Crystal/melt partitioning of volatile and non-volatile elements during peridotite melting: implications for mantle fractionation

 John Adam1*, Michael Turner1, Erik H. Hauri2 and Simon Turner1

1Department of Earth & Planetary Sciences, Macquarie University, N.S.W. 2109, Australia2Carnegie Institution of Washington, 5424 Broad Branch Road, Washington, D.C. 20005, USA

A case study: the nepheline basanite UT-70489 from Bow Hill in Tasmania, Australia

Previous work includes:• An experimental study of liquidus phase equilibria to determine conditions of garnet lherzolite saturation (~2.7 GPa and 1200 °C with 4.5 % of dissolved H2O and 2 % of CO2)

• A LAM-ICP-MS and electron micro-probe study of minor and trace element partitioning between peridotite minerals and the hydrous basanite melt

• A single-crystal X-ray and site refinement study of experimentally produced peridotite phases

Objectives• To produce a comprehensive and self-consistent set of peridotite/melt partition coefficients that include volatile as well as non-volatile elements

• To apply these data to the problem of intraplate magma genesis

Materials and methods

• Piston-cylinder experiments at 1.0-3.5 GPa and 1025-1190 °C using conventional methods

• H2O, C (as CO2), Cl, F, P and S by secondary ion mass spectrometry (SIMS) at the Carnegie Institution of Washington.

• Major, minor and trace elements by electron microprobe and LAM-ICP-MS at Macquarie University, Australia.  

Basanite UT-70489(an intraplate basalt & potential near-solidus melt of garnet lherzolite)

SiO2 44.30 plag 13.77

TiO2 2.36 or 12.41

Al2O3 11.44 ne 15.28

Cr2O3 0.08 di 25.47

Fe2O3 2.01 ol 21.43

FeO* 10.05 ilm 4.50

MnO 0.20 mag 3.83NiO 0.05

ap 3.31MgO 12.11CaO 9.46SrO 0.18Na2O 4.24K2O 2.09P2O5 1.43Total 100.00 100 x Mg/(Mg + Fe+2) = 68.2

Run R79 1075 °C 1.0 GPa

Run R80 1170 °C 3.0 GPa

glass quenched melt(porous crystallite

matrix)

olivine + cpx graphite inner capsule

Pt outer capsule

Pt outer capsule

pyroxenes

4 6 8 10 12 14 16 180

5

10

15

20

Determining H2O concentrations in experimental melts – a comparison of

estimates

from H2O/Laanalytical shortfallsby SIMS

H2O (wt. %) from mass balances of run products and starting materials

H2O

by

othe

r met

hods

1:1

 H2O ppm F ppm

Clinopyroxene  608-1390 187-326Orthopyroxene 649-1211 82-149Olivine 94-166 19-34Garnet 216-352 26-35Pargasite 16900 4983Phlogopite 35100-39100 8177-10423 

• Cl, S and C have negligible concentrations in nominally anhydrous silicate minerals 

• Cl and S have small to moderate solubilities in amphibole and mica

• ~ 0.5 wt. CO2 is soluble in the melt phase at 1-2 GPa

clinopyroxene/melt partitioning of H2O

0.000 0.100 0.200 0.300 0.4000.000

0.010

0.020

0.030

0.040

0.050

0.060

ivAl apfu

DH

2O c

px/m

elt

0 10 20 30 400.000

0.010

0.020

0.030

0.040

0.050

0.060 Bow Hill cpx

Southern Highlands

Kovacs et al. 2012

G & G 1998

Tenner et al. 2009

Aubaud et al. 2008

Aubaud et al. 2004

O'Leary et al. 2010

wt.% H2O in melt

DH

2O c

px/m

elt

orthopyroxene/melt partitioning of H2O

0.000 0.050 0.100 0.150 0.2000.000

0.005

0.010

0.015

0.020

0.025

0.030

ivAl apfu

DH

2O o

px/m

elt

0 10 20 30 400

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

Bow Hill opx

Tenner et al. 2011

G & G 98

Tenner et al. 2009

Kovacs et al. 2012

Grant et al. 2007

Koga et al. 2003

Dobson et al. 1995

Aubaud et al. 2004

Green et al. 2000

wt.% H2O in melt

DH

2O o

px/m

elt

olivine/melt partitioning of H2O

0 10 20 30 400.000

0.002

0.004

0.006

0.008

0.010

0.012 Bow Hill

Southern Highlands

Kovacs et al. 2012

G & G 1998

Tenner et al. 2009

Aubaud et al. 2004

Tenner et al. 2011

Koga et al. 2003

Grant et al. 2007

Novella et al. (2014)

wt.% H2O in melt

DH

2O o

livin

e/m

elt

0.0 5.0 10.0 15.00.000

0.002

0.004

0.006

0.008

0.010

0.012

Pressure (GPa)

DH

2O o

livin

e/m

elt

Garnet/melt partitioning

5 10 15 20 25 300

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009 Bow Hill

Hauri et al. (2006)

Aubaud et al. (2008)

Tenner et al. (2009)

Novella et al. (2014)

weight % H2O in melt

DH

2O g

arne

t/m

elt

Controls on crystal/melt partitioning

1. crystal-chemical effects• Tetraherally co-ordinated Al in pyroxenes

2. melt-activity relations• Burnham’s (1975) solution model for H2O in silicate 

melts• Silver et al.’s (1990) solution model for H2O in silicate 

melts

Effect of ivAl+3 in charge-balancing the addition of H+ to the pyroxene lattice

 

  [pyx]H+ + [iv]Al+3 + [melt]Si+4

[melt]H+ + [melt]Al+3 + [iv]Si+4

KD = ሾ𝑐𝑝𝑥ሿ𝐻+ × ሾ𝑖𝑣ሿ𝐴𝑙+3 × [𝑚𝑒𝑙𝑡 ]𝑆𝑖+4 ሾ𝑚𝑒𝑙𝑡 ሿ𝐻+ × [𝑚𝑒𝑙𝑡 ]𝐴𝑙+3× [𝑖𝑣]𝑆𝑖+4

0 10 20 30 400.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350Bow Hill cpx

Southern Highlands

Kovacs et al. 2012

G & G 1998

Tenner et al. 2009

Aubaud et al. 2008

Aubaud et al. 2004

O'Leary et al. 2010

wt.% H2O in melt

ivAl

apf

u in

cpx

Burnham’s speciation model for hydrous meltsmixing between OH- and 8-oxygen melt units

0 10 20 30 400.0

0.2

0.4

0.6

0.8

1.0

weight % H2O in melt

mol

e fr

actio

n O

H- i

n m

elt

0 10 20 30 400

0.01

0.02

0.03

0.04

0.05 Bow Hill cpx

Southern Highlands

Kovacs et al. 2012

G & G 1998

Tenner et al. 2009

Aubaud et al. 2008

Aubaud et al. 2004

O'Leary et al. 2010

Ideal mixing of 8-oxygen melt units & OH

wt.% H2O in melt

DH2O

 cpx/m

elt

KD = ሾ𝑐𝑝𝑥ሿ𝐻+ × ሾ𝑖𝑣ሿ𝐴𝑙+3 × [𝑚𝑒𝑙𝑡 ]𝑆𝑖+4 ሾ𝑚𝑒𝑙𝑡 ሿ𝐻+ × [𝑚𝑒𝑙𝑡 ]𝐴𝑙+3× [𝑖𝑣]𝑆𝑖+4

with KD = 0.0014

Silver et al.’s (1990) speciation model for hydrous meltsmixing between OH-, molecular H2O and O2-

0 10 20 300

5

10

15

20

25

30

weight % H2O in melt

wei

ght %

mol

ecul

ar

spec

ies

in m

elt

0 10 20 30 40-0.00999999999999997

2.60208521396521E-17

0.01

0.02

0.03

0.04

0.05Bow Hill cpx

Southern Highlands

Kovacs et al. 2012

G & G 1998

Tenner et al. 2009

Aubaud et al. 2008

Aubaud et al. 2004

O'Leary et al. 2010

Stolper & Silver model

wt.% H2O in melt

DH2O

cpx/

mel

t

 with DOHcpx/melt = 0.05

molecular H2O

OH-

• Melt activity relations as well as mineral composition play a role in the determination of mineral/melt (Nernst) partition coefficients for H2O

Comparisons with non-volatile elementsThere is a constancy of some volatile to non-volatile element ratios in intraplate (ocean island) and mid-ocean-ridge magmas 

• H2O/Ce = 200 ± 50 (Michael 1995)o Higher ratios in Atlantic than Pacific, in some cases the correlation is better for La and/or varies with 87Sr/86Sr

• F/Nd• Cl/Ba, Cl/K• CO2/Nb, CO2/Ba

Similar mineral/melt partition coefficients during intra-mantle fractionation involving the migration of small-degree melts from local MORB sources?

Rb Ba K Cl Th UCO

2N

b Ta LaH2

O Ce Pb Sr FN

d Zr Hf Sm Ti Tb Lu

0.001

0.01

0.1

1

10

100pa

rtitio

n co

effici

ent o

r M

ORB

-nor

mal

ized

va

lue

La

Average OIB (MORB-normalized)

Nd

H2O

F

Cl

Cl and F partitioning data from Dalou et al. (2012) 

Garnet lherzolite/melt Partition coefficients

Crystal-chemical controls on DH2O/DCe

2.47 2.475 2.48 2.485 2.49 2.4950.00

0.10

0.20

0.30

0.40Bow Hill

M2 site radius (Å)

DH

2O /

DCe

for C

px/M

elt

0.400 0.600 0.800 1.0000.00

0.10

0.20

0.30

0.40Bow Hill

Southern High-lands

Ca (apfu) in Cpx

DH

2O /

DCe

for C

px/M

elt

2.38 2.39 2.4 2.41 2.42 2.430.00

0.10

0.20

0.30

0.40Bow Hill

Southern High-lands

r0+3 M2 site cations + 1.38

DH2O

/DC

e fo

r Cpx

/Mel

tMust also consider the contributing influence of H2O concentrations in melts (significant for subduction zones)

ConclusionsDuring peridotite melting • DH2O/DCe increases with increasing pressure

and temperature (and therefore depth in the mantle), but decreases with increasing melt H2O

• Therefore - although coupled volatile and non-volatile element enrichments in OIB are consistent with peridotite/melt partitioning, this may require particular circumstances

Thank You

0.00001

0.0001

0.001

0.01

0.1

1

10

100

Rb Ba K Cl Th U CO2 Nb Ta La H2O Ce Pb Sr F P Nd Zr Hf Sm Ti Tb Ho Lu

bulk partiti

on coefficient o

r rati

o

gt lherzolite/basanite melt

garnet lherzolite/H2O-fluid

intraplate basalts

C. Crust & Hydrosphere

Mexican Volcanoes

Fuego, Guatemala

Pinatubo, the Philippines

H2O Pb

La Ce

CO2

F

Clav. OIB normalized to av. MORB

DZperidotite/melt

The influence of ivAl on F in pyroxenes

0.040 0.060 0.080 0.100 0.120 0.1400

50

100

150

200

250

300

350

cpx

opx

ivAl  apfu

ppm F in pyroxenes

The influence of Ti and melt H2O concentrations on OH in amphibole O3 sites

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0.0 0.2 0.4 0.6 0.8

O2- at O3 (apfu)D

Ti a

mph

/mel

t

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 5 10 15 20

melt H2O (wt. %)

O

2- a

t O

3 ap

fu

[melt]Ti+4 + 2[melt]O2- + [M1,3]Mg+2 + 2[O3]OH-  [melt]Mg+2 + 2[melt]OH- + [M1,3]Ti + 2O3O2-