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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?
ÖNCEL AKADEMİ: SOLID EARTH GEOPHYSICS
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 LMÜHENDISLIK BİLİMLERİ-GLOBAL JEOFIZIK-MUBİ7004
ÖNCEKİ DERSPlates and plates margins/boundariesIgneous Rocks: ClassificationBasaltic RocksTotal Sediment Thickness of the World’sOceansThe Rock CycleBasaltic MagmaAndesitic Magma/Line and Its Generation
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 ÖZETİSEMINER TEMELLI GENEL OZETLEME (EXTENDED ABSTRACT): USGSseminerleri kendinize özgü bir dille özetlenecek, ve sanki biruluslararası toplantıya bildiri yazıyormuşsunuz gibi 500 kelimeyigeçmeyecek şekilde OZET yazılacak.
SEMINER HAZıRLAMADA STRATEJI• Semineri seçin• Slaytlarını bulun• Terminolojiyi anlayın ve açıklayın• Referans makaleleri bulun• Semineri orijinalinden dikkatle not alarak dinleyin
DERS SEMİNERLERİSEDA SEDA EMREEMRE SELCEN EMRESELCEN SEDA SELCEN
Okyanusal ve Kıtasal Kabukların FarklarıKITASAL- Continental Crust Okyanusal -Oceanic Crust(Granitic) (Basaltic)•Residue of Long-Continued • Derived Directly FromPartial Melting Mantle•Thick and Light • Thin and Dense•Ancient: > 2.5 b.y. • Young: < 200 m.y.
MARINE SEISMIC ACQUISITION-The details of the seismicstructure of the oceanic crusthave been determined by Surveyusing seismic-refraction andreflection profiling and wide- Ship www.geopro.comangle-reflection techniques.-In the absence of direct Sourcesampling of the crust, itscomposition must beestimated from measurements Hydrophoneof its physical properties (e.g.,seismic velocity and density),which vary with lithology.These estimates are frequentlyambiguous (Fowler, 2005,pp.397). http://woodshole.er.usgs.gov/operations/sfmapping/images/sfm_all.jpg WIDE-ANGLE REFLECTION TECHNIQUE
Hidrofon ve OBS tabanlı DenizJeofiziği Çalışmaları Nasıl Yapılır?
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 notenable 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 scientistsa while to realize that granite samples dredged from the seabed were not representative of the ocean crustbut had been dropped by icebergs, these samples being ice-rafted granite) (Fowler, 398).
DRILLING INTO OCEANIC CRUSTThe dots on the map above are sites wheredeep-sea cores have been taken andarchived at the Lamont Deep-Sea SampleRepository. How do we use cores for research?http://www.ldeo.columbia.edu/res/fac/CORE_REPOSITORY/RHP1.html
…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 operationsSource: 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 http://www.odplegacy.org/operations/ship.html Resolution”Source: Presentation of Dr. Jill Weinberger from LDEO, 29 Sep 2007
MODERN MARVELS: DRILLING Courtesy of Integrated Ocean Drıllıng Program http://www.iodp.org/audiovisual/
MODERN MARVELS: DRILLINGC 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/
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
Sea Floor: Depth versus Age Depth = 2.5 km + 0.3(Age)1/2Up to about 70 Ma, the depth is proportional to the √ (age) . This is consistentwith 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?
Question 4The ocean depth at a distance of 1600 km from the Mid-Atlantic Ridge is4700 m. (a) Calculate: (i) the age of the crust at this location (ii) the meanspreading rate represented by this age. (b) Is this a half or a full spreadingrate?