Geography 111 - Principles of Geology
Plate tectonics
- Plate tectonics as a unifying theory for explaining observed
patterns
of geological phenomena
- Physical features (much of this is covered briefly in ch.
1 and in detail later, in ch. 13, but the GEODE CD also covers many of
these features):
- continents
- mountain belts: high relief, tectonically active,
areas where uplifted rocks are exposed by erosion; aligned paralle to
continental margins and plate boundaries
- stable platforms: low relief, sedimentary cover over
igneous/metamorphic basement
- continental shields: deeply eroded roots of ancient
mountain
belts; metamorphic rock exposed at surface, very low relief, earth's
oldest
exposed rocks
- ocean floors
- passive continental margins: continental shelf, slope, and
rise; ancient normal faults beneath sediment cover at passive margins
- trenches and subduction zones, volcanic island arcs, and
tectonically
active continental margins with accretionary wedges
- submarine canyons
- abyssal plains
- mid-ocean ridges and transform fault/fracture zones; note
symmetrical
pattern of topography on opposite sides of ridges
- spreading rates
- seamounts and guyots, coral reefs and atolls
- structure of oceanic crust
- "fit" of the continents; Wegener's continental drift hypothesis
and
its rejection
- additional evidence from fossils and distribution of rock
types; correlation between South America and Africa; Appalachian and
Caledonian mountain belts; Paleozoic glaciations
- Other geologic evidence for sea-floor spreading (first proposed
by
Hess in early 1960's
- Age of rocks:
- continental rocks up to 4 billion years old, oldest rocks in
shield
areas
- oceanic crust generally < 200 million years old,
distributed in
symmetrical age bands around mid-ocean ridges
- Paleomagnetism
- Apparent polar wandering
- Polarity reversals in earth's magnetic field
- Magnetic "stripes" on the ocean floors and Vine and
Matthews' hypothesis of sea-floor as a recording "strip chart" of the
earth's changing magnetic field
- stages of rifting and ocean-floor development at divergent
boundaries: East African rift valleys, Red Sea and Gulf of Aden
- Convergent boundaries, trenches and subduction zones
- spatial distribution of volcanic activity in relation to
trenches
- oceanic-continental convergence and continental volcanic arcs
- subduction zones and oceanic-oceanic convergence: volcanic
island-arc mountain chains
- suture zones and mountain belts at locations of
continent-continent
convergence
- Transform faults, fracture zones and their origins
- Hot spots as indicators of plate motion
- Measuring rates of plate motion
- Paleogeography of Pangaea: a supercontinent and its breakup
- Competing hypotheses about the driving mechanisms causing plate
motion: slab pull, ridge push, slab suction; models of mantle convection
- The importance of plate tectonics as a theory