Abstract
In the mid-1950s, Alfred Wegener’s long-discarded drift hypothesis was revived by paleomagnetic studies, primarily by comparing results from Europe and North America, with interpretations that a decade later – with emphasis on the North Atlantic evolution, led to the plate tectonic (PT) revolution. But in their later years, the two iconic figures behind this upheaval – Keith Runcorn and John Tuzo Wilson – acknowledged that the sudden change around 1968 had been a complete mistake. Due to a combination of neglected facts and misinterpretation of crucial observations, an entirely new paradigm was needed, Tuzo Wilson (1992) argued. Therefore, it is of paramount importance to look at some of the central scientific problems of the North Atlantic that already existed when PT took root – and none of the critical problems have later been resolved. Based on published data and conclusions from numerous independent and diverse geophysical and geological studies, this paper summarizes the unsustainable situation and points towards a new coherent understanding. It is beyond doubt that the shallow transoceanic ridge – from Shetland to Greenland via Iceland – has variably thick continental crust making it senseless to talk about North Atlantic seafloor spreading. Moreover, along the Mid-Atlantic Ridge there is an abundance of ultramafic mantle rocks and Precambrian metamorphics, while fresh basalts are very rare. Thus, a paleomagnetic source rock for the linear marine magnetic anomalies – a crucial prerequisite for the seafloor spreading model – does seemingly not exist.
Deep-sea drilling in the North Atlantic and elsewhere has shown that the main sequence of deep-marine sediments is of Upper Mesozoic age. This means that the ocean basins must also be correspondingly young. Also, the large volume of the world’s oceans implies that the main volume of water emitted from the Earth’s interior have occurred in tandem with delamination of the crust – with associated isostatic subsidence of deep-sea basins. Progressive gravitative loss of the lower crust (thinning upwards) depends on it having become eclogitized, for which sufficient hydrous pressure apparently is required. The fact that the ocean basins, the bulk of seawater, and the varyingly thin deep-sea crust have late Mesozoic origins imply that surface conditions, crustal constitution and crustal thickness must have been completely different in pre-Mesozoic times. In this respect, modern geophysics and rock evidence suggest that the original pan-global crust must have been continental, and with the Cambro-Silurian higher life forms described as cosmopolitan, it follows that the early surface was relatively featureless and capped by a shallow continental sea of relatively warm water discharged from the mantle. Thus, the early Cambrian expulsion of virgin water flooded a Precambrian surface of weathered and loose blocks, giving rise to the Great Unconformity. Furthermore, the advancing pulse-like water supply with frontal accumulation of eroded rock debris is the likely explanation for the terminal Precambrian and Paleozoic diamictites on the North Atlantic continents and elsewhere in the world. With the assumed late Precambrian and Palaeozoic surface conditions, glaciation seems unlikely, even at palaeopolar latitudes. Therefore, the concept of a “Snowball Earth” is dismissed. The slow outgassing of the Earth and its associated episodic rotational changes can further be seen as providing the main dynamo-tectonic driving forces for Earth history. In that context, brief considerations of two unresolved phenomena –hydrocarbons and Upper Mesozoic metal-bearing black shales are discussed.
