Project funded by the B.C. Dept. of Energy and Mines, and the Geological Survey of Canada Apatite...

Project funded by the B.C. Dept. of Energy and Mines,Project funded by the B.C. Dept. of Energy and Mines,and the Geological Survey of Canada and the Geological Survey of Canada

Apatite Fission Track (AFT) thermochronology of Apatite Fission Track (AFT) thermochronology of the Northern Bowser and Sustut Basins:the Northern Bowser and Sustut Basins:

Constraints on the Latest Cretaceous through Constraints on the Latest Cretaceous through Cenozoic thermal historyCenozoic thermal history

Apatite Fission Track (AFT) thermochronology of Apatite Fission Track (AFT) thermochronology of the Northern Bowser and Sustut Basins:the Northern Bowser and Sustut Basins:

Constraints on the Latest Cretaceous through Constraints on the Latest Cretaceous through Cenozoic thermal historyCenozoic thermal history

Paul O’SullivanPaul O’Sullivan - Apatite to Zircon, Inc.- Apatite to Zircon, Inc.

Fil FerriFil Ferri - British Columbia Dept. Energy and Mines- British Columbia Dept. Energy and Mines

Carol EvenchickCarol Evenchick - Geological Survey of Canada- Geological Survey of Canada

Kirk OsadetzKirk Osadetz - Geological Survey of Canada- Geological Survey of Canada

Ray DonelickRay Donelick - Apatite to Zircon, Inc.- Apatite to Zircon, Inc.

Overview of PresentationOverview of PresentationOverview of PresentationOverview of Presentation

- - Introduce some general background concerning apatite Introduce some general background concerning apatite fission track (AFT) analyses and interpretation of AFT fission track (AFT) analyses and interpretation of AFT datadata

- Introduce some regional geologic constraints within the - Introduce some regional geologic constraints within the Bowser Basin - Bowser Basin - thesethese help explain why samples were help explain why samples were originally collected for AFT analysisoriginally collected for AFT analysis

- - Present representative AFT results from study regionPresent representative AFT results from study region

- Summarize the Late Cretaceous to Tertiary thermal - Summarize the Late Cretaceous to Tertiary thermal history of the study region based on the AFT results*history of the study region based on the AFT results*

**NOTE - I will leave the geologic implications of these results to thoseNOTE - I will leave the geologic implications of these results to those

most familiar with the regional geologymost familiar with the regional geology

- - Introduce some general background concerning apatite Introduce some general background concerning apatite fission track (AFT) analyses and interpretation of AFT fission track (AFT) analyses and interpretation of AFT datadata

- Introduce some regional geologic constraints within the - Introduce some regional geologic constraints within the Bowser Basin - Bowser Basin - thesethese help explain why samples were help explain why samples were originally collected for AFT analysisoriginally collected for AFT analysis

- - Present representative AFT results from study regionPresent representative AFT results from study region

- Summarize the Late Cretaceous to Tertiary thermal - Summarize the Late Cretaceous to Tertiary thermal history of the study region based on the AFT results*history of the study region based on the AFT results*

**NOTE - I will leave the geologic implications of these results to thoseNOTE - I will leave the geologic implications of these results to those

most familiar with the regional geologymost familiar with the regional geology

ThermochronometersThermochronometersThermochronometersThermochronometersT

emp

erat

ure

(°C

)T

emp

erat

ure

(°C

)

Argon/ArgonArgon/Argon Fission TrackFission Track U/Th-HeliumU/Th-Helium

00

100100

200200

300300

400400

500500

600600

700700

800800

TopographyTopographySurface processesSurface processes

Sedimentary BasinsSedimentary BasinsBurial/Burial/

MetamorphismMetamorphism

Igneous processesIgneous processes

MetamorphismMetamorphismMid-crustalMid-crustalprocessesprocessesHornblendeHornblende

ZirconZircon

SpheneSphene

ApatiteApatite

SpheneSphene

ApatiteApatite

K-SparK-Spar

MuscoviteMuscovite

ZirconZircon

Apatite Fission-Track (AFT)ThermochronologyApatite Fission-Track (AFT)ThermochronologyApatite Fission-Track (AFT)ThermochronologyApatite Fission-Track (AFT)Thermochronology

Fission-track ageFission-track agearea density of fossil tracksarea density of fossil tracks

induced fission tracks (U conc)induced fission tracks (U conc)

Fission-track lengthsFission-track lengthsmean track lengthmean track length

distribution of lengthsdistribution of lengths

Fission-track kineticsFission-track kineticsmeasure Dpar for each grain analyzedmeasure Dpar for each grain analyzed

Fission-track ageFission-track agearea density of fossil tracksarea density of fossil tracks

induced fission tracks (U conc)induced fission tracks (U conc)

Fission-track lengthsFission-track lengthsmean track lengthmean track length

distribution of lengthsdistribution of lengths

Fission-track kineticsFission-track kineticsmeasure Dpar for each grain analyzedmeasure Dpar for each grain analyzed

Constrains maximum paleotemperatures plus timing and style of coolingConstrains maximum paleotemperatures plus timing and style of coolingfrom maximum paleotemperaturesfrom maximum paleotemperatures

Constrains maximum paleotemperatures plus timing and style of coolingConstrains maximum paleotemperatures plus timing and style of coolingfrom maximum paleotemperaturesfrom maximum paleotemperatures

“ “time” of coolingtime” of cooling “ “time” of coolingtime” of cooling

“ “rate” & “style” of coolingrate” & “style” of cooling “ “rate” & “style” of coolingrate” & “style” of cooling

1250x1250x

‘‘confined’confined’lengthslengths

‘‘confined’confined’lengthslengths

annealing “resistivity”annealing “resistivity”annealing “resistivity”annealing “resistivity”

Number of tracks provides a Number of tracks provides a measure of time over which measure of time over which

tracks have accumulatedtracks have accumulated

Both grains have same Both grains have same Uranium concentrationUranium concentration

Pretty youngPretty young

Bloody oldBloody old

Apatite Fission-Track (AFT)ThermochronologyApatite Fission-Track (AFT)Thermochronology- Fission-Track Age -- Fission-Track Age -

Apatite Fission-Track (AFT)ThermochronologyApatite Fission-Track (AFT)Thermochronology- Fission-Track Age -- Fission-Track Age -

2000x2000x

220 Ma220 Ma

Length of a track today is Length of a track today is determined by the maximum determined by the maximum paleotemperatures since that paleotemperatures since that

track formedtrack formed

Apatite Fission-Track (AFT)ThermochronologyApatite Fission-Track (AFT)Thermochronology- Fission-Track Lengths -- Fission-Track Lengths -

Apatite Fission-Track (AFT)ThermochronologyApatite Fission-Track (AFT)Thermochronology- Fission-Track Lengths -- Fission-Track Lengths -

2250x2250x

““Confined” tracksConfined” tracks

PrettyPrettycoolcool

BloodyBloodyhothot

Dpar (µm)Dpar (µm)

Apatite Fission-Track (AFT)ThermochronologyApatite Fission-Track (AFT)Thermochronology- Fission-Track Kinetics -- Fission-Track Kinetics -

Apatite Fission-Track (AFT)ThermochronologyApatite Fission-Track (AFT)Thermochronology- Fission-Track Kinetics -- Fission-Track Kinetics -

2250x2250x2000x2000x

““Confined” trackConfined” track

Etch pitEtch pit

SpontaneousSpontaneoustrackstracks

Dpar is essentially a measure of apatite solubility in a grain.Dpar is essentially a measure of apatite solubility in a grain.Solubility in apatite is related to the grain’s compositionSolubility in apatite is related to the grain’s composition

C-axisC-axis

Little variationLittle variationbetween grainsbetween grains

AFTSolve:AFTSolve: Measure kinetic variation (Dpar) Measure kinetic variation (Dpar)AFTSolve:AFTSolve: Measure kinetic variation (Dpar) Measure kinetic variation (Dpar)

Significant variationSignificant variationbetween grainsbetween grains

Dpar is essentially a measure of apatite solubility in a grain.Dpar is essentially a measure of apatite solubility in a grain.Solubility in apatite is related to the grain’s compositionSolubility in apatite is related to the grain’s composition

TotalTotalresettingresetting~100°C~100°C

TotalTotalresettingresetting~115°C~115°C~145°C~145°C~160°C~160°C

Oil

Oil

gen

erat

ion

gen

erat

ion

Wet

gas

Wet

gas

gen

erat

ion

gen

erat

ion

Potential oil generationPotential oil generation

AFTSolve:AFTSolve: Modeled Thermal History Modeled Thermal History (not reset)(not reset)AFTSolve:AFTSolve: Modeled Thermal History Modeled Thermal History (not reset)(not reset)

AFT resetAFT reset

AFT Age103±6 Ma

Onset of cooling88±4 Ma

Stratigraphic Age ~130 Ma

Oil

Oil

gen

erat

ion

gen

erat

ion

Wet

gas

Wet

gas

gen

erat

ion

gen

erat

ion

Lack of controlLack of controlprior to ~56 Maprior to ~56 Ma

AFTSolve:AFTSolve: Modeled Thermal History Modeled Thermal History (reset)(reset)AFTSolve:AFTSolve: Modeled Thermal History Modeled Thermal History (reset)(reset)

AFT resetAFT reset

real / predictedAFT Age = 53±4 Ma / 53±4 Ma

M.L. = 14.3±0.2 µm / 14.2±0.2 µmOnset of cooling = 56±5 Ma

Stratigraphic Age ~180 Ma

Bowser Basin (Skeena FB)Bowser Basin (Skeena FB)- regional stratigraphic framework -- regional stratigraphic framework -

Bowser Basin (Skeena FB)Bowser Basin (Skeena FB)- regional stratigraphic framework -- regional stratigraphic framework -

Sustut GroupSustut Groupcoarsening upward deltaic to coarsening upward deltaic to

fluvial successionfluvial succession

Bowser Lake GroupBowser Lake Groupcoarsening upward coarsening upward

deep marine to deltaic deep marine to deltaic successionsuccession

Hazelton GroupHazelton Groupvolcanic and volcanic and

volcaniclastic stratavolcaniclastic strata

Cre

tace

ou

sC

reta

ceo

us

Jura

ssic

Jura

ssic

0

1000

2000

3000

meters

~200 my

~175 my~155 my

~144 my~138 my

~75 my

Tertiary Plutonic RocksTertiary Plutonic Rocks

- Tertiary sedimentary rocks have been eroded from the Skeena Fold Belt - Tertiary sedimentary rocks have been eroded from the Skeena Fold Belt - thus the majority of the post-Cretaceous geologic record has been deleted- thus the majority of the post-Cretaceous geologic record has been deleted - requires - requires regional relationshipsregional relationships and/or and/or thermochronologythermochronology to help to help constrain geologic history since ~75 Maconstrain geologic history since ~75 Ma

At least 2 distinct episodes of folding recognized:At least 2 distinct episodes of folding recognized:- BLG rocks folded pre-Sustat Basin deposition - BLG rocks folded pre-Sustat Basin deposition - older folding <150 Ma and >95 Ma- older folding <150 Ma and >95 Ma- Sustat Basin rocks themselves are folded - Sustat Basin rocks themselves are folded - so younger episode of folding <75 Ma- so younger episode of folding <75 Ma- Folds in Sustat Basin rocks truncated a by 53 Ma pluton - Folds in Sustat Basin rocks truncated a by 53 Ma pluton - folds are >53 Ma- folds are >53 Ma

Coast PlutonicCoast PlutonicBeltBelt

North American CratonNorth American Craton

StikiniaStikinia

EEWW Intermontane BeltIntermontane BeltSkeena Fold BeltSkeena Fold Belt

Bowser BasinBowser Basin SustatSustatBasinBasin

Omineca BeltOmineca BeltRocky MountainRocky Mountain

Fold & Thrust BeltFold & Thrust Belt

Subducting Farallon/Kula plateSubducting Farallon/Kula platebeneath the Coast Complexbeneath the Coast Complex

Bowser Basin (Skeena FB)Bowser Basin (Skeena FB)1) regional relationships1) regional relationships

Bowser Basin (Skeena FB)Bowser Basin (Skeena FB)1) regional relationships1) regional relationships

- Diving force for deformation within the basin related to subduction of Pacific plates- Diving force for deformation within the basin related to subduction of Pacific plates beneath North American Cratonbeneath North American Craton- Skeena Fold Belt has experienced ~50% horizontal shortening - Skeena Fold Belt has experienced ~50% horizontal shortening (initially >360 km wide)(initially >360 km wide)



StikiniaStikinia






Rapid cooling at Rapid cooling at some time between:some time between:

~100-80 Ma~100-80 Ma~65-60 Ma~65-60 Ma~45-35 Ma~45-35 Ma~10-8 Ma~10-8 Ma




~65-60 Ma~65-60 Ma~45-40 Ma~45-40 Ma


~65-60 Ma~65-60 Ma~45-40 Ma~45-40 Ma


~65-60 Ma~65-60 Ma~45-40 Ma~45-40 Ma


~65-60 Ma~65-60 Ma~45-40 Ma~45-40 Ma

Bowser Basin (Skeena FB)Bowser Basin (Skeena FB)2) regional AFT results2) regional AFT results

Bowser Basin (Skeena FB)Bowser Basin (Skeena FB)2) regional AFT results2) regional AFT results

????

AFT SamplesAFT SamplesAFT SamplesAFT Samples

- locations - - locations -

On GSC ThermalOn GSC Thermal

Maturity Base*Maturity Base*

- locations - - locations -

On GSC ThermalOn GSC Thermal

Maturity Base*Maturity Base*

** GSC Report 4343 GSC Report 4343

Evenchick et al. (2002)Evenchick et al. (2002)

1) Triangle Zone &1) Triangle Zone & Upper Sustut BasinUpper Sustut Basin2) Groundhog coalfield2) Groundhog coalfield3) Mount Ritchie3) Mount Ritchie

1) Triangle Zone &1) Triangle Zone & Upper Sustut BasinUpper Sustut Basin2) Groundhog coalfield2) Groundhog coalfield3) Mount Ritchie3) Mount Ritchie

Triangle Zone /Triangle Zone / Upper SustutUpper SustutTriangle Zone /Triangle Zone / Upper SustutUpper Sustut

BLGBLG

BPFBPF

BLGBLG

AFT AgeAFT Age

59±3 Ma59±3 MaOnset of Onset of CoolingCooling

62±3 Ma62±3 Ma

AFT AgeAFT Age


62±3 Ma62±3 Ma

AFT AgeAFT Age


46±4 Ma46±4 Ma

AFT AgeAFT Age


46±4 Ma46±4 Ma

AFT AgeAFT Age


44±3 Ma44±3 Ma

AFT AgeAFT Age


44±3 Ma44±3 Ma

- Significant Eocene cooling- Significant Eocene cooling- Note recent cooling- Note recent cooling

PaleocenePaleocenecoolingcooling

Triangle Zone /Triangle Zone / Upper SustutUpper SustutTriangle Zone /Triangle Zone / Upper SustutUpper Sustut

NotNotallall

resetreset

GroundhogGroundhogGroundhogGroundhog

BLGBLG

BLGBLG

BLGBLG

GroundhogGroundhogGroundhogGroundhogAFT AgeAFT Age


59±4 Ma59±4 Ma

AFT AgeAFT Age


59±4 Ma59±4 Ma

AFT AgeAFT Age


44±4 Ma44±4 Ma

AFT AgeAFT Age


44±4 Ma44±4 Ma

AFT AgeAFT Age


48±4 Ma48±4 Ma

AFT AgeAFT Age


48±4 Ma48±4 Ma


Mt. RitchieMt. RitchieMt. RitchieMt. Ritchie

BLGBLG

BLGBLG

a-3-Ja-3-J

BLGBLG


a-3-Ja-3-J

AFT AgeAFT Age


41±3 Ma41±3 Ma

AFT AgeAFT Age


41±3 Ma41±3 Ma

AFT AgeAFT Age


43±4 Ma43±4 Ma

AFT AgeAFT Age


43±4 Ma43±4 Ma

AFT AgeAFT Age


49±5 Ma49±5 Ma

AFT AgeAFT Age


49±5 Ma49±5 Ma



No known tectonic mechanism to justify higher paleogeothermal gradients - No known tectonic mechanism to justify higher paleogeothermal gradients - thus we prefer the constant gradient solution (A)thus we prefer the constant gradient solution (A)

TimingTimingTimingTiming

Western BowserWestern Bowser

Northern BowserNorthern Bowser

Constant Values:Constant Values:~65-60 Ma~65-60 Ma~45-30 Ma~45-30 Ma~10-5 Ma~10-5 Ma

Constant Values:Constant Values:~65-60 Ma~65-60 Ma~45-30 Ma~45-30 Ma~10-5 Ma~10-5 Ma



StikiniaStikinia






Bowser Basin (Skeena FB)Bowser Basin (Skeena FB)- regional AFT results -- regional AFT results -

Bowser Basin (Skeena FB)Bowser Basin (Skeena FB)- regional AFT results -- regional AFT results -

Rapid cooling Rapid cooling sometime:sometime:~65-60 Ma~65-60 Ma~45-30 Ma~45-30 Ma~10-5 Ma~10-5 Ma

Rapid cooling Rapid cooling sometime:sometime:~65-60 Ma~65-60 Ma~45-30 Ma~45-30 Ma~10-5 Ma~10-5 Ma






~65-60 Ma~65-60 Ma~45-40 Ma~45-40 Ma

????


~65-60 Ma~65-60 Ma~45-40 Ma~45-40 Ma

????


~65-60 Ma~65-60 Ma~45-40 Ma~45-40 Ma

????


~65-60 Ma~65-60 Ma~45-40 Ma~45-40 Ma

????

So what do AFT results suggest?So what do AFT results suggest?So what do AFT results suggest?So what do AFT results suggest?

- - AFT results are interpreted to record rapid cooling from paleotemperatures AFT results are interpreted to record rapid cooling from paleotemperatures ≥110-160°C ≥110-160°C (range based on different annealing resistivities from Dpar)(range based on different annealing resistivities from Dpar)

- Cooling is interpreted to have occurred in association with km-scale - Cooling is interpreted to have occurred in association with km-scale denudation throughout the region during the Paleocene, Eocene, Miocenedenudation throughout the region during the Paleocene, Eocene, Miocene

- M- Major episodes of denudation occurred within the Skeena Fold Belt after the ajor episodes of denudation occurred within the Skeena Fold Belt after the last known phase of contractional deformation last known phase of contractional deformation (between 75-53 Ma)(between 75-53 Ma)

- Results do not discount the possibility that minor reactivation within the fold - Results do not discount the possibility that minor reactivation within the fold belt might have occurred more recently than previously documentedbelt might have occurred more recently than previously documented

- - AFT results are interpreted to record rapid cooling from paleotemperatures AFT results are interpreted to record rapid cooling from paleotemperatures ≥110-160°C ≥110-160°C (range based on different annealing resistivities from Dpar)(range based on different annealing resistivities from Dpar)

- Cooling is interpreted to have occurred in association with km-scale - Cooling is interpreted to have occurred in association with km-scale denudation throughout the region during the Paleocene, Eocene, Miocenedenudation throughout the region during the Paleocene, Eocene, Miocene

- M- Major episodes of denudation occurred within the Skeena Fold Belt after the ajor episodes of denudation occurred within the Skeena Fold Belt after the last known phase of contractional deformation last known phase of contractional deformation (between 75-53 Ma)(between 75-53 Ma)

- Results do not discount the possibility that minor reactivation within the fold - Results do not discount the possibility that minor reactivation within the fold belt might have occurred more recently than previously documentedbelt might have occurred more recently than previously documented

Remember:Remember:

- - At least 2 distinct episodes of folding within the Skeena Fold Belt have been At least 2 distinct episodes of folding within the Skeena Fold Belt have been recognized:recognized:

1) >95 Ma, but <150 Ma - BLG rocks folded prior to Sustat Basin deposition1) >95 Ma, but <150 Ma - BLG rocks folded prior to Sustat Basin deposition

2) >53 Ma, but <75 Ma - Sustat Basin rocks folded, trucated by 53 Ma pluton2) >53 Ma, but <75 Ma - Sustat Basin rocks folded, trucated by 53 Ma pluton

Furthermore:Furthermore:Furthermore:Furthermore:

- - Incorporating regional thermal maturity data (%VR) with the AFT Incorporating regional thermal maturity data (%VR) with the AFT results and paleogeothermal gradient information derived from results and paleogeothermal gradient information derived from the a-3-J well, suggests that at least 7.0 to 4.4 km of the a-3-J well, suggests that at least 7.0 to 4.4 km of sedimentary section has been removed over sections of the sedimentary section has been removed over sections of the Bowser Basin Bowser Basin (assuming geothermal gradients of 31°C/km and (assuming geothermal gradients of 31°C/km and 45°C/km respectively)45°C/km respectively)

- Hydrocarbon generation from potential source beds ceased with - Hydrocarbon generation from potential source beds ceased with rapid cooling/denudation sometime between latest Cretaceous rapid cooling/denudation sometime between latest Cretaceous and Paleocene timesand Paleocene times

- Petroleum generation ceased earlier in overmature regions- Petroleum generation ceased earlier in overmature regions

- - Incorporating regional thermal maturity data (%VR) with the AFT Incorporating regional thermal maturity data (%VR) with the AFT results and paleogeothermal gradient information derived from results and paleogeothermal gradient information derived from the a-3-J well, suggests that at least 7.0 to 4.4 km of the a-3-J well, suggests that at least 7.0 to 4.4 km of sedimentary section has been removed over sections of the sedimentary section has been removed over sections of the Bowser Basin Bowser Basin (assuming geothermal gradients of 31°C/km and (assuming geothermal gradients of 31°C/km and 45°C/km respectively)45°C/km respectively)

- Hydrocarbon generation from potential source beds ceased with - Hydrocarbon generation from potential source beds ceased with rapid cooling/denudation sometime between latest Cretaceous rapid cooling/denudation sometime between latest Cretaceous and Paleocene timesand Paleocene times

- Petroleum generation ceased earlier in overmature regions- Petroleum generation ceased earlier in overmature regions

Bowser Basin / Skeena Fold BeltBowser Basin / Skeena Fold Belt

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Te

mp

era

ture

(°C

)T

em

pe

ratu

re (

°C) Time (Ma)Time (Ma)

11

22

33

33

22

11

Nu

mb

er

of

tra

cks

Nu

mb

er

of

tra

cks

Track length (µm)Track length (µm)

Final distributionFinal distribution(at time 3)(at time 3)

Fission Track MethodologyFission Track Methodology- System Response 1 -- System Response 1 -

Small Dpar TA*Small Dpar TA*

Large Dpar TA*Large Dpar TA*

**TA = Total Annealing (resetting)TA = Total Annealing (resetting)

Nu

mb

er

of

tra

cks

Nu

mb

er

of

tra

cks

Track length (µm)Track length (µm)

Final distributionFinal distribution(at time 3)(at time 3)

11

22

33

Fission Track MethodologyFission Track Methodology- System Response 2 -- System Response 2 -

Te

mp

era

ture

(°C

)T

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pe

ratu

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°C) Time (Ma)Time (Ma)

33

22

11

Small Dpar TA*Small Dpar TA*

Large Dpar TA*Large Dpar TA*

**TA = Total Annealing (resetting)TA = Total Annealing (resetting)

Bowser Basin / Skeena Fold BeltBowser Basin / Skeena Fold Belt




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Project funded by the B.C. Dept. of Energy and Mines, and the Geological Survey of Canada Apatite...

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Transcript of Project funded by the B.C. Dept. of Energy and Mines, and the Geological Survey of Canada Apatite...