Global Jeofiziğe Giriş

Okyanusal Litosfer

PROF.DR. ALI OSMAN ÖNCEL

MÜHENDİSLİK B İL İMLERİ -GLOBAL JEOFİZ İK-MUBİ7004

Dr. Ali O. Oncel : Jeofizik, II. Kat

(oncel@istanbul.edu.tr aliosman.oncel@gmail.com)

Salı. 14.00-16:00

Her zaman e-mail yoluyla randevu alabilirsiniz yada açık kapı politikasına dayanarak beni görmeye gelebilirsiniz .

Ofis saatleri çizelgesi

Today’s class: Oceanic LithosphereReading: Fowler Chapter 9, pp.391-416

DERS ÖĞRETİM İZLENCESİ

Global Jeofizik İçin ders içerikleria. Bölüm 1: Dünya’nın İç Yapısıb. Bölüm 2: Okyanusal Litosferc. Bölüm 3: İç yapıyla ilgili sismolojik ölçümler d. Bölüm 4: Levha Hareketlerie. Bölüm 5: Isı Akısı

http://geop503kfupm.pbwiki.com/CourseSyllabus

Ders kitabı: The Solid Earth by C.M.R. Fowler-2005

Final sınavı 15%Bölüm sonu değerlendirmeler

25%

Haftalık sunumlar 25%Dönem Ödevi 25%Görevler 10 %

Derecelendirme

OKYANUS ÇUKURLARI

The crust and lithosphere thicken away from the rift. This is compensated by Isostasy and the crust uplifted in the rift-shoulders. Spreading rates are generally quoted as half plate-separation rate. For example, Mid Atlantic Ridge is spreading at a rate of 1 cm yr-1 but the North American Plates and Eurasian plates are separating at approximately 2 cm-1.

Figure 9.1 of Fowler’s book

KITASAL SINIRLAR

• Continental Shelf – part of the continental margin between the coast and continental slope; slopes 0.1 degree (1:500)

• Continental Slope – part of the continental margin between the continental rise and the continental shelf; slopes about 3-6 degree (1:10 to 1:20)

• Continental Rise – Part of continental margin between the continental slope and abyssal plain; slopes generally 1:40 to 1:2000

• Abyssal Plains – deep, old ocean floor; well sedimented.

Modified after Figure 9.2 of Fowler’s book

KITASAL DEPREMLER

(1929) and Turbidity Currents

CONTINENTAL MARGIN: EXAMPLES

Difference between the narrow shelf on the west coast and wider shelf on the east coast which is passive margin.

Wider continental shelf on the passive continental margin around Britain

Bathymetry map of the UK and Europe

South America

Active Margin

PassiveMargin

Peru-Chile Trench

Africa

SouthAmerica

Europe

Mid

-Atl

anti

c

Question: The width of ocean floor between the spreading ridge in the South Atlantic Ocean at 30°S and the edge of the continental shelves along the east coast of South America and the west coast of southern Africa at 3°S is approximately 3100 and 2700 km respectively. Assuming that the spreading rate on this segment of the ridge is 38 mm y−1, estimate the maximum age of the sea floor on either side of the South Atlantic.

Thousands

of kilometers

North America

South America Africa

Europe

Atlantic Ocean basin

Profile through the Mariana Trench

http://www.aquarius.geomar.de/omc/make_map.html

Age of the

Ocean Floor

http://www.ngdc.noaa.gov/mgg/image/crustageposter.jpg

http://www.ngdc.noaa.gov/mgg/image/crustageposter.jpg

How do we classify the igneous rocks?

CLASSIFICATION OF IGNEOUS ROCKS

pp.395-397 of Fowler’s book

What is the Igneous rock? A rock or mineral that solidified from molten or partly molten

material, i.e. from a magma Etymology: Latin ignis, ''fire”

Simple classification based on Silica content (SiO2) can be done (see Table 9.1) (silica content)

66 wt. % - Acid (eg rhyolite) (“felsic”)52-66 wt% - Intermediate (eg andesite)45-52 wt% - Basic (eg basalt) (“mafic”)< 45 wt % - Ultrabasic (eg peridotite) (“ultramafic”)

 

The Crust and Lithosphere Continental crust: thicker, less dense, older

20 km (weathered areas) to 75 km (younger areas) thick

Oceanic crust: thinner, more dense, more recent~7km thick

Lithosphere: the crust and uppermost (rigid) mantle

http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Inside.shtml

This system is dynamic, not static!

Rock Cycle

Mountains (all types)

Sedimentary Basinserosion,

sedimentation

Subduction Zone (all types)

subduction

Aesthenosphere (metamorphic)

metamorphism

Sea floor (igneous)

extrusion, volcanism

uplift

Frei system diagram

http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Inside.shtml

12

3

4

5

From: Modified after Lecture from Professor Frei

FELSIC VS. MAFIC

Felsic

• Light in color, includes minerals with a lot of aluminum and silicon .

Mafic

• Dark in color, is rich in magnesium and iron (Fe).

Graniteclearly visible crystals

Felsic

Gabbrodark, visible minerals

Mafic

Granite

clearly visible crystals

Felsic Rhyolite

few visible crystals

Acid

Diorite

visible felsic and mafic crystals

Intermediate Andesite

mainly felsic crystals visible

Intermediate

Ultramafic

Basalt

dark, with no visible crystals

Basic

Gabbro

dark, visible minerals

Mafic

Peridotite

BASALTIC ROCKS

Basaltic rocks on Earth, Moon and Mars commonly comprise three minerals: olivine (Mg-Fe silicates, pyroxene (Ca-Mg-Fe silicates) and plagioclase feldspars (Ca-Na-Al silicates)

Olivine in basalt

Olivine - Mg2SiO4 to Fe2SiO4

Pyroxene - Ca(Mg,Fe,Al)(Al,Si)2O6Plagioclase - CaAlSi3O8 to NaAlSi3O8

BASALTIC MAGMA

Most basalts on Earth erupted from Middle Oceanic Ridges (MOR’s) and basaltic magma is an indicator of extensional environments. Large volumes of basalts also erupted (in past) from continental rifts and formed a distinctive composition and are called as Continental Flood Basalts (CFB). Similar flood basalts recognized on Moon, Venus and Mars MOR basalt (MORB) has distinctive composition (particularly trace elements) that in most cases suggest they are sourced from mantle that has already been previously melted (“depleted”) and hence lost some of its lower melting components.

ANDESITIC MAGMA

Andesitic magmas are most commonly associated with arcs (island arcs or continental magmatic arcs). Note these are both

St Helens is part of the Cascades (magmatic arc) generated by subduction of the Juan de Fuca (oceanic) plate beneath the North America continental plate

Mt St Helens

Arc of igneous rocks (plutonic and volcanic) can be on continent (as here) or an island arc in oceans.

Magma (which is most commonly andesite) is generated above the descending slab due to lowering of mp of lithosphere by presence of volatiles (H20) released from slab (and sediments).

ANDESITIC MAGMA

The magmas generated have a composition more silicic than basalt mainly because they are contaminated by passage through the silica-rich continental crust (as shown)

ANDESITE LINE

• Geographic boundary between the basalt/gabbro of the Pacific Ocean basin and the andesites at the subductive margins of the surrounding continents

From: http://www.eos.ncsu.edu/eos/info/mea/mea101_info/chapters_color/KimColor6_04.html