Download Thermal isostasy —a new look at its potential to advance diluvial

Perspectives
Thermal isostasy
—a new look at
its potential to
advance diluvial
geology
Emil Silvestru
Epeirogeny, isostasy and
plate tectonics
L
ong-­term vertical movements of large areas of the earth’s landmasses, particularly cratons (the core areas of most continents, built of continental lithosphere) have been part of geological investigations and models for a long time, well before plate tectonics became the leading paradigm. Moving up and down fault lines (even if they were not visible or detectable) was for most of the time the only explanation, especially when large shallow-­sea sedimentary basins were present inside continental areas, far from the oceans. Alternatively the crustal injection of igneous rocks was invoked as a cause of regional uplift without folding. The term epeirogeny has been used regularly for such movements, being usually coupled with isostasy—the gravitational equilibrium of lighter URFNV µÀRDWLQJ¶ RQ GHQVHU \HW SODVWLF
rock. In plate tectonics that refers to OLWKRVSKHUHÀRDWLQJRQWKHXSSHUPRVW
mantle—the asthenosphere. The crust will sink into the asthenosphere according to its density, heavier rocks sinking deeper than lighter ones. It is therefore expected that if density changes, so will the isostatic position of the crust. Heat is by far the most important source of density variation (assuming the same mineral composition). Rock density is inversely proportional to rock temperature.
Thermal isostasy
Geophysical research1,2 has looked into epeirogeny and isostasy and even managed to quantify thermal isostasy, JOURNAL OF CREATION 26(1) 2012
i.e. how the elevation of the crust (DERYHVHDOHYHOLVLQÀXHQFHGE\WKH
temperature changes (caused by heat ÀRZLQWKHPDQWOHDQGFUXVW,QRUGHU
to achieve that, the compositional effect on isostasy (control of elevation by variation of compositional density of the crust, while assuming the same PDQWOHGHQVLW\KDGWREH¿OWHUHGRXW
There is a marked difference between oceanic crust thermal isostasy and continental crust thermal isostasy. Although oceanic OLWKRVSKHUH KDV D VLJQL¿FDQWO\ ORZHU
lateral compositional variation (making calculations easier) it is affected by ‘heat mining’ i.e. heat loss because of consistent, wide-­spread shallow hydrothermal circulation (the mechanism that creates and fuels hot vents). Surface heat flow measurements therefore are not reliable and bathymetry must also be applied. There are no such processes in the case of continental lithosphere ZKHUHVXUIDFHKHDWÀRZFDQEHXVHG
if a proper model of density and thickness are applied.
The calculations have shown that GRXEOLQJWKHKHDWÀRZLQDQGXQGHUWKH
continental crust in North America will produce ~ 3 km of uplift.1 Conversely, DQ HTXLYDOHQW GURS LQ WKH KHDW ÀRZ
would cause a lowering of the crust of the same order of magnitude. Evidence that the ocean floor rose and dropped suddenly was recently presented for an area north of Scotland, 3 where the sea floor has preserved a complete piece of ancient surface landscape, with valleys organized in a tight and coherent network of hydrographic basins, hills and planes. This unusual feature has been explained by the rapid (“geologic EOLQNRIDQH\H´XSOLIWRIWKHVHDÀRRU
with at least 800 m by a mantle ‘hot blob’. After reaching the surface and being rapidly eroded into a typical landscape, the crustal heat dissipated rapidly, causing a rapid lowering below sea level.
There are two elements of the plate tectonics model to which the above phenomena may apply constructively, namely Large Igneous Provinces (LIP) and Mantle Overturn and Major Orogenies (MOMO). The former represent large areas of the crust LQWR RU RQWR ZKLFK HQRUPRXV ÀRZV
of basaltic lava—RIWHQ FDOOHG µÀRRG
basalts’—have been emplaced in very short geologic times. One of the most famous LIPs—India’s Deccan Traps—
consists of over half a million cubic kilometres of basalt emplaced in less than 30,000 years (from within the uniformitarian paradigm). Much of the original material has been removed by erosion. There are terrestrial LIPs (like the Deccan Traps and the Siberian Traps) and oceanic LIPs (like the Ontong Java Plateau).4 The terrestrial LIPs rocks have not formed by sea floor spreading or subduction. Based on the study of volcanoes on other planets (Venus and Mars) where there is no evidence for plate tectonics (so-­
called ‘one plate planets’) it is now believed that terrestrial LIPs are the result of ultrafast upwelling.5 The reason for this is attributed by some geologists to ‘slab avalanches’5 i.e. massive accumulation of subducted oceanic lithosphere at the base of the asthenosphere managed to break into the more rigid mantle below, causing large overturns in the lower mantle—
MOMOs. The resulting heat plumes ZLOO FDXVH LPPHQVH EDVDOW ÀRZV—
/,3V 7KHUH LV D VLJQL¿FDQW RYHUODS
of LIP episodes and extinctions (most likely caused by repeated peak volcanicity during the Flood), especially of marine creatures as figure 1 reveals. Some geologists5 suspect that what triggered such PDVVLYH ODYD ÀRZV LQ WKH PLGGOH RI
cratons could have been meteorite impacts whose geological signature has been erased by the LIPs.
0202V FDQ DOVR VLJQL¿FDQWO\
amplify dynamic topography,6 which represents the vertical oscillation of the OLWKRVSKHUHEHFDXVHRIKHDWÀRZLQWKH
mantle—the essence of intracratonic epeirogeny. As heat accumulates 13
Perspectives
Columbia River
North Ethiopia & Yemen
Deccan
North Atlantic
Caribbean, Madagascar
30
Otong Java
Karoo & Ferrar
Central Atlantic
40
Siberian Traps
50
Emeishan, Panjal
Extinctions (genus level) %
60
Paraná & Etendeka
Major LIPs
70
References
1. Hasterok, D. and Chapman, D.S., Continental thermal isostasy: 1. Methods and sensitivity, J. Geophysical Research 112:B06414, 2007.
10
2. Hasterok, D. and Chapman, D.S., Continental thermal isostasy: 2. Application to North America, J. Geophysical Research 112:B06415, 2007.
0
3. Williams, C., Pulsating planet, New Scientist 209(2803):41–43, 2011.
20
C Permian
Triassic
Jurassic
Cretaceous
Cenozoic
Age
Figure 1. The correlation between LIPs and extinction of marine biota, according to standard
geological ages (based on data from Coffin et al., ref. 4).
under the thicker continental crust without breaking through it and causing volcanicity (LIP), regional uplift occurs, and conversely, when heat decreases, subsidence follows. Catastrophic Plate Tectonics
and thermal isostasy
All these geophysical processes s e e m t o f a l l w e l l w i t h i n t h e hypothesized conditions at the onset of catastrophic plate tectonics (CPT) and the ensuing global Flood.7 Let us further hypothesize some sort of change in Earth’s core which would have caused massive increase in radioactive decay. Many scientists believe it is radioactive decay in the mantle that is the source of most of the heat that provides the mantle with such a dynamic behaviour. If the decay QDWXUDO QXFOHDU ¿VVLRQ LQFUHDVHG
VR GLG WKH KHDW ÀRZ DQG WKDW FRXOG
have caused massive columns of hot mantle, much larger than mantle plumes today, to rise towards the surface, generating both continental and marine LIPs. Ocean floor underneath these columns would be pushed upwards and the sea level would rise dramatically. The essentially static pre-­Flood 14
hypotheses. It is also my conviction that an integrated, fact-­based model of the Genesis Flood is likely to emerge by including various elements from presently competing diluvial models. lithosphere was thrown into turmoil, with parts starting to slip underneath the continental masses (subduction). It PD\ZHOOEHWKDWWKH¿UVWVXEGXFWLRQ
occurred where the overburden created by submarine LIPs was heavy enough to depress the lithosphere to the subducting point. Being colder, the subducted lithosphere would cause a drop in temperature at the lithosphere/
asthenosphere boundary, resulting in large parts of the landmass subsiding and, combined with the global sea level rise, would end in the complete ÀRRGLQJRIWKHODQGPDVVHV7KHVKHHU
weight of the newly ejected lava onto both continental and oceanic lithosphere is something that needs to be seriously taken into consideration in dynamics calculations. Intensified radioactive decay inside the mantle would have been accompanied by a massive increase in geoneutrino output,8 which would WKHQ LQÀXHQFH QXFOHDU GHFD\ UDWHV9 much more than solar neutrinos.10 This author is very aware of the speculative character of the last few paragraphs. Nevertheless it is in the nature of science to attempt hypotheses whenever new data is available, leaving it to future research to confirm or reject the respective &RI¿Q0)et al, Large Igneous Provinces DQGVFLHQWL¿FRFHDQGULOOLQJ6WDWXVTXRDQG
look ahead, Oceanography 19(4):150–160, 2006. 5. Eyles, N. and Miall, A., Canada Rocks: the geologic journey, Fitzhenry & Whiteside, Markham, Ontario, pp. 50–51, 2007. The most common explanation is that these events represent the interaction of a mantle plume head with the lithosphere. However, there are no documented mantle plumes under some major intracratonic LIPs.
6. Eyles and Miall, ref. 5, pp. 52, 132–134.
7. Baumgardner, J., Catastrophic plate tectonics: the geophysical context of the Genesis Flood, J. Creation (formerly TJ) 16(1):58–63, 2002.
8. Indumathi, D. et al., Neutrino physics: an overview, Proc. Indian Nat. Sci. Acad. 70A± ZZZLPVFUHVLQaLQR
OpenReports/Insa/intro.pdf, Accessed 7 September 2010. 9. Silvestru, E., Neutrinos—the-­not-­so-­neutral particles, J. Creation 24(3):13–14, 2010. 10. Jenkins, J.H. et al., Evidence for correlations between nuclear decay rates and earth–sun distance, Astroparticle Physics 32:42–46, 2009.
JOURNAL OF CREATION 26(1) 2012