classification of rock types - a brief introduction -
TRANSCRIPT
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Classification of Rock Types
- a brief introduction -
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Minerals:
- specific chemical composition- usually (but not necessarily) crystalline
- inorganic
- solid- occur naturally
Minerals are the building blocks of rocks!
Rocks are aggregates of one (monomineralic) or more (polymineralic) minerals!
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The Rock Cycle
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Rocks:
basically three different groups:
igneous rockscrystallized from magma or lava
sedimentary rocksdeposited from wind or water
metamorphic rocksigneous or sedimentary rocks thatrecrystallized at elevated pressureand temperature
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Igneous Rocks
form from melts:
magma (plutonic igneous rocks)
(molten rock within the Earth)
or
lava (volcanic igneous rocks)
(magma that extrudes at the Earth’s surface)
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plutonic rocks (e.g. granite)
are coarse grained
because magma cools slowly within the Earth’s crust
volcanic rocks (e.g. basalt)
are fine grained
because lava cools quickly at the Earth’s surface or is even quenched (volcanic glass)
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granite
basalt
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Igneous Rocks are
ultramafic, mafic, intermediate, or felsic:
ultramafictypical mantle rock (peridotite)Mg and Fe silicates (e.g. olivine)greenish, dark colour
mafictypical oceanic crust rock (basalt, gabbro)forms from low-viscosity melts
mostly Mg and Fe silicates (ol, opx) and minoraluminosilicates (cpx, plag)
greenish-grey dark colour
(also found on Moon, Venus, and Mars!)
increasing silica (SiO2) content
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Igneous Rocks areultramafic, mafic, intermediate, or felsic:
intermediateintermediate between mafic and felsictypical island arc volcanic rock (andesite)aluminosilicates (e.g. cpx, plag, amphibole, mica)greyish colour
felsictypical continental crust rock (granite)forms from high-viscosity melts
aluminosilicates and quartz
light grey colour
Note that in geological maps, cross-sections, and profilesmafic rocks are shown in green and felsic rocks in red!
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Bowen’s reaction series
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Bowen’s reaction series and melt polymerization
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classification of ultramafic rocks
olpl pl
pl
cpx opx
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Streckeisen diagram
Foid minerals may form from SiO2-deficient magma
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volcanic rocks are usually classified according to their chemical composition
TAS diagram = Total Alkali vs. Silica
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CIPW norm:
named after the four petrologists (Cross, Iddings, Pirsson & Washington) who created it in 1931
calculation scheme by which the major element composition of an igneous rock is distributed between ideal mineral compositions
included in most geochemical software packages
for details on the CIPW norm see, for example, http://www.uwgb.edu/dutchs/petrolgy/cipw01.htm
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Sedimentary Rocks:
sediment: unconsolidated (“soft-rock”)
sedimentary rock: consolidated (“hard-rock”)
examples:
mud --> shale
sand --> sandstone
volcanic ash --> tuff
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Two major groups of Sedimentary Rocks:
--> clastic, chemical, and biogenic sediments
clastic sediments:
epiclastic sediments:erosion (and weathering) breaks down rocksgrains (solids!) are transported by wind or watergrains are deposited as epiclastic sediments
pyroclastic sediments:products of explosive volcanic eruptionsfall-out from ash clouds --> pure pyroclasticsparticles (solids!) are transported by wind and water and mix with epiclastic sediments -->
volcanoclastics
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rough sub-division of epiclastics according to their grain size
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breccia:
angular clasts
conglomerate:
rounded clasts
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Classification of Sediments
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things you have to know!
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basic types of sedimentary environments
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various depositional environments
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eolian sediments, Zion Nationalpark, USA
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eolian sandstone, Zion Nationalpark, USA
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eolian sediments: transported by wind
(picture shows eolian cross bedding)
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now whole sequence gets tilted!
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estuarine sedimentary environments
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Chemical Sediments…
…precipitate from aqueous fluids
…their element content was transported as solutes
…we distinguish marine and freshwater precipitates
examples:
carbonate --> limestone, dolomite
silicate --> chert
phosphate --> phosphorite
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Dunham classification of sedimentary carbonates, e.g. limestone
(note: in geological maps and profiles carbonates are always shown in blue!)
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…and a quick and dirty look at metamorphic rocks…
metamorphic rocks are often classified according to their typical mineral assemblages
specific mineral assemblages are typical of specific P-T environments
we distinguish different metamorphic facies, such as low-grade, greenschist, and amphibolite facies (in order of increasing P and T conditions)
we distinguish contact (close to a pluton or a dike) and regional metamorphism (affecting a large area)
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granite metamorphosed granite
= metagranite
= gneiss
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metamorphic facies
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for some pictures of common…
…minerals go to:http://www.uwm.edu/Course/422-100/minerals.index.html
…igneous rocks go to:http://www.uwm.edu/Course/422-100/igrox.index.html
…sedimentary rocks go to:http://www.uwm.edu/Course/422-100/sedrox.index.html
…metamorphic rocks go to:http://www.uwm.edu/Course/422-100/metrox.index.html
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geological timetable
Note:
Knowledge of the geological timetable is a prerequisite for any discussion of geology. Hence, it is mandatory that you know at least the Eons and Eras, and the ages of: the boundaries within the Precambrian and the Precambrian/Cambrian, the Paleozoic/Mesozoic, and the Mesozoic/Cenozoic boundaries!!!
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