basin analysis and petroleum geology

8/10/2019 basin analysis and petroleum geology

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GeodynamicsGeodynamics

Aim is to understand the workings of the solidAim is to understand the workings of the solidEarth and how it has evolved since accretion atEarth and how it has evolved since accretion at4.64.6 GaGa

Semester 1: main objective is to explain theSemester 1: main objective is to explain the

distribution and origin of largedistribution and origin of large--scale structuresscale structures

(e.g. sedimentary basins, mountain belts) in(e.g. sedimentary basins, mountain belts) inrelation to Earth processesrelation to Earth processes

First five teaching slots run in parallel with BasinFirst five teaching slots run in parallel with BasinAnalysis & Petroleum Geology (focus on theAnalysis & Petroleum Geology (focus on thetectonic development of sedimentary basins)tectonic development of sedimentary basins)

GeodynamicsGeodynamicsBasin Analysis & PetroleumBasin Analysis & Petroleum

GeologyGeology

Lecture 1: recap of:Lecture 1: recap of:

Compositional and rheologicalCompositional and rheological zonationzonation ofofEarthEarth

Heat distributionHeat distribution


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Structure of the EarthStructure of the Earth

PP-- and Sand S--waves pass through the planet inwaves pass through the planet inresponse to earthquakesresponse to earthquakes

Velocities vary with pressure (depth), temperature,Velocities vary with pressure (depth), temperature,mineralogy, chemistry and degree of partialmineralogy, chemistry and degree of partialmeltingmelting

Laboratory experiments on effect of highLaboratory experiments on effect of highpressures on common minerals and rock typespressures on common minerals and rock typesprovide clues as to likely composition of the deepprovide clues as to likely composition of the deepEarthEarth

Seismic discontinuities divide the interior up intoSeismic discontinuities divide the interior up intodifferent sectorsdifferent sectors

Structure of the EarthStructure of the Earth

Continental crust dioritic to granodioritic, 30Continental crust dioritic to granodioritic, 30--3535km thick; oceanic crust basaltic and 7km thick; oceanic crust basaltic and 7--8 km thick8 km thick

Lithosphere (50Lithosphere (50--300 km thick) is the strong outer300 km thick) is the strong outerlayer, underlain by the low seismic velocity zonelayer, underlain by the low seismic velocity zone

AsthenosphereAsthenosphere (extending from the base of the(extending from the base of thelithosphere to the 660 km discontinuity) is a weaklithosphere to the 660 km discontinuity) is a weaklayer that deforms by creeplayer that deforms by creep

MantleMantle solid (but deformable by creep),solid (but deformable by creep),chemically homogenous and composed of silicatechemically homogenous and composed of silicatemineralsminerals

Outer liquid core, inner solid core (but nearOuter liquid core, inner solid core (but nearmelting point)melting point)


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Generation and transfer of heat withinGeneration and transfer of heat withinthe Earththe Earth

~40% of the Earths present heat output is~40% of the Earths present heat output isresidual heat loss from accretion and coreresidual heat loss from accretion and coreformationformation

~60% results from the thermal decay of long~60% results from the thermal decay of long--livedlivedradioactive isotopes e.g. U, Th, Kradioactive isotopes e.g. U, Th, K

Thermal contributions of U and Th are >K andThermal contributions of U and Th are >K and~20% of radiogenic heat production occurs within~20% of radiogenic heat production occurs withinthe crustthe crust

Granite has a greater potential for heat generationGranite has a greater potential for heat generationfor a given mass than mafic rocksfor a given mass than mafic rocks

Oceanic lithosphere therefore has less heatOceanic lithosphere therefore has less heatgeneration capacity than continental lithospheregeneration capacity than continental lithosphere

Thermal gradients in the EarthThermal gradients in the Earth

Temperature of a rock depends on:Temperature of a rock depends on:

Depth of burialDepth of burial

Ability to diffuse heatAbility to diffuse heat

Its specific heat capacityIts specific heat capacity

Its densityIts density

Heat generation within and below the rockHeat generation within and below the rock

Rate of erosion or deposition above itRate of erosion or deposition above it

Rate at which T changes with depth is theRate at which T changes with depth is theGEOTHERMAL GRADIENTGEOTHERMAL GRADIENT


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Geothermal gradient for a simple oneGeothermal gradient for a simple one--layer model 50 km thicklayer model 50 km thick

Geothermal gradientGeothermal gradient

Estimated by heat flow measurements downEstimated by heat flow measurements downboreholes several km deep, results thenboreholes several km deep, results thenextrapolated by computer modellingextrapolated by computer modelling

Different curves represent different assumedDifferent curves represent different assumed

parameters (e.g. heat flow, conductivity etc)parameters (e.g. heat flow, conductivity etc)

The effect of increased basal heat flow is to moveThe effect of increased basal heat flow is to movecurves to the right, a reduced heat flow movescurves to the right, a reduced heat flow movescurves to the leftcurves to the left

Heat production probably much higher in theHeat production probably much higher in theArchaeanArchaean -- crust warmer than at presentcrust warmer than at present

Oceanic heat flowOceanic heat flow

Highest in areas ofHighest in areas ofyoung lithosphereyoung lithosphere

Decreases withDecreases withdistance from oceanicdistance from oceanicridgesridges

Data very variableData very variableadjacent to ridges, lessadjacent to ridges, lessvariable further awayvariable further away

Sea floor depthSea floor depthincreases with age asincreases with age aslithosphere cools andlithosphere cools andthickensthickens


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Distribution of temperature withinDistribution of temperature withinoceanic lithospoceanic lithospherehere

Distribution of heat within the oceanicDistribution of heat within the oceaniclithospherelithosphere

Curves indicate that apart from the edge of aCurves indicate that apart from the edge of aplate, T increases smoothly downwards,plate, T increases smoothly downwards,consistent with conductive heat transferconsistent with conductive heat transfer

Beneath the oceanic lithosphere, heat transfer isBeneath the oceanic lithosphere, heat transfer is

by convectionby convection

The convective geotherm is typically steeper thanThe convective geotherm is typically steeper thanthe conductive geotherm within the lithospherethe conductive geotherm within the lithosphere

The thermal boundary layer is the transitionalThe thermal boundary layer is the transitionalzone that separates the outermost rigid oceaniczone that separates the outermost rigid oceaniclithosphere from the underlying convecting mantlelithosphere from the underlying convecting mantle


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Continental heat flowContinental heat flow

Continental lithosphere much varied inContinental lithosphere much varied interms of age, thickness, composition andterms of age, thickness, composition andtectonic historytectonic history

No simple age/heat flow relationshipNo simple age/heat flow relationship

Heat flow depends mainly on amount ofHeat flow depends mainly on amount ofsurface crustal radioactivity and length ofsurface crustal radioactivity and length oftime since last major tectonic eventtime since last major tectonic event

Different places have differentDifferent places have differentcharacteristics and these are termed HEATcharacteristics and these are termed HEATFLOW PROVINCESFLOW PROVINCES

Heat flowHeat flow vsvs, crustal age, crustal age Heat flow averagedHeat flow averaged

into groups accordinginto groups accordingto approximate crustalto approximate crustalage for each siteage for each site

Red boxes aroundRed boxes aroundcrosses (= averagecrosses (= averagevalues) indicatevalues) indicateuncertaintiesuncertainties

General trend towardsGeneral trend towardsincreased heat flow inincreased heat flow inyounger lithosphereyounger lithosphere why?why?


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Heat flowHeat flow vsvs, crustal age, crustal age

Younger lithosphere will have been affected byYounger lithosphere will have been affected bymajor tectonism relatively recentlymajor tectonism relatively recently

Older areas of crust have typically lost largeOlder areas of crust have typically lost largeamounts of radiogenic heatamounts of radiogenic heat--producing elementsproducing elements

due to erosiondue to erosion

Not all heat is generated internallyNot all heat is generated internally some issome isprovided by conduction from underlying deep crustprovided by conduction from underlying deep crustand/or mantleand/or mantle

Reduced heat flowReduced heat flow appears to fall over theappears to fall over theperiod 0period 0--300 Ma, then settles to a mean value for300 Ma, then settles to a mean value forages >300 Maages >300 Ma

Reduced heat flow vs. ageReduced heat flow vs. age

Decrease of mean continental heat flowDecrease of mean continental heat flow

with timewith time

I = radiogenic heatI = radiogenic heatfrom the upper crustfrom the upper crust

II = heat from igneousII = heat from igneousand metamorphicand metamorphic

eventsevents

III = background heatIII = background heatfrom the lower crustfrom the lower crustand mantleand mantle


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Continental vs. oceanic lithosphereContinental vs. oceanic lithosphere

Heat is generated atHeat is generated atshallow depths inshallow depths incontinental lithospherecontinental lithosphere

For a given surfaceFor a given surfaceheat flow, T at depth isheat flow, T at depth islower in continentallower in continentalthan in oceanicthan in oceaniclithospherelithosphere

Continental lithosphereContinental lithosphereis thicker because ofis thicker because ofthe lower temperaturethe lower temperature

Thermal models for oceanic and oldThermal models for oceanic and oldcontinental lithospherecontinental lithosphere

Average geotherms meet below the surfaceAverage geotherms meet below the surfaceof the lithosphere suggesting that there is noof the lithosphere suggesting that there is nosignificant thermal difference betweensignificant thermal difference betweenmantle beneath old continental lithospheremantle beneath old continental lithosphereand old oceanic lithosphereand old oceanic lithosphere

Consistent with the observation thatConsistent with the observation thataverage heat flow in old oceanic lithosphereaverage heat flow in old oceanic lithosphere(>65 Ma) is similar to that for the oldest(>65 Ma) is similar to that for the oldestcontinental lithospherecontinental lithosphere

Thermal models for oceanic and oldThermal models for oceanic and old

continental lithospherecontinental lithosphere


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Strengths and weaknesses in theStrengths and weaknesses in thelithospherelithosphere

Heat flow measured at the surface can be used toHeat flow measured at the surface can be used todevelop models for the thickness of thedevelop models for the thickness of thelithospherelithosphere

Old oceanic lithosphere and continentalOld oceanic lithosphere and continental

lithosphere are similar in terms of heat flowlithosphere are similar in terms of heat flow

However, there are major compositionalHowever, there are major compositionaldifferences between the twodifferences between the two

We now review the physical properties thatWe now review the physical properties thatdetermine the strength of the lithospheredetermine the strength of the lithosphere

Continental vs. oceanic lithosphereContinental vs. oceanic lithosphere

The quartzThe quartz--feldspar rheology of continental crustfeldspar rheology of continental crustwill deform in a ductile manner at much lowerwill deform in a ductile manner at much lowertemperatures than the olivinetemperatures than the olivine--dominated oceanicdominated oceanic

lithospherelithosphere

Thus, oceanic lithosphere is much stronger thanThus, oceanic lithosphere is much stronger thancontinental lithosphere under the same conditionscontinental lithosphere under the same conditions

For realistic stresses of ~25 MPa, unreasonablyFor realistic stresses of ~25 MPa, unreasonablyhigh heat flow (>100 mWmhigh heat flow (>100 mWm--22) would be needed for) would be needed foroceanic lithosphere to become ductileoceanic lithosphere to become ductile

For this reason, ductile deformation is rarely seenFor this reason, ductile deformation is rarely seenin oceanic lithospherein oceanic lithosphere

Schematic strength profiles throughSchematic strength profiles through

oceanic and continental lithosphereoceanic and continental lithosphere


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Summary so farSummary so far

Oceanic lithosphere is stronger than continentalOceanic lithosphere is stronger than continentallithospherelithosphere

Younger lithosphere, characterized by higher heatYounger lithosphere, characterized by higher heatflow, is less strong than older lithosphere (withflow, is less strong than older lithosphere (with

lower heat flow)lower heat flow)

IfIf ArchaeanArchaean geothermsgeotherms were steeper than atwere steeper than atpresent (i.e. higher heat flow), presumablypresent (i.e. higher heat flow), presumablyArchaeanArchaean lithosphere would have been weakerlithosphere would have been weakerthan more recent lithospherethan more recent lithosphere

Principal features of plate tectonicsPrincipal features of plate tectonics(arrows = relative motions)(arrows = relative motions)

Main features of plate theoryMain features of plate theory

Earth is covered in mosaic of rigid plates whichEarth is covered in mosaic of rigid plates whichcan comprise only oceanic crust or oceanic +can comprise only oceanic crust or oceanic +continental crustcontinental crust

Seismic and volcanic activity focused mainly onSeismic and volcanic activity focused mainly onplate boundariesplate boundaries

Plates are constantly in motion with respect toPlates are constantly in motion with respect toeach other and the Earths pole of rotationeach other and the Earths pole of rotation

An increase in the size of one plate must beAn increase in the size of one plate must bebalanced out by a corresponding reduction in thebalanced out by a corresponding reduction in thesize of another plate or platessize of another plate or plates

Provides the main mechanism by which the EarthProvides the main mechanism by which the Earthis able to lose internal heatis able to lose internal heat


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Plate motions and interactionsPlate motions and interactions

Relative plate motionsRelative plate motions

In the ocean basins these will be parallel toIn the ocean basins these will be parallel totransform faults and broadly perpendiculartransform faults and broadly perpendicularto ridgesto ridges

Can be estimated in the ocean basins fromCan be estimated in the ocean basins fromwidth of magnetic stripeswidth of magnetic stripes

On the continents can be now be measuredOn the continents can be now be measuredusing GPS systems accurate to within a fewusing GPS systems accurate to within a fewmms per yrmms per yr

Lengths of arrows related to relative velocityLengths of arrows related to relative velocity

Plate motions and interactionsPlate motions and interactions


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Relative plate motionsRelative plate motions

NN--S convergence in the Himalayas 50mm/yrS convergence in the Himalayas 50mm/yr AfricaAfrica--Europe convergence 10mm/yrEurope convergence 10mm/yr

Rates of subduction around the Pacific 65Rates of subduction around the Pacific 65--106mm/yr but rate of spreading is only 33106mm/yr but rate of spreading is only 33--93mm/yr, so Pacific plate is shrinking as are Nazca93mm/yr, so Pacific plate is shrinking as are Nazcaand Cocos platesand Cocos plates

African & Indian plates are enlarging by aAfrican & Indian plates are enlarging by acorresponding amountcorresponding amount midmid--Atlantic ridge and theAtlantic ridge and theCarlsberg ridge in the Indian Ocean are movingCarlsberg ridge in the Indian Ocean are movingapartapart

The African continent appears to be more or lessThe African continent appears to be more or lessstationarystationary

Absolute plate motionsAbsolute plate motions

Motion of the lithosphere relative to the lowerMotion of the lithosphere relative to the lowermantle which deforms more slowly than either themantle which deforms more slowly than either theasthenosphereasthenosphere or the outer coreor the outer core

By establishing age of linear volcanic island chainsBy establishing age of linear volcanic island chains

(e.g. Hawaii) that are thought to have formed by(e.g. Hawaii) that are thought to have formed byvolcanism on a plate that was moving above avolcanism on a plate that was moving above afixed hotfixed hot--spot (or mantle plume)spot (or mantle plume)

This is the HOT SPOT FRAME OF REFERENCEThis is the HOT SPOT FRAME OF REFERENCEfor calculating the absolute or true motions offor calculating the absolute or true motions ofexisting plates over the last 70existing plates over the last 70--8080 myrmyr

Existing hot spotsExisting hot spots


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Existing hot spotsExisting hot spots

Are all hotspots above longAre all hotspots above long--livedlivedplumes?plumes?

~40~40--50 hotspots active at present day50 hotspots active at present day

Perhaps only seven longPerhaps only seven long--lived primarylived primaryhotspots (Iceland(?), Tristanhotspots (Iceland(?), Tristan dada Cunha, Afar,Cunha, Afar,Reunion, Hawaii, Louisville & Easter)Reunion, Hawaii, Louisville & Easter)

Some originated as LIPs associated withSome originated as LIPs associated withflood basalt provinces formed during riftingflood basalt provinces formed during riftingand breakup of Pangaeaand breakup of Pangaea

Still much controversy about whether or notStill much controversy about whether or nota mantle plume underlies Icelanda mantle plume underlies Iceland


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Plate motions calculated from hot spotsPlate motions calculated from hot spots(arrow length proportional to rate of(arrow length proportional to rate of

movement)movement)

Are hot spots stationary?Are hot spots stationary?

Whole premise of using hot spots to calculateWhole premise of using hot spots to calculaterelative plate motions depends upon therelative plate motions depends upon theassumption that mantle plumes are stationaryassumption that mantle plumes are stationary

This is apparently valid for at least the last 10This is apparently valid for at least the last 10 myrmyr

However, there may be a small relative motion ofHowever, there may be a small relative motion of

hot spots of a few mm/yrhot spots of a few mm/yr

Consistent with plumes that ascend through theConsistent with plumes that ascend through themantle in which horizontal velocities are an ordermantle in which horizontal velocities are an orderof magnitude smaller than plate velocitiesof magnitude smaller than plate velocities

However, some plumes may have travelled moreHowever, some plumes may have travelled moresignificant distancessignificant distances

Hotspot tracks in the Pacific OceanHotspot tracks in the Pacific Ocean

Bend in EmperorBend in Emperor--Hawaii chain muchHawaii chain muchmore pronounced thanmore pronounced than

elsewhereelsewhere

Partly accounted for byPartly accounted for bysouthward movementsouthward movementof 5of 5of the hotspotof the hotspotbetween 65 and 43 Mabetween 65 and 43 Ma


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MesozoicMesozoic--CenozoicCenozoic LIPsLIPs

Evidence for a midEvidence for a mid--Cretaceous Cretaceous superplumesuperplume??

Rate of production ofRate of production ofoceanic crust doubled atoceanic crust doubled at

120120--125 Ma125 Ma

IncreasedIncreased subductionsubductionandand

emplacement of majoremplacement of majorbatholiths in Peru and westbatholiths in Peru and west

USAUSA

Rate of geomagneticRate of geomagnetic

reversals was very low =reversals was very low =quiescent core due toquiescent core due toremoval of large amountsremoval of large amounts

of heat by a plume?of heat by a plume?

Evidence for a midEvidence for a mid--Cretaceous Cretaceous superplumesuperplume??

Global seaGlobal sea--level riselevel risedue to increase indue to increase involume of oceanvolume of ocean

ridgesridges

Rise in global tempsRise in global tempsdue to volcanism anddue to volcanism andincreased COincreased CO22

Increased plankton inIncreased plankton inwide shallow seaswide shallow seasextensive blackextensive black shalesshalesand source rocksand source rocks

basin analysis and petroleum geology

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