*wo phenomena are related. The plate is small enough to be 

 studied as a single geologic entity yet large enough to be 

 representative of the great lithospheric plates that make up 

 the surface of the earth. Since the spreading rate along the 

 East Pacific Rise is among the fastest measured, the volcanic 

 processes producing metalliferous crust and sediments must be 

 quite intense. Furthermore, the dilution process must be mini- 

 mal because the Plate itself receives little sediment from the 

 land. 



The Hawaiian Institute of Geophysics (HIG), Oregon 

 State University (OSU), and the Pacific Oceanographic Lab- 

 oratory of NOAA are studying the plate margins using comple- 

 mentary geochemical, geological, and geophysical techniques. 

 Scientists from Chile, Colombia, Ecuador, and Peru are ac- 

 tively participating in the cruises and data analysis. A large- 

 scale study of the subduction zone under the Andes as it 

 extends from Colombia south through Chile is simultaneously 

 being done. Although this study goes beyond the scope of 

 IDOE, the data on the subduction zone have obvious implica- 

 tions for the Nazca Plate metallogenesis study and vice versa. 



Joint regional investigations by HIG and OSU were 

 begun in 1972, using the HIG RV Kana Keoki and OSU's RV 

 Yaquina, to provide the framework needed for further detailed 

 studies scheduled to be accomplished through 1975. The area 

 that will be surveyed is bounded by the East Pacific Rise and 

 the coast of South America, and by latitudes 4°N and 47°S. 



A series of marine geological and geophysical traverses 

 during the initial field season were located at 6°S and 11°S; 

 operations were concentrated at the East Pacific Rise and the 

 Peru-Chile Trench (fig. 32). 



A combined total of about 36,500 square kilometers was 

 surveyed on the East Pacific Rise crest by the RV Kana 

 Keoki and RV Yaquina. Tracklines were planned so that 

 each ship's survey consisted of four to six traverses, orthogonal 

 to the rise axis, spaced 4 to 6 miles apart. Data obtained 

 include 12 kilohertz bathymetry, gravity, heat flow measure- 

 ments, total field magnetics, as well as seismic reflection and 

 refraction profiles. In addition, 115 cores (including 64 piston 

 cores), dredges, and grabs were collected. 



One of the most significant facts learned on these surveys 



GALAPAGOS 

 ISLANDS 



0° — 



TALARA 



"^^^ e^-^ . ^ 



10°S- 



IICW 



_L_ 



100« 



90° 



80° 



20» 



70° 



Figure 32. — Geological and geophysical 

 survey lines of RV KANA KEOKI and RV 

 YAQUINA. 



32 



