Transcript 05 Tectonic Landforms mod 4i

Lecture 5
Tectonic
Landforms
Landforms that result from crustal movements
Landforms with little erosion so "their shape defines a
fractured or deformed surface" Bloom
Escarpment or "scarp"
• Tectonic Scarp: steep slope from
differential movement of surface
Basaltic Lava Flows
Axial Lake Deposits
Soils
FW
HW
High angle Normal faults, Tanzania Rift Valley
http://travel.mongabay.com/tanzania/images/tz_elf_0560.html
Border Fanglomerate
Flatirons
• Dissection of scarp ( often a side of a
hogback) by many gullies forms triangular
facets
http://en.wikipedia.org/
wiki/File:Flatirons.jpg
Joints: Fractures – with no movement
http://www.pbase.com/dougsherman/image/93468807
And on Mars …
Link courtesy Melissa Hansen
Faults 1: Normal Faults
• Typical of Divergent
Margins
• Rift Valleys and MidOcean Ridges
• High-angle and Listric
• Horst and Graben
Structure
• Hanging wall is down
Divergent Margins @ MOR, Iceland
Graben in
Iceland, a
subaerially
exposed MidOcean Ridge
Source: Simon Fraser/Science Photo Library/Photo Researchers, Inc.
Rift Valley x-sec
Origin of Basaltic magma 2
Faults 2: Reverse Fault Structures
• Typical of Convergent Margins
• E.g. Accretionary Wedges (Santa Catalina
Island’s schists) and Fold and Thrust
Mountains (Himalayas, Alps,
Appalachians)
• Often low-angle thrusts
• Hanging wall is up
Overhanging Block
http://rst.gsfc.nasa.gov/Sect2/05-01_reverse_fault-jyougashima_DSC8766.jpg
http://www.flickr.com/photos/mirkazemian/356833099/sizes/o/
Reverse Fault Scarp
Klippe - Thrust Fault Remnant
A feature of thrust fault
terranes. The klippe is the
remnant portion of a nappe
after erosion.
http://www.pbase.com/dougsherman/image/93469147
Chief Mountain, a klippe outlier of the Lewis Thrust, Glacier National Park, MT
Faults 3:
Transform
Faults
between
MOR's
Strike-slip fault
http://epod.usra.edu/archive/images/wallace_creek_aerial.jpg
Sag pond along San Andreas
Transform (strike-slip) Fault
The linear strike-slip feature
running across this anaglyph is one
of many transform faults in
California. Along it can be seen
good examples of off-set streams
[and] a shutter ridge .
From Drury, text paraphrased.
Structural
Control by
Folds
Overturned folds in the
Paleozoic rocks of the
Marathon Basin of
Texas. The ridges are
controlled by resistant
carbonates.
From Drury, Ch. 4
A Monocline near Cody, Wyoming
Upwarps 1: The Adirondack Mountains
of Northern New York
Source: Clyde H. Smith/Allstock/Tony Stone Images
Although the rocks are ancient, the uplift that formed the Adirondack dome has occurred within the last 5 million years
— relatively recent in geologic time — and is ongoing.
Mantle upwelling, Upwarp Mountains
Upheaval Dome, Canyonlands
Colorado Plateau Uplift
http://www.pbase.com/dougsherman/image/93400984
Salt Dome
Low density
Buoyant Salt
Diapirs
Surrounding
sediments
upwarped
Petroleum exploration
A collapse downwarp
Salt Creek Graben at Arches National Park, UT.
Solution of evaporites in the underlying Pennsylvanian
Paradox Fm. caused the Graben to form.
Plumes under Continent Interiors.
A Rhyolitic Igneous Dome, Yellowstone Caldera
Mars: frost heave?
A 2005 photo of Elysium Planitia by the Mars Express
spacecraft shows what may be ash-covered water ice. The
volume of ice is estimated to be 800 by 900 kilometers in
size and 45 meters deep, similar in size and depth to the
North Sea.
Mounds S. of Elysium
Planitia a few
kilometers in diameter
about 60 meters tall.
Fractures suggest
mounds formed by
uplift
Uplift is not uniform
mounds are probably
solidified lava.
Mounds contiguous
with and texturally
similar to flood lavas
over Elysium Planitia.
Where dilation cracks
provide crosssectional exposure,
the uplifted material is
rocky.
Link courtesy Melissa Hansen
Frost heave on a huge scale?
Review of Cenozoic Tectonics
http://www.globalchange.umich.edu/Ben/Helvetic%20Morcles%20nappe.JPG
A nappe is a large sheetlike body of rock that has been moved more than 2 km (1.2 miles) from its
original position. Nappes form during continental plate collisions, when folds are sheared so much
that they fold back over on themselves and break apart. The resulting structure is a large-scale
recumbent fold. The term stems from the French word for tablecloth.
• Cenozoic Orogenic activity concentrated in two areas
– Alpine-Himalayan belt deformation began in the Mesozoic
and remains geologically active.
Isolation of Tethys to form the modern Mediterranean Sea
– circum-Pacific belt deformation occurred throughout the
Cenozoic
1. The underside of Europe collided with
numerous microplates rifted from Africa
Closing of the Tethys Sea between late
Mesozoic and early Cenozoic time
3. Messinian Salinity Crisis ~ 5.5 mya 4. Thrusts not Subduction
Arabian-African Rift
2. Pliocene three way rift.
3. Arabia Microcontinent collision -> Zagros Mts
Subduction-Zone Features
Note sequence from
land to trench
Note ocean plate
rocks that don’t get
subducted in a
collision
If a continent converges from
the left, what rocks will fold
in the collision? Himalayas
Continent
Back-Arc Basin
Trench
Accretionary wedge
Fore-Arc Basin
Volcanic Arc
• Abyssal plains
– Can be sites of thick
accumulations of sediment
– Sediments thickest away
from MOR
– Abyssal plains found in all
oceans
– Studded by old cold
seamounts and MORs
Drawings of Nappes in the Alps
New Orogen, Nappes still visible
http://www.geol-alp.com/chartreuse/3_tecto_chartreuse/1_ch_occ.html
"A spectacular thrust fault in
the Caledonides of NW
Scotland, which drove
Archaean gneisses over
Cambro-Ordovician
sediments. The thrust plane is
marked by the pronounced
bench on the peninsula, which
is coated with mylonite. The
typical knobbly topography of
the heavily glaciated gneisses
is quite obvious in the upper
part …. "
From Drury, Ch. 4
Definition Nappes previous slide
Himalayan Orogeny
Subduction and TST
Partly subducted so under AW
Himalayan Orogeny
AW
FAB
INDIA under cloud cover
Rain Shadow Desert: Tibetan Plateau
Fold and Thrust Mountains, Himalayas,
Continent-Continent collision
North
Taklamakan Desert
NORTH
Tibetan Plateau
San Andreas Transform
MOR Subducted!
Changed Orientation
15 mya SAF forms
North American Cordillera Topography
WHY SO FAR INLAND?
Basin and Range
Crust very thin there
Columbia River Basalts
Tertiary Tectonic Events
K-T Laramide Continental Override
Buoyant Subduction
North American Cordillera
Rockies: Buoyant Subduction caused Laramide Orogeny
Vertical block uplift
Normal, thin-skinned
Approaching Continent pushes
accretionary wedge sediments
into forearc sediments
The Grand Tetons in Wyoming
Source: Peter French/DRK Photo
High Angle Faults, Buoyant Subduction.
Later origin of Fault Block Mountains
“Basin and Range”
Southwestern North America
But why so Wide? Breakup of flat
buoyantly subducted Farallon Plate?
Huge divergent zone, Basin and Range, not
so far inland as Rockies, more normal
subduction dip resumes, partial melting in
mantle, magma rises similar to rift valley.
Basin and Range province
Range
Extensional Feature
w/ Normal Faults
Basin
Rift vs. Basin and Range
Mirror symmetry, radial cracks about center, divergence, normal faults
Conjugate shear fractures, divergence, normal faults
Displaced terranes – Western Cordillera
These terranes overlap in age but
have different rock types,
paleolatitudes and fossils.
However, we can deduce when
they accreted from their order, and
the metamorphic ages of their
suture zones
Columbia River Basalts
(including the Saddle Mountains Basalt)
17my
Columbia River Basalts and
Yellowstone Plume
http://en.wikipedia.org/wiki/Columbia_River_Basalt_Group