Possibly phase changes of particular primitive minerals?

Hi Richard,

Thank you for your question. Really, I am interested in this problem. Kenoran, Hudsonian, Grenvillian and Pan-African Events in North America coincide with “global” peaks in the U-Pb ages of juvenile matter additions plot after Condie with co-authors. I see the answer in the model of the long-lived supercontinent existed app. from 2.8 to 0.8-0.6 Ga. In this understanding we see, instead of “global” ones, events within single supercontinent. It is easier to imagine that mantle plume (superplume) beneath this continent (supercontinent) can produce such tectono-thermal effects. Juvenile matter was added during and as a result of the within-continent high-temperature events accompanied with granulite-facies metamorphism.

Why these 4 particular episodes? It is unknown, why four … I believe that first one (~2.7 Ga) occurred soon after supercontinent origin, and the last events preceded disruption of long-lived supercontinent and transition to modern plate tectonics.

You can see details of this model in our (Mints and Eriksson, 2016) paper SECULAR CHANGES IN RELATIONSHIPS BETWEEN PLATE-TECTONIC AND MANTLE-PLUME ENGENDERED PROCESSES DURING PRECAMBRIAN TIME. You can find this paper in my page in ResearhGate.

Please, don’t hesitate to ask me more.

Regards,

Michael

Thanks Michael and Norman for comments.

Some very speculative ideas regarding heating and thermal-tectonic Events:

Kenoran Event associated with formation of Archean continental cratons derived from heating of early oceanic crust. Global ocean.

Hudsonian Event with heating and rifting of initial supercraton in Paleoproterozoic (to form linear belts), degassing (GOE) and Superior-type hydrothermally-formed BIFs. Global ocean. Most mixtites not 'glacials' but submarine mass flow deposits.

Grenvillian Event with intense heating and substantial thickening of continental crust in Mesoproterozoic, such that land appeared above the ocean.

(Piper 1983 has one supercontinent before fragmentation in Neoproterozoic).

Pan-African Event with fragmentation of the one supercontinent in the Neoproterozoic. Expulsion of mantle water caused sea level to rise up to Ordovician peak. 87Sr/86Sr ratio for Neoproterozoic indicates erosion of supercontinent (Peters and Gaines) - due to rain? Lower Neoproterozoic sheet flow sandstones from massive continent-crossing water flow systems (Rainbird et al.). Mid-Neoproterozoic mixtites not 'glacials' but submarine mass flow deposits (Schermerhorn 1976).

Hi Michael

Figures 5 and 8 seemed to be missing from your paper on ResearchGate. Also I seemed to miss the caption for Figure 8.

I really enjoy your papers!

Best regards

Richard

Hi Richard,

Thanks for your answer.

Regarding Figures 5 and 8, your comment seems strange. I checked the contents of the file on RG and made sure that everything is OK with these Figures. With regard to the Piper model: in fact, our models of a long-living supercontinent are similar to each other. At the same time, Piper relied exclusively on paleomagnetic data with minimal references to geology. On the contrary, our model is completely based on geological data. All the best,

Michael

Hi Michael

Have got those figures now. Previously had trouble downloading the paper but have it now - computer glitch probably.

Would you please refer me to a concise paper that puts the case for only one Precambrian supercontinent.

Thanks

Best regards

Richard

Hi Michael,

I am one of the multitude of geologists who have absolutely no foundation upon which to comment on Archaen and early Proterozoic geology, —apart from natural curiosity about what happened before the eras of which we have personal experience. (In my case general knowledge from fieldwork on rocks dating from the Cryogenian to the Holocene.) Having clarified that, I found your 2016 linked paper to be a most interesting and profound introduction to the complexities of the subject. I was particularly stuck by your mention that available data show that by ~3.8 Ga, the early Earth had a hydrosphere, and the crust was divided into granitic and mafic domains. This is an image upon which I can build better understanding of a logical sequence of events, which don't depend upon pre-conceived ideas about plate tectonics and mantle plumes projected far back beyond their established realm.

Given an early crust and hydrosphere we can conjecture that the principles of sedimentary isostasy could be applied even in those early times, with metamorphism developing in the deeper parts of oval shaped sedimentary basins. Sinking further, granitisation at the Moho produced a melt that differentiated into basic and acidic magmas. The acidic component would be expelled laterally to cause block uplifts and orogenies elsewhere, whilst the basic components sank to augment the mantle.

Specialists in the Archaean etc. will protest that the range of evidence requires a much more complex explanation. However. my simple mind prefers to begin with a simple image and build layers of complexity on top of that.

Thank you for your link to an excellent paper.

Hi Norman, I am grateful for your interest to our work. In fact, I try to use the data of real geology as a main basis, rocks and structures that can be observed in the field and detailed with the help of modern methods of investigation of minerals and rocks. I am convinced that the basis of any evolutionary models must be a geological map. If there are suitable geophysical data, we are able to rely on a 3-dimensional representation of the geological environment: and not a set of geophysical "heterogeneities." At present, the rapid development of laboratory research methods has entailed a new approach to geological modeling. During a brief geological excursion, the researcher collects several samples, studies these samples in detail and offers models of evolution with far-reaching consequences ... but without a real geological basis. Computer modeling, which today also received powerful tools, is often used to create numerical models, the application of which is not entirely obvious even to their authors. Etc. Thanks again, and all the best, Michael

Hi Richard,

I am sorry to delay my answer.

I'm afraid it's not easy to draw a short article on this complex topic (... a concise paper that puts the case for only one Precambrian supercontinent). I hope you can find a partial answer in my works, mainly devoted to the Early Precambrian history of the East European Craton - alone and together with its North American neighbor. There is much more detail answer in our book (GSA SP 510) and specifically in Chapter 17 of that book. You can find all of them in my page in ResearchGate.

All the best,

Michael

Hello everybody! I want to touch only one side of the problem: Was the Archean Earth really hotter than the modern Earth? This common opinion is based on several whales: long-standing models of the Earth origin from hot star matter; detection of granulites, which were originally considered as derivatives of the hot early Earth; the concentration of komatiites in the Archean; the fundamental law of radioactive decay, according to which this source of heat was several times more effective in the Archaen. We will evaluate these justifications from today's level of knowledge. 1. The Earth is formed as a result of the accretion of cold interstellar matter. The relatively cold environment over 4 billion years ago was recorded by the zircons of Jack Hills. 2. Modern isotope geochronology has placed granulites on all the cells of the geological scale: from the Archean to at least the Paleozoic. 3. The share of komatiites in the greenstone belts is small, 10-20%. But 3.5 Ga ago, the continents had "cold" diamond-bearing roots. Consequently, the temperatures of the Archaean mantle varied considerably. 4. The last. The temperature of the Earth in all periods was determined by the balance of the processes of heat generation and heat loss. Assessing heat loss is much more difficult than heat generation. Therefore, in discussing the temperature of the Archean one should rely on geological data: komatiites, the roots of the continents, terrigenous and chemogenic sediments, which indicate the existence of water basins already in the early Archean, and so on. Any theoretical model must take these constraints into account. All the best to everyone and thank you for an interesting discussion, Michael

Hi Michael

Do you have an English language translation of your 2016 conference paper?:

Neoarchean–Proterozoic supercontinent (2.75–0.9 Ga): An alternative of supercontinental cycles Неоархей-протерозойский суперконтинент (2.75-0.9 млрд лет): альтернатива модели суперконтинентальных циклов

• February 2016
• Conference: XLVIII Tectonic Conference, Moscow, Academy of Sciences, Moscow State University
• At: Moscow Volume: 2
• Thanks
• Best regards
• Richard

Hi Jorge,

Data on the decay parameters of radioactive isotopes in your list are absolutely correct. However, I must insist: the temperature of any medium is determined by the balance of internal heat generation and the efficiency of the heat-release mechanism. It is quite possible to estimate the values ​​of heat generation in different periods of the Earth's life with rather high accuracy. Characterizing the mechanisms of heat release and evaluate the effectiveness of these mechanisms is much more difficult: the uncertainty is too great. Two mechanisms are most likely: (1) conductive heat transfer and dissipation into outer space (insufficiently effective mechanism), and (2) certain versions of convection and displacement to the surface of hot magmas through the system of mid-oceanic ridges and the subsequent dissipation of heat into space. The total length and efficiency of ridges can be estimated only roughly. Metamorphism of sedimentary rocks is another way of utilizing some amount of deep heat flux, the evaluation of which is also very difficult. Therefore, we must refer to geological data. The most important data are: 1) evidence of the presence of liquid water on the Earth's surface about 4 Ga ago: the Nuvvuagittuq greenstone belt contains chemical sedimentary rocks that include a finely banded iron formation (BIF) and a more massive silica-formation (O'Neil et al., 2007, 2011) on 4.3 Ga, and further in the Archean; 2) the existence of "cold" diamond-bearing keels of continents at least to 3.5 Ga (Gurney et al., 2010 and references therein). These data create the boundary conditions for modeling the thermal state of the Earth in the Archaean. For comparison. The powerful nuclear reactors of the Chernobyl and Fukushima power plants have successfully operated in a suitable temperature range, as long as the cooling systems were in good order. The failure in the operation of these systems led to a thermal catastrophe.

Good luck, Michael

Jorge,

Indeed, hot water, but not vapor.

All the best,

Michael