Oceanic Lithosphere-2

1. Okyanusal Litosfer
Reading: Fowler Chapter 9, pp.391-416
P RO F. D R . A L I O S M A N Ö N C E L
MÜHENDISLIK BİLİMLERİ-GLOBAL JEOFIZIK-MUBİ7004

2. ÖNCEKİ DERS
Plates and plates margins/boundaries
Igneous Rocks: Classification
Basaltic Rocks
Total Sediment Thickness of the World’s
Oceans
The Rock Cycle
Basaltic Magma
Andesitic Magma/Line and Its Generation

4. ÖĞRENCİ SUNUMU
• Öğrenci Seminerleri: USGS merkezinde verilen seminerler arasında
Global Jeofizik ile ilgili seminerler seçildi. Her bir OGRENCİ
arkadaşımız bu seminerlerden İKİSİNİ seçsin ve bildirsin. Önce
bildiren yol alır yaklaşımı geçerlidir.
• Seçilen seminerlerin slaytları. USGS sayfasından bulunabilir, ve bu
slaytlar esas alınarak, ve yazarın semineriyle ilgili çalışmaları dikkate
alınarak seminerler hazırlanacak.

5. GENİŞLETİLMİŞ SUNUM ÖZETİ
SEMINER TEMELLI GENEL OZETLEME (EXTENDED ABSTRACT): USGS
seminerleri kendinize özgü bir dille özetlenecek, ve sanki bir
uluslararası toplantıya bildiri yazıyormuşsunuz gibi 500 kelimeyi
geçmeyecek şekilde OZET yazılacak.

6. SEMINER HAZıRLAMADA STRATEJI
• Semineri seçin
• Slaytlarını bulun
• Terminolojiyi anlayın ve
açıklayın
• Referans makaleleri bulun
• Semineri orijinalinden
dikkatle not alarak dinleyin

7. DERS SEMİNERLERİ
SEDA SEDA EMRE
EMRE SELCEN EMRE
SELCEN SEDA
SELCEN

8. Okyanusal ve Kıtasal Kabukların Farkları
KITASAL- Continental Crust Okyanusal -Oceanic Crust
(Granitic) (Basaltic)
•Residue of Long-Continued • Derived Directly From
Partial Melting Mantle
•Thick and Light • Thin and Dense
•Ancient: > 2.5 b.y. • Young: < 200 m.y.

9. MARINE SEISMIC ACQUISITION
-The details of the seismic
structure of the oceanic crust
have been determined by Survey
using seismic-refraction and
reflection profiling and wide- Ship www.geopro.com
angle-reflection techniques.
-In the absence of direct Source
sampling of the crust, its
composition must be
estimated from measurements Hydrophone
of its physical properties (e.g.,
seismic velocity and density),
which vary with lithology.
These estimates are frequently
ambiguous (Fowler, 2005,
pp.397).
http://woodshole.er.usgs.gov/operations/sfmapping/images/sfm_all.jpg
WIDE-ANGLE REFLECTION TECHNIQUE

10. Hidrofon ve OBS tabanlı Deniz
Jeofiziği Çalışmaları Nasıl Yapılır?

11. SUBMERSIBLE
A much more precise way of
sampling the seabed is to use a
submersible, a mini-submarine
capable of descending to great
depths; there the geologists can
sample the exact outcrop and rock
type wanted. Submersibles (both
manned and remotely operated)
have enabled scientists to make
detailed studies of small areas of the
seabed, particularly the axial zones of
the mid-oceanic ridges. Such
operations are, however, extremely
expensive and still sample only the http://en.wikipedia.org/wiki/Submersible
surface (Fowler, 2005, pp.398).
Sampling the rock outcropping at the seabed does not tell us what rocks make up the lower oceanic crust
(even if the fault scarps are such deeper rocks could be exposed at their bases). However, it does not
enable us to make informed guesses; for instance, since seabed samples include basalts, gabbros,
serpentinites and recent sediments, one would not guess at a deep crust made up of granite (it took scientists
a while to realize that granite samples dredged from the seabed were not representative of the ocean crust
but had been dropped by icebergs, these samples being ice-rafted granite) (Fowler, 398).

12. DRILLING INTO OCEANIC CRUST
The dots on the map above are sites where
deep-sea cores have been taken and
archived at the Lamont Deep-Sea Sample
Repository.
How do we use cores for research?
http://www.ldeo.columbia.edu/res/fac/CORE_REPOSITORY/RHP1.html

13. …CREATE A WAY TO DRILL THROUGH
THE OCEAN BOTTOM?
Project Mohole was created in 1958 as the
Earth Science’s response to the Space
Race.
The original goal was to develop
technology capable of drilling through the
Mohorovicic Discontinuity to obtain
samples from the Earth’s mantle.
In 1966, Congress objected to the cost and
ended the project before its objectives had
been achieved.
Source: Modified after Presentation of Dr. Jill Weinberger from LDEO, 2007

14. DSDP–THE DEEP SEA
DRILLING PROJECT
1967
• In 1967, the “Glomar
Challenger” began its
construction as the first
drilling ship designed to
explore the ocean floors
• JOIDES
• Joint Oceanographic
Institutions for Deep Earth
Sampling (JOIDES)
oversaw scientific
operations
Source: Modified after Dr. Jill Weinberger from LDEO, 29 Sep 2007

15. THE “GLOMAR CHALLENGER”
PRODUCED IMPRESSIVE RESULTS FROM THE START!
DSDP Leg 1 Site 2 revealed the existence of underwater salt
domes, still a major petroleum source.On Leg 1 Site 2 under
a water depth of 1067 m (3500 ft), core samples revealed
the existence of salt domes. Oil companies received
samples after an agreement to publish their analyses. The
potential of oil beneath deep ocean salt domes remains an
important avenue for commercial development today ( see
http://www.deepseadrilling.org/about.htm ).
DSDP Leg 3 drilled 17 holes at 10 different sites along a
oceanic ridge between South America and Africa. The core
samples retrieved provided definitive proof for continental
drift and seafloor renewal at rift zones, as well as support for
the new theory of Plate Tectonics.
Source: modified after Dr. Jill Weinberger from LDEO, 29 Sep 2007

16. OTHER EARLY DISCOVERIES
INCLUDED…
• …how youthful the sea floors are
compared with continents. No part of the
ocean bottom is even 300 million years
old, compared with rocks on land that date
back to nearly 3,900 million years.
• DSDP confirmed that oceans are
constantly being destroyed in subduction
zones and created in divergence zones.
Source: Modified after presentation of Dr. Jill Weinberger from LDEO, 2007

17. NEW IMPROVEMENTS, NEW
DISCOVERIES!
• DSDP ended in 1983,
and was succeeded
by the Ocean Drilling
Program (ODP)
• From 1983 – 2003,
ODP continued to
expand international
participation in
ocean exploration,
utilizing the Drilling
Vessel “JOIDES http://www.odplegacy.org/operations/ship.html
Resolution”
Source: Presentation of Dr. Jill Weinberger from LDEO, 29 Sep 2007

18. MODERN MARVELS: DRILLING
Courtesy of Integrated Ocean Drıllıng Program
http://www.iodp.org/audiovisual/

19. MODERN MARVELS:
DRILLING
C O U R T E S Y O F I N T E G R AT E D O C E A N D R ı L L ı N G P R O G R A M
http://www.iodp.org/audiovisual/

20. OCEANIC CRUST
 4 layers distinguished via seismic velocities
 Layer 1 : Sediment about 2 kms-1
 Layer 2: Volcanic layer about 2.5-6.6 kms-1
 Layer 3: Oceanic layer about 6.6-7.6 kms-1
 Layer 4: Upper mantle about 7.9-8.1 kms-1
See Table 9.2 of Fowler’s book after White at al., (1992).
 Deep Sea Drilling Program
 rarely penetrates the volcanics, and then only to a maximum depth of
1500 m
 Dredging of fracture zone scarps
 samples from deeper sources, but no reliable stratigraphic control
 Ophiolites

21. http://www-odp.tamu.edu/publications/111_SR/VOLUME/CHAPTERS/sr111_16.pdf

22. Thin, Less-Buoyant
Oceanic Crust

23. WHY DOES THE
SEA FLOOR
DEEPENS WITH
DISTANCE FROM
THE SPREADING
RIDGES?

24. http://www.ngdc.noaa.gov/mgg/image/sedthick.jpg

25. Sea Floor: Depth versus Age
Depth = 2.5 km + 0.3(Age)1/2
Up to about 70 Ma, the depth is proportional to the √ (age) . This is consistent
with the ocean cooling, becoming denser, and sinking.
After 70 Ma the simple assumption of conductive cooling starts to break down.
If a body cools, what happens to its density?

26. Question 4
The ocean depth at a distance of 1600 km from the Mid-Atlantic Ridge is
4700 m. (a) Calculate: (i) the age of the crust at this location (ii) the mean
spreading rate represented by this age. (b) Is this a half or a full spreading
rate?