structure and composition of lithosphere

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Information about structure and composition of lithosphere

Published on February 26, 2014

Author: debasisray11



A brief desciption about the structure and composition of earth's lithosphere.

पर्यावरण एवं संपोष्र् ववकयस संस्थयन Institute of Environment and Sustainable Development Course: M.Sc.(Tech) Environmental Science and Technology

INTRODUCTION  The Earth is divided into 4 “Sub-systems” or “Spheres” namely:  ATMOS(Gaseous)-SPHERE.  HYDRO(Water)- SPHERE  LITHOS(Rocky)-SPHERE  BIOS(Life)-SPHERE  They are interdependent and function as a whole.

LITHOSPHERE  Derived from GREEK word LITHOS meaning Rocky/ Stone.  It is primarily the rocky and stony part covering the whole earth surface ; on which the interaction of the other Geospheres happen.  The term was coined by JOSEPH BARRELL (1914) who first studied the motion of lithosphere over a molten layer i.e. Aesthenosphere.


PROCESSES OF STUDYING LITHOSPHERE(contd..) •P-WAVES, or primary waves, are the fastest moving waves. They originate in the focus and move outward through all states of matter. P-waves cause back and forth motion in matter. Can pass through liquid medium. •S-WAVES, or secondary waves, originate at the focus and pass only through solids, causing movement from side to side. Cannot pass through liquid medium. •L-WAVES, or long waves, are surface waves. They are the slowest of the three wave types. L-waves affect the surface of the land by causing it to rise and fall like waves on an ocean.

Tectonic Plate Theory

Tectonic Plate Theory (contd..) Three types of plate boundaries exist, characterized by the way the plates move relative to each other. They are associated with different types of surface phenomena. The different types of plate boundaries are: 1. Transform boundaries (Conservative) occur where plates slide or, perhaps more accurately, grind past each other along transform faults. The relative motion of the two plates is either sinistral (left side toward the observer) or dextral (right side toward the observer). The San Andreas Fault in California is an example of a transform boundary exhibiting dextral motion. 2. Divergent boundaries (Constructive) occur where two plates slide apart from each other. Mid-ocean ridges (e.g., Mid-Atlantic Ridge) and active zones of rifting (such as Africa's East African Rift) are both examples of divergent boundaries. 3. Convergent boundaries (Destructive) (or active margins) occur where two plates slide towards each other commonly forming either a subduction zone (if one plate moves underneath the other) or a continental collision (if the two plates contain continental crust). Deep marine trenches are typically associated with subduction zones, and the basins that develop along the active boundary are often called "foreland basins". Examples of this are the Andes mountain range in South America and the Japanese island arc.


STRUCTURE OF LITHOSPHERE(contd..)  Oceanic Lithosphere  It consists mainly of mafic(rich in magnesium and iron) crust and ultramafic(over 90% mafic) mantle and is denser than continental lithosphere. • Continental Lithosphere  It is also called the Continental crust. It is the layer of igneous, sedimentary rock that forms the continents and the continental shelves. This layer consists mostly of granitic rock.  CRUST:  It is the outermost layer of the earth with average density of 2.8- 3.0 g/cm3 and average thickness of 30 km. It consists of the continental crust and the oceanic crust. Life exists in this layer.  MANTLE:  It is the second layer of the earth and extends from 30km- 2900km with an average density of 2.7 g/cm3 .  It contains 83% of the total volume and 68% of the total mass of the earth.  It is made up of silicate rich iron and magnesium and is divided from the crust by a discontinuity called as MOHOROVICIC DISCONTINUITY.  CORE:  It is the deepest layer of earth. It extends from a distance of 2900km – 6371 km with an average density of 4.3- 11 g/cm3 . Mantle and core boundary is called as WEICHART- GUTENBERG Discontinuity.  Core volume is 16% of earth’s total volume and core mass is 32% of earth’s total mass.  It is further divided into 2 sub-zones by the discontinuity called as LEHMANN- BULLEN Discontinuity.  OUTER CORE: (2890km- 5150km)  INNER CORE: (5150km-6371km)

CHEMICAL COMPOSITION OF LITHOSPHERE According to E. Seuss the earth’s layers can be broadly divided into 3 types on the basis of chemical composition:  SIAL- located below crust, average density is 2.7 g/cm3, thickness ranges between 50-300km; dominated by acid materials.  SIMA- located below sialic layer, average density is 2.9- 4.7 g/cm3 , thickness ranges between 1000- 2000km; dominated by basic matter  NIFE- made up of heavy metals, avg. density is 11 g/cm3 . Diameter is 688O km. Magnetic property.

ROCKS  Igneous Rock Igneous rocks are formed from the molten liquid minerals that lie below the earth's crust. They're formed from magma that cools beneath the earth's surface or from lava that cools upon the earth's surface. These two methods of igneous rock formation are known as intrusive and extrusive, respectively. Basalt is the most common type of igneous rock and it covers the ocean floor and thus, exists over two-thirds of the earth's surface.  Sedimentary Rock Sedimentary rocks are formed by the lithification (cementing, compacting, and hardening) of existing rock or the bones, shells, and pieces of formerly living things. Rocks are weathered and eroded into tiny particles which are then transported and deposited along with other pieces of rock called sediments. Approximately three-quarters of the earth's bedrock on the continents is sedimentary.  Metamorphic Rock Metamorphic rock, which comes from the Greek to "change form," is formed by applying great pressure and temperature to existing rock converting it into a new distinct type of rock. Igneous rocks, sedimentary rocks, and even other metamorphic rocks and be modified into metamorphic rocks.

SOIL It can be defined as ‘any part of earth crust on which plants root.’ The whole process of soil formation can generally be divided into 2 stages.:  Weathering  Pedogenesis

SOIL PROFILE Soil depth worldwide averages a mere six inches (15 cm). Soil and its underlying layers are classified into layers known as "horizons." From the surface to the bedrock, these layers are:  O Horizon - The top layer of soil, composed primarily of organic material, such as the litter of leaves and plants, insects, and microorganisms.  A Horizon - Also known as the topsoil, where seeds germinate and plants' roots thrive. Composed of sand and silt. Minerals and clay have been removed in a process known as eluviation.  B Horizon - Also known as the subsoil, this layer contains mineral deposits that have settled down from upper layers. Also called layer of Illuviation.  C Horizon - This layer is called the regolith and consists of rocks and little organic material (even roots don't penetrate this layer).  R Horizon - The "R" in R horizon stands for rock and it refers to the unconsolidated rock or solid bedrock of this layer.

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