Chap 1-GEOLOGY PROF EDY

8/2/2019 Chap 1-GEOLOGY PROF EDY

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SAB 2712

GEOLOGY AND ROCKMECHANICS

rof Madya Dr. Hj. Edy Tonnizam Hj.ohamad03-223/[email protected]


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n Earth 4.5 billion yearsn Origin of universe 14 billion yearsn No water / oxygenn Crust due to coolingn Dinasour died 65 million years ago

Luis Alvarez


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Earth structure

q Crust (10 70km): divided into oceanic and continentalcrust. Low density. Silicon-oxygen based.

q Mantle (2880 3200km): consists of layers of denserocks (olivine & basalt). Temperature within mantle isabout 30000C, thus materials may be in the form of liquid. Silicon-oxygen + iron + magnesium. Density of uppermost peridotite 3.3 g/cm3.

q Core (3480 km): Most dense. Consists of iron nikelalloy. Average density 11g/cm3. Temperature mayexceeds 40000C.


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n The top layer is called the crust .

n Oceanic crust is thinner anddenser than continentalcrust .

n Oceanic crust is more activethan continental crust.

n Under the crust is the rockymantle , which is composed of silicon, oxygen, magnesium,iron, aluminum, and calcium.

n The asthenosphere is a partof the upper mantle thatexhibits plastic properties .

n It is located below thelithosphere, between about100 and 250 kilometers deep


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Plate Tectonics

n Earth's outermostlayer, the

lithosphere, isbroken into 7 large,rigid pieces called plates .

n The place where thetwo plates meet iscalled a plate boundary.


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VOLCANOLOG Y

DEFINITION :Volcanology is the study of volcanoes, lava, magma and related to thegeological phenomena. The term of volcanology is derived from the latinword, Vulcan, the Roman God of fire.


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n Lava fountains (5&shyp;10 m high) spouting from eruptive fissures during the October 1980 eruption of Krafla Volcano.


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WHAT IS VOLCANO??

n Volcanic action is clearly related to theexistence of hot springs and zones of high

heat flow that exist well below the earthsurface.n Heat is generated in the earths core by

nuclear process.

n It is carried up from the core to the upperlayers nearer the surface by complexconvection current.

n Then heating from below causes mantle and

crustal rock become soften and melt


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MAGMA

molten material that is still in the earth and which has notyet been ejected to the surface.

The chemical composition of the magma largelydetermines the eruptive behavior of a volcano.

Magma which is composed of mantle rock has littledissolved gas.

This type of magma erupts as a relatively placid viscousliquid ( lava ), flows smoothly if sufficiently hot and freezesinto a black rock called basalt.


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EXSOLUTION SURFACE

occurs in the magma reservoir beneath the volcano. It separates a zone of magma containing dissolved volatiles from an overlying zone of magma

containing exsolved gas bubblesFRAGMENTATION SURFACE

occurs at the top of the magma column. It separates the zone of magmacontaining exsolved gas from the overlying eruption column. Fragmentation of the magma is generated by rapid gas expansion and bubble explosion.


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n Plate tectonics is a gradual movement of crustal plate on the surface of theearth.

n In certain regions, 2 plates move apart creating a rift, where volcanicmagma can erupt (pacific ocean,hawaiian island).

n In other case, 2 plates crush together and raising huge mountain ranges(Himalaya of Asia, Alps of Europe).

n Subduction the plate being subducted gradually bends downward & plunges into the earth where it eventually encounters sufficient heat tosoften & melt.


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Volcanology

n Gunung Merapi


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PHYSIOGRAPHY BEFORE AND AFTER THE 1883 ERUPTION

The pre-eruption island of Kratatau was composed of three coalscedvolcanoes aligned along a north-northwest direction, parallel to thevolcanoes on Sumatra. From north to south, these were Perboewatan,Danan, and Rakata.

During the eruption, Perboewatan, Danan, and the northern half of Rakataappear to have collapsed into the vacating magma chamber, thus forming asubmarine caldera and destroying the northern two-thirds of the island.Eruptions since 1927 have built a new cone called Anak Krakatau ("childof Krakatau") in the center of the 1883


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Karakatau


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The dynamic earth

q The earth is a dynamic planet.

q The earth surface today was dramaticallydifferent from 4.6 bil years ago.

q The process of altering the earths

surface:- gradation.- volcanism.- tectonism.


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The dynamic earth

q Gradation process: erosion & deposition slowrate.- Agent: atmosphere, water, wind & snow.- When rate of deposition is higher than

erosion, deposits of erosion material willhappened or reflects.

q Volcanism refers to the volcanic activity. source: earth internal heat (magma & lava

flow). create igneous & metamorphic rock, volcanic

structure


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The dynamic earth

q

Tectonics: movement of earths crust (start1960s)- sea floor spreading and continentaldrifting.

q Plate tectonic theory earths rigid at the outer shell, lithosphere is broken into several pieces(plate).

q Plate driven (in motion) by thermal engine result of unequal distribution of internal heat.

q Generate earthquake, volcanic activity &mountain.


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The dynamic earth

q

Types of movement:- Divergent boundaries: zones where platesmove apart, leaving gap between them.

- Convergent boundaries: zones where plates

move together, causing one to go beneath theother, as happens when oceanic crust is involved;or where plates collide, which occurs when theleading edges are made of continental crust.

- Transform fault boundaries: zones whereplates slide past each other, scraping & deformingas they past.


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Divergent Boundaries n Places where plates are pulling apart

are called divergent boundariesn When the lithosphere is pulled apart ,it typically breaks along parallel faultsthat tilt slightly outward from eachother.

n As the plates separate along the

boundary, the block between thefaults cracks and drops down into thesoft, plastic interior (theasthenosphere).

n The sinking of the block forms acentral valley called a rift.

n Magma (liquid rock) seeps upward tofill the cracks .n New crust is formed along the

boundary.n Earthquakes occur along the faults,

and volcanoes form where themagma reaches the surface.


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n This is an example of a divergent plateboundary. The mid-Atlantic Ridge is anarea where new sea floor is beingcreated.

n As the rift valley expands, twocontinental plates have been constructedfrom the original one. The molten rock continues to push the crust apartcreating new crust as it does .

As the rift valley expands, water collectsforming a sea.

The Mid-Atlantic Ridge is now 2,000 metresabove the adjacent sea floor, which is at adepth of about 6,000 metres below sea level.

The sea floor continues to spread and theplates get bigger and bigger.


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Sea floor spreading

5cm per year


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Ocean ridges


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Convergent Boundaries n Places where plates crash or

crunch together are called convergent boundaries.n When two plates collide , some

crust is destroyed in theimpact and the plates becomesmaller.

n Oceanic Plate andContinental Plate

When a thin, dense oceanicplate collides with a relativelylight, thick continental plate,the oceanic plate is forcedunder the continental plate.

This phenomenon is calledsubduction .


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n Two Oceanic Plates When two oceanic plates

collide, one may be pushedunder the other and magmafrom the mantle rises, formingvolcanoes in the vicinity.

n Two Continental Plates When two continental plates

collide, mountain ranges arecreated as the colliding crust iscompressed and pushedupwards.


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Subduction zone


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Tectonic collision


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Fault


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Fault


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Tsunami


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n The convergence of the Nazca and South American Plates has deformed and pushed up limestone strata to form towering peaks of the

Andes


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Transform Boundaries

n When two plates movesideways against each other,there is a tremendousamount of friction whichmakes the movement jerky.

n The plates slip, then stick asthe friction and pressurebuild up to incredible levels.

n When the pressure isreleased suddenly, and theplates suddenly jerk apart,this is an earthquake.


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n Aerial view of the San Andreas fault

slicing through the Carrizo Plain in the Temblor Range east of the city of San

Luis Obispo.


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Three types of plate boundary

n Divergent boundaries n Convergent boundariesn Transform boundaries
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Fossil Evidence in Support ofthe Theory

n Eduard Suess was an Austrian geologist who firstrealized that there had oncebeen a land bridge betweenSouth America, Africa, India,

Australia, and Antarctica.n He named this large land

mass Gondwanaland (namedafter a district in India where

the fossil plant Glossopteriswas found).n He based his deductions on

the plant Glossopteris, whichis found throughout India,South America, southern

Africa, Australia, and
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The jigsaw puzzle

q On the earths crust are continental mass,continental shelf & ocean basin.

q The present continents (e.g. Europe, Australia& Africa) originate from one big piececontinent - Gondwanaland.

q The dynamic position (floating) of the earthscrust on the partly liquid & melting mantle,had broken the crust into several pieces &formed the presence continents.


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