90° 95° 100° 105° 110° 115° 120° 125° 130° 135° 140° 145°150° 



Figure 17. — Six major transects selected for geophysical and 

 geological studies on nietallogenesis, hydrocarbons, and 

 tectonic patterns in east and southeast Asia. (Geotimes 

 December 1975). 



and tectonics of the Banda Sea region during a two-ship pro- 

 gram in the area in late 1976. Researchers at Cornell and 

 Scripps will be cooperating in a study of the deformation along 

 the inner wall of the Java Trench. Scientists doing field work on 

 islands have examined deformed, uplifted trench sediments. 

 Preparation of a Heat Flow Map for the area is under way. In 

 addition to data collected at sea, scientists at Scripps and In- 

 donesia are measuring heat flow from oil wells in Indonesia. In 

 a parallel program, scientists from Japan are making measure- 

 ments in Thailand both on land, in the Gulf of Thailand and in 

 the Andaman Sea. Successful completion of these cooperative 

 efforts should produce the world's second (after North America) 

 most complete heat flow map. 



East and Southeast Asia Bibliography 



D. E. Hayes. 1975: U.S. proposal, East and Southeast Asia, 

 Geotimes 20(12) -.Il-IA. 



Nazca Plate 



Studies of the Nazca Plate by scientists of the Hawaii 

 Institute of Geophysics and Oregon State University have con- 

 centrated on the structure and tectonics along the Peru-Chile 

 Trench and the formation of metalliferous sediments along the 

 East Pacific Rise. Data obtained by the ASPER (Airgun- 

 Sonobuoy-Precision-Echo-Recorder) technique — which provides 

 greater detail of the crustal structure than that obtained from 

 two-ship refraction surveys — indicate faulting of the oceanic 

 crust during subduction. A major offset in crustal layers 300 km 

 west of the trench axis is interpreted as a low angle thrust fault 

 dipping eastward at an average angle of 6° beneath the sea floor. 



This may indicate that horizontal compression extends to the 

 base of the oceanic crust. 



The coast of western South America is composed of three 

 distinct segments. In the northern (4° to 20°S) and southern 

 (28° to 34°S) segments there is evidence that significant 

 amounts of sediments are accreted to the inner wall of the 

 trench. The central segment (20° to 28°S) appears to be an 

 area of nonaccrction and possibly of erosion. Sediment is sub- 

 ducted along with the oceanic crust. 



Analyses of extensive sediment samples from the plate 

 indicate that the metal deposits are derived from four distinct 

 sources: hydrothermal, detrital, hydrogenous, and biogenic. 

 The distribution and relative percentage of each metal in a 

 sample is controlled by: 1) supply from the four basic sources, 

 2) lateral transport by bottom currents, and 3) diagenesis of 

 unstable metalliferous hydroxide in surface sediments to more 

 stable mineral phases, Fe, Mn, and Cu, which are dominantly 

 of hydrothermal origin across most of the plate. Zn also is of 

 dominantly hydrothermal origin, except on the northern por- 

 tion of the East Pacific Rise, where Zn of biogenic origin from 

 overlying surface waters is present. Diagenesis converts much 

 of the hydrothermal iron and biogenic silica to an iron-rich clay 

 mineral. 



Metalliferous sediments accumulate at high rates on both 

 the East Pacific Rise and in the Bauer Basin. A hydrothermal 

 source located along the Rise is consistent with the transition 

 metal and aluminum accumulation rates. In the Bauer Deep 

 the rate of accumulation suggests that either metal-bearing 

 phases are being transported from the Rise or a second hydro- 

 thermal source exists within the Bauer Deep. 



A workshop was held in October 1975 to better define the 

 relation of Andean nietallogenesis and Nazca Plate tectonics, 

 and to identify critical areas for future research emphasis. 

 Important questions that must be answered are the amount and 

 composition of subducted sediments, the degree of hydration 

 and alteration of the oceanic crust, how segmentadon of the 

 oceanic crust relates to ore distribution, and how transition 

 metals behave in silicate melts. 



Nazca Plate Bibliography 



Anderson, Roger N., Marcus G. Langseth, Victor Vacquier, and 

 Jean Francheteau. 1976: New Terrestrial heat flow meas- 

 urements on the Nazca Plate, Earth Plant. Sci. Lett. 29(2) : 



243-254. 



Blakely, R. J., K. O. Klitgord, and J. D. Mudie. 1975: Analysis 

 of marine magnetic data. Rev. Geophys. Space Phys. 13: 

 182-185. 



Dasch, E. 1974: Metallogenesis in the southeastern Pacific: a 

 progress report on the IDOE Nazca Plate Project, Physics 

 of the Earth and Planetary Interiors, 9:249-258. 



Hussong, D. M., M. E. Odegord, and L. K. Wipperman. 1975: 

 Compressional faulting of the oceanic crust prior to sub- 

 duction in the Peru-Chile Trench, Geology 3:33-37. 



Prince, R. A., J. A. Resig, L. D. Kulm, and T. C. Moore, Jr. 

 1974: Uplifted turbide basins on the seaward wall of the 

 Peruvian Trench, Geol. 12(2):607-611. 



Prince, P. A. and L. D. Kulm. 1975: Crustal rupture and the 

 initiation of imbricate thrusting in the Peru Trench, Geol. 

 Soc. Amer. Bull. 86: 1639-1653. 



