CAN A HORIZONTAL ASTRONOMICAL DRIVING FORCE AND AN INDEPENDENT VERTICAL CONVECTIVE FORCE EXPLAIN GLOBAL TECTONICS?

When Wegener first proposed that continents moved, he suggested that astronomical forces drove them. For this he was ridiculed. The force was much too small. In the last edition of his book, he allowed that convective force might be responsible. Despite the rejection and because of the failure to discover a convincing global convective driver, the idea of an astronomical driver has been revisited again and again, most recently by Carlo Doglioni and his colleagues in Italy. The idea of an extraterrestrial westward driving force is compelling in its ability to explain features. Like the idea of continental drift earlier, it will not easily go away.

This poster assumes that the Italians’ arguments effectively address objections regarding viscosity and conservation of angular momentum and that horizontal motions of plates are driven by astronomical interaction. To this I add the notion that subduction at continental margins is the result of independent convective force—an idea perhaps implicit in the notion of an astronomical driver. Consideration of independent horizontal and vertical forces presents a different perspective for global tectonic analysis. Here I look at geophysical constraints and analyze whether some tectonic features may be explained by independent forces. Among the questions considered and answered in the affirmative are these:

• Are rifts mere tears in the crust resulting from differential effect of the horizontal force?
• Can back arc basins can be explained by interaction between the forces where subduction blocks the horizontal motion of the lithosphere and the astronomical force causes a break to the west of the block?
• Once downward convection is triggered, can the astronomical driver push a continental mass over a subduction zone so as to create the subduction-related orogeny we see within continents?
• Does tensional astronomical force facilitate volcanism within arcs where vertical convective motion permits melting?
• Can interaction of convection and independent horizontal movement collapse continents and build mountains as in the Himalayas and Andes?

In the end, a chastened Wegener was certain of only one thing: “The forces which displace continents are the same as those which produce great fold-mountain ranges.” Perhaps it takes two independent forces build the great fold-mountain ranges.