Download - Oceanic Lithosphere-2
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?