High-Technology Investigations Of Rift Propogation And Plate Tectonics

Plate tectonics as originally formulated was so successful in revolutionizing geology that only very few modifications have been necessary. One of these modifications is the suggestion that spreading centers sometimes increase their length by propagation, progressively rifting apart preexisting lithospheric plates and reorganizing the Earth's plate boundary geometry. This small change to plate tectonic theory, known as the propagating rift hypothesis, provides a mechanistic explanation for a wide variety of tectonic puzzles, including the existence of a large class of seafloor and continental margin features which are oblique to both relative and absolute plate motion and thus were inexplicable and seemingly incompatible with previous plate tectonic theory, as well as for the occurrence of spreading center jumps and zones of unusually differentiated FeTi basalts. In addition to routine marine geophysical survey techniques the phenomenon of rift propagation has been investigated with Gloria, Seabeam, Deep-Tow, Sea Marc I, ocean bottom seismometers and transponder-navigated dredging, and ALVIN and ANGUS work is anticipated. We have just completed a very successful investigation of the Galapagos95.5\degW propagating rift system using the new Scripps Seabeam system on the R/V Thomas Washington and the Deep-Tow system of the Marine Physical Lab at Scripps. This was the first time Seabeam and Deep-Tow were used together (except on short test cruises), and the combination is proving to be very powerful in understanding seafloor tectonic evolution. In addition, we were fortunate to have the new NAVSTAR Global Positioning System operating throughout the cruise, providing navigational accuracy of a few tens of meters during the 4-8 hrs/day of favorable satellite geometry, as well as the Deep-Tow transponder navigation net. Our results strongly corroborate the propagating rift hypothesis and indicate that this hypothesis can be confidently added to plate tectonic theory. Furthermore, it's clear that if this process continues for many millions of years it will have important implications for large-scale plate tectonic evolution and that propagating rifting of continental and oceanic plates may have important economic implications.