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 High angle Normal faults, Tanzania Rift Valley HW FW Axial Lake DepositsSoils Border Fanglomerate Basaltic Lava Flows

Flatirons Dissection of scarp ( often a side of a hogback) by many gullies forms triangular facets wiki/File:Flatirons.jpg

Joints: Fractures – with no movement

And on Mars … Link courtesy Melissa Hansen

Faults 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 MOR, Iceland

Graben in Iceland, a subaerially exposed Mid- Ocean 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

Reverse Fault Scarp

Klippe - Thrust Fault Remnant Chief Mountain, a klippe outlier of the Lewis Thrust, Glacier National Park, MT A feature of thrust fault terranes. The klippe is the remnant portion of a nappe after erosion.

Transform Faults between MOR's Faults 3: Transform Faults between MOR's

Strike-slip fault

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 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, Canyonlands Colorado Plateau Uplift

Salt Dome Low density Buoyant Salt Diapirs Surrounding sediments upwarped Petroleum exploration

Salt Creek Graben at Arches National Park, UT. Solution of evaporites in the underlying Pennsylvanian Paradox Fm. caused the Graben to form. A collapse downwarp

A Rhyolitic Igneous Dome, Yellowstone Caldera Plumes under Continent Interiors.

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 Tectonics 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 Rift 1. The underside of Europe collided with numerous microplates rifted from Africa Closing of the Tethys Sea between late Mesozoic and early Cenozoic time 4. Thrusts not Subduction 3. Messinian Salinity Crisis ~ 5.5 mya 2. Pliocene three way rift. 3. Arabia Microcontinent collision -> Zagros Mts

Subduction-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 Trench Accretionary wedge Fore-Arc Basin Volcanic Arc Back-Arc Basin Continent

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 Orogeny Partly subducted so under AW Subduction and TST

Himalayan Orogeny AW FAB

Fold and Thrust Mountains, Himalayas, Continent-Continent collision Rain Shadow Desert: Tibetan Plateau North INDIA under cloud cover

Taklamakan Desert Tibetan Plateau Himalayas NORTH

San Andreas Transform Changed Orientation15 mya SAF forms MOR Subducted!

North American Cordillera Topography Basin and Range Crust very thin there Columbia River Basalts WHY SO FAR INLAND?

Tertiary Tectonic Events K-T Laramide Continental Override Buoyant Subduction

North American Cordillera

Rockies: Buoyant Subduction caused Laramide Orogeny Normal, thin-skinned Vertical block uplift 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 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 flat buoyantly subducted Farallon Plate?

Basin and Range province Extensional Feature w/ Normal Faults Basin Range

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