Download Story of the Red Centre

Story of the Red Centre
Bob Colomb
[email protected]
The landscape we see at Uluru and around Alice Springs
is not only spectacular, but very ancient.
The story of this landscape dates back 2 billion years,
through three supercontinents and three mountain ranges.
Over two sessions, we will look at the processes
producing continental drift and mountain building to tell the
story of the Red Centre.
The Red Centre
The landscape we see at Uluru and around Alice Springs
is not only spectacular, but very ancient:
Uluru
and Kata Tjuta
originated from sediments laid down more than 500 million
years ago, and folded to their present vertical orientation
more than 300 million years ago.
The MacDonnell Ranges around Alice Springs
Mount Gillem
Heavitree Gap
Are the remains of a mountain range, as high as the
Himalayas, formed 300 million years ago.
The Finke River,
drained the Centre from 300 million years ago, but has
been mostly dry for 55 million years.
Lake Amadeus, 70 km north of Uluru,
is the remains of the once enormous Amadeus Basin,
formed about 1.4 billion years ago.
The core of the MacDonnell range mountains is a layer of
Heavitree quartzite. Quartzite is formed when a layer of
sandstone is compressed and heated. This quartzite layer,
formed horizontal, has a steep dip now.
Simpson’s Gap, West MacDonnell Ranges
Corroboree Rock is a spectacular dolomite formation.
Dolomite is formed by marine organisms. This layer, laid
down horizontally at the bottom of a sea, is vertical, 1000
kilometres from the ocean.
Telling the story of this landscape takes us to the drifting
of continents, the formation and breakup of
supercontinents, how mountains and basins are formed,
and how these processes created the Centre, starting two
billion years ago.
Dodgem Continents
Over the past few decades scientists have realised that
the continents are not fixed, but drift around, and that their
configurations have changed radically over geological
time. The continents collide and stick together, and then
break apart. During some periods nearly all the continents
are stuck together in a supercontinent. This has happened
at least three times in the past two billion years.
Supercontinent Columbia 1.9 – 1.5 billion years ago.
Oxygen atmosphere. Paleoproterozoic Era. Life limited to
single-celled aquatic organisms.
http://www.largeigneousprovinces.org/apr11
What would Columbia have been like?
In some ways much like present continents. There would
have been mountains, rivers, lakes, soil, rain, cyclones,
thunderstorms, surf, beaches, floods and droughts.
But no plants and no animals.
Plenty of life, though. Bacteria and blue-green algae had
been around for billions of years. So there would have
been algal blooms and soil bacteria. Stromatolites would
have been common in shallow waters. Protists, including
slime molds, would have also been common and very
diverse.
Stromatolites
Colonies of bacteria which incorporate silt particles in their
mats as a means of shelter and protection from ultraviolet
light.
Slime Mold
Fuligo septica, the "dog vomit" slime mold
Consists of a single cell with many nucleii
Supercontinent Rodinia 1.1 billion to 750 million years
ago. Mesoproterozoic Era. Life limited to aquatic animals:
stromatolites, colonial (e.g. sponges), and soft-bodied
multicellular organisms.
http://maps.unomaha.edu/maher/plate/week12/super.html
Life forms on land would have been similar to those on
Columbia, possibly with the addition of lichens. Although
multi-cellular and colonial organisms were developing in
the seas, the land was still pretty barren.
The map shows the Grenville Orogeny, a long-lived
mountain building episode, which was active in South
Australia and West Australia.
Lichen
Algae and fungi in symbiosis
Pangaea supercontinent. 300 – 100 million years ago.
Permian to Early Cretaceous. Land plants and animals.
http://en.wikipedia.org/wiki/Pangaea
Life forms included amphibians, crocodiles, insects,
reptiles and dinosaurs among the animals, and club
mosses, tree ferns, grasstrees, cycads in the forests.
Birds, flowering plants, and mammals were yet to appear.
Cycads at Standley Chasm
Specimen at Olive Pink Botanic Gardens, Alice Springs
Assembly of Gondwana Supercontinent
Gondwana formed after breakup of Rodinia. Notice that
the Australia/East Antarctica block (Mawson Block) has
been together since Columbia. Gondwana mostly formed
during the Neoproterozoic Era (colonial and soft-bodied
multicellular aquatic organisms), with some of (4) during
the early Cambrian (hard body parts aquatic organisms).
The life on land would have been much like that during
Rodinia.
http://specialpapers.gsapubs.org/content/423/1/F1.expansion.html
Gondwana became part of Pangaea, and separated pretty
well as a unit. Australia and Antarctica finally broke apart
beginning about 85 million years ago (Cretaceous Period
– Dinosaurs), completing about 30 million years ago
(Oligocene – flowering plants, birds, modern mammal
types appearing).
Plate Tectonics: How and Why the Continents Move
Continents are formed from rock that is lighter than the
rock that forms the ocean basins. The movement of the
continents is based on processes called plate tectonics.
The driving force behind plate tectonics is convection in
the mantle.
http://en.wikipedia.org/wiki/Plate_tectonics
Hot material near the Earth's core rises, and colder mantle
rock sinks, in something like the way water boils.
The convection drives plate tectonics through a
combination of pushing and spreading apart at mid-ocean
ridges and pulling and sinking downward at subduction
zones.
Mid-ocean ridges are gaps between tectonic plates that
mantle the Earth like seams on a cricket ball. Hot magma
wells up at the ridges, forming new ocean crust and
shoving the plates apart. At subduction zones, two
tectonic plates meet and one slides beneath the other
back into the mantle, the layer underneath the crust. The
cold, sinking plate pulls the crust behind it downward.
Many spectacular volcanoes are found along subduction
zones, such as the "Ring of Fire" that surrounds the
Pacific Ocean.
Continental crust, being lighter than oceanic crust, tends
to float above subduction zones, so two continental blocks
interacting at a subduction zone get pushed together
rather than being drawn down with the oceanic crust.
Subduction zones, or convergent margins, are one of the
three types of plate boundaries. The others are divergent
and transform margins.
At a divergent margin, two plates are spreading apart, as
at seafloor-spreading ridges or continental rift zones such
as the East Africa Rift.
Transform margins mark slip-sliding plates, such as
California's San Andreas Fault, where the North America
and Pacific plates grind past each other with a mostly
horizontal motion.
http://www.livescience.com/37706-what-is-plate-tectonics.html
Map of the Presently-Active Plate Boundaries.
Notice that India and Australia are on the same plate,
which is moving northward at about 7 centimetres per
year. This movement is driving the formation of the
Himalaya mountains, first by crushing and folding the
continental shelves and now by the Indian subcontinent
driving under the Tibetan plateau.
https://www.e-education.psu.edu/earth520/content/l2_p14.html
The driving force for this movement is the sea floor
spreading at the divergent boundary in the Southern and
Indian Oceans.
Eventually, Australia will collide with Asia. At the present
movement rate of 7 centimetres per year, in 50 million
years the continent will have moved 3500 kilometres north
and east. This is more than the distance from Darwin to
Manila.
As we will see, much of the mountain building in Central
Australia is caused by continental collision. A preliminary
stage in this process, also important in Central Australia,
is the creation of a basin from the continental shelves of
the colliding continents.
https://en.wikipedia.org/wiki/File:ForelandBasinSystem.png