HSDPDrill Site

HSDP - a detailed look at the Hawaiian plume (and CMB?)

1500

2000

2500

3000

0

500

1000 subaerial

submarine

Mauna Kea subaerial(including alkalic lavas)

Mauna Loa subaerial tholeiite

Mauna Kea subaerial tholeiite

rotary drilled intervals

massive

hyaloclastite

intrusive

depth (mbsl)

ash or soil

first intrusive

first pillow

degassed

undegassedpillow low SiO2, high Na+K

254 m

1079 m

~2230 m

~2440 m

TD September 23, 1999 (3097.7 mbsl)

Lithostratigraphy of HSDP-2 Core

0 100 200 300 400 500 600 700

0

500

1000

1500

2000

2500

3000

HSDP1

HSDP2

Ar-Ar age

Mauna Kea Age

(Sharp et al., 2004)

0

5

10

15

20

25

100 200 300 400 500 600Model Age (ka)

HSDP Mauna Kea(Kurz, 2002)

MORB Range

edge center

20 km

N

Melt Supplymax = 5 cm/yr

0.001

0.1

0.3

0.5

0.7

0.9

1.0

0.05

Present

200 Ka

400 Ka

600 Ka

800 Ka

Kohala

Hualalai

Mauna Loa

Loihi

Kilauea

Mauna Kea

Magma CaptureArea

HSDP

Mahukona

Melting region

Sampling issues: Pt. 1

4

5

6

7

8

9

10

100 200 300 400 500 600

εNd

( )Model Age ka

EPR MORB range

r = 130 km

r = 30 km

5

10

15

20

25

30

100 200 300 400 500 600

Model Age (ka)

0.7026

0.7030

0.7034

0.7038

100 200 300 400 500 600Model Age (ka)

MORB

MORB

2.440

2.445

2.450

2.455

2.460

2.465

2.470

100 200 300 400 500 600

Model Age (ka)

0.126

0.128

0.130

0.132

0.134

0.136

0.138

100 200 300 400 500 600Age (ka)

He-3 anomaly(Pb anomaly?)

Sr anomaly

Core or core-mantling dense layer

Width of melting region 5 10 15 20 25 30 35 40

0.7025 0.7035

0

500

1000

1500

2000

2500

3000

3He/

4He

87Sr/

86Sr

Sr

He

The isotopic stratigraphy at the base of the mantle is not simple

He-3 anomaly(Pb anomaly?)

Sr anomaly

Core or core-mantling dense layer

Width of melting region 5 10 15 20 25 30 35 40

0.7025 0.7035

0

500

1000

1500

2000

2500

3000

3He/

4He

87Sr/

86Sr

Sr

He

The isotopic stratigraphy at the base of the mantle is not simple

Jellinek & Manga (2002)

QuickTime™ and aTIFF (LZW) decompressorare needed to see this picture.

186Os data also interpreted as entrained outer core material; correlates w/ 3He

Brandon et al. (1999)

(R. Walker et al. 1997; Brandon et al. 1998; Meibom & Frei 2002)

Re, Os, Pt and core-mantle interaction?Re, Os, Pt and core-mantle interaction?

Observations: high values of 186Os/188Os and 187Os/188Os in Hawaiian lavas, Siberian lavas, and Os-rich alloys

Hypothesis:Entrainment of ~1 wt% outer core material in plume

Depends on:Inner core-outer core partition coefficients for Re, Os, PtInner

core

Outercore

mantle

crust

Re Os Pt

(Brandon et al. 1998; Shen et al.1996; D.Walker 2000)

Re, Os, Pt systematicsRe, Os, Pt systematics

Inner core

Outercore

mantle

crust

Re Os Pt

Re Os Pt

high Re/Os

high Re/Os

high Pt/Oshigh 187Os/188Oshigh 186Os/188Os

high 187Os/188Os

187Re 187Os 190Pt 186Os

outer core = only reservoir with high 187Os/188Os and 186Os/188Os

Std gchems story

0

2

4

6

8

10

0 100 200 300 400 500 600

MK (HSDP2rev)Mauna LoaMK (HSDP 1)Kilauea

εNd

( )Model Age ka

EPR MORB

Anomalous Mauna Loa

0.7032

0.7034

0.7036

0.7038

0.7040

0.7042

0 100 200 300 400 500 600

87Sr/

86Sr

Model Age (ka)

(b)

Mauna Loa data suggest that core of plume islongitudinally heterogeneous

0

2

4

6

8

10

0 100 200 300 400 500 600

MK (HSDP2rev)Mauna LoaMK (HSDP 1)Kilauea

εNd

( )Model Age ka

EPR MORB

Anomalous Mauna Loa

-2

0

2

4

6

8

10

12

1300 1350 1400 1450 1500 1550 1600 1650

εNd

(° )Potential Temperature C

Plume core( < 15 )r km

Fringe of melting region

( = 15 - 60 )r km

MORB

inferred unmelted plume fringe

(?)D''UpperMantle

LowerMantle

Recent deviant lavas from Mauna Loa require longitudinal heterogeneity along the axis of the plume

He-3 anomaly(Pb anomaly?)

Sr anomaly

Core or core-mantling dense layer

Width of melting region

The axial part of the plume is longitudinally heterogeneous;

The inner fringe of the plume is less heterogeneous

The outer fringe is invisible (no melting)

Conclusions

• Different isotopic anomalies are not spatially correlated in the lowermost mantle

• The 3He anomaly is not a general feature of the “lower mantle” but is a feature of the base of the mantle

• Most of the mantle between the plume source and the surface could have R/Ra ≈ 8; however, there are no lavas to represent this entrained material

• The Sr isotope anomaly (87Sr/86Sr ≈ 0.70365) at Hawaii is a broad feature and the isotopic composition could represent a large volume of the lower mantle under Hawaii

• Patterns for Hf, Nd, Os resemble Sr; but 208Pb resembles 3He• Juxtaposing isotopic data with physical models can yield new

perspectives