Upper astenopshere

UPPER ASTENOPSHERE - THE SOURCE OF HEAT AND NATURAL DISASTERS OF EARTH

Deep heat of Earth has become a component of many countries energy balance, though Earth heat is currently extracted only from near surface sources with the temperatures not exceeding 400;С being insufficient for generating power comparable to that produced by fossil fuel and hydraulic power stations [8]. The above results in hydrothermal resources share of developed countries energy balance only reaching 5 to 10%, This is due to insufficient studies performed on said phenomenon resulting in the key problem of geothermics - "nature of heat flow from Earth depth” is still to be solved. The lack of studies turns into enormous expenses of economic, environmental and, as a result – political nature caused by continuous shortage of conventional energy sources. In particular, this shortage has caused the use of such considerably unsafe energy source as nuclear power. Dramatic experience of recent decades has demonstrated nuclear energy as a “time bomb”, making a number of countries to have given up using nuclear power.  Hence the large scale use of safe, cheap and virtually exhaustless Earth depth heat should become the main challenge for scientists in the nearest future

Deep seismic probing data of Siberian platform are of apparent interest for investigation of said phenomena in order to develop a strategy heat extraction from deep Earth [2]. The obtained data drastically change our ideas on profile of Earth rigid shell bottom resting on “C” geosphere, i.e. on upper astenosphere. The investigation has shown Earth rigid shell in this area being of considerably irregular thickness: 50 to 200 km. (Fig.. 2). Special attention should be given to 300х500 km area located in Nizhnyaya Tunguska middle reach basin. This area features the thinnest (50-80 km) Earth shell and the highest heat flow: >50 MW/m2 [1] (Fig. 2). This area is a central component of huge structure - the so called lithospheric «volcanogenic plume», where volcanic activity was the most prolonged and only stopped in mid Triassic period [7].

Heat flow reduction is observed in the areas with thicker Earth rigid shell (Fig.2). The above example demonstrates clear correlation of heat flow against Earth rigid shell thickness. the thinner the shell, the more intensive is heat flow on the daylight surface.

The area could be converted into a "center of heat and power generation" required for Siberian region featuring unique complex of mineral deposits. Areas similar to Nizhyaya Tunguska zone should be considered as prospective for deep Earth heat extraction. Identification of such areas in other regions shall require temperature measurements combined with deep seismic probing to determine the profile of Earth rigid shell.

Thus, the depth heat of Earth originates from the geosphere below the Earth rigid shell - the so called upper asthenosphere (Fig. 1). Its bottom is found at 410 km below the daylight surface corresponding to geophysical "Leman Boundary" [4]. Upper boundary is uneven, resulting from varying thickness of overlying lithosphere (geosphere “B”) [7]: geosphere “C" may be of zero thickness below the continents, while being up to 300 km thick below the oceans. [6]. This type of geosphere features abnormal heating – up to 1300-1500;C [6]. Such heating seems to be caused by effect of enormous heat flows called "superplumes" [3]. The latter, having emerged close do the Earth internal core, namely in the geosphere “F” [6,7] (Fig. 1) and heated up to 4000;С “burn the Earth mantle through, reaching the upper Earth shells causing thermal effect through hundreds of millions of years” [3].

Starting from the Jurassic period (about 160 million years ago) said effect only impacts the geosphere "C". This occurred due to formation of rigid Earth shell above the said geosphere by that time, having blocked free discharge of heat to the outer space. All heat transferred by superplumes since then started to accumulate in said geosphere causing its abnormal heating. Earth rigid shell is known to be made up of 2 layers. The upper layer, the so called Earth crust (geosphere “A”), particularly its foundation was formed 3,5 to 4 billion years ago, represented by separate slabs (continents in future) up to 40 km thick. Separated, they could not block free discharge of Earth heat to the outer space. The lower layer, the so called lithosphere (geosphere “B”) gradually soldered to the upper layer slabs from below, increasing in thickness and laterally and filling the clearances between slabs. Said process gradually decreased the possibility of heat discharge to outer space. This process came to its end some 160 million years ago, i.e. in Jurassic period, along with complete formation of planetary lithospheric slabs of variable thickness starting from dozens of km below oceans reaching 100 to 250 km below continents. Since then only limited heat could be discharged to open in the areas of incomplete mating of lithosphere slabs. Thus, below the geosphere “B” a planet wide Earth heat accumulation zone has been formed. This is how the main problem of geotermics (nature of heat flow from Earth depth) is solved: geosphere “C” is the accumulator and the main source of Earth heat.

Upper astenosphere is not only a source of heat. Processes within this geosphere may result in recurring disasters as well as planet wide catastrophes. Thus, burial of overheated upper astenosphere below the lithosphere caused drastic changes of planetary climate towards cooling having resulted in mass mortality of cold-blooded giant reptiles and severe reduction of thermophilic flora areal.  Constant inflow of heat transferred by superplumes is still ongoing process causing heat misbalance within this geosphere and resulting in “explosive” processes continuously occurring at the joints of lithospheric slabs Therefore earthquakes are most evidently caused by explosive emissions of excessive heat accumulated within local focal points along lithospheric slabs contact areas. It is confirmed by data regarding spatial location of earthquake focuses [6]. Therefore, earthquakes are the result of instant recovery of geosphere "C" heat balance.

Moreover, enormous stresses of Earth rigid shell caused by excessive heat started causing breaches of its continuity, such as deep faults and tensile zones. Excessive heat penetrating these fractures facilitates formation of magma focuses within geospheres “A” and “B” with its subsequent discharge via central or fissure type volcanoes followed by earthquakes as well.

Volcanic activity and earthquakes often bring dramatic subsequences. Though the availability of such limited possibility of discharging excessive heat is of great use for our planet. As soon as this possibility disappears, i.e. when lithospheric slabs will probably completely close in the nearest geologic future, making up the continuous impermeable shell, the catastrophic explosion will occur.  Then Earth may follow the fate of the planet once existed between Mars and Jupiter and destroyed after the same explosion. Numerous fragments of irregular shape discovered between those planets probably were making up its rigid shell. The largest of those fragments (770 km across) was named Ceres.

That is to say that the things will follow the scenario described in the Jules Verne “The Mysterious Island", his message to the mankind, where the island instantly destroyed by a disaster represents the whole of Earth. There he has demonstrated that all of so called "progress” of humans are worth nothing compared to the power of Nature. Studying this power must become the top priority for mankind willing to secure their existence within the dreadful ocean of space.


Conclusions

1. Geosphere “C", the so called “upper astenosphere” is the source and accumulator of Earth deep heat;
2. Misbalance of heat within geosphere "C" results in explosive processes causing earthquakes and volcanic activity;
3. Development of deep Earth heat extraction methods in order to eliminate energy shortage should become top priority objective of world science in the nearest future.


References

1. A.D. Duchkov et al. Temperature of cryolithic zone and radiogenic heat generation in North Asia earth crust. Novosibirsk. NICOIGGM SORAN publishing, 1994, 143 p.;
2. V.A. Epifanov, R.S. Rodin. Lithosphere bottom profile as definitive factor of trap and kimberlite magmatism arrangement within Siberian platform. Proceedings of sscientific conference devoted to 30th anniversary of YaNIGP CNIGRI AK "ALROSA", Mirny, 1998, pp. 258 - 260;
3. F.A. Letnikov “Degassing of Earth as global self-arrangement process" Proceedings of P.N. Kropotkin Memorial International conference, May 20-24, 2002, Moscow, GEOS, 2002, pp. 6-7
4. Yu.M Pusharovsky, D.Yu. Pusharovsky, Earth mantle geospheres. Geotectonics, 1999, No.1, pp 3-14;
5. Soviet encyclopedic dictionary. Moscow, “Soviet Encyclopedia”, 1984
6. O.G. Sorokhtin, S.A. Ushakov, Genesis of Earth Moscow, MGU Publishing, 2002, pp. 240-258;
7. Yu.M. Fomin East Siberian lithospheric volcanogenic plume. http://www.proza.ru/2011/02/18/1151;
8. M.D. Khutorskoy Introduction to geothermics. RUDN publishing, 1996. 156 p.