Geog 101 Geog 101
Minnesota State University, Mankato
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This 4 page Class Notes was uploaded by Hallie Notetaker on Friday September 16, 2016. The Class Notes belongs to Geog 101 at Minnesota State University - Mankato taught by Phillip Larson in Fall 2016. Since its upload, it has received 26 views. For similar materials see Introductory Physical Geography in Geography at Minnesota State University - Mankato.
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Date Created: 09/16/16
Earth Materials Rock basics – background to understand Earth’s landscapes The Wave – WesternAustralia and Utah Composition of the Continental Crust 47 % oxygen 28% silicon 8.1% aluminum 5% iron 3.6% calcium 2.8% sodium 2.6% potassium 2.1% magnesium How much do you consume? 40,000 lbs. Earth/year in a lifetime o 1050 lbs. lead o 1050 lbs. zinc o 1750 lbs. copper o 4550 lbs. aluminum o 91,000 lbs. iron o 360,500 lbs. coal o 1 million lbs. industrial materials Calcite, clay, borate Introduction to Minerals Rocks – various combinations of naturally occurring substances called minerals Minerals – naturally occurring substance which has a specific chemical and crystalline structure o Natural – iron ore (hematite) o Solid – sand (quartz) o Inorganic – rock salt (halite) Nonmineral o Artificial – cast iron (metallic iron) o Liquid – seawater (H20 salts) o Organic – vegetation (cellulose) o Gas – air (oxygen) Examples o Silicates – have Si as base, Quartz (SiO2) Obvious 75% o Feldspars – have Si andAl base Add Ca, K, Na to get feldspar o Clay minerals that have layered structures Basic Rock Types Igneous – made by “fire” o Solidified from molten rock (i.e. magma) Sedimentary – deposited and buried close to Earth’s surface Metamorphic – “changed form” o Transformed from preexisting rocks under high pressure, temperature and fluids Type of rock and source material o Igneous – melting of rocks in hot, deep crust and upper mantle Rock forming process – crystallization (solidification of magma or lava) Example – coarsely crystallized granite o Sedimentary – weathering and erosion of rocks exposed at surface Rock forming process – deposition, burial and lithification Example – bedded sandstone o Metamorphic – rocks under high temperatures and pressures deep in crust and upper mantle Rock forming process – recrystallization in solid state of new minerals Example – gneiss Rocks Anaturally occurring, solid aggregate of minerals Granite o Constituent minerals Orthoclase feldspar, plagioclase feldspar, biotite, quartz Rock types o Sedimentary rocks are most abundant near Earth’s surface Poor preservation o Igneous rocks and metamorphic rocks make up most of the crustal volume Limited exposure Igneous Rocks Minerals crystallize from melt, derived from deep within Earth’s crust or mantle o High temperatures, 700 degrees Celsius and more o Crystal size depends on cooling rate Intrusive rocks – cool slowly within deep magma chambers o Course, interlocking crystals Extrusive rocks – cool rapidly at or near the surface of the earth o Fine-grained, often “glassy” Common in volcanic areas and plate boundaries Extrusive Intrusive Felsic Rhyolite Granite Andesite Diorite Mafic Basalt Gabbro Pluton – intrusive igneous magma chamber Formation and texture o Pyroclasts – form from airborne lava in violent eruption o Intrusive – cools slowly in the Earth’s interior allowing large crystals to form o Extrusive – cools rapidly on the Earth’s surface o Porphyry – starts to grow below the surface but before solidification is brought to the surface Sedimentary Rocks Loose particles (sand, silt, marine shells) accumulate on shorelines, basins, rivers, etc. o Clastic sediments Minerals precipitate from dissolved chemicals in water o Chemical and biochemical sediments All are the products of weathering and erosion o Weathering – breaks up and decays rocks o Erosion – transports from source to point of deposition Common along passive margins (and other basins) Evaporite, sandstone, conglomerate, breccia, shale Sedimentary process o Unconsolidated sediments o Compaction o Cementation Silicates o Quartz, clay minerals, feldspar Carbonates, sulfates and halides (precipitates) o Calcite, dolomite, gypsum, halite Metamorphic Rocks High temperatures and pressures at depth cause changes in mineralology, texture and composition o Change takes place in solid state by recrystallization and chemical reactions o Temperatures greater than 250 degrees, less than 700 degrees Regional metamorphism – high pressures and temperatures derive from regional collision, deformation and mountain building Contact metamorphism – locally high temperature, adjacent to intrusions Common at convergent plate boundaries Not foliated – distinct low pressure minerals o Limestone + heat and pressure = marble Foliations – planar fabric defined by: o Alignments of platy minerals (mica/clay) o Alternating bands of mineral types o Granite + heat and pressure = gneiss o Indicative of high pressures and deformation during formation Pressure-temperature-time paths Silicates predominate o Quartz, feldspar, mica, garnet, pyroxene, staurolite, kyanite o Due to silicate source rocks o Distinctive mineral types indicative of solid state reactions Typical Rock Types Seen by Geologic Origin Sedimentary Sedimentary Metamorphic Metamorphic Igneous Igneous Grain Clastic Solution Foliated Non-foliated Intrusive Extrusive aspects (carbonate) Coarse Conglomerate, Limestone, Gneiss Marble Granite, breccia dolomite gabbro, diorite Medium Sandstone, Limestone, Schist, Quartzite siltstone dolomite phyllite Fine Shale Calcareous, Slate Amphibolite Basalt, (mudstone) mudstone, rhyolite, chert obsidian Disconformity – a time when deposition is temporarily stopped “Great unconformity” – showing uplift and then erosion The Rock Cycle Melting and intrusion Solidification of melt Mountain building Uplift and exposure Weathering Erosion and transport Deposition and burial Metamorphism Melting and intrusion Geologic Time Large blocks of time represented by changes in evolution AbsoluteAge Dating Radioactive atoms – clocks in the rocks Isotopic dating – natural radioactivity decay of an unstable nucleus to a stable one o Associated with natural radiation Decay rates characterized by half-life o The time required for one half of the original number of atoms to decay
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