oceanic lithosphere - 1
TRANSCRIPT
Global Jeofiziğe Giriş
Okyanusal Litosfer
PROF.DR. ALI OSMAN ÖNCEL
MÜHENDİSLİK B İL İMLERİ -GLOBAL JEOFİZ İK-MUBİ7004
Dr. Ali O. Oncel : Jeofizik, II. Kat
([email protected] [email protected])
Salı. 14.00-16:00
Her zaman e-mail yoluyla randevu alabilirsiniz yada açık kapı politikasına dayanarak beni görmeye gelebilirsiniz .
Ofis saatleri çizelgesi
Today’s class: Oceanic LithosphereReading: Fowler Chapter 9, pp.391-416
DERS ÖĞRETİM İZLENCESİ
Global Jeofizik İçin ders içerikleria. Bölüm 1: Dünya’nın İç Yapısıb. Bölüm 2: Okyanusal Litosferc. Bölüm 3: İç yapıyla ilgili sismolojik ölçümler d. Bölüm 4: Levha Hareketlerie. Bölüm 5: Isı Akısı
http://geop503kfupm.pbwiki.com/CourseSyllabus
Ders kitabı: The Solid Earth by C.M.R. Fowler-2005
Final sınavı 15%Bölüm sonu değerlendirmeler
25%
Haftalık sunumlar 25%Dönem Ödevi 25%Görevler 10 %
Derecelendirme
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
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
• Abyssal Plains – deep, old ocean floor; well sedimented.
Modified after Figure 9.2 of Fowler’s book
KITASAL DEPREMLER
(1929) and Turbidity Currents
CONTINENTAL MARGIN: EXAMPLES
Difference between the narrow shelf on the west coast and wider shelf on the east coast which is passive margin.
Wider continental shelf on the passive continental margin around Britain
Bathymetry map of the UK and Europe
South America
Active Margin
PassiveMargin
Peru-Chile Trench
Africa
SouthAmerica
Europe
Mid
-Atl
anti
c
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.
Thousands
of kilometers
North America
South America Africa
Europe
Atlantic Ocean basin
Profile through the Mariana Trench
http://www.aquarius.geomar.de/omc/make_map.html
Age of the
Ocean Floor
http://www.ngdc.noaa.gov/mgg/image/crustageposter.jpg
http://www.ngdc.noaa.gov/mgg/image/crustageposter.jpg
How do we classify the igneous rocks?
CLASSIFICATION OF IGNEOUS ROCKS
pp.395-397 of Fowler’s book
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”
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”)
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
http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Inside.shtml
This system is dynamic, not static!
Rock Cycle
Mountains (all types)
Sedimentary Basinserosion,
sedimentation
Subduction Zone (all types)
subduction
Aesthenosphere (metamorphic)
metamorphism
Sea floor (igneous)
extrusion, volcanism
uplift
Frei system diagram
http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Inside.shtml
12
3
4
5
From: Modified after Lecture from Professor Frei
FELSIC VS. MAFIC
Felsic
• Light in color, includes minerals with a lot of aluminum and silicon .
Mafic
• Dark in color, is rich in magnesium and iron (Fe).
Graniteclearly visible crystals
Felsic
Gabbrodark, visible minerals
Mafic
Granite
clearly visible crystals
Felsic Rhyolite
few visible crystals
Acid
Diorite
visible felsic and mafic crystals
Intermediate Andesite
mainly felsic crystals visible
Intermediate
Ultramafic
Basalt
dark, with no visible crystals
Basic
Gabbro
dark, visible minerals
Mafic
Peridotite
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)2O6Plagioclase - CaAlSi3O8 to NaAlSi3O8
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.
ANDESITIC MAGMA
Andesitic magmas are most commonly associated with arcs (island arcs or continental magmatic arcs). Note these are both
St Helens is part of the Cascades (magmatic arc) generated by subduction of the Juan de Fuca (oceanic) plate beneath the North America continental plate
Mt St Helens
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).
ANDESITIC MAGMA
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)
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