Experimental constraints on subduction-related magmatism I: Hydrous Melting of upper mantle perdotites

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Experimental constraints on subduction-related
magmatism IHydrous Melting of upper mantle
perdotites Peter Ulmer
(Blumone, Adamello, Italy)
Garnet-peridotite in kimberlite
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Topics

• Mantle composition? How do we constrain them?
• Dry Melting of mantle peridotites
• Hydrous Melting Basic concepts
• Hydrous Mantle Melting P-T-f-x relationships

• Conclusion Arc primary mantle magmas are
• basaltic, representing relatively large melt
  fractions
• wet (hydrous)
• hot (gt1200C)
• oxidized (NNO NNO2)

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Arc-Genesis Model I
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P-T Lherzolite (Dry) Melting
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What is the composition of the (upper)
mantle?How do we obtain this information?

• Geophysics Seismology seismic tomography
  Geodesy (density and density
  distribution) Geomagnetics
  (core dynamo)
• Natural observation of high pressure rocks and
  minerals originating from the Earths interior
• Cosmochemistry, analogy with meteorites and solar
  element abundances
• Experimentation (at pressure and temperature
  relevant for the Earths interior) need to fit
  the geophysical constraints
• Thermo-mechanical modeling of Earth materials

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Seismic Constraints on the Earths interior
Seismic data Preliminary Reference Earth Model
PREM (Dziewonski Anderson 1981)
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Mineral constituents and compositions of high
pressure rock samples

• Peridotite Massifs (mantle segments)
• Mantle xenoliths (in basalts, kimberlites)
• Diamonds and their inclusions

Garnet-peridotite in kimberlite
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Evidence for Mass transfer Metasomatic
Peridotites
Carbonatite-globule
phl
olivine
CO2-rich fluid inclusions
olivine
phl
Phlogopite-Peridotite in kimberlite
Mantle-cpx in basanite
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Cosmochemistry Formation of the Earth from
primitive solar nebula
Chondritic meteorites represent the primitive
solar nebula composition
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Bulk Earth chondritic

• We know the composition of the Earths crust
• We have a good idea about the composition of the
  Earths mantle
• We have no access to the core
• Bulk Earth 0.007 crust 0.65 mantle
  0.32 core

Bulk Silicate Earth (BSE)
Metal Earth
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Estimates of various parts of the Earth based on
Cosmochemistry and Petrology
Oxide CI carb. BSE BSE undepleted Peridotite Lower Core
  chondrite (CI) (Pyrolite) Upper M DM  Mantle 15 LE
  -volatiles MS 95 MS 95 PN 85 Anders. 89 estimate (Elements)
SiO2 34.20 49.90 45.00 46.20 44.10 49.80 -
TiO2 0.11 0.16 0.20 0.23 0.13 - -
Al2O3 2.44 3.65 4.45 4.75 1.57 3.60 -
FeO 35.80 8.00 8.05 7.70 8.31 9.70 78.00
MgO 23.70 35.15 37.80 35.50 43.90 34.10 -
CaO 1.89 2.90 3.55 4.36 1.40 2.80 -
Na2O 0.98 0.34 0.36 0.40 0.15 - -
K2O 0.10 0.02 0.03 - lt0.1 - -
Cr2O3 0.58 0.44 0.38 0.43 0.34 - 0.80
NiO 2.10 0.25 0.25 0.43 0.34 - 4.90
Mg 0.54 0.89 0.89 0.89 0.90 0.86 -
Ca/Al 0.70 0.72 0.73 0.83 0.81 0.71 -
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Dry Lherzolite Melting

• Fundamental Principles (Phase Equilibria)
• Pressure effects on melting and composition of
  primary melts
• Temperature effects on melting and compositions
  of primary melts

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Fundamentals Forsterite SiO2
Pressure lt 1.4 kbar
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Fundamentals Forsterite SiO2
Peritectic
Cotectic (thermal max)
Pressure lt 1.4 kbar
Pressure gt 1.4 kbar
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Schematic Phase Diagram showing LOW Pressure
Lherzolite Melting
Schematic Phase Diagram showing HIGH Pressure
Lherzolite Melting
Plt7kbar (or PH2O High)
Pgt7kbar (dry) (gt12 kbar wet)
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The Tools Piston Cylinder Solid Media Presses
0.5 - 4 (5) GPa, 2000C
Pressure Force / Area
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P-T slopes of dry melting in simple systems
Albite and Diopside
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Anhydrous Peridotite Melting Experiments
for fertile lherzolite gt15-20 melting
Base of basalt tetrahedron projected from cpx
(Ulmer, 2001)
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Anhydrous Peridotite Melting Melt fraction as a
function of pressure and source composition
Ulmer (2001)
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Anhydrous Peridotite Melting Solidus
temperatures and melt compositions as a function
of source composition at 3 GPa
Hirschmann (2003)
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Hydrous Lherzolite Melting

• Fundamental principles (phase equilibria)
• Pressure H2O effects on melting and composition
  of primary melts
• Temperature effects on melting and compositions
  of primary melts
• Geochemical signatures of Arc magmas

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Diopside Peridotite H2O - Melting
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H2O solubility in basalt and albite liquids at
1100C
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Early hydrous (H2O-saturated) experiments
Green DH (1973)
Kushiro et al (1968)
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Peridotite H2O Melting ACMA Average Current
Mantle Adiabat
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Schematic diagram showing melting phase relations
for a system containing Anhydrous minerals
(A) Hydrous mineral (H) H2O (V) Important
(univariant) curves H2O-saturated solidus
(A) Dehydration solidus (V) Dry solidus (V) (low
right)
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Peridotite H2O Melting ACMA Average Current
Mantle Adiabat (diamond symbols multiply
saturated primary liquids extraction depth?)
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multiple saturation (olopxcpx)of primitive
arc magmas
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Inverse multiple saturation experiments on
primary arc basalts
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Picrobasalt (3 wt. H2O) phase diagram with
multiple saturation
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Hydrous Peridotite Melting Melt fraction as
function of MELT H2O-content
Ulmer (2001)
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Effects of small amounts of H2O (in source) on
melt-fractions
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T.L. Groves new Chlorite-Solidus
Grove et al. (09)
Grove et al. (06)
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Parameterization (mostly thermodynamically based,
including PMELTS)
Katz et al (2003)
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Hydrous Peridotite Melting Experiments Comparison
with anhydrous melting
Low percentage melts plot to the left of Plag-Ol
gt alkaline, SiO2-undersaturated, Ne-normative
unlike gt99 of all arc rocks (volcanics and
plutonics, LP thermal divide) (jadeite component
of cpx is preferentially entering the melt gt 1/F
relationship)
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• Evidences for hydrous nature of arc magmas and
  geochemical characteristics of supra-subduction
  magmas
• Violent, explosive, gas-rich (H2O) eruptions
  typical for differentiated magmas (andesite
  rhyolite)
• Melt inclusions (up to gt10 wt. H2O in primitive
  Olivine inclusions (e.g. Shasta, Hess, Grove,
  Sisson and co-workers)
• Early amphibole (and biotite) saturation
  indicating gt 4 wt H2O at time of crystallization
• Geochemical characteristics of supra-subduction
  magmas (major and traces) gt Calc-alkaline and
  arc trace element signature of magmas and their
  (metasomatized) mantle sources
• high fO2 probably related to oxidation by
  slab-derived fluids (Fe-isotopes indicate reduced
  arc mantle prior to fluid metasomatism)

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Spiderdiagram of Island Arc Basalts (IAB)
HFSE depletion, LILE and LREE enrichment, fluid
mobile elements, residual rutile and garnet to
retain HFSE and HREE in slab source during
dehydration
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Spiderdiagram of Philippine Mantle Xenoliths
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Major Element composition of MORB - IAB
Arcs Silica enrichment and FeO-suppression due
to late plag, early amph and mag
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Mantle melting trend to high-SiO2 - low FeO/MgO
is controlled by reaction relations during ascent
to the base of the crust
Opx Olivine Liquid (SiO2-component)
Grove et al. (03)
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Composition of primitive arc magmas
wt. Picro- Olivine- SiO2-rich High-Mg Boninite
Basalt Tholeiite Tholeiite Andesite
SiO2 46.8 48.5 51.5 56.6 55.0
TiO2 0.7 1.0 1.8 0.9 0.2
Al2O3 12.4 14.4 13.8 17.6 12.5
Fe2O3 2.0 1.0 2.2 1.9 6.6
FeO 7.5 11.9 8.9 5.0 6.5
MgO 17.0 12.4 9.4 6.0 12.0
CaO 10.3 12.9 8.9 8.1 6.5
Na2O 1.2 1.5 2.5 3.4 1.9
K2O 0.4 0.5 0.7 1.0 0.7
xMg 0.77 0.65 0.65 0.68 0.77
max. Press 30kb 18kb 12kb 7-10kb ca.10
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Oxygen Fugacity from Ol-Spinel oxybarometry
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Oxygen Fugacity from volcanic glasses
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Effect of Oxygen Fugacity crystallization sequenes
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Mature Island Arc (after Ringwood, 1974)
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• 4 points to remember
• Presence of H2O during melting leads to enormous
  solidus depression (function of pressure gt
  solubility)
• However, geochemistry (major elements) and
  experimental constraints indicate significant
  melt fractions (10-20) generated at conditions
  close to the mantle adiabat (gt1200C)
• Arc magmas are more siliceous at a given pressure
  compared to dry tholeiites (MORB, OIB) gt
  calc-alkaline
• Arc magmas carry particular signatures (trace
  elements, fO2, fH2O) that can be linked to
  slab-derived components
• gt Primary mantle melts are basaltic, hot, wet,
  oxidized