An early thrust of the program is to acquire seismic data on the continental margins with 

 tuned-source arrays and high-speed digital recording systems. Sufficient resources will be used 

 to maintain effective data acquisition and data analysis centers along with the critical mass of 

 scientists, technicians, and students required for operations. An expanded number of seismic 

 experiments ($2.7M in FY 1989, $6.2M in FY 1990, and increasing to $I2M by FY 1992) for 

 studying deep structure in constrasting regions will be integrated with lithologic and acoustic 

 stratigraphic analysis, structural analysis, subsidence analysis, and heatflow, gravity, and 

 magnetic measurements. The initial studies will use upgraded capabilities of existing ships 

 followed by a transition to a proposed new research ship in FY 1991 . 



An additional requirement is correlation of marine geological and geophysical studies with 

 onshore geologic studies of the Continental Lithosphere program and offshore drilling by the 

 Ocean Drilling Program. Geologic samples from continental margins will provide controls on 

 the age and nature of basement, on age correlations for seismic reflectors, on biostratigraphic 

 data for subsidence models, and on the composition and facies of geologic sections. Other 

 significant measurement techniques include using arrays of ocean-bottom seismometers, the 

 Long Coring Facility, and upgraded laboratory facilities for geophysical, geological, and 

 geochemical analyses of data and samples. 



b. Ridge Crest Processes 



Oceanic ridges are a major component of the dynamic geologic system that forms, modifies, and 

 changes the surface of the earth. They are the source of major transfers of heat and chemical 

 elements from the earth's interior to surficial geologic layers and into the oceans by volcanic 

 and hydrothermal processes. Active "vent systems" also support specialized biological 

 communities that draw a significant part of their energy needs from geochemical fluxes. 



Much more is known about kinematics of seafloor spreading than about plate mechanics, their 

 physical and chemical properties, or the forces acting to drive the plates. These questions plus 

 their geological, chemical, and biological effects remain unresolved because of a lack of 

 state-of-the-art observational data to test hypotheses and speculations. A major limitation is 

 the lack of knowledge of the internal structure of ridge systems and the spatial and temporal 

 scales of volcanic activity needed to constrain dynamic calculations. 



The objective is to provide integrated geochemical and structural models defining spatial and 

 temporal scales of seafloor creation and evolution. Particular emphasis will be directed to 

 developing techniques for long-term monitoring of hydrothermal vent systems to quantify their 

 full geochemical cycle. 



Some of the major questions to be addressed are: 



• How does the ocean lithosphere respond mechanically to large surface loads, to 

 compression, to bending, to stretching? With an understanding of these factors, what can 

 we learn about deeper processes in the earth, such as mantle convection, by looking 

 through the "ocean lithospheric window?" 



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