Cenozoic Orogenic Events (final exam) Flashcards
What are the 3 periods in the Cenozoic Era?
Paleogene (Paleocene, Eocene, Oligocene)
Neogene (Miocene, Pliocene)
Quaternary (Pleistocene, Holocene)
What is the overview/summary of the Cenozoic plate tectonics?
- continents separated by start of Cenozoic
- India moving north
- Africa moving north
- Rifting begins in East African Rift
- North and South America moving west > eventually connect
When was the Eocene? What were the main plate tectonic events of this epoch?
(56-34 mya)
- Atlantic Ocean had widely separated the Americas from Europe and Africa - created large gap
- In the eastern Pacific Ocean, much of the oceanic crust had been subducted under the North and South American plates
When was the Miocene?
(23-5 mya)
- India had moved northward and collided with Asia (Himalayan mountains)
- Northward movement of the African plate closed the Tethys Sea and initiated tectonic activity that continues today from the Mediterranean to northern India
- rifting began in eastern Africa and continues today > in the late Pliocene, oceanic crust formed in the rifting Red Sea (opening of the red sea)
What are the two main Cenozoic orogenic belts?
Alpine-Himalayan Belt
Circum-Pacific Orogenic Belt
What caused the Alpine-Himalayan orogenic belt? When did it begin?
- caused by northward movement of African and Arabian plates into Eurasia
- began in Mesozoic > extensive deformation during Eocene to late Miocene
Explain the main geologic activity of the alpine-himalayan orogenic belt (what did it cause and activity today?)
- it nearly completely isolated the Mediterranean Sea > evaporite deposits 2km thick
- Mt Everest (Himalayas), Mt Vesuvius (Alps)
- still geologically active today > active volcanoes in Italy and Greece and earthquakes
Explain the geologic activity of specifically the Himalayan orogen
- India colliding with and subducting under Asia
- 40-50 million years ago the rate of subduction decreased rapidly
- 2000km of continental crust underthrust beneath Asia (obduction) > obduction is what’s thickening the crust and uplifting the Tibetan plateau
- no volcanism (because no more subduction)
- earthquakes
What is the significance of Mr Everest and Mt Vesuvius (alpine-himalayan belt)
Mt Everest - tallest peak
Mt Vesuvius - volcano eruption that wiped out Pompei
How is Mt Everest still growing? How fast is it growing? What are the forces pushing it down and making it grow?
India is moving north 5cm/yr
*Everest is growing 4mm/yr
Forces pushing/pulling down: weathering, glacial abrasion, rock falls/landslides
Forces lifting: Plate tectonics and snow cap - protecting the rocks underneath from some of the breakdown processes
It is still growing because the uplift processes are greater than the processes pulling it down
What are the mountain names for the south american and north american parts of the circum-pacific orogenic belt?
South American = the Andes
North American = Cordillera
Explain the tectonic activity of The Andes - what did it result from?
- on South American west coast
- active plate convergence zone since the Mesozoic
- active volcanoes that result from the subduction of the oceanic Nazca plate under the continental South American plate
Explain the North American Cordillera - its evolution and the different orogenys involved
Evolution of the Cordillera began in the Neoproterozoic with deposition of large amounts of sediment on the western margin of North America
Sediment deposition continued in the Paleozoic
> the antler orogeny began during the Devonian
> Cordilleran orogeny began in Late Jurassic > made up of the Nevadan, Sevier, and Laramide orogenies
Name the coast ranges that are part of the Cordilleran mountain-building episodes
- Laramide
- Sevier
- Nevadan
Explain the Laramide Orogeny > when was it? how was it different from previous orogenies?
*late Cretaceous to mid-Eocene
Different from previous orogenies:
- further inland
- igneous activity not common (don’t have the type of subduction and melting that could give us volcanism)
- deformation mostly vertical
- shallower angle of subduction than during Nevadan and Sevier orogenies (magma helped push the plate at a shallower level)
*Farallon plate subducting under north america
After the subduction of the Farallon plate beneath North America on the pacific coast, what 2 remnants remain?
- Juan de Fuca plate (off North America)
- Cocos plate (off Central and northern South America)
What / where is the Cascade Range? What did they result from? What is one of the most famous volcanos in this range?
The Cascade Range extends from BC to northern California and contains dozens of dominantly andesite to rhyolite volcanoes
The cascades are the result of the subduction of the Juan de Fuca Plate under North America which began at least by the Oligocene
- Mt. St. Helens (Washington) was a cascade volcano that famously erupted in dramatic fashion in 1980 > **lateral eruption with a horseshoe shaped crater
- before the eruption it was a very pretty and symmetrical peak
What is the Yellowstone Caldera?
In Yellowstone National Park
- it is known as a super volcano because it creates massive craters
- caldera = the exploded crater of a volcano
Describe the Zuni and Tejas sequences and how they’re different (where are they)?
Zuni:
- Zuni epeiric sea regressed Early Paleogene
- terrestrial deposits (fluvial) > sediment eroded from Laramide highlands
- some localized volcanics mixed with sediments
Tejas:
*is a lot smaller than Zuni sequence > didn’t really extend onto the interior
- restricted to coastal regions (Atlantic, Gulf Coast, parts of California)
- at least 8 transgressive-regressive cycles recorded in Gulf Coast region
- interrupted by glaciation in continental interior
What is the main significance of the Gulf Coastal Plain (Tejas sequence)
- Tejas sea regressed towards the gulf of Mexico with minor transgressions
- 8 transgressive-regressive episodes recorded in the sedimentary rocks of the Gulf Coast Plain
** significance is the many Gulf Coast Plain sedimentary rocks contain valuable petroleum (salt deposits) > there’s a salt dome created which is a good cap rock for petroleum reservoirs
Explain how the east coast Appalachians changed from the Late Triassic to Cretaceous to Cenozoic to Recent
Late Triassic > Appalachians were formed
Cretaceous > sea level very high so they were covered
Cenozoic > sea level dropped which made drainage features (water gaps) - canyons
Recent > further weathering - canyon features eroded away
Summary: As the uplift proceeded, upturned resistant rocks formed northeast-southwest trending ridges with intervening valleys forming in the less resistant rocks
- streams cut water gaps (canyons) into the uplifting ridges
- wind gaps are old water gaps that no longer contain streams
