the present Atlantic Ocean and
resulted in extension throughout New England.
• Extension reactivated faults formed during earlier periods.
• Extension also resulted in magmatism in the Green Mountains,
producing lamprophyric dikes and small alkaline bodies.
• Magmatism could be related to a mantle plume beneath the
North American plate or due to the rifting of the continental
plate.
Pleistocene Glaciation
• During the late Pleistocene, the
Laurentide Ice Sheet spread across
New England.
• The glacial till that separated the ice
from the underlying bedrock ground
against the Green Mountains as it
advanced.
• The ice flowed obliquely across the
mountains from northwest to
southeast, but changed direction and
flowed from northeast to southwest
as the ice sheet retreated.
• Possibility of local post-Laurentide
mountain glaciation within the
Green Mountains, though this is
questioned.
Figure showing the strike of striations in the Green Mountains
from Pleistocene Glaciation (Wright, 2013).
Recent Geomorphic Processes
• Erosional processes currently comprise the main geomorphologic
influence on the Green Mountains.
• The absence or presence of vegetation on the Green Mountains is
one of the most influential factors contributing to hillside erosion.
• More extreme amounts of hydrologic activity due to climate change
has also increased hillside erosion.
• The stability of the Green Mountain slopes is decreased by the
prominence of moisture-laden storms and freeze-thaw cycles.
References
•
Ackerly, Spafford C., 1989: Reconstructions of mountain glacier profiles, northeastern United States. Geological Society of America Bulletin, v. 101, no. 4, p. 561-572.
•
Bierman, Paul, 1997: Postglacial Ponds and Alluvial Fans: Recorders of Holocene Landscape History. GSA Today, v. 7, no. 10, p. 1-8.
•
Coish, Raymond A., 2010: Magmatism in the Vermont Appalachians. Geological Society of America, v. 206, p. 91-110.
•
Conrad, Diane, and D. Vanacek, 1990: Welcome to Industrial Minerals of Vermont: 200 Years and Going Strong. Vermont Geological Survey, p. 1-2.
•
Davis, P. Thompson, 1999: Cirques of the Presidential Range, New Hampshire, and surrounding alpine areas in the northeastern United States. Géographie physique et
quaternaire, v. 53, p. 25-45.
•
De Souza, S., A. Tremblay, and G. Ruffet, 2014; Taconian orogenesis, sedimentation and magmatism in the southern Quebec–northern Vermont Appalachians: Stratigraphic and
detrital mineral record of Iapetan suturing. American Journal of Science, v. 314, p. 1065-1103.
•
Doolan, Barry, 1996: The Geology of Vermont. Rocks and Minerals, Vermont Issue, v. 71, p. 218-224.
•
Karabinos, Paul, 1984: Deformation and metamorphism on the east side of the Green Mountain massif in southern Vermont. Geological Society of America Bulletin, v. 95, no. 5,
p.584-593.
•
Karabinos, Paul, 1988: Tectonic Significance of Basement-Cover Relationships in the Green Mountain Massif, Vermont. The Journal of Geology, v. 96, no. 4, p. 445-454.
•
Ratcliffe, Nicholas M., 1990: Comparative tectonics of basement massifs in the Northern Appalachians with special reference to the Green Mountain Massif of Vermont. Vermont
Geological Society, v. 6, p. 55-56.
•
Springston, George E., 2009: Analysis of rock fall and debris flow hazards in Smugglers Notch, Green Mountains, Northern Vermont. Geological Society of America Abstracts with
Programs, v. 41, p. 82.
•
Sullivan, W.A., 2014: An introduction to the plate-tectonic evolution of northern New England and adjacent Canada with special emphasis on central and coastal Maine. Colby
College Department of Geology, p. 1-3.
•
Thompson, Douglas M., 1991: The effects of large organic debris on sediment processes in the Green Mountains of Vermont. Green Mountain Geologist, v. 17, p. 11-12.
•
Wagner, Philip W, 1970: Pleistocene Mountain Glaciation, Northern Vermont. Geological Society of America Bulletin, v. 81, p. 2465-2469.
•
Wright, Stephen F., 2003: Glacial Geology of the Burlington and Colchester 7.5’ Quadrangles, Northern Vermont. Vermont Geological Survey, p. 1-12.
•
Wright, Stephen F., 2013: Laurentide Ice Sheet Flow across the Central Green Mountains, Vermont. Geological Society of America Abstracts with Programs, v. 45, p. 105.
Images:
http://www.findandgoseek.net/blog/2012/10/02/deals-and-steals-for-families-skiing-in-vermont-this-winter/
http://dailyoffice.org/2012/10/20/morning-prayer-10-20-12-proper-23-ordinary-time/