GENERAL GEOLOGY Fall Chapter 18: The Sea Floor. Partial Examination IV Study Guide Dr. Glen S. Mattioli

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1 GENERAL GEOLOGY Fall 2008 Partial Examination IV Study Guide Dr. Glen S. Mattioli Note that these are NOT questions, but rather are a list of topics that we have covered either in class or are contained within the reading assignments. You should use this list as a guide to help you review what topics are important for the exam. Chapter 18: The Sea Floor 1) Methods to study the sea floor what are they and how do they work? a. Rock dredges b. Sea-floor drilling c. Submersibles d. Echo sounding e. Seismic profiling f. Deep-sea cameras g. Marine gravity surveys h. Marine magnetic surveys 2) Different types of data acquired from each of the above techniques a. Rock type (composition, mineralogy, etc.) b. Sediment or rock ages (based on paleontologic or radiometric methods) c. Bathymetry (i.e. sea floor topography) d. Sub-surface geological structures e. Sea-floor surface geological features 3) Primary features of the sea floor a. Average profiles across prominent ocean features i. Shelf, slope, rise ii. Abyssal plain iii. Oceanic trench iv. Mid-oceanic ridges and rift valleys v. Seamounts b. Basic distinction between Active vs. Passive Continental Margins c. Active Margin features i. Trenches ii. Waditi-Benioff Zones iii. Accretionary prisms iv. Volcanoes d. Passive Margin features i. Continental Shelves and Slopes Dimensions and slope angles ii. Relationship to mean sea level rise and fall iii. Rifted continental crust and its relationship to shelf/slope iv. Submarine Canyons

2 1. Location 2. Dimensions 3. Processes 4. Abyssal Fans v. Turbidity Currents 1. Features 2. How were they discovered? 3. Velocity and run out distances vi. Contour Currents 4) Ridge crest features and processes a. Creation of new oceanic lithosphere by basalt eruptions b. High heat flow c. Shallow focus, small earthquakes d. Black Smokers and hydrothermal circulation e. Biological activity and mineralization 5) Transform faults and Fracture Zones a. Basic distinction between these features b. Dimensions c. Relative motion and difference in relief d. Location of earthquakes 6) Seamounts, Guyots, and Aseismic Ridges a. Definitions b. Possible mechanisms for formation c. Relationship to Hot Spots d. Age and depth relations e. Atolls and reefs 7) Sea floor sediments a. Distinction between sediment source i. Pelagic sediments 1. Composition and source a. Siliceous b. Carbonaceous 2. Thickness vs. distance from ridge crest ii. Terrigenous sediments 1. Composition and source 2. Relationship to turbidity and contour currents 8) Oceanic crust structure and ophiolites a. Structure and dimensions of each b. Methods of study Chapter 19: Plate Tectonics 1) Present plate distribution a. Major vs. minor plates b. Types of boundaries

3 i. Divergent ii. Convergent iii. Transform c. Relative motion and approximate plate velocities 2) Alfred Wegener s case for Continental Drift a. Plate reconstructions through geologic time b. Definitions of super-continents i. Pangaea 1. Laurasia 2. Gondwanaland ii. Approximate time of super-continent separation and brake-up c. Evidence supporting Continental Drift i. Fossil distribution ii. Glacial deposits and striae orientation iii. Climate zones d. Hypothesis of Polar Wander i. Continental motion ii. Polar motion iii. Both e. Arguments against Continental Drift i. Continents pushing through ocean basins? ii. Rock strength iii. Strength of Driving forces 1. Centrifugal force 2. Tidal forces 3) Paleomagnetism a. Definition of Curie point b. Observed variation in magnetic inclination and declination in ancient rocks c. Apparent magnetic pole location in geological past d. Magnetic polar wander paths i. Interpretation of North American vs. European path difference 4) Recent evidence supporting Continental Drift a. Fit of continents b. Continuity of age and lithology of major rock units c. Glacial striae orientation 5) Harry Hess and the proposal of Sea Floor Spreading a. Conveyor Belt concept and the definition of plates b. Proposal that the motion of the plates was driven by heat escape from a convecting mantle c. Evidence to support Sea Floor Spreading i. Heat flow variations between ridges and trenches ii. Deep vs, shallow earthquakes iii. Young age of ocean basin rocks and sediments 6) Basic definition of plates and plate motion a. Oceanic vs. Continental crust

4 b. Difference between crust and mantle c. Definition of lithosphere and asthenosphere d. Mohorovic discontinuity (Moho) and its relationship to seismic wave velocity 7) Marine magnetic anomalies Vine and Matthews hypothesis a. Generally symmetrical pattern relative to ridge crest b. Relationship of marine magnetic anomalies and polarity reversals on land c. Theory for the generation of magnetic anomalies d. Prediction of sea floor ages e. Sea Floor Age map NO oceanic crust older than 160 My. f. Relationship of age pattern to spreading rate 8) Geometric and kinematic relations of Fracture Zones and Transform Faults a. Euler poles (see web link) and the relationship of ridges and transforms to great vs. small circles b. Earthquake distribution 9) Current plate rates a. Average rates: 1 to 10 cm/yr b. Geological (geophysical methods) 1-3 My rates i. Orientations of Transforms and Ridges ii. Convergent boundary slip vectors iii. Magnetic anomalies c. Direct measurements from satellite geodesy year rates i. GPS methods and current global velocity field 10) Divergent plate boundaries a. Models for early continental rifting i. Horizontal tension ii. Uplift from mantle upwelling (plume?) iii. Passive vs. active upwelling b. Consequences and sequences of rifting i. Examples of stages 1. East African Rift (early) 2. Rea Sea Rift (intermediate) 3. Atlantic Ocean Basin (mature) ii. Detailed structure of Rifted Passive Margin (eastern US example) 11) Transform boundaries a. Basic types i. Ridge-ridge ii. Ridge-trench iii. Trench-trench b. San Andreas fault system c. Oceanic vs. Continental difference in ridge-transform geometry 12) Convergent boundaries a. Ocean-Ocean type (Examples: Lesser Antilles, Marianas) i. Main features 1. Oceanic crust 2. Trench

5 3. Accretionary wedge (or prism) 4. Forearc basin 5. Volcanic Island Arc 6. Backarc basin ii. Origin of convergent margin curvature iii. Origin of Arc-Trench gap and its relationship to andesitic volcanism b. Ocean-Continent type (Examples: Andes, Cascades) i. Main features 1. Oceanic crust 2. Trench 3. Accretionary wedge (or prism) 4. Forearc basin 5. Magmatic Arc (Mountain Belt) a. Batholiths b. Metamorphic rocks 6. Backarc thrust belt 7. Sedimentary Basin 8. Craton c. Trench migration i. Overlying plate push ii. Subducting plate pull d. Continent-Continent type (Examples: Himalaya, Appalachians) i. Structure and sequence of events 1. Suture Zone 2. Opposing Trust Belt Zones 3. Basins on either side of high alpine zone e. Backarc Spreading i. Typical scenarios ii. Probable causes 13) Dynamics of plate boundaries and sizes 14) Causes of plate motion a. Ridge Push b. Slab Pull (likely more important than ridge push) i. Trench Suction c. Relationship with deep mantle convection and circulation? 15) Mantle plumes and Hot Spots a. Dynamic nature of plume head shape and its interaction of the crust b. Global distribution of Hot Spots c. Depth-Age relations of Hot Spot Tracks (e.g. Hawaiian chain) d. Continental breakup driven by plumes e. Triple junctions and failed rifts 16) Relationship of Ore Deposits and Plate Tectonics a. Ridge crest environment b. Arc environment c. Convergent boundary environment

6 Chapter 20: Mountain Belts and the Continental Crust 1) Global Distribution of Major Mountain Belts a. Distinction between mountain ranges and belts 2) Characteristics of Major Mountain Belts a. Size and alignment b. Ages and relationship to gross continental structure c. Mountain belts of North America i. The Cordillera and its ranges d. Definition and characteristics of craton and Precambrian shield e. Schematic cross-section through a mountain belt and craton/shield f. Detailed schematic cross-section through a Cordilleran Fold and Thrust Belt g. Relative thickness and characteristics of cratonic rock sequences h. Metamorphism and plutonism i. Normal faulting in ancient mountain belts 3) Evolution of Mountain Belts a. Accumulation Stage i. Opening ocean basin ii. Convergent margin b. Orogenic Stage i. Ocean-Continent convergence 1. Gravitational collapse and spreading ii. Arc-Continent convergence 1. Accretion of suspect terranes (see below) 2. Subduction polarity reversal iii. Continent-Continent convergence 1. The Wilson Cycle and the Evolution of the Southern Appalachians c. Uplift and Block Faulting Stage i. Isostatic adjustment and its relationship to erosion ii. Normal faulting 1. Related to mantle upwelling 2. Related to crustal extension 3. Related to delamination iii. Delamination and thinning lithosphere models 4) Continental Growth a. Definition of tectonostratigraphic terranes and its relationship to displaced terranes b. Suspect, accreted, and exotic terranes c. Western North American example d. Evolution of the Southern Pacific and accretion of crustal terranes in Alaska