Geology 101, Unit 2

Nicolas Steno

1638-1686, Catholic Priest from Denmark, saw shark teeth fossils are the same as modern shark teeth. Father of stratiography, idea that fossils were animal remains not yet accepted. Hutton based his ideas on steno's work.

William Smith

1769-1839 observed different layers of strata at Somerset had different fossils, could tell one layer from another by which fossils were in them. Smith traveled across Britain collecting fossils and rocks, prepared first geological map,made a living by selling it, went bankrupt and sent to prison. Principle of Faunal Succession, uses fossils to date rocks from oldest to youngest. Useful because specific fossils occur only during specific periods of earth's history.

Henri Becqueral

1896, French, saw how Uranium emitted radiation without any external energy from the Sun.

Ernest Rutherford and Frederick Siddy

1902, discovered the exponential nature of isotope decay, 1905, U/He and U/PB ratios can be used to date rocks. 1908, Rutherford recieved nobel prize for how rate of decay, minerals cystalize in magma, trap radioactive isotopes.

Arthur Holmes

1911 used U/PB to date rocks, father of Modern geochemistry, 1946, revised methods after Alfred Nier determined exact decay rate of U into PB, he also developed Mass Spectrometry, easy method to date rocks using radiometric dating. Holmes dated rocks to 2 billion years at first, >3 with revised methods

Clair Patterson

1922-1995, Iowa, Caltech, 1950's U-Pb dates using mass spectronomy, environmentalist, worked on lead contamination from industry,lead to EPA on lead in 1973,, Barrington Crater,50,000 years old, from Canyon Diablo meteorite impact, he date it to 4,56 billion years old.

Sequatchie Valley

5 miles wide, 100 miles long, 1000 ft below surrounding plateau. Formed along thrust fault, originally a hill of limestone, limestone eroded away, leaving valley behind.

Taj Mahal

Agra, India, built 1631-48, Agra India, Mughal Architecture, 1983 UNESCO World Heritage Site. Built by Shah Jahan for his wife Mumtaj Mahal, both buried there. Combines elements of Islamic, Indian, Persian, and Turkish design. Marble vulnerable to acid rain, earthquake in 2011 damaged dome, predicted collapse.

Deformation

All changes in the size, shape, or position of a rock body. Rocks deform when stress exceeds strength, stress=amount of applied force. Strength-refers to the ability of an object to resist deformation. Quartzite, Granite strong, salt, shale weak. 3 types of Deformation: Elastic (springs back into place after being deformed), Ductile (doesn't spring back into place), and Brittle (doesn't show any stress, then breaks all of a sudden) Brittle deformation can cause normal, reverse, and strike-slip faulting. Strong rocks are brittle, weak ductile, non are elastic.

Stratigraphy

Branch of geology which deals with how time is recorded in sedimentary rocks, ability to read these is key in understanding history of the earth. Principle of Original Horizontality, sediments are deposited in water in wide flat layers, flat rocks have not been disturbed and are in their original state with oldest rocks on bottom, youngest on top. Law of Lateral Continuity, material forming any stratum was continously deposited over the earth unless a solid body stood in the way. Also, sometimes sediments are not always deposited completely flat, causing dunes or ripples. Law of superposition in undisturbed sequence of rock, each layer is older than one above, younger than one below.

Relative Dating

Can determine age of rocks in relation to one another, tree rings and ice cores can help. Doesn't give an exact age for rocks or age differences between rocks. Sedimentary rocks most important source for relative dating.

Plate Tectonic Settings

Contact or thermal metamorphism occurs when intrusive magma heats the surrounding rock. Changes mineralogy and texture of host rocks. Regional metamorphism: occurs when mountain building creates a lot of stress over a wide area. Burial Metamorphism: occurs when sedimentary strata on ocean floor are subducted beneath another plate, begins at 6-10 km/ 200C. Impact metamorphism: occurs when an asteroid of comet impacts the earth's surface. Largest known crater in S. Africa, object moves at 100,000 miles/hour, converts motion into heat when it hits earth Comet vaporized, Rocks instantly transformed into rare metamorphic minerals.

Isotasy/ Collapse

Crust can only hold so much weight, so Mts can only reach a certain height, also have core going into crust. Mts eventually get eroded by gravity, suffer gravitational collapse.

Three types of differential stress

Differential stress: stress is applied in unequal directions. Compression: rocks squashed together (Garbage compactor in Star Wars) Tension: rocks stretched apart( medieval torture rack), Shear rocks move past each other (transform plate boundary).

Focus, Earthquake, Epicenter

Earthquake: result of sudden release of energy in earth's crust that creates seismic waves. Focus, point movement occurs first, Epicenter, point on earth's surface above the focus. Earthquake reports include depth of focus, location of epicenter.

Appalachian MTs.

Eastern Margin of north America, from Alabama into NE, formed by three distinct events, made up of all types of rocks. MTs in British Isles, Scandinavia, NW Africa, and Greenland all formed at same time, process of orogeny lasted a few 100 mill years, one of the stages of building Pangaea.

Folitation

Fiolated rocks are classified by degree of cleavage, shistosity, and banding, which corresponds to the intensity of metamorphism.

Fault Block Mts.

Formed by continental rifting, example Sierra Nevada, Grand Tetons in Wyoming. Basin and Ridge, Western US stretched to twice its original width. Horst, elongate uplifted block bounded by faults on 2 sides. Graben elongate down dropped bounded by fault.

Vastness of Geological Time

Geology deals with a massive time scale spanning billions of years, differs from other sciences

Corundum

High grade metamorphism. Forms sapphires (Montana, 4k-6k/k) and rubies (15k/k), variety of hues and colors for both, black star sapphires most valued, Pink-orange sapphires most. rare Rubies in Burma, have chromium. Pigeon's Blood color.

Metamorphic Grade

Higher Grade, higher temperature and pressure rock was under, deeper in crust. Coarseness of foliation and crystal size increase with Grade.

Uniformitarianism

James Hutton (1726-1797) Father of Geology, rejected catastrophism, processes like erosion and deposition are always same, present is key to the pass, rock recycle themselves, geological processes occur gradually over vast time scale.

Catastrophism

James Ussher, Protestant Archbishop of Ireland (1625-1656) Counted generations in bible, deduced that earth was created at 6:00 Pm October 22nd, 4004 B.C. Catastrophism explains how so much geological change happened in so little time, needs violent events such as floods, volcanoes to cause so much change. But human records were too short to document all of time.

Crystal sizes

Metamorphic rock have great variety of crystal sizes, some like garnet, staurolite, and andalusite have large cystals, muscovite, biotite, and quartz, small crystals. Porphyroblast: metamorphic rocks with large crystals in a large fine-grained matrix. Metamorphic minerals occur in a regular and predictable sequence

Most intense earthquakes.

Most earthquake deaths caused by tsunamis, debris, etc.

Ocean floor mapping and topography

Most of human history the ocean floor has been a mystery, 140 years ago, 1872-6 HMS Challenger went on voyage to study Ocean and its floors. Beggining of Oceanography, used weighted ropes to measure Ocean depth, visited all oceans. Today we use radar, sound waves, satellites to measure ocean floor, correction needed for waves, tides, currents, etc Large number of geological features on ocean floor, only 5% mapped, takes long time and lots of effort to map even a little.

Orogenesis

Mountain building, type of mountain range depends on plate tectonics. MTS evidence of massive forces that have shaped large areas of earths crust. Mountains show signs of weathering, eventually all mountains will be completely weathered away. Most young MTS less than 100 mill.years old . Mountain- large landform which rises vertically above surronding landscape, created by tectonics or volcanism.

Accreted Terranes

Mountains along West Coast have complex geology which defies geologists. Formed by collision and accretion of number of crustal fragments and island arcs to the continental margin. These fragments, called terranes, have distinct geology from surrounding rock

Examples of tall mountains

Mt everesy, 29030 ft, Mauna Loa, 13860 ft above sea level, 30080 total, Olympus Mons 17 miles above Martian surface.

Formation of Appalachians

NA America formed by 2.5 billion year old rock, Grenville Mts formed 1 billion years ago. Rodinia, split apart 750 years ago, NA separated from Africa and Europe, formed Iapetus Ocean, two micocotinents (Taconic and Avalonia island arc) formed by two subduction zones. 500-450 mya, Taconic microcontinet collided with NA, formed Blue Ridge MTs. formed metamorphosed schist from gneiss, core of collision 10-35 km depth. 400 mya, Avalonia collided with Na, in Acadian Orogeny, formed Carolina State Belt and Eastern Piedmont, metamorphic and volcanic rocks. 350-200 mya, Alleghenian Orogeny occurred, Africa rammed into NA, part of formation of Pangaea,formed Mts in Missouri (Ozarks), and Marathon Mts in Texas. Displace continental shelf, sediments, pushed Piedmont and Blue Ridge 250 km West. Created Ridge and Valley Province.

Nonconfomity

Nonconformity, is when sedimentary rock is deposited on igneous or metamorphic rock.

Mega-thrust earthquakes

Planet's most powerful, magnitude of 9 or above. Sumatra quake, oceanic crust subduction under sunda plate.

Pressure in Metamorphism

Pressure also changes the mineral composition of a metamorphic rock in a predictable manner, increases at constant rate, 1 kbar per 4.4 kilometers. Confining pressure: pressure equally on all side, compacts rocks making them of a greater density. High pressures make rocks flow like plastic, low pressure causes them to shatter.

Other folded structures

Recumbant- flipped onto side, Dome anticline in circle, Basin syncline in circle, Monoclines, large-step like folds. All folds can end in a plunge into the earth, because of different rates of erosion. In Eastern Us more anti/syn clines are plunging.

Absolute versus Relative time

Relative: Civil War happened before WWII, Absolute: Civil War occurred between 1861-1865.

Marble

Results from metamorphism of limestone or dolostone, complete recrystallization of rock, mosaic of calcite, aragonite, and/or dolomite. Pure white marble from Italy and China used to make statues, soft, easy to carve, polish, Venus de Milo, David out of Marble. Mountains of Carrara, Italy have yielded high quality marble for thousands of years. Common building material, 50 billion/year industry.

Richter Magnitude Scale and Moment Magnitude Scale

Richter:1900-1985, developed in 1935 at Caltech, Developed the Richter Magnitude scale, measured energy received 100 km from epicenter, logarithm scale. Every unit displacements increase *10, energy released by *30. Moment magnitude scale, based on the seismic energy released by the earthquake, more accurate.

Liquefaction, Sand Blows, Boils

Stength and stiffness of soil/sediment is reduced by earthquake shaking, increased water-filled spaces, sand rises to surface in sand blow volcanoes and boils.

Paleontology-Relative Dating

Study of fossils of organism, found in sedimentary rocks (never metamorphic or igneous) Petrified wood, cast and mold of trilobite, carbon film, impressions, in amber, coprolite is fossil dung, bones, eggs are other types of fossils.

Temperature in Metamorphism

Temperature most important factor in metamorphism. Temperature drives chemical changes that result in recrystallization. Heat breaks chemical bonds, alters crystal structure, ions and atoms rearrange into new minerals. Crystals grow larger than they were in parent rock. Heat comes from energy left over from the formation of our planet, or released by radioactive formation. Geothermal gradient: rate at which temperature increases as depth increases. Affected by lithosphere thickness, rising magma raises gradient, subduction of ocean plate depresses it. Average 30 C increase every kilometer down into the earth. You can tell the temperature a metamorphic rock formed at by the minerals present in it, called facies.

Geological Time

Two centuries of research and lab work have allowed to unravel history of the earth using divisions in stratigraphic columns worldwide, using fossils and carbon dating as baselines. Eons divided into eras, eras into periods, periods into epochs. However, not all fossils are everywhere, not all records are complete as rocks have been eroded.

Disconformity

Unconformity, when page in geological book of sedimentary layers is missing

Young versus Old Mts.

Urals and Appalachian Mountains hundreds of million of years old. Himalayas are only 45 million years old, still be created. Rocky mountains are 50-80 years old.

Three main types of orogenesis, 2 formed by subduction of ocean plate

Volcanic Island Arc- develops when ocean plate is subducted by another ocean plate forms deep ocean trenches, volcanic island arcs. common in Pacific ocean, Caribbean Islands another example. Deep ocean trenches, deepest formation on earth, some deeper than 10,000 m, more alta than mount Everest. Marianas Trench, deepest trench, only visited twice, once in 60's, onces by James Cameroon. Continental island arc- develops when ocean plate is subducted by continental plate, forms plutons, continental volcanoes. Ocean crusts melts, then rises forming basaltic and rhyolitic lava, very violent and explosive volcanic eruptions. Most mountain ranges, formed by compressional forces between volcanic arcs and continents, subduction zone likes a conveyor belt, squeeze mountains.

Angular unconformity

Younger flat-lying rock on top of angular bent rock, which was distorted by Plate tectonics. Out west desert environment allows Geologists to easily see all the rock layers.

Zicron

Zicron: ZiSio4, very tiny crystals, very durable, small amounts of Uranium, Thorium which can be dated. Oldest rock in Jack Hills, Western Australia, 4.3 Billion years old, Zincron Dioxide made to make fake diamonds

New Madrid Fault Zone

ancient tectonic boundary, dates from Grenville time buried beneath layers of sediments, quakes every 200-800 years. 30 ft offset, affected 232,000 square miles, sparsely populated, few deaths, now 11-12 million people live there.

How Geologists collect samples

bash rock with hammer, separate out zicron from other minerals, send zicron samples to lab, take average of all samples.

Selecting which isotope to use

chose isotope in sample, with appropriate age range, can then use to date rock. Halflives U-238-PB 206, 4.56 Billion Years,, U-235-PB 207 7.3 million, TR 232-Pb 208, 14 million. Igneous rocks most accurate, metamorphic rocks may lose daughter element during reheating, sedimentary from so many different places its impossible to tell.

Folding

during MT. building flat-lying rocks deform into wave-like bends called folds.

Paleoseimisity on New Madrid

evidence from 100 sites suggest, 900 AD and 1450, Prehistoric liquefaction, 4040 BC, AD 780 in Illinois.

Faults

features where there has been relative movement on both sides of rock, evidence of brittle deformation. 3 types: Normal (tension forces), reverse/thrust (compression forces), strike-slip (shearing forces).

Garnet

found only in metamorphic rock, used to judge grade, most not gem quality, used in sandpaper. Variety of colors, blue, green most expensive, can mine in Finland and Russia. 1.5k/k

Unconformity

gap in rock layers, where there should be a layer, but there isn't. Either marks period of weathering or a time where no deposition took place.

Seismographs

instrument used to detect and record ground motion caused by seismic waves. Ancient Chinese seismographs invented by Zhang Heng, 132. Modern ones buried in bedrock, still until moved by earthshaking. Can determine epicenter by triangulating from 3 locations, most only last a few moments.

Where do EQ's occur

majority of earthquakes, occur around tectonic plate boundaries and margins, deepest earthquakes at convergent plate boundaries.

Classification of Metamorphic Rocks

metamorphism creates new textures, crystal grain size increases as the grade of metamorphism increases. 4 main criteria: metamorphic grade, degree of banding, shape of mineral grain, size of crystals.

Metamorphism of parent rocks

most metamorphic rocks have the same overall elemental composition as the parent rock they formed from.

Inter-plate earthquakes

not all earthquakes occur along plate boundaires, interplate earthquakes occur in plate interiors, at areas of crustal weakness, locations of ancient faults. New Madrid earthquakes 1811-12, Charleston 1886 quake.

Granoblastic Texture

not all metamorphic rocks have foliated texture, Granoblastic- have a course or massive granular appearance, no deformation. Composed of crystals that grow in equal-dimensional shapes. Cataloged by composition, not texture. Quartzite, marble

SynCline

o-y-o, youngest rock along axial plain

Strain and depth of Deformation

occurs when stress causes an irreversible change in the shape and size of a rock body. Shallow rocks are more likely to break, deeper depths, under high temperature and pressure, rocks are more likely to bend.

Zicron on Moon

oldest rock in solar system on moon, collected in 1972, 4.42 billion years old. NA oldest rock in Canada, 4.3 Billion years old, in America UP of Michigan, Virginia Blue Mts, 1 billion years old.Oldest ocean floor, 180 million years old. Geologists use absolute dating to build geological timeline, as relative dating is very imprecise.

Foreshocks and Aftershocks

one of many smaller earthquakes that precede a larger earthquake, occurs in the same vicinity as larger earthquake, not all earthquakes preceded by these. Aftershocks-same as foreshocks, but after, can occur for years.

Normal Faults

pull aparted by tensional forces, African Rift Valley, Basin and Range of US, Mid ocean ridges

Thrust Faults

push together, occur when one tectonic plate is being subducted another another, or two continental plates colliding, collisions create compressional forces.

Metamorphic Rocks

rocks whose mineral have recrystallized under intense heat and pressure deep within the earth. Remain in solid state. Metamorphism determined by temperature, pressure, fluids.

What happens in an EQ

rupture expands circularly on fault plane, sending out seismic waves in all directions, 5 seconds, rupture expands as a crack along fault, displacements occur, rupture front progresses down the fault plane, allowing rocks to rebound, seismic waves emitted in all directions.

Strike-Slip Faults

shoving, lurching, occur when one tectonic fault slides past another, San Andreas fault most famous. Thrust faults create largest and most damaging earthquakes.

Seismic Waves

siesmic waves, three types: P:primary waves, expands and contracts horizontally, 6-8 km/s S: secondary push materials from side to side (look like ocean waves). Surface waves: Rayleigh/Love waves: slower than S, moves in a rolling elliptical motion/ ground shakes sideways no vertical notion

Breakup of Pangaea

starting 220-180 mya, Pangaea pulled apart, Atlantic Ocean formed, weathering reduced huge mts into sediments. Appalachians used to be very spectacular, tall as Himalayas, but have been reduced by weathering over hundreds of million of years, sediments in Gulf of Mexico today.

Structural geology

study of the deformation of rocks and its effects. 18th and 19th century geologists were puzzled at how rocks could be bent, tilted, or fractured, now we know that every rock will eventual bend or fracture under enough stress. Depends on type of stress, pressure, temperature, and mineral composition of rock. Can be studied using sand box experiments, crushing rocks in compactor.

Elastic rebound theory

two sides of the fault are locked, stress begins, elastic deformation begins. Stress continue to build up over decades, elastic deformation continue to get worse. Stress exceeds the strength, the fault slips and the earthquake occurs, rocks rebound, elastically, can be smooth and gradual, creep slip, cannot be felt , rarely cause damage.

Radiometric Dating

usage of radioactive isotopes to date rocks by measuring the proportion of parent radioactive isotopes to the stable daughter isotopes they decay into using half-lives.Each radioactive isotope has a specific stable daughter element it decays into. Radioisotopes, are elements that go through this process.

Quartzite

very hard metamorphic rock formed from quartz sandstone, pure quartzite is white, red/pink/grey caused by impurities. Counter-tops not real quartzite. Very durable, found at mountains changes, convergent plate boundaries, crests of mountains, flanks

Fluids in Metamorphism

water is part of the structure of many minerals, metamorphism can add or remove chemicals dissolve in water, higher temperatures water is expelled from rocks, lower temps it moves between minerals, carrying grains and ions with them.

Anticline

y-o-y, forms ridges, oldest rock along axial plain

Himalayan Mountain Range

youngest and highest on earth, still forming, began 40-45 mya. Compressional forces cause the sedimentary rock to be folded and uplifted, faulting occurs, partial melting and heat from subduction forms metamorphic and igneous core of mountain, Suture zone. India penetrated 2000 km into Asia, still moving north, China and Indochina squeezed eastward out of the collision zone. Asia deformed but not India because Asian crust is weak and form, deforms easier, Indian crust cold solid 2 billion year old slab