AN IMPORTANT PPT ON TECTONICS, WEATHERING & EROSION

1. Dr.PANKAJ MEHTA
Assistant Professor
Department of Environmental Sciences
Central University of Jammu, Jammu.
Email:drpankajmehta79@gmail.com
THE EARTH’S ENGINE
TECTONICS, WEATHERING AND EROSION

2. FRAMEWORK
INTRODUCTIONINTRODUCTION
WEATHERING AND GLOBAL CLIMATEWEATHERING AND GLOBAL CLIMATE
WEATHERING AND MOBILIZATION OF ELEMENTSWEATHERING AND MOBILIZATION OF ELEMENTS
DYNAMIC WEATHERING:
HOW DOES ROCK WEATHERING PROCEED IN NATURE?
SUMMARY

3. • Acts on Non-living system “rocks” to make a life supporting system-
“soil”.
• Involves Rocks, water, air, soil, & life.
• Controlling factors:
– Structure & texture of the rocks.
– Tectonics : climate, relief and vegetation.
Importance of Rock Weathering
• Rock Weathering is the basis of formation of farmland in flood plain
and delta
• Rock Weathering Controls:
– Water Chemistry
– Chemistry of soil and sediments
– Soil Fertility and Maintanance
– Geochemical cycling of elements
– Climate ( Weathering of rock forming silicates esp. Ca-Mg bearing
ones, is an important sink for atmospheric CO2.)
Weathering

5. Rock Weathering : Important Aspects
Rock Weathering studies gaining importance
1. In context of increased soil erosion and climate change.
2. For better management of the landscape / environment.
3. To understand weathering process in monsoonal
climate regions, e.g. India, with shorter spell of rains and
longer spell of semi-aridity

6. Factors Controlling Weathering
•Lithology - Lithology exerts a major control on weathering rate (Bluth and Kump,
1991; Bluth and Kump, 1994) by influencing the availability of minerals with varying
reactivity. Texture influences permeability and therefore the degree of infiltration of
rainwater into the rock.
•Climate- Moisture and heat promote chemical reactions. In cold climates, chemical
weathering proceeds very slowly. In such regions the effects of mechanical weathering are
generally more obvious. Many studies have found that rates of chemical weathering are
directly correlated to temperature (Drever and Zobrist, 1992; Velbel, 1993; Brady and
Carroll, 1994) and precipitation or runoff (Dunne, 1978; White and Blum, 1995)
•Topography-. It exerts this influence in several ways, by controlling (a) the rate of
surface runoff of rain water and hence the rate of moisture intake by the parent rock, (b) the
rate of subsurface drainage and therefore the rate of leaching of the soluble constituents,
and(c) the rate of erosion of the weathered products and thereby the rate of exposure of fresh
mineral surfaces

7. Biological activity and Vegetation:
•Recently it has been realized that biological activities play an important role in weathering
processes (White and Brantley, 1995; Neaman et al., 2005). Similarly, in reactions at bio-
mineral interfaces, release of organic acids causes enhanced mineral dissolution by forming
complexes with minerals at the surface (Stumm et al., 1984; Krishanswami and Singh,
2005). The mechanism of bio-reactions make soil formation a positive feedback process
(Soil is needed to form more soil)
•Vegetation cover can affect silicate rock weathering rates by increasing soil CO2 content,
stabilizing soil cover and producing organic acids (Keeney, 1983; Heyes and Moore, 1992;
Drever, 1994; Caldeira, 2005)

8. CLIMATIC ZONES & RATES OF
WEATHERING

9. WEATHERING AND GLOBAL CLIMATE
Silicate weathering in particular is thought to control global climate over long time
scales through the consumption of atmospheric CO2 that is initially stored as soil
carbon and eventually stored as carbonates in the oceans (Walker et al.,1981) This
process is governed by the rate of carbonic acid dissolution reactions, as originally
proposed by (Ebelmen,1845).
2CO2 +3H2O+ CaAl2Si2O8 = Ca+2 + 2 HCO3- +Al2 Si2 O5(OH4)
The temperature- dependence of this reaction on Earth surface settings is thought to
provide the feedback that regulates climate over geological time (Walker et al., 1981;
Berner et al., 1983) and maintains equable climate conditions on Earth (J.Kasting, 1987;
Krishanswami and Singh, 2005).
The surface area of continental basalts plays a major role in the carbon cycle
(Dessert et al., 2003) It is important to note that the estimate of 4.08 X 1012
mol/year
of CO2 consumed by weathering of basalts was determined from the present-day
basalt surface area (Dessert et al., 2003).

10. CHEMICAL WEATHERING AND GLOBAL CLIMATE

11. WEATHERING AND MOBILIZATION OF ELEMENTS
Mineralogy is the predominant factor controlling the mobility of major elements (Harris
and Adams, 1966) whereas trace element mobilization and redistribution during
weathering are controlled by dissolution of primary minerals, formation of secondary
phases, transport of materials, redox processes, co-precipitation and ion exchange of
various minerals (; Nesbitt, 1979; Nesbitt et al.,1980; Fritz and Regland, 1980; Chesworth
et al,1981; Cramer and Nesbitt, 1983; Fritz and Mohr, 1984; Middleberg et al, 1988;
Condie et al, 1995;) The retention of trace elements in the weathering profile depends on
the formation and stability of secondary minerals
During rock weathering, elements can be either mobile or immobile. Mobile
elements like Ca, Na, K, Sr, Mg and Si are derived mainly from leachable
minerals such as feldspar, ferromagnesian minerals and apatite, whereas immobile
elements like, Zr, Hf, Fe, Al, Th, Nb, and REE are either concentrated in resistant
phases or strongly adsorbed by secondary minerals (gibbsite, kaolinite)
(Middleberg et al, 1988)

12. WEATHERING AND MOBILIZATION OF ELEMENTS

13. Rocks weather to produce soils which become sediments after erosion, transport and
deposition. It is well known that tectonics and denudational processes continuously shape
the Earth’s surface (Ledley et al, 1999) However, our knowledge of the associated
processes is inadequate. The rate and nature of weathering vary widely and are controlled
by many variables such as parent rock-type, topography, climate and biological activities.
It involves interaction between the lithosphere, hydrosphere, atmosphere and biosphere.
Weathering profoundly alters the surface of the earth and the chemistry of water bodies.
We document here five different ways of water entry into the rocks and weathering of
hard rocks in the field and these are:
•Physical heterogeneities present in the rocks and these include –
•(a) foliation planes (b) lithological contacts (c) compositional layers (d) joints &
fractures (e) shear zones.
•Secondary fractures developed during uplift and unroofing – Fracture induced
weathering.
•Spheroidal Weathering.
•Regolith Induced Weathering – Regolith accumulating on slopes and foothills.
•Life Induced Weathering – Through plant root system, animals etc
DYNAMIC WEATHERINGDYNAMIC WEATHERING

14. Field documentation of weatheringField documentation of weathering
processprocess
 Physical heterogeneities present in the rocks and these includePhysical heterogeneities present in the rocks and these include
(a) foliation planes (b) lithological contacts (c) compositional(a) foliation planes (b) lithological contacts (c) compositional
layers (d) joints & fractures (e) shear zones.layers (d) joints & fractures (e) shear zones.
 Secondary fractures developed during uplift and unroofing –Secondary fractures developed during uplift and unroofing –
Fracture induced weathering.Fracture induced weathering.
 Spheroidal Weathering.Spheroidal Weathering.
 Regolith Induced Weathering – Regolith accumulating onRegolith Induced Weathering – Regolith accumulating on
slopes and foothills.slopes and foothills.
 Life Induced Weathering – Through plant root system, animalsLife Induced Weathering – Through plant root system, animals
etcetc

15. Field photographs showing physical heterogeneities inherent inField photographs showing physical heterogeneities inherent in
the rock (structural induced weathering)the rock (structural induced weathering)

16. Field photographs showing fracture induced weatheringField photographs showing fracture induced weathering
in the rock.in the rock.

17. Field photographs showing spheroidal weathering in the rock.Field photographs showing spheroidal weathering in the rock.

18. Field photographs showing regolith induced weathering in the rock.Field photographs showing regolith induced weathering in the rock.

19. Field photographs showing life induced weathering in the rock.Field photographs showing life induced weathering in the rock.

20. DYNAMICS OF WEATHERING
 In semi-arid climatic set-up. Physical heterogeneities andIn semi-arid climatic set-up. Physical heterogeneities and
fracture induced are the major weathering processesfracture induced are the major weathering processes
 In the humid climatic set-up. Regolith-induced and life-inducedIn the humid climatic set-up. Regolith-induced and life-induced
are the major processes undergone by rocks to weather.are the major processes undergone by rocks to weather.
 The process of spheroidal weathering is common in both semi-The process of spheroidal weathering is common in both semi-
arid as well as humid climatic set-uparid as well as humid climatic set-up
 The processes of rock weathering are in continuous motion atThe processes of rock weathering are in continuous motion at
different levels with different climatic condition and withdifferent levels with different climatic condition and with
different set of processes enlisted above, thus the process ofdifferent set of processes enlisted above, thus the process of
Weathering is not static rather it is Dynamic in natureWeathering is not static rather it is Dynamic in nature

21. IMPORTANCE OF WEATHERING IN FARMLAND, SEDIMENT
GEOCHEMISTRY AND WATER CHEMISTRY
•A region subjected to uplift experiences a high rate of erosion because of several
geological, climatic and biological factors. It is well known that soil formation is a
positive feedback process, where the product of the process accelerates the product
formation by the process.
•The chemical weathering under the semi-arid condition and limited water
availability but under the influence of structural heterogeneities produces
less weathered materials and the erosion of less weathered materials forms
the fertile farmlands in the downstream floodplains.
•Extensive weathering under humid climatic setup cannot supply the
nutrient rich sediment, however nutrients in the solute forms are delivered
to the river and then to the sea controlling the water chemistry also.
•The extensive chemical weathering taking place in humid climatic setup
is responsible for controlling the marine productivity by transporting
nutrients in water.
SUMMARY

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