D. Marine Geology and Geophysics Program 

 Long-Range Planning 



I. Core Program 



Major changes in marine geoscience research have occurred in the fifteen years since acceptance 

 of plate tectonics theory. Reconnaissance studies of sediment distribution and composition, 

 crustal age and chemistry, and ocean basin structure and history have set the stage for detailed 

 examination of (1) the "how" and "why" of plate tectonic processes; (2) the mechanisms of 

 global climate and ocean circulation changes as recorded in deep sea sediments; (3) the temporal 

 and spatial scales of seafloor formation and their control on crustal heterogeneity; (4) seawater 

 chemistry and formation of mineral deposits; (5) the stretching and subsidence of rifted 

 continental margins; and (6) the mechanisms for crustal accretion and erosion in deep sea 

 trenches. 



New instruments allow the geologist to image the seafloor in real time on spatial scales of meters 

 to kilometers (swath mapping, side-scan sonars, and cameras) and permit the geophysicist to 

 probe the deepest sedimentary and igneous layers beneath the margins and ocean basins 

 (large-aperture seismic arrays, broadband digital reflection profiling systems, satellite 

 geodesy, and ocean bottom seismometers). The geological and geochemical significance of 

 remotely sensed features can be determined by precision sampling from submersibles and deep 

 ocean drilling, with subsequent analyses using modern analytical instrumentation. 



Marine geosciences are at a point where these new techniques can be integrated and utilized in 

 major new programs to provide a comprehensive understanding of the processes which create 

 and modify 70% of the earth's crust and which have controlled global environmental changes for 

 the last 150 million years. The basic scientific manpower, theory, and technology exist for such 

 programs. The present status and future trends for the five major program areas at existing 

 support levels are summarized below. 



1. Structure and Evolution of Continental Margins. The use and development of 

 multichannel seismic techniques, swath-mapping, sonar systems, and seismic stratigraphic 

 analysis have lead to new conceptual models of margin formation and evolution. On a few passive 

 margins, such techniques have been coupled with heat flow, gravity, and sediment analyses to 

 quantify faulting, crustal stretching, and subsidence which accompany continental rifting. 

 Limited study of active margins has begun to clarify the process of continental accretion and 

 provided unexpected evidence of crustal erosion. 



The geological structure of the transition from ocean to continent is a direct result of, and varies 

 with the processes causing rifting and subsidence (passive margins) or convergence and uplift 

 (active margins). A major limitation is the lack of field data from these contrasting tectonic 

 areas to construct and constrain geologic models. 



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