The zone of convergence is not only of scientific interest but of social 

 and economic importance since it is the site and cause of one of the 

 earth's two major zones of seismicity. It is an area marked by extensive 

 recurring volcanism, intrusion, crustal unlift, and mountain building. 

 Very nearly all the world's major resources of hard minerals are pres- 

 ently found in modern or ancient zones of plate convergence. 



The purpose of the Na,sca Lithospheric Plate Study is to examine in 

 detail the processes of crustal formation and destruction that take place 

 at the diverging and converging edges of a well-defined lithospheric plate, 

 shown in Figure 28, in the southeastern Pacific. The diverging edge of 

 this plate has recently been identified as a potentially important locality 

 of mineralization of the crust and sediments. The converging edge, at the 

 South American block, is an old and important area containing striking 

 and outstanding examples of all the major effects of such convergence. 

 The Nasca Plate project emphasizes geophysical, geochemical, and marine 

 geological studies at the two plate edges and will attempt to link events 

 and processes by geophysical studies of the structure of the plate itself. 



The regional investigation at sea will be carried out on a series of 

 approximately 14 marine geological and geophysical traverses oriented ap- 

 proximately east-west across the area bounded by the East Pacific Rise 

 and the coast of South America, and latitudes 1° N. and 47° S. The ocean 

 traverses will be conducted as a joint operation involving research ves- 

 sels from the Hawaii Institute of Geophysics, Oregon State University, 

 and the Pacific Oceanographic Laboratory (POL) of NOAA. 



On the basis of existing data, and as the structure of the plate is 55 



analyzed, detailed surveys of selected portions of the East Pacific Rise 

 crest and the Peru-Chile Trench will be carried out. The University of 

 Hawaii and the Pacific Oceanographic Laboratory will emphasize the geo- 

 physical study of the Nasca Plate edges ; Oregon State University will con- 

 centrate on local marine geological and geophysical studies of the con- 

 vergent edge (the trench and the continental margin) and on problems 

 regarding mineralization processes and igneous activity on the crest of the 

 East Pacific Rise. 



The total effort, including field operations, laboratory investigations, 

 and data processing and analysis is divided into three subprograms of about 

 equal size: 1) regional studies of the Nasca Plate to the extent required 

 to interpret the findings at its boundaries and its interaction with the 

 South American Plate; 2) detailed studies of significant areas of structure, 

 stratigraphy, and recent sediments of the Trench margin; and 3) detailed 

 studies of significant areas of the Rise crest, its new crust, and its miner- 

 alization. 



The first work, in 1971, was to compile all existing data on the Plate 

 and to evaluate them in view of the overall objectives of the study. Cruise 

 track lines presently planned are shown in Figure 29. 



Beginning in May 1971, both the Hawaii Institute of Geophysics and 

 Oregon State University began equipping their respective research vessels 

 for the IDOE cruise in the first part of 1972. Oregon State's Yaquina, 

 outfitted for the geological, geophysical, and geochemical work to be 

 carried out on the Nasca Plate, sailed 18 August 1971 for a 9-month 



