The document discusses oceanic lithosphere and includes the following key points: 1) Oceanic crust is thinner and more dense than continental crust, being approximately 7km thick. The lithosphere includes both the crust and upper rigid mantle. 2) Basalt is the most common igneous rock in oceanic crust, forming at mid-ocean ridges and being indicative of extensional environments. It commonly contains olivine, pyroxene, and plagioclase minerals. 3) Andesitic magmas are more commonly associated with subduction zones, where the lowering of the mantle solidus allows partial melting above the subducting slab. This produces more silica-rich magmas through contamination with

1. Global Jeofiziğe Giriş
Okyanusal Litosfer
P RO F. D R . A L I O S M A N Ö N C E L
MÜHENDISLIK BİLİMLERİ-GLOBAL JEOFIZIK-MUBİ7004

2. Ofis saatleri çizelgesi
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 .
Today’s class: Oceanic Lithosphere
Reading: Fowler Chapter 9, pp.391-416

4. DERS ÖĞRETİM İZLENCESİ
Global Jeofizik İçin ders içerikleri
a. Bölüm 1: Dünya’nın İç Yapısı
b. Bölüm 2: Okyanusal Litosfer
c. Bölüm 3: İç yapıyla ilgili sismolojik ölçümler
d. Bölüm 4: Levha Hareketleri
e. Bölüm 5: Isı Akısı
http://geop503kfupm.pbwiki.com/CourseSyllabus

5. Ders kitabı: The Solid Earth
by C.M.R. Fowler-2005
Derecelendirme
Görevler 10 %

6. 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

7. 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 Modified after Figure 9.2 of Fowler’s book
• Abyssal Plains – deep, old ocean
floor; well sedimented.

8. KITASAL DEPREMLER
(1929) and Turbidity Currents

9. CONTINENTAL MARGIN: EXAMPLES
Difference between the narrow Wider continental shelf on
shelf on the west coast and
wider shelf on the east coast the passive continental
which is passive margin. margin around Britain
South
America
Bathymetry
map of the UK
and Europe
Passive
Active Margin
Margin
Peru-Chile
Trench

10. Europe
Africa
South
America

11. 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.

13. North America
Europe
Atlantic Ocean
South America
basin Africa

14. Profile through the Mariana Trench
http://www.aquarius.geomar.de/omc/make_map.html

15. Age of the
Ocean
Floor
http://www.ngdc.noaa.gov/mgg/image/crustageposter.jpg

16. CLASSIFICATION OF IGNEOUS ROCKS
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”
How do we classify the igneous rocks?
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”)
pp.395-397 of Fowler’s book

17. 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
This system is dynamic, not static!
http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Inside.shtml

18. Rock
Cycle
http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Inside.shtml
Mountains 1 Sedimentary
(all types) erosion, Basins 2
5 subduction
uplift sedimentation
Sea floor Frei system diagram Subduction Zone
(igneous) (all types)
4
extrusion, Aesthenosphere metamorphism
volcanism (metamorphic) 3
From: Modified after Lecture from Professor Frei

19. FELSIC VS. MAFIC
Felsic Mafic
• Light in color, includes • Dark in color, is rich in
minerals with a lot of magnesium and iron
aluminum and silicon . (Fe).
Mafic
Felsic
Granite Gabbro
clearly visible crystals dark, visible minerals

20. Granite Felsic Rhyolite Acid
clearly visible crystals few visible crystals
Intermediate
Diorite Intermediate Andesite
visible felsic and mafic crystals mainly felsic crystals visible

21. Peridotite Ultramafic
Gabbro Basalt
Mafic Basic
dark, visible minerals dark, with no visible crystals

22. 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)2O6
Plagioclase - CaAlSi3O8 to NaAlSi3O8

23. 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.

24. ANDESITIC MAGMA
St Helens is part of the Cascades (magmatic arc)
Andesitic magmas are most commonly generated by subduction of the Juan de Fuca
associated with arcs (island arcs or continental (oceanic) plate beneath the North America
magmatic arcs). Note these are both continental plate
Mt St
Helens

25. ANDESITIC
MAGMA
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).
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)

26. 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