Lecture 5Lecture 5Tectonic Tectonic
LandformsLandforms
Landforms that result from crustal movementsLandforms that result from crustal movementsLandforms with little erosion so "their shape defines a Landforms with little erosion so "their shape defines a
fractured or deformed surface" Bloomfractured or deformed surface" Bloom
Escarpment or "scarp"Escarpment or "scarp"
• Tectonic Scarp: steep slope from differential movement of surface
High angle Normal faults, Tanzania Rift Valley
http://travel.mongabay.com/tanzania/images/tz_elf_0560.html
HW
FWAxial Lake Deposits Soils
Border Fanglomerate
Basaltic Lava Flows
FlatironsFlatirons
• 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 movementJoints: Fractures – with no movement
http://www.pbase.com/dougsherman/image/93468807
And on Mars …And on Mars …
Link courtesy Melissa Hansen
Faults 1: Normal FaultsFaults 1: Normal Faults
• Typical of Divergent Margins
• Rift Valleys and Mid-Ocean Ridges
• High-angle and Listric
• Horst and Graben Structure
• Hanging wall is down
Divergent Margins Divergent Margins @ MOR, Iceland @ MOR, Iceland
Graben in Graben in Iceland, a Iceland, a subaerially subaerially exposed Mid-exposed Mid-Ocean RidgeOcean Ridge
Source: Simon Fraser/Science Photo Library/Photo Researchers, Inc.
Rift Valley x-secRift Valley x-sec
Origin of Basaltic magma 2
Faults 2: Reverse Fault StructuresFaults 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
http://rst.gsfc.nasa.gov/Sect2/05-01_reverse_fault-jyougashima_DSC8766.jpg
Overhanging Block
http://www.flickr.com/photos/mirkazemian/356833099/sizes/o/
Reverse Fault ScarpReverse Fault Scarp
Klippe - Thrust Fault RemnantKlippe - Thrust Fault Remnant
Chief Mountain, a klippe outlier of the Lewis Thrust, Glacier National Park, MT
http://www.pbase.com/dougsherman/image/93469147
A feature of thrust fault terranes. The klippe is the remnant portion of a nappe after erosion.
Faults 3: Transform Transform Faults Faults between between MOR'sMOR's
http://epod.usra.edu/archive/images/wallace_creek_aerial.jpg
Strike-slip fault
Sag pond along San Andreas Sag pond along San Andreas Transform (strike-slip) FaultTransform (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 Structural Control by Control by
Folds 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 Upwarps 1: The Adirondack Mountains of Northern New Yorkof Northern New York
Source: Clyde H. Smith/Allstock/Tony Stone Images
Mantle upwelling, Upwarp Mountains
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.
Upheaval Dome, CanyonlandsUpheaval Dome, Canyonlands
http://www.pbase.com/dougsherman/image/93400984
Colorado Plateau Uplift
Salt Dome
Low density Buoyant Salt Diapirs
Surrounding sediments upwarped
Petroleum exploration
Salt Creek Graben at Arches National Park, UT. Salt Creek Graben at Arches National Park, UT. Solution of evaporites in the underlying Pennsylvanian Solution of evaporites in the underlying Pennsylvanian Paradox Fm. caused the Graben to form.Paradox Fm. caused the Graben to form.
A collapse downwarpA collapse downwarp
A Rhyolitic Igneous Dome, Yellowstone CalderaPlumes under Continent Interiors.
Mars: frost heave?Mars: frost heave?
Link courtesy Melissa Hansen
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 cross-sectional exposure, the uplifted material is rocky.
Frost heave on a huge scale?
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.
Review of Cenozoic TectonicsReview 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
Arabian-African RiftArabian-African Rift1. The underside of Europe collided with numerous microplates rifted from Africa Closing of the Tethys Sea between late Mesozoic and early Cenozoic time4. Thrusts not Subduction3. Messinian Salinity Crisis ~ 5.5 mya
2. Pliocene three way rift.
3. Arabia Microcontinent collision -> Zagros Mts
Subduction-Zone FeaturesSubduction-Zone Features
Note sequence from land to trench
If a continent converges from the left, what rocks will fold in the collision? Himalayas
Note ocean plate rocks that don’t get subducted in a collision
• 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
TrenchAccretionary wedgeFore-Arc BasinVolcanic Arc
Back-Arc Basin
Continent
http://www.geol-alp.com/chartreuse/3_tecto_chartreuse/1_ch_occ.html
New Orogen, Nappes still visible
Drawings of Nappes in the Alps
"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 OrogenyHimalayan Orogeny
Partly subducted so under AW
Subduction and TST
Himalayan OrogenyHimalayan Orogeny
AW
FAB
Fold and Thrust Mountains, Himalayas, Continent-Continent collision
Rain Shadow Desert: Tibetan Plateau
North
INDIA under cloud cover
Taklamakan DesertTaklamakan Desert
Tibetan PlateauTibetan Plateau
Himalayas
Himalayas
NORTHNORTH
San Andreas TransformSan Andreas Transform
Changed Orientation 15 mya SAF forms
MOR Subducted!
North American Cordillera TopographyNorth American Cordillera Topography
Basin and RangeCrust very thin there
Columbia River BasaltsWHY SO FAR INLAND?
Tertiary Tectonic EventsTertiary Tectonic Events
K-T Laramide Continental OverrideBuoyant Subduction
North American Cordillera
Rockies: Buoyant Subduction caused Laramide OrogenyRockies: Buoyant Subduction caused Laramide Orogeny
Normal, thin-skinned
Vertical block uplift
Approaching Continent pushesaccretionary wedge sediments
into forearc sediments
The Grand Tetons in WyomingThe Grand Tetons in Wyoming
Source: Peter French/DRK Photo
High Angle Faults, Buoyant Subduction.
Later origin of Fault Block Mountains Later origin of Fault Block Mountains “Basin and Range” “Basin and Range”
Southwestern North AmericaSouthwestern North America
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.
But why so Wide? Breakup of flatbuoyantly subducted Farallon Plate?
Basin and Range provinceBasin and Range province
Extensional Featurew/ Normal Faults
BasinRange
Rift vs. Basin and RangeRift vs. Basin and Range
Mirror symmetry, radial cracks about center, divergence, normal faults
Conjugate shear fractures, divergence, normal faults
Displaced terranes – Western CordilleraDisplaced 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 BasaltsColumbia River Basalts(including the Saddle Mountains Basalt)(including the Saddle Mountains Basalt)
17my
Columbia River Basalts and Columbia River Basalts and Yellowstone PlumeYellowstone Plume
http://en.wikipedia.org/wiki/Columbia_River_Basalt_Group