Observations of Heat Flow on Hotspot Swells

Robert N. Harris, Oregon State Univ.Marcia K. McNutt, MBARI

1. Marine Heat and Fluid Flow2. Heat Flow on Hotspot Swells3. Conclusions

H

B

C

CV

R

seafloor

thermistors

Tem

pera

ture

Time

each thermistor

q = -k dT/dz

dT/dz = thermal gradient

k = thermal conductivity

Marine Heat Flow

Subaerial versus Subsea Fluid Flow

Costa Rica

Fisher et al., 2003

Seafloor

SBI

NESW 1000 m

? ?

?

0

100

200

300

3.5

4.0

4.5

5.04600 4800 5000 5200

CDP

Heat flow (mW m -2)0 100 300 500 600200 400 700

Depth (m)-5500 -4500 -3500 -2500 -1500 -500

87o

86o

8o

9o

10o

0o

10o

80o90o

CocosPlate

Cocos-NazcaSpreading

Hawaii

-6

-4

-2

0

-170o -160o -150o

20o

30o

Oahu

Maro Reef

0

2

4

60-200-400-600 200 400 600

Distance (km)

70

65

60

55

50

50 100 150 200 250

4

5

6

7

2040

60

80

100

120

Oahu Profile

5

6

760 22080 100 120 140 160 180 200 240

Distance (km)

20

40

60

80

100

120Site 4, average valueVon Herzen et al. (1989)

Maro Reef Profile

Reunion

Bonneville et al., 19970 50 100 150 200 250 300 350 400

Distance (km)

6

4

2

020406080

100

Profile 2

4

6

0 50 100 150 200 250 300 350Distance (km)

W E

50

100

150

Profile 10

Crozet

40

60

80

100

120

Distance (km)0 50 100 150 200 250 300 350 400 450 500

6

4

2

0

GDH1

GDH1

Courtney and Recq (1986)

M6

M3

M4M5

45o 50o 55o 60o

-50o

-45o

M3M4

M6

M5

Distance (km)0 2 4 6 8 10 12 14

70

80

90

3.8

3.7

3.9b) Site M4

Cape Verde

40

50

60

70

BC

D E

F1F2 G

-30o -20o

o

20o

G

B

CD

EF

Distance from Geoid High (km)0 100 200 300 400 500 600 700

6

4

2

0

Courtney and White (1986)

GDH1

GDH1

40

50

60

70

80

90

0 5 10 15 20 25 30Distance (km)

5

4

3

seafloor

basement

Station C

Bermuda80o 70o 60o 50o

20o

30o

40o

A B

C

1

65

43

2

40

50

60

Detrick et al. (1986)

6

4

2

0

0 200 400 600 800 1000 1200 1400 1600 1800 2000Distance (km)

GDH1

GDH1

0 2 4 6 8 10 12 14

40

60

80

100

120

Distance (km)

6

5

4seafloor

basement

Site 6, W-E Profile

C

R

OM B CV

Summary of Hotspot Heat Flow DataHotspot Swell Age

Ma

1Obs qmW m-2

GDH1mW m-2

2Anomaly Reference

Crozet 66 96 ± 16 63 33 ± 16 , 1986Reunion 77 58 ± 6 59 1± 6 , 1997Oahu 83 74 ± 15 58 14± 15 , 2000aMaro Reef 102 64 ± 15 54 10± 15 , 2000aBermuda 125 57 ± 3 50 7 ± 3 ., 1986Cape Verde 125 63 ± 4 50 13± 4 , 19861Obs q is observed heat flow at station closest to the axis of hotspot swell2 Uncertainties on anomalies only reflect data uncertainties and should be considered a minimum.

Take Home Points

1. High-resolution heat flow surveys at Hawaii and Reunion show large variability. Coarse surveys on other hotspot swells show increasing variability as volcanic edifices are approached. Both observations are consistent with fluid flow.

2. The most likely driving force is the bathymetric relief of the volcanic edices coupled with thin to nonexistant sediment cover.

3. One potential outcome of fluid flow is that the heat flux is diminished where sublithospheric heat flow anomalies are expected to be the greatest.

4. In areas of hydrothermal circulation, conductive thermal models should be used with caution.