PART II— DYNAMICS OF THE SOLID EARTH 



chemical cycles, we are still deficient 

 in detailed quantitative knowledge of 

 the geochemical cycles of practically 

 all elements. Research on geochemical 

 cycles of the elements, such as es- 

 sential carbon, for example, should be 

 intensitied. Research on the behavior 



of fugitive constituents (e.g., water 

 and sulfur dioxide) in igneous and 

 metamorphic processes is also criti- 

 cally needed to improve our under- 

 standing of continental geochemical 

 processes and their relations to tec- 

 tonics. 



If research on continental struc- 

 ture and processes is intensified and 

 strengthened, we can expect the 

 1970's to be as exciting a decade of 

 discovery for the continents as the 

 1960's were for the oceans and the 

 continental margins. 



Practical Implications of Major Continental Processes 



Recent verification that the crust of 

 the earth moves readily over the 

 earth's interior in the form of large 

 sliding plates has reoriented geologi- 

 cal thinking in a number of ways 

 that affect our understanding of where 

 many natural resources occur. We 

 also have new insights into such 

 natural hazards as biological extinc- 

 tions, the development of ice ages, 

 major earthquake belts, and regions 

 of volcanism, to cite just a few natural 

 hazards that are of continuing inter- 

 est. In fact, the new ideas of conti- 

 nental drift and sea-floor spreading 

 have demanded a re-evaluation of 

 many of the premises underlying the 

 subjects of geology, geochemistry, 

 oceanography, and long-term changes 

 in atmospheric circulations. 



Resource Distribution 



Much of our information on geo- 

 logical and geochemical distributions 

 comes from a study of ancient sys- 

 tems that have existed over great 

 lengths of geological time. In many 

 instances, it is clear that these ancient 

 systems operated differently from 

 those of today. It now appears that 

 the earth's sliding-plate mechanism 

 has caused relative motions between 

 continental and oceanic regions, 

 formed and destroyed ocean floors, 

 developed mountain belts, and 

 changed the positions of land masses 

 with respect to the equator or to the 

 poles in times that are short com- 

 pared to the time it took to form 

 many of our major natural resources. 



Evidence is building up that we are 

 currently in a stage in earth history 

 that is considerably more active than 

 that pertaining over much of the geo- 

 logical past. It is beginning to appear 

 that mountain belts are longer and 

 higher, earthquake activity greater, 

 and a large array of other features 

 more pronounced in present times 

 than in an average geological period 

 in the past. Furthermore, by relative 

 motions between the continental land 

 masses and the pole of rotation of 

 the earth, it seems that climates may 

 have changed rather radically in the 

 recent geological past. 



This means that we must take a 

 new look at theories of the origin of 

 many mineral deposits, natural fuels, 

 and surface deposits, so that we may 

 better predict their locations and ex- 

 tensions. For example, it is clear that 

 the petroleum deposits in the Prudhoe 

 Bay area of Alaska were formed at 

 much lower latitudes, the potash 

 salt deposits of Saskatchewan were 

 formed closer to the equator, and the 

 onset of the devastating ice ages was 

 brought about by shifts in oceanic 

 circulation resulting from shifting 

 land masses. It is necessary to know 

 these correlations if we are to under- 

 stand the processes that cause the de- 

 velopment of petroleum and salt de- 

 posits, polar ice-caps, and many other 

 resources or hazards that are of con- 

 cern to man. 



Minerals — The new understand- 

 ing of the down-thrusting of ocean 

 floor beneath continental edges has 



led to correlations between these 

 zones of downward motion and a 

 superjacent distribution of certain 

 types of mineral deposits. For ex- 

 ample, it has been discovered that 

 copper deposits of the type found in 

 the southwestern United States, which 

 supply most of our copper today, 

 occur in belts that lie above these 

 zones and that the age of emplace- 

 ment of the deposits generally coin- 

 cides with the time of the down- 

 thrusting movement. Thus, it appears 

 that the disappearance of crust, the 

 development of volcanoes, and asso- 

 ciated mineral deposits are tied to- 

 gether by a process that involves the 

 melting and fractionating of down- 

 dragged materials. This has led to 

 much prospecting activity in regions 

 where the downward disappearance 

 of crust is known from large-scale 

 effects. The result has been the devel- 

 opment and discovery of a number of 

 new, hitherto unsuspected deposits. 



Another way of seeking new areas 

 for prospecting has been the predic- 

 tion of extensions of known mineral 

 belts where they occurred before con- 

 tinental land masses were separated. 

 For example, South America fitted 

 into Africa in a single supercontinent 

 not too long ago, geologically speak- 

 ing. (See Figure II-4) The locations 

 of gold, manganese, iron, tin, ura- 

 nium, diamonds, and other mineral 

 deposits in Africa are much better 

 known than those in South America, 

 although it is expected that South 

 America's mineral potential east of 

 the Andean chain will eventually be 



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