III. Marine Geology and Geophysics Component of the Global Program 



The Ocean Lithosphere Studies component of the Global Program provides for a broad research 

 effort based on modern technology to be directed toward understanding the dynamics, structure, 

 evolution, and origin of ocean basins. It has two major aspects: (1) Tectonics and Structure of 

 Submerged Continental Margins and (2) Ocean Lithosphere and Ridge Crest Processes. They 

 focus respectively on ocean-continent transition zones and tectonics and on hydrothermal 

 processes at ocean ridge systems. Together they provide a balance between (1) examining 

 crustal formation processes responsible for the basic structure of 70% of the earth's crust and 

 the associated biological and chemical questions, and (2) determining the processes of formation 

 of oceanic sedimentary basins, destruction of oceanic crust, and aggregation of continents. Both 

 components share the need for expanded facilities and their application. The approach to these 

 problems balances upgraded and expanded field programs with improvements in laboratory 

 equipment and development of new in situ measurement technologies. 



1. Ocean Lithosphere Studies 



a. Tectonics and Structure of Submerged Continental Margins 



The transition zones between continents and oceans represent the boundary between the two 

 major physiographic provinces on our planet. In some cases they are also past or present 

 boundaries of the lithospheric plates forming the earth's surface. A much deeper understanding 

 of the structure, tectonics, and dynamic evolution of these fundamental geologic features is 

 within our grasp. The basic scientific manpower, theory, and technology exist for developing a 

 comprehensive understanding of continental margins. 



Some of the major questions to be addressed are: 



• What are the geologic units underlying passive and active continental margins? How is 



their geology coupled to formation of ocean-continent boundaries? What are the 

 dominant tectonic, geochemical, and thermal processes? 



• How does the geology vary along continental margins? What are the differences between 

 old and young margins, island arc and trench regions, fast and slow convergence sites, and 

 thick and thin sedimentary sequences? What is the coupling to adjacent geologic 

 provinces, to onshore basins and trenches? 



• What causes initial rifting? How are conjugate sites on the opposite side of ocean basins 

 related? What are the controlling factors for subsidence rates, sediment accretion 

 rates, thermal histories, and regional basin formation? 



To answer these questions modern geophysical, geological, and geochemical methods and 

 equipment for measuring and interpreting the physical properties of crustal structure are 

 needed. A primary technique is multichannel seismic profiling with large numbers of detectors 

 and large receiving apertures. The Large Aperture Seismic Experiment (LASE) showed that 

 multiship techniques can map the deep structure of the margins. A major limitation is the lack 

 of field data from contrasting tectonic areas to construct and constrain geologic models and the 

 lack of state-of-the-art multichannel seismic systems. 



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