Exam 2- Earth System Sciences  

Metamorphism means what?

Chapters 6-9

Chapter 6: Metamorphism  

Metamorphic Rocks

∙ Metamorphism- means to “change form”

∙ Solid-state change (no melt involved)

o Agents against metamorphism:

 Heat  

 Pressure

 Differential stress

 Chemically active (HOT)

 Solutions- water  

∙ Key thing = a new metamorphic rock is stable and in equilibrium  in its new environment of higher heat & pressure (often deep  within the earth)

∙ Major categories of metamorphism:

o 1) Contact (therma) metamorphism- metamorphic aureole  o 2) Dynamic (pressure) metamorphism  

o 3) Dynamo-Thermal (regional) metamorphism  

 Gneiss (High grade  

 Schist Metamorphic Rocks)  

∙ Regional Dynamo Thermal Metamorphism  

o Banded gneiss (felsic, mafic bands often folded)

∙ Regional Dynamo- Thermal metamorphism  

What are the Major categories of metamorphism?

o Amphibolite (dark layers & “pods”, “hornblende rich”)

∙ PARA GNEISS- sedimentary rock

∙ ORTHO GNEISS- igneous rock

∙ Schist= individual mica minerals that are visible to the naked  eye.

∙ Contact metamorphism- thermal metamorphic limestone  (marble)

o Contact or thermal metamorphism  

∙ Pressure metamorphism causes:

o 1) Metamorphism or deep burial ~~~~ p lithostatic=  pgz

o 2) Tectonic pressures

 Z- (thickness in earth, the depth below the surface)  G- (Gravity within the earth

 P- (2,700 kg/m3)

∙ P= density of continental crust

∙ High pressure metamorphism causes atoms to move closer  together

o Low pressure atomic spaces  

Chapter 7: Mountain Building and Geological Structures

 ∙    Crags, Cracks & Crumples  

o Mountain building & geological structure

What is Regional Dynamothermal Metamorphism?

We also discuss several other topics like sonia bardy

∙ Mountain Belt: orogens  

∙ Orogeny: process of mountain belt formation

∙ Deformation: process during which rocks bend/break/or flow ∙ Geologic structures: features produced by deform, joints, faults,  folds and foliations  

∙ Displacement: Change in location

o Occurs when a block of rock moves from one location to  another

∙ Rotation: a change in orientation

o Occurs when a body of rock undergoes tilting  

∙ Distortion: change in shape

o When a body of rock changes shape, development of a fold represents one type of distortion.  

∙ Strain: Change in shape/volume, stretching 

o A measure of the amount of distortion during deformation ∙ Strain: Sheer

o Transforms the cube into a parallelogram and changes  angular relationships

∙ Brittle Deformation:

o Process which a material cracks or fractures, creating joints or faults in rocks

∙ Plastic Deformation:

o Process by which objects change shape without visibility  breaking creating folds in rocks  

∙ Deformation Factors:  

o Temperature: heat makes materials softer & more prone  to plastic deformation

o Pressure: greater pressures causes rocks to behave more  like plastic  

o Deformation Rate: sudden changes make materials more prone to brittle deformation, whereas slower change allows more plastic deformation  Don't forget about the age old question of psych 410 class notes

∙ Stress compression:

o Takes place when an object is squeezed

∙ Stress tension:

o When the opposite ends of an object are pulled in opposite  directions.  

∙ Stress: sheer

o Develop when one surface of an object slides relative to  the other surface.  

∙ Stress: pressure

o Occurs when an object feels the same stress in all sides. ∙ Faults: surfaces of slip

o Dip Slip

o Hanging wall: block above fault lie

o Footwall: block below fault line.  

Types of Faults;

o Fault Scarps: a small step or offset on the ground surface  where one side of a fault has moved vertically with respect to the other We also discuss several other topics like ingeted

o Slicken slides: a smoothly polished surface cause by frictional  movement between rocks along two sides of a fault

o Slip lineation’s: linear groves on fault surfaces

o Folds: a curve in the shape of a rock later

o Anticline: arch, limbs dip away from hinge, big oil and gas exportation

o Syncline: looks like trough, limbs dip toward hinge  o Recumbent fold: has two horizontal axial plane

o Monoclines: looks like stair step, usually draped over a  fault block

o Plunging Folds: occurs where the hinge of the fold is  tilted relative to the surface

o Domes: dome shape of an overturned bowl.

Chapter 8: Earthquakes  

o Seismic Waves:

o Body waves:

 P waves: compressional

 S waves: shear

o Surface Waves:

 R waves: vertical undulations  

 L waves: back & forth movement  If you want to learn more check out which of the following is not a way geology informs us about earth's past?

o Mw: moment magnitude: provides consistent scale for  comparing earthquakes  

o Seismic belts: mark plate boundaries

o Reverse faults

o Thrust faults

 How do earthquakes cause damage?

o Disease

o Fire

o Tsunami  

o Sediment liquefaction

o Landslides

o Ground shake/displacement  

 Sediment liquefaction

o Liquid sand layer causes the ground to crack and sand  volcano’s to erupt.  

 WORLDS LARGEST EARTHQUAKE:

o With an instrumentally documented magnitude occurred  on May 22nd, 1960 near Valdivia, in Southern Chile.

o Magnitude 9.5 by USGS

o Referred to as the “Great Chilean Earthquake” & the “1960  Valdivia Earthquake”

 Earthquakes at plate boundaries:  

o Divergent-boundary seismicity  

o Convergent-boundary seismicity  

o Transform-boundary seismicity on continents  

Chapter 9: Deep Time

 Geologic Time:  

o Deep time: How do we age natural disasters?

o James Hutlon: lived during Age of Enlightenment in the  1700’s, Europe

 Uniformitarianism:  

o Physical processes we observe today also operated in the  past & were responsible for the formation of geological  features we see in outcrops If you want to learn more check out michael hogg tulane

o Geological time (changes) occurs over long periods of  time.

 Modern view of geological process/time change: o Punctuated Equilibrium

 Earth age based on dating estimates (~4.6 BYO =  

Deep time)

o Absolute (radiometric) Dating of Mineral & Rocks: o Mostly used for dating: Igneous & metamorphic rocks o Minerals contain radioactive isotopes 

o Isotopes: atoms that have the same atomic number but  different mass numbers.  Don't forget about the age old question of wronskian method

o 1) Decay Rate- unique for each isotope

o 2) Half-lite- function of decay rate  

o Radiometric Geochronology:

o This system works because of High Heat, which causes  parents to separate from daughters during heat/melting &  radioactive clocks are reset to 0 at the time of cooling  (“block temperature”)

o Rate of decay: n/N

o n- # of atoms that decay in a given time

o N- total # of atoms

o Geological Time Scale: name of Eons (youngest at top) o Phanerozoic- “visible life” (542 Ma to present time) o Proterozoic- “before life” (2.5 to .542 Ga)

o Archean- “ancient” (3.8 to 2.5 Ga)

o Hadean- “hell” (4.6 to ~4.0 Ga)

∙ Fossils & Eudution  

o Fossils important for understanding “deep time”/construct  geological time-scale.  

 Fossils mean ‘dug up’ in Latin  

∙ What it takes to become a fossil:  

o 1) Hard parts: shelly exoskeleton  

o 2) Minimal Post- morten transport (usually by scavenging  organisms)

o 3) Rapid Burial in subsiding sedimentary basins

o 4) Diagenic alteration after burial that does not chemically  destroy the remains  

o 5) Uplift, erosion & exposure to the elements