GEOL120 Flashcards
What are some types of Volcanic Rock?
Gabbro, Diorite, and Granite are all plutonic Volcanic rock.
What are some other types of Volcanic Rock?
Trachyte
Dacite
Komatiite
Tuff
Ignimbrite
Kimberlite
Explain the volcanic rock Trachyte?
Trachyte is a volcanic product of parent magma differentiation
Explain Dacite?
It’s the volcanic equivalent to Granodiorite, and formed by subduction of early oceanic crust, under thick felsic continental plate.
Explain Komatiite
It’s the volcanic equivalent to Peridotite
Oldest ultramafic magmatic rocks (~3.4 GA)
Spinifex bladed Acicular olivine and pyroxene in fine matrix
Explain what a Tuff and Ignimbrite is?
Explain Kimberlite
Ultramafic mantle-derived material brought to the surface by kimerblite pipes, Dykes, Sills.
Brecciated (rubble/broken fragments)
Brings up diamonds from depths via several emplacement models.
Economically viable Kimberlites tend to occur on Precambrian and Archaean Cratons.
What does a Ancient Kimberlite Volcano look like?
What is a Hypabyssal Rock?
Rocks that have intruded at shallow depths and characteristics between plutonic and igneous rocks. It’s grain size is typically 1 mm.
What’s the difference between Hypabyssal and Subvolcanic?
They’re the same.
What are some Hypabyssal rocks?
Regarding Volacanism and Plate tectonics, what are three main ways to produce a magma?
Decompression melting
Flux Melting
Increasing temperature
(All methods are controlled by the tectonic environment)
A map of Volcanism and plate tectonics
Explain Basaltic Volcanism?
It’s the most common form of volcanism on earth,
Occurs in a wide range of tectonic environments such as:
- MOR’s
- Island/volcanic Arcs
- Intraplate Volcanoe’s
What are Submarine eruptions? And what percentage of the earth do they cover?
They are a product of Ridge Volcanism in the Mid Ocean ridge, and they cover for 70% of earth’s surface.
They develop along fissures, parallel to the ridge.
What happens in a Submarine eruption?
Hot Mantle rock rises to shallow depths and undergoes decompression melting-
Basaltic lava cools quickly underwater and forms pillows-
Circulation of seawater in the crust creates hydrothermal vents, convection - circulating “black smokers” and temperature, where unique organisms and sea life live in abundence.
What is does this picture represent?
An outcrop or formation of pillowing from a submarine eruption,
Due to their pillowing and sausage shapes this tells us they were formed underwater.
Desribe the shield volcano of the “Hawaiin” volcanism
The large broad shield volcanoes are due to their thin low viscosity basaltic lava flow.
Emitt very little pyroclastic material during eruptions.
They have a steady production of lava fountaining and are considered the safest of volcanoes.
What does this picture represent?
The different types of volcanoes, and the diagrams that represent their structure or size relative to one another.
What is a hot spot and how does it form?
There are two types of hot spots:
- Oceanic hot spots:
Large Igneous provinces are?
Enormous sheets of low viscosity basaltic magma continue to be erupted over long timescales producing a basltic plateau.
Developed by a mantle plume beneath an are that is undergoing rifitng.
They are usually basaltic but compose a diverse range of composition.
Frequently assosciated with extinction periods eg Siberian Traps - Permian ex
What are Columnar Basalt’s?
It’s a basalt that commonly breaks into regular columns because of contraction when cooling.
This indiccates subaerial cooling.
Exactly, what types of formation is this?
Culumnar Basalt.
What can you share about Andesitic and Rhyolitic volcanism?
- It’s more viscous than basalt lava and do not folw as easily.
- Andesitic volcanism commonly associated with subduction but not all.
What is the Andesite line?
It’s a line around the Pacific Ocean that seperates basaltic oceanic crust from more felsic andesitic crust around continental margins.
Describe the silica content in Andesitic and rhylitic volcanism?
Andesitic and Rhyolitic has high viscosity due to high silica content, they are explosive (rather then effusive)
How does Rhyolitic volacanism present in eruption?
More often erupted as a pyroclastic material (rock ash) then a flow.
If Volcanic magma is more felsic, what does that indicate about the eruption?
The more Felsic composition the more explosive
Why is Felsic eruptions more explosive?
Felsic magmas have more silica = polymerisation of the silica tetrahedra making the magma more viscous therefor more explosive.
Why else are eruptions explosive?
Sudden degassing of the magma and releasing of pressure, and increase of volume to the magma shatters into violent fragments.
Classifying and plotting rock types?
Andesitc and Rhyolitic volcanoes can be produced by:
Are pyroclastic flows the most hazardous of Volcanic processes?
Yes.
What are the sources of energy in the flows and surges in pyroclastic eruptions?
- Gravity
- Fluidisation
What is Cratonisation?
The folding of Mobile Belts over geological time, of igneous emplacement, crustal thickening into zones of continental crust, resulting into Cratons.
How would you describe the stage of Cratonisation?
Almost all mobile belts pass through an orogenic stage of intense folding and metamorphism, then, transitional stage of block-fault mountain building. Followed by late orogenic magmatism, involving extrusion of Felsic volcanoes and developing tectonic stability.
Define Epicratonic Basins
They are sedimentry basins which form on the craton after it has stabilised.
What was geologically happening in Australia 2500 million years ago?
Formation of the oldest Australian Cratons - Archaean Pilbara and Yilgram blocks, possibly even before 3000 million years ago in the case of the Pilbara block.
Significant Glaciation events in Australia occured in what period?
The Creteceous
Is Granite a Hypabyssal rock?
No
The New England Oregon developed on the eastern-most edge of Australia by?
Accretion of Oceanic crust along subduction zones in the devonian.
A Tuff can be classified as?
Both Volcanic and Sedimentry deposit.
The Tasman Line seperates?
Precambrian Australia and Phanerozoic Australia
Basaltic pillow lavas form in what conditions?
Eruptions on the seafloor.
Melting that is caused by thinning of the crust and uplift of mantle material is called?
Decompression melting.
Obidian and Pumice are same chemical composition:
True or False
True.
Match the style of volcanism to the tectonic environment:
- Hot Spot volcanism
- Mid ocean ridge volcanism
- Continental rift
- Continental arc
- Island arc
- Hot spot - Intraplate; (continental or oceanic)
- Mid ocean ridge - Extension
- Continental rift - Extension
- Continental arc - Oceanic to continent collision (subduction)
- Island arc - Oceanic to Oceanic collision (subduction)
Diamon rich kimberlites tend to occur in younger cratons:
True or False?
False.
The Australian continentant was formally part of which supercontinents?
- Pangea
- Gondwana
Felsic lavas are runnier and therefor have more of a gentle safe eruption style:
True or False?
False.
What is a Terrane?
A region with essentially similar geology and geological history.
The oldest mineral grains on earth are located in?
Western Australia.
The following Orogens that make up the Tasman Orogens are?
- New England Orogen
- Lachlan Orogen
The Largest volcano in the solarl system is on which planet or moon?
Mars, Olympus Mons.
Hot spot volcanoes in Eastern Australia are associated with?
The Northward migration of Australia towards Papua New Guinea and Indonesia.
The Yilgarn Craton in Western Australia is associated with this type of major mineralisation:
Gold.
