The role of magnetic surveying in developing the concept of plate tectonics

Abstract

I feel somewhat disadvantaged speaking on the subject of Plate Tectonics as I changed from this field of endeavour shortly after unsu~ssfu~y putting forward the theory explaining the geomagnetic striping of the ocean basin floors in January 1963. The enhanced theory of Plate Tectonics proposed by Tuzo Wilson, Harry Hess and Fred Vine, as well as the radioactive dating of the recent reversals of the earth’s field by Cox and Doe11 all took place since then. I have been totally immersed in remote sensing and space research since about 1965. A twenty-two year “time warp” however may provide me with a somewhat different perspective than those who are presently active in the field. In fact, most of my intensive work in rock magnetism (as it was called then) was done as a graduate student under Tuzo Wilson from 1949-1952. In this paper I wish to stress the important role that the use of magnetic survey data played in helping to integrate the otherwise disparate theories of continental drift and ocean floor spreading as propounded by Hess and Dietz and that of the periodically reversing geomagnetic field. These theories would probably have remained in the category of speculation had it not been for the ship-borne magnetic survey data taken by Raff and Mason in the years from 1957-1962 in the East Pacific Basin. These data together with later survey data by Heirtzler of Lamont gave proof to the theories, by quantitatively knitting them together. Yet somehow, in spite of the importance of these data in the development of the Plate Tectonic Theory, the rate of magnetic surveying of the ocean basin has greatly fallen off. The objective of this paper is to encourage more extensive use of ma~etometers and magnetic gradiometers in order to further delineate past movements of the basin floors and those of the overiding land masses. It is noted that Victor Vacquier in his excellent review monograph “Geomagnetism in Marine Geology” published in 1972 concludes that “‘further contributions of geomagnetism to unraveling palaeogeography are likely to come from palaeomagnetic investigations on the continents, but only in a minor way to the oceans”. I believe, however, that there still is a wealth of unexpected information magneticaliy frozen in the rocks of the ocean basin floors and that extensive, ~~-qu~ty three-component magnetic gradiometer surveys are the most cost-effective way of getting at it. Until now, the high cost of electronic positioning systems has inhibited conducting high-quality surveys. There was a tendency to use less accurate means of track recovery and to place the lines too far apart. Now with the advent of the Satellite Global Positioning System (G.P.S), allowing accurate navigation and track recovery at a relatively low cost, this draw-back has been removed. Another draw-back has been the inadequacy of vector magnetometers. When fluxgate and proton total-field magnetometers were invented, they were so thankful that a way was found of orienting them, that all survey techniques and indeed interpretative mathematics, with grossly inaccurate simplifying assumptions were constructed to deal with total field data. However, in recent years, small light-weight inertial systems which are capable of providing a