The double helix in global tectonics

Abstract

Contemporary studies of the earth's surface reveal continental tectonic patterns containing many large linear belts and trends that follow systematic directions. The same directions appear to be repeated in tectonic patterns in the northern and southern hemispheres. At continental scale, four major lineament directions appear to predominate, viz., WNW, NNW, NNE and ENE and reflect the same trend directions that emerged in studies of Australian lineaments by Sherbon Hills more than three decades ago. They have since been confirmed through the integrated results of studies of Landsat imagery, gravity, magnetic and seismic data. Major linear features in the system are found to be associated with major ore deposits and major basin patterns of various ages. Correlations with sub-surface data indicate that the linear features are zones of crustal disturbance and attenuation characterised by discontinuities such as faults and shear zones. A synthesis of continental data with sea floor data suggests that there is a fundamental spiral pattern encircling the globe. This pattern, sinistral in sense, appears to have two spiral arms or zones of maxima diametrically opposite one another, forming what is analogous to a double helix. One of the spiral arms corresponds to the west-northwest zone of Tethyan torsion which follows a course from the southwest Pacific area to India and on through the Mediterranean region. The other arm follows a course south of continental Australia through southern Africa and on through the West Indies. This spiral system has been referred to as the Tethyan system. Left-lateral crustal movements associated with it are indicated by appropriate sinistral displacements of continental features and mid-ocean ridges. This movement is in consonance with the widespread development in many parts of the globe of elliptic configurations, including the development of folds with north-northwest axes corresponding to the long axes of the appropriate deformation ellipsoids. A subordinate global counter-spiral, dextral in sense, is named the Laurasian system. The Tethyan and Laurasian spiral systems together appear to influence global deformation phenomena, including island arc (volcanogenic) development. They are regarded as fundamental shapers of continents through geologic time. The spiral trends appear to transgress some plate boundaries and follow along others. A plot of the principal pattern on a polar projection resembles the two arms of a spiral nebula and offers a commentary on the ultimate origin of the earth.