Endogenic Processes , Deformation of the Earth's Crust , Continental Drift & Plate Techtonics

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Endogenic Processes

The geological phenomena and processes which is located, formed or occurring beneath the Earth's surface. These processes are the reasons behind major landform features.

The principal energy sources for endogenic processes are:

1.    heat in Earth’s interior
2.    the redistribution of material in the earth’s interior according to density

Heat in Earth’s interior

The earth’s deep heat originates chiefly from radiation. The continuous generation of heat in the earth’s interior results in the flow of heat toward the surface.  With  the  proper combination of materials, temperature,  and pressure, chambers  and layers  of partial  melting  may occur at certain depths within the earth.

Experts have estimated the internal temperature of the Earth from geotherm curve. It can be deduced that the mantle is considerably hotter than the crust, and the core is much hotter than the mantle.

- Core-mantle boundary: 3,700°C
- Inner-core – outer-core boundary: 5,000°C±500°C
- Earth’s center: 6,400°C±600°C

Magma Formation

The primary source of magma formation is the asthenosphere. It is the layer in the upper  mantle where convection currents may arise from and move to the lithosphere.
Magma is formed when hot rocks in the Earth partially melt which occurs when

(1) the pressure decreases,
(2) when volatiles are added to hot rocks and
(3) when heat is transferred by a magma rising from the mantle into the crust.

Magma chambers form in the crust itself due to influence of the heat flow or under the direct influence of the heat carried by rising abyssal magma.  When magma reaches the near surface parts, it may form variously shaped intrusive bodies or can be extruded onto the surface, in the form of volcanoes.

VOLCANO

Volcano is a point on the earth’s crust where magma forces its way to the surface

Magma - the mixture of molten rock, suspended mineral grains and dissolved gases that form in the crust or mantle when temperature are sufficiently high.

Three types of magma

1. Basaltic magma - contains about 50% SiO2 and very little dissolved gas. The two common igneous rock derived from basaltic magma are basalt and gabbro.
2. Andesitic magma - contains about 60% SiO2, and lot of dissolved gas, andesite and diorite are the common IR
3. Rhyolithic magma - contains about 70% SiO2 and the highest gas content. The two common igneous rock derived from rhyolithic magma are rhyolite and granite.

Types of Volcano Based on Shape

1. Cinder Cone - the simplest type of volcano, cinder falls around the vent to form a circle or oval cone. Examples: Sunset Crater, Arizona and Taal Volcano
2. Composite Volcano - Steep –sided, symmetrical cones.
Examples: Mt. Fuji, Japan and Mt. Mayon, Philippines
3. Shield Volcanoes - a sloping dome shape like a warriors shield.
Examples: Mauna Loa, Hawaii and Kilauea, Hawaii

Types of a Volcano based on Volcanic Activity
1. Active - eruptions can be anytime and often.
2. Dormant - has been a while since it has erupted, but could at anytime.
3. Extinct -it hasn't erupted in a very long, long time so it probably won't ever again.

Calderas - collapsed volcanoes
1. Magma chamber has emptied and the ground has sunk often becomes a lake
2. New volcanoes can form, or pressure can build from below, lifting the ground
3. If acidic, this can cause a catastrophic eruption in the form of a ”super-volcano”
Ex. Santorini and Mt. Pinatubo

Where does magma occur?
• On subduction zones
• On constructive plate boundaries
• On hot spots

Hotspots
Hotspots are caused by the upwelling of super heated rocks in the mantle plumes
Ex: Hawaii – basic      Yellowstone - acid

Volcanic Explosivity index (VEI)
1 – Hawaiian                           gentle                          Kilauea
2 – Strombolian                       explosive                     Stromboli
3 – Vulcanian                          severe
4 – Peléan                               cataclysmic                 Mt.Pelée
5 – Plinian                               paroxysmal                 St.Helens
6 – plinian/ultra-plinian            colossal                       Krakatoa
7 – ultra-plinian                        super-colossal             Tambora
8 – supervolcanic                    mega-colossal             Yellowstone

*Number 8 has never been experienced in human history.

Volcanic hazards
1. lava flows
2. pyroclastic flow                 
3. ash clouds
4. lahars
5. lava bombs

EARTHQUAKE
Earthquakes are the shaking, rolling or sudden shock of the earth’s surface caused by a sudden release of strain in the earth's interior.
Gravitational differentiation has also led to the stratification of the earth into geospheres of varying density.  Is also manifested in the form of tectonic movements , which, in turn, lead  to the tectonic deformation of crustal and upper mantle rocks.

The accumulation  and  subsequent  discharge of tectonic stresses along active faults causes earthquakes.

Some Terms Related To Earthquake

    Focus (Hypocenter) - the site of the first movement on a fault and the center of energy release.
    Epicenter - point on the Earth’s surface that lies vertically above the focus.
    Fault / Geological Fault - is a fracture in the ground or rock strata with its two adjacent surfaces along the plane of fracture.

Related image


Seismic waves, which are produced due to earthquake, is divided into two:


1. Body waves - travels through the interior(body) of earth as they leave the focus


    P waves (primary waves) – first recorded in a seismograph; type of seismic waves that arrive at the surface first and move by compressing and expanding the ground like an accordion; can travel through solid, liquid and gas.
    S waves (secondary waves) – slower than P waves thus recorded later.


2. Surface waves - travels parallel to the earth’s surface and these waves are slowest and most damaging.


    Love waves - It moves the ground from side to side in a horizontal plane but at right angles to the direction of propagation
    Rayleigh waves - wave move both vertically and horizontally in a vertical plane pointed in the direction in which the waves are travelling.


Instruments used to detect earthquake


1. Seismograph - a sensitive instrument that measures and record seismic waves.

2. Richter scale - is used to rate the magnitude of an earthquake (that is the amount of energy released during an earthquake.)

3. Mercalli intensity scale - is a seismic scale used for measuring the intensity of an earthquake.

Lesson 9.2 – Deformation in the Earth’s Crust



I. Deformation of rocks in Earth's crust takes many forms;


A. Changes in volume, shape, and position may occur alone or in combination.


1. Stress = applied force = cause of the deformation


    Types of stress


1)    Tensional-stretching, 

-increased volume


2)  Compressional

      - squeezing,

decreased volume


3)  Shear - change in shape




2. Strain (resulting deformation)


a. Elastic - recoverable,  small  amounts  of  strain, 

doesn’t  happen  to rocks


b. Plastic - permanent;

rocks flow as  movement occurs along small structural defects.


3. Fracture (Brittle deformation) - rupture

rock moves in opposite directions on either side of a break.


B. Causes of deformation


1. Confining pressure - due to the load of overlying  rocks


2. Stresses applied at plate boundaries

- usually  not  uniform  instead  this is directed pressure



II. Strike and dip are used to describe the orientation of  planar features.


A. Outcrop - site  where  rocks  are  exposed  at  the surface


B. Dip -  the  angle of  inclination  of  the  bedding surface down off the horizontal


C. Strike -  the  trend  or  direction  of  the strata  or the bearing of any horizontal

            line on the plane perpendicular to the direction of dip.


III. Features of plastic deformation - Folds


Folds


Folds are wavelike undulations caused by bending of rocks usually produced by horizontal compressive stresses. It occurs at great depths inside the Earth under great temperatures and pressures.


Anatomy of Fold


1.Axial plane - a plane through a rock fold  that includes the axis-divides the fold as symmetrically as possible.

2. Axis - the ridge or place of sharpest folding.

3. Limb - 1 of 2 parts of the fold-on either side of axis.

4. Plunge - angle that fold axis makes with the   horizontal


Types of folds


    Monocline - double flexure of rock layers. This is the simplest type of fold.


This fold involves a slight bend in otherwise parallel layers of rock.

    Anticline - arching or upwarping of rock layers.


It is a convex up fold in rock that resembles an arch like structure with the rock beds (or limbs) dipping way from the center of the structure.

    Syncline-  downwarping of rock layers .


This is a fold where the rock layers are warped downward.  Both anticlines and synclines are the result of compressional stress.



    Dome - non-linear,  anticlinal fold-beds dip away from central area in all directions


    Basin -  non - linear, synclinal  fold-beds  dip towards central area from all directions.

More complex fold types can develop in situations where lateral pressures become greater.


The greater pressure results in anticlines and synclines that are inclined and asymmetrical.

    Recumbent fold - develops if the center of the fold moves from being once vertical to a horizontal position.


Recumbent folds are commonly found in the core of mountain ranges and indicate that compression and/or shear forces were stronger in one direction.

Faults


Faults are breaks in rock mass where appreciable movement of rocks on opposite sides of the break has occurred.


Faults are formed in rocks when the stresses overcome the internal strength of the rock resulting in a fracture. Faults occur from both tensional and compressional forces.


a. Hanging  wall - block of rock  immediately above fault surface

b. Footwall - block of rock immediately below fault surface
Types of Fault

Faults are classified by type of stress that acts on the rock and by the nature of the movement of the rock blocks either side of the fault plane.


1. Dip-slip faults - movement of the two blocks is up and down the dip of the fault-primarily vertical

a. Normal fault - footwall  moves  up  with  respect  to hanging  wall (associated with tensional  stress); occurs in Divergent plate boundary.

Normal faults occur when tensional forces act in opposite directions and cause one slab of the rock to be displaced up and the other slab down.

Reverse/ thrust fault - footwall  moves  down  with respect to hanging wall  (associated   with compressional  stress and  usually lots of folding); occurs in Convergent plate boundary.

Reverse faults develop when compressional forces exist. Compression causes one block to be pushed up and over the other block.

c. Graben fault - produced when tensional stresses result in the subsidence of a block of rock. On a large scale these features are known as Rift Valleys.

Horst fault - the development of two reverse faults causing a block of rock to be pushed up.
Graben and horst - features characterized by down-dropped and uplifted blocks of rock, respectively, bordered by pairs of normal faults.

2. Strike-slip faults - movement of  the two  blocks on either side of the break is along the strike and dominantly horizontal (associated with shear stress); occurs in Transform fault boundary.

Left-lateral strike-slip fault (sinistral)

It is one on which the displacement of the far block is to the left when viewed from either side.

Right-lateral strike-slip fault (dextral)

It is one on which the displacement of the far block is to the right when viewed from either side.

The  San Andreas  Fault in California is  a  right lateral strike-slip transform fault.   
The West Valley Fault (WVF) is one of the two major fault segments of the Valley Fault System.

It runs through Metro Manila to the cities of
Marikina, Quezon City ,
Pasig , Makati ,
Taguig and Muntinlupa

It moves in a dominantly dextral strike-slip motion.

Lesson 9.3 – Continental Drift

The continental drift hypothesis was first articulated by Alfred Wegener, a German meteorologist, in 1912. He proposed that a single supercontinent, Pangaea, separated into the current continents and moved across Earth’s surface to their present locations.


In 1915, he published his work through a book entitled ‘The Origin of Continents and Oceans’ .


Scientists were reluctant to believe that continents could drift. During the 1950s-60s, it was still widely held that that continents and ocean basins had fixed geographic positions.


During the 1960s, advances in oceanography generated a lot of new data. They found out that the ocean floor was characterized by deep depressions called trenches and a network of ridges that encircled the globe.


Together with heat flow measurements, these topographic data led to the emergence of the Seafloor Spreading Hypothesis. This findings in turn revived interest in Alfred Wegener’s idea of drifting continents.




Evidences supporting Continental Drift


• The fit of the continents


- Opponents of Wegener’s idea disputed his continental fit evidence, arguing that the fit of the continents’ margins was crude, and that shorelines were continuously being modified by wave erosion and depositional processes.



- A perfect fit could not be achieved. The process of stretching and thinning of the continental margins and sedimentary processes could explain some of the overlaps.











• Similarity in geological units and structure

-  rocks on both sides of the Atlantic Ocean were identical in terms of type and age.


- mountain ranges with the same rock types, structures, and ages, that were now on opposite sides of the Atlantic Ocean.


The Appalachians of the eastern United States and Canada, for example, were just like mountain ranges in eastern Greenland, Ireland, Great Britain, and Norway.


Wegener concluded that they once formed a single mountain range that just became separated.



• Fossil match


- Similar fossils of extinct plants and animals in rocks of the same age were found on different continents, which are now separated by large bodies of water.


Organisms were adapted to a specific type of environment and their dispersal could be limited by biogeographic boundaries (e.g. oceans, mountain ranges, etc.)


Wegener argued that these organisms could not have physically crossed the oceans; rather, the continents were in fact part of a large contiguous landmass which later on broke apart and drifted.


• Glacial and paleoclimate evidence


- Wegener analyzed glacial tills and striations of ancient times and found out that glaciers

of the same period (late Paleozoic age, around 300 million years ago) are located in

Australia, South America, Africa, India, and Antarctica.



Except for Antarctica, these countries did not have subpolar climate that allowed glaciation.


Putting the continents together in accordance to Wegener’s Pangaea shows that the glaciation only occurred in a small region in Gondwana (around the South Pole) which then moved outward to the aforementioned continents.


His studies showed that South Africa was originally at the South Pole, which explains the flow direction of the ancient glaciers.


Fitting the continents together places the northern half of Pangaea closer to the tropics and was proven correct by fossil and climatological evidences.












Lesson 9.4 – Plate Tectonics


Seafloor spreading hypothesis


Harry Hess advanced the theory of seafloor spreading during the 1960s. He proposed that seafloor separates at mid-ocean ridges where new crust forms by upwelling magma.


Newly formed oceanic crust moves laterally away from the mid-ocean ridge with the motion like that of a conveyor belt. Old oceanic crusts are dragged down at the trenches and re-incorporated back into the mantle.


Proof for seafloor spreading


- Magnetic stripes on the seafloor: detailed mapping of magnetism recorded in rocks of the seafloor shows that these rocks recorded reversals in direction and strength of the Earth’s magnetic field. Alternating high and low magnetic anomalies run parallel to mid ocean ridges. Pattern of magnetic anomalies also matches the pattern of magnetic reversal already known from studies of continental lava flows.


Theory of Plate Tectonics


Plate Tectonics states that the Earth’s outermost rigid layer (lithosphere)is broken into discrete plates which are moving more or less as a unit. The process is mostly driven by mantle convection, the lithospheric plates ride over the soft, ductile asthenosphere. Gravity also accounts since dense plates slips beneath less dense plates.


The different types of lithosphere at plate boundaries and their relative movements create the distinctive sets of geologic features.


Concept of lithospheric plate


a. The lithosphere consists of the crust and the uppermost mantle.


- Average thickness of continental lithosphere : 150km

- Average thickness of old oceanic lithosphere : 100km


b. Composition of both continental and oceanic crusts affect their respective densities.


c. The lithosphere floats on a soft, plastic layer called asthenosphere.


d. Most plates contain both oceanic and continental crust; a few contain only oceanic crust.


e. A plate is not the same as a continent.