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EPSC Abstracts,
Vol. 3, EPSC2008-A-00495, 2008
European Planetary Science Congress, © Author(s) 2008
Irreversible evolution of the terrestrial planets (geological and petrological data)
E. Sharkov and O. Bogatikov
(1) Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry RAS, Moscow, Russia
([email protected] / Fax: +7-495-9511587)
Abstract
Comparative studying of tectonomagmatic evolution
of the Earth and the Moon shows that cardinal
irreversible change in character of tectonomagmatic
processes occurred at middle stages of their evolution;
very likely such changes took place on other terrestrial
planets (Venus, Mars and Mercury). As a result,
primordial crusts of the planets were in considerable
degree replaced by secondary basaltic ones. The
established succession of events on the Earth could be
provided by a combination of two independent factors:
(1) it was originally heterogeneous and 2) its
downward heating was followed by the cooling of its
outer shells. As a result the primary iron core material
was long time remained untouched and was involved
into global tectonomagmatic processes at ca. 2.4-2.3
Ga. We concluded about a similar scenario for the
evolution of Moon and other terrestrial planets.
Tectonomagmatic evolution of the terrestrial planets
(Earth, Venus, Mars, Mercury and Moon) was studied.
What did major stages of their irreversible evolution
occur before they turned into “dead” stone balls? We
discuss these problems on examples of the Earth and
the Moon, which evolution studied the best. According
to modern views, after accretion of these bodies,
magma oceans of some hundreds km deep appeared on
their surface. According to Jeffries [1], solidification of
large molted bodies, because of the difference between
adiabatic gradient in silicate melts (0.3oC/km) and
gradient of their melting points (3oC/km), could be
going only upwards, from the bottom to the surface. As
a result a powerful crystallizing differentiation of the
oceans’ magmas occurred with accumulation of the
most low-melting components to the surface. Due to
different deep of the magma oceans on the Earth and
the Moon, the primordial crusts on these bodies were
rather different: sialic on the Earth and basic
(anorthosite) on the Moon.
Terrestrial tectonomagmatic activity in Archean
and early Paleoproterozoic
Geological evolution of the Earth began ~4 Ga
ago from appearance of Archean granite-greenstone
terranes (GGTs) and divided them granulite belts. The
GGTs consisting of greenstone belts “submerged” in
tonalite-trondhjemite-granodiorite matrix (TTG) were
the areas of extension, uplifting and denudation,
whereas the granulite belts were dominated by
compression, sinking and sedimentation. They were
interspaced by intermediate zones of tectonic flowage.
GGTs mantle-derived magmatism of high-Mg
komatiite-basaltic series and boninite-like volcanics
was located in greenstone belts. It suggests that GGTs
appeared above mantle superplumes of the first
generation, composed by depleted ultramafic material;
granulite belts were formed on places of descending
mantle flows. The situation could be described in terms
of plume-tectonics.
By the Proterozoic the crust became rigid resulting in
formation of rifts, dike swarms and large mafic-ultramafic
layered intrusions. In the early Proterozoic the character of
the tectono-magmatic activity remained almost the same:
cratons separated by greenstone belts appeared in the
place of GGT. The magmatism was dominated by
siliceous high-Mg series (SHMS) forming large igneous
provinces (LIPs). Geochemically, they were similar to the
Phanerozoic boninites but with higher TiO2 and negative
εNd implying an important assimilation of Archean lower
crustal rocks. The SHMS and possible Archean
geochemical analogues of boninites possibly resulted from
the ascent of deep HT ultramafic melts and their
percolation through the lithosphere, like zone refinement,
implying melting at the top and crystallization at the
bottom. This provided large-scale assimilation of upper
mantle and lower crust rocks.
The appearance of large igneous provinces requires
first generation mantle superplumes located beneath them
and consisting of depleted mantle material. Such a
situation can be described in terms of plume-tectonics
typical of the Early Precambrian [2].
Cardinal change in the Earth’s evolution
The cardinal change of the magmatic activity with
appearance in global scale of geochemical-enriched Fe-Ti
picrites and basalts occurred in interval 2.3-2.0 Ga ago.
Such melts was typical for Phanerozoic within-plate
magmatism and linked with thermochemical mantle
superplumes of the second generation, which ascended
from the liquid core-mantle boundary (CMB). Change
of composition of magmatic melts was followed
and, probably, initiated sharp changing in ecological
situation on the Earth’s surface; appearance of oxidative
atmosphere, global glaciations, positive shift in carbon
isotopy in sedimentary carbonates, appearance of
phosphorites, hydrocarbons, and, also, to important
changing in biosphere – prosperity of cyanobacterias,
multicellular organisms, etc.[3].
According to Jeffries model, the superplumes
draw away the heat from the liquid core resulting in its
solidification, which goes upwards and thus provide
the growth of the inner (solid) core. Such a process
relieves big amounts of the fluids dissolved in the melt
and initiates the ascent of the thermochemical plumes.
deformation directed inside the planets after they accretion
finished as a result of materials compaction and shortening
of their sizes which led to acceleration of their rotation
around axes. That wave could reach the interior of the
planets thus heating deep mantle material and generating
first superplumes. Finally, it reached the metallic core,
melted it and produced secondary thermochemical plumes,
which are still active on the Earth.
We suggest that the terrestrial planets were developed
at the same, but shortened scenario, and more quick. At
the Moon the earliest magmatism of highlands were close
to terrestrial early Paleoproterozoic SHMS and at the
boundary 3.9-3.8 Ga was changed by maria magmatism,
close in composition to MORB and OIB. By analogy with
the Earth, we suggest that maria magmatism was linked
with ascending of thermochemical superplumes, generated
Tectonomagmatic evolution of the Moon and other at the lunar CMB, when it’s liquid iron core was yet
existed. Ancient planums on Mars and tesseras at the
terrestrial planets
The study of the samples which became available Venus among vast planides, composed by basaltic flows
due to the American and Russian space missions the can also evidence about two stages of their development.
Moon’s oldest magmatism in lunar highlands is dated Probably, drastic changing of environmental situations on
by 4.4-4.0 Ga. It was characterized by the low-Ti their surfaces, like on the Earth, were also depend on
magnesium suite analogous to the terrestrial change in tectononagmatic activity. Judging on absence of
Paleoproterozoic SHMS [4]. A geological catastrophe magnetic field, their liquid metallic cores (“energetic
analogous to that on the Earth happed on the Moon ca. hearts”) are of no consequence and they are “dead” bodies
3.9 Ga to form lunar maria with signatures of plume now.
magmatism (high-Ti melts, etc). Probably, the lunar
maria are analogues of Earth’s oceans to some extent,
CONCLUSIONS
therefore this stage of the Moon evolution can be 1.The Early Precambrian (Archean, early Paleoproterozoic)
correlated with the continental-oceanic stage of the tectonomagmatic activity on the Earth was different from
Earth’s evolution. In the Venus and Mars, two main the Phanerozoic one: the mean features were granitetypes of morphostructures, which are vast fields of greenstone terranes and their separating granulite belts;
flood basalts, and older uplifted segments with a mantle melt were derived from a depleted source.
complicated topography (tesseras in the Venus and 2. A drastic change of the tectonomagamtic processes
terras in the Mars) possible suggest a two-stage occurred at ca. 2.3-2.0 Ga: the plume tectonic was
evolution of these planets. During the first stage the changed by the plate tectonics, which is still active. Since
primordial lithospheres formed due to the solidification that time the primordial sialic crust has been replaced by
of global magmatic “oceans”. During the second stage the secondary basaltic crust.
the secondary basaltic crust formed due to the ascent of 3. The established succession of events could be provided
thermochemical plume from the CMB. The Mercury is by a combination of two independent factors: (1) the Earth
less studied, however, its relief also suggests two originally was heterogeneous and 2) the downward
groups of morhostructures resembling lunar highlands heating of the Earth was followed by the cooling of its
and maria.
outer shells. As a result the primary iron core material was
long time remained untouched and was involved into
Causes of irreversible tectonomagmatic evolution of global tectonomagmatic processes at ca. 2.4-2.3 Ga.
4. We concluded about a similar scenario for the evolution
the terrestrial planets
Our data show that at ca. 2.5 Ga on the Earth and of Moon and other terrestrial planets.
Work was supported by grant RFBR 07-05-00496.
1.5 Ga on the Moon the tectonomagmatic processes
started to involve previously absent geochemically
enriched material. Where the enriched matter was References
stored, how it was activated and why its participation [1] Jeffries H. (1929) The Earth, 2nd Ed. London:
resulted in such drastic consequences? The established Cambridge Univ. Press,.
succession of events could be provided by a [2] Bogatikov O.A., Kovalenko V.I., Sharkov E.V.,
combination of two independent factors: 1) The Earth Yarmolyuk V.V. (2000) Magmatism and Geodynamics.
originally was heterogeneous, i.e. formed due to the Terrestrial Magmatism Throughout the Earth's History.
heterogeneous accretion and 2) the downward heating Amsterdam: Gordon and Breach Science Publ.
of the Earth – from the surface to the iron core – was [3] Melezhik V.A., Fallik A.E., Hanski E. et al. (2005)
followed by the cooling of its outer shells.
GSA Today, 15 (11), 4-10.
The most probable cause of the centripetal heating of[4] Sharkov E.V., Bogatikov O.A. (2001) Petrology, 9.
the Earth was appearance of zone/wave of heat-generating97-118.
The thermochemical plume matter possessed less
density and could reach shallower depths. The spread
of the head parts led to their active interaction with the
upper part of the ancient lithosphere including the crust.
This, in turn, resulted in crust fracturing, oceanic
spreading, formation and movement of plates,
subduction, etc., i.e. plate tectonics, existed till now.
From this particular time, ancient Earth’s continental
crust began to involved in subduction processes and
interchange by secondary oceanic crust which forms
about 70% of the present-day crust. Thus, during the
period from 2.3 to 2.0 Ga, the tectonic processes and
the composition of mantle melts irretrievably changed
over the whole Earth. This triggered the processes of
plate tectonics which are still active.