CONTINENTAL STRUCTURES AND PROCESSES AND SEA-FLOOR SPREADING 



districts on a geologic-tectonic map. 

 This effort is well under way. Ameri- 

 can geologists are participating in an 

 international committee for the Geo- 

 logic Map of the World, sponsored 

 by a commission of the International 

 Union of Geological Sciences which is 

 compiling a world metallogenic map. 

 A first version of the North America 

 map has been completed. 



Although the scale of the map 

 (1 : 5,000,000) necessitates severe 

 condensation of data, the general dis- 

 tribution of many ore types can be 

 represented and compared. For ex- 

 ample, the relation of the strata-bound 

 massive sulfide deposits to volcanic 

 (eugeosynclinal) belts of Precambrian 

 rocks in the Shield, Paleozoic rocks in 

 the Appalachians, and Mesozoic rocks 

 in the Cordillera shows rather clearly. 

 Nickel sulfide ores are distributed 

 around the periphery of the Superior 

 Province. A rather distinct class of 

 magnetite-chalcopyrite replace- 

 ment deposits in carbonate rock seems 

 to follow the Cordilleran margin of 

 the continent. Tungsten deposits lie 

 east of the quartz-diorite line. Many 

 epigenetic deposits in the interior of 

 the continent seem related to trans- 

 verse structures (lineaments), and a 

 suggestion of zonation on a conti- 

 nental scale seems to be emerging. 



Further refinement of the metal- 

 logenic map is under way. In combi- 

 nation with general studies of conti- 

 nental processes and structures, this 

 will enable exploration geologists to 

 locate promising areas in which to 

 search for additional mineral deposits. 



Needed Research on 

 Continental Processes 



The Continental Margins — The 

 concepts of global plate tectonics for 

 the first time give earth scientists a 

 general working hypothesis to explain 

 the varied continental processes that 

 characterize the mountain-building as- 

 sociated with active continental mar- 

 gins: transcurrent faulting, volcanism, 

 thrust faulting, and the like. Clearly, 



an intensification and broadening of 

 geological and geophysical research 

 along continental margins such as the 

 coastlines of California, Oregon, and 

 Washington is critically needed. 



Geologic Processes in the Conti- 

 nental Interior — All earth scientists 

 recognize that the continental plates 

 have been actively deformed, and that 

 concepts of rigid continental plates 

 must be modified in practice. In par- 

 ticular, many students of the geology 

 of the western United States recognize 

 that the continental crust in and west 

 of the Rocky Mountains has been ac- 

 tively deformed over the past 100 mil- 

 lion years or so, and is still being 

 actively deformed in many places. 

 Plate tectonics is not irrelevant, how- 

 ever. Application of the attitudes and 

 study methods that led to the con- 

 cepts of global plate tectonics can be 

 expected to lead to significant and 

 dramatic advances in our knowledge 

 of continental processes. 



If the westward-drifting continent 

 overrode the eastward-spreading Pa- 

 cific Ocean plate and continental mar- 

 gin features such as oceanic ridges 

 and trenches, where are these features 

 now? Is the Basin and Range Province 

 behaving similarly to a spreading 

 ocean floor? If so, where are the 

 spreading centers? Are they along 

 the Wasatch Mountain front, or the 

 Rio Grande rift zone? What dynamic 

 continental processes are occurring 

 east of the Rocky Mountains, and 

 how do they relate to the active 

 processes of the western crust? 



Seismic Monitoring — Seismology 

 is now being focused in unprecedented 

 detail on the active continental proc- 

 esses along the California continental 

 margin. A similar focusing of seis- 

 mological effort on the earthquake 

 zones of Washington and the conti- 

 nental interior is needed. In particu- 

 lar, intensification of seismological 

 effort is recommended for the Ven- 

 tura-Winnemucca earthquake zone of 

 California and Nevada; the Rocky 

 Mountain zone of Arizona, Utah, 



Idaho, Wyoming, and Montana; the 

 Rio Grande rift zone of Colorado and 

 New Mexico; the Mississippi Valley 

 earthquake zone of Illinois and Mis- 

 souri; and the earthquake zones of 

 the New England region. Seismic 

 monitoring should be accompanied by 

 measurements of crustal strain and 

 appropriate geological and geophysi- 

 cal exploration of major crustal fea- 

 tures. 



Structural and sedimentary basins, 

 in which large reserves of petroleum 

 and other economic fuels and minerals 

 are concentrated, are among the most 

 prominent and significant geologic 

 features of the continents, but the 

 processes of their formation are poorly 

 understood. An intensive three- 

 dimensional study of all aspects of the 

 development of one or more struc- 

 tural and sedimentary basins through 

 geologic time, relating that develop- 

 ment to economic deposits and envi- 

 ronmental assets and liabilities perti- 

 nent to wise long-term use of the 

 land, would make a great contribution 

 to our knowledge of continental proc- 

 esses. The beginning of such a study 

 has been made in the Wind River 

 Basin of central Wyoming, but this 

 study has been concentrated mainly 

 on the upper part of the earth's crust. 

 Basin development is necessarily con- 

 trolled by upper-mantle as well as 

 crustal processes, and therefore de- 

 tailed geophysical study of the deep 

 crustal and upper-mantle foundations 

 of one or more large basins is needed. 



Deep Continental Drilling — Our 

 knowledge of the composition of the 

 lower continental crust is clearly in- 

 adequate. In addition to more detailed 

 geophysical exploration of the deep 

 crust, a program of deep continental 

 drilling is critically needed. Locations 

 for penetrating the lower crust that 

 will be within the reach of present 

 drilling technology can be selected 

 from geophysical studies. 



Geochemical Research — Although 

 we have good qualitative understand- 

 ing of the major features of the geo- 



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