Karl W. Luckert, 22 September 1997

In April of 1997, in GSA Today, Stephen P. Grand, Rob D. van der Hilst, and Sri Widiyantoro published a treatise on "Global Seismic Tomography: A Snapshot of Convection in the Earth." A parallel essay by van der Hilst, Widiyantoro, and E. R. Engdahl, "Evidence for deep mantle circulation from global tomography," appeared in Nature (vol. 386, 10 April 1997). Both articles add up to an epoch-making breakthrough in our knowledge about tectonics in the Earth’s interior. Then, in a well-written summary in Science News, vol. 152, 19 July 1997, Richard Monastersky popularized this scientific breakthrough by way of metaphorically renaming the Earth’s mantle as a "Global Graveyard."

A major feature of this scientific breakthrough is the fact that two different methods—one calculating on the basis of seismic P-waves, and the other on the basis of S-waves—have produced encouraging similar results. So, regardless of what from here on I might write or say on that subject, I heartily congratulate these scientists for their accomplishment, for having opened a new window to the interior tectonics of our planet. This feat, as it now stands, secures them a place of honor in the annals of science. I wish to go on record as having said this, because I believe that the larger contextual framework upon which these scientists have based their broader interpretations is doomed to be revised in the near future. I welcome their "global seismic tomography" even while I have serious doubts about whether they actually have given us the "snapshot of convection in the Earth," which they claimed, or have demonstrated "deep mantle circulation."

The most popular branch of Plate Tectonics today happens to be the one that concerns itself with Monastersky’s "global graveyard" and with all the types of geological burial that are possible therein. Upon recognizing ocean floor spreading, scientists who work on that "graveyard" solve the problem, of getting excess ocean floor, by way of postulating (1) convection currents in the mantle, (2) subduction of ocean floor crust down into the mantle, and (3) underthrusting continental crusts with cooled ocean floor slabs, so as to heave up mountain ranges along the continental peripheries. The tricky business of obtaining a crust light enough to float and lift up those mountain ranges, which at the same time is heavy enough to dive all the way down to the core, is generally left to the care of hypothetical convection currents.

Indeed, the new tomographic cross-sections of the mantle reveal "slabs" of denser materials that seem to slant downward, and some of these reach as deep as the core-mantle-boundary. Or are they slanting upward? The fact that such configurations of denser material exist anywhere in the mantle seems, from the point of view of the prevailing "graveyard" theory, to be sufficient evidence for convection, subduction, and everything that goes with these notions.

My counsel however is to suspend judgment on these matters until a few more of the pros and cons have been sorted out. The standard philosophical method for checking scientific propositions calls for an application of the "principle of falsification." This test should have been applied all along, as a matter of course. (1) Where in the mantle should "downward moving ocean floor slabs" be expected to appear in the tomographic cross-sections, relative to continental coastlines? Occurring at what places can they legitimately be suspected of having been subducted? And (2) once the subduction sites have been identified, can we actually perceive some kind of corresponding motion at these places? And finally, (3) to apply the razor’s edge, if for some reason our data should not fulfill expectations (in science we should remain open to opposite possibilities to the very end), where and how would the slabs have to be located to indicate an absence of subduction? If all possible data are eligible to prove subduction, then what might the word "subduction" mean in the end?

Let me illustrate what I mean, on hand of the now famous "Farallon Slab" cross-section (GSA Today, April 1997, Fig. 1). We are told that it descends, right under the middle of North America. Are subduction slabs supposed to be under the middle of continental crusts? (I am fully aware that Fig. 3 is supposed to solve this problem). And then, at the far left of the cross-section, where underthrusting is supposed to happen right now, no freshly cooled plate is seen underthrusting. And yes, there appears a small "tail" under the north-west Atlantic. Is it a slab actually going down? Or, how would it look different if it were merely a tail dragged along by the lithosphere? And the "Farallon Slab" itself, is it a high-density unit that is actually descending, or what would its image be if it were a remnant "tail" of the 200 million year old mantle that was torn loose from its moorings when continental crusts were being lifted outward by the expanding mantle magma?

The Central American cross-section (Nature, vol. 386, Fig. 5a) is inconclusive, at best. The continental crust in this area is too narrow to be useful for general hypothesizing about subduction. Moreover, like the great Farallon Slab in the North American cross-section, it too fails to show contact with a cooled Pacific ocean floor slab. Such a one is supposed to be subducting there at an angle.

The strongest case that can be made for a "subduction slab," among the evidence presented by the tomographers so far, is a blue configuration that reaches downward from Central Japan—from the area of a well known deep ocean trench (Nature, vol. 386, Fig. 6). The problem remains, however, that this slab appears forked at the higher elevations. While its eastern branch touches the crust of Central Japan, its western branch connects, like the stem of a mushroom, with the dense substratum of the Asian lithosphere. At the lower end, near the core, the combined stem appears rooted in a broad base of the same dense materials. If, as I have long believed, the Sea of Japan is a tensile feature in our planet’s lithosphere (as are the other seas along the eastern coast of continental Asia), then the bifurcation of the stem underneath that expansion zone would, in all probability, rule out a process of subduction. Two "subduction plates," coming together for their descent in this manner, would be something remarkable to ponder, indeed. How could such descending slabs have gotten connected with the basements of continental portions in the first place?

Most of the dense "slabs" which have been identified tomographically as potential evidence for subduction, are being found underneath continents. The upper mantle regions under the oceans, where subduction is supposed to happen right now, are relatively free of them. In this manner, and so far, the overall pattern of tomography supports a model of Expansion Tectonics better than it supports the popular notions of convection currents, subduction, and underthrustment.

According to the Expansion Tectonics model, some 200 million years ago the dense "blue" materials made up a smaller mantle around the core, of an Earth roughly 55 to 60 percent its present size. Then gradually, around the planet’s core and in the mantle, nuclear and chemical reactions began fluffing up the material—to increase mantle volume, to make portions of it less conductive (to make tomography work). This fluffed up material still is dense enough to prevent the relatively harder columns of mantle materials, as well as the harder slabs of continental crust overhead, from sinking back down toward the core. All blue features in these tomographic cross-sections, including the continental crusts, might therefore be older mantle materials that have been lifted upward, more or less efficiently, by mantle expansion. Near the core we find the "roots" of continents, whereas overhead, underneath continental crusts, dangle their truncated appendages or "tails." Only the largest and most stable of the continents appear to have some of their root lengths still intact. The others had them torn or twisted off.

Over several years I have been pondering the evidence available in ocean floor chronology, which corroborates my theory of Expansion Tectonics. I have discovered that all three deep oceans—Atlantic, Indian, and Pacific-Antarctic—exhibit orderly sequences of chronological zones from the Jurassic to the present. And together these zone sequences establish the fact of expansion that has occurred in the mantle during the past 200 million years. Now I am prepared to show as well how my conclusions are supported by the new global tomography.

The basic scientific article which presents my theory of Expansion Tectonics was published under the title "A Unified Theory of Earth Expansion, Pacific Evacuation and Orogenesis," in Theophrastus’s Contributions to Advanced Studies in Geology, 61-73, Athens, Greece, 1996. My Warsaw lecture on "Expansion Tectonics" (1 June 1996) was released in its final video format in December that same year, by LUFA Studio. It presents simulated animation of the formation of the deep oceans, based on the ocean floor chronology that had become available in 1988 in the UNESCO Geological World Atlas. Essentially the same ocean floor data have been summarized in "Age of the Ocean Floor," a NOAA map (Boulder, CO, October 1969).

Sooner or later the tomographers will have to correlate their cross-sections of the Earth’s interior with the ocean floor chronology at the surface. The latter has been obtained in an equally scientific respectable manner, by the Challenger Ship project. A correlation with Expansion Tectonics will in the longer run become unavoidable. But even with the limited published tomographic data that are now available to me, I venture to predict that some kind of Expansion Tectonics will be vindicated as tomography is being refined. If certain cross-cuts from around the globe are chosen for tomographic treatment, strictly with the Expansion Tectonics model in mind, I am confident that the results will astonish. Continental roots near the core, and trailing tails beneath continental crusts, will indicate the direction of their expansion movement—their rising, their twisting, their twisting off, as well as the distances of horizontal drifting. There has been far less horizontal movement than most earth scientists presently anticipate. According to my 1996 simulated video model (anticipated already in 1979), only the Antarctic plate and the Australian/New Zealand plate have experienced appreciable horizontal movement relative to the positions of their roots near the Earth’s core.

The published tomographic materials are still rather limited with regard to the Antarctic plate, as such. But they are amazingly suggestive regarding the path of Australia’s movement. My demonstration from here on will be based on figures 1b-f and 6a-b, in Nature, vol. 386. It will also be based on my video simulations in Expansion Tectonics (LUFA Studio, 1996). A rudimentary version of thumbnail images of this process—with perhaps enough detail to illustrate my present point—can be seen at the top two rows of globes in the homepage of my web site kwluckert.com.

According to my theory and simulations, the tip of South America and the bight of Australia were still together in pre-Eocene times. Mantle expansion then broke the two continents apart. This happened at the same time when mantle expansion sprung loose the Antarctic Plate from the western shore of the Americas. While the Australian plate quickly put distance between itself and the tip of South America, the Antarctic plate slid "southward" through the gap, bumping its rear against the tip of South America, and subsequently twisting itself free by the size of the Scotia Sea, into its present position. All the while Australia, when the Austronesian tension pulled it northward, drifted for a while east into the low-density area that was being vacated by the southbound Antarctic plate. The eastern boundary of the Australian plate is still visible today at the Tonga Trench . Some Cretaceous stretches of ocean floor were pushed "eastward" by the Australian plate far enough to touch the back of the slowly turning Antarctic plate. Thereafter the Australian plate adjusted itself westward, and probably still is doing so today. This entire process is on record, simulated and explained in my 1996 video lecture titled "Expansion Tectonics."

Now we are ready to turn for substantiation of my theory to the new global seismic tomography. On the formentioned figures (1f and 6b) one sees, at 2750km depth, the blue root of Australia down near the core—precisely at the place where I have shown it in my animations. At the 2000km level the tail of Australia (probably severed from its root by then) comes into view to the east of the continent (Fig. 1e). The column of dense blue then rises to the 1300km level (Figs. 1d and 6a) and slants westward as the continent dragged the column’s top end along its westward path. Somewhere along that last stretch of movement there appears to have been another partial break in the column. A detailed description will have to await the publication of full tomographic cross-sections from that region.