Holmes enters the room and starts talking while still walking.
Holmes: Before we start today, Watson – have you ever heard the expression “Occam’s Razor”?
– Eh, well, I might have. What is the significance of that expression about our musings, Dr. Watson asks.
Part 1: Sherlock Holmes and the Hippopotamus in the Basin
Part 2: Sherlock Holmes applies “meteorology” to geology
Part 3: Sherlock Holmes gets a big surprise from Dr. Watson
Part 4: Dr. Watson on the Coriolis Effect and Drifting Continental Plates
Part 5: Sherlock Holmes Explains the Coriolis Effect on Subduction
Holmes continues: Occam`s Razor is the problem-solving principle that recommends searching for explanations constructed with the smallest possible set of elements.
What we have done is expand on a well-known principle in physics and apply it to a field of science to explain many different phenomena that ought to be affected by this principle. It does not get any simpler than that, Watson. Of course, we should not deny that other additional effects might influence a situation or process. However, the Coriolis Effect should be included when interpreting the geological history of a region.
One more thing that must be considered, Watson: the Coriolis Effect relates to a fixed longitudinal- and latitudinal grid on Earth. You cannot anticipate the effect by using a movable coordinate system or viewing movements relative to a continent or something else that is also moving relative to a fixed grid.
– You are not afraid that real geologists will dismiss our explanations because tectonic movements are so slow and rocks are so solid, Dr. Watson asks.
Holmes: They might. That is the nature and psychology of science, I am afraid. However, a meteorologist named Alfred Wegener is claiming that continental plates ARE moving for some reason, even if rocks are solid. His claims ought to be obvious to anybody; Africa and South America fit together like two pieces of a jigsaw puzzle. Since they are no longer joined together, they must have moved. Nevertheless, not being a geologist, the reception he and his obvious explanation got, is quite predictable.
Holmes asks: To your point on slow movements, do you know what proves this argument wrong, assuming that it was valid in the first place?
– No – I don`t, Dr. Watson replies.
Holmes: Earthquakes.
Dr. Watson stares back at him. His face looks like a question mark.
Holmes:
If you don`t mind Watson, I might add another thing related to the execution of science. You can never prove that a theory within natural science is correct. Although lots of evidence might support a certain theory, the same or other evidence, might also support another theory. The fact that two or more things appear to be related does not prove a cause-and-effect relationship. However, if a theory is valid, more and more observations should be made consistent with that theory – and, importantly; no observations should be made that are inconsistent with the theory.
I would like to mention that the movement of India between ca 30 o S and ca 30 o N would have been affected by the location and behavior of upwelling mantle plumes in addition to the Coriolis Effect due to the northwards movement of India itself. The result is always a composite of different forces as the Coriolis Effect may work on all moving masses in and around a continental plate. Anyway, the oceanic ridges connecting the east coast of Madagascar and western India initially deviate westwards before crossing the Equator where they deviate eastwards. If the ridges are related to the position of western India during its northward drifting, it would be consistent with our theory.
With that said, we will leave it to the professionals to sort out the movements of India.
Before we wrap up everything Watson, I would like to mention other geologic processes related to the Coriolis Effect.
The first process worth mentioning is mantle delamination or mantle dripping. You see, – continued exposure of the upper mantle and lower crust from the fluids and heat provided by an upwelling mantle may in some instances lead to mineral reactions whereby the rocks are sorted into dense and less dense mineral phases. This may create “downwelling” of the dense phase. If downwelling occurs as a large continuous mass, it might rotate clockwise on the northern hemisphere while creating a downward suction as it descends. The suction might even pull the crust downwards for a period until the effect is canceled out by an upwelling mantle replacing the descended volume. Another similar situation may occur if a subducting slab is torn off and descends into the mantle.
In sum, these two processes may create down and up movements of the crust, that might seem quite confusing when trying to interpret the evidence left behind.
The Coriolis Effect on all of this might also be quite confusing if observable in the fault patterns of the upper crust. In general, the most recent and most elevated process might leave the clearest indications of its former presence.
The second process that I would like to return to is retreating subduction zones. They might even be closely related to the phenomena I just described to you. Do you think that they might persist in eastwards dipping subduction zones – or even northwards- or southwards dipping subduction zones, Watson?
– Well Holmes, Dr. Watson explains, that would require some mechanism acting within the crust or upper mantle that is capable of bending the subducting slab backward from its initial direction. I guess such bending might be possible if the overriding plate for some reason pushes the subduction trench and the slab backwards. However, only in a westwards-directed subduction would the slab be deviating eastwards due to the Coriolis Effect. In other directions, the same effect would tend to flatten the slabs or tear them sideways.
– In the end, the long-lived retreating subduction zones should include slabs oriented steeply westwards with a subduction trench retreating eastwards. As discussed before, this occurs because during descent, westwards subducting slabs move into deeper regions that are rotating slower than the surface and therefore cause the slab to deviate eastwards as it descends.
Holmes: Indeed Watson, but what happens to the western side of the subduction trench if the trench retreats eastwards? Moreover, what happens if the initial direction of subduction is not truly westwards, but northwest-, or southwest-oriented?
– That sounds complicated even to me Holmes. Still, I guess the answer to your first question might be the creation of a so-called back-arc basin with evidence of upwelling mantle and rotational movements, volcanism, and accretionary crustal rocks, that is, if the subduction zone involved continental rocks. Upwelling of the mantle would certainly have to occur to fill in the void behind the retreating slab.
– Your second question is even more complicated however, the answer might probably be found in nature.
Dr. Watson continues:
At present, we have two retreating subduction zones on the northern hemisphere beginning their subduction history by subducting in a southwestern direction. In the southern hemisphere, we have a third that began subducting to the northwest.
The Carpathian and the Caribbean subduction zones are retreating with the present direction of the slabs pointing westwards while retreating due east. They both started with southwestern-directed slabs. The third case is the Scotia subduction zone. It is presently located in the South-Atlantic retreating due east after initially subducting towards the north-west.
There is also evidence of several retreating subduction zones in the Mediterranean turning eastwards after initially retreating in a southwestern direction.
To understand the reason for this, we have to combine what we discussed earlier about plate and slab movements in different directions. As usual, we look at the northern hemisphere. In our scenario, the southern plate is moving both northwards and eastwards as it is pulled into the subduction trench. We assume that the dip angle of the subducting slab is steep enough to bring it into regions rotating slower than the surface velocity. Thus creating eastwards deviation both from the N-S-, and E-W-directed components of the slab movement.
In my drawing Holmes, I have illustrated the advancing plate in black and the subducting plate in green. The movement of the advancing surface plate is shown using black arrows. The initial northwards component of the plate movement causes eastwards deviation while rotating clockwise. This would tend to rotate the subduction trench clockwise during retreat. The eastwards component will not create a Coriolis Effect on the surface plate, however, that is not the case for the subducting slab itself.
The Coriolis Effect will influence the subducting slab along two different axes. The effects caused by the N-S-component of the movements are shown using blue symbols and the influence of the E-W- component of the movement is shown in red.
In combination, this would make the subduction trench expand northwestwards while turning clockwise over time. As observed in our real examples, after millions of years, the subduction trench might look like a clockwise-distorted letter U, with the opening at the location of the initial retreating subduction trench.
– As the subduction trench is pulled back, or as slabs are torn off and sink in, the mantle will rise to fill the voids. A rising mantle in the northern hemisphere would rotate in a counter-clockwise direction. This might become visible as a distinct pattern of strike-slip faults in continental crusts or transforms in oceanic crusts. That is my take on a relatively complex set of questions from you Holmes, Dr. Watson finishes.
Holmes is getting ready to proceed with the drinks that are now ready:
Before we finish off with some concrete evidence in support of our discussions, I would like to present my conclusion to the matters we have discussed.
First, I would say that the geologic community is missing three things that are crucial to the understanding of tectonics and structural geology in general.
The three things are – Watson, – hold on to your chair: Water, Water, and the Coriolis Effect.
Water makes the mantle expand and become buoyant, and less viscous, and allows the upwelling of it. Hence, water is responsible for the crustal uplift and therefore the extension of it that leads to normal faulting, erosion, and crustal thinning in the area later to become a basin with a hiatus and deep-seated wrench faults in the basement due to the rotating mantle.
Water is also the “mostly unknown” element that when it escapes from the mantle, brings with it many different dissolved elements. However, the property most overlooked by the geologic community is the fact that water and dissolved elements have volume and mass. If this volume and mass ascends from a location within the mantle to the surface and settles there, it might create solid deposits above – and subsidence of – the original surface with minimal changes in isostasy. Without taking into account the possible escape of volume and mass from the mantle, isostasy calculations and subsidence models in basins will yield incorrect results. I might also add that heat models of such basins will end up being incorrect during periods due to the massive heat transport related to the volume/mass ascending from the hot mantle.
Without taking into account the escape of mass and volume from the mantle, salt deposition in rift basins or intracratonic basins might be calculated to have occurred at 1-3 km below sea level, something completely incompatible with solar evaporation.
To illustrate what this loss of volume from the mantle might mean for possible sediment buildup in an intracratonic basin, let`s consider the Pre-Caspian basin, Watson. You do remember our U-tube experiments. Let`s do some more of them.
The Pre-Caspian basin is ca. 20 km deep in the deepest sections and is filled with salts and sediments. The average salt thickness in the Pre-Caspian basin may be estimated at 2.5 km (4-4.5 km in the center and 1-2 km at the rims). If we assume that this salt was ascending as a brine with 3 times more water volume than salt volume (A brine salinity of ca. 40 wt. %), the loss of volume in the mantle would be equivalent to 10 km in elevation on average. To this loss of volume, we might add 1 km subsidence due to localized erosion during the uplift phase before loss of mantle volume. Relative to the surroundings, this yields a total of 11 km of possible subsidence of the basin floor caused by “volume loss”.
If we assume that the water has escaped from the region and that the basin is filled with sediments (of density 2 g/cm3 on top of a mantle with density 3 g/cm3) to regain isostatic balance, this would be achieved after filling in (11-2.5) x 3/2 km of sediments in addition to the salt. This is equivalent to 12.75 km of sediments. This implies an average lowering of the basin floor by more than 15 km. After thermal cooling and contraction of the mantle, the basin might subside even more.
How about that Watson, as a model for creating ultra-deep, intracratonic basins?
I have not forgotten my third point, Holmes adds; the Coriolis Effect is what creates the systematic fault patterns – and the somewhat unexpected behavior when continental or oceanic plates are subducting, drifting, or subjected to the movements caused by mantle upwelling. The understanding of the Coriolis Effect will enable geologists to better understand what processes preceded the present status.
– Very good indeed, Holmes. The drinks you promised have arrived and we have to make a toast to celebrate this endeavor, Watson says in admiration.
– However, might I also add a conclusion?
Holmes, awaiting the final verdict: By all means, Watson.
Dr. Watson raises his glass and states with a solemn voice:
– We have turned major parts of geology upside down – and given it a twist! Cheers and congratulations!
Holmes: Indeed, Watson. Cheers!
After recovering from the celebration, Holmes manages to add:
Before you leave for bed Watson, I would like to provide you with some snippets and references that are related to some of the subjects we have touched on. I am confident that you will find them interesting. Let me know if you need more.
HANS K JOHNSEN
Inspired by Arthur Conan Doyle
Mantle upwelling and crustal uplift/extension
Ten major rift zones on Earth were investigated by Esedo et al. All of them were found to have been uplifted by 1-3 km by mantle upwelling before rifting. Esedo et al. also explain the influence of mantle delamination and the role of water in the rate of mantle movement, albeit without taking into account its volume, mass, and potential escape about subsidence and isostasy. No rotation of the upwelling mantle is reported in their article:
Esedo, R., Van Wijk, J., Coblentz, D., Meyer, R., 2012, Uplift before continental breakup: Indication for removal of mantle lithosphere? Geosphere, 8, no. 5, 1078–1085, doi:10.1130/GES00748.1.
Wannamaker et al. investigated a zone of present mantle upwelling next to a 1.7 -1.9 billion years old subduction zone, in the Great Basin – Colorado Plateau transition, Utah. They observed uplift, saline fluids in the upper mantle and crust, and extensional faulting allowing the flow of conducting/saline fluids to the surface. Indication of mantle downwelling was also observed:
Wannamaker, P. E., Hasterok, D., P., Johnston, J., M., Stodt, J., A., Hall, D., B., Sodergren, T., L., Pellerin, L., Maris, V., Doerner, W., M., Groenewold, K., A., Unsworth, M., J., 2008, Lithospheric dismemberment and magmatic processes of the Great Basin – Colorado Plateau transition, Utah, implied from magnetotellurics, Geochem. Geophys. Geosyst., 9, Q05019, doi:10.1029/2007GC001886.
Rotation of upwelling mantle
The counter-clockwise rotation of the Fiji Island is described in:
Begg, D., R., Gray, G., 2002, Arc dynamics and tectonic history of Fiji based on stress and kinematic analysis of dikes and faults of the Tavua Volcano, Viti Levu Island, Fiji. Tectonics, vol. 21, NO. 4, 1023, doi:10.1029/2000TC001259.
The Tatra Mountains are located on top of an upwelling mantle behind the retreating Carpathian subduction zone. Counter-clockwise of the Tatra Mountains have been reported by:
Szaniawski, R., Ludwiniak, M., Rubinkiewicz, J., 2012, Minor counterclockwise rotation of the Tatra Mountains (Central Western Carpathians) as derived from paleomagnetic results achieved in hematite-bearing Lower Triassic sandstones, Tecnophysics, 560-561, 51-61 http://dx.doi.org/10.1016/j.tecto.2012.06.027.
The counter-clockwise rotation of the upwelling mantle in Turkey’s subduction zone is described by:
Güvercin, S., E., Konca, A., Ö., Özbakır, A., D., Ergintav, S., Karabulut, H., 2021, New focal mechanisms reveal fragmentation and active subduction of the Antalya slab in the Eastern Mediterranean, Tectonophysics, Volume 805, 2021, 228792, ISSN 0040-1951, https://doi.org/10.1016/j.tecto.2021.228792
Some comments on Antarctica
The properties of mantle and crust in Antarctica has been investigated by Wiens et al. They observe mantle upwelling and rifting parallel to the Trans Antarctic Mountains ending in the Ross embayment – as predicted by movement of Antarctica while being subjected to Coriolis Effects; “The western side of the Ross Embayment accommodated almost 100 km of extension from 40 to 26 Ma associated with plate motion between EA and WA”.
Wiens, D., A., Shen, W., Lloyd, A., J., The seismic structure of the Antarctic upper mantle. From: Martin, A. P. and van der Wal, W. (eds) 2023. The Geochemistry and Geophysics of the Antarctic Mantle. Geological Society, London, Memoirs, 56, 195–212 https://doi.org/10.1144/M56-2020-18.
A few notes on intracratonic basins
Many investigators have proposed models for the formation of intracratonic basins as they sometimes are exceptionally deep and filled with relatively light sediments that normally would not make the base of the basins descend to the observed depths. Uplift before basin formation is observed. One of the common problems is fitting the direction of strike-slip faults with their suggested, compressional model for the uplift. Many authors document initial extension in the area, a thinned basement due to erosion, the presence of metamorphic rocks, and volcanism, thus indicating the presence of an upwelling mantle and fluids. Episodic subsidence is often observed, and interpreted to be caused by metamorphic processes and cooling/contraction of the mantle. The fact that many intracratonic basins never had access to the sea, and nevertheless are hosting major salt deposits is largely overlooked. The role of fluid volume and mass having escaped from the mantle is not mentioned in subsidence and isostasy. See:
Akhmetzhanov, A., Zholtayev, G., Djeddou, A., Akhmetzhanova, G., Oraz, B., 2020, Post‑salt trapping mechanism of south‑east Pre‑Caspian and its application to petroleum exploration, Journal of Petroleum Exploration and Production Technology (2020), 10:2645–2653https://doi.org/10.1007/s13202-020-00971-9
Middleton, M., F., 1980, A model of intracratonic basin formation, entailing deep crustal metamorphism, Geophys. J. R.asfr. SOC., (1980) 62, 1-14
Bender, A., A., 2000, Mechanisms of intracratonic and rift basin formation: Insights from Canning Basin, Northwest Australia, PhD thesis Columbia University. UMI Number: 9970148.
Crosby, A., Fishwick, G., S., White, N., 2010, Structure and evolution of the intracratonic Congo Basin, Geochem. Geophys. Geosyst., 11, Q06010, doi:10.1029/2009GC003014.
Ewing, T., E., 2019, Tectonics and Subsidence in the West Texas (Permian) Basin: A Model for Complex Intracratonic Basin Development, Search and Discovery Article #30606 (2019), DOI:10.1306/30606Ewing2019
High-temperature salt deposits without traces of marine life indicate mantle source
Machado (2020) applied the concepts of biostratigraphy to salt accumulations. This was performed by sampling sections of salts/anhydrite and carefully dissolving the salts to observe what living organisms had been trapped in different layers of the salt. The examined locations were:
Loulé salt mine in southern Portugal, in the Early Jurassic, mobile salt. Impure halite, coaly shales, and dolomitised/silicified gypsum were sampled.
Souss-Massa salt mine in Morocco – an Early Jurassic non-mobile salt, where core samples from halite and shales were obtained.
Wieliczka salt mine in southern Poland, which comprises Miocene mobile salt. Several types of salt and interbedded shales were sampled.
Zechstein salt in northern Poland, where red and grey shales, impure black halite, dolomites, and black shales were sampled.
Santana gypsum quarry in central Portugal, where outcrop samples of recrystallized and re-precipitated gypsum and primary gypsum were obtained.
The conclusion from this study is:
«Overall, assemblages are dominated by spores and pollen and other terrestrially-derived organic particles. This suggests that the salt was being deposited or formed in a terrestrial environment or that seawater was only sporadically present. Normal seawater conditions – notably salinity – were probably not the norm as dinoflagellates and other marine organisms are either very rare or absent in all the studied samples».
This conclusion is quite surprising if the evaporation of normal seawater was the source of these varied salt accumulations. The results from this study therefore confirm that other processes might be involved – for example, hydrothermal processes. See:
Machado, G., 2020, Salt Biostratigraphy in Oil and Gas Exploration: An Untapped Source of Data? Geoexpro, vol 17, No. 1
Tobola, and later Tobola and Wachowiak studied different minerals found in the salt within the Klodawa salt mine in Poland and concluded that they had formed at temperatures consistent with high-temperature, hydrothermal conditions:
Tobola, T., 2016, Inclusions in anhydrite crystals from blue halite veins in the Klodawa Salt Dome (Zechstein, Poland), Geological Quarterly, 60-3, 572–585.
Tobola, T., Wachowiak, J., 2018, Evidence of high-temperature rock salt transformations in areas of occurrence of borate minerals (Zechstein, Klodawa salt dome, Poland), Geological Quarterly, 62-1, 134–145.
Subduction zones retreating eastwards
The Carpathian subduction zone development has been described in detail by many authors. See:
Matenco, L., and D. Radivojević (2012), On the formation and evolution of the Pannonian Basin: Constraints derived from the structure of the junction area between the Carpathians and Dinarides, Tectonics, 31, TC6007, doi:10.1029/2012TC003206.
The Caribbean subduction zone history is described by:
Braszus, B., Goes, S., Allen, R. et al. Subduction history of the Caribbean from upper-mantle seismic imaging and plate reconstruction. Nat Commun 12, 4211 (2021). https://doi.org/10.1038/s41467-021-24413-0
A description of the development of the Scotia subduction zone is presented by:
van de Lagemaat S., H.A., Swart, M., L., A., Vaes, B., Kosters, M., E., Boschman, L., M., Burton-Johnson, A., Bijl, P., K., Spakman, W., D., J., J., van Hinsbergen, 2021, Subduction initiation in the Scotia Sea region and opening of the Drake Passage: When and why? Earth-Science Reviews, https://doi.org/10.1016/j.earscirev.2021.103551
Eastwards retreating Mediterranean subduction is reported in:
Rosenbaum, G., Lister, G. S. and Duboz, C. 2002. Reconstruction of the tectonic evolution of the western Mediterranean since the Oligocene. In: Rosenbaum, G. and Lister, G. S. 2002. Reconstruction of the evolution of the Alpine-Himalayan Orogen. Journal of the Virtual Explorer, 8, 107 – 130