Course materials for Plate Tectonics, GEOL
3700, University of Nebraska at Omaha. Instructor: H. D. Maher Jr., copyright.
This material may be used for non-profit educational purposes with appropriate
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Some answers to questions for Week 1: When the earth
moves: an introduction to vertical and horizontal tectonics through history
of geologic thought.
What are various indications
of vertical movement, uplift and subsidence?
- emergent shorelines.
- submerged ruins.
- uplift events during earthquakes.
- sedimentary basins.
- development of sedimentary sources.
- mountains composed of marine strata.
- exposure of rocks from the deeps (plutonic and metamorphic
What were unsatisfactory
aspects of geosynclinal theory?
- models for the amount of contracton caused by thermal
contraction are inadequate to explain observed contraction amounts.
- the pattern of contractional structures of mountain belts,
is not that expected from a thermal contraction model.
- it did not explain areas of rifting!
What is isostasy? Simply put,
the crust acts like it is floating. Put a load on and it sinks. Take it
off and it rises. Response time is on the order of thousands to tens of
thousands of years.
the general rejection of Wegener's hypothesis:
- baby with the bath water: since some of Wegener's evidence
or ideas could be shown infeasible, the whole theory was suspect. The impossibility
of the weaker continental material plowing through and over stronger oceanic
material as pointed out by Sir Harold Jeffrey's is one example.
- scientific inertia. Acceptance doesn't come until the
old guard dies.
- it was a radical hypothesis.
- alternate explanations existed.
- not invented here. Wegener was not a geologist.
- Wegener was German, at a time there was some anti-German
Where does the rock's magnetic
field component comes from?
Curie temperature = point at which a stable magnetic field
is imprinted or destroyed in a rock.
If rock has magnetic minerals these align with the earth's
field at time they pass through Curie temperature, or if at lower T, at
time the mineral forms. A fossil field or Natural Remanent Magnetization
(NRM) is thus acquired. Various types exist such as:
- Thermal remanent magnetization.
- Chemical remanent magnetization.
- Detrital remanent magnetization.
- Biologic remanent magnetization.