ES 1100 Exam 2 Study Guide Professor Durand Chapter 11 Mountain Building Mountain Building Occurs via many processes Continental collision Himalayas Subduction zone compression Andes Rifting East African Rift Zone Volcanic mountains Hawaii Continental Collision Continental crust ends subduction Collision leads to significant stress and forces on rocks Thrust faulting occurs Metamorphic rock often forms Subduction Zones Compression can squeeze crust together leading to uplift Exotic terranes This will cause rocks to fold and lead to thrust faults side of the continent Dominate the western coast of North Africa Island fragments of continental crust that are added on to the Rift Zones Crust pulls apart leading to normal faults Fault blocks rotate leading to sediment basins and ridges Volcanic mounts form due to rising magma Brittle And Ductile Deformation Brittle Rocks break like plate hitting ground and shattering Occurs at low temperature and pressure Leads to faults and joints Occurs at high temperature and pressure Leads to folds Ductile Rocks bend like dough being flattened by a book Joints Faults Natural crack or fracture resulting from brittle deformation No displacement occurs at a joint different than a fault Fractures in rock where displacement has occurred They are ubiquitous and occur at all scales Show whether rocks were being compressed or pulled apart Strike slip Dipping or dip slip No vertical motion Vertical motion Fault Identification On a dipping fault the blocks are classified as the Hanging wall block above the fault and the Footwall block below the fault Standing in a tunnel excavated along the fault Your head is near the hanging wall block You are standing of the footwall block Types of Faults Reverse and Thrust faults Hanging wall is pushed up the footwall Normal Fault Hanging wall is pulled down the footwall Normal Fault a rift zone Reverse and Thrust Faults At a normal fault displacement results from the crust being pulled apart e g in Displacement occurs from compression of the crust Reverse faults are steeper than 35 degrees close to vertical Thrust faults have less of a slope Thrust Faults Common in places where uplift is occurring due to continental collision An example of ductile deformation Folds reveal something of the process that has shaped rocks in these areas An anticline is a fold that looks like an arch looks like an upside down U A syncline is a fold that opens upward like a trough looks like a U Folds Anticline Syncline Cratons Crust that has been formed in 1 Ga Cratonic Platforms Sedimentary rock covering old Pre Cambrian basement Chapters 12 and 13 Geologic Time and Earth Bio How was Earth s geologic history created By correlating global statigraphic records and by radiometric dating Earth s Geologic History Principles of Stigraphy Statigraphy The branch of geology concerned with the order and relative position of strata and their relationship to the geological time scale Principle of Succesion Water borne sediments are deposited in horizontal layers or strata In undisturbed strata age increases with depth A rock unit must be older than ay feature that cuts across it Baked contacts Age increases with depth When an igneous intrusion bakes surrounding rocks The baked rock must have been there first it is older A rock fragment within another rock Inclusions are always older than the enclosing material Inclusions Statigraphy alone gives relative ages only Rates of sedimentation vary greatly Sediments are often compressed Gaps exist in the sedimentary records An unconformity is a boundary between A surface representing a period of nondeposition and possibly Unconformity layers representing a gap erosion Types of Unconformities Angular unconformity orientation Nonconformity Disconformity Fossils Tilt or fold before unconformity developed different Sedimentary rocks on igneous or metamorphic rocks Sedimentary rocks on older sedimentary rocks Fossils play a role in correlating strata from different regions Fossils and Strata Correlation The principle of fossil succession Uses the strata layers to give relative ages of fossils youngest fossils found in highest youngest strata oldest fossils found in lowest oldest strata Geologic maps are formed as the result of correlation working out rock history and thinking in three dimensions Absolute age and Radioactive Decay Isotopes Radioactivity same element or another element Elements that have varying numbers of neutrons Elements transform spontaneously into another isotope of the Rate of decay is unaffected by environmental changes Radiometric dating uses of naturally occurring radioactive isotopes to determine the absolute age of minerals or rocks What do Isotopic Dates mean Closure temperature Temperature at which crystals cool enough to lock into a lattice After closure temperature isotopes cannot move Dates refer to Igneous rocks when rocks originally froze Metamorphic rocks when rocks dropped below closure temperature Sedimentary rocks cannot be directly dated isotopically Radiometric Dating Radioactivity isotope of the same element or another element daughter Transformation decay of an element parent into another Half Life and Radioactive Decay Half life Once a mineral grain has formed atoms are locked in and decay occurs at a Time needed for the number of parent atoms to be reduced by one half constant rate By measuring the number of remaining parents and the number of daughter atoms the age when the mineral was formed can be determined Using the rate of radioactive decay the absolute ages can be associated with the stratigraphic column Arachean Eon Proterozoic Eon Cambrian Explosion During the Archean Eon continental crust formed 2 5 4 Ga During this time the atmosphere developed Oxygen increased 2 5 Ga 5 Ga Life and geologic time Prior to the Cambrian there are no invertebrates with shells Everything after this is the phanerozoic eon The Cambrian explosion was 542 Ma triggered in part by increased Oxygen levels Paleozoic Era and North America Repeated transgressions and regressions formed much of the sedimentary rock we see in North America By the late Paleozoic Pangea had formed Pangea breaks up beginning of meso and modern geography emerges This was the era of large dinosaurs This is the boundary between the Paleozoic and Cenozoic Era in which we live A 13 km diameter meteorite led to mass extinctions Mesozoic Era K T Extinction Event The Cenozoic Numerous continental collisions Numerous