421 



FUTURE DIRECTIONS IN OCEAN SCIENCES 83 



derstanding of how this two-dimensional plate-driven flow devel- 

 ops into a more three-dimensional upwelling pattern along some 

 ridges and how this flow affects, or is affected by, the observed 

 segmentation of oceanic spreading centers. 



By deploying an array of ocean bottom seismometers across a 

 section of the mid-ocean ridge and recording a sufficient number 

 of seismic events at different ranges and angles, it should be pos- 

 sible to improve the resolution of the seismic structure of the 

 shallow mantle beneath a ridge crest. A major goal for the next 

 decade is to carry out one or more of these studies on the mid- 

 ocean ridge. . 



Processes That Transform Magma into Oceanic Crust 



The transformation of magma into oceanic crust at spreading 

 centers has fundamental implications for the mechanisms of heat 

 and material transport from deep within Earth to the lithosphere, 

 hydrosphere, and biosphere. The important processes that trans- 

 form mantle melt into oceanic crust and the role of crustal cham- 

 bers are poorly understood. The global distribution and physical 

 properties of magma chambers at oceanic ridges and their tempo- 

 ral and spatial variability should be determined. Internal dynam- 

 ics of magma chambers are important factors that must be under- 

 stood, along with their effects on the structure and composition 

 of the crust, the transfer of heat from the magma chamber, and 

 the physical and chemical processes occurring at the interface 

 between the magma chamber and the overlying region of seawater 

 circulation. 



Processes That Control the Segmentation and Episodicity 

 of Lithospheric Accretion 



The use of new technology, such as satellites, swath mapping, 

 and side-scan sonar, has revealed that the global rift system is 

 segmented and that the pattern of segmentation varies temporally 

 and spatially. It is essential to understand the physical processes 

 controlling segmentation and its temporal and spatial variation as 

 well as the processes causing episodic production along individual 

 segments and their boundary zones. Melt migration and eruption, 

 faulting, fissuring, and stretching must also be better understood 

 so that the individual processes and their possible interactions 

 can be studied and interpreted. 



