Environmental Geology Lecture Outline: Plate Tectonics - the how and why of earthquakes and volcanoes.

From Pluto, the Greek God of the Underworld, to plutonism, the production and movement of molted rock at depth, people have known the earth's interior as the source of awesome and sometimes fearful forces. This is the focus of study in this second part of the course.

Tectonism - earth movements.

Vertical movements are easy to document, and during earthquakes can be experienced, as Darwin did in 1835 along the coast of Chile, where portions of the sea bottom were permanently raised out of the water.


Figure taken from Dana, 1894, Manual of Geology, 5th edition, American Book Company.

"The temple is that of Jupiter Serapsis at Pozzouli. ... supported by 46 columns, each 42 feet high, and five feet in diameter. Three of the columns are now standing, and they bear evidence of submergence for a considerable time to half their height. The lower twelve feet are smooth; for nine feet above this, they are penetrated by lithodomus or stone-bearing shells, remains of which (a species now living in the Meditteranean) were found in the holes. The columns when submerged, were consequently buried in the mud of the bottom for 12 feet, and were surrounded by water nine feet deep. The pavement of the temple is now underwater. Five feet below it there is a second pavement, proving that these oscillations had gone on before the temple was deserted by the Romans."


That the top of Mount Everest is composed of marine strata is also telling.

Geosynclinal theory - early idea from 1800s to 1950s; characterized by vertical movements with secondary gravity driven slumping, and by thermal shrinkage of outer crust; stabilist paradigm. Many problems

Alfred Wegener and continental drift (1910-1930).

1960s and the plate tectonic revolution:

Sidebar: Why doing all this geophysical exploration in the 1950s? Demonstration of the importance of serendipity in science.

Definition of the basic tenants of plate tectonic theory: An outer shell of the earth , the lithosphere, is composed of distinct, curved and semi-rigid plates that move large distances with respect to each other at rates of cms/year. Geologic activity of various types is concentrated at or near plate boundaries of various types.


Conceptual framework for plate boundary classification: Based on relative motion across boundary and type of crust involved.

Continental vs. oceanic crust:

Importance of concept of rheidity (non-intuitive behavior).

Types of plate boundaries:

Divergent:

Convergent boundaries:

Transcurrent:

Hybrid:


Significance of plate tectonics in environmental geology?


Below are two maps showing the configuration of continents and oceanic basins 237 Ma ago and 100 Ma years ago. Compare them to each other and the present configuration and you begin to get some idea of how dynamic the outer shell of the earth is. These maps were generated by C. R. Scotese (cscotese@uta.edu).


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