Ocean Crust

 

Layer 1

Average 400 m thick, thicker in Atlantic/Indian Oceans (no trenches)

Sea floor sediments

Layer 2

Average 1.4 km; 1-2.5 km thick

Basalt

  • 2A--Pillow lavas, 0.5 km

  • 2B--Sheeted dikes, 1.5 km

Layer 3

Average 5 km thick

Gabbro

Upper mantle

Average, below 7 km of crust

Peridotite

 

When obducted onto land during a plate collision, the sea floors becomes an ophiolite.  It is generally characterized as "dismembered", because it is severely faulted and broken up.  The peridotite in the ophiolite is usually serpentenized, which means the olivine hydrates by taking water into the crystalline structure.  The 30% expansion reduces the density, which make the serpentenite buoyant.

Famous, well preserved ophiolites occur in Oman, Cyprus where it is the source of the copper mines that make the island famous, and Newfoundland.


Last revision  11/29/2015