G208 Notes

April 23 2005

Divergent-Moving apart, create new ocean floor, destroyed at subduction zones, (rift valley)

Melting at midocean ridges-lowering of pressure underline mantle, move pressure to melt, (basalt-mafic

Making of divergent plate boundary

crustal upward

pull apart- normal faults: drop block down on fault- strechting landscape

Continental shelf: down drop continental crust below sealevel.

Erupt basalt:  New ocean floor, linear sea then ocean

Spherical Plant: upwelling triple rifts

Failed Rift: aulocogen   (East Africa rift valley- aulocogen)

***Erupt new ocean floor, pillow basalts

When basalts sodifies underwater get a pillow structure***

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Most form mid ocean ridge:

    Sequence ocean floor

        -Time deposited, sediments, clay, mud, silica-Skeletons,

layer 1. Mud

layer 2. Pillow basalt

layer 3. Vertical dikes overlying gabbro, layer 3 upper  mantle

****Basaltice sheet dikes****

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Dike: planar intrusion that cuts across pre-existing rock layers

Ophiolite: Segment of oceanic lithosphere caught up between two pieces continental material

No oceanice crust older than 180 million yrs,  except rare ophiolite up on continent.

Iceland: 2 sources magma

            1. Convection

            2. Hot spots- allows iceland generate enough magma

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Why Mid Atlantic Ridges high?

        - convective upwelling pushing crust up

        -fresher erupted basalt (water),  than cooler water

FROM OVERHEAD IN CLASS::::

        A. Narow volume mid ocean ridge results from slow spreading

        B. High volume, mid ocean ridge results from rapid spreading

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Surtsey: island off Iceland

Heimaey, then little islands then surtsey

Location of vents associated with eruption, of surtsey, Surtia, Syrtlingur, and Jolnir are satellite vents that were active early in eruption

Syrtlingur and Jolnir formed islands that were exroded away, (Tephra) 

Not to significant to powerful eruptions

4/20/64 Basaltic lava into sea

Tomography 1988: measurements 0.024km3 down

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Submarine volcanic eruptions has begun in the vicinity of westman islands.  Photos taken 3rd day of eruption. 11/16/63

Magma/water explosive- pillow basalt

Lava- close to surface basalt water steam, blows out big explosive eruption, sea accessed to vent, basalt 30 meters less than 100ft.

between 90-100 below sea level erupted explosively

Stean and volcanic ash blend together in eruption column (tephra cone) an island being born, 1st days of eruption

Low spots tendancy to fill with water.

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Plagonites: basaltic blast begin, to grow crystald (devitrified) Basaltic glass

Hydrothermal vents:

        -Vents sea water heated

        -squirted back up at vents

        -erupting in water

        - black smokers

                -hottest water

                -350C  close to 6-700F

 Cooler sea water, suferide particles

        -White smokers

                -No sufides

                -Chimneys, bacteria, live off, tube worms

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