fi-6121 system fisis bumi · aksi utama tektonik lempeng terjadi pada pinggiran lempeng © by dr....

FI-6121 System Fisis Bumi Lecturer: Dr.M.Edisar, MT

The Composition of the Earth

(Adapted from, Beatty, 1990.)

W.J. Kious and R.I. Tilling, This Dynamic Earth: The

Story of Plate Tectonics, U.S. Geological Survey, 1996.

Komposisi Bumi Bedasarkan:

Komposisi Kimia

Unsur-unsur utama

Sifat Fisis

Komposisi Kimia Inti Bumi

Zona Pusat Bumi

Mulai pada kedalaman ~ 2,900 km

Disususun dari Fe-alloys

Inti bagian luar

Fe, Ni, S

Inti bagian luar

Padat (akibat tekanan yang sangat besar)

Batas Inti –mantle (CMB) didefinisikan oleh diskontinuitas Gutenberg

Zone dari 200 - 300 km, ditandai D11

Mantle

Daerah sekitar inti

~ 83 % dari volume Bumi

< kerapatannya dari inti

Seluruh mantle disusun dari dua silikat Fe dan Mg

Olivine (Mg, Fe)2SiO4

Pyroxene (Mg, Fe)SiO3

Mineral ini berubah bentuknya pada tekanan yang berbeda.

Akibatnya ada batas dalam mantle yang menggambarkan perubahan fasa, atau ikatan atom dari mineral tersebut.

Dua perubahan fase yang paling penting terjadi pada kedalaman 410-km, dan 660-km.

Pada mantle bagian atas (diatas 660-km) olivine and pyroxene ditemukan sebagau peridotite

Pada mantle bagian bawah (dibawah 660-km) olivine and pyroxene berbentuk perovskites dan jauh lebih sedikit jumlahnya dari oxide, magnesiowüstite

Batas 660-km adalah penting untuk beberapa alasan:

Menggambarkan gempa bumi paling dalam

Perubahan fase mineral pada kedalam ini dapat di buat di laboratorium, temperature pada kealaman harus ~ 1700°C

Kerak (Crust)

Batas Mantle – Kerak dibangun oleh diskontinuitas Mohorovičić

Daerah ketebalannya dari 10 - 70 km

Terdiri dari dua jenis

1. Samudra

2. Benua

Kerak Samudra Kerak tipis dibawah lautan

Basalt

Ketebalan rata-rata sekitar 8 km ~ 2-km Basalt bantal

~ 6-km Gabbro

Densitasnya 3.2 g/cm3

Kompoisisi kaya akan Ca, Mg, Fe

< 50 % SiO2

Kerak Benua

Ketebalannya dari 30 - 70 km Paling tipis dimana lempeng benua

bergerak menjauh dan terpisah

Paling tebal ada dibawah pegunungan

Densitasnya rata-rata 2.7 g/cm3

Granit

Komposisinya kaya akan Si, Al, Na, K

> 50% SiO2

14© By Dr. Muhammad Edisar, MT

Sifat Fisis

lithosphere

Kulit bagian luar dari Bumi yang Kaku (rigid)

Disusun dari :

Mantel Bagian Atas

Kerak Samudra

Kerak Benua

Ketebalannya 70 - 125 km

asthenosphere

Daerah kulit bagian luar Bumi yang terletak dibawah lithosphere

Meluas sampai kedalaman ~ 220-km

Bersifat plastis

Teori Tektonik Lempeng

Sintesa Modern

Permukaan Bumi terbagi ke pada 12 plat utama

Plate bergerak secara horizontalterhadap satu sama lain

Plate “mengapung” atau“meluncur” diatas lapisan asthenosphere viskositas tinggi.

Lempeng terdiri dari kerak samudra dan kerak benua

Aksi utama tektonik lempeng terjadi pada pinggiran lempeng

Dalam skala waktu manusia batas-batas ini ditandai dengan adanya gunung api dan kejadian-kejadian gempabumi.

Diatas studi waktu geologi tas-batas btersebut adalah tempat-tempat terjadinya splitting, shifting dan crumpling dari benua

Volcanoes of the World (Smithsonian Institution Global Volcanism Program)

Jenis-jenis pergerakan lempeng

Lempeng Divergent

Batas penyebaran (Spreading)

Daerah healed “ kerak ” atau fissures

Contoh :

Rift Valley dari Afrika bagian timur

Mid-Atlantic ridge

Gunung api, gempabumi

Heezen and Tharp

Lempeng Convergent

Pada batas lempeng convergent respons terhadap tumbukan lempeng akan bervariasi dengan jenis kerak yang bersangkutan

Ada tiga kemungkinan kombinasi:

Kerak samudra converging with kerak samudra:

Subduksi satu lempeng

Formasi dari sebuah busur kepulauan

Gunung api

Gempabumi

Contoh kepulauan Japanese

Kerak samudra converging degan kerak benua :

Formasi dari rantai pegunungan

Gunung api

Gempa bumi

Contoh Pegunungan Andes

Kerak benua converging dengan kerak benua :

Overriding dari satu lempeng

Formasi dari daerah pegunungan

Gempa bumi

Contoh Himalayas

Transform Boundaries

“side-slip boundary”

create fault zones

earthquakes

example San Andreas

Cross section by José F. Vigil from This

Dynamic Planet

50 million years

150 million years

250 million years

Ecosphere

That part of the earth consisting of the atmosphere, hydrosphere, lithosphere, and biosphere

Atmosphere

The gaseous layer which surrounds the earth, and which is held by gravitational attraction. It consists of layers, the bottom ones of which are: Thermosphere > 80 km

Mesopause

Mesosphere 45 - 80 km

Stratopause

Stratosphere 12 - 45 km

Tropopause

Troposphere 0 -12 km

Hydrosphere

Earth's water, in any physical state –

Gaseous

Liquid

Lithosphere

The outermost part of the solid earth, consisting of the entire crust and the upper mantle, from the surface to a depth of about 70 kilometers (km)

It is stronger and mechanically more rigid than the asthenosphere (70 - 250 km), which lies under it

Interior of the Earth

Crust – Continental (0-40 km, to a maximum of 100km)

Oceanic (0-10 km)

Mantle – Upper (bottom of crust to 700 km, and includes

the transition zone (350 to 700 km)

Lower (700 - 2900 km)

Core – Outer (2900 - 4980 km - liquid iron-nickel)

Inner (4980 - 6370 km - solid)

Biosphere

Interface layer between earth's crust, atmosphere, and hydrosphere where life is found

Includes the total ecosystem of the earth

Ecosystem

Community of interacting organisms, of all species

Includes interactions of this community with the chemical and physical systems of earth

Human Activities

Interact with the natural world, causing changes in the ecosystem

Changes vary in magnitude and temporal scale

Environmental Issues

Changes in the ecosphere caused by:

Natural processes

Human activities

Often cause change

Affect the rate at which change occurs

Or both

Changes By Other Species

Humans are not the only species to cause environmental change

Cyanobacteria, the first organisms capable of photosynthesis, gradually changed the atmosphere of earth from one without oxygen to one with the present 21% oxygen content

So What Makes Humans Different?

Humans are the first species to be aware of their influence

Humans assume, to some extent, responsibility for wise management of the planet

Technology Improvements

During the last fifty years

Have greatly contributed to our awareness of environmental change

Especially contributing to our knowledge of global scale processes

Greatly enhanced out knowledge of the temporal scale of global change

Examples of Technological Change

Satellite observations

Computational power

Rapid communication (Internet)

Changes to the Ecosphere

Many examples of modification of ecospheric components have been described

Representative examples of these modifications are shown on the following slides

Atmospheric Modifications

Depletion of ozone (O3) in the ozone layer (stratosphere) which affects UV light absorption Ozone “hole”

Leads to increased rates of skin cancer

Acid deposition – introduction of pollutant gasses into the atmosphere leads to the formation of “acid rain”

Atmospheric Modifications cont.

Modification of the climate system by the introduction of “greenhouse” gases

Major gases are carbon dioxide, freons, methane

Will lead to a warmer earth, and probably increase number and severity of major storms

May affect short and medium term climate, and may modify the areas in which food can be grown

Hydrological Modifications

Diagram shows a local example of the hydrological cycle

Hydrological Cycle Modifications

Withdrawal of water

Pollution of water

Impoundment of water (dams)

Modifications in erosion and depositional rates

Silting of rivers and estuaries

Increased erosion below dams

Biosphere Modifications

Mobilization and redistribution of chemical elements

Most important carbon (C), nitrogen (N), and oxygen (O)

Results in enrichment and depletion of various parts of the system, leading to problems like red tide, depletion of soil productivty, etc.

Biosphere Modifications cont.

Human activities change natural environment Often results in changes if species distribution,

especially in loss of biological diversity (biodiversity)

Rapid expansion of urban and suburban areas decreases available habitat

Deforestation

Expansion of farming into marginal environments

Land use that is insensitive to long term changes Salinization

Results of Environmental Change

Species reduction

Mass mortality - a large number of individuals die, which may lead to a new equilibrium distribution, with a smaller number of individuals of the species in question, or the original equilibrium may be approximately restored, to precatastrophe levels

Extinction - A complete elimination of a species. Extinction can and does occur naturally - Man's activities have increased the rate of extinction

Natural Events

Natural events often lead to mass mortality in many species - extinction may occur in severely geographically restricted species

Examples:

Earthquakes

Volcanoes

Hurricanes

Small meteorite impacts

Overview

Geologic Time

Movements of the Continents

Earth Materials

Tectonic Forces

Weathering and Erosion Processes

Erosional Agents and Deposition

Geologic TimePretend the age of the earth (4.6+ billion years) is compressed

into one calendar year.

January 1 - Earth and planets formed

Early March - liquid water stands in pools.

Late March - earliest life

July - oxygen is important part of atmosphere

October 25 - multicellular organisms

Late November - plants and animals abundant

December 15 to 25 - dinosaurs arise and disappear

11:20 pm, December 31 - Humans appear

One second before midnight - Automobile invented

Formation of the Earth‟s Interior

@5 bya, plantesimals (meterorites,icy comets) collide heat released

(Kinetic energy to thermal energy)

Entire planet melts (still cooling today)

Gravity sorts materials by density

Fe in center

Si and O compounds towards surface

The Upper Mantle and Crust

Crust (5 mi for ocean, 25 mi for continents)

Dense iron-rich basalts (mafic) make up ocean floor Fe, Silica, magnesium

Silica- rich rock makes up the continents (felsic) Silica, aluminum

General trends: temperature, density

Horizon composition, behavior

The Earth‟s Interior

Distance: 6730 km (3963 miles)

What is „tectonics‟? From Greek „tektonikus‟

meaning building or construction

Plate tectonics refers to the process of plate formation, movement, and destruction.

What is a „Plate?‟

Lithospheric plate: crust + upper mantle

Aesthenosphere: plastic mantle

History of Plate Tectonics

„Fit‟ of coastlines recognized early

Sir Francis Bacon (1600s)

No mechanism for motion

1915 Alfred Wegener proposes theory of continental drift.

Supercontinent Pangaea („all-earth‟) [225mya].

Fragmentation and drift to current positions.

Plate Movement History

Wegner‟s evidence

Fit of continents

Fossil plants, animals, rock types / geology

match on opposite shores

deposits inconsistent with current geography

Striking Match of Biological Regions

Striking Match of Geologic Regions

History of Plate Tectonics Problem with continental drift?

No sound mechanism for the „drift‟!

Wegner hypothesizes spin of earth or tides…..

History of Plate Tectonics New theory for motion: Arthur Holmes

(1930s)

thermal convective cells in the upper mantle (aesthenosphere)

theory is largely ignored

History of Plate Tectonics

In the 1960s, Harry Hess and Robert Deitz (geophysicists) propose sea floor spreadingalong mid-oceanic ridges for plate motion.

Sea Floor Spreading

Plate Tectonics Theory Continental Drift + Sea Floor Spreading

+ new data Theory of Plate Tectonics

Plate Tectonics Theory

Plate boundaries: main location for Earth‟s volcanic and earthquake activity. This is main place where mountains are created.

Type of plate boundary determines activity.

3 types

diverging (spreading)

converging (colliding)

transform (sliding past each other)

Crustal Processes

Destruction (subduction)

Creation (volcanism )

Alteration / deformation (folding and

faulting)

Geography of the Plates

7 major plates; several minor plates

Small plates / boundaries still unknown

Plate Margins: how do we know?

Marked by volcanic and tectonic activity

Divergent Plate Boundaries

Landscape features:

land: rift valleys, volcanic mountains, thinning crust

ocean/sea: rift valleys,

mountain ranges

Divergent Plate Boundaries

Examples:

Atlantic Mid-Oceanic Ridge

Red Sea

Rift valleys of eastern Africa

Convergent Plate Boundaries Activity:

subduction; shallow to deep earthquakes; volcanism (continental)

Features:

ocean trench; explosive volcanic mtns on continental margin

Earth Materials

Three major rock types Igneous

Sedimentary

Metamorphic

Igneous Rocks

Igneous (ignus = fire)

Formed from the cooling of molten rock (magma/lava), a process called crystallization.

Slow cooling larger crystals > dense rock

Rapid cooling small crystals > lighter rock

Two classes of igneous rocks

intrusive: formed inside the Earth

extrusive: formed at Earth‟s surface

Igneous Intrusive Rocks Cools slowly (thousands of years)

Visible crystals

Examples

- granite - diorite - gabbro

Igneous Extrusive Rocks Cools rapidly - exposed to surface

No visible crystals

Examples

- rhyolite - andesite -basalt

Some unique rock types

Pumice (vesicular)

- sometimes so light it floats!

Obsidian

glassy, „curved‟ fracturing

used for arrowheads by Native Americans

Typical Igneous Intrusions

Know: Batholith and Dike

Exposed Batholiths

Sierra Nevada, CA

Sills and Dikes

Dike: Grand Canyon, AZ

Granite sill in schistDike: Coast Ranges, BC

Sills and Dikes

Igneous Extrusive Landscapes

Volcanic neck and dike: Shiprock, NM

Volcanic cones, obsidian flow: Mono Craters, CA

Sedimentary Rocks

Compaction Cementing

Sedimentary

Formation

Relative Abundance by

Shale (fine grains)

Limestone (CaCO3)

Where do Sedimentary Rocks Form?

Terrestrial environments (non-marine)

Rivers and floodplains (fluvial environment)

Deserts (aeolian environment)

Marine environments

Continental shelf

Continental slope and rise (deep sea fans)

Abyssal plain

Beach and barrier islands

Metamorphic Rocks or That‟s very Gneiss, but I don‟t give a Schist!

Gneiss (broad foliation)

Schist (narrow foliation)

Which Type?

Sedimentary - limestone and shale

What type?

What type? Metamorphic - Amitsoq

Gneiss, Greenland, Oldest known rocks

What type?

What type? Sedimentary - Sandstone in

What type?

What type? Extrusive Igneous -Reunion Island, S. Pacific

What type?

Morro Rock, CA

What type? Intrusive Igneous

Morro Rock, CADevil’s Tower, Wyoming

The Rock Cycle

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