GLY 1000 Yang Wang Study Guide Final Exam CH 8 1 a Chemical weathering and low temp diagenesis are not included in metamorphism b Metamorphic rocks are formed from preexisting rock or prolith at high temperature and pressure 2 Environments of metamorphic rock formation a Regional dynamo thermal metamorphism i Tectonic collision zones where rocks are caught up in mountain building 1 Heated via geothermal gradient and plutonic intrusions 2 Squeezed and heated by deep burial 3 Smashed and sheared by differential stresses b Thermal contact i Due to heat from magma invading host rock ii Creates zoned bands of alteration in host rock 1 Called a contact or metamorphic aureole 2 Zoned from high near pluton to low grade c Dynamic i Breakage of rock by shearing at a fault zone ii Fault location determines type of alteration 1 Shallow crust 2 Deeper crust a Rocks break to form breccia non metamorphic a Rocks behave in a ductile manner b Minerals smear like taffy to form mylonite d Burial e Hydrothermal i As sediments are buried in a sedimentary basin 1 Pressure increases because of weight of overburden 2 Temperature increases because of geothermal gradient ii Requires burial below diagenetic effects i Alteration by hot chemically aggressive water ii A dominant process near mid ocean ridge magma 1 Cold ocean water seeps into fractured crust 2 Heated by magma this water then reacts with mafic rock 3 The hot water rises and is ejected via black smokers f Shock i Rarely earth is struck by a meteorite 1 Impacts generate high pressure and heat that vaporizes or melts large masses of rock 2 High pressure minerals like Coesite and Stishovite Foliated VS Non Foliated equant minerals only Non foliated no planar fabric is evident Crystallized without differential stress Comprised of Foliated thru going planar fabric subjected to differential stress has a significant component of platy minerals classified by composition grain size foliation type 3 Metamorphism is induced by heat pressure and differential stress Heat can be added by burial depth or contact with hot ground water Pressure is added with depth Differential stress arises at fault zones and over broad regions during orogenesis 4 Metamorphic effects include recrystallization changes in mineral stability and foliation Foliation involves the development of preferred orientation of inequant grains or preferred mineral association by compositional banding 5 Metamorphic Rocks a Slate i Fine clay low grade metamorphic shale ii Distinct foliation called slaty cleavage b Phyllite c Schist i Fine mica rich rock ii Medium grade alteration of slate clay minerals neocrystallize iii Micas have a silky luster i Medium coarse rock with larger micas ii Formed from phyllite at higher T P iii Distinct foliation called schistosity 1 Parallel alignment of large mica crystals iv Often comprised of other minerals 1 Quartz feldspars kyanite garnet staurolite sillimanite d Gneiss i Distinct banded foliation Light bands are felsic quartz feldspar 1 2 Dark bands are mafic biotite and amphibole e Quartzite f Marble almost pure quartz in composition i ii Non foliated i Coarsely crystalline calcite or dolomite ii Non foliated 6 High grade rocks are formed at high T P and low grade rocks are formed at low T P 7 Protoliths can be either igneous sedimentary or metamorphic Alteration of metamorphics into a higher grade is termed prograde the reverse is called retrograde metamorphism Metamorphic rocks are formed from preexisting rock because of high temperature and pressure Foliation and texture are two features that characterize most metamorphic rocks Foliation is rock that has a through going planar fabric These rocks were subjected to differential stress Slate phyllite schist and gneiss all differ from each other in terms of foliation type Subduction creates blueschists Because of the low geothermal gradient it is low temperature even though the pressure is extremely high Metamorphic rocks can be found in shields large regions of ancient high grade rocks in continental interiors Shield rocks form the basement under sedimentary cover CHAPTER 10 1 What is a fault vertical a Faults are like planar breaks in blocks of crust Most faults slope although some are b c fault types are normal reverse thrust Strike slip i ii normal hanging wall goes down relative to footwall due to crustal stretching iii reverse hanging wall goes up relative to footwall due to crustal shortening slope of fault is steeper strike slip fault no vertical motion one block slides sideways past the other fault surface is nearly vertical It is due to lateral shear iv v Thrust hanging wall goes up relative to footwall due to crustal shortening Slope of fault is not steep 2 Theory of elastic rebound why earth quakes occure a The elastic rebound theory is an explanation for how energy is spread during earthquakes As rocks on opposite sides of a fault are subjected to force and shift they accumulate energy and slowly deform until their internal strength is exceeded At that time a sudden movement occurs along the fault releasing the accumulated energy and the rocks snap back to their original undeformed shape 3 Different types of seismic waves a Body primary waves have a push pull motion travel through solid liquid and gases it s the fastest waves Think of these waves moving forward and backwards b Body shear or secondary waves have a shaking motion and only travels through solids and not liquids Moves slower than primary Think of these waves as moving up and down Surface waves have two types the love waves or L waves and Rayleigh waves or R waves c i L waves move back and forth like a writhing snake ii R waves move like ripples on a pond iii 4 using waves to locate and earth quake a waves always arrive in sequence P waves first S waves second and surface waves last b c certain waves will reach certain stations first and from there they can track those waves back to the epicenter this is a picture of travel time curves method above and three station method 5 Two means of describing earth quake size Intensity and magnitude a Intensity the degree of shaking based on damage The Mercalli intensity scale Roman numerals assigned to different levels of damage damage occurs in zones damage diminishes in intensity with distance b Magnitude The amount of energy released Maximum amplitude of motion from a seismogram and increase of 1 unit 10 fold increase in ground motion 6 Predicting earth quakes a Recurrence interval
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