Magma ChamberMagma Chamber Intrusive igneous rocksIntrusive igneous rocks magma chamber is intermittentmagma chamber is intermittent

Idealized Ophiolite StructureIdealized Ophiolite Structure

Layer numbers correspond to acoustic speedsLayer numbers correspond to acoustic speeds depths are typicaldepths are typical

More Realistic More Realistic Spreading Spreading

Center SectionCenter Section

Note :Note : failed magma chambersfailed magma chambers complexity of intrusive layerscomplexity of intrusive layers

Fractionation takes place until the Fractionation takes place until the last magma has solidifiedlast magma has solidified the pressure where it happens the pressure where it happens

determines chemistry / mineral determines chemistry / mineral compositioncomposition

Effects of Plate TectonicsEffects of Plate Tectonics Remember that seafloor subsides with age due to cooling and Remember that seafloor subsides with age due to cooling and

thickening of the lithospherethickening of the lithosphere same rate of subsidence in any oceansame rate of subsidence in any ocean

Age vs Depth CurvesAge vs Depth Curves

Linear when plotted vs Linear when plotted vs square rootsquare root

only works to 60 million only works to 60 million yearsyears

Topography as Topography as f(spreading rate)f(spreading rate)

Faster spreading = shallower topographyFaster spreading = shallower topography

Tectono-eustatic Sea LevelTectono-eustatic Sea Level

Formation of GuyotsFormation of Guyots

Happens on any plate, Happens on any plate, regardless of climateregardless of climate

Atoll / Guyot AnimationAtoll / Guyot Animation

Atoll StructureAtoll Structure

Diego Garcia, British Indian Ocean TerritoryDiego Garcia, British Indian Ocean Territory

CaCOCaCO33 Accumulation Accumulation CaCOCaCO33 chemistry causes it to dissolve at depth chemistry causes it to dissolve at depth

results in a “snow line”results in a “snow line”

CaCOCaCO3 3 DepositionDeposition

This pattern is evident in most oceansThis pattern is evident in most oceans depends a little on biological productivitydepends a little on biological productivity

Hot SpotsHot Spots Deep sources of extra-hot magmaDeep sources of extra-hot magma rise up through mantlerise up through mantle are cause of intra-plate volcanismare cause of intra-plate volcanism

YellowstoneYellowstone

Formation of the Island ChainsFormation of the Island Chains

As plate passes over source of volcanism, a chain of As plate passes over source of volcanism, a chain of islands is formedislands is formed

Island ChainsIsland Chains For example, For example,

the Hawaiian the Hawaiian IslandsIslands

Note agesNote ages Ancient Ancient

Hawaiians Hawaiians noticed thisnoticed this referred to it referred to it

as Pele as Pele moving from moving from island to island to islandisland

Hawaiian / Emperor Seamount ChainHawaiian / Emperor Seamount Chain

All produced by All produced by the same hot the same hot spotspot

age progresses age progresses uniformly out uniformly out the chainthe chain

plate motion plate motion changed to changed to produce the produce the bend in the bend in the chainchain

Hawaiian / Emperor Seamount ChainHawaiian / Emperor Seamount Chain

Age Age progresses progresses well all the well all the way outway out

some error in some error in age age determinationdetermination

Hot Spot TracesHot Spot Traces

The Hawaiian The Hawaiian Islands are only Islands are only one exampleone example

each hot spot each hot spot under the Pacific under the Pacific plate produces an plate produces an island chainisland chain

IcelandIceland Hot spot Hot spot

and ridge and ridge axis co-axis co-locatedlocated

double dose double dose of of volcanismvolcanism

““Twin Aseismic RidgesTwin Aseismic Ridges If the hot spot becomes dormant (dies), the volcanism ceases If the hot spot becomes dormant (dies), the volcanism ceases

but spreading continuesbut spreading continues results in twin ridgesresults in twin ridges

Plate Plate Positions Affect CirculationPlate Plate Positions Affect Circulation

Terminal Eocene EventTerminal Eocene Event

At the end of the Eocene, the Drake Passage opened At the end of the Eocene, the Drake Passage opened upup

This allowed circum-Antarctic circulation for the first This allowed circum-Antarctic circulation for the first timetime

Circulation Circulation in the in the Southern Southern Ocean was Ocean was strongly strongly affectedaffected