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MORB - 1 SEA-FLOOR SPREADING In the 1950’s and early...

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Unformatted text preview: 1 SEA-FLOOR SPREADING In the 1950’s and early 1960’s detailed study of the oceans revealed the following surprising information:- ¡ Detailed bathymetric (depth) studies showed that there was an extensive submarine ridge system that extended around the globe. These became known as MID-OCEAN RIDGES. ¡ Sampling by dredging showed that these mid- ocean ridges were formed of young basalt, referred to as MORB (mid-ocean ridge basalt). Mid-Ocean Ridges Echo Sounding Mid-Atlantic Ridge The entire Mid- Atlantic Ridge 2 The World-Wide Ocean Ridge System (65,000 km in length) Oceanic Crust – is uniformly thick throughout the worlds oceans (5 - 7 km). Assuming this is made from basaltic magma (both extrusive and intrusive) then:- Volume/Year = Thickness x Spreading Rate x Length About 5 - 20 km 3 /year (depending on assumptions) length ~ 65,000 km thickness 5 - 7 km spreading rates 1 –10 cm/yr For Comparison: Hot-Spot Volcanism ~ 1 -2 km 3 /year Subduction Volcanism ~ 2 km 3 /year Therefore ocean ridge volcanism is the most important mechanism for differentiation of the earth – converting mantle peridotite to oceanic crust 3...
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MORB - 1 SEA-FLOOR SPREADING In the 1950’s and early...

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