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Introduction to Geomorphology
Prof. P. K. Mani ,BCKV
At the beginning,,,At the beginning,,,
Matter + antimatterMatter + antimatter
Matter has the advantageMatter has the advantage
baryonsbaryons quarks, leptons,quarks, leptons,
electrons, photons (noelectrons, photons (no
protons or neutrons)protons or neutrons)
Hydrogen, helium (1:10 H:He)Hydrogen, helium (1:10 H:He)
ORIGIN OFORIGIN OF
What is the Solar System made of?
What is the relative abundances of the various elements throughout
This turns out to be a difficult task for one obvious reason. Spectroscopic
measurements of elements from the distant stars are strongly biased
towards only those elements in excited states at or near the stellar
surface. Those elements principally in the interior do not contribute to
surface radiation in the same proportions as actually exist in a star.
The situation is better for the Sun.
When element distributions are stated as Cosmic Abundances, they
actually are rough estimates made from Solar Abundances .
What is the Solar
System made of?
From the figure, we see four patterns:
An overwhelming abundance of
A strong preference for even-
A peak in abundance at iron,
followed by a steady decrease.
Elements 3-5, Lithium,
Beryllium and Boron, are very low
These patterns have to do with
formation) in the stars.
Importance of Solar system in terms of geology
Spectroscopic observation indicates that the relative abundances of different
elements are about the same in every part of the Universe. The most striking
feature is extreme abundance of H (5.1 x 108
atoms of Si) and He
atom of Si) while Oxygen is also quite abundant (2.8 x 106
atom of Si)
Composition of the Earth
For the composition of interiors of planets we must fall back on analogy with our own
planet and the meteorites are classified as
(i) Siderites ( about 98% metal, mostly Ni, Fe)
(ii) Siderolites(stony irons, about 50% metal and 50% silica)
(iii) Aerolites (stones)
(a)Chondrites- Due to presence of chondri which are small rounded bodies
consisting of Olivine, pyroxenen and sometimes the glass (12% Ni , Fe combined,
46% Olivine, 28% Hypersthene, 4% Diopside, 11% Plagioclase)
(b)Achondrites( Do not contain any chondri)
(iv) Tektites: Glassy metorites about 70% Si
According to Goldschmidt, average composition of meteorites are
Triolite - 7.7%
Metal Ni-Fe - 15.4%
On the basis of the studies by Farington and other evidence, Daly concludes that
meteorites originated by the disruption of a planet early in the evolution of solar
system situated between Mars and Jupiter. In the region now occupied by Asteroids.
Meteorites and terrestrial matter differ from stellar materials in the relative scarcity of
gaseous elements but this can be explained by in terms of physical condition
associated with the origin of the solar system.
The variation in lighter elements like H, He, Li, B, N in different part parts
of the universe is due to their participation in thermo nuclear fusion responsible for
From the analysis of abundance data, first compiled by Goldschimdt and
then Corrected by Urey. The following facts come out
(i) the abundances show rapid exponential decrease for elements of the lower
atomic number (Z=30) followed by an almost constant value for the heavier
elements . Elements of even Z are more abundant than those of odd atomic No (Z)
on either side - -----Oddo Harkins Rule
The Oddo-Harkin’s rule
ElementsElements Wt. %Wt. %
(1)(1) H, He, Li, Be andH, He, Li, Be and
B (the lightest fiveB (the lightest five
elements) do notelements) do not
obey the ruleobey the rule
(2)(2) Fe is higher andFe is higher and
Sc is lower thanSc is lower than
(3)(3) Check otherCheck other
Even atomic numbered elements are more dominant
than the adjacent odd numbered ones
The relative abundances for elements of Z> 28 vary less than those of
elements of lower Z.
Only 10 Elements H, He, C, Na, O, Ne, Mg, Si, S, Fe all with Z less than 27
show appreciable abundance although H and He are far out way the other
The above regularities suggest that absolute abundance of elements
depends upon the nuclear rather chemical properties and are related to
inherent stability of the nuclei.
Of more than 1000 isotopes only 270 are stable (non Radioactive). The
elements with Z= 43, 61, 85,87, all having odd Z are completely absent in the
earth. Due to complete instability of any nuclear arrangements for this proton
nos. The light elements Li, Be, B are very rare due to the fact that the nuclei
are most readily disintegrated by bombardment with α-particles as well as
The number of stable nucleii having (even Z and even N) are 163 much
greater than stable species (even N + odd Z; 50) ≈ (odd N + even Z; 55) and
very less than ((odd Z+ odd N); 4, H(1,1), Li(3,3), B(5, 5), N(7,7))
Structure and composition of the earth
To obtain some understanding
of earth’s internal structure we
must use an indirect approach.
Much information is derived
from the analysis of earth
Among the waves of the
various kind, two main types-
the faster primary wave (P-
wave) is transmitted by
vibration in the direction of
propagation and the slower
secondary wave (S-wave)
transmitted at right angles to
the direction of propagation.
The earth is divided into three parts-
(i) crust, (ii) mantle, and (iii) core.
These divisions, which are concentric
zones in depth, are established principally
by their differing behavior with respect to
the transmission of P (compressional)
and S (shear) seismic waves and are
separated from each other by distinct
discontinuities in transmission velocity.
(ii) The Mantle: From the base of 1st
discontinuity to the Wiechert-Gutenberg discontinuity
at a depth of approximately 2,900 km.
(iii) The core : Zone upto the centre of the earth.
The extinction of S waves at the base of the mantle suggest that material of the
underlying core behaves as a fluid state.
(i)The Crust : From the surface to the base of 1st
discontinuity or Mohorovicic discontinuity
at an average depth below sea level ranging from 37 km under parts of the continents to
about 11 km beneath the deep sea basins (Poldervaart, 1955);
Recordings of seismic waves from
earthquakes led to the discovery of the
earth's core and eventual maps of the
layers of the Earth's inside.
Earthquakes generate three types of
seismic waves: P (primary) waves, S
(secondary) waves and surface
waves, which arrive at seismic recording
stations one after another. Both P and S
waves penetrate the interior of the
Earth while surface waves do not. Due
to this, P and S waves are known as
"body waves". Surface waves arrive last
and are the least interesting to seismic
tomographers because they don't
penetrate deep inside the Earth
Velocity of seismic waves in the Earth
versus depth. The negligible S-wave
velocity in the outer core occurs because it
is liquid, while in the solid inner core the S-
wave velocity is non-zero.
P- & S-waves sharing with the propagation
The average density of the earth was determined by Cavendish in 1799 to be about
5.5 g per cm3
(grams per cubic centimeter)
The velocity of the seismic wave changes with density of the medium by the following
The velocity of P-waves in a homogeneous isotropic medium is given by
where K is the bulk modulus (the modulus of incompressibility),
µ is the shear modulus (modulus of rigidity, ρ is the density of
the medium and .Of these, density shows the least variation, so the
velocity is mostly controlled by K and μ.
The density distribution inside the earth follow the curves of the primary
wave velocity (P) with a sharp a break at 2900 km depth while the density of the
surface rock is 2.8, the mean density of earth is 5.48 g/cc
The measured thermal gradient is about 300
/km in the Crust, but in the
Mantle, it is only 0.60
/km. At the core boundary, temp. is calculated to be 27000
The Mohorovicic discontinuity separates the heterogeneous crust from
much more homogeneous mantle as marked by sudden increase in velocity of
At the upper part of the crust below the sea water (4 km) and sediments (2 km) the
material is granitic called Si-Al(SIAL) while the lower layer is basaltic in composition
often called Si-Mg (SIMA) layer. Total depth of the crust is…….
The mantle contains dunite (Olivine), Peridolite (Olivine +Pyroxene) and eclogite
(Pyroxene+ Garnet) and the combined material has elastic properties to give the
observed wave velocities. However, these material are polymorphic and the great
pressure existing, they are transformed to denser polymorph and the change is
almost complete at the depth of 900 km making a transition zone. It may also happen
that the Silicates break up into simple oxides which crystallize in high density phases.
The seismic discontinuity between the mantle and the core is a sharp one
and its position 2900+2.5 km is known with considerable accuracy. Bullen
suggested that the 2nd
order discontinuity at a depth of about 5000 km is due
to change in rigidity and that below this depth the core may be solid.
Analysis of bodily tide of the earth and magnetic field and its secular
(periodic) variation also indicate the presence of liquid Fe-Ni core. To complete
the picture of earth’s structure three further zones may be added over the
(i) Atmosphere: N2, O2 , water vapour, CO2, inert gases.
(ii) Biosphere : Water, organic substances, skeletal material (fossil) - liquid
and solid and often colloidal.
(iii)Hydrosphere: Upto a depth of 4 km from the surface-fresh water, various
salts as well as snow and ice, liquid as well as solid.
(iv)Crust : upto 33 km. Composed of normal silicate rocks-granite and basalt-
(v) Mantle : Upto about 2900 km. There are Fe-Mg silicates with some FeS,
(vi)Core or Siderophore : Below 3500 km. Composed of Fe-Ni alloy, liquid in
the upper part but the inner core may be solid (below 5000 km).
The average composition corresponds to that of igneous rocks since total
sedimentary and metamorphic rocks contribute little.
According to Clarke and Washington, the upper 10 mile of the Crust is made
up of 95% igneous rocks, 4% shell, 0.75% sand stone and 0.25%
limestone. Si-Al shell is then or absent below the ocean basin and silica
percentage is generally low for oceanic rocks.
Poldervaart (1955): analysed the crust in terms of 4 geological divisions
(i) deep oceanic region
(ii) Continental shield region,
(iii) Young folded belts region, and
(iv) Suboceanic (continental platform with slope)
And finally gave the average composition of earth on water free basis (Silica……
55.2%, Al2O3……15.3%, Fe2O3 ……2.8%. , FeO …. 5.8%, MnO …..0.2%,
MgO ……….5.8%, CaO………8.8%, Na2O…..2.9%, K2O……….1.9%, TiO2……
Clarke and Washington, from the analysis of 5159 samples and Goldschimdt
independently from about 80 samples got about similar datas with minor
variation in respect of the following compounds (Fe2O3 …3.14 %, FeO…3.88%,
MgO ……….3.56%, CaO………5.17%, Na2O…..3.9%, K2O……….3.2%).
Recently data for minor and trace elements has also been obtained.
On the whole, eight elements……….. Al, O, Si, Fe, Ca, Na, K, and Mg make up
nearly 99% of the crust and of those O2 alone make up 46.6% by wt or 93.8%
by volume of the crust. Thus the crust is essentially a packing of O2 anions
bonded by Si, Al and some of the common metals.
Accordingly Goldschmidt remarked that the lithosphere may be called the
Some elements although present in the crust in considerable amount are
• Vernadsky called these dispersed elements, eg., Rb in K-minerals, Ga in
Al minerals etc. the elements like Ti and Zr form specific mineral which are
widely dispersed in small amounts in some of the common rocks.
• Vernadsky introduced the term Clarke of concentration, a factor showing
the concentration of the element in a particular deposit or minerals, e.g.,
Clarke of concentration of Mn in Pyrolusite is 639, in Rhodomite is 419,
although the Clarke of Mn is 0.1%.
• And Ore is simply a deposit in which the Clarke of concentration of the
particular metal reaches a figure sufficient to make up its extraction
profitable. The availability of an element depends largely on its ability to
form individual mineral in which it is a major constituent.
• The most unavailable elements are those which forms no minerals of their
own but occurs in less than 1% in other minerals, e.g.; Rb, Ga, In, Re, Hf
etc. Even for common elements, however, the dispersed amount exceeds
vastly the amount available in so called ore deposits.
Fersman made sizable contributions to the solution of an
important theoretical problem of geochemistry: the frequency
of distribution of the chemical elements in the rocks of the
earth’s crust (clarkes). The term “clarke” (the concentration
of an element in the earth’s crust) was proposed by
Fersman in honor of the American scientist F. W. Clarke,
one of the first to consider this problem in his fundamental work,
The Relative Abundance of the Chemical Elements (1889).
Fersman calculated the clarkes for most of the elements.
Before Fersman, clarkes were expressed in weight percentages.
He showed that for geochemical purposes the atomic percentages were more
important, thus introducing into science the concept of “atomic clarkes.” As a
result he discovered the independence of geochemical abundances from
the positions of the elements in the periodic system and the concentration and
depletion of the various elements. He showed that abundances within the
earth’s crust were determined by the effects of the migration of the
elements, while abundances in space were related to the stability of the
A E Fersman after his
geological expedition to
the Khibiny Mountains in
The concentration of an element in a mineral or rock relative to its crustal abundance.
The term is applied to specific as well as average occurrences
Clarke of concentration
According to Vernadsky, the clarke of concentration is the concentration of the chemical
elements in a certain geochemical system relative to its crustal abundance. The use of this
parameter (Kc) made it possible to highlight the particular and general geochemical
properties of the rocks, including the sedimentary varieties, as well as the “geochemical
affinity” of the rocks of different sedimentary formations, groups, and their large successions.
Clarke of copper is about 55 ppm, or 0.006%. In the mineral chalcocite, Cu2S, the Cu
conc. is 79.8% .Thus, the clarke of concn within this mineral is 79.8/0.006,= 13,300
Laboratory investigations indicate that of the common rock types, Dunite,
Periodite and Eclogite satisfy the geochemical requirement such as elastic
property and density for the mantle which is similar to that of chondritic
meteorites. However, a mantle of Periodite composition since more in line with
the evidence. Goldschmidt suggested layer at the lower part of the mantle.
Since Triolite is a common phase in meteorites some quantity of FeS is
probably dispersed throughout the mantle and core.
The core has a mean density of 10.7 g/cc which can hardly be explained
except by the presence of a heavy metal and being most abundant of them
by Fe(then Ni). From the composition of meteorites, it is reasonable to
suggest that the Fe is probably alloyed with appreciable quantity of Ni.
What is the
Earth made of?
Relative abundance by
weight of elements in
the whole Earth and in
the Earth’s crust.
created a light crust
depleted in iron and
enriched in oxygen,
calcium, potassium, and
MOHO - ~40km
3 Major Zones, 2 Transitions
Earth’s ChemicalEarth’s Chemical DifferentiationDifferentiation
Geochemical Classification of elements
In the classification scheme of Goldschmidt, elements are divided according to how
they partition between coexisting silicate liquid, sulfide liquid, metallic liquid, and gas
phase…defined by examining ore smelting slags and meteorites
Gas PhaseGas Phase
Having affinity for
metallic Fe, Ni
Having affinity for
Having affinity for
Atmophile H, He, N, Noble gases
Alkalis, Alkaline Earths,
Halogens, B, O, Al, Si, Sc,
Ti, V, Cr, Mn, Y, Zr, Nb,
Lanthanides, Hf, Ta, Th, U
Cu, Zn, Ga, Ag, Cd, In, Hg,
Tl, As, S, Sb, Se, Pb, Bi,
Fe, Co, Ni, Ru, Rh, Pd, Os,
Ir, Pt, Mo, Re, Au, C, P, Ge,
To first order, the distribution of elements between core and mantle resembles
equilibrium partitioning between metal liquid and silicates…confirmed by iron
and achondrite meteorites (but at high P, no separate sulfide phase)
• Melting a chondrite gives 3 immiscible liquids plus vapor: