Okyanusal Litosfer

MÜHENDİSLİK B İL İMLERİ -GLOBAL JEOFİZ İK-MUBİ7004

PROF.DR. ALI OSMAN ÖNCEL

Reading: Fowler Chapter 9, pp.391-416

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

ÖNCEKİ DERS

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.

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.

SEMİNER HAZIRLAMADA STRATEJİ

• Semineri seçin• Slaytlarını bulun• Terminolojiyi anlayın ve

açıklayın• Referans makaleleri bulun• Semineri orijinalinden

dikkatle not alarak dinleyin

DERS SEMİNERLERİ

SELCEN SELCEN

SELCEN

SEDA

SEDASEDA EMRE

EMRE EMRE

Okyanusal -Oceanic Crust (Basaltic)

• Derived Directly From Mantle

• Thin and Dense• Young: < 200 m.y.

KITASAL- Continental Crust (Granitic)•Residue of Long-Continued Partial Melting•Thick and Light•Ancient: > 2.5 b.y.

Okyanusal ve Kıtasal Kabukların Farkları

MARİNE SEİSMİC ACQUİSİTİON

http://woodshole.er.usgs.gov/operations/sfmapping/images/sfm_all.jpg

www.geopro.com

Source

Hydrophone

Survey Ship

-The details of the seismic structure of the oceanic crust have been determined by using seismic-refraction and reflection profiling and wide-angle-reflection techniques. -In the absence of direct sampling of the crust, its composition must be estimated from measurements of its physical properties (e.g., seismic velocity and density), which vary with lithology. These estimates are frequently ambiguous (Fowler, 2005, pp.397).

WIDE-ANGLE REFLECTION TECHNIQUE

Hidrofon ve OBS tabanlı Deniz Jeofiziği Çalışmaları Nasıl Yapılır?

SUBMERSİBLE

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 surface (Fowler, 2005, pp.398).

http://en.wikipedia.org/wiki/Submersible

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).

DRILLING INTO OCEANIC CRUST

http://www.ldeo.columbia.edu/res/fac/CORE_REPOSITORY/RHP1.html

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?

…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

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

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

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

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 Resolution” http://www.odplegacy.org/operations/ship.html

Source: Presentation of Dr. Jill Weinberger from LDEO, 29 Sep 2007

MODERN MARVELS: DRİLLİNG

Courtesy of Integrated Ocean Drıllıng Program

http://www.iodp.org/audiovisual/

http://www.iodp.org/audiovisual/

MODERN MARVELS: DRİLLİNG CO URT ES Y O F I NT EG RAT ED O CEA N DRI LL I NG PRO G RAM

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

OCEANIC CRUST

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

Thin, Less-Buoyant Oceanic Crust

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

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

Sea Floor: Depth versus Age

After 70 Ma the simple assumption of conductive cooling starts to break down.

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.

If a body cools, what happens to its density?

Question 4The 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?