Study Questions

 Guide #7 (F04)

 GEOL 125: Earth History

 Dr. Hammond

Briefly state the concepts underlying the theory of plate tectonics. List observations that are explained by this theory. What types of plate boundaries exist? What are the driving forces for plate tectonics? Why is the interior of the earth hot? Why can oceanic lithosphere subduct, while continental lithosphere does not?

Why does the earth have a magnetic field? What is a field reversal? How do igneous rocks record field orientation? How does this lead to the presence of magnetic anomalies in the oceanic crust? Draw a graph illustrating the pattern of these anomalies on a transect perpendicular to a mid-ocean ridge, indicating the ridge location and the relative age of the oceanic crust. How can magnetic inclination be used to determine paleolatitude? What is polar wandering?

Name an example (i.e. a specific place) where each of the following features can be found: volcanic arc, trench, hot spot, transform fault, mid-ocean ridge, continent-continent collision.

Draw a cross-section of a subduction zone (convergent plate boundary). Indicate the following features: trench, volcanic arc, zone of partial melting, region where granite batholiths (plutons) form, lithosphere, asthenosphere, region of seismic activity (use xxx for this), and accretionary wedge. Use arrows to indicate relative motion.

Draw a cross-section of a divergent plate boundary. Indicate the following: magma chamber, rift valley, ridge axis, region of faulting, lithosphere, asthenosphere. Indicate motions with arrows.

Draw a map view of a conservative plate boundary, showing a transform fault. Indicate the following: ridge axis, lateral fault, location of seismic activity (use xxx to show this), fracture zone, and arrows to show relative motion. Did you draw a right lateral or left lateral fault?

What clues can we use to reconstruct the positions of continents and past paleogeography?

Draw a map of California and locate each of the following geomorphic provinces: Salton Trough, Coast Ranges, Transverse Ranges, Sierra Nevada, Great Valley, Mojave Block, Modoc Plateau. How did each of these features form? Where do the Cascades begin?

Draw a map of the west coast of North America. Indicate the locations of the San Andreas fault (SAF), the East Pacific Rise (EPR), the Juan de Fuca Ridge (JFR), the Mendocino Fracture zone (MFZ), the Cascade Subduction zone (CSZ), the locations of Los Angeles (LA) and San Francisco (SF), and use arrows to indicate relative plate motions.

List major phases in the geologic evolution of CA and Western N. America during the past 200 my. What event initiated the opening of the Gulf of California?

How does the relative rate of plate convergence determine whether compression or extension occurs behind a volcanic arc? How has this influenced the development of the Rocky Mountains and the Basin and Range? What are the principal types of faulting in these two regions during the present day?

Terms to know

 magnetic reversal accretionary wedge  subduction zone
 lithosphere  asthenosphere  rheology
 Alfred Wegener  orogeny   Laramide orogeny
basaltic composition  granitic composition  isostasy
 Mendocino Triple Junction  Colorado Plateau  Juan de Fuca Plate
 magnetic inclination  magnetic declination   Curie Temperature
 magnetic anomaly  dipole field   Rio Grande rift
 Farallon Plate  accreted terrane  Basin and Range Province
 Rocky Mountains    Pangea
 Gondwanaland